Phacoemulsification
Phacoemulsification 3rd Edition Edited by Sunita Agarwal MS FSVH DO Athiya Agarwal MD DO Amar Agarwal MS FRCS FRCOphth All of Dr Agarwal’s Eye Hospital, Chennai, India Associate Editors I Howard Fine MD FACS Oregon Eye Surgery Center, Eugene OR, USA Mahipal Singh Sachdev MD New Delhi Centre for Sight, New Delhi, India Keiki R Mehta MD Mehta International Eye Institute, Mumbai, India Suresh K Pandey MD Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Charleston NC, USA Foreword by Robert H Osher MD Professor of Ophthalmology, University of Cincinnati College of Medicine, Cincinnati OH, USA Volume I
LONDON AND NEW YORK A MARTIN DUNITZ BOOK
© 1998, 2000, 2004 Sunita Agarwal, Athiya Agarwal, Amar Agarwal
First published in India in 2004 by Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India. EMCA House, 23/23B Ansari Road, Daryaganj, New Delhi 110 002, India Phones: 23272143, 23272703, 23282021, 23245672 m\, Fax: +91–011–23276490 e-mail:
[email protected], Visit our website: http://www.jaypeebrothers.com/ This edition published in the Taylor & Francis e-Library, 2006. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to http://www.ebookstore.tandf.co.uk/.” Transferred to Digital Printing 2005 First published in the United Kingdom by Taylor & Francis, a member of the Taylor & Francis Group in 2004. Exclusively distributed worldwide (excluding the Indian Subcontinent) by Taylor & Francis, a member of the Taylor & Francis Group. Tel.: +44 (0) 20 7583 9855 Fax.: +44 (0) 20 7842 2298 E-mail:
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This two volume book on Phacoemulsification is dedicated to two wonderful people whom we have come to know and worked with
John Bond
Amy McShane
Contributors A Beléndez MD Spain A Fimia MD Universidad de Murcia Murcia, Spain Aamir Asrar MD Consultant Ophthalmic Surgeon Amanat Eye Hospital Pakistan Abhay R Vasavada MS FRCS Raghudeep Eye Clinic Near Shreeji Complex Opp. Gurukul Road, Memnagar Ahmedabad-380 052, India Alejandro Espaillat MD ELK County Eye Clinic 765 Johnsonburg Road, St Marys PA 15857, United States Amar Agarwal MS FRCS FRCOphth Consultant Dr. Agarwal’s Eye Hospital 19 Cathedral Road Chennai-600 086, India 15 Eagle Street, Langford Town Bangalore, India Ana Claudia Arenas MD Calle 104#46 A 10 Casa 9, Santa Fe De Bogota 8 Colombia Andrea M Izak MD 40 Bee St#323 Charleston SC 29403 United States Angel Saiz MD Department of Ophthalmology Hospital De Galdakao Galdakao, Vizcaya, Spain
Anthony Maloof MD Westmead Hospital Hawkesbury Road Westmead, NSW 2145 Australia Asha B MS Dr. Agarwal’s Eye Hospital 15 Eagle Street Bangalore 560 025, India Ashok Garg MS PhD Garg Eye Hospital 235, Model Town Dabra Chowk Hisar, Haryana, India AT Gasch MD Department of Health and Human Services Bethesda, USA Athiya Agarwal MD DO FRSH Consultant Dr. Agarwal’s Eye Hospital 19 Cathedral Road Chennai-600 086, India 15 Eagle Street, Langford Town Bangalore, India Augusto Cezar Lacava MD Brazil Barry S Seibel MD 1515 Vermon Avenue 7th Floor, Station C USA Los Angeles, California USA C González MD Universidad de Murcia Murcia, Spain Carlos Cortes-Valdes MD Chairman Professor of Ophthalmology Department of Ophthalmology Hospital General Universitario Gregorio Maranon Madrid Spain-Europe
C Leon 1A Calle 30–80 Zona 7 Utalan I Guatemala City Guatemala Charles D Kelman MD The Eye Centre, 220 Madison Avenue at 37th Street, New York NY 10016, USA Chi-Chao Chan MD National Institute of Health Building 10, Room 10N/206 Bethesda, MD 20892 United States Clement K Chan MD Southern California Desert Retina Consultants, PO Box 2467 Palm Springs CA 92263 USA Cyres Mehta Mehta International Eye Institute Sea Side, 147 Colaba Road Mumbai-400 005, India D Aron-Rosa France D Bremond Gignac MD France David J Apple MD Centre for Research on Ocular Therapeutics and Biodevices Storm Eye Institute Charleston USA David Meyer MD Faculty of Medicine Department of Ophthalmology Cape Town South Africa Demetrio Pita-Salorio MD Professor and Head Department of Ophthalmology and Ocular Morphology Unit University of Barcelona Spain
E Villegas MD Universidad de Murcia Murcia, Spain Elizabeth A Davis Minnesota Eye Consultants 9117 Lyndale Aves, Bloomington MN 55420, United States Ellen Anderson Penno MD Gimbel Eye Centre Calgary, Alberta Canada Enrique Chipont MD Instituto Oftalmologico De Alicante Alicante, Spain F Mateos MD Universidad Miguel Hernandez de Elche, Alicante, Spain Francisco Contreras-Campos MD Clinica Ricardo Palma Av. Javier Prado Este 1038 PISO 10 San Isidro Lima Peru Gabor Rado MD Budapest, Hungary George Salacz MD Hungary Guillermo L Simon-Castellvi MD Clinica Oftalmologica Simon Simon Eye Clinic Barcelona, Spain Hampton Roy MD Hampton Roy Eye Center 9800 Lile Drive, Suite 660 Little Rock, Arkansas, USA Hiroshi Tsuneoka MD Department of Ophthalmology Jikei University School of Medicine 3–19–18 Nishishinbashi Minato-ku Tokyo, 103–8461, Japan Howard V Gimbel MD Gimbel Eye Centre Suite 450, 4935–40, Avenue N.W. Calgary, Alberta Canada T3A 2N1
I Howard Fine MD FACS Oregon Eye Surgery Center 1550, Oak Street #5, Eugene USA I Pascual MD Departmet I De Optica Universidad De Alicante Apartado 99 E-03080 Alicante, Spain J Agarwal FORCE DO FICS Dr. Agarwal’s Eye Hospital 19 Cathedral Road Chennai-600 086, India 15 Eagle Street, Langford Town Bangalore, India J Hoyos-Chacón Instituto Oftalmologico De Sabadell Barcelona, Spain J Laiseca MD Barcelona, Spain Jack A Singer MD Singer Eye Center 45, South Main Street Randolph, VT 05060, United States J Leon Chirurgie Oculaire BD G Pompidou 20137 Port-Vecchio, France Jagat Ram MD PGI, Chandigarh, India Jairo E Hoyos MD Instituto Oftalmologico De Sabadell Barcelona, Spain James P Gills MD Luke Cataract and Intraocular Lens Institute, 1570 US Highway, 19N PO Box 5000, Tamponsprings Florida 34688–5000, United States Javier Mendicute MD Department of Ophthalmology Hospital De Gipuzkoa, San Sebastian, Gipuzkoa, Spain Javier Orbegazo MD Chairman Department of Ophthalmology Hospital De Galdakao Galdakao, Vizcaya, Spain
Jaya Thakur MD Orbis International Fellow Tilganga Eye Centre Kathmandu, Nepal Jesús Costa-Vila MD Barcelona, Spain JM Legeais MD PhD Ophthalmology Department Hotel Dieu 1 Place Du Parvis Notre Dame Paris-775181, France Johnny L Gayton MD 216 Corder Road Warner Robins, GA 31088, USA Jorge L Alio MD Instituto Oftalmologico De Alicante Alicante, Spain Jose L Urcelay-Segura MD Glaucoma Service-Department of Ophthalmology Hospital General Universitario Gregorio Maranon Madrid, Spain-Europe Jozsef Gyory MD Hungary JP Lassau MD France JR Fontenla MD Barcelona, Spain Juan Carlos Sanchez Caballero MD Brazil Julio Ortega-Usobiaga MD Department of Ophthalmology Hospital General Universitario Gregorio Maranon Madrid, Spain-Europe Kayo Nishi MD Nishi Eye Hospital Osaka, Japan Keiki R Mehta MD Mehta International Eye Institute 147 Shahid Bhagat Singh Road Colaba Road Near Colaba Bus Station Mumbai-400 005, India
L Carretero MD Universidad de Alicante Alicante, Spain Liliana Werner MD Center for Research on Ocular Therapeutics and Biodevices Storm Eye Institute Charleston, USA Lucio Buratto MD Centre Ambrosiano Microchirurgia Oculare, Milano, Italy Luis W Lu MD Eye Physician-ELK County Eye Clinic, 765 Johnsonburg Road ST Marys PA 15857, United States M Edward Wilson MD Miles Center for Pediatric Ophthalmology Charleston, USA Mahipal S Sachdev MD New Delhi Center for Sight A-23 Green Park, Aurobindo Marg New Delhi-110 016, India Marc Canals-Imhor MD Barcelona, Spain Mark Packer MD Oregon Eye Surgery Center 1550, Oak Street, #5 Eugene Or 97401 United States Melania Cigales MD Instituto Oftalmologico De Sabadell Barcelona, Spain Namrata Sharma MD C-18 B, DDA Flats, Munirka New Delhi Nilesh Kanjani DO Dip NB Dr. Agarwal’s Eye Hospital India and Dubai Okihiro Nishi MD Director Jinshikai Medical Foundation Nishi Eye Hospital Higashinari Ku Nacuamichi 4–426–537 Osaka, Japan
P Giardini MD Camo-Centro Ambrosiano Microchirurgia Oculare Milano, Italy Pandelis Papadopoulos MD Director Ophthalmological Diagnostic and Therapeutic Center Ophthalmo-Check Ltd 42 Poseidon Avenue, Paleo Faliro Athens, Hellas, Greece Paul Liebenberg MD Faculty of Medicine Department of Ophthalmology Cape Town South Africa Pradeep Venkatesh MD AIIMS, Delhi, India R Fuentes MD Universidad de Alicante Alicante, Spain Raminder Singh MS Raghudeep Eye Clinic Opp. Gurukul Road Near Shreeji Complex, Memnagar Ahmedabad 380 052, India Randall J Olson MD University of Utah Department of Ophthalmology Moran Eye Centre, 50-N Medical Drive, Salt Lake City UT 84132–0001, United States Richard L Lindstrom Clinical Professor of Ophthalmology University of Minnesota Minneapolis, MN, USA Richard S Hoffman Oregon, USA Robert M Kershner MD PC FACS Orange Grove Eye Center 1925 W, Orange Grove Road #303 Tucson, AZ 85710 United States Roberto Bellucci MD Camo-Cebtro Ambrosiano Microchirurgia Oculare
Milano Italy RR Sasikanth MD Consultant Dr. Agarwal’s Eye Hospital India and Dubai Rupert Menapace MD Professor, Universitats-Augenklinik Vienna General Hospital Wahringer, Gurtel, Wien Vienna, Austria Samuel L Pallin MD FACS Medical Director The Lear Eye Clinic 10615 W Thunderbird A100 Sun City AZ 85351–3018, USA Samuel Masket MD 2080, Century Park East Suite 911, Los Angeles, CA 90067 United States Soosan Jacob MS FRCS Consultant Dr. Agarwal’s Eye Hospital Chennai, Bangalore, India and Dubai Steve Charles MD Charles Retina Institute 6401 Poplar Avenue, Suite 190 Memphis, Tennessee USA Steven G Lin MD Southern California Desert Retina Consultants, Palm Springs USA Sundaram MS Dr. Agarwal’s Eye Hospital 15 Eagle Street Bangalore 560 025, India Sunita Agarwal MS DO FSVH (Germany) Dr. Agarwal’s Eye Hospital 19 Cathedral Road Chennai-600 086, India 15 Eagle Street, Langford Town Bangalore, India
Suresh K Pandey MD Center for Research on Ocular Therapeutics and Biodevices Storm Eye Institute Charleston, USA Susanna Recsan MD Hungary T Agarwal FORCE DO FICS Dr. Agarwal’s Eye Hospital 19 Cathedral Road Chennai-600 086, India 15 Eagle Street Langford Town Bangalore, India Takako Hara MD Hara Eye Hospital Nishi 1–1–11 Utsunomiya, Japan 320 0861 Tetsuro Oshika MD Tokyo University School of Medicine Department of Ophthalmology 7–3–1, Hongo, Bunkyo-Ku Tokyo, Japan 113 8655 Tobias Neuhann MD Founder and Medical Director Aam Augenklinik AM Marienplatz Marienplatz 18, Munich Germany TR Indumathy Dip NB DO Dr. Agarwal’s Eye Hospital India Tsutomu Hara MD Hara Eye Hospital Nishi 1–1–11 Utsunomiya, Japan 320–0861 Valerio De Iorio MD Instituto Oftalmologico De Alicante Alicante, Spain Virgilio Centurion MD Instituto De Molestias Oculares AV, Ibirapuera 624, CEP, Sao Paulo, Brazil Warren E Hill MD 7525 E Broadway Road #6 Mesa, AZ 85208–2057 United States
Wataru Kimura MD Kimura Eye Hospital 2–3–28 Nakadori Kure City Hiroshima Japan 737 William J Fishkind MD FACS Fishkind and Bakewell 5599 North Oracle Road Tucson Arizona 85704–3821, USA
Foreword to the Third Edition Authoring a medical textbook is a labor of love. For months and months, the act of writing, correcting, rewriting, editing, proofreading, corresponding, negotiating, etc. replaces hobbies and recreational pursuits. Yet when all is said and done, an immense sense of satisfaction embraces the author, who by this time has aged considerably. The authors of the third edition are to be congratulated for bringing this collaborative work to fruition. The encyclopedic table of contents in combination with an erudite and highly experienced international faculty offer two volumes of information to the reader. Moreover the microphacoemulsification section reflects the leading contribution that Dr. Agarwal’s group is making in the evolution toward even smaller incision surgery. Being on the “cutting edge” can be a mixed blessing, but investing the time and effort necessary to share information is always a rewarding task for those surgeons who have contributed their work. I hope that the reader is also rewarded by becoming a more knowledgeable cataract surgeon after digesting the contents of the third edition of this textbook on phacoemulsification. Robert H Osher MD Professor of Ophthalmology University of Cincinnati College of Medicine Medical Director Emeritus Cincinnati Eye Institute
Foreword to the Second Edition Dr Amar Agarwal’s brilliant mind has captured the idea of presenting the most advanced techniques of Cataract Surgery, at the dawn of the new millennium in this splendid book, Phacoemulsification, Laser Cataract Surgery and Foldable IOLs. The reader can enjoy not only a skilful description of classic cataract surgery, but also Dr Agarwal’s great experience, opening new horizons in this field. I whole-heartedly recommend the book and am honored to Foreword this second edition which will almost certainly be as great a success as the first one. I am very proud to share the knowledge arising from Dr Agarwal’s book who is one of the leaders in the field of cataract surgery and a great colleague and friend. Spyros Georgaras MD President of the Hellenic Union of Specialized Ophthalmologists Greek Intraocular Implant and Refractive Surgery Society Research & Therapeutic Institute “Ophthalmos” Ophthalmological Center “Hygeia-Ophthalmos”
Foreword to the First Edition One of the great joys and honors in my life was my frequent visits to India and my meetings with great clinicians, surgeons, teachers and human beings of the Indian ophthalmological community…among them, the wonderful Agarwal family of Chennai. So I am very much honored by their request to write a Foreword to the new book edited and written by them and by other superb surgeons and teachers such as Keiki R Mehta, Mahipal Singh Sachdev, Kenneth J Hoffer, I Howard Fine and all the other internationally known and respected teachers and experts. The table of contents, both concerning the titles of the chapters and the authors, speaks for itself. Some of the world’s greatest authorities on the subject, speaking from both scientific and clinical experience, are gracing this book. Every aspect of modern successful cataract surgery is covered, so the book will be extremely useful—not only for the beginners, but also for the accomplished surgeons who need to look at some different points of views and approaches to surgery or for information. The worldwide brotherhood of ophthalmic surgeons, researchers and teachers is deeply and greatly indebted to the editors of the book who assembled the panel and chose the topics and to the writers of the chapters who devoted their time and knowledge to this undertaking. I congratulate and thank the authors and wish them God’s blessings. John J Alpar MD FACS Clinical Professor at Texas Tech University Honorary Member of All India Ophthalmological Society
Preface to the Third Edition A lot of toil, blood, tears, and sweat has been poured through these pages from so many authors working in so many countries serving so many people. This two volume book on cataract surgery in its most advanced fashion, is an attempt to spread knowledge and letting you know that each one of us believes a much greater force has helped us compile this into fruition. We may have claimed many a research project, however each one who has done any research knows fully well and can hear fully well that inner voice calling out. Every time we write whether it is for our own gratification or towards a more sublime learning and teaching once again whether we want to accept it or not we know that it is something else that makes us do these things. It is something far more powerful than we can ever imagine that guides our thinking, our hands, our profession or whatever direction the guide wants us to. And yet there is a choice of free will given to all of us. And yet we choose to burn the midnight oil, we choose to forsake sensual pleasures in a quest of that something that gives us much more peace and understanding of the world, much more joy than owning all the gold in Fort Knox would ever give us. Here my dear friends is where we are today to say Thank You to the world to the Cosmos to everyone of you who read this and to those who benefit through your reading because this may just be a small drop in the ocean of knowledge, yet it is a small drop in the right direction. In the spirit of serving the human race and all who come after us our attempt is to give them a springboard where they can take off where we have left off. Editors
Preface to the Second Edition Coming from a background where ophthalmology ordained the dining table conversation for over seven decades and three generations it is not surprising that the need for revised second editions was thought necessary and mandatory. Especially since our understanding of cataract surgery has been in a perpetually accelerating flux. Sometimes revelations have been quite by accident however most often progress is steady and slow, depending on many factors like available resources and necessity The more we read and more we try to assimilate information the more we realize how far we are from the understanding of the topic. Of late it is difficult to understand progress in the coming years of the new millennium without the assistance and utilization of lasers, computers and advanced technology. More often than nought the space traveler it seems enjoys more information and technological advancements than does the mundane operation theater of medical personnel. However even this equation seems to be changing and much like a science fiction movie our operation theaters reel away progress only thought of to exist in future centuries. Retaining the same concept of cataract surgery this edition throws much light on the why and wherefores with an insight into the modalities of treatment. Along comes research from the offices of Dr David Apple, a person who has brought glamor into ocular pathology and the understanding of different treatment types, along with Dr SK Pandey have explained the reasons why they have come to a conclusion where there seems to be no difference between intracameral anesthesia, topical anesthesia, and now venturing into new grounds—No anesthesia itself. However good a surgery comes to nought when plagued with bacterial or microbial invasion, many ophthalmic surgeons have gone through sleepless nights in the pursuit of infection control and its management. This leads us to believe that it was essential to have detailed chapter written on the subject. Much to our chagrin there was hardly any material on the topic of Sterilization. It seems to be we all know about it, understand its importance in the surgical field, yet have never really written about it. The maximum one finds in known literature is something written as a chapter of a microbiology book. Still nothing much from a clinician’s point of view, still nothing much in terms of explaining to us what works best, and still nothing more telling us how to work it. Quoting a cop friend of mine, “An assassin has to be lucky just once, I have to be lucky every day, every instant.” In the same light we as surgeons have to be on our guard every time, every instant, the bacteria need be lucky only once. Add to this is sometimes the diplomatic approach of instrument engineers who wave aside grave consequences to patient’s wellbeing in the interest of their product image. Sometimes we overlook the obvious, just like we look for the source of light standing right under the sun, similarly the internal tubing of an ultrasound machine that gauges the pressure inside the eye, is actually the prime source of infection in phacoemulsification.
With the Mediterranean influence of L Burrato we have a new chapter on the adversities of a small pupil and still manage to perform phacoemulsification with the greatest of finesse, “Pushing an elephant through a keyhole”. Giving importance to Incisions is S Pallin, small steps of the surgery which go a long way in its success. Posterior Polar Cataract has new light from A Vasavada whose immense knowledge on phacoemulsification makes him a leader in this field. Coupled with this progress is the inroads made by Indian ophthalmology along with Indian engineering and scientific skill that have been displayed for all to see at the pinnacle body internationally as far as cataract and refractive surgery are concerned, the American Society for Cataract and Refractive Surgery (ASCRS) were witness to live surgery telecast from India to America at the 1999 ASCRS meeting. This instruction course made history with it being the first time such an event had occurred and displayed live—No Anesthesia Laser Phakonit (under 1 mm) Cataract Surgery. Thus all that we had written about came to pass when delegates were able to see the surgery in its full form. Such feats would be repeated more often at different meetings since seeing is believing! As the volume of knowledge has expanded, so too the need for multiple contributors. To strengths of diversity and multiple forms of expertise, this trend has created a burden on the editorial. Thus consistency of writing form is difficult to maintain, however this also adds to the texts’ value as a learning and teaching tool. The whole volume of the book has therefore extended and with more color plates and more reading material, we hope dear reader you enjoy reading this as much as we have in writing it! Editors
Preface to the First Edition Forewords rarely touch the reader’s heart unless the writer sends them out from the same location. That gives us a fighting chance, because we have spent our entire life in the pursuit of ophthalmic sciences and still count this as one of our good friends that always reserves its gratitude and encourages our chances of discovering further and further in its wake. To write a book today in the world of entertainment with video, movies and the whirlwind of computers seems gratuitous. Still the beauty and magic of reading will never fade and the history of writing that dates back more than 5000 years can never be surpassed. To the memory of the writers of yore and to encourage the many more writers to come, we have taken the task of bringing you the latest synopsis of the trends in cataract surgery through the nineties. The scientists and researchers of today are full time clinicians who have placed their energy in the development of new ideas. In fact if you go back in time, most discoveries and inventions have been made by the person attempting to correct human malady, and while doing so perchance steps onto some discovery or invention. It was in this same manner the father of Intraocular lenses while treating pilots from the Royal Airforce during the Second World War came to the conclusion that IOLs were a possibility. He noticed that pieces of windshield material lay immersed in ocular tissue producing no reaction and were transparent and could thus be implanted into the eye (in the place) of spectacles. Dr Harold Ridley thus brought about one of the greatest advancements in this century as far as ophthalmic sciences are concerned. To him and his batch of pioneers, ophthalmology down the ages will always have a place of honor. Salutations to such torchbearers and more to come. When we look down at the achievements that the human mind has achieved in the realm of ophthalmology and its progress, we are baffled by its enormity especially when we know that there is still so much more to be discovered and so much more to be invented. The scientific progress that has occurred in the last 100 years has bypassed all that could have occurred in the last 5000 years from the Neanderthal cousin of ours, and that which will occur in the next decade itself will be a renaissance in ophthalmology. We still know only a drop in the ocean of the ophthalmic sciences and we realize that what we can dream, we can certainly achieve in the forthcoming years. This book aims at giving you dear Reader not only food for thought but also in contributing to this Renaissance, thereby, achieving the dreams our forefathers had in this beautiful world of Vision. Through the reading of this book you will find subjects divided into six basic structures to ease you in the understanding of what cataract and its management mean today. The contributing authors are themselves authorities on the topics of their choice. All stages of learning have been taken care of through these six stages from the learner
through the advanced surgeon, bringing you to bear down on mayhap a forgotten episode, for we all know “Trifles make perfection, though perfection is no trifle.” The computer has brought into our world a dream of precision and this has come to become a part of every machinery developed in the modern world. In fact when we look into what “robotics” have done to this factor, we realize we are very close to making the blind man see. Many have been the times that patients have asked their eye surgeon, “Cannot you change my eye itself?” Yes, now we can reply them with the idea of repositioning a video camera and sending the signals into the brain directly. Unthought of till only yesterday, and today will soon be a reality. A surgeon in the midst of surgery in his or her home town can now think of operating in orbit around the world with a little help from satellites and robotics. Now most distant of patients can get the precise expertise from the dexterous experience of the surgeon. Very soon no one will be bereft of resourceful opinion and/or surgery in this world and that beyond the stars. Marching towards the next millennium we have accessed cataract surgery with an intraocular lens insertion under the 2-mm mark with the latest “laser cataract surgery,” becoming a reality. Coupled with changes in ultrasound technology it will create many newer trends in the years “beyond 2000”. Phakonit has brought the incision of cataract surgery to 0.9 mm. Computers and lasers have crossed many marks, and “intrastromal lasers” will soon see the light of the day. Spectacles will not be worn for the want of refractive errors with the latest modalities of the LASIK laser and its contemporaries. This reading hopes to take you down the lane from humble beginnings of a retrobulbar to peribulbar anesthesia and now to the present exodus of topical anesthesia to the advanced “No anesthesia” ophthalmic surgery, taking its first few steps of infancy in India. After all, have we all not seen sudden injuries to the eye reflecting no pain to the patient? It hopes to give you food for thought and may be rethink the corneal reflex, rethink the anatomy and physiology of the eye itself and delve into the basic sciences of our specialty, “the eye”. It is said that the pen is mightier than the sword (here the surgical knife) and in this case both go hand in hand, and thus, whatever the knife has done the pen has put it down for you to read. Contributing authors have already left footprints on the sands of time. Let us further your objective in strengthening the armor of ophthalmology. Editors
Contents VOLUME I
Section I: Cataract and Preoperative Evaluation 1. Cataract Etiology David Meyer, Paul Liebenberg 2. Biochemistry of the Lens Ashok Garg 3. History of Phacoemulsification Charles D Kelman 4. Biometry Sunita Agarwal 5. IOL Power Calculation After Corneal Refractive Surgery Jairo E Hoyos, Melania Cigales, J Hoyos-Chacón 6. IOL Master for Determining the IOL Power at the Time of Surgery Hampton Roy, Warren E Hill 7. Corneal Topography in Cataract Surgery Athiya Agarwal, Sunita Agarwal, Amar Agarwal, Nilesh Kanjani
3 52 64 75 85 97 101
Section II: Instrumentation and Medication 8. The Phaco Machine: How It Acts and Reacts William J Fishkind 9. The Fluidics and Physics of Phaco Barry S Seibel 10. Air Pump to Prevent Surge Sunita Agarwal, Amar Agarwal, Athiya Agarwal 11. Microseal and Other Phaco Tips Hampton Roy 12. Sterilization Sunita Agarwal 13. Local Anesthetic Agents Ashok Garg
116 134 149 154 158 203
14. Anesthesia in Cataract Surgery Ashok Garg 15. Mydriatics and Cycloplegics Ashok Garg 16. Update on Ophthalmic Viscosurgical Devices Suresh K Pandey, Jaya Thakur, Liliana Werner, Andrea M Izak, David J Apple
219 241 251
Section III: Phaco Steps 17. The Dynamics of Sutureless Cataract Incisions Samuel L Pallin 18. Incisions Luis W Lu, Alejandro Espaillat, Ana Claudia Arenas, Francisco ContrerasCampos 19. Capsulorhexis Tobias Neuhann 20. Hydrodissection and Hydrodelineation I Howard Fine, Mark Packer, Richard S Hoffman
280 288
296 310
Section IV: Phaco Techniques 21. Divide and Conquer Nucleofractis Techniques Howard V Gimbel, Ellen Anderson Penno 22. Single Instrument Phacoemulsification through a Clear Corneal Microincision Robert M Kershner 23. The Use of Power Modulations in Phacoemulsification of Cataracts: The Choo Choo Chop and Flip Phacoemulsification Technique I Howard Fine, Mark Packer, Richard S Hoffman 24. Lens Quake Phaco Jack A Singer 25. Supracapsular Phacoemulsification Aamir Asrar 26. New Non-laser Phacoemulsification Technologies I Howard Fine, Mark Packer, Richard S Hoffman
320 343
351
360 366 396
Section V: No Anesthesia Cataract Surgery 27. No Anesthesia Cataract Surgery with the Karate Chop Technique Athiya Agarwal, Sunita Agarwal, Amar Agarwal
405
28. No Anesthesia Cataract Surgery Tobias Neuhann 29. No Anesthesia Cataract Surgery: Comparison Between Topical, Intracameral and No Anesthesia Suresh K Pandey, Liliana Werner, Amar Agarwal 30. Ocular Anesthesia for Small Incision Cataract Surgery Samuel Masket
420 428
442
Section VI: Phakonit 31. Phakonit Amar Agarwal, Athiya Agarwal, Sunita Agarwal 32. Microphaco: Concerns and Opportunities Randall J Olson 33. Ultrasmall Incision Bimanual Phaco Surgery and Foldable IOL Hiroshi Tsuneoka 34. Corneal Topography in Phakonit with a 5 mm Optic Rollable IOL Amar Agarwal, Soosan Jacob, Athiya Agarwal, Sunita Agarwal 35. Phakonit with the Acritec IOL Amar Agarwal
450 470 480 498 506
Section VII: Laser Cataract Surgery 36. Laser Phaco Cataract Surgery Sunita Agarwal, J Agarwal, T Agarwal 37. Erbium-YAG Laser Cataract Surgery Demetrio Pita-Salorio, Guillermo L Simón Castellvi, Jesús Costa-Vila, Marc Canals-Imhor, JR Fontenla, J Laiseca 38. Cataract Surgery with Dodick Laser Photolysis Jorge L Alio, Valerio De Iorio
521 533
559
Section I Cataract and Preoperative Evaluation 1. Cataract Etiology 2. Biochemistry of the Lens 3. History of Phacoemulsification 4. Biometry 5. IOL Power Calculation After Corneal Refractive Surgery 6. IOL Master for Determining the IOL Power at the Time of Surgery 7. Corneal Topography in Cataract Surgery
1 Cataract Etiology David Meyer Paul Liebenberg Introduction The term cataract is derived from the Latin cataracta and from the Greek katarraktes which denotes a waterfall or a portcullis. Analogously a cataract is a complete or partial opacification of sufficient severity, on or in the human lens or capsule, to impair vision. Vision is one of the most valued senses. Proper vision is achieved by a series of eye tissues working harmoniously in concert. Most eye debilities involve dysfunction in the lens or retina, and hence this chapter will focus on and elucidate etiological factors which may affect the proper function of the lens as target organ. The lens is an elegantly simple tissue. It is made up of only two types of cells. • Epithelial cells, which have not yet completely differentiated and not yet elaborated the major gene products, and • Fiber cells, in which these processes have been initiated or even completed. Cataract is one of the major causes of visual impairment leading eventually to blindness. In the USA alone 1,35 million cataract extractions are performed annually. In developing countries the magnitude of the problem is overwhelming. Management of this age-old impairment of vision requires one of the three following approaches, or a combination of these approaches. 1. Surgical, i.e. extracapsular lens extraction (either manually or by phacoemulsification) and intraocular lens (IOL) implantation;
FIGURE 1.1 Mature senile cataract
Phacoemulsification
2
2. Development and application of drug-related strategies to counteract the development of cataract; 3. Identification and elimination of risk factors. It is now well established that cataract formation is a multifactorial disease. Several of the etiological factors are constitutional and hence difficult to manipulate. Others are environmental in nature and a little easier to control whilst a significant number are behavioral in nature and fall well within the individuals’ own ability to control or modify. • This review will briefly touch on congenital and infantile cataract but will focus on etiological factors in adults (Fig. 1.1) and especially those implicated as risk factors in age-related cataract.
Congenital and Infantile Cataract Congenital cataract is numerically the most important cause of remediable blindness in children, being far more common than, for example, retinoblastoma or congenital glaucoma. The prevalence of infantile cataract has been reported to be between 1.2 and 6 cases per 10,000 births. Furthermore it has been estimated that between 10 percent and 38.8 percent of all blindness in children is caused by congenital cataract (Figs 1.2 to 1.4) and that one out of every 250 newborns (0.4%) has some form of congenital cataract. The etiology of infantile cataract (Table 1.1) can be established in up to one-half of children with bilateral cataract, but in a smaller proportion of infants with unilateral cataract. Infantile cataract most commonly occurs secondary to genetic or metabolic diseases, intrauterine infections or trauma. Less commonly they may occur as a side effect of treatment with certain medications or radiation therapy.
FIGURE 1.2 Anterior polar congenital cataract
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FIGURE 1.3 Congenital cortical cataract
FIGURE 1.4 Congenital coronary cataract Genetic Infantile cataract may be inherited as autosomal dominant, autosomal recessive or Xlinked recessive traits. Autosomal dominant cataract are most commonly bilateral nuclear opacities, but marked variability can be present even within the
TABLE 1.1 Etiology of Infantile cataract A. Idiopathic B. Intrauterine infection 1. Rubella 2. Varicella 3. Toxoplasmosis 4. Herpes simplex C. Drug induced Corticosteroids D. Metabolic disorders 1. Galactosemia 2. Galactokinase deficiency 3. Hypocalcemia
K. Inherited with systemic abnormalities • Chromosomal abnormalities 1. Trisomy 21 2. Turner syndrome 3. Trisomy 13 4. Trisomy 18 5. Translocation 3;4 6. Cri-du-chat syndrome 7. Translocation 2;14 • Craniof acial syndromes Cerebro-oculo-facio- skeletal syndrome (COFS) • Mitochondrial abnormalities
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4. Hypoglycemia 5. Mannosidosis E. Trauma 1. Accidental 2. Non-accidental F. Miscellaneous
Complex I deficiency L. Skeletal disease 1. Smith-Lemli-Opitz syndrome 2. Conradi syndrome 3. Weill-Marchesani syndrome M. Syndactyly, polydactyly or digital abnormalities 1. Radiation 1. Bardet-Biedl syndrome 2. Laser photocoagulation 2. Rubenstein-Taybi syndrome G. Other ocular diseases N. Central nervous system abnormalities 1. Microphthalmia 1. Zellweger syndrome 2. Aniridia 2. Meckel-Gruber syndrome 3. Persistent hyperplastic primary vitreous 3. Marinesco-Sjögren syndrome (PHPV) 4. Prematurity 4. Infantile neuronal ceroid-lipofuscinosis (Batten’s disease) 5. Peters’ anomaly 6. Corneal guttata O. Dermatological 7. Endophthalmitis 1. Crystalline cataract and uncombable hair 2. Cockayne syndrome H. Dental anomalies 1. Nance-Roran syndrome 3. Rothmund-Thomson syndrome 4. Atopic dermatitis I. Cardiac disease Hypertrophic cardiomyopathy 5. Incontinentia pigmenti 6. Progeria J. Renal disease 1. Lowe syndrome 7. Ichthyosis 2. Hallermann-Streiff-Francois syndrome 8. Ectodermal dysplasia
same pedigree. In an extended pedigree of 28 patients with autosomal dominant nuclear cataract, Scott et al reported that 19 of the affected family members had unilateral cataract while 9 had bilateral cataract. Less commonly, anterior polar, posterior polar, and posterior lentiglobus cataract can be autosomal dominantly inherited. In the United States, infantile cataract are most commonly inherited as autosomal dominant traits, however, in countries where there is a high prevalence of parental consanguinity, infantile cataract are more commonly inherited as autosomal recessive traits. In Egypt where one-third of all marriages are consanguineous, Mostafa et al reported autosomal recessive inheritance for six of seven pedigrees with inherited infantile cataract. Linkage analysis has been used to determine the genetic loci of certain autosomal dominant cataract. Coppock-like cataract has been linked to the gamma E-crystalline gene on chromosome 2, Coppock cataract to chromosome 1q21–q25, Marner cataract to 16q22, and cerulean cataract to 17q24. The Cerulean cataract links closely to the galactokinase gene, but galactokinase levels in these patients are normal. Metabolic The most common metabolic disturbance causing cataract during infancy is galactosemia. Galactosemia may be caused by a transf erase, galactokinase or epimerase deficiency. Galactose-1-phosphate uridyl transferase (GALT) deficiency occurs in 1:40,000
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newborns in the United States and 1:23,000 newborns in Ireland. A homozygous mutation of Q188R on exon 6 of the GALT gene on chromosome 9 is found in two-third of children with the transferase deficiency. This results in the accumulation of galactose 4-phosphate in the blood. Galactose is then converted to galactitol in the crystalline lens, resulting in an influx of water into the lens by osmosis. The hydration of the lens then disrupts the normal structure of the lens fibers, resulting in a loss of transparency. Early on, these lens changes have the appearance of an oil-droplet in the center of the lens. These changes are initially reversible with the elimination of galactose from the diet. If left untreated, a lamellar cataract develops which may then progress to a total cataract. In addition to cataract, these children have failure to thrive as infants, which may lead to death if milk and milk products are not eliminated from their diet. Later in childhood, these children may have delayed development, abnormal speech, growth delay, ovarian failure and ataxia. While eliminating galactose from the diet can prevent the lifethreatening problems which occur during infancy, dietary compliance does not always correlate closely with the formation of cataract in later childhood or with the associated abnormalities of late childhood. The N314D mutation of the GALT gene causes the milder Duarte form of galactosemia. Combinations of Q188R, N314D and unknown mutations may result in phenotypically different forms of galactosemia. Galactokinase deficiency may cause cataract with few or no systemic abnormalities. The galactokinase gene is on chromosome 17 and has recently been cloned and found to harbor homozygous mutations in some patients with cataract. Heterozygotes for galactokinase deficiency have half normal values on blood tests. Conflicting results have been reported in the literature as to whether partial loss of enzyme activity leads to presenile cataract. Alpha mannosidosis can also be associated with early onset cataract. Lamellar cataract may also develop in children with neonatal hypoglycemia or hypocalcemia. Neonatal hypoglycemia is more common in low birth weight infants. Infectious The congenital rubella syndrome was one of the most common causes of congenital cataract in the United States until the widespread employment of the rubella vaccine. During the rubella epidemic in the United States during 1963–64, 16 percent of all children with the congenital rubella syndrome developed cataract. Infantile cataract also occur occasionally in children after intrauterine varicella, toxoplasmosis and herpes simplex infections, or after bacterial or fungal endophthalmitis. Cataract may also develop after a varicella infection during early childhood. Prematurity Transient cataract occur occasionally in premature infants. They are usually bilateral and begin as clear vacuoles along the apices of the posterior lens suture. They may progress to posterior subcapsular vacuoles. In most cases, they clear completely over the course of several months. All of the premature infants with transient cataract reported by Alden et al were septic and had been treated with Kanamycin, 80 percent of these infants also had an unexplained metabolic acidosis. These authors suggested that osmotic changes in the lens of these infants might have caused these cataract.
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Trauma While trauma is not a common cause of cataract during infancy it should be considered, particularly when a cataract is associated with other ocular signs suggestive of a traumatic injury. The trauma can be either blunt or penetrating. Nonaccidental causes for the trauma must always be considered. Eyes with suspected traumatic cataract should also be examined carefully for both retinal and optic nerve injuries. Laser Photocoagulation Laser photocoagulation has been used in recent years to ablate the avascular retina of infants with threshold retinopathy of prematurity (ROP). Laser-induced cataract are transient in some instances, but progress in some cases to total opacification of the lens. Drack et al reported cataract in six eyes following argon laser photoablation of the avascular retina in four infants with threshold retinopathy of prematurity. Radiation Induced Radiation used to treat ocular and periocular tumors may induce cataract in children. A radiation dose of 15 Gy has been shown to be associated with a 50 percent risk of cataract formation. Radiation usually causes posterior subcapsular cataract, which typically have their onset 1 to 2 years after the completion of radiation therapy. Medications Systemic corticosteroids cause cataract in up to 15 percent of children once a cumulative dose of 1000 mg of prednisone or the equivalent has been reached. This cataract usually begin as central posterior subcapsular opacities, but may progress to involve the entire lens. Idiopathic In most series, at least 50 percent of bilateral infantile cataract are idiopathic. The percentage of idiopathic unilateral infantile cataract is even higher. Age-Related Cataract Personal Factors Gender It has often been observed that more females than males have cataract and undergo cataract surgery. This is partly explicable by the longer life span of women and therefore their over-representation in the age groups where cataract is most common. It does appear however that there is an additional effect—a true excess risk of cataract in females. In
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Nepal the prevalence of cataract was greater in females than in males at all ages. The overall risk ratio was 1.4, which would be detectable only in larger studies. In most casecontrol studies the two groups were age- and sex-matched so that the effect of sex could not be explored. Hiller et al had to combine the results from three earlier studies in the United States and India to find a significant excess relative risk of 1.13 in females. This follow-up study of data from the National Health and Nutrition Examination Survey (NHANES) also suggested that such an excess risk for women is specific to cortical cataract. In a population-based prevalence survey in Beaver Dam, Wisconsin, women had more cortical opacities compared to men within similar age groups. The Beaver Dam Study reported a protective effect for nuclear opacities with current use of postmenopausal estrogens. Older age at menopause was associated with decreased risk of cortical opacities, suggesting hormonal influences in cataractogenesis. It was also suggested that hormone replacement therapy (HRT) may protect against cortical cataract. The Epidemiology of Cataract in Australia study found that a protective relationship of HRT and cortical cataract exists at the univariate level, but that this relationship was not significant in multivariate analysis. Nuclear cataract cases were more likely to be female in the above study, even after age adjustment. They were however unable to support the hypothesis that HRT is protective against nuclear cataract. Tavani et al studied 287 Italian women who had undergone cataract extraction and 1277 control subjects who were in the hospital for acute, non-neoplastic, nonophthalmologic, nonmetabolic, nongastroenterologic diseases in a case-control study in Northern Italy. The results of this study support the association in women between cataract extraction and diabetes, (OR 4.6 for those younger than 60 years and 1.7 for those age 60 and over) current overweight, (OR 2.2) history of clinically relevant obesity, (OR 1.5) hypertension (OR 1.5) and hyperlipidemia (OR 1.8). They suggest that these factors may have some biologically independent impact on the risk of cataract in women and therefore supports the association in women between cataract extraction on the other hand and diabetes, current overweight, history of clinically relevant obesity, hypertension and hyperlipidemia on the other. Body Mass Index Body mass index (BMI) is computed as weight in kilograms divided by the square of the height in meters (kg/m2) and is frequently identified as a risk factor for cataract, but the nature of the association is unclear. Several mechanisms may play a role: • BMI affects glucose levels, which are associated with increased risk of cataract • Higher BMI also increases uric acid concentrations and the risk of gout, which were associated with cataract in some studies • BMI is also an important determinant of hypertension which has a controversial relationship with cataract. Experimental evidence also supports a possible protective effect of restriction of energy intake on the risk of cataract by protection against oxidative stress to the lens. In developing countries some studies have associated low BMI with cataract. A recent case control study in India however failed to confirm this association.
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Hankinson et al in a prospective study examined the association of BMI with cataract extraction in a large cohort of women and found elevated rates of cataract in those with higher BMI. Women with BMI of 23 or above had significantly elevated rates of extraction, between 46 percent and 65 percent higher than those with BMI of less than 21. Glynn et al in a prospective cohort study of a total of 17,764 apparently healthy US male physicians aged 40 to 84 years who were free of cataract at baseline were followed for 5 years. In this group higher BMI was especially strongly related to risk of posterior subcapsular and nuclear sclerotic cataract and was also significantly related to risk of cataract extraction. Furthermore BMI below 22 appeared especially protective against posterior subcapsular cataract, with reductions in risk of 50 percent or more relative to each of the groups with a higher BMI. They concluded that BMI appears to be a strong and independent risk factor for cataract in this well-nourished and socioeconomically homogenous study population. Even modest elevations in weight were associated with increased risk. In so far as BMI index is modifiable, cataract caused by overweight is therefore potentially preventable. Social Economic Status Less education and lower income are related to increased morbidity and mortality from a number of diseases, even after controlling the known risk factors. These relations have been attributed to underuse of health care resources, high-risk behaviors, exposure to noxious work or adverse home environment, and poor nutrition. In population studies, less education and lower income consistently have been associated with impaired vision and cataract. The relationship of education, income, marital status, employment status to age-related cataract and impaired vision was addressed in the population-based Beaver Dam Eye Study. A private census of the population of Beaver Dam, Wisconsin, was performed from September 15, 1987 to May 4, 1988. Eligibility requirements for entry into the study included living in the city or township of Beaver Dam and being 43 to 84 years of age at the time of the census. A total of 5924 eligible people were identified. Of these, 4926 (83.1%) participated in the examination. While controlling for age and sex in this study, less education was significantly (P<0.05) related to higher frequency of nuclear sclerotic and cortical cataract. Lower reported total household income was significantly associated with higher frequencies of cortical and posterior subcapsular cataract. These relations between total household income and cataract were observed in both men and women. Less education has been associated with higher frequencies of history of heavy drinking, cigarette smoking and less vitamin supplement intake, all of which have been found to be related to specific types of cataract. However, the association of education and income with cataract persisted, despite controlling these exposures in their population. It is possible that poorer nutrition occurring earlier in life, may be related to the development of age-related cataract. A second possible reason explaining the relation of education and income to cataract is that people with less education or lower income are less likely to see an ophthalmologist or have cataract surgery.
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Marital status is a measure of social support which is postulated to be an important factor in developing and managing complications associated with disease. While controlling for age and sex, people who were never married had a higher frequency of impaired vision than those currently married. This may be due to the fact that married people may have more social pressure to seek health care and to maintain familial responsibilities, and they may have more transportation assistance than their unmarried/widowed counterparts. In summary, less education and income are related to cataract and visual impairment, but not to age-related maculopathy. These data suggest that access to medical, surgical, and low vision care may be of benefit to people with low socioeconomic status. Social Factors Smoking Tobacco is the leading preventable cause of disease, disability and premature death. Tobacco smoking is considered a major risk factor for 6 of the 15 leading causes of death. An individual who smokes has about twice the risk of premature death as a nonsmoker, and the heavier the cigarette consumption, the higher the risk. Of the 4,000 active substances in tobacco smoke, most are hazardous to human health. More than 40 of these chemicals are carcinogens and many others are deleterious to the cardiovascular and the pulmonary systems. They include nicotine, tars, nitrosamines, polycyclic aromatic hydrocarbons, hydrogen cyanide, formaldehyde, and carbon monoxide. Cigarette smoking is also a substantial source of intake of heavy metals and toxic mineral elements, such as cadmium, aluminum, lead, and mercury, all known to be poisonous in high concentrations. Tobacco smoke also contains numerous compounds with oxidative properties; their existence is linked to the pathogenesis of several of the most common eye disorders, such as cataract and age-related macular degeneration. Epidemiological data link cigarette smoking to several ophthalmologic disorders like ocular irritation, ocular ischemia, age-related macular degeneration (AMD), cataract, thyroid ophthalmopathy, tobacco-alcohol amblyopia, primary open-angle glaucoma, conjunctival intraepithelial neoplasia, uveal melanoma, Leber hereditary optic neuropathy, type II diabetes, ocular sarcoidosis and strabismus in the offspring of smoking mothers. The effects of smoking on ocular disorders show significant dose dependence; higher levels of smoking increase the risk of developing cataract. It is important to note, however that the interpretation of results of different studies may be inherently biased, as smokers in these studies use cigarettes of different types, containing different concentrations of toxic substances. Moreover, some of the cigarettes have filters and others do not. Smoking habits may also be associated with other potentially noxious habits, such as excessive alcohol consumption, which may contribute a further bias to the results. Table 1.2 summarizes five very thought-provoking studies all supporting the view that smoking is associated with the development of cataract.
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Several authors have reported a significant link between tobacco smoking and an increased risk of cataract development. Nuclear sclerosis appears to be the type of cataract most commonly associated with smoking. In the Beaver Dam Eye Study, the relationship between cigarette smoking and lens opacities was examined in 4926 adult subjects. A significant correlation was found between severe levels of nuclear sclerosis and the number of pack-years smoked. For both sexes, the odds ratio associated with 10 years
TABLE 1.2 Smoking and the risk of cataract Study
Relative risk 95% (RR) Cl
Leske et al, 1991 1.68 Hankinson et al, 1.63 1992 Christen et al, 2.16 1992 Klein et al, 1993 1.09 West et al, 1995 2.40
0.96– 1.94 1.8– 2.26 1.46– 3.20 1.04– 1.16 1.00– 6.00
Comments Association was found to nuclear cataract Conducted on 50,828 women; RR for developing posterior subcapsular cataract is 2.59 N=22,071 males; RR for nuclear cataract is 2.24 and for posterior subcapsular, 3.17 Beaver Dam Eye Study; same RR for women and men Conducted on 442 watermen of the Chesapeake Bay
was 1.09 (confidence interval, 1.04–1.16). The frequency of posterior subcapsular opacities was also increased (odds ratios, 1.05 [confidence interval, 1.00–1.11] for men and 1.06 [confidence interval, 0.98–1.14] for woman). Cortical opacities were not found to be linked to smoking. Leske et al studied, 1380 patients with cataract, aged 40 to 79 years, in an attempt to identify possible risk factors for the development of cataract, current smoking was correlated with the risk of developing nuclear cataract (odds ratio, 1.68; confidence interval, 0.96–1.94), but not other forms of cataract. The City Eye Study reported epidemiological data concerning 1029 volunteers, aged 54 to 65 years, from London, UK. The findings showed a significant relationship between nuclear lens opacities and moderate to heavy cigarette smoking. The relative risk for nuclear-type cataract ranged from 1.0 for past light smokers to 2.6 for past heavy smokers, and 2.9 for current heavy smokers. Klein et al presented evidence that smoking has a detrimental effect on the development of cataract in the type II diabetic population. Several prospective studies have investigated the relationship between cataract formation and cigarette smoking. In an 8-year prospective study, Hankinson et al examined the association between cigarette smoking and the risk of cataract extraction in 50,828 female nurses aged 45 to 67 years. The age-adjusted relative risk among female smokers of at least 65 pack-years was 1.63 (confidence interval, 1.18–2.26). Smoking was also strongly associated with posterior subcapsular opacities for smokers of 65 or more pack-years (relative risk 2.59). In a 5-year prospective study of 22,071 men aged 40 to 84 years, current smokers of at least 20 cigarettes a day showed a significantly increased risk of developing cataract (relative risk 2.16; confidence interval, 1.46–3.20). When calculated for the different types, the relative risk was 2.24 for developing nuclear
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sclerosis and 3.17 for posterior subcapsular cataract. Past smokers were also at increased risk of developing posterior subcapsular opacities (relative risk 1.44), whereas current light smokers had the same chance of developing any type of cataract as subjects who had never smoked. In a study of 838 watermen from Chesapeake Bay, Maryland, West et al found a significantly increased risk of development of nuclear opacities associated with cigarette smoking (relative risk 2.40; confidence interval, 1.00–6.00). A 5-year prospective study of this cohort of subjects reported an increase in the incidence and degree of nuclear opacities with increasing age. The risk of progression of nuclear opacities from, less than grade 3 at baseline to grade 3 or worse was 2.4-fold higher among current smokers than among ex-smokers or non-smokers. A significant increase (18%) in the risk of cataract progression was associated with each pack-year that a subject had smoked during the 5-year study period. Mechanism The way in which smoking induces cataract formation is probably through its effect on the oxidant-antioxidant status of the lens. Oxidative damage plays a major role in cataractogenesis. Animal, laboratory clinical, and epidemiological data support the relationship between cataract prevention and diets rich in nutritional factors with antioxidant properties, such as riboflavin, vitamins C and E, and the carotenoids. Smoking appears to further impair lenticular function by imposing an additional oxidative challenge as well as by contributing to the depletion of endogenous anti-oxidant pools. Tobacco smoke also contains large amounts of heavy metals, such as cadmium, lead and copper, which appear to accumulate in the lens and exert further toxicity The above data strongly support an association between tobacco smoking and cataract formation. Given the magnitude and seriousness of the cataract problem, an important preventive measure in fighting this disorder is to quit smoking. It is important to note that smoking is on the increase in the developing world, where cataract surgery is not always readily available. Alcohol Excessive alcohol use is associated with numerous chronic health problems, such as liver disease, varicosities, blood dyscrasias, and elevated blood pressure. Some studies have reported a relationship between alcohol consumption and cataract, while other studies have found no relationship. One study reported that both abstainers and heavy drinkers were more likely to have cataract than moderate users, while another found that total abstainers were more likely to have cataract than alcohol users. As far back as 1973 Sabiston clinically observed in 40 patients over a 5-year period a definite correlation between alcohol intake, Dupuytren’s contracture, and cataract. He stated that the mechanism of cataract formation was uncertain, but that an element of chronic dehydration was possible. In New Zealand, where he did his observations, heavy drinking often commenced with the ingestion of large quantities of beer. The national average consumption of beer there is 100 liters per head annually, with manual labourers ingesting a daily total of 4 liters of beer per person per day on average. These persons were almost invariably heavy cigarette smokers as well. He further noted that the cataract commenced in a posterior subcapsular position, and could progress to almost full maturity in six months. There was almost universally a history of heavy cigarette smoking as well. Malnutrition was only sometimes seen.
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Drews in 1970 also drew attention to the association of ethanol and cataract. Two decades later he writes: “A patient in his or her 40s or 50s who appears with a posterior subcapsular cataract should be investigated for alcoholism… In the author’s practice, about 25 percent of patients younger than age 65 years who present with cataract are found to be alcoholic on careful investigation. It has been his experience that if the opacities are incipient and if the consumption of alcohol is stopped completely, the posterior subcapsular changes may reverse and even disappear.” Two decades later attention is once again drawn to the possible link between alcohol and cataract in the Archives of Ophthalmology by two different sets of authors. Munoz et al from the Wilmer Eye Institute, Baltimore, MD, USA conducted a follow-up study of surgical cases of posterior subcapsular cataract (PSC) and their controls to evaluate the possible association of alcohol intake and posterior subcapsular opacities. Two hundred thirty-eight cases and controls were interviewed. Current alcohol intake and usual and maximum weekly consumption ever were assessed. In this population, 57 percent of the cases and 56 percent of the controls were nondrinkers, 22 percent of the cases and 36 percent of the controls had an average of seven or fewer drinks per week, and 17 percent of the cases and 8 percent of the controls had more than seven drinks per week. Heavy drinkers were more likely to be cases than were nondrinkers (odds ratio, 4.6; P<0.05), and light drinkers were not at an increased risk. Light drinkers, defined as those who drink less than 91 g/wk (i.e. one drink or less per day), were at a lower risk than were nondrinkers, although this difference did not reach statistical significance. Moderate to heavy drinkers, that is, those drinking an average of more than one drink per day (more than 91 g/wk) were 2.7 times more likely to have PSC. This U-shaped relationship between alcohol and the risk of PSC was more pronounced in the logistic regression model when controlling for all the factors found to be related to PSC. Some studies have suggested that heavy drinking patterns are associated with lower socio-economic status. In this study after adjustment for education level, the risk of PSC was still higher among drinkers. Smoking was also not related to PSC. Heavy alcohol use has been linked to poor nutritional status, so the presence of PSC may be related to poor nutrition rather than alcohol consumption per se. Dietary assessment however, was not performed in this study. In summary, this study concluded that moderate to heavy alcohol consumption is associated with a four-fold increase of PSC cataract whereas light drinkers, those consuming one drink per day or less, were not at an increased risk. The second study reported in the same journal was on alcohol use and lens opacities in the Beaver Dam Eye Study group of patients. The relationship between alcohol use and lens opacities was examined in a large (N=4926) population-based study of adults. Alcohol history was determined by a standardized questionnaire and the cataract severity was determined by masked grading of photographs obtained using a slit lamp camera and retroillumination. Several significant findings were made and conclusions drawn: • In both sexes and every age group, a higher percentage of current heavy drinkers had late nuclear sclerotic changes. Similar results were seen for cortical and PSC changes. • Past heavy drinkers were found to have increased odds of nuclear sclerosis (OR, 1.34; 95% confidence interval [CI], 1.12 to 1.59). There was an additional significant effect of past heavy drinking on the severity of cortical opacity (OR, 1.36; 95% CI, 1.04 to 1.77). The presence of posterior subcapsular opacity was also significantly associated with past heavy drinking (OR, 1.57; 95% CI, 1.10 to 2.25).
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• Wine was associated with less severe nuclear sclerosis (OR, 0.84; 95% CI, 0.74 to 0.94) in general. Participants who drank liquor were less likely to have severe nuclear sclerosis than those who did not (OR, 0.81; 95% CI, 0,72 to 0.95). Liquor use was also associated with lower frequencies of any cataract (OR, 0.83; 95% CI, 0.72 to 0.94) and fewer past cataract surgeries (OR, 0.75; 95% CI, 0.57 to 0.98). • A significant relationship was found between beer consumption and cortical cataract. Those who drank larger amounts of beer were more likely to have cortical cataract than those who drank smaller quantity of beer. An increased risk of cortical cataract was associated with increased beer consumption. An increased risk of cortical cataract was not associated with consumption of wine, hard liquor, or a combination of alcohol types when considered as continuous variables. These different relationships for the different types of alcohol (wine and hard-liquor consumption was generally associated with OR’s or less than 1, while beer consumption was associated with OR’s of more than 1) raises the possibility that other components of wine or hard liquor confer protective effects on cataract development. However, no such theoretical links have yet been established. Alcohol has many metabolic effects, and modifies the absorption of drugs and dietary components. These effects may be important in the alcohol-cataract relationship. However, one cannot exclude the possibility that alcohol itself, especially when consumed in high volume, may be a direct toxin to the human phacos. Metabolic Factors Diabetes Mellitus Juvenile diabetic cataract classically known as the “snow flake cataract” is now uncommon with the advent of effective hypoglycemic therapy. It occurs in insulindependent diabetics whose onset was before the age of 30. The limited period over which snow flake cataract may occur (chiefly in the first two decades of life) contrasts with the extended period over which lenticular change occurs (from youth into the eighth decade). It is of interest that snow flake cataract occurs at a period of life when the lens is undergoing a major physiological shape change, with negligible sagittal and major equatorial expansion. It may very well be that the mechanisms for refractive change and cataract are the same but age-related factors such as the decreasing ability of the lens to swell may protect the older lens from this type of cataract formation. Other typical features of this type of cataract are subcapsular and cortical “snow flakes”, and polychromatic opacities and vacuoles (Fig. 1.5). These may proceed to mature cataract within weeks or months and rarely, may be reversible after normalization of blood glucose over some weeks or even as rapidly as 24 hours. The rat sugar cataract model is an attractive model for juvenile diabetic cataract in terms of its acute development and other features. It is also relevant to human galactosemic cataract, in which the lens is exposed to high levels of aqueous galactose. The first visible indication of galactosemic cataract is the “oil-droplet” change on retroillumination, due to a change in refractive index between the inner and outer parts of the lens.
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FIGURE 1.5 Diabetic cataract It has been noted that there are difficulties in accepting a role of aldose reductase in human cataract. Even though sorbitol is found in increased amount in the human diabetic lens, the amounts detected have been quite low, and insufficient on a lens mass basis to account for osmotic damage. Data on a cell-to-cell basis, which would be appropriate, are not available. Although Vadot and Guibal considered that there was sufficient sorbitol in young diabetic lenses to induce cataract, Lerman and Moran could not demonstrate the accumulation of significant amounts in sugar-incubated lenses over the age of 20 years. There is no information about levels in juvenile diabetic cataract itself. Jedziniak et al found a higher aldose reductase activity in the young lens than in the adult lens and calculated that it was sufficient to generate a significant osmotic stress. However, these calculations referred to the lens epithelium and assumed that sorbitol was not removed. Since polyol dehydrogenase is more active than aldose reductase in the human lens, the calculated levels would be expected to be lower. Lin et al demonstrated accumulation of dulcitol and loss of myoinositol in 72-hour cultures of infantile human lens epithelium in a 30 mlQI galactose medium, associated with vacuolar changes at ultrastructural level. Sorbinil and AL1576 reversed these changes. Similar changes have been produced in dog epithelial culture within 6 hours. Lin et al suggest that damage in the human lens may reflect compartmentalization of aldose reductase activity, for instance in the epithelium. If sorbitol accumulation in the epithelium (and not the fibers) were the basis of juvenile cataract, then a failure of epithelial permeability or pumping functions would be a more likely cause of lens swelling and cataract than an osmotic mechanism. There is no information available as to whether an oxidative mechanism, dependent on the polyol pathway or not, is operative in juvenile diabetic cataract. Cataract in diabetic adults Cataract has a greater prevalence in diabetics with a greater risk for women, and is dependent on the duration of diabetics. The morphology is no different from that of age-related cataract, although the frequency of some subtypes is increased. Klein et al in a population study found cataract to be more prevalent in early and late onset diabetes with significant association with age, severity of retinopathy and diuretic usage. Diabetes duration and the level of glycosylated hemoglobin were also associations in early onset diabetics. In a second report, cataract was found to be the second most
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common cause of severe visual loss in adult onset diabetics. Various other reports have shown an association between cataract, and diabetes duration or retinopathy. The frequency of cataract extraction is greater in diabetics than non-diabetics. The Framingham study showed a significant excess risk in the 50 to 64 year age group (relative risk 4.02), while the HANES study showed a relative risk of 2.97 in this age group and 1.63 in the 65 to 74 year age group. Both studies reported an excess prevalence of cataract in diabetics in 50 to 64 year age groups, which disappeared at an older age. This has been attributed to the higher mortality in diabetics with cataract. However, a case-control study in Oxford found an increased risk for cataract extraction in diabetics in the age group of 50 to 79 years, and a small increase in risk for women relative to men. As has been noted the morphology of cataract in the adult diabetic resembles that seen in age-related cataract in the absence of diabetes. Thus the major features are nuclear cataract (increased nuclear scattering and brunescence) and cortical spoke and posterior subcapsular cataract. In the Lens Opacity Case Control study, diabetes increased the risk of posterior subcapsular, cortical and mixed forms of cataract. Individual features may not have an identical etiology, but it is likely that those metabolic changes identified in experimental cataract are relevant for the human are in varying degrees. There is no relation between cataract type, and the level of either sorbitol or myoinositol in lens epithelium from patients with cataract and diabetes. It has been suggested that the increased nuclear scattering and brunescence in diabetic lenses is likely to be the result of increased glycation and the formation of advanced glycation end products. There is evidence for a fall in free lysine amino groups in the human diabetic lens. It is also possible to induce a change in tertiary structure in alpha-crystalline (bovine) incubated with glucose and glucose-6-phosphate. A three-fold increase in glycation was measured in diabetics and controls by Vidal et al but there was no correlation with the degree of browning of the lenses measured spectrophotometrically, and they concluded that other chromophores were responsible for the browning at the relevant wavelengths. Certainly a number of other factors have been proposed to contribute to nuclear brunescence of the non-diabetic lens, but since the diabetic state is not anticipated to increase their concentration, glycation products are still the most likely candidates responsible for diabetic cataract. Cortical cataract can be caused experimentally by agents which interfere with membrane permeability, ion and water control. The non-diabetic, aging human lens, free of cataract, has an increased membrane permeability which parallels the increase in optical density which occurs from about the fifth decade. There is evidence of degradation of the lens protein MIP26 with age in non-diabetics, which could be responsible for a functional abnormality. This channel protein has until recently been regarded as the gap junctional protein, but may in fact serve as a volume regulating channel. Disturbance of either function could increase the risk of cataract. It would be of interest to examine these events in the diabetic lens. The greater thickness of the diabetic compared to the non-diabetic lens could be relevant to this point. The disturbance in Na′ K′-ATPase kinetics reported by Garner and Spector during exposure to glucose-6phosphate is similar to the change noted in diabetic human lenses. Hydrogen peroxide is present in normal human aqueous, and present at raised levels in the aqueous of patients
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with cataract. Higher levels are found in the aqueous of diabetic patients with cataract. Simonelli et al have also shown an increase in malondialdehyde in cataractous compared with non-cataractous lenses which is greater in the cataract of diabetic patients. Malondialdehyde is a product of lipid peroxidation of cell membranes, and is regarded as an indicator of oxidative membrane damage. These are important findings, although the methods of measurement are not entirely specific. The potential role of the sorbitol (polyol) pathway in juvenile cataract was discussed earlier. Recent studies of cultured lens epithelium from cataract patients have shown negligible or absent levels of sorbitol in the epithelium of non-diabetics. In diabetic epithelium sorbitol levels are higher than blood glucose levels, while there is an inverse relationship between blood glucose and myoinositol. It has been noted that oxidative stress may cause lens membrane damage experimentally. It may also cause damage to DNA. Subcapsular cataract may be regarded as due to an aberration of lens mitosis and lens fiber differentiation, and could be the result of oxidative damage. There are no data, which link this to human subcapsular cataract. Other cataract-related events A higher rate of capsular rupture reported in diabetics undergoing intracapsular or extracapsular extraction could be related to structural and chemical changes which are known to occur in the capsule. There is an increased risk for death in patients with cataract and diabetes. Cohen et al found lens opacities to be a powerful predictor of death, independent of other factors and with an odd ratio of 2.4 (95% confidence interval 1.5–3.9). Dyslipidemia Lens opacification and cardiovascular disease are two of the main causes of morbidity worldwide. Lens opacity, manifesting as cataract, is responsible for an estimated 40 percent of the 42 million cases of blindness in the world. On the other hand, heart disease is the single greatest cause of death in developed countries. The relationship between cholesterol and cardiovascular heart disease is well documented. The relationship between cholesterol and lens opacity is, however, far less well appreciated. Issues relating to drug safety and inherited defects in enzymes mediating cholesterol metabolism have brought renewed attention to a possible interrelationship between lipid metabolism and cataract induction in humans. The lens is unique in that it contains a relative abundance of cholesterol in the fiber cell plasma membrane, (the highest of any cell group in the body) and furnishes its needs for cholesterol by onsite biosynthesis. It has been shown that inhibition of cholesterol synthesis in the lens leads to cataract formation in man. Smith-Limli-Opitz syndrome, me valonic aciduria and cerebrotendinous xanthomatosis are inherited disorders of cholesterol metabolism and affected patients may present with lens opacities. Triparanol, a hypolipidemic agent that inhibits cholesterol biosynthesis was withdrawn from clinical use because of its propensity to induce cataract formation in humans. The very widely used vastatin class of hypolipidemic medicines is potent inhibitors of cholesterol biosynthesis and is able to lower serum lipid concentration effectively. Although high ocular safety in older patients over periods of up to 5 years, has been reported, it is still not clear whether these agents
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have the potential to be cataractogenic, particularly in younger patients and over longer periods. In order to assess the prevalence of lenticular opacities in patients with dyslipidemia (raised serum cholesterol and triglycerides) a group of 80 dyslipidemic patients were subjected to a general physical examination and an ophthalmic examination of the fully dilated eye at the Tygerberg Academic Hospital, University of Stellenbosch, South Africa (unpublished data). Patients (n=80) of both genders and irrespective of age were enrolled in the trial if they met the inclusion criteria for dyslipidemia. Patients were included if their fasting serum cholesterol and triglyceride concentrations were >5.2 mmol/l and >2.3 mmol/l, respectively when measured on three separate occasions over a one-month period (Fig. 1.6). Patients were excluded if they suffered from any condition known to cause or predispose them to elevated lipid levels or lenticular opacification. Results The study group was predominantly male Caucasian and smokers. Most patients—68.8 percent admitted regular alcohol consumption. The mean systolic and diastolic blood pressure data, 134±18 and 84±9 mm Hg, respectively, fell within the normal range for age. The BMI of the group was significantly greater than the norm (i.e. 28.89±4.82 kg/m2). The prevalence of lenticular opacities divided the study group into two cohorts, i.e. those with normal lenses (62%) and those with opacities (39%) (Fig. 1.7).
FIGURE 1.6 The lipid profile of the study group The prevalence of lenticular opacity in dyslipidemic patients in the age group of 30 to 40 years was 33 percent. This age group was not studied in the Barbados Eye Study (BES) or in The Beaver Dam Eye Study (BDES) and consequently data for comparison are not available (Table 1.3). In the 40 to 50 year age group, the prevalence of lenticular opacity in our patients was 50 percent compared to 4.7 percent in the BES and 8.3 percent in BDES. Differences in the older age groups were not prominent (Fig. 1.8). Modern medicine today aspires to early detection of disease processes with the aim of early intervention in an attempt either to halt the progression or to reverse the process.
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Although the classic systemic signs of dyslipidemia are well appreciated, i.e. xanthomata, xanthelasma, thickening of the Achilles tendon and corneal arcus, in our study the prevalence of one or more of the ocular signs was far greater than that of the systemic signs, 23.8 percent for the former as opposed to 47.3 percent for the latter. The distribution of dyslipidemia-related signs in this study was: • Xanthelasma—7.5 percent • Corneal arcus—8.8 percent • Achilles tendon involvement—16.3 percent • Cortical lenticular opacity—31.0 percent.
TABLE 1.3 Age distribution of patients with lenticular opacities compared to other population based studies Age group Study group Percentage of opacities BES BDES (years) 30–40 33.33 40–50 50.00 50–60 18.51 60–70 33.33 70–80 66.67 80+ 33.33 BES: Barbados Eye Study BDES: Beaver Dam Eye Study N/A: Not available.
N/A 4.7 24.5 57.5 85.9 98.3
N/A 8.3 26.5 56.7 70.5 N/A
FIGURE 1.7 The prevalence of lens opacities in the study group
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FIGURE 1.8 Prevalence of lenticular opacities in two population-based studies compared to the dyslipidemic study group
FIGURE 1.9 Physical signs associated with dyslipidemia It is noteworthy that the most frequent ocular sign—cortical lenticular opacity—occurred twice as frequently as the most frequent systemic sign—Achilles tendon thickening (Fig. 1.9). This work leads the investigators to conclude that: • Dyslipidemic patients are more likely to develop cortical opacification than the normal population. • Cortical lens opacification in dyslipidemics manifests at a younger age than does nuclear opacification.
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• Cortical lens opacification in the patient younger than 50 years of age should alert the ophthalmologist to arrange for diagnostic serum lipid assessment. • Cortical lenticular opacification should be regarded as one of the most common, and hence reliable, clinical signs of dyslipidemia. Jahn et al attempted to determine the role of glucose and lipid metabolism in the formation of cataract in elderly people undergoing cataract extraction. They found that patients with posterior subcapsular cataract had higher concentrations of fasting serum triglycerides and were significantly younger than patients with nuclear or cortical cataract. Their results furthermore suggest that the association of hypertriglyceridemia, hyperglycemia and obesity favors the formation of a specific morphologic type of lens opacity, posterior subcapsular cataract, occurring at an early age. Because these factors are potentially modifiable by lifestyle changes, these observations may prove important as the modification of these parameters could constitute an effective mode of prevention or retardation in a subgroup of patients developing cataract at an early age. Acetylator Status The human acetylation polymorphism has been known for more than three decades since its discovery during the metabolic investigation of the antituberculous hydrazine drug, isoniazid. The trait was originally known as the “isoniazid acetylation polymorphism” but is now usually abbreviated as “acetylation polymorphism” because acetylation of numerous hydrazine and arylamine drugs and other chemicals are subject to this trait. Individuals phenotype as “slow” acetylators when homozygous for the slow acetylator gene, “rapid” when homozygous for the rapid acetylator gene or “intermediate” when heterozygous. The acetylator phenotype is a lifelong, relatively stable characteristic of the individual that can phenotypically be determined by procedures using any of several test agents (e.g. caffeine, isoniazid, sulfamethazine, sulfapyridine). Certain disease states such as AIDS can change the phenotype expression in an individual. On the other hand, acetylator genotype can be determined by specialized polymerase chain reaction (PCR) methods. Several diseases have been linked to acetylator pheno- and/or genotype. The best documented are bladder cancer (slow), colorectal adenomas (rapid), Gilbert’s syndrome (slow), allergic diseases Type I diabetes mellitus (fast), Type II diabetes mellitus (slow) and familial Parkinson’s disease (slow). Recent work (PhD level, unpublished) at the departments of Ophthalmology and Pharmacology at the University of Stellenbosch, South Africa have also established an association between age-related cataract and acetylation status as determined both phenotypically and genotypically. Sixty adult patients of both sexes with classic agerelated lens opacities presenting for cataract surgery were enrolled in a prospective controlled study. Patients were included in the trial if they perceived themselves to be colored and if this was verified by at least one independent observer. The South African population of mixed ancestry (including Malay, Khoisan, Negroid and Caucasoid stock) is referred to as “colored” and all patients were selected from this well studied subgroup of the population. Care was taken to exclude all patients with well known etiological factors for cataract formation such as diabetes mellitus, previous ocular trauma, other
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metabolic and/or inherited diseases. One hundred and twenty patients of the same race group served as controls. Figure 1.10 demonstrates that in the control group (representing the population at large) the distribution of the phenotypic acetylation status was 20 percent “rapid”, 50 percent “intermediate” and 30 percent “slow”. In the cataract group the distribution was 5 percent “rapid”, 42 percent “intermediate” and 53 percent “slow”. This clearly seems to suggest that cataract possibly occur more frequently in slow acetylators than in the rest of the population. Could this finding perhaps suggest a possible etiologic role for chemical substances possessing a primary aromatic amine or hydrazine group in human lenticular opacification? Lipid Peroxidation, Free Radicals and Nutritional Influences on Cataract Formation Oxygen and oxygen-derived free radicals and a failure of intracellular calcium homeostatic mechanisms are recurring themes in a wide variety of cell injuries. The addition of electrons to molecular oxygen leads to the formation of toxic free oxygen radicals or reactive oxygen species (ROS), e.g. O2− = superoxide (one electron) H2O2 = hydrogen peroxide (two electrons) OH− = hydroxyl radical (three electrons)
FIGURE 1.10 Acetylator status of cataract vs normal patients Iron is very important in this process according to the Haber-Weiss reaction: H2O2+O2−Fe2+.OH+OH−+O2 These free radical species cause lipid peroxidation and other deleterious effects on cell structure. Recent studies have shown that lipid peroxidation, an event caused by
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imbalance between free radical production and antioxidant defense, may play a role in the genesis of cataract. Higher levels of malondialdehyde (MDA), a final product of the lipid peroxidation process, have been observed in diabetic and myopic cataract compared with senile cataract. Protection of the cell against damage by these free radicals takes place indirectly (enzymatically) by antioxidant enzymes—superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase (CAT). Direct protection is offered by mainly dietary antioxidants—ascorbate (Vit C), tocopherol (Vit E), carotenoids (Vit A) and glutathione (GSH). Light and oxygen as risk factors for cataract Various epidemiological studies demonstrate associations between elevated risk of various forms of cataract and exposure to higher intensities of incident and/or reflected ultraviolet light (Table 1.4). Elevated levels of oxygen exposure perhaps show the clearest causal relationship between oxidative stress and cataract. Nuclear cataract was observed in patients treated with hyperbaric oxygen therapy, and markedly elevated levels of mature cataract were observed in mice that survived exposure to 100 percent oxygen twice weekly for 3 hours. A higher incidence of cataract was noted in lenses exposed to hyperbaric oxygen in vitro. Very early stages of cataract in guinea pigs exposed to hyperbaric oxygen was noted by Giblin. Role of cellular antioxidants against lens damage Protection of the organism against photooxidative insult can be viewed as two interrelated processes. Primary defenses offer protection of proteins and other lens constituents by lens antioxidants and antioxidant enzymes whereas secondary defenses include proteolytic and repair processes. The primary defenses shall form the focus of our attention. The major aqueous antioxidants in the lens are ascorbate and GSH. Ascorbate is probably the most effective, least toxic antioxidant identified in mammalian systems. The following has been observed • The lens and aqueous concentrate ascorbate >10 times the level found in human plasma.
TABLE 1.4 Extent of light expoxure and the risk of cataract Study
Exposure
USA: NHANES Daily hours of sunlight survey in area; ages 65−74
PR 95% CI
<6.6 h 1.0 7.1–7.7 h 1.7 1.2–2.7 >8.2 h 2.7 1.6–4.6 Australia Daily hours of sunlight <8 h 1.0 in area 8.5–9 h 2.9 0.6–13.2 >9.5 h 4.2 0.9–18.9 Average mean erythemal 2000 1.0 dose of area 2500 1.3 0.8–2.3 3000 1.8 1.0–3.4 Nepal Average hours of sunlight 7–9 h 1.0 10–11 h 1.2 0.9–1.4 >12 h 2.5 2.1–3.0 PR=prevalence ratio CI=confidence interval
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• The concentration of ascorbate in the lens nucleus is only 25 percent that of the surrounding cortex. • Ascorbate levels in normal lenses are higher than in cataractous lenses. • Ascorbate levels are higher in the older guinea pig lens than in younger animals despite the same dietary intake of ascorbate. • Increasing lens ascorbate concentrations by two-fold is associated with protection against cataract-like damage. With this basic science knowledge several epidemiological, clinical and even interventional studies have been undertaken. Vitamin C was considered in approximately 9 published studies and observed to be inversely associated with at least one type of cataract in eight of these studies. In the Nutrition and Vision Project, age-adjusted analyses bases on 165 women with high vitamin C intake (mean=294 mg/day) and 136 women with low vitamin C intake (mean=77 mg/day) indicated that the women who took vitamin C supplements for ≥10 years had >70 percent lower prevalence of early opacities (RR: 0.23; CI: 0.09–0.60) and >80 percent lower risk of moderate opacities (RR: 0.17; CI: 0.03–0.87) at any site compared with women who did not use vitamin C supplements. In comparison to the above data, Mares-Perlman and et al report that past use of supplements containing vitamin C was associated with a reduced prevalence of nuclear cataract, but an increased prevalence of cortical cataract after controlling for age, sex, smoking, and history of heavy alcohol consumption. Glutathione (GSH) levels in the lens are several fold the levels found in whole blood and plasma. GSH levels also diminish in the older and cataractous lenses. Pharmacological opportunities could be suggested by observations that incorporating the industrial 0.4 percent butylated hydroxytoluene in diets of galactose-fed (50% of diet) rats diminished prevalence of cataract. Clinical studies however have not yet been forthcoming. Vitamin E, a natural lipid-soluble antioxidant, can inhibit lipid peroxidation and appears to stabilize lens cell membranes. Consumption of Vit E supplements was inversely correlated with cataract risk in two studies. Robertson et al found among ageand sex-matched cases and controls that the prevalence of advanced cataract was 56 percent lower (RR: 0.44; CI: 0.24–0.77) in persons who consumed vitamin E supplements (>400 IU/ day) than in persons not consuming supplements. Jacques and Chylack (unpublished) observed a 67 percent (RR: 0.33; CI: 0.12–0.96) reduction in prevalence of cataract for vitamin E supplement users after adjusting for age, sex, race and diabetes. Two prospective studies demonstrated a reduced cataract progress among individuals with higher plasma vitamin E. Rouhianen et al found a 73 percent reduction in risk for cortical cataract progression (RR: 027; CI: 0.08–0.83), whereas Leske et al reported a 42 percent reduction in risk for nuclear cataract progression (RR: 0.58; CI: 0.36–0.94). Vitamin E supplementation was related to a lower risk for progress of nuclear opacity (RR: 0.43; CI: 0.19–0.99). The carotenoids, like vitamine E, are also natural lipid-soluble antioxidants. Betacarotene is the best known carotenoid because of its importance as a vitamin A precursor. However, it is only one of the 400 naturally occurring carotenoids, and other carotenoids
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may have similar or greater antioxidant potential. In addition to β-carotene, α-carotene, lutein and lycopene are important carotenoid components of the human diet. Jacques and Chylack were the first to observe that persons with carotene intakes above 18,700 IU/ day had the same prevalence of cataract as those with intakes below 5,677 IU/day (RR: 0.91; CI: 0.23–3.78). Hankinson et al followed this report with a study that reported that the multivariate-adjusted rate of cataract surgery was about 30 percent lower (RR: 0.73; CI: 0.55–0.97) for women with high carotene intakes (median=14,558 IU/day) compared with women with low intakes of this nutrient (median=2,935 IU/day). However, while cataract surgery was inversely associated with total carotene intake, it was not strongly associated with consumption of carotene-rich foods, such as carrots. Rather, cataract surgery was associated with lower intakes of foods such as spinach that are rich in lutein and xanthin carotenoids, rather than β-carotene. This would appear to be consistent with the observation that the human lens contains lutein and zeaxanthin but no β-carotene. This observation would appear to be consistent with the observation that lutein and zeaxanthin are the most prevalent carotenoids in lens. However, Mares-Perlman did not detect a significantly altered risk for cataract among consumers of these nutrients. Intervention studies To date only one intervention trial designed to assess the effect of vitamin supplements on cataract risk has been completed. Sperduto et al took advantage of two ongoing, randomized, double-blinded vitamin and cancer trials to assess the impact of vitamin supplements on cataract prevalence. The trials were conducted among almost 4,000 participants aged 45 to 74 years from rural communities in Linxian, China. Participants in one trial received either a multisupplement or placebo. In the second trial, a more complex factorial design was used to evaluate the effects of four different vitamin/mineral combinations: • Retinol (5000 IU) and zinc (22 mg) • Riboflavin (3 mg) and niacin (40 mg) • Vitamin C (120 mg) and molybdenum (30 mg) • Vitamin E (30 mg), β-carotene (15 mg), and selenium (50 µg). At the end of the five to six year follow-up, the investigators conducted eye examinations to determine the prevalence of cataract. In the first trial there was a significant 43 percent reduction in the prevalence of nuclear cataract for persons aged 65 to 74 years receiving the multisupplement (RR: 0.57; CI: 0.36–0.90). The second trial demonstrated a significantly reduced prevalence of nuclear cataract in persons receiving the riboflavin/niacin supplement relative to those persons not receiving the supplement (RR: 0.59; CI: 0.45–0.79). The effect was strongest in those aged 65 to 74 years (RR: 0.45; CI: 0.31–0.64). However, the riboflavin/niacin supplement appeared to increase the risk of posterior subcapsular cataract (RR: 2.64; CI: 1.31–5.35). The results further suggested a protective effect of the retinol/zinc supplement (RR: 0.77; CI: 0.58–1.02) and the vitamin C/molybdenum supplement (RR: 0.78; CI: 0.50–1.04) on prevalence of nuclear cataract. Conclusion Although light and oxygen are necessary for physiological function, when present in excess they seem to be causally related to cataractogenesis. Aging might diminish the bodies primary antioxidant reserves, antioxidant enzyme abilities, and diminished secondary defenses such as proteases.
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The literature creates the strong impression that antioxidant intake might diminish the risk for cataract formation. Longitudinal studies and more intervention studies are essential in order to establish the value of dietary antioxidants and to determine the extent to which cataract progress is affected by nutritional supplements. This fact becomes significant when one appreciates that poor education and lower socioeconomic status are directly related to poor nutrition. It is therefore not irrational to contemplate the value of intervention for populations at risk. The work available, albeit preliminary, indicates that nutrition may provide the least costly and most practicable means to attempt the objectives of delaying cataract. Ocular Disease Many ocular diseases have been associated with cataract formation either as direct cause and effect relationships or as common associations. Myopia Weale suggested that lenses of myopes are subject to excessive mechanical stress which could lead to cataract. This hypothesis was tested by several investigators and Harding et al during their Oxford case-control studies found that the risk of cataract after the age of 50 was doubled in myopes. Weale (1980) also suggested that there is a graded risk for increasing degrees of myopia. This was eloquently confirmed two decades later by Lim et al in the Blue Mountains Eye Study. Eyes with onset of myopia before age 20 had the greatest posterior subcapsular (PSC) cataract risk (odds ratio [OR] 3.9; confidence interval [CI] 2.0–7.9) Refraction-related increasing odds were found between PSC cataract and myopia: low myopia (OR 2.1; CI: 1.4–3.5), moderate myopia (OR 3.1; CI: 1.6–5.7), and high myopia (OR 5.5; CI: 2.8–10.9). High myopia was associated with PSC, cortical, and late nuclear cataract. Conversely PSC cataract was inversely associated with hyperopia (OR 0.6; CI: 0.4–0.9). They finally concluded that early-onset myopia (before 20 years of age) may be a strong and independent risk factor for PSC cataract, that nuclear cataract was associated with presumed acquired myopia, whereas high myopia was associated with all three types of cataract. Wensor et al demonstrated that a myopic shift is associated with nuclear cataract. In the population based study of 3,271 Australians an association between myopia of 1 diopter or more and both nuclear and cortical cataract was observed. Between posterior subcapsular cataract and myopia such a relationship did not exist. It is not sure that a causal relationship exists between cortical cataract and myopia or rather that a myopic shift occurs after people develop cortical cataract. The temporality of this relationship should still be explored in future prospective analyses. Glaucoma Glaucoma has been shown to be strongly associated with the pathogenesis of cataract in many studies undertaken in many countries. The relative risk (odds ratio [OR]) of cataract developing in a glaucoma patient can be as high as six times normal. This risk more than doubles to an OR of 14.3 after glaucoma filtration surgery. This rise in risk is
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most probably due to the trauma of surgery for glaucoma. Vesti in Helsinki, Finland investigated cataract progression after trabeculectomy in a study of 47 eyes with exfoliative glaucoma (EXG) and in 20 eyes with primary open-angle glaucoma (POAG). EXG, age, hypotony (IOP
or= 5 days and early postoperative IOP rise>30 mm Hg were observed to be risk factors for cataract progression. Besides formal filtering procedures like full thickness procedures, laser procedures for the management of different types of glaucomas are frequently performed such as argon laser trabeculoplasty, argon laser iridoplasty and Nd-YAG peripheral iridotomy. Each of these procedures carries the risk of inducing a cataract especially of the focal type. Zadok et al has described a previously unreported complication of a posterior chamber intraocular lens (IOL) implanted in a phakic eye. The left eye of a 25-year old patient with high myopia was treated prophylactically with Nd: YAG laser iridotomy prior to phakic IOL implantation. Slit lamp examination of the same eye disclosed an opacity of the anterior capsule of the crystalline lens under the iridotomy site. Miotics, particularly long-acting cholinesterase inhibitors, if used for long term, may cause tiny
FIGURE 1.11 Anterior subcapsular flecks after acute closed angle glaucoma anterior subcapsular vacuoles and, occasionally, more advanced opacities. Cessation of medication may stop, retard or occasionally reverse their progression. Acute congestive angle-closure glaucoma is associated with the subsequent formation of glaukomflecken consisting of small, gray-white, anterior, subcapsular or capsular opacities in the pupillary zone (Fig. 1.11). Ophthalmic Surgical Procedures Many different ophthalmic procedures carry the risk of inducing cataract. Among others are surgical iridectomy, filtration surgery, corneal transplants, retinal detachment surgery with and without intraocular silicone oil as well as pars plana vitrectomy especially in diabetics. Assessing the surgical outcome in a series of 63 consecutive patients treated for rhegmatogenous retinal detachment by primary vitrectomy Oshima reported the reattachment rate by final examination as 100 percent, but there was a high incidence (53.8%) of cataract progression in phakic eyes.
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More recently with the advent of minus power phakic IOL implantation surgery, several reports have appeared of cataract induction secondary to the implantation of these lenses into the ciliary sulcus. These cataract have occurred both with silicone and collamer materials. Some have taken as short a time as 6 months, whilst others took 7 years to form. In another series of 38 consecutive eyes with high myopia implanted with a silicone posterior chamber plate-style intraocular lens (Chiron, Adatomed) over a period of 21 months and followed for between 3 and 24 months not a single cataract occurred. The lens style and design may play a significant role in the cataract pathogenesis, because in a recent study Brauweiler et al attempted to assess the effectiveness and safety of implantation of a silicone, posterior chamber IOL in the ciliary sulcus of phakic, highly myopic eyes in a noncomparative consecutive interventional series. Eighteen eyes of 10 patients underwent implantation of a Fyodorov 094M-1 IOL by the same surgeon and were evaluated for a 2-year postoperative period. Cataract formation of the anterior subcapsular (8 eyes) or nuclear (only 1 eye) type was observed in overall 9 (52.9%) of 17 eyes. When considering only the patients with a follow-up of 2 years, the incidence of cataract formation was 81.9 percent (9 of 11 eyes). Obviously this very high incidence of cataract formation should discourage the implantation of the type of IOL used in this study. Ocular Trauma The development of cataract is a known complication following blunt or penetrating ocular trauma. However traumatic cataract and zonular dehiscence is only one complication of the injured ocular tissues. Other complications include glaucoma, retinal detachment, optic nerve damage, extraocular muscle imbalance and injury to the bony orbit. Ocular trauma is a major cause of monocular blindness in both the developed and developing world, but this is not seen as a significant cause of bilateral blindness. Trauma can therefore be considered as a major cause of blind eyes but not of blind people. Crystalline lens subluxation, total dislocation, or localized cortical or diffuse opacities are often observed secondary to blunt ocular trauma. An unusual complication of blunt trauma is rupture of the posterior capsule with subsequent lens fiber hydration leading to rapidly progressive lens opacification (Fig. 1.12). Posterior capsular breaks have been reported to develop thick, fibrous, opaque margins approximately 6 weeks after blunt trauma. Secondary Cataract Uveitis A secondary cataract develops as a result of some other primary ocular disease. The most common cause of secondary cataract is chronic anterior uveitis. The earliest finding is a polychromatic luster at the posterior pole of the lens. If the uveitis is controlled, the progression of cataract may be arrested. If the inflammation cannot be controlled, anterior and posterior subcapsular opacities develop and the lens may become completely opaque. The lens opacification seems to progress more rapidly in the presence of posterior synechiae.
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FIGURE 1.12 Vossius’ ring after blunt ocular trauma Hereditary posterior segment disease Hereditary fundus dystrophies such as retinitis pigmentosa, Leber’s congenital amaurosis, gyrate atrophy, Wagner’s and Stickler’s syndromes may be associated with posterior subcapsular lens opacities. In a study of 384 eyes of 192 patients with a mean age of 39.1 years who presented with typical retinitis pigmentosa, cataract was found in 46.4 percent of the eyes. Among these, 93.6 percent showed posterior subcapsular opacification. The incidence of cataract increased with age. Wagner’s vitreoretinal degeneration is characteristically associated with high myopia, glaucoma, choroidal atrophy, retinal detachment and presenile cataract. Persistent hyperplastic primary vitreous (PHPV) is a congenital disorder that manifests a range of ocular anomalies including leukoria, microphthalmia, a retrolental fibrovascular membrane and cataract. In general the prognosis for visual acuity with PHPV is poor. Iris color McCarty et al in their Australian population study of 3,271 adults aged 40 years and older found an association between cortical cataract and brown or dark brown irides for all ages that was not explained by country of birth or language spoken. In all age categories, brown iris color was also associated with nuclear cataract. No such association was found for posterior subcapsular cataract however. In the Italian-American Cataract Study, there was an increased, although not significant, risk of cortical cataract in people with brown irides. Dark iris color was not associated with cortical cataract in the Lens Opacities Case-Control Study. In the National Health and Nutrition Examination Survey, blacks, who have dark brown irides, were found to have significantly increased risk of cortical cataract. In both the above mentioned studies, dark iris color was also found to be a significant risk factor for nuclear cataract. The relationship of nuclear cataract and iris color could result from genetic susceptibility associated with iris color or other factors not yet determined. This finding may partially explain the variation in the prevalence of nuclear cataract observed in different countries with different racial groups.
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Systemic Diseases Hypertension The association between hypertension and cataract was first noted in the Framingham study where earlier detection of elevated blood pressure was more common in those later found to have cataract. It was also noted in the same study that consumption of diuretics which restores normal blood pressure in many patients does not protect against this risk. There may however be a variety of interactions in these patients in that hypertension may be associated with high blood glucose, diabetes and other conditions as well as with use of diuretics. Diuretics have different effects on plasma urea levels, with frusemide and acetazolamide associated with the highest levels, and parallel effects on cataract. Overall diuretic use was associated with an odds ratio of 1:6 but cyclopenthiazide (Navidrex), which had least effect on plasma urea, was reported by a greater proportion of controls than cases. Loop diuretics were reported by more than twice the proportion of cases than of controls. Hypertension and diuretic consumption did not appear as risk factors in Oxford but the graded properties of different diuretics did emerge and with a similar sequence to that found in Edinburgh. The only significant association of individual diuretics was an apparent protective effect by cyclopenthiazide and a risk associated with spironolactone which itself is a steroid. There was no significant association of particular sites of opacity with diuretic use. Dehydrational Crisis Harding has proposed that frequent episodes of diarrhea may be related to cataractogenesis and may account for the excess prevalence in some developing countries. Four intermediate events have been suggested to explain the role of diarrhea in the development of cataract • Malnutrition secondary to malabsorption of nutrients • Relative alkalosis from administration of rehydrating fluids with bicarbonate • Dehydration induced osmotic disturbance between the lens and the aqueous humor and • Increased levels of urea and ammonium cyanate which may denature lens proteins by the process of carbamylation. Six case-control studies have examined the relationship of severe diarrhea and increased risk of cataract, with discordant results. Two case-control, clinic-based studies done in Madhya Pradesh and Orissa, India have suggested a three-to four-fold increase in the risk for cataract for those with remembered episodes of life-threatening dehydration crises, severe enough to render the patient bedridden for at least three days. However, these findings were not replicated in two other epidemiologic investigations done in India. Using a less stringent definition of diarrhea (confinement to bed for one day), the IndiaUS Case-Control Study found no associations with cataract. Also, a village-based casecontrol study in Southern India showed no association between severe diarrhea and risk of cataract. Furthermore, an observational study done in Matlab, Bangladesh, revealed that diarrhea from all causes was not significantly associated with cataract, although it
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was difficult to determine how cataract was defined in the study. The case-control study in Oxford found a marginally significant excess risk of cataract with reported severe diarrhea, but a significant risk in the subgroup aged 70 and older. Adjustments for the other possible confounding factors also found in the study were not done. Considering the potential public health importance of diarrhea as a risk factor, as well as the biologically plausible role of dehydration in cataractogenesis, further research to clarify this association is needed. Prospective studies involving closer follow-up of groups of patients who suffered from acute life-threatening diarrhea may provide more convincing evidence. Moreover, studies that examine the cumulative effect of milder, chronic dehydration episodes in cataractogenesis may also add to the current understanding of this issue. Renal Failure Cataract has been reported in many cases of renal failure. Sometimes cataract, often transient, was associated with hemodialysis and thought to be caused by the osmotic shock that dialysis causes, but Laqua (1972) noted lens opacities before dialysis and suggested they were caused by uremia. Increased blood urea could lead to cataract in a similar way to that postulated in severe diarrhea. After renal transplantation patients are treated with immunosuppressants usually including corticosteroids that may cause cataract. Posterior subcapsular lens opacities were observed in 19 out of 22 renal transplant recipients, aged 21 to 54 years in Hiroshima. Half of the patients suffered visual loss, attributed to steroid-induced cataract. In a study of diabetic patients receiving renal transplants in the USA only one patient developed a visually-impairing cataract but lesser degrees of lens opacification were seen in 26 percent of eyes. Fourteen of 55 nondiabetic renal transplant patients were found to have cataract. The case-control study in Edinburgh did not report on renal failure as such but did find that the mean urea level was significantly higher in the plasma of cataract patients compared with controls. The level was not high enough to indicate renal failure. The raised urea levels are still present when subjects are subdivided by age and sex. Diuretics may raise urea levels and thus contribute to these differences but when all diabetics and individuals receiving diuretics were excluded, a relationship between high plasma urea and cataract remained. Environmental Factors: Ultraviolet Radiation There is considerable international interest in the association between solar ultraviolet B (UVB) radiation and cataract. Much of this interest has resulted from concern about the health effects of the increasing levels of UVB reaching the earth’s surface as a consequence of depletion of the stratospheric ozone layer. Young suggests that sunlight is the primary causal factor in cataractogenesis, and strongly advocates the widespread distribution of sunglasses to prevent cataract. Harding on the other hand suggests that sunlight is not a major etiological factor in human cataract formation. The lens is known to absorb UVB and UVA and change in lens clarity has been linked in animal experiments with short-term, high intensity exposure and chronic exposure to UVB.
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Epidemiologic studies have demonstrated cataract to be more prevalent in sunny countries, such as Israel, than in cloudy countries, such as England. Moreover, in Romania and the United States, cataract are more prevalent in dry hot areas with more sun exposure within each country than in areas with prolonged cloud cover. The Beaver Dam Eye Study, found an association between ultraviolet B radiation exposure and cortical cataract in men only. The Lens Opacity Case-Control Study did not find an association between sun exposure and any type of cataract development. However, this study investigated only urban populations, and this may explain why no association was found. In both the Italian-American Cataract Study and India-US Case-Control Study, sunlight exposure was associated with cataract formation. Taylor studied 797 watermen and went to great lengths to calculate an ultraviolet radiation exposure index on the basis of field variables such as outdoor hours worked, work location, and attenuation due to spectacle use and hat cover. He found a significant association between ultraviolet B radiation index and cortical cataract but found no association with other morphological cataract types. Bochow et al studied the relationship between ultraviolet radiation exposure and posterior subcapsular cataract. He not only discovered a significant association but also a dose-response relationship. Two unique studies, one prospective and one case-control, provide indirect evidence that ultraviolet light plays a role in cataract formation. Schein et al studied the distribution of cortical opacities by lens quadrant in a prospective study of Chesapeake Bay watermen. The prevalence of cortical lens opacities increased with age, with a high degree of concordance between eyes. The inferonasal lens quadrant was the most common location involved both for new cataract development and for progression of preexisting cataract. Cataract formation in this quadrant was presumed to be the most consistent with ultraviolet radiation damage on the basis of greater exposure in this area of the lens. Resnikoff et al studied the association of lens opacities with two other presumed ultraviolet radiation-associated ocular diseases, climatic droplet keratopathy and exfoliation syndrome. There was a strong correlation between the diseases in this case-control study. Based on the available epidemiological evidence, the following conclusions can be drawn • There is sufficient experimental evidence that exposure to artificial sources of UVB can cause lens opacities in laboratory animals. • There is limited evidence suggesting that exposure to solar UVB causes cortical opacities in humans. • There is also limited evidence suggesting that exposure to solar UVB causes posterior subcapsular cataract in humans. • The epidemiological evidence is consistent in suggesting that nuclear cataract are not causally associated with exposure to solar UVB. Drug Related Factors A number of well-known and widely used drugs have been implicated in cataract etiology with oral corticosteroids probably the widest recognized of all.
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Corticosteroids In 1930, Hench postulated that a naturally occurring substance might be responsible for the clinical improvement seen in women with rheumatoid arthritis when they became pregnant. He called this substance “compound E”, but it was not until 1948 that this substance (soon to be called cortisone) was synthesized and became available for clinical use. In the 50 years since then, corticosteroids have had an enormous impact in medicine, however it soon became clear that hydrocortisone has significant mineral corticoid as well as antiinflammatory activity and that this could produce dose-related toxicity It is now known that the principal naturally occurring corticosteroids secreted by the adrenal cortex are hydrocortisone (cortisol), a glucocorticoid involved in the regulation of carbohydrate, protein and lipid metabolism and aldosterone, a mineralocorticoid affecting fluid and electrolyte balance. Because hydrocortisone also exerts some mineralocorticoid (salt-retaining) effects, several structurally modified glucocorticoids with relatively greater antiinflammatory and lower salt-retaining properties were synthesized once the therapeutic potential of their antiinflammatory and immuno-suppressive properties became apparent. Antiinflammatory and immunosuppressive effects occur at doses above the normal physiological levels of daily glucocorticoid production, i.e. at pharmacological doses. However since many physiological and pharmacological actions are mediated by the same receptor, it is not surprising that prolonged use of pharmacological doses can lead to adverse physiological effects. It is estimated that between 10 to 60 percent of patients using systemic corticosteroids develop cataract, especially of the posterior subcapsular (PSC) type. Glucocorticosteroids are lipophilic and therefore diffuse easily across the cell membrane after which they bind and activate a cytoplasmic glucocorticoid receptor. The resulting receptor steroid complex enters the cell nucleus, binds to the glucocorticoid response elements on the DNA and up- or downregulates the expression of corticosteroid-responsive genes with resultant effects on protein synthesis in target tissues.
FIGURE 1.13 Progession of steroidinduced cataract
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FIGURE 1.14 Posterior subcapsular cataract Several ways have been identified in which corticosteroids may induce cataract formation (Fig. 1.13) including: • Elevation of glucose level • Inhibition of Na, K-ATPase • Increased cation permeability • Inhibition of glucose-6-dehydrogenase • Inhibition of RNA-synthesis • Loss of ATP • Covalent bonding of steroids to lens proteins. Posterior subcapsular cataract is the hallmark of steroid cataract (Fig. 1.14). It starts as fine granular and vacuolated opacities at the posterior aspect of the lens. PSC opacities occur frequently with high doses (more than 15 mg prednisone or equivalent per day) and prolonged use (more than one year) of corticosteroids. Clinical trials have shown that PSC opacities secondary to oral corticosteroids may develop within as short a time as 4 months. Recent studies have suggested that the use of inhaled corticosteroids may be a significant risk factor for the development of cataract, may be even more so than the use of oral corticosteroids. These studies have again pointed out the importance of the “firstorder effect”. A drug absorbed through the nasal mucosa or conjunctiva “drains” to the right atrium and ventricle. The drug is then pumped in part, to the head (i.e. the eye as a target organ) before returning to the left atrium and ventricle. The second passage is then to the liver and kidneys, where the drug is metabolized and detoxified. With oral medication—the first pass includes absorption from the gut via the liver where, depending on the drug, more than 90 percent of the drug is detoxified before going to the right atrium. Therefore, oral medications are metabolized even before the first pass, while ocular or nasally administered drugs are not metabolized until the second pass. This, in part, may be a reason why more potent steroid inhalants have greater ocular exposure and some ocular medications cause significant systemic adverse effects. Considering the widespread use of corticosteroids and their association with PSC cataract, clinicians should be aware of a patient’s medication history and recognize the distinguishing features of PSC cataract.
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Allopurinol Allopurinol is an antihyperuricemic drug widely used for the treatment of hyperuricemia and chronic gout. It inhibits the terminal step in uric acid synthesis, which results in a reduction of uric acid concentrations in both serum and urine. In about 85 percent of patients with gout, serum urate concentrations can be normalized by an allopurinol dose of 300 mg/d, and in some patients a dose of 100 to 200 mg/d is sufficient. Treatment with allopurinol is usually well tolerated, with hypersensitivity reactions constituting the most common adverse effects. In 1982, Fraunfelder et al reported 30 cases of cortical and subcapsular cataract associated with long-term use of allopurinol reported to the National Registry of DrugInduced Ocular Side Effects (Oregon Health Sciences University, Portland). The observed lens changes appeared to have the characteristics of early age-related cataract. At about the same time, Lerman et al used phosphorescence spectroscopy to demonstrate in vitro the probable presence of allopurinol in cataractous lenses that had been extracted from patients treated with allopurinol. The phosphorescence peaks characteristic of allopurinol could not be demonstrated in lenses from patients who had not ingested allopurinol. Evidence from epidemiologic studies on the possible cataractogenic effects of allopurinol is however inconclusive. Two separate epidemiologic studies did not show an increased risk. Another study reported an unusual morphologic thinning of the anterior clear zone of the lens in patients receiving long-term treatment with allopurinol. In the Lens Opacities Case Control Study, wherein gout medications were found to be associated with a 2.5-fold increased risk of mixed cataract, no distinction was made between allopurinol and other medications for gout. In a case control study conducted by Garbe et al using data from the Quebec universal health program for all elderly patients they established that a clear relationship exists between the long-term administration of allopurinol and an increased risk for cataract extraction. Phenothiazines In 1965, the occurrence of ocular pigmentation and lens opacity in patients on high dose phenothiazine drugs, particularly chlorpromazine, was reported in several papers. Phenothiazine has been thought to cause pigmentation by virtue of its ability to combine with melanin and form a photosensitive product. It is also postulated that this process might accelerate any predisposition to lens opacification from environmental insults such as solar radiation. A study involving schizophrenic patients showed an association between severity or grade of lenticular pigmentation and equivalent dose of phenothiazine intake. Epidemiologic research on the role of phenothiazines in cataractogenesis is limited. A case-control study done in North Carolina found a two-fold increased risk of cataract in those with history of tranquilizer use, although the types of tranquilizers and cataract were not characterized. A health maintenance organization based, non-concurrent prospective study that controlled for steroid use and diabetes documented at least three-fold increased risk for cataract extraction among current and past (two to five years prior to extraction) users of two groups of tranquilizers: “antipsychotic phenothiazine drugs” (chlorpromazine, thioridazine, trifluoperazine, perphenazine, fluphenazine) and “other phenothiazine drugs” (chlorperazine, prochlorperazine, promethazine, trimeprazine).
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Given the paucity and limitations of available epidemiologic data, more studies, such as those characterizing the specific types of senile cataract and phenothiazines, are needed to verify any association. Diuretics and Antihypertensives Harding and van Heyningen reported that thiazide diuretics were used less frequently by patients who underwent cataract surgery than control subjects. More recently, the Beaver Dam Eye Study found that use of thiazides was associated with lower prevalence of nuclear cataract and increased prevalence of posterior subcapsular cataract. Several other studies have found that use of diuretics was associated with increased risk of cataract. The Beaver Dam Eye Study also found a raised overall risk (OR, 1.3) for potassiumsparing diuretics, but this was not statistically significant. A cataractogenic effect of potassium-sparing diuretics is biologically plausible, as these diuretics disturb sodium transport across the lens fiber membrane. The calcium channel blocker nif edipine has been associated with increased risk of cataract extraction and angiotensin-converting enzyme inhibitors with decreased risk of nuclear cataract. Hypertension and other cardiovascular conditions is a potential confounding problem in studies of cataract and antihypertensive medications, including diuretics. Antimalarial Drugs Most drugs used in the treatment of malaria produce phototoxic side effects in both the skin and the eye. Cutaneous and ocular effects that may be caused by light include: cataract formation, changes in skin pigmentation, corneal opacity and other visual disturbances including irreversible retinal damage (retinopathy) leading to blindness. The mechanism for these reactions in humans is unknown. A number of studies have been published that suggest a strong relationship between chloroquine use and cataract formation. The basis of the relationship seems to lie in the phototoxicity of chloroquine and related drugs. Because malaria is a disease most prevalent in regions of high light intensity, protective measures (clothing, sunblock, sunglasses or eye wraps) should be recommended whilst taking antimalarial drugs. Amiodarone Amiodarone hydrochloride is a benzofurane derivative used for cardiac abnormalities. Its use is commonly associated with an asymptomatic keratopathy. The antiarrhythmic drug also produces anterior subcapsular lens opacities that are usually asymptomatic. Anterior subcapsular lens opacities were observed in 7 of 14 patients treated with moderate to high doses of amiodarone at the Veterans Administration Medical Center in San Francisco in 1982. In 1993, a report was published that summarized the status of these same 14 patients 10 years later. Anterior subcapsular lens opacities developed or progressed in all patients continuing treatment with this antiarrhythmic agent during the ensuing 10-year interval. Although Snellen visual acuities were not decreased, subtle visual impairment
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was present as measured by contrast sensitivity measurements with and without glare. The authors of the report concluded that decrease in visual acuity should not be a contraindication for therapy with this potentially life saving drug.
FIGURE 1.15 Tempo of lens opacification with Vastatin therapy Hypocholesterolemic Drugs Cataract in animals and men are in some instances associated with genetic defects in enzymes that regulate cholesterol metabolism and the use of drugs which inhibit lens cholesterol biosynthesis. The basis of this relationship apparently lies in the need of the lens to satisfy its sustained requirement for cholesterol by on-site synthesis, and impairing this synthesis can lead to alteration of lens membrane structure. The lens membrane contains the highest cholesterol content of any known membrane. The genetic defects Smith-Lemli-Opitz syndrome, mevalonic aciduria, and cerebrotendinous xanthomatosis all involve mutations in enzymes of cholesterol metabolism, and affected patients can develop cataract. Questions about the ocular safety of drugs, which can inhibit lens cholesterol biosynthesis, persist. Concern over potential damage to the lens from the use of hypocholesterolemic drugs stems from the reports in 1962 by Kirby et al and Laughlin et al that treatment of patients with Triparanol (Mer 29, Wm. S.Merrel Co.) to lower blood cholesterol was associated with development of cataract. Drugs used to lower blood cholesterol are among the most widely prescribed medicines. One drug in the group, lovostatin (Mevacor, Merck), is alone the third most prescribed drug in the United States. This drug can inhibit cholesterol synthesis in lens and produce cataract in dogs. Whether these drugs inhibit cholesterol biosynthesis in human lenses at therapeutic doses is unknown. The clinical safety trials indicate that treatment with lovastatin for up to five years does not significantly increase the development of cataract or grossly alter visual function. The ocular safety in an older patient population (>50 years) appears high. This seems also to apply to simvastin, except that one clinical trial showed a significant increase in cortical opacities with the use of this drug (Fig. 1.15).
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An unpublished study conducted at the University of Stellenbosch Medical School found that the rate at which opacification occurs in dyslipidemic patients on Cerivastatin was 4.5 percent per year (Fig. 1.15). Although this rate of opacification is not statistically noteworthy it would seem that if this data is projected over a period of 20 years and compared the normal rate of opacification reported by Boccuzzi and Leino et al, an alarming amount of opacities would be present in the group of patients on cerivistatin. Hypolipidemic drugs are intended for life-long use and patients as young as 18 years can receive these drugs. Although the human lens grows throughout life, the rate of growth is slow after 10 years of age. About 40 years are required for the lens cortex to double in width. The size of the nucleus remains essentially constant after 10 years of age. Thus, the consequences of inhibiting lens growth due to block of cholesterol biosynthesis may be difficult to assess in only a 1 to 5 year period. A considerable body of evidence indicates that sustained alteration of lens sterol content and composition due to genetic mutations or exposure to drugs can lead to altered lens clarity. Long-term ocular safety of the vastatin drugs should perhaps be viewed in units of 10 to 20 years. Certainly a 20-year-old person required to have cataract surgery at age 40 because of some chronic treatment would constitute a medical crisis for this individual, particularly if a less toxic treatment had been available. The question of whether the vastatin drugs inhibit lens cholesterol biosynthesis in humans treated with standard therapeutic doses is unanswered. Since very low concentrations of lovastatin and simvastatin are required to inhibit cholesterol synthesis in animal lenses (3–22 nM), and only five times the therapeutic dose of lovostatin decreased cholesterol accumulation by the rat lens, it at least appears possible that therapeutic doses could inhibit lens cholesterol biosynthesis in humans. Conclusion Human lenticular opacification leading to the clinical challenge of cataract formation is etiologically multifactorial. It does seem however that evidence is slowly mounting to encourage clinicians to consider cataract as belonging to the growing list of preventable ocular diseases. Further Reading 1. Adler NE, Boyce T, Chesney MA et al: Socioeconomic inequalities in health. No easy solution. JAMA 269:3140–45, 1993. 2. Alden ER, Ralina RE, Hodson WA: Transient cataract in low-birth-weight infants. J Pediatr 82:318–31, 1973. 3. Amaya LG, Speedwell L, Taylor D: Contact lenses for infant aphakia. Br J Ophthalmol 74:154– 56, 1990. 4. Ames GM, Janes CR: Heavy and problem drinking in an American blue-collar population: implications for prevention. Soc Sci Med 8:949–60, 1987. 5. Ansari NH, Awasthi YG, Srivastava SK: Role of glycosylation in protein disulphide formation and cataractogenesis. Exp Eye Res 31:9–19,1980.
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6. Armitage MM, Kivun JD, Farrell RE: A progressive early onset cataract gene maps to human chromosome 17q24. Nature Facet 937–40, 1995. 7. Assmann et al: Lipid Metabolism Disorders and Coronary Heart Disease. MMV-Medizin-Verl (2nd ed), 1993. 8. Baghdassarian SA, Tabbara KF: Childhood blindness in Lebanon. Am J Ophthalmol 79:827–30, 1975. 9. Bandmann O, Vaughan J, Holmans P et al: Association of slow acetylator genotype for NAcetyltransferase 2 with familial Parkinson’s disease. Lancet 350:1136–39, 1997. 10. Barnes PJ: Anti-inflammatory mechanisms of glucocorticoids. Biochem Soc Trans 23:940–45, 1995. 11. Behrens-Baumann W, Thiery J, Wieland E et al: 3-Hydroxy-3-methylglutaryl coenzyme—a reductase inhibitor simvastatin and the human lens: clinical results of 3-year follow-up. Arzneim-Forsch 42(11):1023–24, 1992. 12. Beigi B, O’Keefe M, Bowell R et al: Ophthalmic findings in classical galactosaemia— prospective study. Br J Ophthalmol 77:1624–64, 1993. 13. Belpoliti M, Maraini G: Sugar alcohols in the lens epithelium of age-related cataract. Exp Eye Res 56:3–6, 1993. 14. Benos DJ: Amiloride: a molecular probe of sodium transport in tissues and cells. Am J Physiol 242:C131–45, 1982. 15. Benson WH, Farber ME, Caplan RJ: Increased mortality rates after cataract surgery: a statistical analysis. Ophthalmology 95:1288–92, 1988. 16. Berger J, Shepard D, Morrow F et al: Relationship between dietary intake and tissue levels of reduced and total vitamin C in the guinea pig. J Nutr 119:1–7, 1989. 17. Bernstein HN: Chloroquine ocular toxicity. Surv Ophthalmol 12(5):415–47, 1967. 18. Bhatnagar R, West KP (Jr), Vitale S et al: Risk of cataract and history of severe diarrheal disease in Southern India. Arch Ophthalmol 109:696–99,1991. 19. Bhuyan KC, Bhuyan DK, Podos SM: Free radical enhancer xenobiotic is an inducer of cataract in rabbit. Free Radical Res Comm 12–13:609–20,1991. 20. Bhuyan KC, Bhuyan DK, Podos SM: Lipid peroxidation in cataract of the human. Life Sci 38:1463–71, 1986. 21. Bialas MC, Routledge PA: Adverse effects of corticosteroids. Adverse Drug React Toxicol Rev 17(4):227–35, 1998. 22. Björkhem, I Boberg KM: Inborn errors in bile biosynthesis and storage of sterols other than cholesterol. Metabolic Basis of Inherited Disease; New York, McGraw-Hill 7: 2073–99, 1995. 23. Blondin J, Baragi VJ, Schwartz E et al: Delay of UV-induced eye lens protein damage in guinea pigs by dietary ascorbate. Free Radic Biol Med 2:275–81, 1986. 24. Boccuzzi SJ, Bocanegra TS, Walker JF et al: Long-term safety and efficiency profile of simvastatin. Am J Cardiol 86:1127–31, 1991. 25. Bochow TW, West SK, Axar A et al: Ultraviolet light exposure and risk of posterior subcapsular cataract. Arch Ophthalmol 107:369–72, 1989. 26. Bonting SJ: Na’K’ activated adenosine triphosphatase and active cation transport in the lens. Invest Ophthalmol 4:723, 1965. 27. Brauweiler PH, Wehler T, Busin M. High incidence of cataract formation after implantation of a silicone posterior chamber lens in phakic, highly myopic eyes. Ophthalmology 106(9):1651– 55, 1999. 28. Brilliant LB, Grasset NC, Pokrel RP et al: Associations among cataract prevalence, sunlight hours and altitude in the Himalayas. Am J Epidemiol 118:250–64, 1983. 29. Brown CA, Burman D: Transient cataract in a diabetic child with hyperosmolar coma. Br J Ophthalmol 57:429–33, 1973. 30. Burke JP, O’Keefe M, Bowell R et al: Ophthalmic findings in classical galactosemia: a screened population. Pediatr Ophthal Strabismus 26:165–68, 1989. 31. Caird Fl, Pirie A, Ramsell TG: Diabetes and the Eye. Blackwell Scientific: Oxford 1969.
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32. Caird Rl, Hutchinson M, Pirie A: Cataract and diabetes. BMJ 2:665–68, 1964. 33. Cenedella RJ: Cholesterol and cataract. Surv Ophthalmol 40: 320–37, 1996. 34. Chatterjee A, Milton RC, Thyle S: Prevalence and aetiology of cataract in Punjab. Br J Ophthalmol 66:35–42, 1982. 35. Chiba M, Masironi R: Toxic and trace elements in tobacco and tobacco smoke. Bull World Health Organ 70:270–76, 1992. 36. Christen WG, Manson JE, Seddon JM et al: A prospective study of cigaret smoking and risk of cataract in men. JAMA 268:989–93, 1992. 37. Chylack LT Jr, Henriques H, Tung W: Inhibition of sorbitol production in human lenses by an aldose reductase inhibitor. Invest Ophthalmol Vis Sci 17: ARVO (Suppl): 300, 1978. 38. Cigala O, Pancallo MT, Della Valle M et al: La simvastatina nel trattamento delle piercolesterolemie. La Clinica Terapeu 137:333–37, 1991. 39. Clair WK, Chylack LTJ, Cook EF et al: Allopurinol use and the risk of cataract formation. Br J Ophthalmol 73:173–76, 1989. 40. Clayton RM, Cuthbert J, Duffy J et al: Some risk factors associated with cataract in SE Scotland: a pilot study. Trans Ophthalmol Soc UK 102:331–36, 1982. 41. Clayton RM, Cuthbert J, Philips CJ et al: Analysis of individual cataract patients and the lenses: a progress report. Exp Eye Res 31:553–66. 42. Clayton RM, Cuthbert J, Philips CJ et al: Epidemiological and other studies in the assessment of factors contributing to cataractogenesis. Ciba Fdn Symp 106:25–47, 1984. 43. Clayton RM, Cuthbert J, Philips CJ et al: Some risk factors associated with cataract in SE Scotland: A pilot study. Trans Ophthalmol Soc UK, 102:331–36, 1982. 44. Clayton RM, CuthbertJ, Phillios CI et al: Analysis of individual cataract patients and their lenses: a progress report. Exp Eye Res 1980; 31:553–56. 45. Cohen DL, Neil HA, Sparrow J et al: Lens opacity and mortality in diabetes. Diabetic Med 7:615–17, 1990. 46. Collman GW, Shore DL, Shy CH et al: Sunlight and other risk factors for cataract: an epidemiological study. Am J Public Health 78:1459–62, 1988. 47. Cooperative Study of Lipoproteins and Atherosclerosis. Evaluation of serum lipoprotein and cholesterol measurements as predictors of clinical complications of atherosclerosis. Circulation 14.2:691–741, 1956. 48. Cotlier E, Kwan B, Beatty C: The lens as an osmometer. Bioctfm Biophys Acta 150:705, 1968. 49. Cotlier E, Rice P: Cataract in the Smith-Lemli-Opitz syndrome. Am J Ophthalmol 72:955–59, 1971. 50. Cotlier E: Congenital rubella cataract. In Cotlier E, Lambert SR, Taylor D (Eds): Congenital Cataract. RG Landes/ CRC: Boca Raton, 65–76, 1994. 51. Cotlier E: Congenital varicella cataract. Am Ophihalmol 86: 627–29, 1978. 52. Cruickshanks KI, Klein BEK, Klein R: Ultraviolet light exposure and lens opacities: the Beaver Dam Eye Study. Am J Public Health 82:1658–62, 1992. 53. Cuthbert J, Clayton RM, Philips: Cuneiform cataract: a special case? Colloq D’INSERM, 147:387–96. 54. Dawber TR: The Framingham Study: The Eipidemiology of Atherosclerotic Disease. Cambridge Harvard University Press: London 1980. 55. de Vries ACJ, Cohen LH: Different effects of the hypolipidemic drugs pravastatin and lovastatin on the cholesterol biosynthesis of the human ocular lens in organ culture and on the cholesterol content of the rat lens in viva. Biochim Biophys Acta 1167:63–69, 1993. 56. Dohi K, Fukuda K et al: Cataract in kidney transplant patients. Horishima J Med Sci 33:275– 78, 1984. 57. Dolan BJ, Flach AJ, Peterson JS: Amiodarone keratopathy and lens opacities. J Am Optom Assoc 56(6):468–70, 1985. 58. Donahue RP, Bias WB, Renwickj H et al: Probable assignment of the Duffy blood group locus to chromosome I in man. Proc Natl Acad Sci USA 61:949–55, 1968.
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240. Shun Shin GA, Ratcliffe P, Bron AJ et al: The lens after renal transplantation. Br J Ophthalmol 73:522–27, 1990. 241. Siddall JR: The ocular toxic findings with prolonged and high dosage chlorpromazine intake. Arch Ophthalmol 74: 460–64, 1965. 242. Siegmund W, Fengler JD, Frane G et al: N-Acetylation and debrisoquine hydroxylation polymorphisms in patients with Gilbert’s syndrome. Br J Clin Pharmacol 32(4):467–72, 1991. 243. Simonelli F, Nesti A, Pensa M et al: Lipid peroxidation and human cataractogenesis in diabetes and severe myopia. Exp Eye Res 49:181–87, 1989. 244. Simons LA: Interrelations of lipids and lipoproteins with coronary artery disease mortality in 19 countries. Am J Cardiol 57:5G–10G, 1985. 245. Sirtori CR: Tissue selectivity of hydroxymethylglutaryl co-enzyme A (HMG CoA) reductase inhibitors. Pharmacol Ther 60:431–59, 1993. 246. Solberg Y, Rosner M, Belkin M: The association between cigaret smoking and ocular diseases. Surv Ophthalmol 42: 535–57, 1998. 247. Spector A, Garner WH: Hydrogen peroxide and human cataract. Exp Eye Res 33:673–81, 1981. 248. Sperduto RD, Hu T-S, Milton RC et al: The Linxian Cataract Studies: two nutrition intervention trials. Arch Ophthalmol 111:1246–53, 1993. 249. Srivastava S, Ansari NH: Prevention of sugar induced cataractogenesis in rats by mutilated hydroxytoluene. Diabetes 37:1505–08, 1988. 250. Stambolian D: Galactose and cataract. Surv Ophthalmol 32: 333–49, 1988. 251. Stayte M, Reeves B, Wortham C: Ocular and vision defects in preschool children. Br J Ophthalmol 77:228–32, 1993. 252. Steele G, Peters R: Persistent hyperplastic primary vitreous with myopia: a case study. J Am Optom Assoc 70(9):593–97, 1999. 253. Stewart Brown SL, Raslum MN: Partial sight and blindness in children of the 1970 birth cohort at 10 years of age. J Epidemiol Community Health 42:17–23, 1988. 254. Stoll C, Alembik Y, Dott B, Roth MP: Epidemiology of congenital eye malformations in 131,760 consecutive births. Ophthalmic Pediatr Genet 39:433–35, 1993. 255. Stryker WS, Kaplan LA, Stein EA et al: The relation of diet, cigaret smoking, and alcohol consumption to plasma beta-carotene and alpha-tocopherol levels. Am J Epidemiol 127: 283– 296, 1988. 256. Subar AF, Block G: Use of vitamin and mineral supplements: demographics and amounts of nutrients consumed—the 1987 Health Interview Survey. Am J Epidemiol 132:1091–1101, 1990. 257. Summers CG, Letson RD: Is the phakic eye normal in monocular pediatric aphakia? J Pediatr Ophthalmol Strabismus 29:324–27, 1992. 258. Szmyd L Jr, Schwartz B: Association of systemic hypertension and diabetes mellitus with cataract extraction: A case-control study. Ophthalmology 96:1248–52, 1989. 259. Takemoto L, Takehana M, Horwitz J: Covalent changes in MIP 26K during aging of the human lens membrane. Invest Ophthalmol Vis Sci 27:443–46, 1986. 260. Tavani A, Negri E, La Vecchia C: Selected diseases and risk of cataract in Women. A casecontrol study from northern Italy. Ann Epidemiol 5(3):234–38, 1995. 261. Taylor A, Jacques P, Nadler D et al: Relationship in humans between ascorbic acid consumption and levels of total and reduced ascorbic acid in lens, aqueous humor, and plasma. Curr Eye Res 16:857–64, 1997. 262. Taylor A, Jacques PF, Nadler D et al. Relationship in humans between ascorbic acid consumption and levels of total and reduced ascorbic acid in lens, aqueous humor, and plasma. Curr Eye Res 10:751–59, 1991. 263. Taylor A, Jaques PF, Epstein EM: Relations among aging, antioxidant status, and cataract. Am J Clin Nutr 62(Suppl): 1439S–47S, 1995. 264. Taylor A: Nutritional and Environmental Influences on the Eye. CRC Press, London; 1–5, 1999.
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265. Taylor A: Nutritional and Environmental Influences on the Eye. CRC Press: London. 56–81, 1999. 266. Taylor D, Rice NSC: Congenital cataract, a cause of preventable child blindness. Arch Dis Child 57:165–67, 1982. 267. Taylor HR, West S, Munoz B et al: The long-term effects of visible light on the eye. Arch Ophthalmol 110:99–104,1992. 268. Taylor HR: The environment and the lens. Br J Ophthalmol 64:303–10, 1980. 269. Taylor HR: Ultraviolet radiation and the eye: an epidemiologic study. Trans Am Ophthalmol Soc 87:802–53, 1989. 270. Teramoto S, Fukuchi Y, Uejima Y: Influences of chronic tobacco smoke inhalation on ageing and oxidant-antioxidant balance in the senescence-accelerated mouse (SAM)-P/2. Exp Gerontol 28:87–95, 1993. 271. Thaler JS, Curinga R, Kiracofe G: Relation of graded ocular anterior chamber pigmentation to phenothiazine intake in schizophrenics: quantification procedures. Am J Optom Physiol Optics 62:600–04, 1985. 272. The Italian-American Cataract Study Group: Risk factors for age-related cortical, nuclear, and posterior subcapsular cataract. Am J Epidemiol 133:541–53, 1991. 273. Tielsch JM, Sommer A, Katz J et al: Socioeconomic status and visual impairment among urban Americans. Arch Ophthalmol 109:637–41, 1991. 274. Tint et al: Defective cholesterol biosynthesis associated with the Smith-Lemli-Opitz syndrome. N Engl J Ed 330:107–13, 1994. 275. Tobert JA: New developtments in lipid-lowering therapy: the role of inhibitors of hydroxymethylglutaryl-coenzyme A reductase. Circulation 76:534–38, 1987. 276. Traboulsi El, Weinberg RJ: Familial congenital cornea guttata with anterior polar cataract. Am J Ophthalmol 108:123–25, 1989. 277. Trindade F, Pereira F: Cataract formation after posterior chamber phakic intraocular lens implantation. Cataract Refract Surg 24(12):1661–63, 1998. 278. Tsutomu Y, Mihori K, Yoshito H: Traumatic cataract with ruptured posterior capsule from a nonpenetrating ocular injury. 279. Tuormaa TE: The adverse effects of tobacco smoking on reproductive and health: A review from the literature. Nutr Health 10:105–120, 1995. 280. Ughade SN, Zodpey SP, Khanolkar VA: Risk factors for cataract: a case control study. 281. Urban RC (Jr), Cotlier E: Corticosteroid-induced cataract. Surv Ophthalmol 31:102–110,1986. 282. Vadot E, Guibal JP: Pathogenic de la cataracte diabetique. Bull Soc Ophthalmol Fr 82:1513– 14, 1982. 283. Vajpayee RB, Angra SK, Honavar SG et al: Pre-existing posterior capsular breaks from penetrating ocular injuries. J Cataract Refract Surg 20:991–94,1994. 284. Van Heyningen R, Harding JJ: A case-control study of cataract in Oxford: some risk factors. Br J Ophthalmol 72: 804–08, 1988. 285. van Heyningen R, Harding JJ: Do aspirin-like analgesics protect against cataract? Lancet i:1111–13, 1986. 286. van Heyningen R: The human lens. I—a comparison of cataracts extracted in Oxford (England) and Shikarpur (W Pakistan). Exp Eye Res 13:136–47, 1972. 287. Varma S, Schocket SS, Richards RD: Implications of aldose reductase in cataract in human diabetes. Invest Ophthalmol Vis Sci 18:237–41, 1979. 288. Vesti E. Development of cataract after trabeculectomy. Acta Ophthalmol 71(6):777–81, 1993. 289. Vidal P, Fernandez-Vigo J, Cabezas-Cerrato J: Low glycation level and browning in human cataract. Acta Ophthalmol 66:220–22,1988. 290. Vitale S, West S, Hallfrisch J et al: Plasma antioxidants and risk of cortical and nuclear cataract. Epidemiol 4:195–203, 1994. 291. Waxman SL, Bergen RL: Wagner’s vitreoretinal degeneration. Ann Ophthalmol 12(10):1150– 51, 1980.
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292. Weale R: A note on a possible relation between refraction and a disposition for senile nuclear cataract. Br J Ophthalmol 64:311–14, 1980. 293. Weber WW: Acetylation. Birth Defects Orig Artic Ser 26(1): 43–65, 1990. 294. Wensor MD, McCarty CA, Taylor HR. The prevalence and risk factors of myopia in Victoria, Australia. Arch Ophthalmol 117:658–63, 1999. 295. West S, Munoz B, Emmett EA et al: Cigaret smoking and risk of nuclear cataract. Arch Ophthalmol 107:1166–69, 1989. 296. West S, Munoz B, Schein OD et al: Cigaret smoking and risk for progression nuclear opacities. Arch Ophthalmol 113: 1377–80, 1995. 297. Wiechens B, Winter M, Haigis W et al: Bilateral cataract after phakic posterior chamber top hat-style silicone intraocular lens. J Refract Surg 13(4):392–97, 1997. 298. Wilczek M, Zygulska-Machowa H: Zawartosc witaminy C W.roznych typackzaem. J Klin Oczna 38:477–80, 1968. 299. Winkleby MA, Fortmann SP, Barret DC: Social class disparities in risk factors for disease: eight-year prevalence patterns by level of education. Prev Med 19:1–12,1990. 300. Wolff SM: The ocular manifestations of congenital rubella. Sri Am Ophthalmol Soc 70:577– 14, 1972. 301. World Health Organization: Management of Cataract in Primary Health Care Services. WHO: Geneva 1990. 302. Ye JJ, Zadunaisky JA: A Na+/H+ exchanger and its relation to oxidative effects in plasma membrane vesicles from lens fibers. Exp Eye Res 55:251–60, 1992. 303. Young RW. Optometry and the preservation of visual health. Optom Vis Sd 70:255–62, 1993. 304. Zadok D, Chayet A: Lens opacity after neodymium: YAG iridectomy for phakic intraocular lens implantation. J Cataract Refract Surg 25(4):592–93, 1999. 305. Zelenka PS: Lens lipids. Curr Eye Res 3:1337–59, 1984.
2 Biochemistry of the Lens Ashok Garg Introduction The crystalline lens which is positioned behind the iris is the chief refractive medium of the eye having the maximum refractory power. It is a transparent, elastic and biconvex lens enclosed in a capsule. It refracts the light entering the eye through the pupil and focuses it on the retina. Biochemistry of the Lens The human lens is the least hydrated organ of the body. It contains 66 percent water, and the 33 percent remaining bulk is composed mainly of protein. The lens cortex is more hydrated than the lens nucleus. Lens dehydration is maintained by an active Na+ ion water pump that resides within the membranes of cells in the lens epithelium and each lens fiber. The inside of the lens is electronegative. There is a −23 mV difference between anterior and posterior surfaces of the lens. Thus, the flow of electrolytes into the lens is directed by an electrical gradient. Crystalline Lens as an Osmometer The capsule of the lens acts as an intact cell and induces properties like swelling in hypotonic media and dehydration in hypertonic media. The osmolarity of the human lens is 302 mOsm and equals the osmolarity of aqueous. Cations like sodium and potassium with concentration of 145 mEq/L and anions (chloride, bicarbonate, sulfate, ascorbate and glutathione) with concentration of 50 to 60 mEq/L contribute to lens osmolarity. An anionic deficit of 90 mEq/L is probably made by acidic groups of lens protein and glycoproteins. The water equilibrium between the lens and the surrounding fluids is disrupted if the concentration of osmotically active compounds (Na+, K+, etc.) increases inside the lens. Increase in Na+ and K+ levels also follows lens exposure to surface active detergents or antibiotics. When retained inside the cell, abnormal products of sugar metabolism such as sorbitol can exert osmotic effects and result in water influx and lens swelling.
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Lens Proteins The human lens contains the highest concentration of proteins (33%) of any tissue in the body. Proteins, are synthesized in the anterior epithelium and the equatorial region. The perfect physiochemical arrangement of the lens protein living in an optimum environment of water, electrolytes and sulfhydryl gives transparency to the lens. Amino acids which are actively transported by the anterior lens epithelium are used by the lens to synthesize lens proteins. Since lens protein is sequestered from the body immune system during embryonic life, later exposure of the lens protein can result in an autoimmune reaction. The separation of lens proteins is based initially on their solubility of water. Fifteen percent of the lens proteins are insoluble in water. These form the albuminoid fraction which is thought to include membrane bound protein and aggregated crystallins. The remaining 85 percent are soluble in water and are classified as alpha, beta and gamma crystallins on the basis of molecular weight, electrophoretic mobility and presence or absence of subunits as shown in Figure 2.1. The soluble alpha and gamma crystallins leak into the aqueous humor during cataract formation causing a reduction in total lens protein. The water soluble lens proteins are grouped as: (i) α-crystallins (15%), (ii) βcrystallins (55%), and (iii) γ-cystallins (15%). On the basis of their electrophoretic mobility towards the anode, α-crystallin is fastest, β-crystallin is intermediate and γcrystallins is slowest. The molecular weight of crystallins in daltons is α-crystallin 1,000,000, β-crystallin 50,000–100,000 and γ-crystallin 20,000. α and β-crystallins are made of subunits and aggregation or separation of these subunits determines the physiochemical characteristics of each crystallin. The protein subunits are assembled by the alignment of amino acids through ribonucleic acid (RNA) as specified by the genetic code (Fig. 2.2). Lens proteins are degraded by proteases and amino peptidases. In the normal lens the membrane of lens fibers and lens capsule do not allow the passage of protein molecules from the lens to the aqueous humor. When a mature cataract develops, the membranes of the lens fibers are
FIGURE 2.1 Human lens protein composition
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FIGURE 2.2 Biochemistry of lens protein synthesis lysed, the capsule becomes more permeable and protein can leak out of the lens. Lens proteins in the anterior chamber can act as an antigen which lead to inflammation of the uveal tissues known as lens induced or phacogenic uveitis. Sometimes degraded lens proteins leak through the capsule into the aqueous humor and are engulfed by macrophages which plug up the trabecular meshwork thus blocking aqueous humor outflow and producing increased intraocular pressure (IOP)—phacolytic glaucoma. Active Transport Processes Water and Electrolyte Transport The electrolyte and water content of the lens resembles that of an intact cell as shown in Figure 2.3. Whereas the Na+, Cl− and K+ ion and water content of aqueous and vitreous is similar to that in plasma or extracellular fluids. To maintain electrolyte and water gradients against the surrounding fluids, the lens generates chemical and electrical energy.
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FIGURE 2.3 Chemical composition of human lens. (All values in mmol/kg of lens water), unless otherwise stated Chemical energy extrudes Na+ ions and water is provided by ATP through glucose metabolism. Cation Transport The energy dependent cation pump in the lens accumulates K+ intracellularly and extrudes sodium (Na+). The influx of K+ and efflux of Na+ are thought to be linked and mediated by the membrane bound enzyme, Na+-K+-ATPase which degrades ATP to adenosine diphosphate (ADP) inorganic phosphate and energy with which to power this cation pump. The action of Na+-K+-ATPase of lens can be inhibited by cardiac glycoside such as digitalis thereby stopping the cation pump. It is generally believed that the cation pump of the lens functions at the anterior epithelial surface because the concentration of Na+-K+-ATPase is greater in this area than elsewhere. When K+ is pumped into the lens and Na+ is pumped out at the anterior surface, a chemical gradient is generated that stimulates a diffusion of Na+ into the lens and K+ out of the primarily through the posterior surface. This process of active transport (pump)
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FIGURE 2.4 Active transport process of lens (pump-leak) mechanism stimulating passive diffusion (leak) has been termed as “pump and leak” theory of cation transport (Fig. 2.4). This cation transport system performs three important functions. • It regulates the water content of the lens, thereby allowing the lens to act as a perfect osmometer. This prevents colloid osmotic swelling. • It produces and maintains an electrical potential difference (approximately −70 mV) between the lens and the medium surrounding it. • It promotes the proper physiochemical environment within the lens to maintain transparency and optimal enzymatic activity. Surface active agents (antibiotics, detergents, lysophospholipids and fatty acids) disrupt the physiochemical integrity of the membrane and Na+ extrusion pump with subsequent gain of Na+ ions and water by the lens, lens swelling and eventually complete loss of lens transparency follow. Amino Acids Amino acids and inositol are actively transported into the lens at the anterior epithelial surface (Fig. 2.5). Once in the lens, free amino acids are incor-
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FIGURE 2.5 Schematic diagram showing amino acid active transport into the lens (epithelial pump) porated into RNA to form lens protein, can be metabolized with formation of CO2, or can efflux from the lens. The turnover of free amino acids in the lens is very rapid, the renewal rate for lysine being 16 percent of the total in the lens per hour. There are three separate pumps for acidic, basic and neutral amino acids. Once in the lens these amino acids are metabolized and used for energy. Glutathione-Sulfhydryl Proteins Glutathione, a polypeptide is actively synthesized in the lens. It is a tripeptide containing glycine, cysteine and glutamic acid. The levels of glutathione in the lens are high and in most of lens glutathione is in the reduced form (GSH). Only 6.8 percent of all lens glutathione is in the oxidized form (GSSG). GSH and GSSG are in equilibrium.
GSH concentrations are 12.0 micromoles/gm in the human lens. GSH levels are much higher in the cortex than in the nucleus of the lens. A reducing agent by virtue of its free sulfhydryl group, glutathione maintains membrane stability in the lens by supporting the protein complexes of the membrane. GSH levels decrease slightly with age. One of the earliest changes noted in the lens in different types of cataracts is the loss of glutathione. This allows the cross-linkage of proteins by the formation of disulfide bonds through sulfhydryl oxidation. Another polypeptide ophthalmic acid is also found in the lens in concentrations of 1/10 to 1/ 100 those of GSH. The pentose shunt of glucose metabolism active in the lens generates NADPH (reduced nicotinamide-adenine dinucleotide phosphate) that maintains glutathione in the reduced state by the following reductase:
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Lens proteins contain reduced sulfhydryl groups (PSH) and oxidized disulfide groups (PSSP) maintaining high levels of GSH as shown in the following reaction 2PSH+GSSG—2GSH+PSSP Thus, decreased GSH or increased GSSG will result in PSH oxidation and alterations in protein linkages, their solubility and their transparency. The main functions of lens GSH are: • To preserve the physiochemical equilibrium of lens proteins by maintaining high levels of reduced sulfhydryl (SH−) groups. • To maintain transport pumps and the molecular integrity of lens fiber membranes. Synthesis of lens glutathione proceeds via α-glutamylcysteine synthetase which is markedly decreased in human senile cataracts. The enzyme glutathione peroxidase removes H2O2 or toxic lipid peroxides but decreases rapidly with age and in senile cataracts. Thus, the ability of lens to remove toxic oxygen appears impaired in early senile cataracts. Lipids The lipids of human lens are unique and differ markedly from those of other species. Lipids represent about 3 to 5 percent of the dry weight of lens. In human lens cholesterol is about 50 percent of lipids followed by phospholipids (45%) and glycosphingolipids and ceramides (5%). The lipids are major components of the lens fiber membranes and either decrease in their synthesis or impaired degradation brings about lens membrane damage and lens opacities. Cataracts develop in humans if treated with anticholesterolemic agents such as triparanol. Esterification of cholesterol takes place in human lens where 25 percent of total cholesterol is in the ester form. Among phospholipids, the human lens is specially rich in sphingomyelin and its precursor ceramides may increase in senile cataracts. Cer amide synthesis proceeds via fatty acids and sphingosine. Its degradative enzyme ceramidase is present in the human lens. Sphingomyelin is degraded by sphingomyelinase which is somewhat decreased in senile cataract. The cholesterol-phospholipid ratio of human lens fiber membranes is the highest among cell or organelle membranes, thus conferring the lens resistance to deformation. Lipids as structural components of lens fiber membranes are associated with the insoluble lens proteins. The increased insolubility of the proteins with age or during cataract formation may be due to derangements in the stereochemical arrangement between lipids and proteins in the membrane and soluble proteins inside the fibers.
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Ascorbic Acid In human lens ascorbic acid values are higher in the lens than in the aqueous. The role of ascorbic acid in the lens is not clear, but it could participate in oxidation-reduction reactions alone or coupled to glutathione. Glucose Metabolism Lens is avascular and surrounded by aqueous and vitreous humors. Both of which are rich in glucose and poor in oxygen. Glucose used by the lens is metabolized through following four main pathways. • The glycolytic pathway • The Krebs (oxidative) cycle • The hexose monophosphate (pentose) shunt • The sorbitol pathway. End products of glucose metabolism are lactic acid, carbon dioxide and water. Lactic acid from the
FIGURE 2.6 Lens glucose metabolism pathway (Krebs’ cycle) lens diffuses to the aqueous and is eliminated via this circulating fluid. About 80 percent of glucose used by the lens is metabolized anaerobically by the glycolytic pathway to produce lactic acid and adenosine triphosphate (ATP). A small proportion of lens glucose may be metabolized via oxidative Krebs’ citric acid cycle which is 18 times more efficient in producing ATP than glycolysis (Fig. 2.6). About 15 percent of the glucose consumed by the lens is metabolized by the pentose or hexose
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monophosphate shunt. Although this pathway produces no energy in the form of ATP it does provide five carbon sugars (pentoses) for the synthesis of RNA and NADPH to maintain glutathione in a reduced state. The sorbitol pathway in which glucose is converted to sorbitol by aldose reductase in the normal lens is relatively insignificant, but it is extremely important in the production of cataracts in diabetic and galactosemic patients (Fig. 2.7). The lens uses the energy of metabolism for two principle processes, reproduction and growth and active transport processes. The synthesis of RNA, DNA, lens fiber membrane constituents, enzymes and other lens proteins
FIGURE 2.7 Lens glucose metabolism (sorbitol pathway) occurs mainly at the anterior surface and equatorial region of the lens. Glucose metabolism generates adenosine triphosphate. ATP breakdown is required for active transport of ions and amino acids, maintenance of lens dehydration, lens transparency and for continuous protein and GSH synthesis. The pentose shunt does not generate ATP, but it forms pentoses required for RNA synthesis. NADPH generated from the shunt is needed to maintain lens glutathione in the reduced state. The pentose shunt is extremely active in the lens. In addition, an active mechanism for pyruvate decarboxylation exists in the lens which results in formation of carbon dioxide and acetaldehyde. The latter is metabolized through lens aldehyde dehydrogenase. The carbon dioxide combination with water to form bicarbonate (HCO3−) may be partially active in the lens nucleus where the levels of carbonic anhydrase exceed those in lens cortex. However, carbonic anhydrase inhibitors do not produce cataracts. The enzymes hexokinase and phosphofructokinase regulate the rate of glucose metabolism by the lens whereas oxygen is not essential for glucose metabolism. Conversion of glucose to amino acids such as glutamic acid, aspartic acid, glycine and others may account for 6 to 8 percent of glucose metabolism. Oxygen consumption by the lens is minimal 0.5 µmol/glens/hour. The Krebs’ cycle requires oxygen and it is very inactive in the lens as there is paucity of mitochondria and oxidative enzymes. If the lens is deprived of glucose, it will utilize its own endogenous energy reserves. When deprived of glucose the lens will gain water and lose transparency. In infantile hypoglycemia, cataract develops because of the low plasma glucose level are present. The levels of glucose are higher in the aqueous (5.5 µmol/ml) than in the lens (1 µmol/ml) and glucose diffuses readily into the lens. Transport of glucose into the lens is
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not affected by the absence of sodium or calcium ions. However other sugars or phloretin can inhibit lens glucose transport. Studies of intact lens metabolism or protein structure can be done by noninvasive techniques. The 31P nuclear magnetic resonance (NMR) spectra of intact lens sugar phosphates and dinucleoside phosphate are among the best resolved in biological tissues. For lens protein analysis, laser spectroscopy techniques are available. The Raman laser signals allow determination of the axial distribution of protein subgroups such as tryptophan, sulfhydryl and disulfide which suffer modifications during cataract formation. Applied Physiology Chemical Changes in Lens Proteins in Senile Cataractogenesis Lens proteins glycosylation happens on exposure to high glucose levels. These high glucose levels lead to protein conformational changes, near similar to those that occurs in glycosylated hemoglobin. The amino acid terminals of lens α- and β-crystallins are acetylated. Thus sugar attachment in lens proteins occurs primarily by binding to amino groups of lysine and formation of covalent sugarlysine bonds. Glucosyl-lysine combination results in conformational protein changes, protein formation of S-S bonds through oxidation of adjacent sulfhydryl groups, protein aggregation and opacification. These findings explain in part the protein aggregation in human cataracts. Levels of Σamino acids in diabetic senile cataracts are substantially reduced as compared to agerelated cataract. Another chemical modification of lens protein includes carbamylation, i.e. addition of cyanate which occurs secondary to accumulation of urea cycle metabolites in uremia or secondary to dehydration. Urea cycle enzymes are active in human lens and cataracts. Research studies have now clearly shown that formation of protein S-S bonds is the major primary or secondary event associated in senile cataracts. Oxidation of lens protein SH groups with H2O2 induces protein conformation changes leading to opacification. Protection against oxidation of protein SH groups is vital. Cysteine and glutathione have proven effective to prevent formation of S-S protein bonds. Protein unfolding due to primary modification of exposed lysine amine groups can be prevented by lysine acetylation. Lysine acetylation of protein prevents attachment of glycosyl, cyanate or other reactive groups like keto groups of steroids. Biochemistry of Cortical Cataracts Cortical cataract is characterized by abnormalities in fiber permeability that causes vacuoles or clefts in the lens cortex. Damage to the membranes of lens fibers represents the initial insult due to X-rays, diabetes, galactosemia, arachidonic acid or other surface active agents. The various chemical changes some of which develop prior to clinical cortical changes include: • Loss of glutathione with compensatory increase in NADPH synthesis
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• Increase K+ ion efflux • Loss of K+ ions, inositol and amino acids from lens • Gain in Na+ ions • Decrease lens protein synthesis with decrease in the proportional of soluble protein and increase in insoluble protein • Increase in protein S-S groups and in Ca++ ions. • Decreased activity of most enzymes and increased activities of hydrolytic enzymes • Decreased ATP content. The majority of cataractogenic agents damage the ability of the lens to maintain GSH synthesis or increase its efflux through more permeable membranes. Thus a cycle of increased exudation of K+ ions, amino acids and inositol is initiated. The lens epithelium tries to maintain the concentration of these compounds by increased pumping. Depending upon the magnitude of cataractogenic stimuli, the GSH leak out may continue or stop. To maintain normal levels of NADPH is required which in turn stimulate the glucose metabolism through the pentose shunt. If the epithelium or lens fibers are structurally damaged and are unable to extrude Na+ ions water gain will occur. This is followed by a decrease in protein synthesis which manifest itself by decreased levels of soluble lens proteins. This is compounded by the retention of cations and formation of disulfide S-S bonds with increased turbidity and protein insolubility. At this stage of cataractogenesis, the increased activity of glycolysis and other enzymes is detected. The generalized disarray of lens metabolism is accompanied by ATP loss. The end result is a total opaque or cataractous lens. Nuclear Sclerosis The human lens normally undergoes changes with age. It slowly increases in size as new lens fibers develop throughout life. Older lens fibers in the center of the lens become dehydrated and compacted. The cross-linking of proteins in the nucleus increases its optical density and decreases its transparency. Clinically this condition is known as nuclear sclerosis which may cause refractive changes. Simultaneously splits in sutures or clefts in the cortical fibers are visible causing damage to the permeability of the lens. The nucleus of the lens becomes more compact and resists mechanical disruption with aging. There is extensive cross-linkage of the lens protein. The cataract protein cross-linkage is accompanied by increased pigmentation in certain cases. In senile cataracts, changes in lens color to dark yellow, yellow brown or brown and hardening of the nucleus parallel lead to decreased transparency. Three major types of cross-links are identified in senile cataracts. • Disulfide cross-links (S-S) • Lysine modification • Dityrosine cross-links. Protein SH groups are oxidized and noncovalent S-S protein cross-links are formed in senile cataracts. These S-S bonds are susceptible to dissociation by a variety of reducing agents. The origin of oxidative insult is attributed to either the loss of lens glutathione, excessive
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H2O2 or lipid peroxidase in aqueous humor, increased permeability to oxygen into the aqueous or lack of oxygen detoxifying enzymes. S-S cross-links may explain the conformational changes in protein causing opacity, the presence of covalent bonds is a feature of senile cataracts. Superoxide anion-free radicals (O2−) or its derivative peroxide (H2O2), singlet, oxygen 1 ( O2) and OH− induce oxidative damage to a variety of cells. The lens is highly susceptible to these radicals. Peroxide (H2O2) is catalyzed through catalase and peroxidase and synthesized through superoxide dismutase. This oxidative damage as a result of free radicals to human lens leads to cataract formation (Fig. 2.8).
FIGURE 2.8 Oxidative damage of lens (by free radicals) Diabetic Cataract Snow flake cortical lens opacities also known as metabolic cataract is found in diabetic patients. Increased levels of glucose in the aqueous and lens are found in patients with diabetes mellitus. In general glucose concentration in the aqueous is similar to concentrations in the plasma. From the aqueous glucose diffuses rapidly into the lens. The lens metabolizes glucose through the four main pathways as already mentioned in this chapter. In diabetes excessive glucose in the lens (more than 200 mg/100 ml) saturates hexokinase. Excessive glycosylation of lens proteins takes place and glucose is converted to sorbitol by autooxidation and protein binding (aldose reductase). These chemical changes are present in human diabetic cataract. However, glucose oxidation to sorbitol plays a more important role in the rapidly developing diabetic cataract. Whereas abnormal protein glycosylation is of greater significance in the slowly developing senile cataracts in patients with diabetes.
3 History of Phacoemulsification Charles D Kelman A resident in ophthalmology today, seeing his first cataract performed by a surgeon who uses Kelman phacoemulsification, might wonder how it could be performed any other way. Seated comfortably at the operating microscope, the surgeon makes a tiny incision, neatly peels open the anterior capsule, emulsifies and aspirates the lens within the remaining capsule, and then, through the same incision inserts a foldable lens. On the first postoperative day, in most cases, it is difficult to tell with the naked eye, which eye has been operated. In contrast, in 1960, when I finished my residency at Wills Eye Hospital, general anesthesia was common, no microscopes were used for any ophthalmic surgery anywhere in the world (except for a surgeon in Chicago, Richard Peritz), a 180 degree incision was made, a large sector iridectomy was performed, and then the lens was grasped by a capsule forceps, and the entire lens was pulled from the eye. Eight or more sutures closed the incision, and the patient remained hospitalized for 7 to 10 days. The eyes were red, the lids swollen, and irritated for up to six weeks. One might ask how the idea for phaco came to me. Did I one day think, “I’ll just take an ultrasonic needle and remove the cataract that way”? As brilliant as that leap of thought would have been, I cannot pretend to claim credit for making it. Actually, it is so far from the truth, that the real answer serves to illustrate a point— the final solution to a problem is usually far afield from the first attempts at its solution. First, the impetus for wanting to find a better way to remove cataracts: I was in the process of writing a grant application to the John A Hartford Foundation to investigate the effects of freezing on the eye, and after finishing the final draft, I went to bed. But I couldnot sleep. The application seemed “boring”. And I knew that the foundation looked to support breakthrough procedures, not boring scientific studies. I knew in my heart that the application would be rejected. I needed something exciting but I did not know what. Without knowing what I was doing, I put my subconscious mind to work, and went to bed. Sometime in the night I got out of bed, and wrote a phrase which would forever change my life, and would forever change the practice of cataract surgery. That phrase was, “The author will also find a way to remove a cataract through a tiny incision, eliminating the need for hospitalization, general anesthesia, and dramatically shortening the recovery period.” That statement looked well on paper. I had no idea how I would accomplish this feat. I was however, confident that I could do so easily—this confidence sprang from three factors: (i) I had quite easily discovered cryoretinopexy, and had published the first paper on that subject,1 (ii) I had quite easily codiscovered (Krwawicz, in Poland had also, independently discovered the same thing)
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cryoextraction of cataracts,2 and (iii) I was blissfully and naively unaware of the complexity of the task I had set out for myself. It is certainly possible, that had I known the number of problems I would have to solve, I would have been intimidated, and might have never started. It is for this reason that often people outside of a particular discipline are able to make breakthroughs. Those more knowledgeable are too aware of the difficulties. The Hartford Foundation director, E Pierre Roy, called me a few days later to tell me that he was not interested in the effects of freezing on the eye, but that he would give the grant for the new cataract operation. I was ecstatic! This was going to be easy! The first “method” for removing the lens through a small incision revolved around a collapsible “butterfly net” (Fig. 3.1), the net portion being made out of condom thin latex. The idea I had was to dilate the pupil, instill an enzyme to loosen the zonule, turn the patient over on his or her face and vibrate his or her head with a manual vibrator, until the lens fell into the anterior chamber, then instill acetylcholine to constrict the pupil. Once the
FIGURE 3.1 Folding lens bags cataract would be trapped in the anterior chamber, the collapsed latex net would be introduced to trap the cataract, which would then be simply mushed up with a needle, until the net and the squashed cataract could be pulled through the small incision. It is important for the reader to note how far from the sophisticated phaco machines this original, naive idea was. It would have been so easy to listen to those who said to me, “I told you you could not do it”, and admit defeat, just as it may be easy for you the reader to abandon your first idea on a subject, and never get to the second generation, the third, the fourth, the fifth, the sixth, etc. until you come up with a solution totally unrelated to your original idea. This “cat in the bag method” could not be made to work (all attempts with this device were made on animal and eye bank eyes). It was too traumatic to the cornea, the bag was too thick and took too much volume in the anterior chamber, the bag kept breaking, etc. It had taken six months to fabricate this “butterfly net” and to test it. I had used up one-sixth of my three year grant, and I began to worry. I then began investigating devices which would break up a cataract, so that it could be irrigated and aspirated from the eye.
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Various drills, rotary devices, and various types of microblenders were constructed and tried (Figs 3.2 to 3.4). Each failed for several reasons. If the iris was touched with a rotating tip, it would immediately become completely ensnared and a total 360 iridodialysis would inadvertently be performed.
FIGURE 3.2 Various unsuccessful devices
FIGURE 3.3 Rotating devices
FIGURE 3.4 Rotary cutters Usually, uncontrollable hemorrhage would ensue. Furthermore, the iris did not even have to be close
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FIGURE 3.5 Microblenders to the rotating tip. The eddy currents set up within the chamber were enough to draw the iris to the rotating tip and instantaneously disinsert and remove it. The second obstacle to fast rotating devices was that the eddy currents set up in the anterior chamber would throw lens particles against the endothelium and completely denude it in a few seconds, leading to permanent opacification and vascularization. Thirdly, the lens itself when caught on the rotating tip would also spin in the chamber with the consequent destruction of the endothelium. The microblender (Fig. 3.5) with needles rotating in opposite directions was intended to prevent the lens from spinning, but it was unsatisfactory. It also increased the chances of incarcerating the iris in the two rotating tips. Slow turning drills (Fig. 3.6) were designed, but these, too, were unable to prevent the lens from turning. Rocking vibrators still rubbed off endothelium. These abandoned devices are similar to the rotorooter-type devices which others are reevaluating at present. Steps were taken to fix the lens from the opposite side with the use of the prongs. The sharp tips, however, endangered the posterior capsule. Low-frequency vibrators were tried, but the lens merely vibrated with the tip. None of the aforementioned devices were ever used clinically, as they were considered dangerous and ineffective. Two years, and most of the grant money, had now elapsed. The solution of this problem had become more than a challenge—it had become an obsession.
FIGURE 3.6 Worm gear feeder
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In analyzing the difficulties I had so far, it became clear that the main problem was that the lens was moving, rotating, or vibrating inside of the anterior chamber and, therefore, rubbing against the endothelium. This realization eventually led to the solution only a few months before the expiration of the grant. At this time, it became obvious that in order to let the lens remain stationary in the chamber, the acceleration of the moving tip against it had to be high enough so that the standing inertia of the lens would not be overcome, in other words, high enough acceleration was required so that the lens could not back away, vibrate, or rotate with the tip. To demonstrate this principle, imagine a sharp knife slowly punching against a punching bag. The punching bag will move with the knife. If, however, the knife is quickly plunged against the bag, the knife will enter and the bag will not move. In this analogy, the punching bag represents the lens, and the knife represents the tool used to enter the lens. The high acceleration could only be achieved with an ultrasonic frequency. Early experiments with a dental ultrasonic unit using irrigation only and a nonlongitudinal motion were encouraging, but were clinically unsuccessful because of the high energy radiated and the relative inefficiency requiring many minutes of ultrasonic time in the anterior chamber. Substitution of a longitudinal motion at the tip was introduced to prevent disinsertion of the iris and to reduce radiation. This type of motion also significantly reduced flaking (originally published in 1974, courtesy of the American Academy of Ophthalmology3). Once I had discovered the method of breaking up the lens, I thought the rest would be easy. It was not. There were three types of problems lurking ahead, which as they were discovered, had to be overcome: i. surgical problems, ii. instrument problems, and iii. political problems.
Surgical Problems Pupil Constriction In the first attempt to do phacoemulsification, the pupil constricted during the surgery There had to be new drugs and methods to maintain dilatation. In the early cases, the pupil constricted rapidly in the procedure, since we did not have potent mydriatics at that time. At first, I performed large sector iridectomies so that I could see behind the iris, but in many cases the iris became aspirated into the tip and became badly frayed. Because of this problem, I began to bring the lens into the anterior chamber before performing the phaco, and before the pupil constricted. For several years I, then, taught anterior chamber phaco, which I believe is still a viable alternative to posterior chamber phaco, for those less skilled. There is a slight increase in endothelial cell loss over the posterior chamber phaco, but not enough to be significant. After a few years, mydriatics were placed in the irrigating solution, and antiinflammatory drops were used on the cornea in combination with more powerful mydriatics. Once viscoelastics came into use, they too aided in pupillary dilation, and posterior chamber phaco became much easier. For those pupils which are fibrotic, several models of iris hooks are available.
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Anterior Capsular Opening A method of opening the anterior capsule had to be developed which would be consistent, exposing the lens, but not extending to the zonules.
FIGURE 3.7 Christmas tree opening My first attempts to incise the anterior capsule in several directions, with criss-crossing lines taught me that these incisions in the capsule, if subjected to traction, could extend around the anterior surface of the lens into the zonule, and perhaps even onto the posterior capsule. One day, I observed on an animal eye, that if I used a dull cystotome rather than a sharp one, instead of cutting the capsule, the cystotome tore it. And that tear was always in the form of a triangle. I named this technique the Christmas Tree Opening (Fig. 3.7). If I could rewrite history, I would call it a triangular capsulorhexis, a more accurate description, and one which would place it in its proper historical position, the forerunner of the continuous tear capsulorhexis. Once the triangular tear was made, the pie-shaped flap would be grasped with a forceps, gently extracted, and then cut at its base. This method was in general use until the “can opener technique” was introduced, and then finally the continuous tear technique widely used today. Magnification and Visualization Using loups (the standard method of magnification at that time), the magnification was not adequate. Using existing surgical microscopes gave no depth perception, since the lighting was flat, and there was no red reflex. This technique involved acute visualization of the intraocular structures never really seen before. No surgeon had ever really seen at surgery, cortical material lying on top of a capsule, or a tiny zonular dehiscence, or a minute opening in the capsule, and yet this type of visualization was required if phaco was ever going to be successful. The first microscopes I tried were table top dissecting microscopes, and they had inadequate side illumination. In examining other types of microscopes, I came upon an exciting discovery. Using an ENT microscope, the red reflex from the coaxial light gave me an incredible depth perception intraocularly. From then on, only ENT microscopes were used until Zeiss finally made one more suitable for ophthalmology.
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Protection of the Posterior Capsule The posterior capsule is not a strong membrane. Techniques had to be developed which would protect it during the lens removal. It became evident to me very early on, that the big obstacle to phaco would be the rupture of the posterior capsule. The early phaco machines did not have the power or the suction that present models have, and the tip had to be pushed into a hard nucleus in order to emulsify it. Like a dull knife must be pushed harder onto tissue than a sharp one. This pushing often broke the capsule. One must remember that there were no viscoelastics at that time. In order to make the procedure safer for me, and especially for others learning it, I devised a technique for prolapsing the entire nucleus into the anterior chamber, where it could be emulsified at some distance from the capsule. This method remained in vogue until the equipment was improved, at which time phaco in the posterior chamber (where phaco began) was reintroduced. Protection of Iris and Cornea A technique of surgery had to be developed which would allow the surgeon to safely emulsify the nucleus without damaging the endothelium, or the iris. In the early cases, the cornea collapsed many times against the vibrating needle, and the corneas had severe striate for sometimes up to one month. There was no method at this time of counting endothelial cells, but later studies showed up to 50 percent cell loss in these first cases. It is interesting to note that these corneas eventually cleared, giving the patients good vision. Cortical Clean-up A technique would be needed to safely pull the cortex out of the fornices of the capsule, and then to aspirate it. In the early cases, the same phaco tip and sleeve were used to remove cortex, but it became obvious that this terminal opening endangered the capsule. I modified the tip, so that it had a closed terminal end, with the lumen on the side, so that it could be directed away from the capsule. Instrument Problems An instrument powerful enough to emulsify all types of cataracts, without damaging adjacent structures would have to be developed. The first phacoemulsifier used on animals and patients consisted of a table with various parts and devices connected to each other. One of the parts was a dental apparatus used to remove tartar from the teeth. This was modified, so as to add suction and irrigation. The ultrasonic stroke was not only too small to act on hard cataracts, but it got dampened even further when a load (the cataract) was put on. I found that with piezoelectric crystals, rather than magnetostrictive stacks, a greater stroke could be achieved, and that dampening could be prevented. Today there is no cataract too hard to be emulsified.
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Heat Build-up Ultrasonic frequencies build up sufficient heat to denature tissue. Cooling would have to be guaranteed. After actually cooking and denaturing the protein of the lens in some animal eyes, it became clear to me that constant irrigation of the vibrating tip had to be assured. My original idea of having a water tight, close fitting incision was not going to work, since when the tip was occluded, the outflow through the tip was blocked, and since the incision was tight around the tip, no fluid could escape. It then became necessary to have the incision slightly larger than the tip so that fluid could always escape from the eye, and also to insure that the amount of fluid flowing into the eye always exceeded the amount being aspirated. Once these concepts were put into effect, heat build-up ceased to be a problem. Anterior Chamber Collapse Considerable suction was necessary to hold lens material onto the vibrating tip. Once this material was aspirated, in a few milliseconds, there was enough suction build up to collapse the chamber. The result of this collapse was to see the cornea touching the vibrating tip, with the endothelium being emulsified. A method had to be found to prevent this. In order for the lens material (especially if it is hard nucleus) to remain fixed to the tip while that tip is vibrating, a fairly high level of vacuum must be achieved. If we started with a high level of vacuum, copious amounts of fluid would always be entering and leaving the eye. Also, if the capsule or iris were inadvertently engaged, these tissues would be more susceptible to damage, than if the suction were lower. It became obvious that a peristaltic type pump could apply minimum suction until such a time as the tip became occluded, at that time the suction would rise, holding the lens material onto the tip while it was being emulsified. The problem created with this system was that as soon as the lens material became suddenly aspirated, the high level of suction in the system would collapse the chamber. For the first 50 or so cases, I had no other solution to this problem, than that of trying to anticipate the collapse, and just before the morcel would be aspirated, I would take my foot off the foot pedal. This was very ineffective, and many times during the first cases, the cornea would collapse onto the vibrating tip. Although I am sure that the endothelium was damaged, to my good fortune, these eyes always cleared after a few days, permitting me to continue developing the instrument and technique. After much searching, I finally found a fluid control system which monitored flow in arteries by creation of an electrical current from the ions as they rushed through the arteries. I adapted this system so that the fluid flow through the aspiration line was monitored. When it stopped (tip occlusion), a valve was put into the alert position. Within a few milliseconds after flow started up again (aspiration of the morcel), this valve would open to the atmosphere, killing the suction. This was a very satisfactory system, and was used for several generations of phacoemulsifiers. After having suffered through hundreds of actual collapses on my first cases, I still remember the joy of seeing the tiny “beat” of the cornea, instead of a collapse, once the system was working.
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Handpiece Design The early handpieces were extremely heavy and cumbersome. The original procedures took up to four hours, with over one hour of ultrasonic time. A special three-dimensional parallelogram had to be invented and constructed to hold the handpiece. Ophthalmic surgeons are used to tiny instruments which fit into the fingers. The original phaco handpiece was about the size of a large flashlight, and weighed almost a pound. I was willing to use it while I was developing the techniques, but I knew no one else would be willing. While looking for ways to make the handpiece lighter and smaller, I developed the three-dimensional parallelogram to hold the handpiece, with all axes of rotation around the incision (Fig. 3.8). The original handpiece was magnetostrictive, and had a frequency of 25,000 cycles. By substituting piezo electric crystals for the heavy magnetostrictive plates, the size and weight were greatly reduced, and the frequency was raised to 40,000 cycles. I now had a handpiece that others might be willing to try. Handpiece Heat Build-up The original handpiece was magnetostrictive, and had to be water cooled. This cooling water had to be isolated from the sterile end of the handpiece. The original handpiece was water cooled. Non-sterile water flowed in, around and out of the magnetostrictive plates. The first handpiece had a set of O-rings to isolate this nonsterile water from the sterile irrigation fluid, but in one instance the O-rings failed, causing an infection. The interim
FIGURE 3.8 Three-dimensional parallelogram support for handpiece
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solution was to add a second set of O-rings, but finally, when the piezoelectric crystal replaced the magnetostrictive, air cooling was sufficient, and no O-rings were needed. Flaking of the Tips The original tips were steel, and flaking was a problem, with the possibility of leaving iron shavings inside the eye. Titanium is a completely inert metal, and is silent in tissue. It is also less friable than steel, and therefore the steel tips were replaced with this metal, and in millions of cases now, there has not been any report of adverse effects from this material. It is extremely rare to see any particle in any operated eye. Insulating the Vibrating Tip The vibrating tip had to be insulated from the corneo-scleral wound to prevent heating. Various materials were tried and the two best found were silicon and Teflon. Since silicon was softer, it was the final choice. Irrigating Solution Since a fair amount of solution would be washing over the cornea during the procedure, it was important to find the best possible irrigating solution. Rather than embark on a scientific quest as to which solution would be the safest, I had observed in Barcelona, that Jouquim Barraquer employed a solution, made in Spain, which closely approximated the fluid in the anterior chamber. I began importing and using this solution. Political Problems It is difficult enough for a serious scientist to introduce a dramatic change in a procedure which everyone thinks is already ideal. But when this new technique involves considerable training, using an operating microscope when one has never used one before, when those who are unable to perform the new technique announce that you have to lose a “bucketful of eyes” before you are adept at it, and when that technique is developed by a saxophone player who is still appearing in Carnegie Hall, and doing stand-up comedy in the casinos of Atlantic city, it sounds like getting this procedure accepted would be a hopeless proposition. At this point, I must say again, that if I had known in advance how many problems there were, I might well never have started the project. The Chinese proverb is appropriate here, “The longest journey in the world begins with the first step”. Although the surgical and instrument problems outlined above were difficult to solve, they were a constant challenge and their solution brought a great deal of satisfaction. Not so for the political problems! When I first introduced phacoemulsification and aspiration, it was met with more than scientific reserve. It was met with scorn. How dare I, a young nobody presume to change what the University professors were proclaiming the safest
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and most sophisticated surgical procedure ever devised (intracapsular surgery)? At meetings where I presented the concept, there was considerable derision, mockery and hostility in the questions from the floor. At Manhattan Eye and Ear Hospital where I was assistant attending surgeon, the hospital voted to allow only one case per week, for every year an attending was on the staff. This vote cut down on the number of cataract cases I could do. Since that edict only affected me, I was, after a great battle, able to get this ruling considered “restraint of trade”, and the hospital had to withdraw that ruling. When I began doing phacoemulsification, the Surgeon Directors advised me that I would have to stop immediately if I had even one case of serious complications. When you put that sword of Damocles together with the problems outlined above with the technique and instrument, one can imagine the pressure involved in every procedure. Once the technique had been taken up by several others in various parts of the country, each investigator was met with the same hostility that I had encountered. Once it began to be accepted by several dozen surgeons, the political forces against it had the operation declared “experimental” by Medicare, meaning that there would be no reimbursement for the procedure. It took several months, and letters from a thousand patients from all over the country to get this ruling by the government reversed. The American Academy of Ophthalmology then commissioned one of the most vociferous antagonists to the procedure to do an “unbiased” study comparing the results of phaco to intracapsular surgery. I was put on the panel, but was never allowed to see any of the results of this study until they were ready to be submitted. It came as no surprise to find that intracapsular surgery was found to be infinitely superior to phacoemulsification. Since the justification of this conclusion was rather suspect, I was able to engage the professor of statistics at Columbia Presbyterian University to examine the methods and conclusions drawn. His report was so scathing, that the original report was discarded, and the final verdict submitted to the Academy was that phaco was at least as safe and effective as intracapsular surgery. The increase in the percentage of cases done with phaco slowly increased over the years, until foldable lenses were introduced. At that time, Phaco cases increased dramatically, until today, more than 85 percent of cataracts removed use phacoemulsification and aspiration. I am grateful to the early pioneers who stood with me, and grateful to all those who even today are improving this technique. References 1. Kelman CD, Cooper IS: Cryosurgery of retinal detachment and other ocular conditions. The Eye, Ear, Nose and Throat Monthly 42:42–46, 1963. 2. Cryogenic surgery: N Engl J Med 268:1963. 3. Kelman CD: Symposium; phacoemulsification. History of emulsification and aspiration of senile cataracts. Transactions American Academy of Ophthalmology and Otolaryngology 78:OP7– OP9, 1974.
4 Biometry Sunita Agarwal Introduction It is necessary for every ophthalmologist who is working with intraocular lenses to know how to calculate the power of the IOL. Axial Length Measurement For IOL implantation, the ultrasonic method affords the best way to calculate the axial length and achieves the desired postoperative refraction. The instruments available to make these measurements are of two basic types: i. instruments with rigid probe tips, and ii. instruments with distensible tips or with water baths. Those instruments with distensible membranes on the front of the probe are approximately 5 percent more accurate in making measurements than those with the rigid tip. The reasons why the distensible tip are better are as follows. 1. The distensible tip prevents indenting the cornea when the measurement is made, and does not cause the eye to appear artificially shortened. A rigid tip can cause corneal indentation between 0.1 and 0.3 mm, resulting in error from 0.3 to 1.0 diopters (Fig. 4.1). In other words if one is buying an A-scan, one should get one with a distensible tip.
FIGURE 4.1 Disadvantage of hard tip transducer—note indentation on the cornea
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2. The distensible tip helps to separate the corneal reflection from the signal sent out from the front surface of the transducer, i.e. it makes it more accurate to determine exactly where the front surface of the cornea is, and when it is not in direct contact with the transducer.
Keratometric Measurements The keratometric measurements can be done through a keratometer or through an autokeratometer. Many biometers (Fig. 4.2) have provision for connecting the autokeratometer to their computer so that once the keratometer reading is taken automatically, the value is entered into the biometer, and one does not have to feed it in again. IOL Formula There are two major categories of IOL formulae.
FIGURE 4.2 Biometer Theoretical Formula Introduction This formula is based on an optical model of the eye. An optics equation is solved to determine the IOL power needed to focus light from a distant object onto the retina. In the different formulae, different assumptions are made about the refractive index of the cornea, the distance of the cornea to the IOL, the distance of the IOL to the retina as well as other factors. These are called theoretical formulae because they are based on a theoretical optical model of the eye. All of these theoretical equations make simplifying assumptions about the optics of the eye, and hence, provide a good (but not perfect) prediction of IOL power.
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The most popular formula in this group is the Binkhorst formula. This is based on sound theory. All the theoretical formulae can be algebrically transformed into the following P=[N/(L−C)]−[NK/(N−KC)] where, P = Dioptric power of the lens for emmetropia, N = Aqueous and vitreous refractive index, L = Axial length (mm) C = Estimated postoperative anterior chamber depth (mm), and K = Corneal curvature [D].
Binkhorst Formula Binkhorst has made a correction in his formula for surgically induced flattening of the cornea, using a corneal index of refraction of 1.333. Binkhorst also corrects for the thickness of the lens implant by subtracting approximately 0.05 mm from the measured axial length. Thus with the Binkhorst formula, 0.25 mm is added to the measured axial length to account for the distance between the vitreoretinal interface and the photoreceptor layer, and 0.05 mm is subtracted for lens thickness, resulting in a net addition of 0.20 mm to the measured axial length. The Binkhorst’s formula is: D=1336 (4r−a)/(a−d) (4r−d) where, D = Dioptric power of IOL in aqueous humor, 1336 = Index of refraction of vitreous and aqueous, r = Radius of curvature of the anterior surface of the cornea, a = Axial length of the globe (mm), and d = Distance between the anterior cornea and the IOL.
Disadvantages The problem in the theoretical formula is in the axial length measurement. The reason why it is difficult to measure the axial length accurately is that one must know the exact velocities of the ultrasound as it travels through the various structures of the eye. Because of the variation of the acoustic density of a cataract, these velocities cannot be known exactly. As a result, when cataractous lenses are much more acoustically dense than the average lens, the sound wave will move more rapidly through the lens and return to the transducer much more quickly than would have been expected for a given axial length. As a result of the velocity error, the eyes appear to be shorter. The formula consequently calculates an IOL power for an axial length which is too short. The patient then becomes overminused (too myopic). Theoretical formulae help the surgeon to anticipate what should result, not what will result from implantation.
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Regression Formula (Empirical formula) Introduction The regression formulae or empirical formulae are derived from empirical data and are based on retrospective analysis of postoperative refraction after IOL implantation. The results of a large number of IOL implantations are plotted with respect to the corneal power, axial length of the eye, and emmetropic IOL power. The best-fit equation is then determined by the statistical procedure of regression analysis of the data. Unlike the theoretical formulae, no assumptions are made about the optics of the eye. These regression equations are only as good as the accuracy of the data used to derive them. Advantages Implant power calculations can be made much more accurately through the use of regression formulae that are based on the analysis of the actual results of many uncomplicated IOL implantations in previous cataract surgeries. Since regression analysis is based on the results of actual operations, it includes the vagaries of the eye and measuring devices, vagaries that theoretical formulae attempt to address with correction factors. Sanders-Retzlaff-Kraff (SRK) Formula The most popular regression formula is the SRK formula which was developed by Sanders, Retzlaff and Kraff in 1980. This is P=A−2.5 L−0.9 K where, P = Implant power to produce emmetropia, L = Axial length (mm), K = Average keratometer reading, and A = Specific constant for each lens type and manufacture.
The SRK formula calculates the IOL power by linearly regressing the results of previous implants. As this is a linear formula, it will underestimate the power of high-powered lenses and it will overestimate the power of the low-powered lenses compared to the theoretical calculation. For example, if the Binkhorst formula predicts that a 28-diopter lens should be used, the SRK formula will predict that a 26-diopter lens should be used. In lenses with low power, if the Binkhorst formula predicts that a 10-diopter lens is necessary, the SRK will predict that a 12-diopter lens should be used.
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Relation of Equipment to Specific Formulae Most of the instruments calculate the desired power for the IOL at least by three different methods including a regression formula and a theoretical formula. It is the responsibility of the doctor to select which of the formulae he or she wants to use. Rarely, between 18 and 22 diopters, is there a significant difference between the calculated lens powers. But outside this range, there will be a progressive increase in difference between that determined by the theoretical formula and the one calculated by the regression formula. Since the regression formula has turned out to be statistically more accurate, 5 percent at these extremes, it is presently more reliable than the theoretical formulae. The manufacturers vary as to which programs they provide. One should anyway make sure that both the regression and theoretical formulae are included so that one has the opportunity to personally select the most reliable technique for one’s surgery. Targeting IOL Postoperative Refraction The question that comes to one’s mind next is “How to predetermine what postoperative refraction the patient should have?” This is the one parameter which the doctor has to decide upon and feed into the computer. The other parameters like axial length, etc. we have no control over. The answer depends on whether we are doing a monocular or binocular correction. Monocular Correction If we are considering only one eye (i.e. if the other eye has cataract or is amblyopic), targeting the postoperative refraction for approximately −1.00 diopter is probably the best choice. This is usually best because most people have visual needs for both distance and near. This means that the patient wants to be able to drive and to read without wearing glasses. If we target the postoperative refraction to −1.00D, it will allow the patient to perform most tasks with no glasses. At times, when they need finer acuity, they can wear regular bifocals, which will correct them for distance and near. The second reason for targeting the postoperative refraction to −1.00D is that statistically, between 70 percent and 90 percent of the patients will fall within +1.00D error of the desired postoperative refraction. The errors, as mentioned earlier are due to our inexact measurements. Therefore, the patient will fall between piano and −2.00D 90 percent of the time. This will assure most patients of useful vision without glasses. Hence, the error of the ultrasound is best handled by choosing the postoperative refraction to −1.00D. If we would target for piano, then 90 percent of the patients will be between −1.00 and +1.00D. When the patient’s refraction is on the +1 side he or she has no useful vision at any distance because he or she is hyperopic and does not have the ability to accommodate. Consequently, because it is very undesirable to have a hyperopic correction, targeting for −1.00D not only optimizes the best vision at all distances, but
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also minimizes the chance for hyperopia that can result from inaccurate ultrasonic measurements. Binocular Correction When the vision in the other eye is good, its refraction must be considered for binocular vision. One overriding rule when prescribing glasses is that one should never prescribe spectacles which gives the patient a difference in the power between the right and left lens greater than 3D. The reason for this is that even though the patient may have 6/6 vision in primary gaze, when the patient looks up or down, the induced vertical prism difference in the two eyes is so great that it will create double vision. In a patient who has good vision in the nonoperative eye, one must target the IOL power for a refraction within 2D of his or her present prescription in the nonoperative eye. Two dipoters, not three, due to our 1D A-scan variability. For example, if we have a patient who is hyperopic and has +5D correction in each eye, we cannot target the IOL for a postoperative refraction of −1.00D because this would produce a 6D difference between the two lenses resulting in double vision. We must therefore select the IOL power to obtain a refraction which is approximately 2D less than the nonoperative eye. Consequently, on our patient who is +5D in both eyes, we should target the postoperative refraction in the eye with the cataract for +3D, so that there is a 90 percent probability that there will be less than a 3D difference. In contrast, if the patient were highly myopic in each eye, for example, −10D in both eyes, we should target the IOL power to produce refraction of approximately −8D. Again, we have limited the difference in the spectacles lenses to a 2D difference in the final prescription. Again, target, for a 2D difference not a 3D, because there is approximately a 1D tolerance in the accuracy of the ultrasonic measurement. If the operation on the second eye is to be done shortly after the first, the preoperative spectacles refraction can be ignored, and the patient is treated as if he or she were monocular. Factors Affecting Accuracy of IOL Power Calculation Many factors can affect the accuracy of the power of the IOL calculated. Keratometry Keratometers only measure the radius of curvature of the anterior corneal surface. This measurement must be converted to an estimate of the refracting power of the cornea in diopters, using a fictitious index (the true corneal refractive index of 1.376 could be used only if both the anterior and posterior corneal radii of curvature were known). The variability can alter calculated corneal dioptric power by 0.7D.
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Axial Length Measurement As explained earlier, indentation of the cornea by the A-scan instrument tip can alter the axial length affecting the accuracy of the power of the IOL. Axial Length Correction Factor The distance from the vitreoretinal interface to the photoreceptor layer has been estimated to be about 0.15 to 0.5 mm. This distance can affect the accuracy of the IOL power calculated. Site of Loop Implantation Posterior chamber IOLs may be implanted with both loops in the ciliary sulcus or in the capsular bag, or with one loop in the sulcus and one loop in the capsular bag. Positioning the implants within the capsular bag places the implant further back in the eye and decreases the effective power of the lens. There is usually a 0.5 to 1.5D loss of effectivity by placing the implant in the capsular bag as opposed to the ciliary sulcus. A higher power lens should therefore be used when the implant is placed in the capsular bag. Orientation of Planoconvex Implants Some surgeons implant planoconvex posterior chamber lenses with the piano surface forward.
FIGURE 4.3 Ultrasonic reading in dense cataract Such flipping of the implant decreases the effective power of the lens by 0.75D even if the position of the lens is unchanged. An additional 0.5D loss of effectivity occurs because the principal plane of the lens is usually displaced further back into the eye. Thus, a total loss in effectivity of 1.25D is expected by turning the lens around.
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Postoperative Change in Corneal Curvature Suturing of a cataract incision has a tendency to steepen the vertical meridian. These changes affect the postoperative refraction of the patient. Density of the Cataract The density of the cataract also makes a difference. In a dense cataract (Fig. 4.3), the ultrasonic waves travel faster whereas in an early cataract (Fig. 4.4) the ultrasonic waves travel slower. IOL Tilt and Decentration When a lens is tilted, its effective power increases and plus cylinder astigmatism is induced about the axis of the lens tilt. The tilting of the lens occurs if one loop is in the capsular bag and the other in the sulcus (Fig. 4.5). Alternatively, residual cortex being left behind can cause an inflammatory response which causes contraction and pulling unequally on parts of the loops and the optic.
FIGURE 4.4 Ultrasonic reading in early cataract
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FIGURE 4.5 Captive iris syndrome Pseudophakic Lasik If a patient has had a wrong biometry then the solution can be to remove the IOL and replace it with a correct powered IOL. Another alternative is to perform LASIK and correct the problem. Figure 4.6
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FIGURE 4.6 Topograph of a patient in whom a wrong power IOL was implanted
FIGURE 4.7 Topograph of the same patient as in Figure 4.6 after LASIK is the topograph before LASIK of a patient who had a power of −10.0 dioptres after IOL implantation. The patient was referred to us and we did a LASIK as the patient was operated a year back, We felt that the IOL might be fixed firmly in the bag. Figure 4.7 is the topograph after LASIK.
5 IOL Power Calculation After Corneal Refractive Surgery Jairo E Hoyos Melania Cigales J Hoyos-Chacón Corneal refractive surgery corrects refractive errors by modifying the anterior surface of the cornea. The problem appears years later when, as a result of the normal aging process, these patients develop cataracts and require lens extraction surgery and intraocular lens (IOL) implantation. Figure 5.1 shows one eye with cataract surgery after corneal refractive surgery. The question arises about which should be the basis for calculating this lens implant. Being able to determine the accurate power of the IOL to be implanted in a patient undergoing cataract surgery is a big challenge, even more so when the patient has had prior refractive surgery. A patient with prior refractive surgery is very special both medically and psychologically because he or she will not want to use glasses permanently after having spent time without them.
FIGURE 5.1 (Hoyos). High myope patient operated on with “in situ” queratomileusis and radial keratotomy for the residual error, who developed cataract 10 years later. A phacoemulsification technique was
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performed and an IOL foldable was implanted Formulas for calculating the IOL power include multiple variables, but with the current standardized cataract surgery techniques, these are reduced to only three: lens constant, corneal diopter power and axial length of the eye. The lens constant is standard for each lens model; refractive corneal surgery does not change axial length; however, postrefractive surgery produces a significant change in corneal curvature. At present, the best system for measuring corneal curvature is computerized corneal topography, although this method overestimates the central diopter power of a flattened cornea resulting from corneal refractive surgery. Consequently, the IOL power calculation will depend primarily on how accurately the cornea’s central refractive power is calculated. In this chapter we will analyze the information from the patient’s refractive surgery history, the current systems for measuring corneal power and the proposed methods for patients with previous corneal refractive surgery. In addition to this, the scan measurement of axial length and the IOL power calculation formulas we also be reviewed. Ocular History The refractive success of cataract surgery in eyes with prior refractive corneal surgery will depend mainly on the ability to calculate the current keratometric power of the cornea accurately. This requires knowledge of the patient’s ocular history before and after refractive surgery, as well as of the current ocular status. a. The history prior to refractive surgery will provide information about refraction, corneal power and axial length before refractive surgery. b. The postrefractive surgery history will provide information about stable refraction obtained following the procedure. c. The current ocular history must include biometry and computerized corneal topography besides the complete ophthalmological examination.
Keratometric Readings The refractive change of the anterior surface of the cornea as measured by topographic and keratometric readings has been and continues to be the basis for a large number of surgical techniques designed to correct refractive errors. Everything started with the early observations by Christopher Scheiner in 1619, based on the reflection of the grid of windowpanes on the cornea, which later led to the use of simple versatile keratoscopy and keratometry. Until the development of the modern computerized equipment for corneal topography, ophthalmologists used different instruments for studying the anterior corneal surface whose sensitivity and specificity have improved with time and as a result of technological breakthroughs.1–3
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The old devices such as Javal were, for many years, of great help in keratometric study. However, it was not until the late 1980’s when computerized devices were implemented and marketed that we were able to obtain a much more reliable assessment of the central power of the cornea in patients with prior refractive surgery. The keratometer is capable of measuring a regular spherocylindrical surface with accuracy greater than 0.25 diopters. However, the major limitations of the keratometer are that it assumes that the cornea is an spherocylindrical surface. It provides no information regarding the topography central or peripheral to the points of measurement, and mild corneal surface irregularity causes distortion, precluding meaningful measurement. Despite these slight drawbacks, the Javal keratometer was of great help to us when we began performing keratomileusis in the late 1980’s. Topographic parameters are studied in computerized corneal topography using the absolute and normalized scale and topographic maps: a. Sim K (Simulated keratoscope reading) is derived from maximum K readings for rings 6, 7 and 8. b. Min K (Minimum keratoscope reading) corresponds to the minimum keratometric power of rings 6, 7 and 8. c. Central K (Central keratoscope reading) corresponds to the central topographic area within the central 3 mm of the cornea which coincides with the visual axis and whose value may be obtained from the center of the topographic map and the color code bar in diopters (Fig. 5.2). It is very important to bear in mind that rings 6, 7 and 8 are on the outer limit of the three central millimeters of the corneal fixation center and, therefore, outside the area of refractive treatment in many high myopic patients.
FIGURE 5.2 The central K corresponds to the central topographic area within the central 3 mm of the cornea coinciding with the visual axis
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Corneal Power Calculation Methods The next challenge for the surgeon is to determine the keratometry to be used for calculating the intraocular lens power. The main methods which are normally used to calculate corneal power after refractive surgery are: the calculation method or refractive history method;4 the hard contact lens method5; and corneal topography. A. Calculation method or refractive history method: This is the most accurate method and requires knowing three parameters: K-readings and refraction before the keratorefractive procedure, and stabilized postoperative refraction (before any myopic shifts from nuclear cataract occur). The main concept is to subtract the refractive change on the corneal plane due to the keratorefractive procedure, from the original Kreadings before the procedure, to arrive at a calculated postoperative K-reading. Step I: Calculate the spheroequivalent refraction for refraction on the corneal plane (SEQc) on the basis of the spheroequivalent refraction on the spectacle plane (SEQs) at a given vertex. Step II: Calculate the change in refraction on the corneal plane, where refraction change is equal to preoperative SEQc minus postoperative SEQc. Step III: Determine the calculated postoperative corneal refractive power, where mean postoperative K is equal to the mean preoperative K minus the change in refraction on the corneal plane. The value obtained is the calculated central power of the cornea following the keratorefractive procedure. Once the pre- and postrefractive surgery refraction (spherical equivalent) is known, the refractive change induced on the corneal plane is determined and subtracted from the Kreading present before the corneal refractive surgery. Refraction must be measured on the corneal plane. For this purpose, distance-to-vertex conversion tables or the following formula may be used: Rc=Rg/[1−(d×Rg)], where Rc is the refraction on the corneal plane, Rg is the refraction on the spectacle plane and d is the distance to the vertex in meters (0,012). It is important to determine the stable residual refraction in patients who have undergone prior refractive surgery since it may change with time as a result of cataractinduced myopization of the index or due to an increased axial length in some cases. B. Trial hard contact lens method: This method requires a piano hard contact lens with a known base curve and a patient with a cataract, which allows us to see the retinoscopy, shadows during the refraction. Step I: The patient’s spherical equivalent refraction is determined by normal refraction. Step II: The refraction is repeated with a hard contact lens in place. If the spheroequivalent refraction does not change with the contact lens, the
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patient’s cornea must have the same power as the base curve of the piano contact lens (Fig. 5.3A). If there is a hyperopic shift in the refraction, then the base curve of the contact lens is weaker than the cornea by the shift amount (Fig. 5.3B). If the patient has a myopic shift, then the base curve of the contact lens is stronger than the cornea by the shift amount (Fig. 5.3C). Step III: The appropriate algebraic formula for each case is then made, taking into account that spheroequivalent values greater than ±4.00 D must be converted to corneal plane. This method is limited by the accuracy of the
FIGURE 5.3 Trial hard contact lens method: A If the spheroequivalent refraction does not change with the contact lens, the power of the patient’s cornea must be the same as the base curve of the planocontact lens. B When there is a hyperopic shift in the refraction, then the base curve of the contact lens is weaker than the cornea by the amount of the shift. C If the patient exhibits a myopic shift, then the base curve of the contact lens is stronger than the cornea by the amount of the shift refraction, which is in turn limited by the amount and type of the cataract, and it requires good visual acuity of 20/80 or better. C. Corneal topography method: Corneal topography allows for an accurate determination of the anterior surface of the cornea. For this method, the central corneal power following keratorefractive surgery must be known. This one, like the keratometry
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method, is very inaccurate. Current topographers do not allow us to determine an objective central K-reading and only provide Sim K and Min K values which are always overestimated in patients with prior surgery for myopia and underestimated in cases of hyperopic surgery. If those keratometric values were used for calculating the intraocular lens, postoperative results would be very far from ametropia (Fig. 5.4).
Biometry A-mode ultrasound biometry enables us to measure the eye’s visual axis through echo generation representing the reflection of the ultrasound beams on the different interfaces of the ocular tissues. Corneal ablation used for correcting the refractive
FIGURE 5.4 IOL power calculation using different corneal powers: Sim K, Min K, Calculated K and Central K error is minimal (less than 150 mµ) and has negligible effects in terms of modifying the axial length after refractive surgery.6 Care must be taken when performing biometry in order to avoid errors caused by the loss of alignment with the optic axis, and excessive pressure of the transducer on the cornea which leads to short readings of the axial length (especially in eyes with a thinned-out cornea). It is also important to ensure that a standard deviation of less than 0.1 is obtained for several measurements. In high myopia, the presence of a posterior staphyloma may give rise to inconsistent recordings, but this may be avoided by asking the patient to fix on the transducer light.7,8 During biometry, it is important to ensure that the transducer is applied without indenting the cornea, which may be significantly thinner in high myopes as a result of the refractive technique. A 1 mm error in the axial length determination results in a 3-diopter error, while a 1 mm error in the preoperative determination of the anterior chamber depth will induce a refractive error of 1.4 diopters. Consequently, we recommend using the biometer in automatic mode with five measurements and a standard deviation of less than 0.1. Also, whenever possible, the patient must be made to fix on the transducer light. In our patients, whenever we find variations between the current axial length and the one existing before refractive surgery, we always use the higher value because of the
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possibility of a post-operative increase of the axial length with increased myopia, or because of the possibility of introducing a biometric error as a result of indenting a thin cornea. IOL Power Calculation Formulas A number of theoretical and regression formulas are used. It is generally accepted that both theoretical and regression-derived formulas perform well for eyes of average axial lengths between 22 mm and 24.5 mm. Even in extremely long eyes of more than 28.4 mm in length, excellent accuracy can be achieved with the Holladay and the SRK-T formulas. Regression formulas such as the SRK II, which perform very well in eyes of usual length, should not be used in these extremely long eyes.9 Hoffer10 recommends using his own formula for eyes with axial lengths of less than 22 mm, and the SRK-T and Holladay for axial lengths greater than 24.5 mm. Koch11 discovered that the modern theoretical formulas were far better than regression formulas when evaluating IOL power for radial keratotomy eyes. Therefore, the first thing to do to improve accuracy is to refrain from using a regression formula (SRK, SRK II, etc) to calculate the IOL power for these eyes. A modern third-generation theoretical formula such as the Holladay, the Hoffer Q or the SRK-T should be used; their accuracy is further improved when they are individualized. It is very important to use third-generation formulas, which take into consideration axial length and anterior chamber depth (e.g. Holladay, SRK-T, or Hoffer-Q) since the old ones like SRK I, SRK II and Binkhorst may give rise to significant errors. Accurate power calculation constants are absolutely essential for the effective implant power calculation; the SRK II formula utilizes A-constants, the SRK-T theoretical formula utilizes either A constants or ACD constants, the Holladay formula utilizes the Surgeon Factor (SF) constant, which is an offset of the ACD constant. Manufacturer published constants are first determined for specific IOLs by the manufacturer through closed studies or are estimated by comparison with existing IOLs. Each surgeon should become familiar with, and use the same type of lens as long as the operative conditions allow it, because that would allow the surgeon to determine personal variations and establish a personal constant (A, ACD or SF).12,13 For calculating the power of the intraocular lens in high myopia, it is better to aim for −0.75D, because we have noticed that these patients benefit significantly from their near vision. In many of our patients, despite using an intraocular lens calculated to induce a myopia of −0.75 to −1.00, we have found that there is a minor residual defect or a tendency to emetropization; this observation should be taken into account because the tendency to hyperopia is undesirable in these patients who, aside from having been myopes, have no accommodation.
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Case Report Ocular History A 43-year old male with refraction in the left eye of [−16/−4×170°], with a 20/25 corrected visual acuity, 31.9 mm axial length and the following topographic values: Sim K [46.3D×82°/42.4D×172°] and Min K [42.3D×176°] (Fig. 5.5A). LASIK was performed to correct myopia and astigmatism, and six months later, refraction was −0.50D spherical, and topographic parameters were: Sim K [32.1D×45°/ 31.6D×135°] and Min K [31.4D×172°] (Fig. 5.5B). Three years later the patient developed a cataract and refraction was −4.50D spherical, uncorrected visual acuity was 20/200, corrected visual acuity was 20/30, axial length was 31.06 mm and
FIGURE 5.5A Clinical case: PreLASIK data
FIGURE 5.5B Clinical case: Data 6 months after LASIK surgery
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FIGURE 5.5C Clinical case: Data 3 years after LASIK surgery when the eye shows cataract topographic values were: Sim K [32.7D×55°/32.3 D×145°] (mean 32.50), Min K [32.1D×173°] and Central K [30.30D] (Fig. 5.5C). Corneal Power Calculation We used the refractive history method to calculate the corneal power. 1. Pre-LASIK refraction was −16/−4×170°. The spherical equivalent (SE) was −18 D and the same value towards the cornea was −14.75D. 2. Post-LASIK refraction was −0.50D. 3. Refractive change was the pre-LASIK SE (−14.75) minus the post-LASIK SE (−0.50), that means −14.25D. 4. Preoperative keratometry average was 44.35D (Sim K [46.3D×82°/42.4D×172°]). 5. Calculated corneal power was the preoperative keratometry average (44.35D) minus the refractive change induced by LASIK (−14.25), that equals 30.1D. Axial Length There are two axial length values for this patient: 31.9 mm before LASIK and 31.06 mm before cataract surgery the difference being 0.84 mm. The reduction in axial length is attributed to corneal indentation, which may occur during measurement despite every precaution, especially in very high myopes with thin corneas resulting from refractive surgery. As mentioned previously, axial length does not change statistically Therefore, the axial length selected in this patient was the preoperative axial length of 31.9 mm. IOL Power Calculation The IOL power calculation, using the SRK-T formula, for an IOL with A constant of 118.8 and a −0.75D of desired refraction, was +16.50D.
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Result Uncorrected visual acuity three months after cataract surgery was 20/25 and pianorefraction. (Fig. 5.5D). Summary Refractive corneal surgery induces changes on the corneal surface and, consequently, in topographic
FIGURE 5.5D Clinical case: Postcataract surgery data readings. After refractive corneal surgery, corneal power may be calculated using the data of the patient’s refractive history. Comparisons between the keratometric values obtained with the refractive history method (“calculated K”) and the topographic data, allow us to conclude that the central keratometric value shown by topography (“central K”) is the closest to the calculated value. Sim K and Min K values correspond to rings 6, 7 and 8 on the outer limit of the three central millimeters of the corneal fixation center. For this reason, they cannot reflect the true value of the central cornea or, in other words, the keratometric value of the center of the cornea. Therefore, in calculating the IOL, these topographic values would lead to an undercorrected power calculation, thus inducing a final hyperopic refractive error. Although the calculation method will continue to be used until the computerized system of modern videokeratoscopes allows us to obtain objective central keratometric values, topographic “central K” may be useful when the refractive history is not available. We recommend recording refraction values pre-and postrefractive surgery, corneal topography values and axial length measurements in all patients who will be subjected to corneal refractive surgery, in order to facilitate calculation of intraocular lens power in the future, when the patient requires cataract surgery. As discussed previously, third-generation formulas (SRK-T, Holladay and Hoffer Q) are much more accurate than previous formulas for the more unusual eyes. Old formulas such as SRK, SRK-II and Binkhorst should not be used in these patients (Fig. 5.6). None
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of these formulas provide the desired result if the central corneal power is measured incorrectly. We generally use phacoemulsif ication bi-manual technique with foldable intraocular lens implantation through a 3.5 mm clear cornea incision. On the first day following cataract surgery, patients usually exhibit a hyperopic shift primarily due to transient postoperative corneal edema and intraocular pressure changes. These patients also exhibit
FIGURE 5.6 IOL power calculation using different formulas: SRK, SRKII, SRK-T, Holladay, Binkhorst the same daily fluctuation during the early postoperative period after cataract surgery. Because refractive changes are expected and vary significantly among patients, no lens exchange should be considered until after the first postoperative week or until after the refraction has stabilized, whichever is longer. References 1. Rabinowitz YS, Wilson SE, Klyce SD: Color atlas of corneal topography: Interpreting Videokeratography (1st ed). New York: Igaku-Shoin Medical Publishers Inc, 115, 1993. 2. Sanders DR, Koch DD et al: Atlas of Corneal Topography. (1st ed). Thorofare, NJ: Slack Incorporated, 209, 1993. 3. Klyce SD, Dingeldein SA: The topography of normal corneas. Arch Ophthalmol 107:512–18, 1989. 4. Holladay JT: IOL calculations following radial keratotomy surgery. Refractive & Corneal Surg (Question & Answer) 5(3): 36A, 1989. 5. Hoffer KJ: Intraocular lens power calculation for eyes after refractive keratotomy. J Refract Surg 11:490–3, 1995. 6. Hoffer K: Accuracy of intraocular ultrasound lens calculation. Arch Ophthalmol 99:1819–23, 1981. 7. Olsen, Thim, Cory don: Accuracy of the newer generation IOL power calculation formulas in long and short eyes. J Cataract Refract Surg 17:187–93, 1991. 8. Steele CE, Crabb DP, Edgar DF: Effects of different ocular fixation conditions on A-Scan ultrasound biometry measurements. Ophthal Physiol Opt 12:491–5, 1992.
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9. Retzlaff J, Sanders DR, Kraff MC: Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refractive Surg 16(3):333–40, 1990. 10. Hoffer KJ: The Hoffer Q formula: a comparison of theoretical and regression formulas. J Cataract Refract Surg 19:700–12, 1993. 11. Koch DD, Liu JF, Hyde LL et al: Refractive complications of cataract surgery after radial keratotomy. Am J Ophthalmol, 108:676–82, 1989. 12. Holladay JT, Praeger TC, Chandler TY, Musgrove KH: A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 14:17–24, 1988. 13. Retzaff J, Sanders DR, Kraff MC: A manual of implant Power Calculation: Medfort, Oregon. Retzlaff, Sanders and Kraff, 1982, 1985, 1988.
6 IOL Master for Determining the IOL Power at the Time of Surgery Hampton Roy Warren E Hill Introduction The Zeiss IOLMaster is a noncontact optical device that measures axial length of the eye by partial coherence interferometry, with a consistent accuracy of 0.02 mm (less than 0.10 diopter), or better. It also does automated keratometry, measures anterior chamber depth, the horizontal corneal diameter, and calculates intraocular lens powers, all in a single sitting.1–6 The IOLMaster employs a modified Michelson interferometer to divide, and phase delay, a 780 nm partially coherent beam of light. One beam is reflected from the corneal surface, while the other is reflected from the retinal pigment epithelium. A photodetector and on-board computer translate the interference pattern produced by the two beams into a highly accurate measurement of axial length. Calibrated against the ultra-high resolution 40-MHz Greishaber Biometric System, an internal algorithm then approximates the distance to the vitreo-retinal interface, for the equivalent of the ultrasonic axial length. Considering the fact that axial length measurements by A-scan ultrasonography (using a standard 10-MHz transducer) have a typical resolution of 0.10 mm to 0.12 mm, axial length measurements by the IOLMaster represent a fivefold increase in accuracy. Using the instrument is straightforward. The patient is placed in the chin rest and looks straight ahead at a small red fixation target. The eye is viewed on a video screen by the technician during all phases of measurement, allowing for proper alignment. Modes The following modes are useful: Overview mode This allows the technician to grossly align the instrument. Axial length mode The axial length can be determined in most eyes with a high degree of precision, including high myopes with posterior staphyloma, aphakia, pseudophakia and even for eyes filled with silicon oil. The machine displays a signal-to-noise ratio for each
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measurement, as one indication of reliability, and also compares multiple measurements. If the measurements are all within 0.1 mm, the machine displays an average axial length. If the measurements fall outside this range, the technician is instructed to evaluate the series of measurements before concluding the examination. The characteristics of a proper axial length display are the following: • Signal-to-noise ratio greater than 2.0. • Tall, narrow primary maxima, with a thin, well-centered termination. • At least one set of secondary maxima. However, if the ocular media is poor, secondary maxima may not be displayed. • At least four of the 20 measurements taken should be within 0.02 mm of one another and show the characteristics of a good axial length display. Automated keratometry mode IOLMaster uses an integrated autokeratometer to determine the corneal curvature of the principal meridians with corresponding axes, displayed in diopters, or in millimeters. The instruments take five measurements within 0.5 seconds and averages them. The latest software revision (version 3.01) has an improved keratometry algorithm and will alert the operator if a keratometry measurement is questionable. Anterior chamber depth mode The distance between the optical section of the cornea, and the crystalline lens, is measured using a lateral slit illumination at approximately 30 degrees to the optical axis. This measurement is helpful for intraocular lens power calculation formulas, such as Haigis and Holladay 2, which require a measured anterior chamber depth. Intraocular lens power calculation mode The collected data can be transferred to the intraocular lens power calculation area. Five intraocular lens power calculation formulas (Haigis, Hoffer Q, Holladay 1, SRK II, SRK/T) are included with the IOLMaster software. The surgeons selects the calculation formula that he wishes to use, the target refraction, and the IOLMaster will calculate the power of upto four intraocular lenses in the physician database. The IOLMaster can accommodate as many as 20 surgeons, each with upto 20 preferred intraocular lenses, and corresponding personalized lens constants. The IOLMaster is easy to use, accurate and has excellent reproducibility. New Intraocular Lens Constants Some lenses, like the Alcon SA60AT, show very little difference when compared to immersion A-scan ultrasonography, while others, like the Bausch and Lomb U940A show a larger difference. In order to determine the best initial IOLMaster constant, Dr. Wolfgang Haigis, at the University of Würzburg in Germany has recommended the following approach for calculating the initial A-constant. AIOLMaster = A Ultrasound+3 * (AL IOLMaster−AL Ultrasound) AIOLMaster = Optimized A−constant for IOL Master
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AUltrasound = Optimized A−constant for ultrasonography ALIOLMaster = Average IOLMaster axial length ALUltrasound = Average ultrasound axial length
Advantages of Using the IOL Master • No topical anesthetic is needed. • Multiple measurements, at different instrument stations, are not necessary. • Patients sit upright. • Using the IOLMaster is quick, accurate, and requires minimal training, although some Interpretation by the operator is necessary. • Noncontact technique precludes the occurrence of corneal epithelial injuries, and the transmission of infections.
Disadvantages • Unable to use for dense nuclear cataracts, posterior subcapsular plaques, corneal scars and vitreous hemorrhages. In any case in which the axial opacity interferes with the partially coherent light beams, IOL master cannot be used. • Unable to use on patients that cannot fully cooperate because of physical or psychological reasons. Approximately 95 percent of patients can be measured successfully using the IOL Master. Results of the IOL Master The accuracy of intraocular lens power predictions from the IOLMaster measurements have been found to be as good, or better, than immersion A-scan ultrasonography. With a combination of the IOLMaster, and the Holladay 2 formula, Warren E. Hill, M.D. has been able to consistently achieve refractive outcomes with a mean absolute prediction error of better than ±0.25 diopters. This approaches the theoretic limit of the exercise, given the fact that intraocular lens implants come in 0.50 diopter steps. Summary Think of the IOL Master (Fig. 6.1) as a form of ultra high-resolution immersion A-scan ultrasonography, giving the refractive axial length, rather than the anatomic axial length. Because the IOLMaster is an optical device, measurements may not be possible in the presence of significant axial opacities, such as a corneal scar, mature cataract, vitreous hemorrhage, or dense PSC plaque, etc. IOL constants for the IOLMaster will often be slightly higher than the manufacturer’s suggested numbers and are very close to those used for
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FIGURE 6.1 IOL master immersion A-scans. It is suggested that IOLMaster-specific intraocular lens constants be used with the various popular intraocular lens power calculation formulas. The IOLMaster is a highly reliable tool for determining the intraocular lens power prior to surgery. References 1. Vogel A, Dick B, Krummenauer F: Reproducibility of optical biometry using partial coherence interferometry. Intraobserver and interobserver reliability. J Cataract Refract Surg 27:1961–68, 2001. 2. Schachar RA, Levy NS, Bonney RC: Accuracy of intraocular lens powers calculated from Ascan biometry with the Echo-Oculometer. Ophthalmic Surg 11:856–58, 1980. 3. Drexler, W, Findl O, Menapace R et al: Partial Coherence Inferometry: A Novel Approach to Biometry in Cataract Surgery. Am J Ophthalmol 126:524–34, 1998. 4. Holladay JT, Musgrove KH, Praeger TC et al: A three-part system for refining intraocular lens power calculations. J Cataract Refractive Surgery 14:17–24, 1988. 5. Wallace RB: IOLMaster Optical Coherence Biometry: Accurate Axial Length Measurement for Cataract Surgery and Refractive Lensectomy. Refractive Eyecare for Ophthalmologists 4:17– 20, 2000. 6. Retzlaff J, Sanders DR, Kraff MC: Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refractive Surgery 16:333–40, 1990.
7 Corneal Topography in Cataract Surgery Athiya Agarwal, Sunita Agarwal Amar Agarwal, Nilesh Kanjani Introduction Topography is defined as the science of describing or representing the features of a particular place in detail. In corneal topography, the place is the cornea, i.e. we describe the features of the cornea in detail. The word Topography is derived1,2 from two Greek words: TOPOS- meaning place and GRAPHIEN- meaning to write Cornea There are basically three refractive elements of the eye- namely; axial length, lens and cornea. The cornea is the most important plane or tissue for refraction. This is because it has the highest refractive power (which is about+45 D) and it is easily accessible to the surgeon without going inside the eye. To understand the cornea, one should realize that the cornea is a parabolic curve—its radius of curvature differs from center to periphery. It is steepest in the center and flatter in the periphery. For all practical purposes the central cornea, that is the optical zone is taken into consideration, when you are doing a refractive surgery. A flatter cornea has less refraction power and a steeper cornea has a higher refraction power. If we want to change the refraction we must make the steeper diameter flatter and the flatter diameter steeper. Keratometry The keratometer was invented by Hermann Von Helmholtz and modified by Javal, Schiotz etc. If we place an object in front of a convex mirror we get a virtual, erect and minified image (Fig. 7.1). A keratometer in relation to the cornea is just like an object in front of a convex reflecting mirror. Like in a convex reflecting surface, the image is located posterior to the cornea. The cornea behaves as a convex reflecting mirror and the mires of the keratometer are the objects. The radius of curvature of the cornea’s anterior surface determines the size of the image.
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FIGURE 7.1 Physics of a convex mirror. Note the image is virtual, erect and minified. The cornea acts like the convex mirror and the mire of the keratometer is the object The keratometer projects a single mire on the cornea and the separation of the two points on the mire is used to determine corneal curvature. The zone measured depends upon corneal curvature—the steeper the cornea, the smaller the zone. For example, for a 36-D cornea, the keratometer measures a 4-mm zone and for a 50-D cornea, the size of the cone is 2.88 mm. Keratometers are accurate only when the corneal surface is a sphere or a spherocylinder. Actually, the shape of the anterior surface of the cornea is more than a sphere or a spherocylinder. But keratometers measure the central 3-mm of the cornea, which behaves like a sphere or a spherocylinder. This is the reason why Helmholtz could manage with the keratometer (Fig. 7.2). This is also the reason why most ophthalmologists can manage management of cataract surgery with the keratometer. But today, with refractive surgery, the ball game has changed. This is because when the cornea has complex central curves like in keratoconus or after refractive surgery, the keratometer cannot give good results and becomes inaccurate. Thus, the advantages of the keratometer like speed, ease of use, low cost and minimum maintenance is obscured.
FIGURE 7.2 Keratometers measure the central 3-mm of the cornea, which
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generally behaves like a sphere or a spherocylinder. This is the reason why keratometers are generally accurate. But in complex situations like in keratoconus or refractive surgery they become inaccurate The objects used in the keratometer are referred to as mires. Separation of two points on the mire are used to determine corneal curvature. The object in the keratometer can be rotated with respect to the axis. The disadvantages of the keratometer are that they measure only a small region of the cornea. The peripheral regions are ignored. They also lose accuracy when measuring very steep or flat corneas. As the keratometer assumes the cornea to be symmetrical it becomes at a disadvantage if the cornea is asymmetrical as after refractive surgery. Keratoscopy To solve the problem of keratometers, scientists worked on a system called Keratoscopy. In this, they projected a beam of concentric rings and observed them over a wide expanse of the corneal surface. But this was not enough and the next step was to move into computerized videokeratography. Computerized Videokeratography In this, some form of light like a placido disk is projected onto the cornea. The cornea modifies this
FIGURE 7.3 Placido type corneal topography machine
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light and this modification is captured by a video camera. This information is analyzed by computer software and the data is then displayed in a variety of formats. To simplify the results to an ophthalmologist, Klyce in 1988 started the corneal color maps. The corneal color maps display the estimate of corneal shape in a fashion that is understandable to the ophthalmologist. Each color on the map is assigned a defined range of measurement. The placido type topographic machines (Fig. 7.3) do not assess the posterior surface of the cornea. The details of the corneal assessment can be done only with the Orbscan (Bausch and Lomb) as both anterior and posterior surface of the cornea are assessed. Orbscan The ORBSCAN (BAUSCH and LOMB) corneal topography system (Fig. 7.4) uses a scanning optical slit scan that is fundamentally different than the corneal topography that analyses the reflected images from the anterior corneal surface. The high-resolution video camera captures 40 light slits at 45 degrees angle projected through the cornea similarly as seen during slit lamp examination. The slits are projected on to the anterior segment of the eye: the anterior cornea, the posterior cornea, the anterior iris and anterior lens. The data collected from these four surfaces are used to create a topographic map.
FIGURE 7.4 Orbscan Normal Cornea In a normal cornea (Fig. 7.5), the nasal cornea is flatter than the temporal cornea. This is similar to the curvature of the long end of an ellipse. If we see figure 5 then we will notice the values written on the right end of the pictures. These indicate the astigmatic values. In that is written Max K is 45 @ 84 degrees and Min K is 44 @ 174 degrees. This means the astigmatism is +1.0D at 84 degrees. This is with the rule astigmatism as the astigmatism is plus at 90 degrees axis. If the astigmatism was plus at 180 degrees then it is against the rule astigmatim. The normal corneal topography can be round, oval, irregular, symmetric bow tie or asymmetric bow tie in appearance. If we see Figure 7.6 we will see a case of astigmatism in which the astigmatism is +4.9D at 146 degrees. These figures show the curvature of the anterior surface of the cornea. It is important to
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remember that these are not the keratometric maps. So the blue/green color denote steepening and the red color denote flattening. If we want the red to denote steepening then we can invert the colors. Cataract Surgery Corneal topography is extremely important in cataract surgery. The smaller the size of the incision lesser the astigmatism and earlier stability of the astigmatism will occur. One
FIGURE 7.5 Topography of a normal cornea
FIGURE 7.6 Topography showing an astigmatic cornea
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FIGURE 7.7 Topography after extracapsular cataract extraction (ecce).The figure on the left shows astigmatism of +1.1 d at 12 degrees preoperatively. The astigmatism has increased to +4.8 d as seen in the figure on the right can reduce the astigmatism or increase the astigmatism of a patient after cataract surgery. The simple rule to follow is that wherever you make an incision that area will flatten and wherever you apply sutures that area will steepen. Extracapsular Cataract Extraction One of the problems in extracapsular cataract extraction is the astigmatism which is created as the incision size is about 10 to 12 mm. In Figure 7.7, you can see the topographic picture of a patient after extracapsular cataract extraction (ECCE). You can see the picture on the left is the preoperative photo and the picture on the right is a postoperative day 1 photo. Preoperatively one will notice the astigmatism is +1.0D at 12 degrees and postoperatively it is +4.8D at 93 degrees. This is the problem in ECCE. In the immediate postoperative period the astigmatism is high which would reduce with time. But the predictability of astigmatism is not there which is why smaller incision cataract surgery is more successful.
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Nonfoldable IOL Some surgeons perform phaco and implant a non-foldable IOL in which the incision is increased to 5.5 to 6 mm. In such cases the astigmatism is better than in an ECCE. In Figure 7.8, the pictures are of a patient who has had a nonfoldable IOL. Notice in this the preoperative astigmatism is +0.8D @ 166 degrees. This is the left eye of the patient. If we had done a phaco with a foldable IOL the astigmatism would have been nearly the same or reduced as our incision would have come in the area of the astigmatism. But in this case after a phaco a non-foldable IOL was implanted. The postoperative astigmatism one week postoperative is +1.8D @ 115 degrees. You can notice from the two pictures the astigmatism has increased. Foldable IOL In phaco with a foldable IOL the amount of astigmatism created is much less than in a nonfoldable IOL. Let us look now at Figure 7.9. The patient as
FIGURE 7.8 Topography of a nonfoldable IOL implantation
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FIGURE 7.9 Topography of phaco cataract surgery with a foldable IOL implantation you can see has negligible astigmatism in the left eye. The picture on the left shows a preoperative astigmatism of +0.8D at 166 degrees axis. Now, we operate generally with a temporal clear corneal approach, so in the left eye, the incision will be generally at the area of the steepend axis. This will reduce the astigmatism. If we see the postoperative photo of day one we will see the astigmatism is only +0.6D @ 126 degrees. This means that after a day, the astigmatism has not changed much and this shows a good result. This patient had a foldable IOL implanted under the no anesthesia cataract surgical technique after a phaco cataract surgery with the size of the incision being 2.8 mm. Astigmatism Increased If we are not careful in selecting the incision depending upon the corneal topography we can burn our hands. Figure 7.10, illustrates a case in which astigmatism has increased due to the incision being made in the wrong meridian. The patient had a 2.8-mm incision with a foldable IOL implanted after a phaco cataract surgery under the no anesthesia cataract surgical technique. Both the pictures are of the right eye. In Figure 7.10, look at the picture on the left. In the picture on the left, you can see the patient has an astigmatism of +1.1D at axis 107 degrees. As this is the right eye with this astigmatism we should have made a superior incision to reduce the preoperative astigmatism. But by mistake we made a temporal clear corneal incision. This has increased the astigmatism. Now, if we wanted to flatten this case, we should have made the incision where the steeper meridian was. That was at the 105 degrees axis. But because we were doing routinely temporal clear corneal incisions, we made the incision in the opposite axis. Now, look at the picture on the right. The astigmatism has increased from +1.1D to +1.7D. This shows a bad result. If
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we had made the incision superiorly at the 107 degrees axis, we would have flattened that axis and the astigmatism would have been reduced. Basic Rule The basic rule to follow is to look at the number written in red. The red numbers indicate the plus axis. If the difference in astigmatism is say 3D at
FIGURE 7.10 Increase in astigmatism after cataract surgery due to incision being made in the wrong meridian. Topography of a phaco with foldable IOL implantation
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FIGURE 7.11 Unique casetopographic changes after suture removal 180 degrees, it means the patient has +3D astigmatism at axis 180 degrees. This is against the rule astigmatism. In such cases, make your clear corneal incision at 180 degrees so that you can flatten this steepness. This will reduce the astigmatism. Unique Case In Figure 7.11, the patient had a temporal clear corneal incision for phaco cataract surgery under no anesthesia with a nonfoldable IOL. Both the pictures are of the left eye. The figure on the left shows the postoperative topographic picture. The postoperative astigmatism was +1.8D at axis 115 degrees. This patient had three sutures in the site of the incision. These sutures were put as a nonfoldable IOL had been implanted in the eye with a clear corneal incision. When this patient came for a follow-up we removed the sutures. The next day the patient came to us with loss of vision. On examination, we found the astigmatism had increased. We then took another topography. The picture on the right is of the topography after removing the sutures. The astigmatism increased to +5.7D. So, one should be very careful in analyzing the corneal topography when one does suture removal also. To solve this problem one can do an astigmatic keratotomy. Phakonit Phakonit is a technique devised by Dr Amar Agarwal in which the cataract is removed through a sub 1.4-mm incision. The advantage of this is obvious. The astigmatism created is very little compared to a 2.6-mm phaco incision. Today with the reliable IOL and the
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acritec IOL’s which are ultrasmall incision IOL’s one can pass IOL’s through sub 1.4 mm incisions. This is seen clearly in Figures 7.12 and 7.13. Figure 7.12 shows the comparison after phakonit with a reliable IOL and Figure 7.13 with an acritec IOL. If you will see the preoperative and the postoperative photographs in comparison you will see there is not much difference between the two. In this case a reliable IOL was implanted. The point which we will notice in this picture is that the difference between the preoperative photo and the one day postoperative photo is not much.
FIGURE 7.12 Topography of a phakonit with a reliable IOL
FIGURE 7.13 Topography of a phakonit with an acritec IOL
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Summary Corneal topography is an extremely important tool for the ophthalmologist. It is not only the refractive surgeon who should utilize this instrument but also the cataract surgeon. The most important refractive surgery done in the world is cataract surgery and not Lasik (Laser-in situ keratomileusis) or PRK (Photorefractive keratectomy). With more advancements in corneal topography, Topographic-Assisted Lasik will become available to everyone with an Excimer Laser. One might also have the corneal topographic machine fixed onto the operating microscope so that one can easily reduce the astigmatism of the patient. References 1. Gills JP et al: Corneal Topography: The State-of-the Art; New Delhi; Jaypee Brothers, 1996 2. Sunita Agarwal, Athiya Agarwal, Mahipal S Sachdev et al: Phacoemulsification, Laser Cataract Surgery and Foldable IOL’s; New Delhi; Second edition; Jaypee Brothers, 2000.
Section II Instrumentation and Medication 8. The Phaco Machine: How It Acts and Reacts 9. The Fluidics and Physics of Phaco 10. Air Pump to Prevent Surge 11. Microseal and Other Phaco Tips 12. Sterilization 13. Local Anesthetic Agents 14. Anesthesia in Cataract Surgery 15. Mydriatics and Cycloplegics 16. Update on Ophthalmic Viscosurgical Devices
8 The Phaco Machine: How It Acts and Reacts William J Fishkind Introduction All phaco machines consist of a computer to generate ultrasonic waveform, and a transducer, piezoelectric crystals, to turn these electronic signals into mechanical energy. The energy thus created is then harnessed, within the eye, to overcome the inertia of the lens and emulsify it. Once turned into emulsate, the fluidic systems remove the emulsate replacing it with balanced salt solution (BSS). There is a delicate balance between phaco power, which tends to push lens material away from the phaco tip, and flow and vacuum which tends to attract and hold lens material on the phaco tip. Many of the principles outlined below will vary dependent upon the individual machine. Therefore the information in this chapter is based on general principles and the reader is encouraged to investigate the function and suggested parameters for the machine that they are using. Power Generation Power is created by the interaction of frequency and stroke length. Frequency is defined as the speed of the needle movement. It is determined by the manufacturer of the machine. Presently, most machines operate at a frequency of between 35,000 cycles per second (Hz) and 45,000 cycles per second, although there are some machines that operate at lower frequencies (Table 8.1). The frequency range which appears to be most efficient for nuclear emulsification is from 30 to 45,000 cycles/sec (Hz). Lower frequencies are less efficient and higher frequencies create excess heat. Frequency is maintained constant by tuning circuitry designed into the machine computer.
TABLE 8.1 Machine technology Company Model
Phaco Machines Freq Pump type Pump comment KHZ
Alcon
40
Turbostatic High vacuum pack 0–500 0–60 Peristaltic
40
Peristaltic
Allergan
Legacy Series 20,000 Diplomax
Microprocessor Control of Pump
Vac Flow Comments range range mm cc/min Hg
0–500 0–44
Flared ABS Tip New Software: Burst/ Pulse Mode Pulse and Burst Mode
The phaco machine
Allergan
Prestige
47.5 Peristaltic
Allergan
Sovereign
38
Bausch Millennium 28 and Lomb
Mentor
SIStem
40
Staar
The Wave
42
Peristaltic
117
Microprocessor Control of Pump Microprocessor Control of Pump Shield-Fluid Coupled Pressure Sensor
0–500 0–40 0–500 0–40
0–550 0–60 Venturi or Venturi Hybrid: Concentrix Programmable to Emulate venturi or Peristaltic Peristaltic Microprocessor 0–500 0–50 Control of Pump Variable Rise Time (VRT) Peristaltic Fluid Coupled 0–500 0–50 Aspiration System
Pulse and Burst Mode Prosync-onboard Computer Control. Power Matrix and Digital Control allows power down to 5% Dual Linear Foot Pedal Modular Upgrades Automatic Surge Suppression
Surge Suppression System CDRom Printout of Events
Tuning is vital for the reason that the phaco tip is required to operate in different media. The resistance of the aqueous is less than the resistance of the cortex, which in turn is less than the resistance of the nucleus. As the resistance to the phaco tip varies, to maintain maximum efficiency, small alterations in frequency and/or stroke length, are created by the tuning circuitry in the machine CPU. The surgeon will be conscious of good tuning circuitry by a subjective sense of smoothness and power. Stroke length is defined as the length of the needle movement. This length is generally 2 to 6 mils (thousandths of an inch). Most machines operate in the 2 to 4 mil range. Longer stroke lengths are prone to generate excess heat. The longer the stroke length the greater will be the physical impact on the nucleus. In addition, the greater the generation of cavitation forces. Stroke length is determined by foot pedal excursion in position three during linear control of phaco. Energy at the Phaco Tip The actual tangible forces that emulsify the nucleus are a blend of the “jackhammer” effect and cavitation. The “jackhammer” effect is the physical striking of the needle against the nucleus. The cavitation effect is more convoluted. The phaco needle, moving through the liquid medium of the aqueous at ultrasonic speeds, creates intense zones of high and low pressure. Low pressure, created with backward movement of the tip, literally pulls dissolved gases out of solution. The gas bubble forms around dissolved particulate matter in the aqueous. This gives rise to microbubbles. Forward tip movement then creates an equally intense zone of high pressure. This produces compression of the microbubbles until they implode. At the moment of implosion, the bubbles create a temperature of 13,000 degrees F, and a shock wave of 75,000 PSI. 75 percent of the microbubbles thus
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created, implode, amassing to create a powerful shock wave, radiating from the phaco tip in the direction of the bevel. 25 percent of the bubbles, however, are too large to implode. These microbubbles are swept up in the shock wave and radiate with it. The shock wave and microbubbles diverge with annular spread (Fig. 8.1).
FIGURE 8.1 Microbubbles generated at the phaco tip The cavitation energy thus created can be directed in any desired direction as the angle of the bevel of the phaco needle governs the direction of the generation of the shock wave and microbubbles. A method of visualization of these forces, called enhanced cavitation, has been developed. Using this process it can be seen that with a 45° tip, the cavitation wave is generated at 45° from the tip and 30° tip generates cavitation at a 30° angle from the comes to a focus 1 mm from it (Fig. 8.1). Similarly a bevel, (Fig. 8.2) and a 15° tip 15° from the bevel. A 0° tip creates the cavitation wave directly in front of the tip and the focal point is ½ mm from the tip (Fig. 8.3). The Kelman tip has a broad band of powerful cavitation that radiates from the area of the angle in the shaft. A weak area of cavitation is developed from the bevel but is inconsequential (Fig. 8.4). From analysis of enhanced cavitation, it can be concluded that emulsification is most efficient when both the jackhammer effect and cavitation energy are coupled. To accomplish this, the bevel of the
FIGURE 8.2 30° Tip. Enhanced cavitation shows ultrasonic wave focused 1 mm from the tip, spreading at an angle of 45°
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FIGURE 8.3 30° Tip. Enhanced cavitation shows ultrasonic wave focused 1/2 mm in front of the tip spreading directly in front of it
FIGURE 8.4 Kelman tip. Enhanced cavitation shows broad band of enhanced cavitation spreading inferiorly from the angled of the tip. A weak band of cavitation spreads from the tip needle should be turned toward the nucleus, or nuclear fragment. This simple maneuver will cause the broad bevel of the needle to strike the nucleus. This will enhance the physical force of the needle striking the nucleus. In addition, the cavitation force is then concentrated into the nucleus rather than away from it (Fig. 8.5). This causes the energy to emulsify the nucleus. When the bevel is turned away from the nucleus the cavitational energy is directed up and away from the nucleus toward the iris and endothelium (Fig. 8.6). The energy thus misdirected will damage the iris and the blood-aqueous barrier leading to prolonged postoperative inflammatory change in the anterior segment. Addi-
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FIGURE 8.5 Turning the bevel of the phaco tip toward the nucleus focuses cavitation and jackhammer energy into the nucleus
FIGURE 8.6 The bevel is turned away from the nucleus. Cavitation energy is wasted and may damage iris and endothelium tionally the powerful shock wave and microbubbles will severely damage endothelial cells leading to endothelial cell loss. Finally, in this configuration, the vacuum force (discussed below) can be maximally made use of as occlusion is encouraged. A 0° tip, by design, directs both the jackhammer force and cavitational energy directly ahead and into the nucleus. The occlusive properties are also enhanced by a cross-sectional area of occlusion which is smaller than a 30° or 45° tip. Therefore the 0° tip is an excellent choice for controlled low power phacoemulsification (Fig. 8.7). Modification of Phaco Power Intensity Application of the minimal amount of phaco power intensity necessary for emulsification of the nucleus is desirable. Unnecessary power intensity is a cause
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FIGURE 8.7 The 0° tip, by its design, focuses both jackhammer and cavitation forces directly ahead, and into the nucleus of heat with subsequent wound damage, endothelial cell damage, and iris damage with alteration of the blood-aqueous barrier. Phaco power intensity can be modified by: (i) alteration in stroke length, (ii) alteration of duration, and (iii) alteration of emission. Alteration of Stroke Length Stroke length is determined by foot pedal regulation. When the machine is set for linear phaco, depression of the foot pedal in position 3, will increase stroke length and consequently power. New foot pedals, such as those found in the Allergan Sovereign and the Alcon Legacy, permit surgeon adjustment of the throw length of the pedal in position 3. This can refine power application. The B&L Millennium dual linear foot pedal permits the separation of the fluidic aspects of the foot pedal from the power elements. Alteration of Duration The duration of application of phaco power has a dramatic effect on overall power delivered. Usage of pulse or burst mode phaco will considerably decrease overall power delivery. New machines, for example, allow for a power pulse of 50 milliseconds duration alternating with a period of aspiration only (Fig. 8.8). Burst mode (parameter is machine dependent) is characterized by 150 milliseconds of power combined with variable periods of aspiration only (Fig. 8.9). Phaco techniques such as choo-choo-chop and phaco chop utilize minimal intervals of power in pulse mode to reduce total power delivery to the anterior chamber. In addition, the use of pulse mode to remove the epinucleus and cortex provides for an added margin of safety. When the epinucleus is emulsified, the posterior capsule is exposed to the phaco tip and may move forward toward it due to surge. Activation of pulse phaco will create a deeper anterior chamber to work within. This occurs because each period of phaco energy is followed by an interval of no energy. During the interval of absence of energy, the epinucleus is drawn toward the phaco tip, producing occlusion, interrupting outflow. This allows irrigation bottle inflow to deepen the anterior chamber immediately prior to onset of another pulse of
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phaco energy. The surgeon will recognize the outcome of this approach as operating in a deeper, more stable anterior chamber. Alteration of Emission The emission of phaco energy is modified by tip selection. Phaco tips can be modified to accentuate: (i) power, (ii) flow, or (iii) a combination of both. • Power intensity is modified by altering bevel tip angle. Noted previously, the bevel of the phaco tip will focus power in the direction of the bevel. The Kelman tip will produce broad powerful cavitation directed away from the angle in the shaft. This tip is excellent for the hardest of nuclei. New flare and cobra tips direct cavitation into the opening of the bevel of the tip. Thus random emission of phaco energy is minimized. Designer tips such as the “flathead” designed by Dr. Barry Seibel and power wedges designed by Douglas Mastel modify the direction and focus delivery of phaco energy intensity. • Power intensity and flow are modified by utilizing a 0° tip. This tip will focus power directly ahead of the tip and enhance occlusion due to the smaller surface area of its orifice. Small diameter tips, such as 21ga. tips, change fluid flow rates. Although they do not actually change power intensity, they appear to have this effect, as the nucleus must be emulsified into smaller pieces for removal through the smaller diameter tip.
FIGURE 8.8 Graphic representation of pulse mode in the Allergan Sovereign Machine
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FIGURE 8.9 Graphic representation of burst mode in the Allergan Sovereign Machine (Photo Courtesy of Allergan)
FIGURE 8.10 Flare tip. Widened tip focuses power close to the tip. Narrow neck acts as a flow restriction decreasing postocclusion surge (Photo Courtesy of Microsurgical Technology)
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FIGURE 8.11 A 0.175 mm hole drilled in the shaft of the ABS tip provides an alternate path for fluid to flow into the needle when there is an occlusion at the phaco tip (Photo Courtesy of Alcon) The Alcon ABS (aspiration bypass system) tip modification is now available with a 0° tip, a Kelman tip, or a flare tip. The flare is a modification of power intensity due to its ability to focus power near the needle opening, and a flow modification as the narrowed area proximal to the tip acts to decrease flow and thus dampen surge (Fig. 8.10). The ABS tip is a flow modification. In the ABS system a 0.175 mm hole in the needle shaft permits a variable flow of fluid into the needle during occlusion. This flow adjustment serves to prevent total occlusion and consequently minimize surge (Fig. 8.11). • Finally flow can be modified by utilizing one of the microseal tips. These tips have a flexible outer sleeve to seal the phaco incision. They also have a rigid inner sleeve or a ribbed shaft configuration to protect cooling irrigant inflow. Thus a tight seal allows low flow phaco without danger of wound burns. Phaco power intensity is the energy that emulsifies the lens nucleus. The phaco tip must operate in a cool environment and with adequate space to isolate its actions from delicate intraocular structures. This portion of the action of the machine is dependent upon its fluidics. Fluidics The fluidics of all machines are fundamentally a balance of fluid inflow and fluid outflow. Inflow is determined by bottle height above the eye of the patient. It is important to recognize that with recent acceptance of temporal surgical approaches, the eye of the patient may be physically higher than in the past. This then requires that the irrigation bottle be adequately elevated. A shallow, unstable anterior chamber will otherwise result.
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Outflow is determined by the sleeve-incision relationship, as well as the aspiration rate and vacuum level commanded. The incision length selected should create a snug fit with the phaco tip selected. This will result in minimal uncontrolled wound outflow with resultant increased anterior chamber stability. Aspiration rate, or flow, is defined as the flow of fluid in cc/min through the tubing. With a peristaltic pump it is determined by the speed of the pump. Flow determines how well particulate mater is attracted to the phaco tip. Aspiration level or vacuum is a level and measured in mm Hg. It is defined as the magnitude of negative pressure created in the tubing, and ultimately, the anterior chamber. Vacuum is the determinant of how well, once occluded on the phaco tip, particulate material will be held to the tip. Vacuum Sources There are three categories of vacuum sources or pumps. These are flow pumps, vacuum pumps, and hybrid pumps.
FIGURE 8.12 The peristaltic pump. Rotating cams compress tubing. The speed of the rotation is determined by the surgeon and governs the flow rate in cc/min • The primary example of the flow pump type is the peristaltic pump. These pumps allow for independent control of both aspiration rate and aspiration level (Fig. 8.12). • The primary example of the vacuum pump is the venturi pump. This pump type allows direct control of only vacuum level. Flow is dependent upon vacuum level setting. Additional examples are the rotary vane and diaphragmatic pumps. • The primary example of the hybrid pump is the Allergan Sovereign peristaltic pump (Fig. 8.13) or the B & L Concentrix pump (Fig. 8.14). These pumps are interesting as they are able to act like either a vacuum or flow pump dependent upon programming.
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They are the most recent supplement to pump types. They are generally controlled by digital inputs creating incredible flexibility and responsiveness. The challenge to the surgeon is to balance the effect of phaco intensity, which tends to push nuclear fragments off the phaco tip, with the effect of flow, which attracts fragments toward the phaco tip, and vacuum, which holds the fragments on the phaco tip. Generally low flow slows down intraocular events, and high vacuum speeds them up. Low or zero vacuum is helpful during sculpting of hard
FIGURE 8.13 Hybrid pump. The Allergan Digital Pump. A peristaltic pump with digital controls allows forward, backward, or to and fro movement to precisely control flow. This pump is capable of performing like a venturi or peristaltic pump (Photo Courtesy of Allergan)
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FIGURE 8.14 Hybrid pump. The B&L Concentrix pump. Inside two cam-shaped disks rotate to generate a vacuum which is regulated to emulate either a peristaltic or venturi pump
FIGURE 8.15 Occlusion. The nucleus has occluded the phaco tip. There is no flow. The vacuum increases to preset. Tubing collapses (Original art by Tony Pazos)
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or a large nucleus, where the high power intensity of the tip may be applied near the iris or anterior capsule. Zero vacuum will prevent inadvertent aspiration of the iris or capsule preventing significant morbidity. Surge A principal limiting factor in the selection of high levels of vacuum or flow is the development of surge. When the phaco tip is occluded, flow is interrupted and vacuum builds to its preset level. Additionally, the aspiration tubing may collapse in the presence of high vacuum levels (Fig. 8.15). Emulsification of the occluding fragment then clears the occlusion. Flow instantaneously begins reaching the preset level immediately. In addition, if the aspiration line tubing is not reinforced to prevent collapse (tubing compliance) the tubing, constricted during occlusion, then expands on occlusion break. The expansion is an additional source of vacuum production. These factors cause a rush of fluid from the anterior segment into the phaco tip. The fluid in the AC may not be replaced rapidly enough by infusion to prevent shallowing of the anterior chamber. Therefore there is subsequent rapid anterior movement of the posterior capsule and collapse of the cornea (Fig. 8.15). This abrupt forceful “snapping” of the posterior capsule as well as the stretching of
FIGURE 8.16 Postocclusion surge. The fragment has been emulsified. Vacuum drops to 0 and flow instantaneously will increase to preset. Fluid will rush into the phaco tip more rapidly than it can be replenished by irrigation inflow. The posterior capsule snaps up and the cornea will collapse. A small tear in the posterior capsule begins (Original art by Tony Pazos)
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the bag around nuclear fragments may be a cause of capsular tears. In addition the posterior capsule can be literally sucked into the phaco tip, tearing it (Fig. 8.16). The magnitude of the surge is contingent on the presurge settings of flow and vacuum. If the surge is considered an event, then the entire sequence can be divided into phases. Thus there is a preocclusive, occlusive, and postocclusive phase. Surge can therefore be modified in each phase. Preocclusion Modification To decrease surge in preocclusion, the vacuum preset, or flow maximum preset should be decreased. Decreased flow will result in slower generation of vacuum. Decreased vacuum will result in less absolute vacuum level during occlusion. The net effect of both is the decrease of postocclusion surge. Attention to wound size and construction, as well as selection of a phaco tip with a soft sleeve of adequate size to adequately seal and prevent excess fluid outflow, will augment anterior chamber stability. Finally, elevating the infusion bottle will increase fluid inflow. Occlusion Modification The Alcon Legacy employs an Aspiration Bypass System (ABS). This consists of “high vacuum tubing” and the “aspiration bypass tip”. The tubing is reinforced to prevent collapse during periods of high vacuum. The tips have 0.175 mm holes drilled in the shaft of the needle. During occlusion the hole provides for a continuous alternate fluid flow. The higher the vacuum the greater will be the flow through the bypass hole. Thus, complete occlusion never occurs. This will cause dampening of the surge on occlusion break. The dual linear foot pedal of the B&L Millennium is another device to control surge in the occlusive phase. It can be programmed to separate both the flow and vacuum, from power. In this way flow or vacuum can be lowered before beginning the emulsification of an occluding fragment. The emulsification therefore occurs in the presence of a lower vacuum or flow. This will dramatically decrease surge. Postocclusion Presently there are four machines that will decrease surge in the postocclusive phase. This type of surge dampening requires instantaneous sensing of resumption of flow after occlusion. Therefore all machines making use of this form of surge control employ sophisticated microprocessors. The microprocessors sense resumption of flow and immediately slow the pump lowering vacuum, the engine for surge. These machines are • The Allergan Diplomax. • The Allergan Sovereign Microprocessors sample vacuum and flow parameters 50 times a second creating a “virtual” model of the events in the anterior chamber. At the moment of surge, the machine computer senses the increase in flow and
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instantaneously slows or even reverses the pump. This allows inflow to establish a new equilibrium and will cut short surge production. • The Staar Wave This machine has patented microprocessors that act in a similar fashion to the Allergan Sovereign to dampen surge. • The Mentor SIStem (Paradigm) This machine has microprocessor controlled variable rise time. Adjustments in rise time slow the generation of vacuum and decrease surge.
Phaco Technique and Machine Technology The patient will have the best visual result when total phaco energy delivered to the anterior segment is minimized. Additionally, phaco energy should be focused into the nucleus. This will prevent damage to iris blood vessels and endothelium. Finally, proficient emulsification will lead to shorter overall surgical time. Therefore a lesser amount of irrigation fluid will pass through the anterior segment. The general principles of power management are to focus phaco energy into the nucleus, vary fluid parameters for efficient sculpting and fragment removal, and minimize surge. Divide and Conquer Phaco Sculpting To focus cavitation energy into the nucleus a zero degree tip or a 15°, or 30° tip turned bevel down should be utilized. Zero or low vacuum (dependent upon the manufacturers recommendation) is mandatory for bevel down phaco. This will prevent occlusion. Occlusion, at best, will cause excessive movement of the nucleus during sculpting. At worst, occlusion occurring near the equator is the cause of tears in the equatorial bag early in the phaco procedure, and occlusion at the bottom of a groove will cause phaco through the posterior capsule. Once the groove is judged to be adequately deep, the bevel of the tip should be rotated to the bevel up position to improve visibility and prevent the possibility of phaco through the posterior nucleus and posterior capsule. Quadrant and Fragment Removal The tip selected, as noted above, is retained. Vacuum and flow are increased to reasonable limits subject to the machine being used. The limiting factor to these levels is the development of surge. The bevel of the tip is turned toward the quadrant or fragment. Low pulsed or burst power is applied at a level high enough to emulsify the fragment without driving it from the phaco tip. Chatter is defined as a fragment bouncing from the phaco tip due to aggressive application of phaco energy.
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Epinucleus and Cortex Removal For removal of epinucleus and cortex the vacuum is decreased while flow is maintained. This will allow for grasping of the epinucleus just deep to the anterior capsule. The low vacuum will help the tip hold the epinucleus on the phaco tip, preventing the fracturing of chunks and poor followability created by undesirable high vacuum. The epinucleus is emulsified for three quadrants and the attached cortex is aspirated around the epinucleus as documented by Dr Howard Fine. The epinucleus and attached cortex is then mobilized so that it scrolls around the equator and can be pulled to the level of the iris. There, low power pulsed phaco is employed for emulsification. If cortical cleaving hydrodissection has been performed, the remainder of the cortex will be removed concurrently. Stop and Chop Phaco Sculpting Groove creation is performed as noted above under divide and conquer sculpting techniques. Heminucleus Creation When the initial trough is considered adequately deep (three phaco tips or 3.0 mm) the initial crack is created using the phaco tip and chopper. If the nucleus will not crack the initial groove is not deep enough and must therefore, be deepened. The nucleus is then rotated 90°. Quadrant and Fragment Removal Once the nucleus is cracked, creating into two halves, vacuum and flow are increased to improve the holding ability of the phaco tip. The tip is then burrowed into the mass of the distal heminucleus using pulsed linear phaco. The sleeve should be 1 mm from the base of the bevel of the phaco tip to create adequate exposed needle length for sufficient holding power. Excessive phaco energy application is to be avoided, as this will cause nucleus immediately adjacent to the tip to be emulsified. The space thus created in the vicinity of the tip is responsible for interfering with the seal around the tip and therefore the capability of vacuum to hold the nucleus. The nucleus will then pop off the phaco tip making chopping more difficult. With a good seal the heminucleus can be drawn toward the incision and the chopper can be inserted at the endonucleus-epinucleus junction. After the first chop, the pie-shaped piece of nucleus thus created is elevated to the plane of the pupil and removed with low power pulsed phaco as discussed in the divide and conquer section. Epinucleus and cortex removal is also performed as noted above.
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Phaco Chop Phaco chop requires no sculpting. Therefore the procedure is initiated with high vacuum and flow and linear pulsed phaco power. For a 0° tip, when emulsifying a hard nucleus, a small trough may be required to create adequate room for the phaco tip to burrow deep into the nucleus. For a 15° or a 30° tip, the tip should be rotated bevel down to engage the nucleus. A few bursts or pulses of phaco energy are necessary to allow the phaco tip to be buried within the nucleus. It then can be drawn toward the incision to allow the chopper access to the epiendo nuclear junction. If the nucleus comes off the phaco tip, so that it cannot be pulled toward the incision, excessive power has produced a space around the tip impeding vacuum holding power as noted above. The first chop is then produced. The first quadrant is then emulsified with low power pulsed phaco. If a beveled tip is used it is turned toward the nuclear material to enhance the occlusive properties of the tip. Then rotation of the nucleus will allow for creation of the second chop. The nuclear fragments are then emulsified in turn. Irrigation and Aspiration Similar to phaco, anterior chamber stability during I and A is due to the balance of inflow and outflow. Fluid outflow can be minimized by employing a soft sleeve around the I and A tip. Combined with a small incision (2.8 to 3 mm), a deep and stable anterior chamber will result. Generally a 0.3 mm I and A tip is used. With this orifice a vacuum of 500 mm Hg and flow of 20 cc/min is excellent to tease cortex from the fornices. Linear vacuum allows the cortex to be grasped under the anterior capsule and drawn into the center of the pupil at the iris plane. There, in the safety of a deep anterior chamber, vacuum can be increased and the cortex aspirated. In an effort to provide an additional margin of safety, the I and A can be performed after insertion of the IOL. The IOL acts as a barrier between I and A tip and the posterior capsule. Thus, the I and A can be performed with less chance of posterior capsular capture and tear. Vitrectomy Most phaco machines are equipped with a vitreous cutter which is activated by compressed air or by electric motor. As noted previously, preservation of a deep anterior chamber is dependent upon a balance of inflow and outflow. For vitrectomy, a 23 gauge cannula, or chamber maintainer, inserted through a paracentesis, provides inflow. Bottle height should be adequate to prevent chamber collapse. The vitrector should be inserted through another paracentesis. If equipped with a Charles sleeve, this should be removed and discarded. Utilizing a flow of 20 cc/min, vacuum of 250 mm Hg, and a cutting rate of 250 to 350 cuts/min the vitrector should be placed through the tear in the posterior capsule, orifice facing upward, pulling vitreous out of the anterior chamber. The vitreous should be removed to the level of the posterior capsule (Fig. 8.17).
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Conclusion It has been said that the phaco procedure is blend of technology and technique. Awareness of the
FIGURE 8.17 The vitrector, with the Charles sleeve removed is placed through a paracentesis into the vitreous. Irrigation is provided by a 23 gauge cannula placed through another paracentesis (Original art by Tony Pazos) principles, which influences phaco machine settings, is requisite for the performance of a proficient and safe operation. Additionally, often during the procedure, there is a demand for changes from the initial parameters. A thorough understanding of fundamental principles will enrich the capability of the surgeon for appropriate response to this requirement. Further Reading 1. Cimino WW, Bond LJ: Physics of ultrasonic surgery using tissue fragmentation Part II, Ultrasound in Medicine and Biology 22(1):101–17, 1996. 2. Doulah MS: Mechanism of disintegration of biological cells in ultrasonic cavitation in biotechnology and bioengineering, John Wiley & Sons Inc., 19:649–60. 3. Fishkind WJ: Pop Goes the Microbubbles ESCRS Film Festival Grand Prize Winner, 1998. 4. Krey HF: Ultrasonic turbulences at the phacoemulsification tip. J Cataract Refract Surg 15:343– 44, 1989. 5. Neuhann TF, Steinert RF: Instrumentation. Cataract Surgery, Technique Complications and Management. WB Saunders: Philadelphia 6:57–67, 1995.
9 The Fluidics and Physics of Phaco Barry S Seibel Introduction Phacoemulsification is comprised of two basic elements: (i) ultrasound energy is used to emulsify the nucleus, and (ii) a fluidic circuit is employed to remove the emulsate through a small incision while maintaining the anterior chamber (Fig. 9.1). This circuit is supplied by an elevated irrigating bottle which supplies both the fluid volume and pressure to maintain the chamber hydrodynamically and hydrostatically, respectively; anterior chamber pressure is directly proportional to the height of the bottle. The fluid circuit is regulated by a pump which not only clears the chamber of the emulsate, but also
FIGURE 9.1 provides significant clinical utility. When the phaco tip is unoccluded, the pump produces currents in the anterior chamber, measured in cc per minute, which attract nuclear fragments. When a fragment completely occludes the tip, the pump provides holding power, measured in mm Hg vacuum, which grips the fragment. In order to fully exploit the potential of a phaco machine the surgeon must understand the logic behind setting the parameters of ultrasound power, vacuum, and flow.
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Categorization of Pumps A discussion of flow and vacuum in phaco surgery must begin with a categorization of the various pumps which are utilized. There are two basic types of pumps in phaco: (i) the flow pump, and (ii) the vacuum pump. Flow Pump The flow pump also known as a positive displacement pump, physically regulates the fluid in the aspiration line via direct contact between the fluid and the pump mechanism. Although the scroll pump is the newest example of a flow pump, the peristaltic pump is the most commonly employed in current phaco machines and serves as a good schematic example of the flow pump’s principles (Fig. 9.2). One important characteristic of a flow pump is its ability to independently control flow and vacuum. Flow rate, also known as aspiration flow rate, is measured in cc per minute and is directly proportional to the rotational speed of the pump head, measured in revolutions per minute (rpm). Note that because the pump head physically interdigitates with the fluidic circuit via the aspiration line tubing, it regulates the flow rate independently of the amount of pressure in the line via the elevated irrigating bottle. Therefore, flow rate is independent of bottle height when using flow pumps. However, actual fluid flow rate is very dependent on the degree of phaco tip occlusion. Flow rate decreases with increasing tip occlusion (i.e. decreased effective aspiration port surface area)
FIGURE 9.2
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FIGURE 9.3 until flow ceases completely with complete tip occlusion. Note that in Figure 9.3 the irrigation bottle’s drip chamber mirrors the activity in the
FIGURE 9.4 anterior chamber. Aspiration flow control on the phaco machine is still important with complete tip occlusion in that it controls the rotational speed of the pump head, and even though no actual flow exists with complete occlusion, the surgeon can control the speed of vacuum build-up via pump speed control; the amount of time required to reach a given vacuum preset, assuming complete tip occlusion, is defined as rise time.
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Rise time is inversely proportional to the rotational speed of the pump head (Fig. 9.4). All graphs represent the same machine, but note that when the flow rate is cut in half (from 40 to 20 cc per minute), the rise time is doubled (from 1 second to two seconds). Rise time is doubled again to four seconds when flow rate is halved again to 10 cc per minute. A longer rise time gives the surgeon more time to react in cases of inadvertent incarceration of iris, capsule, or other unwanted material, although a useful setting for training residents, even experienced surgeons appreciate the enhanced safety margin afforded by a longer rise time. Several points should be made about the preceding discussion on rise time. First, rise time was adjusted via manipulation of the machine’s flow rate control. However, as discussed previously, no actual flow exists with complete occlusion, which is necessary to efficiently build vacuum at the phaco tip. Adjusting the machine’s flow parameter, measured in cc per minute, actually directly affects the rotational speed of the pump head. Vacuum builds more quickly as the rollers more rapidly traverse the aspiration line tubing in the pump head, even though no additional fluid is removed from the anterior chamber through the occluded phaco tip. The second point regarding the rise time discussion concerns the fact that although no fluid flows from the eye with tip occlusion, a minute amount of fluid is pumped from the aspiration line tubing as vacuum is built up, thus, accounting for the relation of pump speed to rise time. Because fluid is noncompressible and nonexpansile, theoretically no change in aspiration line fluid volume would occur as the pump head exerted pressure on the fluid. However, two factors account for this not being true with peristaltic pumps: (i) the use of the aspiration line tubing as a conduit for transmitting the pump rollers’ force results in some inefficiency in the form of slippage both between the pump rollers and the tubing as well as in between the opposed internal surfaces of the aspiration line tubing, and (ii) the mechanism of action of a peristaltic pump requires enough aspiration line tubing compliance to allow for collapse by the pump rollers. This compliance must be overcome during rise time in the form of some tubing constriction as some fluid is removed from the line (not the eye) by the pump even with complete tip occlusion (Fig. 9.5). The most modern peristaltic pumps minimize the system’s compliance to the minimum level compatible with the functioning of the pump, thereby, attaining fairly rapid potential rise times. By placing the pump element directly into aspiration fluid path, a scroll pump further reduces the need for aspiration line compliance to the minimum amount required for ergonomic handpiece control. This type of pump can therefore achieve the tightest potential control of rise time with the most rapid vacuum build-up attainable. The final point concerning rise time and flow pumps is the fact that a maximum attainable vacuum can be preset on the machine. In order to prevent vacuum build-up past this level, a variety of methods are employed. For example, the pump head can be stopped when the preset value is reached. Alternatively, vacuum can be regulated with a moving pump head by venting air or fluid into the aspiration line if the preset value is exceeded. Venting is also employed if the surgeon wishes to release material which is held to the phaco tip with vacuum. Air venting has the disadvantage of increasing the fluidic circuit’s compliance relative to fluid venting. Higher compliance increases rise time and decreases the machine’s responsiveness to foot-pedal vacuum control. Figure 9.6 illustrates this principle, whereby an air-bubble which was vented into the circuit to
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FIGURE 9.6
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decrease vacuum must be first stretched out by the pump before vacuum can begin to build in the aspiration line again. By employing either air or fluid venting to regulate vacuum build-up, a flow pump therefore not only directly controls flow but also allows indirect control of vacuum. Vacuum Pump In contrast, a vacuum pump directly controls vacuum although it can indirectly control flow. Vacuum pumps represent the second main category of phaco pump, with examples being the rotary vane pump, the diaphragm pump, and the Venturi pump. Vacuum pumps have in common a rigid drainage cassette attached to the aspiration line tubing. The various pumps are linked to the cassette and produce vacuum in it which in turn proportionately produces flow when the aspiration port is unoccluded (Fig. 9.7). When the tip is occluded, flow ceases and vacuum is transferred
FIGURE 9.7 from the cassette down the aspiration line to the occluded tip (Fig. 9.8). Because no rollers are required to collapse the tubing as with peristaltic pumps, vacuum pumps can employ more rigid tubing with less compliance. This lower compliance coupled with the short times needed for vacuum transfer from the cassette to the phaco (or IA) tip result in low rise times with vacuum pumps. Low rise times can be a potential liability when using high vacuum techniques, if unwanted material is inadvertently incarcerated in the aspiration port, the surgeon has
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little time to react before potentially permanent damage occurs. Recall that when using a flow pump with a high vacuum preset, low flow rate can be set to produce longer rise times which give the surgeon more time to react to unwanted occlusions. Most vacuum pumps donot allow attenuation of rapid rise times, although the Storz Millennium and Premiere
FIGURE 9.8 machines are exceptions. These pumps allow the surgeon to set at time delay for full commanded vacuum build-up which starts when the surgeon enters pedal position 2. However, once this delay has elapsed, any subsequent engagement of material will be exposed to a typically rapid vacuum pump rise time. An even better, if not elegant, solution to this issue is the dual linear foot control on the millennium (Fig. 9.9), this separates simultaneous linear control of vacuum and ultrasound in two planes of pedal movement (pitch and yaw). With linear control of vacuum in phaco mode, the surgeon can approach material with safer lower vacuum levels and increase it only after desired material is positively engaged. Direct linear control of vacuum has another advantage with vacuum pumps in that it allows subsequently indirect linear control of aspiration flow rate when the tip’s aspiration port is unocclu-
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FIGURE 9.9 ded (Fig. 9.7). However, because flow is thus indirectly controlled by these pumps, it is more sensitive to resistive variances in the fluidic circuit. For example (Fig. 9.10), a vacuum pump will
FIGURE 9.10 produce a certain flow rate at a particular vacuum when using a phaco tip; this same flow rate could also be produced on a flow pump. However, changing to an IA tip (with its smaller surface are aspiration port and subsequently higher fluidic resistance) will decrease actual flow in both systems, but to a greater degree in the vacuum pump. This indirect control of flow by a vacuum pump has another important clinical corollary with regard to bottle height. Unlike a flow pump, a vacuum pump’s flow rate is affected by bottle height as a result of a higher pressure head from a higher bottle height pushing
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fluid through the open circuit more rapidly (compare the fluidic schematics in Figures 9.2 and 9.7, noting again the interdigitation of the flow pump in its fluidic circuit). Application of Ultrasound Power Besides setting fluidic parameters, the surgeon must also decide on the application of ultrasound power, which is produced most often by a piezoelectric crystal oscillating between approximately 20,000 and 60,000 times a second for most machines. This frequency is fixed on a given machine. Ultrasound power is varied by changing the amplification voltage of the handpiece. Increased voltage translates to increased stroke length at the phaco needle tip, up to a maximum of about five microns on most machines (Fig. 9.11). Usually, a maximum ultrasound limit is preset on the machine’s front panel, and the surgeon then titrates with linear pedal control the percentage of this preset maxi-
FIGURE 9.11 mum which is appropriate to a given intraoperative instant. The actual mechanism of action of ultrasonic phacoemulsification is somewhat controversial. One school of thought centers around the acoustic breakdown of lenticular material as a result of sonic wave propagation through the fluid medium. Another theory concerns the microcavitation bubbles produced at the distal phaco tip, the implosion of these bubbles produces brief instances of intense heat and pressure which is thought to emulsify adjacent lens material. Yet another potential mechanism of action is via the tips axial oscillations through its stroke length, this resultant jackhammer affect is thought to mechanically break down lens material. This last mechanism also explains the clinical phenomenon of repulsion of free floating lens material with high ultrasound power levels, these levels need appropriate fluidic titration of the attractive parameters of flow and vacuum to counteract this repulsion. Ultrasonic phaco needles are available in a variety of configurations. One basic design parameter is the distal bevel angle, which is most commonly 0°, 15°, 30°, or 45° as shown in Figure 9.12. The sharper 45° angle is thought to carve dense
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FIGURE 9.12
FIGURE 9.13 nuclei more efficiently to the extent that the jack-hammer mechanism of action is valid, whereas the 0° tip would be more efficient to the extent that the microcavitation theory is valid (the 0° tip has more frontal surface area perpendicular to the axis of oscillation, thereby, producing more cavitation bubbles). In practice, it is difficult to quantitatively compare these efficiencies on a standard density nucleus. Another traditional teaching regarding tip angulation is that a 0° tip occludes more readily than 45° tip, this
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observation is correct only in that the smaller surface area and perimeter of the 0° tip does seal more readily than does the tip with a larger bevel. However, this axiom is less relevant intraoperatively. A tip occludes readily when the surface to be occluded is parallel to the needle bevel, the surface can and should be manipulated as necessary to achieve this configuration (Fig. 9.13, which illustrates the attempted gripping of a heminucleus during a stop and chop maneuver).
FIGURE 9.14 When titrating ultrasound power, the surgeon must be aware of interrelated clinical variables affecting the resistance to emulsification, especially sculpting. This resistance is directly proportional to both the linear speed of sculpting as well as the amount of the tip engaged. In Figure 9.14, it can be noted that for the increased resistive load caused by the increased tip engagement, the surgeon must compensate by either increasing phaco power or decreasing in linear speed of sculpting. Either solution is satisfactory, as long as the interrelationship among the above variables is respected, so as to facilitate the needle carving through the nucleus instead of pushing it and stressing the zonules or capsule. Adjustment of Machine Parameters In order to appropriately adjust the machine parameters for various stages of surgery, it is necessary to analyze the function of those parameters for a given stage. For example, sculpting requires titration of ultrasound power as described in the previous paragraph. Furthermore, it requires enough flow to clear the anterior chamber of the emulsate produced by ultrasound as well as sufficient flow to cool the phaco tip, a modest flow of 18 cc/min is usually adequate for these functions. There is little need for vacuum during sculpting, as there are not yet any fragments which need to be occluded and gripped. Furthermore, vacuum is not needed to counteract the repulsive action of ultrasound since the nucleus is held stationary by the capsule, zonules, and its intact structure at this point.
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Therefore, a low vacuum is adequate for sculpting. Although 0 mm Hg is advocated by some surgeons, a slightly higher level of 15 to 30 mmHg still provides significant safety (in case of contraincisional peripheral epinuclear or capsule incarceration) while decreasing the likelihood of a clogged aspiration line. Once the nucleus is debulked or grooved, it then needs manipulation such as rotation or cracking. These maneuvers should be performed in pedal position 1 so that the chamber will be pressurized without any pump action which might inadvertently aspirate unwanted material. Once the nucleus is debulked or cracked into fragments, machine parameters need to adapt to the needs to emulsifying these fragments. Ultrasound power requirements are lower at this stage relative to sculpting because of the increased efficiency of phacoaspiration with complete or almost complete tip occlusion. Even with only moderate ultrasound levels, though, flow rate and vacuum usually must be increased from their sculpting levels in order to overcome the repulsive action of ultrasound at the axially vibrating needle tip. Although 26 cc/min flow rate and 120 mmHg vacuum are reasonable baseline values at this stage, these parameters should ideally be linearly titrated intraoperatively to a given ultrasound level and nuclear density. This level of control has only recently been available to the surgeon with the advent of the dual linear pedal as previously described. Chopping maneuvers often require further manipulation of parameters. The actual chop may require only moderate vacuum because the nucleus is mechanically fixated between the phaco tip and the chopper. However, higher vacuum levels of 200 to 250 mmHg can be used advantageously to grip
FIGURE 9.15 and manipulate the nucleus. For example, the gripped nucleus can be displaced so that the chopper is more centrally located when engaging the nuclear periphery. This maneuver is especially effective if the nucleus was previously grooved and hemisected as has been described by Drs. Paul Koch and Ron Stasiuk (Fig. 9.15). If a flow pump is used, 26 cc/min is a useful compromise between a reasonably rapid rise time and a reasonable safety margin against surge. If a vacuum pump is used at 200 to 250 mmHg, the surge potential is especially high. When the chop is completed and the occlusion breaks, the subsequent induced flow with a standard needle would be over 60 cc/min. A Microflow or similar needle with a reduced inner diameter (therefore increased fluidic resistance)
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reduces this flow by about 40 percent to a safer level. The safest technique, though, would be to use the high vacuum level during the actual manipulation and chop when gripping the nucleus and then to dynamically decrease the vacuum with pedal control just as the chop is completed to minimize the surge potential. Surge, as has been discussed, occurs when an occluded fragment is held by high vacuum and is then abruptly aspirated (i.e. with a burst of ultrasound), fluid tends to rush into the tip to equilibrate the built-up vacuum in the aspiration line with potentially consequent shallowing or collapse of the anterior chamber (Fig. 9.16). In addition to the preventive measures mentioned in
FIGURE 9.16 the previous paragraph, phaco machines employ a variety of methods to combat surge. Fluidic circuits are engineered with minimal compliance which will still allow adequate ergonomic manipulation of the tubing as well as functioning of the pump mechanism, the latter being primarily important for peristaltic pumps. Small bore aspiration line tubing, utilized by Allergan and Alcon, provide increased fluidic resistance which obtunds surges in a manner similar to that of the Microflow needle previously discussed. The Surgical Designs machine incorporates a second, higher irrigating bottle whose fluidic circuit is engaged upon detection of a surge. While all of these designs are helpful, it is ultimately up to the surgeon to set parameters which optimize a given machine for a given patient with regard to surge prevention. The parameter of bottle height has a constant function during all phases of surgery—to keep the chamber safely formed without overpressurization which might stress zonules, misdirect aqueous into the vitreous, or cause excessive incisional leakage. Approximately, 10 mm Hg hydrostatic pressure is produced intraocularly for every 15 cm bottle height above the eye. However, it is vital that the appropriate bottle height be set hydrodynamically with the pump operating (pedal position 2 or 3) and the tip unoccluded so that an adequate pressure head will be established to keep up with the induced aspiration outflow from the eye.
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This chapter has stressed the importance of appropriate machine parameter settings. It should also be stressed, of course, that surgical technique is not only just as important, but is moreover integrally related. For example, if a surgeon wishes to grip and pull a heminucleus in preparation for chopping yet finds that the tip instead pulls away from the lens material, the tendency would be to increase the vacuum parameter to give a stronger grip. However, it is critical to remember that the full preset vacuum can be produced at the phaco tip only with complete tip occlusion. Therefore, if an adequate vacuum seal is not obtained, the preset value will not be reached. Increasing the vacuum preset will not affect the clinical performance in the absence of a good vacuum seal, which is obtained by embedding the phaco tip at least 1 to 1.5 mm with light ultrasound energy so as to avoid excessive cavitation (Fig. 9.17). The tip is also embedded in the central densest
FIGURE 9.17
FIGURE 9.18
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nucleus as opposed to more peripheral, softer material which might irregularly aspirate, again causing a loss of the vacuum seal (Fig. 9.18). This subtle attention to technique pays off with the machine being used to its most effective potential. Summary Modern phaco machines offer unprecedented levels of control and safety. In order to fully exploit these values, a thorough understanding of the principles by which the machines operate is essential. In particular, the surgeon must appropriately adjust flow rate, vacuum, ultrasound power, and bottle height as necessary for a given patient and for a given stage in the operation. This vigilance and attention, coupled with meticulous technique designed to optimize the machine’s performance, will result in the safest, most efficient phacoemulsification surgery.
10 Air Pump to Prevent Surge Sunita Agarwal Amar Agarwal Athiya Agarwal Introduction One of the main bugbears of phacoemulsification is surge.1 The problem is that as the nuclear piece gets occluded in the phaco tip and we emulsify it, surge occurs. Many people have tried various methods to solve this problem. Some phaco machines like the Sovereign have been devised with the help of I Howard Fine, Barry Seibel and William Fishkind to solve this problem. Others have tried to use an anterior chamber maintainer to get more fluid into the eye. The problem with the anterior chamber maintainer is that another port has to be made. In other words, now we have three ports and if you are doing the case under topical or no anesthesia (as we do in our hospital) it becomes quite cumbersome. Another method to solve surge is to use more of phacoaspiration and chop the nuclear pieces with the left hand (non-dominant hand). The problem by this is the surgical time decreases and if the case is of a hard brown cataract, phacoaspiration will not suffice. Surge Surge1 occurs when an occluded fragment is held by high vacuum and is then abruptly aspirated with a burst of ultrasound. What happens is that fluid from the anterior chamber rushes into the phaco tip and this leads to collapse of the anterior chamber. New Technique One of us (Sunita Agarwal), then thought of a method to solve surge using an air pump. We got this idea as when we were operating cases with Phakonit (a new technique in which cataract is removed through a sub 1.4 mm opening), we wanted more fluid entering the eye. Now we, routinely use the air pump to solve the problem of surge.
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Method • First of all (Fig. 10.1), we use two balanced salt solution (BSS) bottles and not one. These are put in the IV stand. • Instead of using an IV set for the fluid to move from the bottle to the phaco handpiece, we use a TUR set. This is a transurethral tubing set, which is used by urologists. The advantage of this is that, the bore of the tubing is quite large and so more fluid passes from the infusion bottle to the phaco handpiece. The TUR set has two tubes, which go into each infusion bottle, and then the TUR set becomes one, which then passes into the phaco handpiece. • Now we take an air pump. This air pump is the same air pump, which is used in fish tanks to
FIGURE 10.1 Diagrammatic representation of the air pump and infusion bottle. Note two infusion bottles connected to a TUR set. Also note the air pump connects to one of the infusion bottles
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FIGURE 10.2 Air pump connected to the infusion bottle. Note two infusion bottles. The black box on the left over the phaco machine is the air pump. On the right is the phaco handpiece lying in a tray give oxygen to the fishes. The air pump is plugged on to the electrical connection. • An IV set now connects the air pump to the infusion bottle. The tubing passes from the air pump and the end of the tubing is passed into one of the infusion bottles (Fig. 10.2). • What happens now is that when the air pump is switched on, it pumps air into the infusion bottle. This air goes to the top of the bottle and because of the pressure, it pumps the fluid down with greater force. With this, the TUR set also is in place and so the fluid now flows from the infusion bottle into the TUR set to reach the phaco handpiece. The amount of fluid now coming out of the handpiece is much more than what would normally come out and with more force. • One can use an air filter between the air pump and the infusion bottle so that the air which is being pumped into the bottle is sterile. • This extra amount of fluid coming out compensates for the surge which would occur.
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Continuous Infusion Before we enter the eye, we fill the eye with visco-elastic. Then once the tip of the phaco handpiece is inside the anterior chamber we shift to continuous irrigation. This is very helpful especially for surgeons who are starting phaco. This way, the surgeon, never comes to position zero and the anterior chamber never collapses. Even for excellent surgeons this helps a lot. Advantages • With the air pump, the posterior capsule is pushed back and there is a deep anterior chamber. • The phenomenon of surge is neutralized. This prevents the unnecessary posterior capsular rupture. • Striate keratitis postoperatively is reduced, as there is a deep anterior chamber. • One can operate hard cataracts also quite comfortably, as striate keratitis does not occur postoperatively. • The surgical time is shorter as we can go quite fast in removing the nuclear pieces, as surge does not occur. • One can easily operate cases with the Phakonit technique as quite a lot of fluid now passes into the eye. Thus, the cataract can be removed through a 0.9 mm opening. • It is quite comfortable to do cases under topical or no anesthesia.
Topical or No Anesthesia Cataract Surgery When one operates under topical or no anesthesia, the main problem is sometimes the pressure is high especially if the patient squeezes the eye. In such cases, the posterior capsule comes up anteriorly and one can produce a posterior capsular rupture. To solve this problem, surgeons tend to work more anteriorly, performing supracapsular phacoemulsification. The disadvantage of this is that striate keratitis tends to occur. With the air pump, this problem does not occur. When we use the air pump, the posterior capsule is quite back, as if we are operating a patient under a block. In other words, there is a lot of space between the posterior capsule and the cornea, preventing striate keratitis. Disadvantages • As we tend to use two bottles instead of one, the cost is a bit more expensive. • The TUR set is slightly more expensive than a normal IV set.
Summary
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The air pump is a new device, which helps to prevent surge. This helps to prevent posterior capsular rupture, helps deepen the anterior chamber and one can work comfortably even in hard cataracts. The air pump pumps air into the infusion bottle thus tending to push more of fluid into the eye and with greater force. Now, we routinely use the air pump in all our cases. Reference 1. Agarwal S, Agarwal A et al: Phacoemulsification, Laser Cataract Surgery and Foldable IOLs. New Delhi: Jaypee Brothers, 1998.
11 Microseal and Other Phaco Tips Hampton Roy Introduction The cutting part of the phacoemulsification instrument is the phaco tip. This chapter will discuss the various types of phaco tips that are currently in the market. There are several more in a developmental stage that are not discussed in this chapter. Some of the efficiency of the phaco tip is related to the type of handpiece. For example, the cobra tip is especially designed for the magnetorestrictive handpiece because this generally heats up faster than the piezoelectric handpiece. Another interesting feature of the tips has to do with the sleeve surrounding the tip. With the higher efficiency tips, there is more danger of getting a burn of the cornea. Thus, several tips are designed to reduce the burn. For example, the microflow has grooves in the outer shaft to allow the fluid to keep the shaft cooler. The microseal has an insulated sleeve that is thicker and cuts down on the possibility of heat transfer through the sleeve with a corneal wound burn. Characteristics of Phaco Tips The phacoemulsification tips are attached to a handpiece, and it is important that you understand the dynamic range. The dynamic range is the relationship between the balanced application of fluidics [vacuum, aspiration flow rate (AFR), and irrigation] and ultrasonic power. The relationship between fluidics and ultrasonics should be one of balance. The preset maximums of each of these parameters will vary depending on the dominant parameter employed. Type of Phaco Tips Standard Tip The standard tip has a straight shaft of 19 gauge and requires a 3.0 to 3.2 mm incision. With the traditional divide and conquer surgery, this is the tip of choice (Fig. 11.1).
FIGURE 11.1 Standard tip
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0-degree tip The 0-degree phaco tip was designed by Kunihiro Nagahara and James Little. It does not have any angle at the tip end. There is no bevel at the tip, but there is an internal 60 degree bevel that provides a cutting surface. The 0 degree tip has the enhanced ability to gain occlusion and vacuum rise. Dr. Roger Steinert performs a phaco chop through a 2.8 mm sutureless wound with topical anesthesia. His preferred vacuum sets are 200 mm Hg for 2+ cataracts, 300 mm Hg for 3+ cataracts, and 400 mm Hg for 4+ cataracts. He generally uses linear flow 26 cc per minute flow and 70 percent linear phaco power. His bottle height varies. He enters initially with a low height because of the clear cornea topical anesthesis technique. The height then varies depending on the maximum vacuum settings. At the 300 mm Hg and above set-tings, height will be at its maximum allowable pole setting. 15-degree tip It is becoming much more common with the high vacuum capabilities for phacoemulsification. 30-degree tip The most common tip that is used. A 30-degree tip of the same diameter presents 15 percent more cross-sectional area to the cataract than the 0-degree tip. 45-degree tip The 45-degree tip is generally considered more effective in cutting hard cataracts over a 30 degree tip. However, it is more difficult to occlude because the 45 degree bevel has a larger cross-sectional area. In fact, a 45-degree tip presents 40 percent more area than a 0 degree tip. KelmanTip Kelman tip is a 19 gauge needle that has the advantage of increased cutting ability. It has a disadvantage that it has 180 degree cutting edge that can be dangerous because it can cut toward the periphery of the lens. It provides circular cutting. It has a higher stroke length, thus, the increased frequency leads to more energy (joules) that is used during the procedure. This tip has a higher incidence of wound burn. It can be very efficient if it is used in combination with a thermal protective sleeve in the hands of an excellent surgeon (Fig. 11.2).
FIGURE 11.2 Kelman tip Microflow The microflow needle is a 19 gauge needle and has grooves in the outer shaft. It has an advantage that the grooves in the outer shaft help to cool down the phaco tip. It is generally used with a 2.85 to 3.2 mm incision size (Fig. 11.3).
FIGURE 11.3 Microflow tip
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Cobra Tip The cobra tip is a 19 gauge needle that has an increased size on the end of the needle shaft. It is used for magnetorestrictive handpieces that have a tendency to heat up faster than the piezoelectric handpieces. It is used very rarely (Fig. 11.4).
FIGURE 11.4 Cobra tip Microseal The microseal is a 19 gauge needle. It is similar to the Mackool with its insulated sleeve. It has the advantage of having a thicker sleeve that closes down the fluid outflow for a totally enclosed system, and so you maintain the chamber better than if you use another system (Fig. 11.5).
FIGURE 11.5 Microseal Masket “Ergo” Tip The Masket Ergo tip is a 19 gauge needle. It is bent at the hub for more control. It is safer than the Kelman system because it cuts with a longer stroke length. It is not used much because it is not very well known. Particularly with an insulated sleeve, it would be an excellent choice. The manufacturer gives the following benefits. • Ergonomics design for a more comfortable hand position reducing fatigue • Greater efficiency during phaco requiring less ultrasound being delivered to the eye • Tip maintains a more parallel position to the iris and posterior capsule, reducing the risk of breaking the capsule • Easier access into the deep set eye (Fig. 11.6).
FIGURE 11.6 Masket “Ergo” tip Mackool Tip The Mackool tip is a 21 gauge needle. It has an insulated sleeve with thermal protection. It requires a 2.75 mm incision size scleral tunnel or a 2.85 mm clear corneal incision. It
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has the advantage that if the doctor spends much time in the position 3 of phaco ultrasound, there is less chance of wound burn (Fig. 11.7).
FIGURE 11.7 Mackool tip Mackool-Kelman Tip The Mackool-Kelman tip is a 21 gauge needle. It has the advantage of having a smaller gauge with precise cutting control. It has a bent tip with greater cutting space and an oscillating stroke length. The insulated sleeve reduces the thermal heating. It has the disadvantage of cutting all the way around the tip, and it takes a skillful surgeon to reduce cutting unwanted tissue. There can be a reduction in the outflow particularly if the incision size is in the range of 2.65 mm. It has an increase in the high vacuum capabilities, but the tip is generally a 45 degree tip such that the holding capabilities are not as good as a lesser angle tip (Fig. 11.8).
FIGURE 11.8 Mackool-Kelman tip Summary Eight major types of phacoemulsification tips that are used to remove the cataract are discussed in this chapter. Each has advantages and disadvantages, and it is important for the surgeon to realize the various types that are on the market and what is best suited for the characteristics of the surgeon, the type of handpiece available, and other factors. The author’s personal preference is the use of the Mackool-Kelman tip.
12 Sterilization Sunita Agarwal Introduction When viewed upon from the broader angle however good a surgery may have been performed should it be complicated with infection, the result is fraught with peril. The patient suffers ultimately and the surgeon goes through hell. We have all had our share of infection and its disastrous effects. Should a surgeon say they have never had infection spoiling their case, either they have never done surgery or the truth lies hidden elsewhere. Be that as it may we need to understand microorganisms in a much better manner. We need to give this topic full attention in our hospitals and conti-nue to give it the importance it requires by continuing quality checks at every interval regularly every day and in every case. Some basic facts of postsurgical infection in human eyes whether cataract surgery or any intraocular surgery is concerned, are that we need to regard all infections to arise from the operation theatre unless proved otherwise. The operating room is certainly the most guilty in providing the microorganism for postsurgical infection. It may be very easy to complain about patient compliance and dirtiness to be the cause of infection, and sometimes that may be true, however in our hearts it is safer and better for us to accept that this infection has come from the operating room and then work ourselves backwards in removing the source of the disease. We may be able to shift blame to a tooth infection or septic foci in the sinus, however, should we be able to first accept the operating room to be at fault, our energies would be directed in improving our facilities, thus averting further mishaps from occurring. The first rule in sterilization at least where developing countries are concerned is not to believe any manufacturer when they claim to have sterilized their wares. To be taken as guilty of infection unless proved otherwise. This is true of not only suture material, disposable needles and syringes but also of intravenous and intraocular fluids. Many cases have been reported in India where bacteria have grown from the Ringer lactate used. A startling study was carried out in the early 90s where several eyes were lost due to balanced salt solution (BSS) not being of pH 7.4, because the last rinse did not wash of the remnant soap from the glass bottle. What we all need to remember is that when everything is going fine nobody complains, but as soon as there is a complication the surgeon is the first and often the last person to be held totally responsible for all misdemeanors on anybody’s part. Thus, as captain of the ship the surgeon has to sink with his or her ship. However, all this can be avoided by taking precautions before entering the operating room.
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History Dating back to the time that Sushruta from 500 BC explained the importance of washing hands and draping wounds with clean cloth, as well as having a clean environment for surgical procedures, Indian medicine has always kept this part of medical practice in good stead. Practicing principles of Dhanvantri medicine a Hindu physician-oculist wrote that surgeons should clean their nails prior to operating, wear fresh clothing, and spray sweet smelling vapors around the operating room. Little did he know the importance of these instructions. However, these were carried down through the ages by the Vaidyas (Hindu physicians), now with better knowledge there is more understanding of the topic on infection and sterilization control. The middle ages saw European medicine catching ground however, sterilization tactics were still very rudimentary. Most surgeons thought it to be fashionable not to wash hands, mayhap due to the cold climate of the temperate zones. Thus, centuries of unknown prevailed with thousands being lost to infection and disease even inside the operating room. It was considered hazardous to lay a surgeons hand in the fear of losing the patient to “fever” as it was called then. However, Hieronymus Fracastorus in 1546 published a landmark book that may have led to the discovery of bacteria. His theory of contagious diseases and their treatment sparked off the original microbe hunter, to identify bacteria with his own saliva in 1675, using his microscope screwed together with some lenses, Antoni van Leeuwenhoek had set about 2 centuries of hot debate amongst the European scientists. In 1840, Jakob Henle postulated the theory of the contagion. This was further specified by Robert Koch in 1876 where he showed that by isolating the anthrax bacillus and was able to infect a normal animal with the same that the theory of contagion was true. This work won him the Nobel Prize for medicine and physiology in 1905. It took Louis Pasteur to bring out the emphasis of the “little beings” as those responsible for disease. His paper on the importance of washing hands before starting a obstetrical delivery shows the utmost significance of this one act towards a sterile atmosphere. Throughout the 1800s pioneering technologies of Pasteur, Nizer, Klebs, Escherich, Cohn and Ehrlich played major roles in the evolution of discovery of pathological germs. Today the science of microbiology and medicine are occupied by their names forming important landmarks in the discovery of the importance of sterilization techniques. Where hospital wards are concerned, making surgery safe and banishing sepsis from hospital wards, an era of pre-Lister and post-Lister can be demarcated. This was the importance of Joseph Lister on surgical outcome. He based a lot of his studies however on Ignaz Semmelweiss (1818–1865)—who was cruelly maligned for his theory of the origins of child-bed fever that led him to be institutionalized and die an unhappy man. The irony of the situation was his studies brought about a revolution in hospital wards and the prevention of infection by antiseptics and cleanliness reiterated by Joseph Lister. By the time Daimler brought out his first motor cycle in 1884, scientists round the globe had devised the autoclave deriving from the fact that boiling did away with microbes. This revolutionized hospital wards and operation theatre sepsis to a great extent. So much so that till date some contraption of the autoclave is still used in every operation theatre in existence in the modem world.
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By 1899 a century was going by and scientists believed this was the ultimate and that internal sepsis was not going to be much more advanced beyond theory and that the field was not likely to advance further. Today with much more information and knowledge we think contrary, that we still know only a drop in this ocean of knowledge against disease and infection. Change is the spice of life and just as today changes to another day, of more discovery and more scientific achievements so to these pioneers were to discover much more. Sulfanilamide first discovered by Paul Gelmo in 1908 was found to be effective on surgical wounds, by Gerhard Domagk who first used the drug on humans in 1935. This won Domagk the Nobel Prize for Medicine and Physiology in 1939. Paul Ehrlich and Toju Hata discovered Salvarsan, the arsenic derivative for the treatment of syphilis, it heralded yet another era, that of the antibiotic. In 1929, Alexander Fleming published his classical work on Penicillin from London and history followed his every achievement. Through the World Wars his medicine was of immense use in the control of infection and weeding out of disease. He showed first through in-vitro studies that a contaminant of Staphylococcus medium, Penicillium notatum had a destructive effect on the Staphylococcus bacteria that was growing on the agar plate. In further experiments he showed that this mold also had strong antibacterial activity against other pathogenic gram-positive bacteria as well as gram-negative cocci and bacilli but was not effective against organisms such as Escherichia coli. While the world raged with War, yet another kind of war was being fought for mankind inside the laboratories of HW Florey at Oxford University. By 1940 Ernst Chain showed the curative effects of penicillin in vivo. In 1945, by the end of the World War II, these three men were awarded the Nobel Prize for Medicine and Physiology. SelmanWaksman discovered spates of antibiotics in succession with streptomycin in 1944 for tuberculosis and neomycin in 1949. Much of today’s discoveries have been dependent on the way we see these small “animalcules” of Leeuwenhoek, in 1933. Our eyes could see the destruction of the world with Hitler as the Chancellor of Germany, and could see even greater destruction by microbes since the invention of the first transmission electron microscope by Ruska. Further developed to a phase contrast microscope by 1953, by which time the World War had ended and humanity was once again allowed to prosper. So much so that the scanning tunneling microscope could be developed by 1980 and its fast developing clones that are in use today. However, very soon the side effects of antibiotics were noted with the classic example of chloramphenicol the first broad-spectrum antibiotic, discovered in 1949, effective against rickettsial infection, typhoid. A link was established between severe bone marrow depression and aplastic anemia with its use. This curtailed the use of these eyedrops and oral regime in USA. We owe a lot to these forefathers of modern medicine and surgery, and today’s technological advancements have made us more wary of the microbe. It seems to be the more we advance the more microbes we find the cause of disease. Stress and other dietary factors were believed to be the cause for peptic ulcers, though now we know bacteria to be the root. In a similar manner, there are many more diseases that still retain their shroud of mystery.
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Let us not rest on previous laurels and with the close of this century believe that we have reached the ultimate. In reality, we have only skimmed the surface there is much more to be unraveled in this body beautiful of the Homo sapiens. Tempting to say in the words of Louis Pasteur, “Science knows no country, because knowledge belongs to humanity, and is a torch which illuminates the world.” Areas of Sterilization Once we enter the operating room we expect that everything must be in order, and somebody else is in charge, not me. However, much to our utter astonishment seldom does anything go wrong, though when it does, the blame is once again pushed on to somebody else, not me. This is where the first principle of surgery has to be changed and restructured. The first and only person responsible for the whole team at work inside an operating room is the main surgeon. This is the person who everybody in the operation theatre must report to. This is the person who before entering the theatre has to ensure that everything inside this pious area is under strict control of the surgeon. This is the person who must take responsibility if an infection should arise in the patient’s eye within one week of surgery. After carrying out so many tests and sterilization techniques I would rather believe for the benefit of all future patients that infection in a postsurgical eye arises from the operation theatre facilities. It is very difficult to put infection inside a closed eyeball, though it is easy enough while the eye coats are still open. More often than not infection is carried into the eye by instruments themselves. There is however a small possibility that this may not be the case and there may be a septic foci residing in some corner of the human body like a tooth abscess or such. Still these occurrences are very rare and far between. Moreover, it is far more beneficial to all concerned to garner our resources and give a thorough job of the operating room than to be witch hunting on the patients habits and dirtiness. It is my belief that even a dirty patient cannot infect the inside of his or her eye, if he or she has a postsurgical infection for sure it has been carried in through the workings of the operation theatre. Going in a methodical manner from without to within anything entering the theatre has to be sterile. First the operating room itself has to be sterile. The Operating Room Air The air we breathe can be filled with pollutants, viruses, bacteria and irritants such as pollen, chemical gases, odors and smog. In critical situations—military command centers and public arenas—there is also a threat of chemical and biological agents being released into the air. All these air borne pollutants can be treated by using various technologies. We forget about the air coming into the operating room, though however we should understand that if this itself is clean it is much easier to retain the cleanliness within. There are many ways of filtering clean air into the operating room. One of the easiest and best is to first make sure the rooms pertaining to the operation theatre complex are sealed
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shut, with only one entry into the complex. Now, we need to bring in clean air into the operating rooms. Air Conditioning Ideally the whole operating area complex must be air-conditioned with the units stationed well outside the complex and only ducts bringing in fresh temperature-controlled air into the complex. The air conditioning units could be in the form of towers or split units stationed on the terrace or window firmaments outside. Filtration of air The ducts bringing in the clean oxygenated air need to have the air passing through filters that can ward off bacteria which means they should be 0.2 micron filters. More often these filters need to be changed and or cleansed on a daily pattern. Ultraviolet radiation Ultraviolet light bulbs could be placed in the path of the filtered air to make sure the air is disinfected as it enters the operating rooms. Alternately these bulbs could be left in the operating area and kept on throughout the night, this would also ensure clean areas the next morning after 12 hours of exposure to the ultraviolet light. Ozone treatment Another technology gaining ground for clean air is the ozone treatment plants that generate ozone into the air. This breaks up the microorganisms and clean, disinfected air is ensured. One unit for 5000 cubic feet of air space is recommended. Ozone is a reactive molecule comprising three atoms of oxygen. Because ozone is a reactive molecule it acts as a powerful oxidizing agent against all microbial contaminants, organic toxins and most volatile organic compounds (VOC’s) and because of its short half-life it rapidly reverts to water and oxygen. When a combination of UV, moisture and ozone are used a synergistic effect is seen. The absorption of UV by the ozone-producing highly reactive substances that effectively kill microorganisms including hard to kill spore forming bacteria. Positive pressure A positive pressure pump is maintained to make sure the air entering the operating rooms are kept at a pressure above the rest of the area. These pumps can be installed in the ducting and positive pressure inside the operating areas would ensure that the air comes only from this area and not through leaks from windows or doors. The main door of the operating room must function for only air escaping the operating area and not for entering it. Air curtain Entry points in the operating area would do well to have automatic door closers so that the door does not remain open unnecessarily. Also the door can be fitted with an air curtain so that the outside air is curtailed off from entering. Quality Check Quality check is ensured by every day/regularly carrying out the PLATE TEST. This means leaving a bowl of clean sterile water in the room to be tested for 20 minutes. Microorganisms present in the air would settle down on the surface of the water, a small sample is taken from this and grown on a culture plate. If the sterilization techniques have been effective the culture should be sterile in 24 to 48 hours. If the culture grows positive growth remedial means have to be taken to ensure sterile cultures.
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The Operating Room Water The water coming into the operating room needs to be free of microorganisms. After all the water with which we are cleaning the most important area of the hospital needs to be totally clean. If microorganisms are present in water then they would remain on the items cleansed and the cleaning would be bad. The water coming into the operating room must also contain adequate amounts of minerals. Filtration This still finds the safest use in bringing in clean water into the operating area. It could be done by many methods, ceramic is one of them. However, today membrane filters seem to have replaced all else as here they bring out the fluid bereft of bacteria. Sometimes a suction pump is attached to the water jet so that the filtration can take place at a faster pace. Reverse Osmosis A high pressure is set about in the clean water and a system of reverse osmosis sends back the mineral content of the water while a filtration process blocks out the microbial content. In this way water is able to reach the operating room withless minerals and is absolutely sterile with no bacteria. This is also one of the techniques used in the manufacture of bottled mineral water and can be used very effectively in operating area complexes. This water is now used for cleaning the operating rooms, machines, and for surgeons while scrubbing. The water coming from such a plant is placed in a storage drum, preferrably made of stainless steel. Electronic Control Water can be made to contain low mineral counts and no bacteria through another technique of manufacturing mineral water. This is by producing cathode and anode electrodes on two ends of the water channel. The anions and cations would respectively move to their corresponding electrodes and this would clear the fluid of mineral content. A filter present below would clear the water of microorganisms. This is another method of producing sterile bottled mineral water. The Operating Room Walls, Floor, Ceiling and Fixtures All elements of the operating room need to be first cleansed, then disinfected and last but not the least totally sterile. The three steps in this process can be done by three different fluids and chemicals.
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Cleansing This is best done with a soap and water wash. Every surface, every table, every chair and every fixture needs to be cleansed with a direct application of soap and water on the surface. After cleaning with this it needs to be cleaned with plain water. Disinfection Benzalkonium chloride solution 4.5 percent could be used as a disinfectant and as a general cleaning agent for floors. One of the best solutions used worldwide towards the disinfection of operation theatres and consultation suites is the Bacillocid made by Bode from Germany. This contains 1,6 dihydroxy 2,5 dioxyhexane (chemically bound formaldehyde) with glutaraldehyde, benzalkonium chloride and alkyl urea derivative. A 2 percent solution is used for the operation theatre and a 0.5 percent solution for the consultation areas. With this solution all areas mopped and cleansed of vegetative organisms, fungus and viruses (Figs 12.1 to 12.3). Formaldehyde in the form of liquid, tablets or gas has been used extensively in the past, however, today its use is put to question since culture tests have proved positive with growth even after formaldehyde sterilization.
FIGURE 12.1 Cleaning of the operation table and chair, external surfaces of the microscope, instrument table, IV poles with Bacillocid
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FIGURE 12.2 Cleaning of the operation theatre walls with Bacillocid
FIGURE 12.3 Cleaning of the operation theatre floor with Bacillocid The Operating Room Macroinstruments All fixtures including fans, lights, air conditioning have to be first cleansed carefully with a dry cloth and then mopped with Bacillocid so that they can be disinfected. Chairs, stools, operating tables, trays have to be first cleansed with soap water and then mopped with Bacillocid (Fig. 12.1) and left alone for over four hours to ensure disinfection. Care needs to be taken on operating theatre instruments like Boyles apparatus, microscopes, phaco machines, diathermy machines, suction machines, laser machines. Though delicate these instruments need to be thoroughly cleansed everyday. Many a time infection is found to be harboring in these areas and they are difficult to clean. More sophisticated the machine more care need to be taken in its cleanliness. This task cannot be given to an untrained personnel and even then ideally there should be a doctor supervising their cleaning.
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Microscope The rest of the microscope can be cleansed with soap water as well as Bacillocid however the optics need special care and need to cleaned only with a clean cloth preferrably silicon paper. Antifog chemical coating could be given to the optics. After cleaning and before closing for the day the optics should be ideally wrapped in its original cloth or plastic casing and drying agents placed inside like silicon oxide. This allows the moisture inside to be absorbed by the chemical and with less moisture, formation of fungus and other microorganisms on the optics is rare. Phaco Machines As eye surgeons we need to be well aware of the pressure maintained inside the eye during phacoemulsification procedures for cataract surgery, but little do we realize the importance of the machinery involved in giving us this information. When the phaco probe is inside the eye of the patient there is a continuous flow of fluid. The fluid arises from the bottle suspended 65 cm above the head of the patient and this produces a certain pressure inside the eye. The fluid then goes through the irrigation line to the phaco tip which enters the eye and leaves the eye through the suction tubing entering the phaco machine. From the phaco machine another set of tubings takes the excess fluid away into a drainage bag. What we have overlooked is between the tubing entering the phaco machine and exiting into the drainage bag, it goes through a channel inside the phaco machine. This part of the tubing is never sterilized in the proper manner that is required before a cataract surgery. In fact, it cannot be sterilized as well. This part of the tubing is attached to two manometers that gauge the pressure in the tubing and give us a reading on the panel in front. A vent exists that can release the pressure in the tubing to atmospheric levels as soon as our footswitch transfers from position 3 to 2 to 1. In so doing the air from the operating room directly enters the tubings thus if there should be bacteria in the air they would now have an easy access to the most sterile line that we have been trying to maintain. These facts were not known to us for a long time, and we had a spate of infections as Pseudomonas had managed entry into the tubings present inside the phaco machine. None of the companies’ representatives ever let us know of this tubing and its existence and we never racked our brains hard enough to trace the tubings, until this major catastrophy occurred. Over a spate of 12 months we had taken out 4 intraocular lenses (IOL’s) from eyes with infection. We were able to save the eyes from blindness however rendering them aphakic. We first accepted that the infection came from the operating room and now with a technology of omission went about in a scientific manner trying to decipher where the infection came from. First the microsurgical instruments and tubings were taken through the 10-step procedure as you will read later on. Now, they were tested for sterility by flowing fluids through them and taking this fluid on a culture plate. They were sterile, after fixing the tubings and probe onto the phaco machine the fluids were collected from the drainage bag and sent for culture. The second one was positive. This told us that our sterilization techniques were good however something was amiss.
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We opened the phaco machine and found this tubing running through it and found the vent as well. This vent ideally should have an air filter attached to it. We sent the tubing for culture and replaced it with a fresh sterile piece. The culture proved to us where the culprit lay, the Pseudomonas was grown from this tubing. The internal tubing cannot be changed with every case, though this would be ideal. So, we have devised a better structure for its disinfection. That is to keep the air totally sterile and make sure no infection goes into the tubing through the vent. This is ensured with the ozone generator for the total operating room areas. What we did realize through this study was that not all cases turned up with infection even though the bacteria must have been residing in the tubing for many a day. The cases turned up with infection had something to do with being the last few of the day. The cases which turned up with infection had low immune status, either diabetes or hypertension or such. The cases which turned up with infection had a complication most often a posterior capsular rupture on table thus resorting to vitrectomy This shows us some characters of infection that we may already have known but not given them their due acknowledgement.
FIGURE 12.4 Collection of Ringer lactate solution from the aspiration tube before the operation
FIGURE 12.5 Collection of Ringer lactate solution from the aspiration tube after the operation
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However, what we have realized is that the phaco machine has to be cleansed very well and air filters placed on the vent. The tubing changed every week. And culture tests done for every case before and after surgery (Figs 12.4 and 12.5). What this means is when the tubings and probe are attached to the machine before starting the case first few drops of fluid entering the drainage bag is taken for culture (Fig. 12.6). Once again at the end of the case this is repeated. If and when at anytime a culture should turn positive we would know the problem immediately. After these stringent measures have been installed at our hospitals we have neither had even one infection coming from
FIGURE 12.6 Collection of Ringer lactate solution from the front end of the internal tubing the operating room nor had to remove any more IOls lenses from infected eyes. Boyles Apparatus Regular cleaning of all parts of the machine is necessary with spirit as this evaporates and does not leave a residue on it. However, the parts of the tubings that enter the human system or are connected to them need to be thoroughly cleansed, disinfected and then sterilized. The method of choice for sterilization here is the ethylene oxide gas chambers (Fig. 12.7). As most of the tubings are plastic temperature of below 60°C are comfortably taken by them. Needless to say that oxygen, nitrogen dioxide, halogen levels should be monitored on a daily basis with every case in particular. The Operating Room Microinstruments Every case must be treated separately and all instruments must be cleansed thoroughly before the next case. Once a day a 10-step cleansing routine must be established. This 10step routine includes 1. Soap water wash with toothbrush 2. Ultrasonic cleansing with Lysol 3. Cidex cleansing and soaking for half an hour
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4. Isopropyl alcohol cleansing 5. Plain sterile water cleansing
FIGURE 12.7 Ethylene oxide sterilizer 6. Plain sterile water cleansing 7. Plain sterile water cleansing 8. Boiling in sterile water 9. Ethylene oxide sterilization overnight 10. Flash autoclave sterilization three times. Four trays are kept aside on a long side table (Fig. 12.8). Water used in this sterilization must be mineral sterile water, as this water is totally sterile, prove it by growing the water on a culture plate and making sure it is sterile. The trays are filled with the respective fluids. Each tray is numbered and labeled so that mixing does not occur.
FIGURE 12.8 Four trays arranged in sequence containing carbonic soap with mineral water, 2 percent glutaraldehyde, 70 percent isopropyl alcohol and mineral water
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FIGURE 12.9 Wash all instruments in a tray of carbonic soap and water with toothbrush In each tray a toothbrush and 50 ml syringe with a yellow tubing taken off from an IV set is kept. All microsurgical instruments are dipped in each tray periodically. Every instrument is cleansed delicately with gloved hands and toothbrush. When and where required every lumen of every instrument is injected with 50 ml of the liquid that it is dipped in. Thus, the cleansing action is from the outside as well as from the inside of every instrument. This is specially true of probes and tubings. Tray I with Liquid Soap and Sterile Water The first step in sterilization of instruments is its proper cleansing as whenever the microbial load will be less on the sterilization technique used the better would be the results that can be achieved. This is best done with the old soap and water wash (Fig. 12.9). Liquid soap is used in a tray with clean sterile mineral water. First a plain cleansing with gloved hands is completed and then using a toothbrush into the small crevices of instruments. This is of special importance to instruments filled with blood and tissue. In ophthalmic matters special reference has to be given to machines like the automated flapper in LASIK (laserassisted in situ keratomileusis) cases, as it is known that corneal tissue gets clogged into the tracks and other areas of the flapper. This can be removed much better using palmolive liquid soap as it contains some of the safest and yet cleanest ways to get grid out of the system. Ultrasonic Cleansing The mainstay of cleansing into cervices where the toothbrush cannot reach and this gets into the fulcrum of forceps and scissors to clean the instruments. A chemical solution like Lysol (Cresol and soap solution) could be used as an adjuvant to remove the debris from clogged surfaces. This breaks up the protein and organic matter so that it can come clean
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from instrument surfaces. Most of the fluids used in the ultrasonic cleanser need to be antiseptics as well so they can be used as disinfectants on the instruments cleaned. Cidex or Glutaraldehyde 2% Once activated Cidex solution manufactured by Johnsons and Johnsons must be used within 14 days. Some facts like these go unnoticed in hospital environments and the use of substandard procedures and drugs come into play. Reiterating the fact that the doctor has to be on top of all these activities. Instruments are left immersed in this solution (Fig. 12.10) for 30 minutes, which is sufficient time for disinfection however for sterilization 10 hours would be needed. Within 10 minutes at room
FIGURE 12.10 Wash all instruments in a tray of 2 percent glutaraldehyde
FIGURE 12.11 Wash all instruments in a tray of 70 percent isopropyl alcohol
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temperature most vegetative organisms would be destroyed, including Pseudomonas, fungi, and viruses. The solution is very toxic to the eye and great care has to be taken to get the solution out of the instruments before using on humans. Isopropyl Alcohol 70% This is still one of the best ways of killing the microorganisms (Fig. 12.11). Instruments are soaked in the solution for over 15 minutes and then cleansed using a toothbrush and syringe to wash the internal elements of probes and tubings. Sterile Water Care must be taken to wash of the deleterious effects of the above mentioned solutions. This is done effectively by first soaking and then washing all the instruments through three trays of sterile water (Fig. 12.12). The lumen of the tubings must be clean with sterile water each time 50 ml of the fluid passing through the probes and tubings. Sterile Water Once again cleansed with sterile water. Sterile Water Once again cleansed with sterile water.
FIGURE 12.12 Wash all instruments in a tray of mineral water Boiling After going through a number of tests and methods of sterilization we still find one of the best methods remains the age-old custom of boiling. This brings about total death of the microorganisms. Most rudimentary of operation theatres would still contain means and
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methods of performing this essential act of sterilization. However, what needs to be detailed is whether the particular article can withstand temperatures of over 100°C. After having a spate of infections and removing IOLs from infected eyes to save the eyes, my hospital and staff got spurned to find the cause of the infection. Towards this a whole new regimen was set-up on cleansing, disinfection and sterilization of microsurgical instruments. After each methodology culture tests would be taken to prove its efficacy. We did understand that the silicon tubings had gram-positive cocci growing in them. In a process of eliminating them we found that the cocci inside the silicon tubing withstood many sterilization techniques like ethylene oxide and autoclave. However, when subjected to boiling for 20 minutes the tubings would be sterile. This once again reiterated our belief in this age-old custom of boiling (Figs 12.13 to 12.15). Ethylene Oxide Sterilization This is not a preferred technology of sterilization for microsurgical instruments because of the time duration taken is over 16 hours. However, we have started using this as one more step towards the end of the day. By the time we finish all the cases of the day we take our instruments through this 10-step procedure ending it with a bout of ethylene oxide where the instruments rest for the night. However, the only aspect of this technology is that the instruments must be cleansed of the ethylene glycol residues that may be found over them. This is effectively done by steam autoclave and washing intraocular instruments with ringer lactate meant for intravenous use.
FIGURE 12.13 Diamond blades are cleaned using steam
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FIGURE 12.14 The external tubings, internal tubings, I/A probe and metal knobs are boiled for 30 minutes
FIGURE 12.15 The instruments are separately boiled for 30 minutes Autoclave As the last step in the sterilization cycle of instruments, they are passed through the flash autoclave for 134°C for 5 minutes and this cycle is repeated three times in the Statim autoclave from Canada (Fig. 12.16). It has a built-in computer that tells us of the efficiency of the cycle. However, color indicators would also tell us of the physical measurements reaching the desired levels.
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FIGURE 12.16 Statim autoclave cassette containing the tubings and instruments is kept in the ethylene oxide sterilizer for a period of six hours After doing this, the instruments are laid on the operating table and each instrument that enters the eye is dipped in Ringer’s lactate before entering the eye. The Operating Room Linen and Accessories All operation theatre linen and accessories must be cleansed before entering the complex. Particular slots should be kept ready and clean for them everyday. Otherwise the operation theatre should be totally bereft of any other article. Anything that is not used everyday need not be found in the operating room. This is not the place to keep stocks and inventory of medicines. They could be kept in the prefunction area of the operating room but not in the operating room itself. Linen Sterile operation theatre gowns, towels, gloves could be of disposable variety, this is internationally accepted to be the best. However, it is not practical in all kinds of atmospheres. In India we still recycle our operating clothes which are usually made of cloth. The methodology approached towards their care is explained in the same 3-step procedure. Cleaning This is done by taking all the sullied clothes and first taking away all clothes coming from an infected patient being operated or from the septic operation theatre are treated separately than that coming from a clean operating room. These clothes are preferrably disposed off in an incinerator. If they cannot then they are soaked in Dettol solution, before the cleaning process begins. The clothes are cleansed preferrably in a washing machine with adequate soap being used. Then the clothes are passed into a drying machine. Try not to leave these clothes on the drying rope for nature to dry, because with this outside bacteria and fungus can settle
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on these clothes. Inadvertently they may fly off the clothes line and this would also create much increase of the microbial load for sterilization. However, if machinary is not available these clothes are first soaked for half an hour in hot water with soap solution inside a large tub. A rod is taken and rotated round and round for five minutes. This will shake off the dirt and grind from the clothes. After this each cloth is taken separately and washed with hand and the clothes thrown into another tub of hot water with a few drops of Dettol solution in it. The clothes are left for another half an hour in this solution and then rinsed off with plain water. A separate enclosure should be made for the drying of these clothes. When the clothes are placed on the clothesline they should be pinned there as they may fly and hit the floor picking up germs. This could be avoided. Once dry they are picked up, folded and sealed for sterilization. Sterilization Clothes could be sterilized by two methods, whichever method is used what is important is that they be folded away keeping each procedure in mind. That is to say if for one cataract procedure we need three operating gowns, ten towels and six shoulder bags, then they should be folded in such a way that these are all kept together. One does not have to search for the small items by opening up every item sterilized. Autoclave: This still finds the pride of place in being the most accepted form of sterilization. However, one needs to be aware that the clothes must not come out damp. The steam in the autoclave must be saturated but dry. This means all the water vapor present in the air should be gas and no droplets of water in the steam. If an autoclave is giving out damp clothes that means it is not working efficiently. The drums kept in the autoclave must be closed immediately on removal from the autoclave, ensuring that outside air does not enter the drum. Once autoclaved the items can be considered sterile for only 24 hours which means to say they need to be reautoclaved to improve efficiency in sterilization techniques. Ethylene oxide sterilization: With todays emphasis on better sterilization techniques and total dependence on them, a move has come into using the gas industrial sterilization for hospital purposes. As there is more surety on its efficacy this is even a preferred technology over the autoclave. However, it does have its drawbacks which are that the hospital needs to keep a bigger inventory. This is due to the fact that these clothing need to be aired out for over 48 hours before they can come into contact with human skin. Easily achieved by having four times the number of gowns and towels one would ordinarily keep. The advantage of ethylene oxide sterilization for linen over autoclave is that we never get damp clothing which should be regarded as not sterile. Moreover, the personnel are always sure of ready stocks for operating at anytime. We do not have to start the autoclave and wait for sterilization, we always have sterile clothing ready. Sealing and packing In ethylene oxide sterilization the methodology employed towards its packaging is very important. High-grade thick plastic bags could be used, alternately custom-designed bags are available for ethylene oxide sterilization. However, these custom-designed bags are more expensive than plain plastic bags used commercially. Sealing of these bags has to be immaculate as any porthole left gaping will now allow the atmospheric air containing microbes into the bag and once the seal is broken the
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contents are not any more registered as sterile. Sealing machines are available in the market and their use is much better than burning the bags with a candle and sealing them. Ethylene oxide chamber The ethylene oxide (ETO) gas comes compressed in gas cylinders that are attached to the machine. These machines which use the gas cylinder have a vacuum pump attached which first empties the air in the ETO chamber, then we let in the compressed ethylene oxide gas and leave it at about 50°C for over 6 to 12 hours. Now, when the chamber has to be opened, once again the vacuum pump empties the gas out. The outlet from the machine needs to be placed 6 ft above and outside into the atmosphere. This gas is toxic and its inadvertent entry inside the hospital premises is a health hazard for personnel. Care must be taken that the outlet tubing is placed well outside the hospital premises, onto the terrace if possible. Once the ETO has escaped out the atmospheric air is let in and the chamber pressure maintained at atmospheric pressure before it is opened. The materials can now be kept on a shelf for airing. The shelf should be just racks with ample room on either side for the gas to escape from its whereabouts. The linen can be now used as sterile after 48 hours of airing. Alternately gas ampules are present which can be placed inside the chamber, these ETO gas ampules need neither the vacuum pump nor the temperature maintenance and can be easily placed inside a big plastic bag also prescribed by the company that manufactures the ETO gas ampules. All the clothing is stacked after sealing inside the big plastic bag that occupies the whole of the gas chamber. The ampule is broken and this allows the ETO gas to permeate through the whole closed plastic bag inside the chamber. This is left so for 12 hours and for another 14 hours when the gas escapes the chamber. After which the contents can be taken out and placed on airing shelves. Medication Parenteral IV fluids and intraocular fluids: Fluids used inside the eye should be regarded as not sterile unless proved otherwise. Towards this exercise we sterilize all our fluids, like Ringer lactate, saline and even 2 percent methylcellulose. Many a surgeon in developing countries has suffered immense loss by placing Ringer lactate into the eye without prior sterilization. E. coli has been known to be grown from these fluids. At the moment of an infection occurring not just one eye will be lost, but the whole batch of Ringer lactate would and will be used on several eyes at a time and many losses have been reported. From the Ringer lactate one surgeon lost over 12 eyes to infection from the fluid. This cannot be really taken as a mistake as we understand that fluids meant for IV therapy must be totally sterile, however this is not always the case. So to protect our patients from such a malady occurring we resterilize these bottles in the autoclave. It is preferrable to use glass bottles. Studies have shown the plastic polymers react with the fluids and can have drastic effects on the cornea of patients. Thus, world over glass is a preferred carrier for use of fluids inside the eye. Moreover, plastic bottles cannot be autoclaved as they would melt with the over 100°C needed for autoclave sterilization. Even when we are sterilizing these glass bottles care has to be taken in their placement in the autoclave bins. Autoclave indicator stickers are used on every bottle. The bottles
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are placed head up, and kept in the bin with space all around. Preferrably wrapped in some cloth towel so that should they inadvertently break and blow up, they would do so inside the wrapping. Care has to be taken to let the fluids reach a level of below 80°C temperature before opening the autoclave chamber as they may blow up on exposure to room temperature. All fluids used inside the eye are kept at 4°C for better trauma control on the eye. As we know cold itself is an anesthetic and controls blood vessels by constricting them we prefer to use cold fluids inside the eye. This would also ensure better control on the delicate tissues of the eye and less trauma as well. Methylcellulose 2% (VISCON): Much the same technology is used in autoclaving methylcellulose. Glass containers are once again preferred as plastic would react with the fluids inside. The vials are kept wrapped in cloth and placed inside the autoclave bins. Once sterile these are shifted into a refrigerator to keep them at 4°C, the preferred temperature for methylcellulose as we know at this temperature the viscosity is the greatest and best for intraocular use. All other medication: These too need our undivided attention as to their expiry. Most drugs are not resterilized since the methodologies used might just denature the medication. However, place has to be kept in the operating area complex for essential medication necessary during the course of a surgery. These medicines should not be stocked inside the main operating room but in prefunction area. Care needs to be taken regularly to keep dusting and keeping the area where medicines are kept to be clean and free from germs. Thus, to do so every day this area must be cleaned, drawers, shelves all cleaned with plain cloth and at least once a week with soap water and/or Bacillocid. Probes and Tubings All probes and tubings are usually of disposable variety, and they could be kept in clean shelves or drawers with names written on the outside. Alternately today we could recycle probes and tubings by first cleaning them well and then passing them through ethylene oxide sterilization. However, these tubings and probes are usually made of plastic and for the gas sterilization to be totally safe and nontoxic they need to be kept on the shelf for airing for over 15 days. So the date and time of ETO sterilization needs to be marked on the color indicators when sterilizing these items. A preferred methodology for sharp instruments to be sterilized is also the ETO chamber, some of these sharp instruments like disposable knives are also made of plastic handles, which can withstand ETO temperatures but not the autoclave. These too need to be kept on a shelf for 15 days before use on human tissues. The I/A probes, the internal tubing, external tubing, rectal knibs are all cleaned with various disinfectants (Figs 12.17 to 12.26). The Operating Room Personnel Most often surgeons like to operate in the morning, sometimes they need to operate through the whole day, however, it is a good exercise to see that all operating area personnel have a regular bath first thing in the morning before entering the operating
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area. All street clothing and footwear should be removed before entering the operating area. Thus, most hospitals would keep the changing rooms as the first area of the operating area complex.
FIGURE 12.17 Flushing of I/A probe with 70 percent isoproppyl alcohol passing 200 ml of alcohol into every lumen
FIGURE 12.18 Flushing of the lumen of the internal tubing and the metal knobs with carbonic soap and mineral water passing 200 ml of the same into the lumen
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FIGURE 12.19 Flushing of the lumen of the internal tubing and the metal knobs with 2 percent glutaraldehyde passing 200 ml of the same into the lumen Footwear Separate areas should be demarcated to keep footwear. This should be kept outside the operating area complex. However, sometimes they could be kept just inside the door as we have seen many a surgeon goes in taking out his or her shoes and when he or she comes back his or her shoes are gone. This is
FIGURE 12.20 Flushing of the lumen of the internal tubing and the metal knobs with 70 percent isoproppyl alcohol passing 200 ml of alcohol into the lumen
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FIGURE 12.21 Flushing of the lumen of the internal tubing and the metal knobs with mineral water passing 200 ml of the same into the lumen specially true if he or she wears lovely expensive new shoes. The personnel take off their shoes and are given alternate operating area clogs, slippers or sandals. The operating area footwear should also undergo vigorous cleaning procedures everyday. At the end of the day, all the footwear is taken in and washed with soap water and cleansed with plain water and left for drying.
FIGURE 12.22 Flushing of the lumen of the external tubing with carbonic soap and mineral water passing 200 ml of the same into the lumen
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FIGURE 12.23 Flushing of the lumen of the external tubing with 2 percent glutaraldehyde passing 200 ml of the same into the lumen Clothing After changing the footwear all clothing needs to be changed. A changing room has to be kept clean and with lockers so that operating room personnel can keep their clothes and valuables safely. The most often used personnel clothing are pant with elasticated waist and shirts with loose necks so that they could be slided into. It is preferrable not to keep buttons and other such accessories on these
FIGURE 12.24 Flushing of the lumen of the external tubings with 70 percent isoproppyl alcohol passing 200 ml of alcohol into the lumen
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FIGURE 12.25 Flushing of the lumen of the external tubings with mineral water passing 200 ml of same into the lumen clothing as they would get damaged in the vigorous routine that these clothing should go through. After the operation theatre has finished for the day clothes from the personnel lockers are taken ideally into a washing machine and then through the dryer and sent for sealing and packing through ethylene oxide sterilization ready for use four days from the day of sterilization. Towards this rigmarole the hospital would need to keep six times the number of clothes actually required.
FIGURE 12.26 100 ml of Ringer lactate solution is passed through the
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lumen of the internal tubings, external tubings, I/A probe and metal knobs However, if this is not possible the clothes could be washed by hand dried and then sent into the autoclave for sterilization. In these clothes one is not really looking for sterility but for disinfection and thus it is better to go a step further and make them sterile before use. Cap and Mask The cap and mask need not be sterile, however they should be clean and disinfected. Ideally the cap and mask used can be of disposable variety since their cleaning will then not become necessary. However, if they are not and the hospital needs to use cloth cap and mask, they can go through the same cycle of events like the other clothing. The Patient The patient should also be made to go through a process to make him or her clean and disinfected. Ideally all patients should be told to have a bath before they go in for elective planned surgery. This simple process does give large benefits. Shaving where men are concerned is essential and removal of make-up is necessary where women are concerned. Change of Clothes The patient should change into operating room clothes and take out all street clothes. Footwear has to be removed before entering the operating room. Ideally patients are requested to remove all their clothing including undergarments and a patient gown given to them. This is done in the benefit of the patient so that at any particular time should an emergency procedure be called for it can be applied without interference from essential clothing. Moreover, all patients need to be monitored for their heart and blood oxygen these electrodes are usually placed close to the heart. However, in ophthalmic practice it is customary in a day care surgical center that the clothes need not come off the patient. Simple removal of shoes and shirt or dress is sufficient. Patients are then given sterile disposable gowns that can be worn over their undergarments. This process is found to be satisfactory for ophthalmic patients. All patients are also given a disposable cap so that all hair can be placed inside the cap and not interfere in surgical procedures. Skin and Incision Site Disinfection Many solutions are available for wound disinfection some of the best used worldwide are povidone-iodine and chlorhexidine gluconate 1.5 percent with cetrimide 7.5 percent. All these antiseptics will be put to better use if they are used in conjunction with simple cleaning procedures first. The patient’s face could be washed with soap and water and all jewellery and accessories removed. Once the patient lies down on the operating table and is ready for
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surgery, a scrubbed nurse paints povidone-iodine or any other antiseptic on the skin. This is removed with plain gauze. If anesthesia is necessary it can be given now after preliminary cleaning of the site. After injections are given the site to be operated is once again cleansed by a scrubbed personnel with antiseptic solution. Sterile Disposable Surgical Drape Where the eye is concerned, in todays world the lashes do not have to be cut for intraocular surgery. However, whenever this is not done, then a plastic surgical disposable sterile drape is used over the eyes. This has a gummy on the undersurface, keeping the eyes open the surgeon places the gummy directly on the cornea and keeps the lashes turned out so that they could stick to the gummy surface and keep out of the surgical field. The drape used in the ophthalmic field manufactured by Dr. Agarwal’s Pharma is also equipped with a drainage bag. So, once the drape is stuck to the patient’s eye, the central plastic over the palpebral fissure is cut open with sterile scissors after the surgeon has scrubbed and changed. A whole 20 cc of sterile refrigerated 4°C Ringer lactate fluid is squirted over the eye, to carryout a thorough cleaning procedure as well as to produce cryoanalgesia. The surgery can now be started. This cleaning process is found to be very necessary for a clean fornix and conjunctival sac. Sterilizers Methods of Sterilization For a very long-time we had no idea that sterilization is the basis of surgical correction, after all performing the best of surgery though introducing harmful microbes could mar the effects of surgery irreparably. With the advent of the autoclave in 1884 we got to know a lot of details. However, most surgical ward history can be detailed as that before Lister and the era after Lister as this one person was responsible in explaining antiseptic surgery as we understand it today. Terminology To better understand this vast and varied aspect of surgery, first let us understand the terms and conditions often used. Sterilization: is a process used to achieve sterility—an absolute term meaning the absence of all viable micro-organisms. Disinfection: is a process which reduces the number of contaminating microorganisms, particularly those liable to cause infection, to a level which is deemed no longer harmful to health. Antisepsis: is used to describe disinfection applied to living tissue such as a wound.
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Cleaning: is a soil-removing process which removes many microorganisms. The reduction in contamination by cleaning processes is difficult to quantify other than visually. Decontamination: is a general term for the treatment used to make equipment safe to handle and includes microbiological, chemical, radioactive and other contamination. Sterilization An article may be regarded as sterile if it can be demonstrated that there is a probability of less than I in a million of there being viable microorganisms on it. Methods Five main methods are used for sterilization. Head: A widely used method needs to reach temperatures above 100°C to ensure bacterial spores are killed. Moist heat is more effective than dry as it coagulates and denatures the protein, where water participates in the reaction. This requires 121°C for 15 minutes with moist heat. Temperatures above that of boiling water can be attained more easily by raising the pressure in a vessel, this is the principle of the autoclave. At sea level water would boil and produce steam at 100°C, increasing the pressure to 2.4 bar would produce steam at 125°C and increasing to 3 bar at 134°C. However, at subatmospheric pressures this temperature would fall, thus at higher altitudes water will boil at lower temperatures. 1. Quality of steam for sterilization: Steam is non-toxic and non-corrosive, though for sterilization it should also be saturated, which means it should hold all the water it can hold. It must also be dry, so it should not contain water droplets. This has a greater lethal action and is quicker in heating up the article to be sterilized. When dry saturated steam meets a cooler surface it condenses into a small amount of water and liberates latent heat of vaporization. The energy available from this latent heat is considerable. For example, 6 liters of steam at a temperature of 134°C will condense into 10 ml of water and liberate 2162 J of heat energy. By comparison less than 100 J of heat energy is released by the sensible heat from air at 134°C to an article in contact with dry heat. Steam at a higher temperature than the corresponding pressure would allow is referred to as superheated steam and behaves like hot air. Steam with water droplets is called wet steam and is less efficient. 2. Types of steam sterilizers A. Sterilizers for porous loads: For linen, and wrapped instruments, so air could get trapped in the textiles used. Thus, this type of sterilizer should have a vacuum-assisted air removal stage to ensure that adequate air is removed from the load before admission of steam. The vacuum pulsing of air also ensures that the load is dry on completion of cycle. B. Sterilizers for fluids in sealed containers: Must have a safety feature to ensure that the door cannot be opened till the temperature in the glass containers has fallen below 80°C. Otherwise the thermal stress of cold air on opening the door may cause the bottles to explode under pressure. C. Sterilizers for unwrapped instruments and utensils: These should not be used for wrapped articles, recommended for dental clinics and LASIK stations.
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D. Laboratory sterilizers: Culture media in containers, laboratory glassware and equipment may be contaminated, thus proper cleansing is necessary before sterilization. 3. Monitoring of steam sterilizers: Every load everyday every time needs monitoring of some important physical measurements. • Temperature • Pressure • Time with thermometers. Detailed tests are undertaken with temperature-sensitive probes (thermocouples) inserted into standard test packs. Though most indicators show color change on reaching particular temperatures. Biological indicators comprising dried spore suspensions of a reference heat-resistant bacterium Bacillus stearothermopiles, are not used for routine testing. Although spore indicators are essential for low-temperature gaseous processes in which the physical measurements are very little to kill spores or not reliable. Most often used for ethylene oxide sterilization. Bowie-Dick test monitors penetration of steam into wrapped pack and detects uneven steam penetration by a bubble of residual air in the pack. Dry heat causes a destructive oxidation of the essential cell constituents. Thus, killing spores here requires 160°C for 2 hours. This may also cause charring of paper, cotton, organic material. 4. Types of sterilization by dry heat A. Incineration: Most cities around the world have made it mandatory for most hospitals to have incinerators in their campus for efficient waste disposal where contaminated materials like dressings, sharp needles and other clinical wastes. The high temperature reached kills all organisms and disposes by charring and burning the material. B. Red heat: Diathermy in ophthalmic hospitals would be done by burning a loop over a flame, this would sterilize as well as cauterize the bleeding vessel. However, this is still used to sterile loops, wires, points of forceps. It is a still very much used in emergency situations. C. Flaming: Inoculating loops and needles are sometimes treated by immersing them in methylated spirit and burning off the alcohol, though this does not produce a sufficiently high temperature for sterilization. This is also done for sterilizing drums and trays over which sterile linen is placed. Once again this is not totally sterile as spores may persist over the short-term flame that is produced with alcohol. D. Hot and sterilizer: Oil, powders, carbon steel instruments, and empty glassware and laboratory dishes are sterilized with hot air sterilizers, though the over-all heating up and cooling may take several hours. E. Microwave sterilizer: This is the latest in roads into sterilizers and can offer better results than hot air sterilizers with shorter time spans. Within 10 minutes the material can be sterilized. However, because of the high temperatures reached it is not very good for organic material or plastics. Very good for microwave transparent material like glass.
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5. Factors influencing sterilization by heat would include: A. Temperature and time: They are inversely related, i.e. shorter time higher temperatures, holding time is important loading and cooling time would make the total time much longer (Table 12.1).
TABLE 12.1 Relationship between temperature and time Process Temp (in°C) Hold time (min) Dry heat 160 170 180 Moist heat 121 126 134
120 60 30 15 10 3
B. Microbial load: The number of organisms and spores affects the rapidity of sterilization. Thus, it is better to go through vigorous cleaning procedures before sterilization of products. Ionizing radiation: Both beta (electrons) and gamma (photons) irradiation are employed industrially for the sterilization of single use disposables. All accelerated electrons are lethal to living cells, that includes, γ-rays, β-rays, X-rays. Bacterial spores are the most resistant. Sterilization is achieved by the use of high-speed electrons from a machine such as a linear accelerator or by an isotope source such as cobalt-60, a dose of 255 kGy is generally adequate, making this an industrial process. It is used for single use prepackaged items like plastic syringes and catheters. Filtration: Filters are used to remove bacteria and other larger organisms from liquids that are liable to be spoiled by heating. Though virus can crossover they are felt to be unimportant. Filters using pore size of less than 0.45 microns can render fluids free of bacteria. It is used in the preparation of toxins and thermolabile parenteral fluids such as antibiotic solutions, radiopharmaceuticals, and blood products. Viruses and some bacteria like mycoplasmas can pass through pore size of less than 0.22 microns. Filter materials could be unglazed ceramic Chamberland filters, asbestos Seitz filters and sintered glass filters. Though now membrane filters are usually used made of cellulose esters or other polymers. Sterilant gases: Ethylene oxide is used for sterilization of plastics and other thermolabile material. Formaldehyde in combination with subatmospheric steam is more commonly used in hospitals for reprocessing thermolabile equipment. Both processes are toxic and carry hazards to user and patient. 1. Ethylene oxide: Highly penetrative, non-corrosive and microcidal gas which is used to in industry for single use, heat-sensitive medical devices such as prosthetic heart valves and plastic catheters. Ethylene oxide sterilization is usually carried out at temperatures below 60°C in conditions of high relative humidity. To ensure sterility, material should be exposed to a gas concentration of 700 to 1000 mg/1 at 45 to 60°C and a relative humidity above 70 percent for about 2 hours. Care must be taken because of
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toxicity to personnel, flammability and explosion risk. The sterilized product must be aerated to remove residual ethylene oxide before it can be safely used on the patient, and turn round time is consequently slow. Some recommendations for boosting infection control as well as cut costs on EO sterilization: • Cleaning is a necessary and important activity before sterilization. I feel that you need to adopt standardized and effective cleaning method. • Further the items cleaned have to be dried as any wet item will react with ethylene oxide and the efficacy may be reduced. • The items have to be packed in one of the three materials: linen, paper or plastic. Each has its advantage but the limitation is the period that you can store these sterilized items. You can use plastic bags which are of a proper grade and store the product upto one year after sterilization. • The sealer used for sealing packs is inappropriate if the heating is too weak for the packaging material used. This results in small holes in pack after sealing. An impulse heat sealer capable of sealing at higher temperatures. • A safe EO machine which can complete the process of aeration within all items can be used directly without any further handling. • Aeration is a natural process which can be hastened by installing an aerator. 2. Low temperature steam and formaldehyde: A combination process of steam generated at subatmospheric pressure 70 to 80°C and formaldehyde gives an effective sporicidal process. It is appropriate for heat-sensitive articles that can resist temperatures of 80°C 3. Propylene oxide: One of the latest and new techniques is the use of propylene oxide which is a microcidal gas. It has a similar use and toxic effect like propylene oxide. Sterilant liquids: Glutaraldehyde is generally the least effective and most unreliable method. Disinfection Disinfection is applied in circumstances where sterility is unnecessary or impractical, like bed-pans, eating utensils, bed linen and other such items. Similarly, the skin around the site for an invasive procedure should be cleansed to reduce chances of wound infection. Cleaning Thorough cleaning is a prerequisite for successful disinfection and is a process of disinfection by itself. This can be enhanced by ultrasonic baths given to the instruments to remove dried debris. Methods Heat: Steam or water could be used. 1. Moist heat is the first method of choice, can be precisely controlled, leaves no toxic residues and does not promote the development of resistant strains. Washing or rinsing laundry or eating utensils in water at 70 to 80°C for a few minutes will kill most non-
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sporing microorganisms present. Similarly, steam maintained at subatmospheric pressure at 73°C is used in low temperature steam disinfectors in hospitals to disinfect thermolabile reusable equipment. 2. Boiling: Exposure to boiling water for 20 minutes achieves highly effective disinfection, although this is not a sterilization process it can be useful in emergencies if no sterilizer is available. Ultraviolet radiation: It has limited application for disinfection of surfaces, some piped water supplies but lacks penetrative power, however newer modifications in use with ozone treatment plants is very effective in disinfection. This is a low-energy, non-iodising radiation with poor penetrating power that is lethal to microorganisms under optimum conditions. The shorter UV rays that reach the earth’s surface in quantity have a wavelength of about 290 nm, but even more effective radiation of 240 to 280 nm is produced by mercury lamps. It is used in the treatment of water, air, thin films and surfaces such as laboratory safety cabinets. Gases: Formaldehyde is used as a fumigant though it does not have an all pervasive effect. Traditionally formaldehyde gas was used to disinfect rooms previously occupied by patients with contagious diseases such as smallpox. It is still used for disinfection of heat-sensitive equipment, however its efficacy is questionable with better products like Bacillocid available. Filtration: Air and water supplied to operation theatres and other critical environments are filtered to remove hazardous microorganisms, though viruses cannot remain out altogether. However, they are considered harmless in these environments. A properly installed high efficiency particulate air (HEPA) filter achieves 99.9 percent or better resistance to particles of 0.5 microns and can produce sterile air at the filter face. Chemical: Several chemicals with antimicrobial properties are used as disinfectants. Antiseptic can be regarded as a special kind of disinfectant which is sufficiently free from injurious effects to be applied on the surface of the body, though not suitable for systemic or oral administration. Some would restrict the use of antiseptic preparations applied to open wounds or abraded tissue and would use the word skin disinfection for removal of organisms from hands and intact skin surfaces. 1. Factors influencing the performance of chemical disinfectants: A. The concentration of the disinfectant: The optimum concentration required to produce a standardized microbial effect in practice is described as the in-use concentration. Care must be taken in preparing accurate in-use concentrations while diluting product. Accidental or arbitrary over dilution may result in failure of disinfection. B. The number, type and location of microorganism: The velocity of the reaction depends upon the number and type of organisms present. In general gram-positive bacteria are more sensitive to disinfection than gram-negative bacteria. Mycobacteria and fungus are resistant while spores are highly resistant, while viruses are susceptible. Glutaraldehyde is highly active against bacteria, viruses and spores. Other disinfectants such as hexachlorophene have a relatively narrow range of activity, predominantly against gram-positive cocci.
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C. The temperature and pH: Some disinfectants are more active or stable at a particular pH. Though glutaraldehyde is more stable under acidic conditions its microbial effect is seen better when the pH is 8.0 D. The presence of organic or other interfering substances: Disinfectants can be inactivated by hard tapwater, cork, plastics, blood, urine, soaps and detergents, or other disinfectants. Information should be sought from the manufacturer or from reference authorities to confirm that the disinfectant will remain active in these circumstances. 2. Common chemicals in use: A. Alcohols: Isopropanol, ethanol, and industrial methylated spirit have optimal bactericidal activity in aqueous solution at concentrations of 70 to 90 percent and have little bactericidal effect outside this range. They have limited activity against mycobacteria and are not sporicidal. Action against viruses is generally good. Because they are volatile, alchohols are recommended as rapidly drying disinfectants for skin and surfaces. However, they may not achieve adequate penetration and kill, particularly if organic matter such as blood or other protein-based contamination is present. Alcohols are suitable for physically clean surfaces such as washed thermometers or trolley tops but not for dirty surfaces. Care must be taken when used on the skin in conjunction with diathermy and other instances of flammable risk. Alcohols with chlorhexidine or povidone-iodine are good choices for hand disinfection, they are applied to the dry skin often with added emollient to counteract the drying effect. B. Aldehydes: Most aldehyde disinfectants are based on glutaraldehyde or formaldehyde formulations, alone or in combination. Glutaraldehyde has a broad spectrum action against vegetative bacteria, fungi, viruses, but acts more slowly against spores. It is often for equipment such as endoscopes that cannot be sterilized or disinfected by heat. It is an irritant to the eyes, skin and respiratory mucosa, and must be used with adequate protection of staff and ventilation of the working environment. It must be thoroughly rinsed after treated equipment with sterile water to avoid carry-over of toxic residues and recontamination. The alkaline buffered solution is claimed to remain active for several days, but this will vary depending on the in-use situation, including the amount of organic material. C. Biguanides (chlorhexidine): This is commonly used for disinfection of skin and mucous membranes. It is less active against gram-negative bacteria such as Pseudomonas and Proteus sp and in aqueous solution has limited virucidal, tuberculocidal and negligible sporicidal activity. It is often combined with a compatible detergent for handwashing or with alcohol as a handrub. Chlorhexidine has low irritancy and toxicity and is effective even on exposed healing surfaces. It is inactivated by organic matter, soap, anionic detergents, hard water and some natural materials such as cork liners or bottle closures. D. Halogens (hypochlorites): These broad-spectrum inexpensive chlorine-releasing disinfectants are that of choice against viruses. For heavy spillage such as blood, a concentration of 10,000 ppm of available chlorine is recommended. These are inactivated by organic matter and corrode metals, so that contact with metallic instruments and equipment should be avoided. The bleaching action of
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hypochlorites may have a detrimental effect on fabrics and should not be used on carpets. Chlorine-releasing disinfectants are relatively stable in concentrated form as liquid bleach of as tablets (sodium dichloroisocyanurates) but should be stored in well-sealed containers in a cool dark place. On dilution to the required concentration for use, activity is rapidly lost. Hypochlorites have widespread application as laboratory disinfectants on bench surfaces and in discard pots. Care should be taken to remove all chlorinereleasing agents from laboratory areas before the use of formaldehyde fumigation to avoid the production of carcinogenic reaction products. Iodine: Like chlorine, iodine is inactivated by organic matter and has the additional disadvantage of staining and hypersensitivity. The iodophors which contain iodine complexed with an anionic detergent of povidone-iodine a water-soluble complex of iodine, polyvinyl and pyrrolidone are less irritant and cause less staining. Aqueous and alcohol-based povidone-iodine preparations are used widely for skin and ocular disinfection as well as other mucous membrane disinfection. E. Phenolics: These have been widely used as general purpose environmental disinfectants in hospital and laboratory practice. They exhibit broad-spectrum activity and are relatively cheap. Clear soluble phenolics have been used to disinfect environmental surfaces and spillages if organic soil and transmissible pathogens may have been present. As hospital disinfection policies are rationalized, phenolics are being replaced by detergents for cleaning and by hypochlorites for disinfection. Most phenolics are stable and not readily inactivated by organic matter, with the exception of the chloroxylenos (Dettol) which are also inactivated by hard water and not recommended for hospital use. Phenolics are incompatible with cationic detergents. Contact should be avoided with rubber and plastics, such as mattress covers, since they are absorbed and may increase the permeability of the material to body fluids. The slow release of phenol fumes in closed environments and the need to avoid skin contact are other reasons for care in use of phenolics. The bis-phenol hexachlorophane has particular activity against gram-positive cocci, and has been used in powder or emulsion formulations as a skin disinfectant, notably for prophylaxis against staphylococcal infection in nurseries. There has been some concern about the possible toxic effect of absorption across the neonatal skin barrier on repeated exposure. An alternative, which has been used in the control of methicillin-resistant Staphylococcus aureus outbreaks is triclosan. F. Oxidizing agents and hydrogen peroxide: Various agents, including chlorine dioxide, peracetic acid and hydrogen peroxide, have good antimicrobial properties but are corrosive to skin and metals. Hydrogen peroxide is highly reactive and has limited application for the treatment of wounds. G. Surface active agents: Anionic, cationic, non-ionic and amphoteric detergents are generally used as cleaning agents. The cationic (quaternary ammonium compounds) and amphoteric agents have limited antimicrobial activity against vegetative bacteria and some viruses but not mycobacteria or bacterial spores. Quaternary ammonium compounds disrupt the membrane of microorganisms, leading to cell lysis. Care must be taken to avoid overgrowth by gram-negative contaminants and inactivation by
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mixing cationic and anionic agents. Disinfection may be enhanced by appropriate combination of a surface active agent with disinfectant to improve contact spread and cleansing properties. Quality Control Every method used must be validated to demonstrate microbial kill. With heat and irradiation a biological test may not be required if the physical conditions can be proved to have reached their ultimate design. D value The D value or the decimal reduction value is the dose that is required to inactivate 90 percent of the initial population. When the time required or the dose required to reduce the population from 1000000 to 100000 is the same as the time or dose required to reduce the population from 100000 to 10000 the D value remains constant over the full range of the survivor curve. Extending treatment beyond the point where there is one surviving cell does not give rise to fractions of a surviving cell but rather to a statement of the probability of finding one survivor. Thus, by extrapolation from the experimental date it is possible to determine the lethal dose required to give a probability of less than 1 in 1000000 which is required to meet the pharmacopoeial definition of sterile. Factors Influencing Resistance Many factors affect the ability of the microorganism to withstand lethal procedures of sterilization. This in fact is the reason why we need to keep updating ourselves as to the methods of sterilization and their efficacies. This also happens to be the reason why living creatures are able to withstand high amounts of torture only to make sure their breed lives on. Bacteria are not that much different from us in this intrinsic need to propagate, grow and leave their legacy behind. Still we need to be on top of them to allow them to grow where we need them and the operating room is definitely not a place we need any of them at all. Here are some of the reasons why these bacteria do withstand our torture. Species or strain of microorganism As usual the spores are more resistant than vegetative bacteria or viruses. Though some strains of species have wide variations. Enterobacteriaceae D values at 60°C range from a few minutes (E. coli) to 1 hour (Salmonella senftenberg). The typical D value for Staphylococcus aureus at 70°C is less than I min compared with 3 min for Staph. epidermidis. However, an unusual strain of Staph. aureus has been isolated with a D value of 14 min at 70°C. Such variable could be attributed to the morphological and physiological changes such as alterations in cell proteins or specific targets in the cell envelope affecting permeability. Thus, we should not understand the inactivation data for one disease forming organism would withstand by another. Creutzfeldt-Jakob disease is a highly resistant agent requiring six times the normal heat sterilization cycle (134°C for 18 minutes). Physiological stage Organisms grown under nutrient-limiting conditions are typically more resistant than those grown under nutrient-rich conditions. Resistance usually increases through the late logarithmic phase of growth of vegetative cells and declines erratically during the stationery phase.
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Ability to form spores Bacterial endospores are more resistant than fungal spores, some of them are used as bacterial indicators especially for ethylene oxide sterilizers to monitor their efficacy. Disinfection has no efficacy where spores are concerned. Suspending menstrum Microorganisms occluded in salt have greatly enhanced resistance to ethylene oxide, the presence of blood or other organic material will reduce the effectiveness of hypochlorite solution. Thus, suspended particles will alter efficacy of various techniques. Number of microorganisms Quite obviously the initial “bio-burden” the more extensive must the process of sterilization be to achieve the same assurance of sterility. Sterilization and Disinfection Policy All hospitals should go through a rigmarole of infection control and agree on a particular policy to be followed uniformly by all concerned in this infection control team. This should be headed by the chief surgeon and each one must report to the leader of the team everyday. It has been noticed over centuries of medical practice when a surgical team gets to do routine surgeries everyday for many days and years, a kind of apathy sets into the system and somewhere someone lapses. These instances have been the most common cause for infection. To avoid such lapses the infection control team should meet each week to update themselves on the latest happenings in their hospital and to bring to the notice such lapses so that a tightening of procedures can be applied. At each lapse the chief surgeon must be held responsible for the actions of his or her team. All members of the team must familiarize themselves with the items to be sterilized and the chemicals necessary to do so. A microbiologist should be included in this team as they alone can monitor the efficacy of the said processes. Along with should also be a pharmaceutical person who has full knowledge of the various chemicals used, their action and the efficiency in said matters. It is very instrumental to include these persons on the infection control team of a hospital. The hospital policy should be common and should include: • The sources to be sterilized (equipment, skin, environment, air, water, personnel) for which a choice of process is required to be commonly accepted by the team for infection control. • The processes and products available for sterilization and disinfection must be made available for all to see and inspect. An effective policy may include a limited number of process options, restrictions on the range of chemical disinfectants eliminate unnecessary costs, confusion and chemical hazards. • The category of process required for each item, sterilization for surgical instruments and needles, heat disinfection for laundry, crockery, bed-pans, cleaning of floors, walls, furniture and fixtures. • The specific products and method to be used for each item of equipment, the site of use and the staff responsible for the procedure. These should all be earmarked in a record so that one can get back to the lapse when it happens.
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Effective implementation of the policy requires liaison and training of staff and updating the policy. Safety considerations for staff and patients require a careful assessment of specific procedures to minimize risks. The staff for implementation of these processes must wear protective gear where necessary. Gloves, aprons, caps and masks must be included in the policy. Where dangerous gases are used eye goggles similar to swim goggles can be used to protect the eyes from the noxious gases. For proper sterilization control, it is important to go back into every case that gets infected to try and pry and find out what was the reason for the infection. This can effectively be done by the weekly meeting of the infection control team where everyone tries to pitch in their inputs. Staff should not be penalized for accepting their wrong-doings, because if they are penalized they will not accept the cause of the infection next time it occurs. The staff should be goaded into performing better by putting the patients best interests in view and not for witch hunting and blaming. Culture Rate The most important mechanism for the proper functioning of an operation theatre is the fact that no organism should grow from this area. To find out whether an organism is growing or not we need to make sure it is present or not, that can effectively be done by growing it on a culture media. Some of the most common culture media used in hospitals is discussed here. MacConkey’s Agar To make this culture plate (Fig. 12.27) is simple enough. According to directions 51.5 gm of the powder made available through Himedia Laboratories is dissolved in 1000 ml of distilled water. This is allowed to boil till the powder is completely dissolved and the fluid has boiled for over 15 minutes, thus sterilizing the fluid further. It could be still sterilized by autoclaving though most hospitals find 15 minutes of boiling to suffice in its sterilization. This culture medium contains: Peptic digest of animal tissue 17 gm/lit Peptone 3 Lactose 10 Bile salts 1.5 Sodium chloride 5 Neutral red 0.03 Agar 15 At a final pH at 25°C of 7.1
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FIGURE 12.27 MacConkey’s blood agar culture plates Alternately if the readymade powder is not available then the following procedure can be applied to the above-mentioned ingredients. Base solution Dissolve agar in 500 ml of distilled water by autoclaving at 121°C for 20 minutes. Dissolve the peptone, bile salts and sodium chloride in the remaining 500 ml of distilled water, and bring the solution to boil. Combine the two solutions mixing thoroughly. Dissolve the lactose and adjust the pH to 7.2. Distribute in screw-capped bottles and sterilize with autoclaving at 121°C for 15 minutes. Dissolve 1 gm of neutral red in distilled water and make-up the volume to 100 ml. Heat the solution in steam at 100°C for 30 minutes. Dissolve 0.1 gm of crystal violet in distilled water and make-up the volume to 100 ml. Heat the solution in steam at 100°C for 30 minutes. To 200 ml of the base solution, melted and cooled to about 60°C add aseptically 0.6 ml of the neutral red solution and 0.2 ml of solution with crystal violet. Mix well and distribute into sterile Petri dishes.
FIGURE 12.28 Culture specimen taken using sterile swab stick from the instrument table
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Incubate the plates at 37°C for 24 hours (Figs 12.28 to 12.30) and examine for contamination. Inoculate four plates from the following stock culture Salmonella typhi, Escherichia coli, a mixture of Salmonella typhi and E. coli and Shigella flexneri.
FIGURE 12.29 Culture specimen taken using sterile swab stick from the operation table head rest This will prove the efficacy of the culture media prepared and now it can be poured into petri dishes and refrigerated to be used on need for culture plates. It is advisable to keep them for 24 to 48 hours and to keep making fresh batches very often. Nutrient Agar A general purpose medium for the cultication of microorganisms and a base for enriched or special purpose media. It can be made very simply by the
FIGURE 12.30 Culture specimen taken using sterile swab stick being
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streaked on the MacConkey’s blood agar culture plate powder available from Himedia laboratories by dissolving 28 gm of powder in 1000 ml of distilled water and boiling for 15 minutes. This would also sterilize the medium and it is ready for use after cooling. The powder contains: Peptic digest of animal tissue 5 gms/lit Sodium chloride 5 Beef extract 1.5 Yeast extract 1.5 Agar 15 At 25°C the pH is 7.4.
Alternately if the powder is not available the separate entities can be taken, mixed and steamed for 2 hours. The pH should be adjusted first to 6.8 then clear the fluid with egg albumin. Filter and bottle. Autoclave at 15 lbs pressure for 20 minutes or steaming for 30 minutes each day on three successive days. Blood Agar An enriched medium for general use in routine cultivation of the more delicate microorganisms like Neisseria meningitidis, N. gonorrhoeae and Diplococcus pneumoniae. The medium also serves as an indicator of hemolysin production by bacteria. It is very simple to make. Add 6 to 10 percent defibrinated blood to melted nutrient agar and cool to 45 to 60°C. Pour plate or slant, incubate 24 hours to prove sterility. Sterilization Control The infection control team which consists of a microbiologist must take regular samples from the different areas sterilized or disinfected. Some of the quality checks necessary to be carried out are: Plate Test One of the easiest to perform and tells us quite a bit about the cleaning tactics used for the particular room. This test would not be so effective in open areas but is quite reliable for closed areas like operating rooms. For closed rooms Where operating rooms are concerned once we have assured ourselves there is no contaminated air coming in, with door closers, air curtains and filtered airconditioned ducting, cleaning the room with detergents and disinfectants should clear the air of all bacteria. However, this does not remain so through out the day, and it is noticed that after a few surgeries due to human beings inside the operating rooms bacteria do escape to contaminate the air. This can be effectively controlled by keeping a watch on
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the cleaning procedures and making sure a disinfectant mop is used after every procedure and on every item of the operating room. However, testing for the efficacy of the cleaning procedures is devised by the PLATE TEST. Here a sterile bowl is used with sterile water and kept in the concerned room for 20 minutes. Should there be bacteria in the room they would settle down on the surface of the bowl of water. Thus, skimming the surface a few drops are taken and placed on a Petri dish with culture media on it. This is incubated at 38°C for 48 hours and if this grows bacteria then we know our disinfectant procedures were not enough and we need to plough ourselves further. If it is negative then we can proceed with the same policy. This test should be ideally carried out everyday, before every procedure in every room of the operating area. For open areas Lounges where patients wait or the outside arenas are to be cleansed as well, if we would like to have a tight infection control in the operating area. After all these areas lead to the operating area—the most pious sanctum sanctorum of the hospital edifice. The plate test is carried out everyday every few hours, and an optimum time interval given to the hospital authorities where it can be stated that every four hours the hospital lounges should be cleaned with disinfectant to maintain a clean bacteria-free atmosphere. This can now be controlled by taking plate test samples every four hours before cleaning procedures are done and making sure the tests remain negative for growth in all the tests taken. If not the program needs to be revised and the hours shortened. This test should also be carried out in the consultation areas and optimum time intervals for cleaning prescribed by the microbiologist on the infection control team. Culture Test from Walls, Floor, Fixtures and Furnitures Everyday the different areas should be taken for culture, it is advised to take eight different areas for culture from every room everyday. Methodology for taking culture is to take a moist swab, by dipping a cotton tip applicator in sterile water and rubbing it in a streak fashion on the culture plate. The culture plates are made in Petri dishes about 3 inches in diameter. The back surface of the Petri dish can be stroked with a marker pen and each culture plate divided into eight parts. One culture plate can be ear marked for each room, and 8 objects from the room can be cultured. It is preferrable to always include the floor, of the room however different parts of the floor can be taken each day to ensure proper cleaning and disinfectant use. Other objects that can and should be cultured for are the fans, air conditioners, lights, walls, tables, chairs, stools and all the equipment present in that particular room. Like Boyles apparatus, phaco machines, etc. All Fluids to be Cultured All fluids used in the operating room must be sent for culture tests, sometimes this becomes less possible as the fluid is too little and necessary for parenteral application. However, every batch of fluids used can be sent for culture tests. This may not grow
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positive however its not growing positive itself is an indication of the efficacy of the program. This sets aside any debate that the fluid may have contained bacteria. Of special importance is fluids used for intraocular use, or for intravenous use. As soon as each IV bottle is opened the first few drops from the IV set can be placed on a culture plate for incubation. Many eye surgeons from our subcontinent have grown E. coli from the Ringer lactate used intraocularly. However, most often this has happened after a tragedy of multiple eyes have succumbed to post-cataract surgery infection. Thus, by performing this simple step we may be able to thwart further mishaps. Should any one batch of fluids be found to be positive it is a good idea to report the matter so that others can be forewarned and to take every bottle from that batch. All Fluids used Parenterally to be Checked for pH Value Great importance should be given to the pH of fluids inside the body especially where the eye is concerned. We presume that all fluids marked for parenteral or intraocular use come at the pH close to 7.4, however, it is alarming to note the amount of times I have personally seen surgery go wary only due to the fact that the pH was either 5.6 or above 8. This can produce havock on the patient’s cornea. In 1992, over 300 cases were reported lost due to hazy opaque corneas following extracapsular cataract surgery in some states of India. This was followed by a widespread search for the culprit. What was found was alarming to all concerned, a balanced salt solution (BSS) was sold in small bottles. It was learned that this solution carried an alkaline pH, because while cleaning the glass bottles the last rinse of soap solution (BSS) was not totally washed out and the remaining soap solution left behind an alkaline pH which recked havoc on the cornea producing total blindness. It took the investigating authorities over six months to procure this data and cause by which time multiple surgeries had been carried out with much devastation. A simple technology to avoid such future catastrophies is to check out the pH on table before the surgery. A few drops of the fluid can be dropped on a simple litmus strip and one minute later the color change noted with a rough estimate of the pH value noted. This should be ideally carried out for all cases. Specialized Equipment Cultures Special tests are performed for special machines, like the one available for the ethylene oxide sterilizer. Biological chemical indicator One or more biological chemical indicator can be placed in the steam or ethylene oxide test packs and the process passed through the sterilization cycles. If used to monitor a 270°F steam “flash” cycle, place a wire mesh bottom instrument tray and then proceed. After sterilization processing has been completed, allow the biological chemical indicator to cool until safe to handle and open. Remove the indicators and allow to cool an additional 10 to 15 minutes. Observe chemical process exposure indicator on vial label to verify color change corresponding to sterilization cycle, i.e. ethylene oxide turns gas process indicator to gold and steam turns the steam process indicator to brown.
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If chemical process indicator is unchanged, exposure to the sterilization process may not have occurred. Check the sterilization process. If the chemical process exposure indicator on the vial label did change to the proper color and the indicator has cooled to touch, firmly seal the biological indicator by pushing the cap to close till the cap reaches second blue bar on the vial label. Crush the inner ampule from the outside wall of the plastic vial to ensure that the growth medium is released from the crushed ampoule and is in contact with the spore disk. Place the activated indicators in an incubator and incubate it at 37°C for EO sterilization and 55°C for steam sterilization. If there is a color change in the medium from deep blue to bright yellow and turbidity is evident, it means there is a positive growth. Indicators positive for growth will often be evident prior to maximum recommended incubation time, but indicators not evidencing growth mtiust be allowed to incubate for at least 24 hours (steam) and 48 hours (ethylene oxide) to assure confidence in the negative reading. When, where and why to use biologicals When? • Once a day in every sterilizer • Once a week in steam sterilizer cycle used • Every steam load with implants • Every EO load. Three consecutive times before using new sterilizer and after repairs. Where? All sterilization processes. why? • To challenge your sterilizer’s effectiveness • To assure load sterilization parameters were up to standard. Surgeons Hands Cultured Right after scrubbing and ready for operation a surgeon’s hands should be regularly swabbed and taken for culture so that a close check can be carried out to the efficacy of the cleaning and scrubbing solutions. There are many surgeons who believe in different technologies of scrubbing. While some would swear with the pounding away of epithelial tissue by a brush others would want to keep the epithelium intact at all times. While some would swear with a last dip into alcohol, others would keep alcohol well out of the way of surgeon’s hands. However, it has been seen that three times to lather with soap and wash hands is a uniform tendency of most surgeons.
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Linen and Textiles Cultured Efficacy of sterilization on the different linens and textiles used in surgery should be tested by taking culture tests from these items just after surgery.
13 Local Anesthetic Agents Ashok Garg Introduction In modern ophthalmology with the preponderance of elderly patients (due to increased life expectancy) and the move towards high-tech outpatient surgical care, there is a growing emphasis and need of local anesthesia Local anesthesia is the lifeline of modern ophthalmic surgery and is safer and should always be used unless there are specific indications for general anesthesia. Local anesthesia in the eye may be achieved by topical application of anesthetic drops or by infiltration of the sensory nerves with anesthetic solution (injectables). Local Anesthetics (Injectables) Local anesthetics prevent the generation and conduction of nerve impulses by reducing sodium permeability increasing the electrical excitation threshold, slowing the nerve impulses propagation, and reducing the rate of rise of the action potential. Indications Local injectable anesthetics are indicated for infiltration anesthesia in any kind of intraocular surgery. Contraindications Hypersensitivity to local anesthetics, para-amino benzoic acid or parabens. Do not use large doses of local anesthetics in patients with heart block. Precautions during Local Injectable Anesthesia • Use local anesthetic with caution when there is inflammation or sepsis in the region of proposed injection. • Monitor cardiovascular respiratory vital signs and state of consciousness after each injection. • Local anesthetic should be injected with great care in debilitated or elderly patients, acutely ill patients, children and patients with increased intraabdominal pressure or patients with severe shock or heart block.
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• Many drugs used during local anesthesia are considered potential triggering agents for familial malignant hyperthermia, hence the arrangement for supplemental general anesthesia should be there. • Use solutions containing a vasoconstrictor with great caution in patients with history of hypertension, peripheral vascular disease, arteriosclerotic heart disease, cerebral vascular insufficiency, heart block, thyrotoxicosis, diabetes. These patients may exhibit exaggerated vasoconstrictor response. • Watch for hypersensitivity reactions including anaphylaxis to any component of local anesthetics. • Administer ester type local anesthetics cautiously to patients with abnormal or reduced levels of plasma esterases. • Some of these anesthetic products contain sulfites which may cause allergic type reactions in certain susceptible patients. Although prevalence of sulfite sensitivity is low. • Use amide type local anesthetics with care in patients with impaired hepatic function. • Use local anesthetics with caution in patients with renal disease. • Exercise caution regarding toxic equivalence when mixtures of local anesthetics are employed. • Do not use disinfecting agents containing heavy metals for skin (periorbital area) disinfection. • Do not use local anesthetics in any condition in which a sulfonamide drug is employed. • Patients should be asked to avoid touching or rubbing the eye until the anesthesia is worn off. Adverse Reactions of Local Injectable Anesthetics The most common acute adverse reactions are related to the CNS and cardiovascular systems. These are generally dose related and may result from rapid absorption from the injection site, from diminished tolerance or from unintentional intravascular injections. CNS Adverse Reactions Restlessness, anxiety, dizziness, tinnitus, blurred vision, tremors, convulsions, nausea, vomiting, chills, pupil constriction, excitement may be transient or absent. Depressive effects These may or may not be preceded by the excitatory symptoms. These are: drowsiness, sedation, generalized CNS depression, unconsciousness, coma, apnea and respiratory depression and even death from respiratory arrest. Cardiovascular Symptoms of Toxicity • Peripheral vasodilation • Hypertension and tachycardia • Decreased cardiac output • Hypotension • Bradycardia • Methemoglobinemia
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• Heart block, ventricular arrhythmias • Circulatory collapse. Allergic Adverse Reactions • Cutaneous lesions of late onset • Erythema, angioneurotic edema • Sneezing, syncope • Excessive sweating • Elevated temperature and anaphylactoid symptoms. Overdosage Acute emergencies from local injectable anesthetics are generally related to high plasma levels encountered during therapeutic use or to unintended injection overdosage can lead to • Convulsions, apnea and under ventilation • Circulatory depression. If not treated promptly, convulsions and cardiovascular depression can result in hypoxia, acidosis, bradycardia, arrhythmias and cardiac arrest. Various local injectable anesthetics used in ophthalmology are classified as follows. Esters • Procaine • Chloroprocaine • Tetracaine Amides • Lidocaine • Prilocaine • Mepivacaine • Bupivacaine • Etidocaine • Centbucridine Individual drug monographs are described as follows. Esters Procaine Procaine is paraaminobenzoic acid ester of diethylaminoethanol. It was first prepared in 1905. The chemical structure is depicted in Figure 13.1
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FIGURE 13.1 Chemical structure of procaine Indication Procaine is used for infiltration anesthesia prior to any intraocular surgery. It is not used topically. Dosage Procaine is available as 1 percent (2 ml) ampoules. It has rapid onset of action (2–5 minutes) with an average duration of action one hour. Concentration of 0.5 to 2 percent are used with a maximum dose of 14 mg/kg body weight. Detoxification occurs by hydrolysis to para-amino benoic acid and diethylaminoethanol through the enzyme pseudocholinesterase in the plasma. Solution for infiltration anesthesia is freshly prepared. To prepare 60 ml of 0.5 percent solution (5 mg/ml) dilute 30 ml of 1 percent solution with 30 ml sterile distilled water. Add 0.5 to 1 ml of epinephrine (1:1000 per 100 ml) anesthetic solution for vasoconstrictive effect (1:200000 to 1:100000). Precautions and adverse reactions have already been described in general monograph section of local injectable anesthetics. Chloroprocaine Chloroprocaine is a 2 chloro—4 aminobenzoate ester of B-diethylaminoethanol. It was introduced in 1952 as an analog of procaine. The chemical structure is depicted in Figure 13.2.
FIGURE 13.2 Chemical structure of Chloroprocaine
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Chloroprocaine is used for infiltration anesthesia in concentrations of 0.5 to 2 percent. Onset of anesthesia is very rapid (2–5 minutes) and the average duration of action lasts for 1½ hours. It is twice as potent as procaine and has similar
FIGURE 13.3 Chemical structure of tetracaine pharmacological properties. Metabolism is largely through hydrolysis by pseudocholinesterase in the plasma. Tetracaine (Amethocaine) Tetracaine is a parabutylaminobenzoic acid ester of dimethylaminoethanol. It was first prepared in 1933. The chemical structure is depicted in Figure 13.3. Tetracaine is used for infiltration as well as topical anesthesia. Dosage Tetracaine is available in concentration of 0.25 to 2 percent solutions. Tetracaine is a potent and toxic local anesthetic and dangerous overdosage may occur if it is given in doses higher than 1.5 mg/ kg body weight. It should be given with caution for infiltration anesthesia purpose. Amides Lidocaine Lidocaine is one of the most common local injectable anesthetic agent used in ophthalmic surgery worldwide. Lidocaine is 2-diethylamino-2′-6′-acetoxylidine. It was first prepared in 1948. The chemical structure is depicted in Figure 13.4. Indication Lidocaine 2 percent is used for infiltration anesthesia prior to any type of intraocular surgery.
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FIGURE 13.4 Chemical structure of lidocaine Dosage Lidocaine is available in concentration of 0.5 to 4 percent as lidocaine hydrochloride (2, 5 ml ampoules and 30 ml and 50 ml vials). For infiltration anesthesia generally 1 percent and 2 percent solutions are used (In 2 ml, 5 ml and 10 ml ampoules; 30 and 50 ml vials). It has rapid onset of action (0.5–2 minute) and average duration of action lasts for 1½ to 2 hours. Lidocaine is metabolized in the liver to xylidine and diethylaminoacetic acid or is directly excreted into the urine and bile. For infiltration anesthesia it is generally given with mixture of adrenaline and hyaluronidase to prolong the anesthetic effect and better diffusion to the ocular tissue. Hyaluronidase is an enzyme capable of depolymerizing hyaluronic acid found in interstitial spaces and when it gets depolymerized, fluid passes more easily between the tissues. Preferable 1:100,000 solution of adrenaline concentration is used and it causes sufficient vasospasm to reduce significantly the rate of removal of local anesthetic agent. A correctly placed retrobulbar or peribulbar injection of this solution causes complete akinesia and anesthesia of the globe. Hyaluronidase is also mixed with 2 percent lidocaine and adrenaline injection for better diffusion of solution into the tissues. It increases the effective area of anesthesia by 40 percent though inevitably of shorter duration. Various Lidocaine combinations available commercially are • Lidocaine HCl 0.5–2 percent with 1:100000 to 1:200000 epinephrine (in 5 ml and 10 ml ampoules, 20, 30 and 50 ml vials). • Lidocaine HCl 1.5–5 percent with 7.5 percent Dextrose (in 2 ml ampoules). Safe dose for lidocaine HCl is—7 mg/kg body weight with vasoconstrictors and 2.9 mg/kg body weight without vasoconstrictors. Recently preservative free 1 percent lidocaine hydrochloride (0.5 ml) ampoules have been available commercially for intracameral use during intraocular surgery. Usual dosage is to inject 0.25 cc of 1 percent preservative free lidocaine into the anterior chamber through the cannula though 1 mm stab incision made in the peripheral cornea, 5 seconds later eye is anesthetized. Advantages of intracameral injection of lidocaine • It relieves all discomfort and apprehension of the patient. • It decreases the need of sedation.
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• Surgery is quicker and less tense and patient responds faster with no complications or adverse effects. • Has an excellent deeper depth of anesthesis. • Eliminates blocks and their potential complications. • Has good effect in conjunction with topical anesthesia. Prilocaine Prilocaine is α-propylamino 2 methylproprionanilide. It was first prepared in 1960. The chemical structure is depicted in Figure 13.5. Its pharmacological properties are similar to those of lidocaine and its onset of action takes 5 to 15 minutes and duration of action lasts for 1 to 3 hours. Prilocaine is used for infiltration and regional nerve block anesthesia. It is available in concentration of 0.5 to 3 percent. The suggested maximum dose is 10 mg/kg body weight.
FIGURE 13.5 Chemical structure of prilocaine Unusual toxic effect seen after administration of large doses (more than 800 mg) is cyanosis due to methemoglobinemia. Mepivacaine Mepivacaine is N-methyl pipecolic acid 2,6 dimethyl anilide. It was first prepared in 1956. The chemical structure is depicted in Figure 13.6. Mepivacaine has pharmacological properties similar to those of lidocaine. Notable exception is its effect on blood vessels. It is shown to have mild vasoconstrictor effect which reduces its absorption. The effect of mepivacaine on the peripheral circulation is a potentiation of the action of norepinephrine on nerve endings. The onset of action starts within 3 to 5 minutes and duration of action is from 2 to 2½ hours (with epinephrine). The suggested maximum dose is 7.0 mg/kg body weight. It is used for infiltration and nerve block anesthesia.
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FIGURE 13.6 Chemical structure of mepivacaine Dosage Mepivacaine is commercially available as mepivacaine HCl 1 to 2 percent injectable solutions (in 20, 30 and 50 ml vials). For infiltration anesthesia, 1 percent concentration is used. Bupivacaine Bupivacaine is structurally similar to mepivacaine and is one of the common anesthetic agents used in the ophthalmology for infiltration anesthesia. It was first prepared in 1963. The chemical structure is depicted in Figure 13.7. Bupivacaine is 3 to 4 times more potent than lidocaine. Its onset of action starts within 5 to 10
FIGURE 13.7 Chemical structure of bupivacaine minutes and duration of action lasts for 3 to 5 hours (with epinephrine). Dosage Bupivacaine is available as bupivacaine HCl injectable solution in concentration of 0.25 to 0.75 percent (in 2 ml ampoules and 10, 30 and 50 ml vials). For retrobulbar or peribulbar injection 0.75 percent strength solution is used. Bupivacaine is also available in combination with epinephrine commercially. Bupivacaine HCl 0.25 to 0.75 percent (in 2 ml ampoules, 10 ml, 30 ml and 50 ml vials). The maximum safe dose is 2.0 mg/kg body weight. Practically for infiltration anesthesia prior to intraocular surgery it is used in combination of 2 percent lidocaine to produce complete akinesia and anesthesia of globe for more than 2 hours. Usually 50:50 percent of both solutions (0.5% bupivacaine HCl and 2% lidocaine HCl in addition to adrenaline and hylase) are used to produce anesthesia for major ocular surgeries.
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Etidocaine Etidocaine is used for infiltration anesthesia in ophthalmic surgery. It is available as 0.5 to 1 percent injectable solutions (in 30 ml vials and 20 ml ampoules). Its onset of action start in 5 to 15 minutes and duration of action lasts for 3 to 5 hours. It is also available commercially with epinephrine. Etidocaine HCl 1.0 to 1.5 percent with 1:20000 epinephrine (30 ml vials). Centbucridine Centbucridine is 4-N-butylamino-1, 2, 3, 4, tetrahydroacridine hydrochloride. It is recently introduced anesthetic agent. It has been shown 5 to 8 times more potent than lidocaine. It is used for infiltration anesthesia and topical anesthesia. Dosage Centbucridine is available as 0.5 percent Centbucridine injectable solution (in 10 ml and 30 ml vials). Its onset of action starts in 2 to 5 minutes and duration of action lasts for 1 to 1½ hours. Local Anesthetics (Topical) Topical anesthesia is the mainstay of modern ophthalmic surgery. Topical anesthesia is now widely used from superficial minor surgery of conjunctiva and cornea to high-tech phacoemulsification, excimer laser PRK and LASIK surgery. Topical anesthetic agents produce their effect by blocking nerve conduction in the superficial cornea and conjunctiva. The physiological effect of all topical anesthetic agents occur in a similar fashion. They work at the level of cell membrane by preventing the sodium flux by closing the pores through which the ions migrate in the lipid layer of nerve cell membrane. The anesthetic agents block conduction of afferent nerve impulses thereby abolishing sensation and producing local anesthetic action. Indications Corneal anesthesia of short duration for any diagnostic and surgical procedure on the eye. Contraindications Known hypersensitivity to the drug or to any other ingredient in these preparations. Prolonged used specially for self-medication is not recommended. Precautions These anesthetic agents are for topical ophthalmic use only. Prolonged use is not recommended as it may diminish duration of anesthesia, retard would healing and cause epithelial erosions. It may produce permanent corneal opacification with accompanying
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visual loss, severe keratitis, scarring or corneal perforation, if signs of sensitivity develops discontinue the use. • Tolerance varies with the status of the patient. Give debilitated, elderly or acutely ill patients reduced doses commensurate with their weight, age and physical status. • Use with caution in patients with abnormal or reduced levels of plasma esterases. • Use with caution in patients with known allergies, cardiac disease or hyperthyroidism. • Protection of the eye from irritating chemicals, foreign bodies and rubbing during the period of anesthesia is important. Adverse Reactions On topical use these anesthetic agents may cause • Mild stinging and burning sensation, vasodilation • Shortening of tear break-up time • Decreased blinking • Corneal edema • Decreased epithelial mitosis and migration • Slow epithelial healing • Punctate epithelial keratitis • Epithelial desquamation • Allergic reactions of lid and conjunctiva • Iritis Various anesthetic agents used in ophthalmology as topical agents are • Benoxinate • Proparacaine • Tetracaine • Lidocaine • Centbucridine • Cocaine • Phenacaine • Dimethocaine • Piperocaine • Dibucaine • Naepaine • Butacaine In today ophthalmic surgery and in diagnostic procedures, proparacaine, benoxinate and tetracaine are commonly used. Their action starts within 15 to 20 seconds and effects last for 15 to 20 minutes. Other topically applied anesthetic agent is 4 percent Xylocaine, its use is becoming lesser and lesser due to problems with irritation, allergy, etc. Individual drug monograph of topical anesthetic agent is as follows.
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Benoxinate HCl (Oxybuprocaine) Benoxinate HCI is a paraaminobenzoic acid ester. The chemical structure is depicted in Figure 13.8. It is available as 0.4 percent topical solution. Its action starts within 10 seconds of topical instillation and effect lasts for 15 minutes. 1 to 2 drops of 0.4 percent solution is sufficient to anesthetize the cornea. For deep anesthesia 3 instillations at 90 second interval is sufficient. Because of high degree of safety it is most suitable for topical use. It is also available as 0.4 percent benoxinate HCI solution with 0.25 percent fluorescein sodium (in 5 ml pack). It is associated with less irritation on instillation. Another topical anesthetic agent having properties and uses similar to benoxinate is proxymetacaine (0.5%). Proparacaine Proparacaine is one of the most common topical anesthetic agents for topical anesthesia in intra-ocular surgery (phacoemulsification, cataract surgery, excimer laser PRK and LASIK surgery) It is a benzoic acid ester. The chemical structure is depicted in Figure 13.9.
FIGURE 13.8 Chemical structure of benoxinate
FIGURE 13.9 Chemical structure of proparacaine It is available as 0.5 percent and 0.75 percent topical solution. It is used 2 to 5 minutes prior to intraocular surgery. Its effect starts within 15 to 20 seconds and lasts for 15 minutes. Potency is similar to that of tetracaine. Maximum dose is 10 mg (about 20 crops of 0.5 percent solution on topical instillation). Due to higher degree of potency and safety it is most appropriate choice for topical ocular anesthesia. It is available as 0.5 percent proparacaine HCl solution and 0.25 percent fluorescein sodium.
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Tetracaine Tetracaine is para-butylaminobenzoic acid ester of dimethylaminoethanol. It is one of the most popular topical anesthetic agents currently used in ophthalmology. It is available as 0.25 to 1 percent topical solution usually 0.5 percent strength is used for topical anesthesia. Tetracaine HCl penetrates tissue more deeply than proparacaine and benoxinate. Its action starts in 20 seconds and lasts for 10 to 12 minutes after topical instillation. It is instilled 2 to 5 minutes prior to the surgery. 1 to 2 drops are instilled topically 2 to 3 times at 60 second duration. Maximum dose is 5 mg (10 drops to each eye of 0.5% solution). On topical instillation however it produces stinging sensation for 30 seconds. Lidocaine HCl Lidocaine is 2-diethyl amino, 2,6 aceto xylidine. Prior to introduction of topical benoxinate, proparacaine and tetracaine anesthetic agents, 4 percent lidocaine HCl was commonly used for topical anesthesia. One drop of 4 percent lidocaine solution renders the cornea anesthetized within 30 to 60 seconds and effect lasts for 10 minutes. It is rapidly acting and does not cause dilation of pupil. On topical instillation however it causes marked stinging sensation for 30 seconds. Due to its stinging sensation problem, it is now less commonly used for topical anesthesia purpose. Centbucridine Centbucridine is recently introduced topical anesthetic agent. It is available as 1 percent topical solution and effect lasts for 15 minutes. It causes very less stinging than 4 percent lidocaine and is safe on topical use. Usual dosage is one drop to be instilled topically and sufficient to produce topical anesthesia. Cocaine Cocaine is an alkaloid of erythoxylon coca. It was first introduced in 1884. The chemical structure is given in Figure 13.10.
FIGURE 13.10 Chemical structure of cocaine
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Cocaine was quite extensively used in late fifties of last century. It is available as topical solution in concentration of 1 to 10 percent as cocaine HCl. One drop of 2 percent solution renders the cornea anesthetized within 30 seconds and effect lasts for 12 minutes. Maximum dose is 20 mg (about 10 drops to each eye of 2% solution). It is however toxic directly to corneal epithelium. It may be used to aid penetration of the other drugs (like cycloplegics) into the cornea and anterior chamber. Cocaine causes mydriasis and when absorbed systemically it may be associated with dangerous drug interactions and hypertensive crisis and CNS stimulation. Toxic doses of cocaine cause fatal circulatory and respiratory collapse. It is now not commonly used for topical purpose as better topical agents are available. Phenocaine Phenocaine is derivative of phenetidine. It is N, N, Bis (p-ethoxy-phenyl) acetamidine. The chemical structure is depicted in Figure 13.11.
FIGURE 13.11 Chemical structure of phenocaine As it is not an ester, it can be considered as an alternative agent for use in patient sensitive to ester group. It is used as 1 percent topical solution for instillation. Phenocaine is no longer used because it causes excessive irritation and highly toxic. Dimethocaine Dimethocaine was first prepared in 1932. It is 3-diethylamino, 2,2 dimethyl propyl pamino benzoate. The chemical structure is depicted in Figure 13.12. It has been used in ophthalmology as topical agent in concentration of 2 to 5 percent. It is derivative of paraaminobenzoic acid.
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FIGURE 13.12 Chemical structure of dimethocaine
FIGURE 13.13 Chemical structure of piperocaine Piperocaine Piperocaine is benzoic acid ester of methyl piperidinopropanol. The chemical structure is depicted in Figure 13.13. It is used as topical 2 percent solution for topical anesthesia. It has effect of regeneration of corneal epithelium. Piperocaine alongwith lidocaine are the only agents associated with normal healing of the cornea. Dibucaine Dibucaine is 2 butoxy-N (2-diethyl aminoethyl) cinchoninamide. It is quinolone derivative and is not an ester. The chemical structure is depicted in Figure 13.14. Dibucaine is probably the most potent local anesthetic agent but its use has declined because
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FIGURE 13.14 Chemical structure of dibucaine of toxicity. It is used as 0.1 percent topical solution for instillation. Naepaine Naepaine is mono-n-amylamino ethyl-p-amino benzoate. Its chemical structure is depicted in Figure 13.15. One topical use, it does not cause mydriasis of alteration in intraocular pressure. It is not associated with local irritation. It is derivative of paraaminobenzoic acid and is used 2 to 4 percent topical ophthalmic solution. Butacaine Butacaine is paraminobenzoic acid ester of dibutylaminopropanol. The chemical structure is depicted in Figure 13.16. It is used topically as 2 percent solution.
FIGURE 13.15 Chemical structure of naepaine
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FIGURE 13.16 Chemical structure of butacaine
14 Anesthesia in Cataract Surgery Ashok Garg Introduction Anesthesia for Cataract Surgery has undergone tremendous changes and advancements in last century. In 1846 general anesthesia techniques were developed which were not found suitable and satisfactory for ophthalmic surgery. In 1884 Koller discovered surface anesthesia techniques using topical cocaine for cataract surgeries which found favor with the ophthalmologists. However, due to significant complications and side effects of cocaine Herman Knopp in 1884 described retrobulbar injection as local anesthetic technique for ocular surgery. He used 4 percent cocaine solution injected into the orbital tissue close to posterior part of the globe to achieve adequate anesthesia but in the subsequent injections patients experienced pain. In 1914 Van Lint introduced orbicularis akinesia by local injection to supplement subconjunctival and topical anesthesia. However, this technique found favor only after 1930 when procaine (Novocaine) a safer injectable agent made it feasible. With the development of hyaluronidase as an additive to the local anesthetic solution Atkinson (1948) reported that large volumes could be injected with less orbital pressure and improved safety injections into the cone (Retrobulbar) were recommended and gained rapid favor becoming anesthetic route of choice among ophthalmologists. In mid 1970s, Kellman introduced an alternative technique of local anesthesia for ocular surgery known as peribulbar injection. However, till 1985 this new technique was not published in ophthalmic literature. In 1985 Davis and Mandel reported local anesthetic injection outside the cone into the posterior peribulbar space (periocular). Further modifications of both retrobulbar and periocular injection techniques were made by Bloomberg, Weiss and Deichaman, Hamilton and colleagues, Whitsett, Murdoch Shriver and coworkers. These modifications consisted of more anterior deposition of anesthetic solution with shorter needles and smaller dosages. With the introduction of small incision cataract surgery, Phaco emulsification and other microsurgical procedures in ophthalmology, use of shorter needles with smaller dosages became more common. Fukasawa and Furata et al reintroduced subconjunctival anesthetic techniques. Fichman in 1992 first reported the use of topical tetracaine anesthesia for phacoemulsification and intraocular lens implantation starting an era of topical anesthesia in ocular surgery. With the advent of many ocular anesthetic techniques in past two decades indicates the need for the development of an ideal anesthetic and technique for ocular surgery. Every existing technique has its own advantages and disadvantages. General anesthesia for cataract surgery is virtually out of favor with ophthalmologists. Retrobulbar anesthesia, periocular (peribulbar, subconjunctival, orbital and epidural) and topical anesthesia or a
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combination of peribulbar and topical are being used in present day ocular surgery Now with the advent of below 1 mm incision technique, foldable and reliable intraocular lenses, no anesthesia cataract surgery is becoming popular with increased frequency. Anesthesia for Cataract Surgery Cataract extraction may be performed under general anesthesia, local anesthesia or topical anesthesia, depending upon condition of patient cataract status and surgeon choice. General Anesthesia Usually for cataract surgery general anesthesia is not given. It is advisable only in highly anxious/ nervous patient or when cataract surgery requires a long time for completion. Patients who are extremely apprehensive, deaf, mentally retarded, unstable or cannot communicate well with the surgeon are more suitable for general anesthesia. General anesthetic facilities with expert anesthetist are mandatory. General Anesthesia Procedure Preoperative Preparation A patient who is to be given a general anesthetic needs proper preoperative assessment and examination, preferably on the day before the anesthetic is to be administered, although preparation earlier on the day of surgery may be acceptable in many cases. Patients with cataracts are often elderly and not infrequently have other medical problems that must be considered before anesthesia is induced. These are: Chronic (Obstructive) Respiratory Disease These patients require more careful assessment. Their condition in severe cases can be adversely affected by anesthetic drugs and muscle relaxants. On the other hand, the inability to control obstructed respiration can lead to hazardous cataract surgery and a high incidence of failure. Preoperative preparation with antibiotics, bronchodilators, and physiotherapy often enable a sick patient to undergo a safe procedure with the benefit of a general anesthetic. Cardiovascular Disease Because many patients with cardiovascular disease will already be on diuretic treatment, preoperative assessment to detect and treat cardiac failure or hypokalemia is most important. The adequate control of hypertension is also an essential safety requirement, especially for the middle aged.
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Diabetes Mellitus Diabetes mellitus is commonly found in those for whom cataract surgery is indicated. Preadmission stabilization is necessary, and when this is in doubt, a longer period of preoperative inpatient assessment and management is required to eliminate any ketonuria or gross hyperglycemia. Oral diabetic medication should be omitted on the day of surgery because the effects may persist for up to 24 hours. During surgery and throughout the early postoperative period, control is effected by using 5 percent glucose intravenously and insulin as required, as shown by the blood glucose levels. When the patient resumes normal oral intake postoperatively, the normal regimen is rapidly resumed. Dystrophia Myotonica These patients frequently require cataract surgery while they are quite young. They are particularly sensitive to anesthetic drugs and subject to prolonged respiratory depression. Suxamethonium is contraindicated; minimal doses of other drugs such as atracurium should be used. Premedication The aim of premedication is to allow a smooth induction of anesthesia. Most patients appreciate some sedation to alleviate the natural anxiety associated with any eye surgery. Opiates, however, are to be avoided because of their association with respiratory depression and postoperative vomiting. For the aged and anxious, oral premedication with diazepam, 5 to 10 mg, according to fitness and size or Lorazepam, 1 to 2 mg, works well. An antiemetic can then be administered during surgery. For the younger and more robust, one can use a combination of pethidine, promethazine hydrochloride, and atropine. This is also a helpful combination for those with established respiratory disease. Children over 1 year of age required sedation with trimeprazine tartrate syrup (3 to 4 mg per kg) 2 hours preoperatively. Younger babies should not require sedation. Atropine may be given either intramuscularly (0.2 to 0.6 mg 30 minutes preoperatively) or intravenously (0.015 to 0.02 mg with induction). Method of Anesthesia Induction A smooth induction avoids the problems of increased central nervous pressure with its consequent adverse effect on the intraocular pressure. The drug most commonly used is thiopentone, which produces a rapid loss of consciousness. When it is used in doses of 3 to 4 mg per kg, the onset is relatively slow in the elderly, who frequently have a slower circulation time. For the very frail, methohexitone is useful, producing less change in blood pressure. More recently disoprofol (Diprivan) has been found to be useful; it also has a rapid onset of action and induces little nausea and vomiting.
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Intubation of the trachea with a non-kinking endotracheal tube is achieved with suxamethonium. Its use is associated with a transient rise in the intraocular pressure due to choroidal expansion. Ventilation with nitrous oxide and oxygen with 0.5 to 1 percent halothane is continued until the effects of the suxamethonium have subsided. More recently techniques have been described for rapid sequence induction with vecuronium. These methods do not seem to be associated with a significant rise in the intraocular pressure and they avoid the problems of suxamethonium. Maintenance A nondepolarizing muscle relaxant is used throughout the surgical procedure, dosages depending on the size, age, and health of the patient. Available drugs include tubocurarine, which is inclined to produce hypotension (occasionally severe), pancuronium, and more recently vecuronium and atracurium. Vecuronium has been demonstrated to lower intraocular pressure. Because both atracurium and vecuronium act and subside rapidly, their effectiveness must be monitored regularly by a peripheral nerve stimulator. Intermittent positive pressure ventilation is maintained by nitrous oxide, oxygen, and an anesthetic drug. One-half percent halothane has long been considered effective and also lowers the intraocular pressure. Other anesthetic drugs include enflurane (associated with more postoperative vomiting and restlessness, though less hypotension) and isoflurane. The latter does not appear to adversely affect the stability of the cardiovascular system. Its effect on intraocular pressure has not been reported. Throughout the procedure the pulse, blood pressure, electrocardiographic record, and arterial oxygen saturation must be regularly monitored, along with the nerve stimulation needed for the nondepolarizing muscle relaxant being used. All ventilators should be fitted with an alarm to warn of malfunction. Completion Recovery from anesthesia after cataract surgery must be as smooth as the induction, care being taken to avoid gagging, coughing, and of course vomiting. Modern ophthalmic sutures are good but not foolproof! The neuromuscular blockade is reversed with atropine and prostigmine. Gentle extubation is associated with careful pharyngeal suction. Patients are encouraged to resume normal activity as soon as the effects of the anesthetic drugs have worn off. Anesthesia for Children Adequate premedication and careful handling should insure a calm and quiet child and allow a smooth induction. Because the cataract is dealt with by using a closed system, the surgical risks of a rise in intraocular pressure are not so severe. Inhalational anesthesia using nitrous oxide and oxygen with halothane is usually sufficient.
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Complications of General Anesthesia The complications associated with a general anesthetic range from death to the less serious but irritating nuisances of protracted nausea and vomiting or sore throats. This chapter covers only those complications producing serious morbidity or mortality and those peculiar to the patient with eye disease. 1. Hypoxemia (insufficient oxygen in the arterial blood to sustain life) is the most common cause of disaster, and failure to ventilate is the most common cause of hypoxemia. Unrecognized esophageal intubation, ventilator disconnection, and, most distressing of all, inability to ventilate after unconsciousness and paralysis have been obtained are all possible causes of failure to ventilate. Delivery of an inadequate oxygen concentration is a less common cause of hypoxemia. Most but not all of the foregoing are preventable with the monitoring and fail-safe devices available today, provided a competent anesthetist is monitoring the devices. 2. Aspiration of gastric contents remains a common complication despite such preventive measures as overnight fasting, the use of metoclopramide to enhance gastric emptying, and rapid sequence induction with cricoid pressure in emergency procedures. The two life-threatening results of aspiration are airway obstruction from large food particles and chemical pneumonitis from acidic gastric contents. 3. The two most serious cardiovascular complications, aside from cardiovascular collapse secondary to hypoxemia and acute anaphylaxis, are myocardial infarction and cerebrovascular accident. Surgery performed under general anesthesia within 3 months after a myocardial infarction carries a 40 percent incidence of repeat infraction. This figure decreases to about 10 percent at 6 months, after which the incidence is approximately the same as in the general population. All elective surgery is delayed until after 3 months, and a 6-month wait is encouraged unless poor visual acuity seriously limits activities. 4. Renal and hepatic toxic effects from anesthetic drugs are seldom seen in our practice. Careful preanesthetic screening identifies all patients with renal and hepatic disease. Halothane, which gained notoriety because of its hepatotoxicity, especially when administered repeatedly, is not used in adults and is usually used for induction only in children. The metabolic byproducts of methoxyflurane and enflurane are inorganic fluorides, which can produce nephrogenic diabetes insipidus. We no longer use these drugs because so many of our patients have diabetes and severe renal disease in our population. 5. Failure to resume respiration at the end of the surgery occurs often enough to merit mention. The most common causes are simple respiratory depression from the anesthetic drugs or narcotics, electrolyte disturbance (i.e. hypokalemia), hypothermia (particularly in infants), and the use of the combination of mycin antibiotics and nondepolarizing muscle relaxants. It also may occur after the administration of succinyl choline when there is a pseudocholinesterase deficiency. Respirations are maintained until the cause is found and remedied. Cardiovascular complications are the most commonly seen events in our practice. If diagnosed and treated properly, they need not result in a disaster. Hypertension is the most prevalent problem. The usual causes are apprehension, Neosynephrine eyedrops,
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pain, distended bladder if mannitol was given, and autonomic nervous system imbalance secondary to the general anesthetic. Apprehension can be allayed with intravenous injections of 1 to 3 mg of Valium or 0.5 to 2 mg Zolpidem. Nitropaste applied to the skin and sublingual doses of nifedipine have proved invaluable, but an intravenous line should be in place before their use. Hypotension must be treated immediately and vigorously because it is tolerated less well than hypertension. Arrhythmias are the most frequent cause of cancellation on the day of surgery in the elderly patient with eye disease. The sudden onset of atrial fibrillation is the most common arrhythmia. An electrocardiographic monitor is mandatory for eye surgery. Extrusion of ocular contents during administration of a geneal anesthetic is a serious complication in eye surgery. The entire anesthetic process is geared to minimize this possibility. Once the eye is opened, patients are kept deeply anesthetized or paralyzed with non-depolarizing relaxants to insure immobility. Local Anesthesia Local ocular anesthesia is the mainstay of cataract surgery. Local anesthesia minimizes the risk of wound rupture a complication frequently associated with coughing during extubation and postoperative nausea and vomiting (in general anesthesia) (Fig. 14.1). Generally the use of 1:1 mixture of 2 percent Xylocaine and 0.50 percent Bupivacaine alongwith Adrenaline and Hyaluronidase in Facial, Retrobulbar and Peribulbar blocks achieve rapid anesthesia, akinesia and post-operative analgesia for several hours. Care should be taken to avoid intravascular injections of anesthetic agents because refractory cardiopulmonary arrest may result from an inadvertent intravenous or intraarterial injections.
FIGURE 14.1 Diagrammatic surface distribution of sensory nerves. Note branches derived from ophthalmic nerve (V1) and maxillary nerve (V2) a division of the trigeminal nerve Many patients express pain of facial and retrobulbar injections so proper preoperative sedation and good rapport with the surgeon make them quite comfortable.
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Following techniques are used for giving local anesthesia. These include: Orbicularis Oculi Akinesia Temporary paralysis of the orbicularis oculi muscle is essential before making section for the cataract surgery to prevent potential damage from squeezing of the lids. Following methods are used, for getting orbicularis oculi akinesia. a. O’Brien’s technique Usually 10 ml of mixture of 2 percent Lidocaine solution (5 ml) and 0.5 percent bupivacaine solution (5 ml) with 1:100,000 epinephrine and 150 units of Hyaluronidase are infiltrated for local anesthesia. O’Brien’s method is the injection of above mentioned local anesthetic solution down to the periosteum covering the neck of the mandible where the temporofacial division of facial nerve passes forwards and upwards (Fig. 14.2). A 10 ml syringe with preferably No. 17 or 18 needle and 2.5 cm in length is used. The patient is asked to open his mouth and the position of the condyle and temporomandibular joint is located by the forefinger of the operators’s left hand.
FIGURE 14.2 Diagrammatic presentation of O’Brien technique of local anesthesia
FIGURE 14.3 Needle position for Van Lint akinesia (Courtesy: Ciba Geigy Clinical Symposia)
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After closing the jaw, the injection is given on a horizontal line through the junction of the upper and middle third of the distance between the zygoma and angle of the mandible. The needle should pass straight down the periosteum. 2–3 ml of local anesthetic solution is injected and after withdrawing the needle firm pressure and massage are applied. Paralysis of orbicularis oculi should occur normally within 7 minutes. The injection is unlikely to injure the external carotid artery which lies posterior and at a deeper level. However, damage may be done to posterior facial vein and the transverse facial artery. Movement of jaws is sometime painful for few days after this injection. b. Van Lint’s akinesia Van Lint’s method is a better alternative. The injection of local anesthetic solution is made across the course of branches of the seventh nerve as they pass over the zygomatic bone (Fig. 14.3). In this technique a 5 cm in length and 25 gauge needle is passed through the wheal down to the periosteum of the zygomatic bone. The needle is then passed upward towards the temporal fossa without touching the periosteum (as it may be painful) and 4 ml of solution is injected and then forwards medially and downwards towards the infraorbital foramen to inject 2 ml and downwards and backwards along the lower margin of the zygoma for 2.5 cm where 3 ml of solution is injected. It is essential to massage the infiltrated area with a gauze
FIGURE 14.4 Atkinson akinesia (intercepting the facial nerve fibers as they cross the zygomatic arch) swab. Motor nerves are less susceptible than sensory nerves to a block with local anesthetic agents. The advantage of Van Lint’s method is that it provides regional anesthesia as well as paralysis of the orbicularis muscle. After waiting for 5–7 minutes akinesia is tested by holding the eyelids open with a small swab on to a holder and asking the patient to close his eyelids. If slightest action is observed then injection may be repeated to obtain adequate akinesia.
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c. Atkinson block The needle enters through a skin wheal at the inferior border of the zygoma just inferior to the lateral orbital rim. The path of the needle is along the inferior edge of the zygomatic bone and then superiorly across the zygomatic arch, ending at the top of the ear. 3 to 4 ml of the anesthetic is injected as the needle is advanced (Figs 14.4 and 14.5). d. Spaeth block The Spaeth block avoids the inconsistencies of the O’Brien block as well as the postoperative discomfort caused by going through the parotid gland and entering the temporomandibular joint. An injection is made into the back of the mandibulbar condyle just below the ear, catching the facial nerve before it divides (Fig. 14.6). To locate the landmarks, the
FIGURE 14.5 Diagrammatic presentation of O’Brien and Atkinson techniques. (A) Classic O’Brien technique (B) Modified O’Brien technique (C) Atkinson technique fingers are placed along the posterior border of the mandible as superiorly as possible. The needle is placed just anterior to the most superior finger. Bone should be reached shortly. If not, the needle is withdrawn and the position rechecked before a second attempt is made. After the bone is reached, the needle is pulled back slightly and suction is placed on the syringe to make sure that a vessel has not been punctured; 5 ml of anesthetic is then injected. Although rarely required,
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FIGURE 14.6 Spaeth block (facial nerve is blocked where it crosses the posterior edge of the mandible)
FIGURE 14.7 Needle positions for O’Brien and Nadbath ocular akinesia (Courtesy: Ciba Geigy Clinical Symposia) the needle can be redirected superiorly towards the outer canthus for 1.5 inches and an additional 5 ml is injected. After 30 seconds, nearly complete facial palsy should be evident. e. Nadbath block An injection is made into the cavity between the mastoid process and the posterior border of the mandibular ramus. The skin is pierced, and a skin wheal is made 1 or 2 mm anterior to the mastoid process and inferior to the external auditory canal. A 12 mm, 26 gauge needle is used, with the injection of anesthetic extending from the skin wheal, passing through a taut membrane midway, to the full depth of the needle; 3 ml is injected (Fig. 14.7). The Nadbath block insures ease of performance, and there are few complaints relating to the original injection or subsequent pain in the jaw area. The most
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common side effect is a bitter taste as the parotid gland secretes the anesthetic. Other problems reported are dysphonia, swallowing difficulty, and respiratory distress. Judging from the fact that these complications are seen predominantly in very thin patients and most certainly are secondary to the diffusion of anesthetic to the jugular foramen, 1 cm deeper than the stylomastoid foramen, the length of the needle—i.e. the depth of injection—is critical. Preexisting unilateral oropharyngeal or vocal cord dysfunction is a definite contraindication, for bilateral vocal cord paralysis could result. The nadbath block should never be done bilaterally. If, after a unilateral Nadbath block, dysphonia or difficulty with swallowing or respiration occurs, lateral positioning will allow the paralyzed vocal cord to fall out of the way, clearing the airway. Proper administration of local anesthesia requires knowledge of orbital anatomy, various anesthetic techniques, and the properties of the drugs used. Prompt recognition of side effects and complications following injection results in the best possible patient care. f. Retro-ocular (retrobulbar) injection Anesthesia and akinesia of the eye are achieved by injecting a local anesthetic solution into the retrobulbar space within the muscle cone (Fig. 14.8).
FIGURE 14.8 Local anesthesia techniques (A) Van Lint akinesia (dotted arrows) (B) Nadbath facial nerve block (C) Retrobulbar needle position
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FIGURE 14.9 Needle positions for retrobulbar and peribulbar anesthesia (frontal view) (Courtesy: Ciba Geigy Clinical Symposia) In this method patient is asked to look upwards and to the opposite side. A 3.5 cm length 23 gauge sharp edge round tipped needle is inserted in the quadrant between the inferior and the lateral rectus muscles and directed posteriorly until the resistance of orbital septum is encountered. After it has penetrated the orbit the needle is directed towards the apex of the orbit and advanced until it meets the resistance of the intermuscular septum. When this structure is penetrated, the needle tip is in the retrobulbar space. About 3–4 ml of local anesthetic mixture solution is injected taking care, to minimize the needle movement to prevent possible vessels lacerations. Following the injection the globe should be intermittently compressed for several minutes for distributing the anesthetic solution and to ensure hemostasis. A properly placed retrobulbar injection is effective within seconds. It blocks all extraocular muscles except superior oblique muscle, affects the ciliary ganglion and anesthetize the entire globe (Fig. 14.9). Gills-Loyd Modified Retrobulbar Block Before the anesthetic is administered, the patient’s vision is checked and the A scan examined. Then, prior to the first injection, 2 drops of proparacaine 0.5 percent are given topically. The eyes are either fixed in primary gaze or directed slightly superiorly, avoiding the superonasal position. With sharp 27 gauge needle, enter is effected at LE 4:00, RE 8:00, 5 mm medial to the lateral canthus. The needle is inserted parallel to the optic nerve. A preretrobulbar injection of 1.5 ml of pH adjusted Xylocaine is administered subconjunctivally. After 30 seconds, a 5 ml retrobulbar injection of pH adjusted bupivacaine and hyaluronidase is injected with a 25 gauge, 1¼ inch needle. After 8 to 9 minutes, the eye is checked for akinesia. A 1 to 3 ml supplemental injection of full strength anesthetic is given as needed to complete the block. 1.0 ml bolus is
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administered subdermally into the inferolateral lid to anesthetize the distal branches of the seventh cranial nerve; this technique does not require a total seventh nerve block. Next 0.5 ml of cefazole is injected subconjunctivally, and gentle eye compression is administered for 30 to 60 minutes with a Super Pinky Decompressor prior to surgery. Complications of Retrobulbar Injection A number of complications can occur as a result of retrobulbar injection, among them retrobulbar hemorrhage, perforation of the globe, retinal vascular obstruction, and subarachnoid injection. Retrobulbar Hemorrhage Retrobulbar hemorrhage probably occurs in 1 to 5 percent of the cases. It seems to occur less frequently if a blunt tipped needle is used, but this has not been demonstrated in any controlled study. Retrobulbar bleeding may occur at a number of sites. The four vortex veins leave the globe approximately 4 mm posterior to the equator and could well be subjected to the shearing forces of an inserted needle, as could the central retinal or ophthalmic vein. An arterial source of bleeding must be postulated to explain severe hemorrhages that produce the rapid onset of proptosis, hemorrhage, chemosis, and immobility of the globe. The posterior ciliary arteries supplying the choroid, the central retinal artery, and other ophthalmic artery branches are all subject to damage. Even the ophthalmic artery can be reached in the area of the optic foramen with a 1½ inch needle. Most instances of retrobulbar hemorrhage resolve without complication, but should a complication arise, particularly during elective surgery, it is prudent to postpone the operation for at least 3 to 4 weeks and then consider general anesthesia if the patient can tolerate it. Even when general anesthesia is employed, severe positive pressure can develop in an open eye if the operation is performed within several days after the hemorrhage. Vision may be permanently decreased following a retrobular hemorrhage. This probably occurs as a result of closure of the central retinal artery or damage to the smaller vessels that supply the retrobulbar optic nerve. If examination reveals that the central retinal artery has closed because of increased intraorbital and intraocular pressures, a lateral canthotomy should be performed. Other possible therapeutic modalities include anterior chamber paracentesis and orbital decompression. Prior of decompression of the orbit, computed tomographic scanning of the region should be undertaken to help localize the blood and rule out the possibility of bleeding within the optic nerve sheath, which also might have to be decompressed. Perforation of the Globe This is another sight-threatening complications of ophthalmic surgery with retrobular anesthesia. Highly myopic eyes are particularly suscepticle to this complication because
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of their long axial lengths. General anesthesia should be considered as an alternative in such eyes. The scleral perforation should be repaired as soon as possible. Cryopexy or laser treatment of the break(s) may suffice, although vitreous traction that develops along the needle tract through the vitreous gel is better negated by a scleral buckling procedure. If the fundus view is obscured by vitreous hemorrhage, a pars plana vitrectomy is warranted to visualize the break(s). Although double scleral perforations probably have a worse prognosis than the single variant, the latter also can be devastating. I have seen one case in which the retina in the posterior pole was partially aspirated through the needle following a scleral perforation anterior to the equator. Inadvertent injection of lidocaine into the vitreous cavity appears to be tolerated by the globe. However, it can cause an extreme elevation of the intraocular pressure and rapid opacification of the cornea. Retinal Vascular Obstruction Retinal vascular obstruction has been reported after retrobular anesthesia. The most common types are central retinal artery obstruction and combined central retinal arterycentral retinal vein obstructions. Central retinal artery obstruction seems to occur more commonly in conjunction with diseases that affect the retinal vasculature, such as diabetes mellitus and sickling hemoglobinopathies. Nevertheless, it also can be seen in people with good health. Fortunately, the condition more often than not reverses spontaneously and the central retinal artery reperfuses within several hours. The causes are uncertain, but spasm of the artery, direct trauma to the vessel from the needle, and external compression by blood or an injected solution are possible mechanisms that could cause obstruction. Ophthalmic artery obstruction also can be induced, possibly by injection and subsequent compression within the optic foramen. Therapy is directed towards relieving the obstruction and keeping the retina viable. Anterior chamber paracentesis may help, the aim being to lower the intraocular pressure and decrease the resistance to blood through the central retinal artery. Although paracentesis widens vessels narrowed by artery obstruction, fluorescein angiography shows that the filling occurs in a retrograde fashion, via the retinal veins. Hence its value is questionable. Combined obstruction of the central retinal artery central retinal vein is a much more serious complication. Ophthalmoscopically a cheery-red spot is seen, as well as numerous intraretinal hemorrhages and dilated retinal veins. The mechanisms of obstruction include direct trauma to the central retinal vessels from the needle or compression from blood or fluid injected into the nerve sheath. Blood within a dilated optic nerve sheath has been demonstrated in these cases. The visual prognosis of these eyes is generally grim. Computed tomography of the retrobulbar optic nerve may be used to determine whether a nerve sheath hemorrhage is present. If an optic nerve sheath hematoma is discovered, decompression of the nerve sheath may be of limited benefit. Neovascularization of the iris may develop after combined central retinal arterycentral retinal vein obstruction. If the anterior chamber angle is not yet closed by a
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fibrovascular membrane, aggressive, full scatter panretinal photocoagulation treatment should be administered in an attempt to prevent neovascular glaucoma. Injecting with the eye in the primary position may help prevent this complication. In contrast, injecting with the eye looking up and in, places the optic nerve and central retinal vessels more in the pathway of the needle and thus probably should be avoided. Multiple emboli with the retinal arterial system have caused vascular obstruction following retrobulbar corticosteroid injection. No therapy is available for this visually devastating complication which likely results from injection into the central retinal or ophthalmic artery. In theory, the use of a needle shorter than 1½ inches may help to prevent the complication, as can having the patient gaze in the primary position during the injection. Subarachnoid Injection Among the most recently recognized complications of retrobulbar, anesthesia, inadvertent injection into the subarachnoid space may be the most serious. The subarachnoid space extends around the retrobulbar optic nerve up to the globe and can be violated with a retrobulbar needle at any point along its course. Optic atrophy and blindness have also been reported following retrobulbar blocks but they are fortunately rare. Due to these potential complications retroocular injection is out of favor with eye surgeon worldwide. Peribulbar (Periocular) Technique Since the exit of retrobulbar akinesia, Peribulbar akinesia is considered a safe and effective technique of local anesthesia for cataract surgery. It is method of choice with eye surgeons for giving local anesthesia to cataract. As the name indicates, peribulbar anesthesia is a technique in which a local anesthetic is injected into peribulbar space and is not aimed at blocking a perticular nerve. Technique Periocular anesthesia is administered at two sites lower temporal quadrant and nasal to caruncle (Fig. 14.10). The required local anesthetics are Lidocaine 1 percent and Bupivacaine 0.75 percent with hyaluronidase. Bupivacaine is preferred as it is a longer acting anesthetic agent which can provide prolonged anesthesia and analgesia. In the first stage, injection of 0.5 cc of 1 percent lidocaine with a 26 G needle is done under the skin at about I cm away from the lateral canthus in the lower lid, along the orbital rim. The same needle is passed deeper to inject 0.5 cc of lidocaine into the orbicularis muscle and 1.0 cc into the muscle sheath. A second injection is done in the similar fashion in the upper eyelid just below the supraorbital notch. Pressure is applied at both for a minute using gauze pieces.
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In the second stage, combination of 6.0 ml of 0.75 percent bupivacaine, 3 ml of 1 percent lidocaine and 0.25 cc of hyaluronidase is filled into a 10 ml Disposable syringe fitted with a, 1–1/4 inch 23 G, hypodermic needle. The needle is first introduced deep into the orbit through the anesthetized site in the lower eyelid. One ml is injected just beneath the orbicularis muscle and then the needle is advanced up to the equator of the globe to inject 2 to 3 ml of the solution. The same procedure is followed in the upper nasal quadrant through the preanesthetized site to inject 1 ml and another 1 ml may be injected around superior orbital fissure, by deeper penetration. At the end of the procedure, fullness of the lids is noted due to the volume of the injected. Firm
FIGURE 14.10 Needle positions for peribulbar and retrobulbar akinesia (Courtesy: Ciba Geigy Clinical Symposia) pressure with the flat of the hand is applied over the globe and is maintained for a minute. Then, before surgery, any pressure device as per the surgeon’s choice like Honan’s balloon, super pinky ball, balance weight or simple pad-bandage is applied for 20 to 30 minutes, to achieve the desire response of hypotony. The efficacy of the anesthesia is evaluated after about 10 minutes of injection and if inadequate, 2 to 4 ml more can be injected. In case of persistent inferior or lateral movement injection lower temporal quadrant and in case of persistent movements upwards of nasally, the upper quadrant could be infiltrated in the same fashion. Hyaluronidase is essential as it helps in the spread of the drug. Otherwise, there are chances of the eye being proptosed due to high orbital pressure induced by the large quantity of the fluid injected. Single injection of 5 to 6 ml of anesthetic mixture injected from any site posterior to equator of the globe also achieves same results. For convenience, however, it may be done through lower lid the junction of lateral and middle one-third, along the floor of the orbit.
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Adequacy of akinesia is determined by the absence of ocular movements in all directions. This technique is certainly better than retroocular technique and has least complications. Advantages The advantages reported are: 1. The injection is done outside the muscle cone and so, the inherent complications of passing the needle into the muscle cone is completely eliminated. 2. It does not enter the retrobulbar space and thereby avoids retrobulbar hemorrhage, injury to optic nerve and entry of anesthetic agents into subarachnoid space and other complications like respiratory arrest. 3. Since the needle is constantly kept parallel to the bony orbit, it avoids injury to globe and entry of anesthetic agents into the eyeball. 4. It causes less pain on injection. 5. The procedure is easier and can be performed without causing damage to vital structures. 6. It does not reduce vision on table. 7. No facial block is required. Drawback The possible drawbacks of this procedure are: 1. Chemosis of conjunctiva. 2. Delayed onset of anesthetic effect, and 3. Potential risk of orbital hemorrhage. Though it occurs rarely, the magnitude of the problem is comparable to retrobulbar hemorrhage and necessitates postponement of surgery. Mechanism The exact mechanism is not known but this procedure may best be described as ‘infiltration anesthesia’ where nerve endings in all tissues in the area of injection get anesthetized. Peribulbar anesthesia is a safe and reliable technique for achieving akinesia and anesthesia of the globe. In case of inadequate anesthesia, repeat injections in the similar manner can be safely used to achieve the purpose. Superior Rectus Injection The induction of temporary paralysis of the superior rectus muscle is essential for any intra ocular operation where the surgical field is upper half of the eye. This injection also affects the action of levator palpebrae superioris.
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In this injection patient is asked to look down. The upper lid is retracted and 2.5 cm long needle is passed into Tenon’s capsule at the temporal edge of the superior rectus muscle. The needle is directed posteromedially and about 1 ml of anesthetic mixture of 2 percent Xylocaine is injected around the muscle belly behind the equator. This injection can also be made through the skin of the upper orbital sulcus. Tenon’s Capsule Injection The injection of anesthetic mixture can be given into Tenon’s capsule around the upper half of the eyeball and into the belly of superior rectus muscle. It is considered safer than the retroocular injection across the postganglionic fibers of the ciliary body and may be effective in inducing extraocular muscle akinesia.
FIGURE 14.11 Parabulbar (flush) local anesthesia (cross-section view)
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FIGURE 14.12 Parabulbar (flush) local anesthesia (surgeon view) Parabulbar (Flush) Akinesia Parabulbar (flush) administration is a new route for local anesthesia which is highly useful, safe, effective and technically easier (Figs 14.11 and 14.12). This method consists of a limbal sub-tenon administration of retrobulbar anesthesia using a blunt irrigating cannula. This technique can be used for anterior and posterior segment surgery. Topical Anesthesia Since the advent of retrobulbar and peribulbar techniques in the early part of this century, both procedures are mainstay of local anesthesia for intraocular surgery till today. They do carry the risk of perforation of globe, optic nerve and the inadvertent injection of anesthetic at wrong places. These accidents are mainly due to: • Carelessness on the part of ophthalmologist who considers the procedures lightly and occurs more often with senior eye surgeons. • Using long needles for these techniques endangers the perforation of globe, piercing the optic nerve and entering crowded retrobular space and even touching the intracranial space on forceful injection of copious amounts. • Anesthetics given through local injection with little knowledge of anatomy of this area. • Retrobulbar hemorrhage with its adverse effects on nerve and globe is very common complication of this technique. • Injury caused by perforation of globe can lead to hole formation, retinal detachment, vitreous hemorrhage and central and branch vein occlusions.
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To overcome all these practical difficulties use of topical anesthesia in intraocular surgery has been widely suggested and used at an International ophthalmic level. Topical anesthesia meaning topical application of 4 percent Xylocaine or 0.5–0.75 percent proparacaine one drop 3–4 times at regular intervals in the eye has become increasingly popular and accepted. In present day hightech intraocular surgery specially phaco surgery topical anesthesia is the anesthesia of choice with the eye surgeons worldwide. Indications to use Topical Anesthesia • Its indications in intraocular surgery are mainly when performing phacoemulsification and IOL implantation through a clear corneal tunnel and corneoscleral incisions. • Topical anesthesia is ideally suited for small incision and stitchless cataract surgery. However, it is not a advocated to perform standard/ manual extracapsular cataract extraction and IOL implantation. • Proper selection of patient is of great importance in this technique. It is important to have a patient who will comply with the instructions given during surgery. • Patients who are non-cooperative, hard of hearing, with language problem and anxious patients are poor candidates for surgery under topical anesthesia. Capsulorhexis requires the maximum cooperation of the patient. • Intraocular surgery likely to be problematic in patients with rigid small pupils responding poorly to dilating drops and eys with lenticular subluxation and high grade nuclear sclerosis are relative contraindications for topical anesthesia. • Eye surgeon operating with topical anesthesia should be proficient and experienced at phacoemulsification. • This procedure requires the use of foldable IOL either as a silicone lens or an acrylic lens. This is essential because corneal tunnel suture lens incision cannot be larger than 3.5 mm. Otherwise corneal complications may arise and the incision would not be self-sealing.
How to Achieve Surface Anesthesia for Intraocular Surgery Generally 3 applications of 4 percent Xylocaine or 0.4 percent Benoxinate HCl or 0.5– 0.75 percent proparacaine 10 minutes apart starting 30 minutes before surgery are recommended. A drop is thereafter instilled prior to the incision. 1 CC of 4 percent Xylocaine or 0.4 percent Benoxinate HCI or 0.5–0.75 proparacaine (from fresh vail) is drawn into sterile disposable syringe and OT staff person is asked to instil a few drops of the same prior to cauterization of bleeders and if required during surgery conjunctival anesthesia is used (pinpoint and mini pinpoint surface anesthesia) Apart from giving topical anesthesia one has to give systemic analgesia. Besides it, surgeon should have a commanding hypnotic voice (vocal local anesthesia). • Most surgeons doing corneal tunnel incision under topical anesthesia prefer to do it from temporal side.
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Can One Convert Half Way Through Surgery Under Topical Anesthesia Intraoperative conversion from topical to peribulbar anesthesia can definitely be achieved if surgical situation. Warrants it. Since corneal tunnel incision is sutureless and selfhealing a peribulbar injection can safely be given during the surgery. Advantages of Topical Anesthesia 1. Phacoemulsification experts feel that use of topical anesthesia with a clear corneal tunnel self-healing incision is a significant advancement in intraocular surgery. With topical anesthesia visual recovery is immediate. 2. It prevents the well known complications of retrobulbar and peribulbar injections as mentioned in the early part of this chapter. 3. It lessens the time of operating room use thereby lowering costs. 4. There is no immediate postoperative ptosis as seen in retrobulbar or peribulbar and Van Lint, O’Brien infiltrations lasts for 6–8 hours due to temporary akinesia of the lids. 5. With topical anesthesia photon laser intraocular surgery can be OPD procedure. 6. In practice we have seen the anxiety of patients to peribulbar and retrobulbar injections prior to surgery. With topical anesthesia this problem is over and patient compliance will be better during intraoperative period. 7. The need of qualified anesthesiologist is over in operation theater during the operation as a number of ophthalmologists have been seen to prefer anesthesiologist by their side for local anesthesia (retrobulbar and peribulbar anesthesia). 8. No risk of postponement of intraocular surgery as seen in cases of retrobulbar hemorrhage. Again its main advantage is that it provides for immediate postoperative visual recovery. Disadvantages of Topical Anesthesia 1. Only a highly experienced surgeon can operate with topical anesthesia. The eye can move which makes the operation more difficult. If the eye movement occurs when capsulorrhexis is being done, an undesirable capsular tear may take place leading to failure of this important step of the operation. 2. The chances of intraoperative complications with topical anesthesia can be high if the surgeon is not highly skilled. If such complications arise surgeon should be ready to convert to other methods of local anesthesia during the intraoperative stage, because topical anesthesia along may not be adequate to handle intraoperative complications. Surgeon should be of cool temperament who can handle such a situation without anxiety. 3. Topical anesthesia is not indicated in all patients specially in anxious stressed patients, people with hearing difficulties, children and very young patients.
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4. As in our country a large number of patients come from rural areas who are illiterate and poor. Their compliance remains very poor and they do not respond adequately to the command during surgery with topical anesthesia. 5. The presence of very opaque cataract is a contraindication to the use of topical anesthesia. This is because surgeon depends on the patient’s ability to visually concentrate on the operating microscope light in order to avoid eye movement during the operation. Patients, who are not able to fix the eyes, may lead to complications. 6. Some patients may feel pain during surgery with topical anesthesia. One patient observed a lot more pain and felt as if a sword was being used to cut him up. The pain continued postoperatively for quite some time. 7. In principle, adequate selection of patients is fundamental when considering the use of topical anesthesia. In spite of these hurdles topical anesthesia will be a safe and common technique for local anesthesia during intraocular surgery in the near future. No Anesthesia Cataract Surgery This is the latest technique of cataract surgery in which no anesthesia is required (whether local or topical). Neither topical or intracameral anesthetics agents are used. This technique is devised by Dr. Amar Agarwal (India) and has been acclaimed and accepted worldwide. Further Reading 1. Arora R et al: Peribulbar anesthesia. J Cataract Ref Surg 17:506–08, 1991. 2. Bloomberg L: Administration of periocular anesthesia. J Cataract Ref Surg 12:677–79, 1986. 3. Bloomberg L: Anterior peribulbar anesthesia. J Cataract Ref Surg 17:508–11, 1991. 4. Davis DB: Posterior peribulbar anesthesia. J Cataract Ref Surg 12:182–84, 1986. 5. Fichman RA: Topical anesthesia, Sanders DR, Slack 1661–72, 1993. 6. Furuta M et al: Limbal anesthesia for cataract surgery. Ophthalmic Surg 21:22–25, 1990. 7. Garg A: Topical anesthesia: Current trends in ophthalmology. New Delhi: Jaypee Brothers Medical Publishers (P) Ltd., 1–5, 1997. 8. Hay A et al: Needle perforation of the globe during retrobulbar and peribulbar injection. Ophthalmology 98: 1017–24, 1991. 9. Kimble JA et al: Globe perforation from peribulbar injection. Arch Ophthalmol 105:749, 1987. 10. Shriver PA et al: Effectiveness of retrobulbar and peribulbar anesthesia. J Cataract Ref Surg 18:162–65, 1992. 11. Zahl K et al: Ophthalmol Clin North Am. Philadelphia: WB Saunders, 1990.
15 Mydriatics and Cycloplegics Ashok Garg Introduction Mydriatics are drugs which dilate the pupil while cycloplegics are agents which cause paralysis of ciliary muscle (paralysis of accommodation). Mydriatics usually produce paralysis of ciliary muscle in greater or lesser degree. • All these drugs when instilled into the conjunctival sac are rapidly absorbed through the cornea and become effective in the inner eye. Currently two classes of drugs: (i) adrenergic agonist, and (ii) cholinergic antagonist are available for mydriatic purpose. For most dilatation procedures, the adrenergic or anticholinergic agents can be used either alone or in combination for maximum mydriasis. Anticholinergic agents used topically in the eye for the purpose of inhibiting accommodation are termed cycloplegics. Their primary use is for cycloplegic refraction and in the treatment of uveitis. Since these agents also inhibit action of the iris sphincter muscle they are effective mydriatics and are commonly used for routine pupillary dilatation. Mydriatic Adrenergic Agents (Sympathomimetic Agents) The effect of sympathomimetic agents on the eye include pupil dilatation, increase in the outflow of aqueous humor and vasoconstriction (α-adrenergic effects), relaxation of ciliary muscle and decrease in the formation of aqueous humor. The various agents of this group used in ophthalmology are as follows. Adrenaline (Epinephrine) Adrenaline acts on dilator fibers and directly produces dilatation after the instillation of four drops of 1:1000 solution, the instillation being repeated in 5 minutes. It is mainly used in the treatment of open angle glaucoma. Adrenaline may be combined with procaine and atropine as a subconjunctival injection to achieve mydriasis in severe cases of iritis. Cocaine Hydrochloride Cocaine hydrochloride is an alkaloid and is used as cocaine hydrochloride 2 percent and 4 percent drops. It acts as a mydriatic by inhibiting the action of amine oxidase. It is toxic
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to the cells of corneal epithelium and this effect may be used to advantage in that the damage to the epithelium allows a greater penetration of drugs through the cornea. It does not cause dilatation of pupil and pupil continues to react to light even after prolonged application. It is, therefore, ineffective when the sympathetic nerve is paralyzed. Phenylephrine Phenylephrine is one of the most common sympathomimetic agents (α-adrenergic stimulant) used in ophthalmology for dilatation purposes. It is used in the form of hydrochloride. It acts directly on the α-receptors of the dilator pupillae causing pupil dilatation. Following topical instillation, it acts on the dilator muscles and smooth muscles or conjunctival arterioles causing pupillary dilatation and blanching of conjunctiva. Its action can be reversed by thymoxamine 0.1 percent. Indications For pupil dilatation in diagnostic purposes (for complete fundus exam) and in various pathological conditions of the eye [in uveitis (posterior synechiae)], open-angle glaucoma in conjunction with miotics, refraction, ophthalmoscopic examination and before intraocular surgery. Contraindications Hypersensitivity to any of these agents, narrow-angle glaucoma, patients with long standing insulin-dependent diabetes, hypertensive patients receiving reserpine or guanethedine, aneurysm, cardiac diseases, debilitated and elderly patients and patients with IOL implantation. Dosage For pupillary dilatation commercial concentrations of 2.5 percent and 10 percent (in 2.5 ml and 15 ml packs) ophthalmic solutions are available. Maximum dilatation occurs in 45 to 60 minutes depending upon the concentration used and number of drops instilled. The pupil size usually returns to predrug levels within 4 to 6 hours. Since phenylephrine has little or no effect on the ciliary muscle, mydriasis occurs without cycloplegia. Phenylephrine 1 percent solution can be used in diagnosis of Horner syndrome. Significantly mydriasis can occur in the eye with a postganglionic lesion as compared to normal innervation. The mydriatic response may be affected in cases of injury to corneal epithelium (corneal abrasions and trauma). Concentration as small as 0.125 percent present in decongestant solution has been reported to cause mydriasis if the corneal epithelium is damaged. In general 2.5 percent topical concentration is used for routine dilatation, specially in children and elderly patients because 10 percent concentration has clinical ocular and systemic side effects. For diagnostic purpose usual dosage is 1 drop of 2.5 percent solution in each eye followed by one drop more in 5 to 10 minutes. Sufficient mydriasis is produced in 15 to 30 minutes and effect lasts for 4 to 6 hours. For pathological condition usual dosage is 1 drop of 2.5 percent or 10 percent solution (depending upon the condition) three times a day till the desired result is obtained. Topical phenylephrine can be used alone or in combination with other mydriatic/cycloplegic agents in diagnostic procedures and pathological conditions of the eye.
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Adverse reactions On topical use it may cause transient stinging on initial instillation, blurring of vision and rarely maculopathy with a central scotoma results from use in aphakic patients. Prompt reversal generally follows discontinuation. Phenylephrine may cause rebound miosis and decreased mydriatic response to therapy in older persons. Systemic side effects include CVS effects like palpitation, tachycardia, extrasystole, cardiac arrhythmia, hypertension, headache and browache but usually diminishes as the treatment is continued. Other effects include reflex bradycardia, pulmonary embolism, myocardial infarction, stroke and death associated with cardiac reactions. Sometimes 10 percent phenylephrine on conjunctival instillation may cause significant elevation of blood pressure. Exercise caution with elderly patients and children and carefully monitor the blood pressure in such cases. Hydroxyamphetamine Hydroxyamphetamine is an indirect acting adrenergic agonist. Its pharmacological action is primarily due to release of norepinephrine from postganglionic adrenergic nerve terminals. It has very little effect on accommodation. Indications To dilate the pupil for diagnostic procedure and ophthalmoscopic examination of the eye. Dosage Hydroxyamphetamine is available as 1 percent topical solution (15 ml pack). It has mydriatic effect comparable to 2.5 percent phenylephrine. Maximum pupillary dilatation occurs in 25 to 40 minutes and effect lasts for 4 to 6 hours. Since the drug stimulates the release of norepinephrine from adrenergic nerve terminals, its mydriatic effect depends on the integrity of the adrenergic innervation to the pupil. A pupil with postganglionic sympathetic lesion will fail to dilate. Hydroxyamphetamine can be used to differentiate clinically postganglionic Horner’s syndrome from one that is central or preganglionic. Hydroxyamphetamine is a slightly weaker mydriatic in young children and infants because the adrenergic innervation to the iris is not yet fully developed in this age group. Adverse effects are similar to those reported with phenylephrine. Cholinergic Antagonist as Mydriatic Agents Cholinergic antagonist specially tropicamide differs from phenylephrine and hydroxyamphetamine in its mechanism of action. Tropicamide blocks the effects of acetylcholine released from cholinergic nerve endings at the iris sphincter and ciliary muscle. The drug, therefore, causes mydriasis and cycloplegia. Compared to other cycloplegics, the accommodative effect of tropicamide is less pronounced and of shorter duration. Dosage Following topical instillation of 0.5 percent or 1 percent ophthalmic preparation. Mydriasis occurs within 20 to 30 minutes and effect lasts for 6 to 8 hours. The advantage of tropicamide over adrenergic mydriatics is that mydriasis with it is more pronounced
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and bright illumination has no significant effect on pupil size. The mydriatic effect appears independently of iris pigmentation. Adverse reactions to tropicamide are quite rare. Since it is devoid of vasopressor action, it is safe for use in patients with cardiac disease and hypertension. Due to its relatively faster onset, short duration and intensity of mydriatic action, tropicamide is presently the drug of choice for pupil dilatation. For clinical situations where maximum pupillary dilatation is desirable, tropicamide is combined with phenylephrine or hydroxyamphetamine. Various commercial combinations are available. The details are given at the end of this chapter. Cycloplegic Mydriatics Cycloplegic mydriatics are commonly used for both objective and subjective refractive procedures. In different pathological conditions of the eye as treatment, specially strabismus in children (esotropia), uveitis (anterior and posterior uveitis) these agents are commonly used. Parasympatholytic agents are commonly used as cycloplegic mydriatics. Mechanism of Action Anticholinergic agents block the responses of the sphincter muscle of the iris and the muscles of the ciliary body to cholinergic stimulation producing pupillary dilatation (mydriasis) and paralysis of accommodation (cycloplegia). Indications For cycloplegic refraction and for dilatation of pupil in the inflammatory conditions of the iris and uveal tract. Contraindications Narrow angle glaucoma, sensitivity to belladona alkaloids or any component. In elderly patients specially with atropine where undiagnosed glaucoma or extensive pressure in the eye may be present. Precautions • Avoid excessive systemic absorption by compressing the lacrimal sac by digital pressure for 1 to 2 minutes after instillation. • Permanent mydriasis may occur in patients with keratoconus. • Use with caution longer acting agents (atropine and scopolamine) and they may cause posterior synechiae formation when treating anterior segment inflammation. • Acute hypersensitivity reaction, discontinue use and have 1:1000 epinephrine solution available.
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• Sulfite sensitivity. • Avoid potentially hazardous tasks (observe caution while driving or performing other tasks requiring alertness). • Do not exceed recommended dosages. • Excessive use in children and suspectible cases should be avoided. Adverse Reactions of Parasympatholytic Agents On topical use adverse effects reported are increased IOP, transient stinging and burning sensation, allergic lid reactions, hyperemia, follicular conjunctivitis vascular congestion, edema, exudate, photophobia and eczematoid dermatitis. Systemic adverse effects include systemic atropine toxicity manifested by flushing and dryness of the skin, blurred vision, photophobia with or without corneal staining, dryness of mouth and nose, anhydrosis, fever, rapid pulse, bladder distention, hallucinosis, loss of neuromuscular coordination. Severe reactions are manifested by hypotension with progressive respiratory depression, coma, medullary paralysis and death. Other adverse effects reported are cardiac dysrhythmias especially in patients undergoing surgery for glaucoma. Headache, parasympathetic stimulation, allergic reactions and toxic manifestations of anticholinergic drugs. In addition, use of cyclopentolate and tropicamide has been associated with psychotic reactions and behavioral disturbances in children. CNS disturbances like ataxia, incoherent speech, restlessness, seizures, disorientation to time and place and failure to recognize peoples. Overdosage When symptoms of atropine toxicity develop (see adverse reactions) administer parenteral physostigmine. Various parasympatholytic agents used in ophthalmology as cycloplegic mydriatics (Table 15.1) are: • Atropine • Homatropine • Scopolamine • Cyclopentolate • Tropicamide. Individual drug monograph is as follows:
TABLE 15.1 Cycloplegic mydriatics Drug Atropine Homatropine Scopolamine
Onset (minutes) 30–40 40–60 20–30
Mydriasis Duration (hours/days) 7–10 d 1–3 d 3–7 d
Cycloplegia Onset Duration (minutes) (hours) 60–90 30–60 30–60
7–10 1–3 5–7
Solution Available 0.5–3% 2–5% 0.25%
Phacoemulsification
Cyclopentolate Tropicamide
30–60 20–40
1d 4–8 hours
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20–45 20–30
1d 4–8
0.5–2% 0.5–1%
Atropine Sulfate Atropine sulfate is a potent parasympatholytic agent for use in producing cycloplegia and mydriasis. It is the strongest mydriatic for common use in ophthalmology. It completely paralyzes the sphincter pupillae and ciliary muscle. It takes considerable time to cause complete paralysis. It is an alkaloid used in water soluble form (atropine sulfate). Indication Atropine sulfate is used both for its cycloplegic and mydriatic effects for cycloplegic refraction or for pupil dilatation in acute inflammatory conditions of the iris and uveal tract. For cycloplegic refraction its use is on decline due to the availability of faster acting, short duration parasympatholytic agents. Dosage Atropine sulfate is available as topical ophthalmic solution in concentration of 0.5 percent, 1 percent, 2 percent and 3 percent. Atropine ointment is available in 0.5 percent and 1 percent concentrations. A single drop of 1 percent atropine solution results in maximal mydriasis in about three hours and effect of single dose lasts for 3 to 7 days. • For uveitis treatment usual dosage is to instill 1 to 2 drops of 1 percent solution into the eyes four times daily while in children recommended dosage is to instill 1 to 2 drops of 0.5 percent solution three times a day. • For refraction—instill one drop of 1 percent solution into the eye twice a day 1 to 2 days prior to examination. While in children recommended dosage is 1 to 2 drops of 0.5 percent solution twice daily 1 to 3 days before the examination and 1 hour before examination. Ophthalmologists consider atropine as first drug of choice for the first refraction in all children under the age of 7 years or when there is risk of convergent strabismus. It may also be used as type of occlusion in amblyopia, latent nystagmus and in difficult cases of accommodative spasms. Atropine is drug of choice in severe anterior segment inflammation reducing the risk of posterior synechiae. Adverse reactions Generalized adverse reactions of parasympatholytic agents are already discussed in this chapter. As atropine has potential local and systemic side effects, it is necessary to discuss these effects separately. Ocular adverse effects Atropine may cause local irritation, accommodative spasm, anterior movement of lens-iris-diaphragm, breakdown of blood-aqueous barrier, decreased anterior chamber depth, drug-induced cicatrizing conjunctivitis, hyperemia, corneal toxicity, increased intraocular pressure, cataract formation, allergic blepharoconjunctivitis, twitching of orbicularis oculi, iris cyst, miosis, increased peripheral vitreal traction. Systemic effects Dose related side effects are depicted in Table 15.2.
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TABLE 15.2 Side effects of atropine Dose
Effects
0.5–2 mg (1–4 drops of 1% solution)
– Tachycardia dry mouth Mydriasis/cycloplegia 5 mg (10 drops, 1% solution) – In addition to above one speech disturbance. Restlessness confusion. Hot/dry skin Decreased GI motility urinary retention >10 mg (20 drops or more of 1% solution) – Above side effect and ataxia, hyperexcitability – Hallucination – Coma – Convulsion – Death
Homatropine Homatropine is semisynthetic alkaloid prepared from atropine. It is used in its water soluble form—homatropine hydrobromide. Indications Homatropine is moderately long-acting mydriatic and cycloplegic for refraction and in treatment of inflammatory conditions of the uveal tract, for preoperative and postoperative states when mydriasis is required and as an optical aid in certain cases of axial lens opacities. Dosage Homatropine is available as 2 percent and 5 percent ophthalmic solution. For refraction instill 1 to 2 drops of 2 percent solution into the eyes and repeat it 5 to 10 minutes if necessary. For uveitis instill 1 to 2 drops of 2 percent solution into the eyes every 3 to 4 hour interval. It acts more quickly than atropine, mydriasis being usually complete within 40 minutes and cycloplegia after one hour of instillation. The duration of action is shorter than atropine and recovery occurs in about 24 hours. Adverse effects have already been covered in general monograph of parasympatholytic agents. Scopolamine Scopolamine is used in its water soluble form of scopolamine hydrobromide. Indications Scopolamine is an anticholinergic agent for use in producing cycloplegia and mydriasis, for preoperative and postoperative states in the treatment of iridocyclitis. Dosage Scopolamine is available as 0.25 percent ophthalmic solution. Usual dosage for refraction is to instill 1 to 2 drops into the eye 1 hour before refraction. For uveitis, instill 1 to 2 drops four times daily into the affected eyes. Its mydriatic effect starts in 20 to 30 minutes and cycloplegic effect appears in 30 to 60 minutes and duration of effect lasts for 3 to 7 days.
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Cyclopentolate HCl Cyclopentolate hydrochloride is a synthetic mydriatic and cycloplegic agent. It is very effective and short-acting. Indications Cyclopentolate hydrochloride is used for mydriasis and cycloplegia in diagnostic procedures. Dosage Cyclopentolate is available as 0.5, 1 and 2 percent ophthalmic solution. Maximal mydriasis occurs in 30 minutes and cycloplegia is usually complete in 40 minutes. To ensure complete cycloplegia two applications of Cyclopentolate HCl are used at 10 minutes interval. Recovery of accommodation usually occurs in 8 to 24 hours. Recommended dosage in adults—instill one drop of 1 percent solution, repeat in 5 to 10 minutes. Although complete recovery occurs in 24 hours time, yet 1 to 2 drops of 1 percent or 2 percent pilocarpine reduces recovery time to 3 to 6 hours in most eyes. In children usual dosage is to instill 1 drop of 0.5 percent, 1 percent or 2 percent solution in each eye followed 5 minutes later by second application. Observe patient closely for at least 30 minutes following instillation. Tropicamide Tropicamide is another rapidly acting mydriatic and cycloplegic agent and acts faster than Cyclopentolate (Short-acting anticholinergic agent). It blocks the parasympathetic fibers and causes relaxation of sphincter pupillae muscle of the iris producing mydriasis. Indications For mydriasis and cycloplegia for diagnostic purposes, when short-acting mydriatic is needed for some preoperative and postoperative states. It prevents constriction of pupil caused by intense light stimulation during indirect ophthalmoscopy or retinal photography. Dosage Tropicamide is available as 0.5 percent and 1 percent ophthalmic solutions. Recommended dosage for refraction is to instill 1 to 2 drops of 1 percent solution into the eyes, repeat after 5 minutes an additional drop to prolong mydriatic effect. For fundus examination, instill 1 to 2 drops of 0.5 percent solution 15 to 20 minutes prior to examination. On account of its short latency, brief duration and effective mydriasis, it is perhaps the best mydriatic for the usual fundus examination. Due to shorter duration of action, it is used as provocative test for acute glaucoma though under strictly controlled conditions. It is used alone or in combination of sympathomimetic agent (phenylephrine) to produce much better response and mydriatic effect persists to facilitate ocular examination. Some other drugs of this group were previously used for mydriatic and cycloplegic effect but now not in use. 1. Duboisine (0.1–1.0% drops) 2. Lachesine or E3 (0.5 drops)
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TABLE 15.3 Relative efficiency of cycloplegics Drug
% Efficiency
1% Atropine 1% Cyclopentolate 1% Tropicamide 5% Homatropine 0.25% Scopolamine
100 92 80 54 48
Mydriatic Combinations Phenylephrine is commonly used with tropicamide, cyclopentolate or scopolamine to induce mydriasis which is greater than of either drug alone. Phenylephrine 5 percent and Cyclopentolate HCl 1 percent Instill 1 drop into each eye every 5 to 10 minutes not to exceed three times. Phenylephrine 10 percent and Scopolamine 0.3 percent For mydriasis, cycloplegia and to break posterior synechiae in iritis. Dosage For mydriasis 1 to 2 drops into the eye and repeat in 5 minutes if necessary. Postoperatively 1 to 2 drops into the eyes 3 to 4 times daily. Phenylephrine 5 percent with tropicamide 0.8 percent • For short acting mydriasis in refraction and in pre- and postoperative states. • For refraction instill 1 to 2 drops and repeat at 5 minutes interval, if necessary. • For postoperative stage instill 1 to 2 drops three times a day. Cyclopentolate HCl 1 percent with Dexamethasone sodium phosphate 0.1 percent • For postoperative inflammation where mydriatic and inflammatory therapy is simultaneously required. Dosage Instill 1 to 2 drops into the affected eyes three times a day. Atropine Sulfate 1 percent solution with Dexamethasone sodium phosphate 0.1 percent For postoperative inflammation and anterior and posterior uveitis where mydriatic and inflammatory therapies are required in addition also. Dosage Instill 1 to 2 drops into the affected eyes three a day. Phenylephrine (5%) and tropicamide (0.8%) combination is commonly used in ophthalmology today. The major advantage of this combination is that it produces quick mydriasis and mydriatic effect persists to facilitate ocular examination. Indications This preparation is mainly indicated for • Ophthalmoscopic examination • Slit lamp examination • Retinal photography • Prior to ocular surgery and other diagnostic procedures. It is also used
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• As an adjunct in the treatment of anterior uveitis • In the management of anterior segment burns (to dilate the pupil and prevent iris adhesions to the lens) • In cycloplegic refraction • For the management of iridocyclitis associated with stromal keratitis • For the management of uveal inflammation associated with fungal keratitis. Dosage This combination is available as topical ophthalmic solution (in 5 ml pack). For ophthalmological examinations, 1 to 2 drops in the eye 15 to 30 minutes prior to the procedure are advised. For other indications frequency should be as per direction of ophthalmologists. This preparation is contraindicated in patients suffering from closed angle glaucoma and hypersensitivity to any ingredient of this formulation. Adverse reactions On topical application there may be transient burning or stinging sensation and lacrimation. Blurred vision, photophobia and allergic reactions may occur.
16 Update on Ophthalmic Viscosurgical Devices Suresh K Pandey, Jaya Thakur Liliana Werner, Andrea M Izak David J Apple Background Viscoelastic substances are solutions with dual properties; they act as viscous liquids as well as elastic solids or gels. The ideal viscoelastic substance in ophthalmology should be viscous enough to prevent collapse of the anterior chamber at rest, yet liquid enough to be injected precisely through a small cannula. It should be elastic or shock absorbing and should enhance coating yet have minimal surface activity. It should be cohesive enough to be easily removed from the anterior chamber but not so cohesive that it is aspirated during irrigation and aspiration, which would provide no protection to endothelial cells during surgical manipulations. It should be eliminated from the eye in the postoperative period without an effect on intraocular pressure.6–8,20,22,23 Viscosurgery was a term coined by Balazs10,11 to describe the use of these solutions that had viscous, elastic and pseudo plastic properties during and after surgical procedures. During viscosurgery, viscoelastic substances are used as a fluid or a soft surgical instrument. The viscoelastic sodium hyaluronate was first used in ophthalmic surgery in 1972, when it was introduced as a replacement for vitreous and aqueous humor.10,11 Since then ophthalmic surgical procedures had undergone considerable advancement. The use of viscoelastic materials has become common place in anterior and posterior segment surgeries. These agents facilitate delicate and often difficult intraocular manipulations during various ophthalmic surgical procedures. They are used during cataract surgery and intraocular lens (IOL) implantation to maintain the anterior chamber depth and capsular bag disten-tion, thus creating and preserving working space for the ophthalmic surgeon. These agents are designed to protect the delicate corneal endothelial cells during the surgery.20 The viscoelastic substances has been termed as “ophthalmic viscosurgical devices” (OVDs).9 A detailed discussion regarding biocompatibility, physical, and rheological properties of the OVDs are beyond the scope of this chapter. Interested readers may consult the excellent review article(s) published by Liesegang on this topic.21,22 The viscoelastic substances must be non-toxic, nonpyrogenic, noninflammatory, nonimmunogenic, and sterile for use in the human eyes. The substance should not interfere with the normal metabolism of the cells in contact with it. Substances that are immunogenic, may cause granulation or capsule formation, stimulate cell invasion, or interfere with epithelization or blood coagulation cannot be used in the eyes.17,22,23 Each viscoelastic substance has unique physicochemical properties which determines its
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clinical appilications.22,23,38,39,44 Figures 16.1 A to C is a gross photograph showing physical characteristics (viscosity) of 3 different concentration of the sodium hyaluronate solution (Healon®, Healon-GV® and Healon-5®). In this chapter, we will provide an update of currently used OVDs and will focus on the newly available viscoadaptive viscoelastics (e.g. Healon-5®), their clinical applications and complications. Some of the details related to OVDs had been discussed in the previous chapter of this textbook.14 The current chapter is based on the review of the published literature on this topic and also derived from the information and illustrations available from the manufacturer. Classification of the OVDs Table 16.1 presents summary of the currently available OVDs. OVDs can be classified according to their Zero shear viscosity and cohesion. The zero shear viscosity is directly proportional to the molecular weight. This classification describes the surgical behavior of the viscoelastics and is as follows.7 1. High viscosity-cohesive OVDs a. Super viscous-cohesive OVDs (>1,000,000 mPs)
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FIGURES 16.1A TO C Gross photograph showing physical characteristics (viscosity) of 3 different concentration of the sodium hyaluronate solution (A) Healon®. (B) Healon-GV® (C) Healon-5®
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TABLE 16.1 Classification of ophthalmic Viscosurgical devices (OVDs) Higher viscosity: Cohesive OVDs Viscosurgical Manufacturer Molecular Source Chemical compound Osmolality Viscosity Vo agents Wt (D) (mOsm/liter) (mPs) Viscoadaptive (fracturable) Healon-5® Pharmacia 5.0 M Rooster Hyaluronic Acid 322 2.3 Na Ha 7.0 M Inc. Coombs (23mg/ml) Super Viscous 5.0 M Rooster Hyaluronic Acid 310 1.4 Na Ha 2.0 M Healon-GV® Pharmacia Inc. Coombs (14 mg/ml) I-Visc Plus® I-Med 7.9 M Rooster Hyaluronic Acid – 1.4 Na Ha 4.8 M Pharma Coombs (14 mg/ml) Viscous I-Visc® I-Med 6.1 M Roster Hyaluronic Acid 336 1.0 Na Ha 1.0 M Pharma Coombs (10 mg/ml) Healon® Pharmacia 4.0 M Rooster Hyaluronic Acid 302 1.0 Na Ha 230 Inc. Coombs (10 mg/ml) K Provisc® Alcon 2.0 M Microbial Hyaluronic Acid 307 1.0 Na Ha 280 fermentation (10 mg/ml) K IO lab (B and 1.0 M Rooster Hyaluronic Acid 340 1.6 Na Ha 100 Amvisc L surgical) Coombs (16 mg/ml) K Plus® Amvisc® IO Lab (B 1.0 M Rooster Hyaluronic Acid 318 1.2 Na Ha 100 and L Coombs (12 mg/ml) K surgical) Biolon® Biotech 3.0 M Bacterial Hyaluronic Acid 279 1.0 Na Ha 215 general corp Fermentation (12 mg/ml) K Low viscosity: Dispersive OVDs Medium Viscosity Alcon 500 K Bacterial Hyaluronic acid Chondriotin 325 3.0 NaHa 41K Viscoat® Fermentation Sulphate 4.0 CDS Shark Fin (40 mg/ml) Vitrax® Allergan 500 K Rooster Hyaluronic Acid 310 3.0 Na Ha 25 K Coombs (30 mg/ml) Cellugel® Vision 100 K Synthetic Hydroxypropylmethylcellulose 305 2.0 38 K biology Chemically (Alcon) modified HPMC Ocucoat® Storz (B and 86 K Wood pulp Hydroxypropylmethylcellulose 285 2.0 HPMC 4 K L surgical) (20 mg/ml) Visilon® Shah and 86 K – – – 2.0 HPMC 4 K Shah (20 mg/ml) Viscon Dr. 86 K – Hydroxypropylmethylcellulose 2.0 HPMC 4 K Agarwal’s (20 mg/ml) Pharma Visicrome® Croma – – – – 2.0 HPMC – Pharma (20 mg/ml) Vo (mPs)= Zero shear Viscosity (milli Pascal Seconds); (D)=Daltons; M=Millions; K=Thousand; NaHa=Sodium hyaluronate; HPMC=Hydroxypropylmethylcellulose; CDS=Chondroitin sulphate
b. Viscous-cohesive OVDs (Between 100,000 and 1,000,000 mPs)
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2. Lower viscosity-dispersive OVDs 3. Viscoadaptive OVDs (e.g. Healon-5®) High Viscous-cohesive OVDs The super viscous-cohesive group includes Healon-GV® and I-visc plus® while the viscous-cohesive group includes products like I-visc®, Provisc®, Healon®, Amvisc®, Amvisc plus® and others. All these products contain sodium hyaluronate. High viscous-cohesive OVDs are indicated in many routine procedures and are used to create space and also stabilize the surgical microenvironment. Examples of situations where they are used include deepening the anterior chamber, to enlarge small pupils, to dissect adhesions, and during IOL implantation to push back the iris and vitreous. Super Viscous-cohesive OVDs ®
Healon-GV (greater viscosity) is a sterile, nonpyrogenic agent produced from rooster coombs. It has a concentration of 1.4 percent sodium hyaluronate and a molecular weight of 5 million Daltons. It is used as a surgical aid in various anterior segment procedures such as cataract extraction, IOL implantation, corneal transplant surgery and glaucoma surgery. In presence of high positive pressure, Healon-GV® has 3 times more resistance to pressure than Healon®. I-Visc® was introduced as a Healon-GV® clone. It has superior viscous and cohesive properties at low shear viscosity when compared to Healon-GV® (Table 16.1). Super viscous-cohesive agents are better in current day techniques where topical and intracameral anesthesia are used and the surgeries are “entirely in-the-bag” phacoemulsification. High cohesiveness of superviscous and viscous materials result in easy removal as a single mass at the end of the surgical procedure, thus preventing the increased intraocular pressure postoperatively. Lower Viscosity-dispersive OVDs Dispersive agents have low molecular weight and shorter molecular chains. Medium viscosity, dispersive OVDs possess zero shear viscosities between 10,000 and 100,000 mPs. Very Low viscosity, dispersive agents include all of the unmodified hydroxypropylmethylcellulose (HPMC) agents. These dispersive materials when injected into the eye have the property of fracturing and breaking into smaller bits and thus disperse in the anterior chamber. They include Viscoat®, Cellugel®, Vitrax®, Ocucoat® and others (Table 16.1). Most of the dispersive OVDs are HPMC-hydroxypropyl methylcellulose, derived from wood pulp. Cellugel® is a chemically modified HPMC. Viscoat® is a combination of sodium hyaluronate and chondroitin sulphate. Vitrax® is a compound of low molecular weight molecular hyaluronate. The clinical use of these agents is to hold back vitreous out of the surgical field especially in cases of zonular disinsertion. They are helpful in a compromised corneal endothelium conditions, as they are capable of dividing the anterior chamber into OVD-
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occupied space and surgical zone in which irrigation/aspiration can be continued without the mixing of the two areas-known as surgical compartilization. The disadvantage of lower viscosity dispersive OVDs is that they do not maintain or stabilize spaces as compared to higher viscosity cohesive agents. They tend to be aspirated in smaller fragments during irrigation/aspiration thus leading to irregular viscoelastic aqueous interface, thus partially obscuring the surgical view of the posterior capsule. They also form microbubbles and can be trapped at the irregular interface thus further obscuring visibility. Moreover they are difficult to remove at the end of the surgery because of low cohesion. Soft Shell Technique This technique was developed by Arshinoff, in order to take advantage of the best properties of both lower viscosity-dispersive agents and high viscosity-cohesive agents and to minimize the drawbacks of each by using them together.8 In this technique first the lower viscosity dispersive is injected into the anterior chamber, followed by high viscosity-cohesive agent, which is injected into the center of the lower viscositydispersive viscoelastic thus pushing it outwards and compressing it into a smooth, even layer against the corneal endothelium. This protects the endothelium during lens removal. Prior to the implantation of the IOL, the reverse is done. High viscosity cohesive is injected first to partially fill the anterior chamber and the capsular bag, followed by injection of lower viscosity dispersive into the center of high viscosity cohesive agent. This allows the free movement of the IOL through the dispersive agent, with better stabilization of the surrounding iris and the capsular bag by the high viscosity agent.48 Removal of the OVDs is easily accomplished at the end of the surgery, since low viscosity dispersive OVA can be aspirated from the central anterior segment first, followed by higher cohesive agent. Duo Visc®-a combination of high viscosity-cohesive Provisc® and the lower viscosity dispersive Viscoat®. Viscoadaptive OVD-Healon-5® The existing viscoelastic products all have drawbacks. A cohesive viscous product used to create and maintain space may not stay in the eye during phacoemulsification. On the other hand, a less viscous dispersive product stays during phacoemulsification but often traps fragments or air bubbles and does not maintain adequate space during the surgical procedure. Recently the new viscoadaptive viscoelastic Healon-5® has been developed to change its behavior at different flow rates.3 It acts as a viscous cohesive viscoelastic agent at lower flow rates and as a pseudodispersive viscoelastic agent at higher flow rates. It is all in one device that adapts its behavior to the surgeons needs during the entire course of surgery. This is a steam sterilized, non-pyrogenic solution. It is highly purified noninflammatory, high molecular weight sodium hyaluronate at a concentration of 23 mg/ml (2.3%) dissolved in a physiological buffer. It has an osmolality and a pH similar to those of the aqueous humor. It has a viscosity at rest about 7 million times higher than aqueous humor. It is extracted from rooster coombs.
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Hyaluronate is a polysaccharide made up of disaccharide units linked by glycosides bonds. It occurs naturally on the corneal endothelium bound to specific receptors. The natural hyaluronate is reduced during irrigation but can be restored by an exogenous one. Healon-5® has a high affinity to the receptors. It acts as a scavenger by neutralizing the free radicals formed during cataract surgery using ultrasound. Characteristics and Advantages of the Viscoadaptive OVDs 1. Viscoadaptive OVD (Healon-5®) is specifically developed so that, at different flow rates it has different functions. At lower flow rates it behaves as a very cohesive viscoelastic like a Healon-GV®. At higher flow rates, e.g. in chopping techniques, it begins to fracture and behaves similarly to a dispersive viscoelastic, such as Viscoat®. Hence Healon-5® has features that can change according to the needs of the surgeon during various stages of cataract surgery. 2. It is crystal clear as pure water and has somewhat higher refractive index than the aqueous humor. Hence it increases the clarity within the surgical field. 3. It also has the ability to protect the delicate corneal endothelial cells from debris and turbulence during phacoemulsification, particularly with very low endothelial cell count. In a recent study by Holzer et al,16 the average loss of corneal endothelial cells was lowest for their surgeries using Healon-5® compared to other OVDs. 4. Viscoadaptive OVD (Healon-5®) is also helpful in patients with suboptimal pupil size because the viscomydriasis allows for a larger capsulorhexis and keeps the pupil larger during phacoemulsification thus increasing the visibility. 5. It also neutralizes the positive vitreous pressure and prevents capsulorhexis from extending by temporarily stopping all action, thus allowing the surgeon to determine what is going on inside the eye, analyze his or her options and effect the appropriate management. 6. The high viscosity of Healon-5® creates space and stabilizes the anterior segment. The elasticity absorbs shock and protects ocular tissues during IOL unfolding, which is slowed down and is more controlled. 7. Healon-5® is also easy to remove. The “Rock and Roll” technique10 with suitable settings for each type of phacoemulsifications, was found to be a safe method for complete removal of it. In this technique there is sufficient turbulence created and this fractures Healon-5® into small pieces. The other method for Healon-5® removal is the two compartment technique (TCT).50 Full advantage of the agent’s viscoadaptive properties is taken in this technique. The superior space maintaining capacity of Healon-5® in the anterior chamber is utilized while removing the substance from the capsular bag. In the second step the anterior chamber is cleaned. There is a learning curve for surgeons using Healon-5®, but as surgeons begin making a number of small procedural adaptations, the advantages of the viscoadaptive OVD will increasingly become apparent.
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Clinical Application of the OVDs In recent years the field of viscosurgery has broadened rapidly. It has been used both intraocularly as well as extraocularly, which includes cataract, cornea, glaucoma, vitreoretinal, strabismus and oculoplastic surgeries.7,22,23,30 Use of OVDs in Cataract Surgery OVDs are helpful in each step of modern cataract surgery using phacoemulsification with IOL implantation.5,13,41,43 Some of these details are shown in the schematic photograph (Figs 16.2A to F and 16.3). Capsulorhexis In order to perform an intact and successful capsulorhexis, the contents of the anterior chamber have an important role. Till date balanced salt solution (BSS®), air and OVDs have been used. Out of these three the best is viscoelastic as it is considered the easiest, safest, and the most reproducible method in both routine and difficult cases (Figs 16.2A and B). To perform a good capsulorhexis, the viscoelastic to be used should have the four basic features: 1. High molecular weight and high viscosity at zero shear rate, which maintains the anterior chamber. 2. Excellent visibility provided by high transparency. 3. Make surgical maneuvers easy, due to high elasticity and pseudoplasticity. 4. It should give a good capsular flap control, providing the soft and permanent spatula effect. Cleavage of Lens Structure It is best performed with the use of OVDs. The ideal viscoelastic material keeps the anterior chamber shape unchanged during BSS® injection and also avoids increase in pressure, which can be produced with excessive amount of BSS® known as capsular blockade. Nuclear Emulsification During phacoemulsification, the viscoelastic is likely to remain in the anterior chamber instead of leaking out of the eye (Fig. 16.2C). OVDs help in preserving the space and also because of their low cohesiveness, they remain in the anterior chamber despite high irrigation flow. Moreover OVDs adhere to the corneal endothelium, thus protecting the corneal endothelial cells. Healon® and Healon-GV® does not trap the air bubble and provide excellent endothelial protection (Fig. 16.2D). This is because of:
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1. Scavenger effect: This effect captures the free radicals released during phaco with consequent inactivation. 2. Binding sites: There are chemical receptors for viscoelastic materials on the corneal endothelium. A molecular bond seems to occur between the viscoelastic solution and the corneal endothelium. 3. High elasticity: This also smoothes the possible impacts of the lens material against the endothelium.
FIGURES 16.2A TO F Schematic photograph showing use of the OVD (viscoadaptive OVD-Healon-5® in this figure) during the various steps of the cataract surgery. (Courtesy: Pharmacia Inc. Peapack, NJ, USA). (A) Injection of the viscoadaptive OVD in the anterior chamber through a 25 G cannula. (B) Capsulorhexis is in progress. (C) Phacoemulsification in
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progress. (D) Viscoadaptive OVD is transparent and easy to see during removal (left). Note the presence of the air bubbles within the anterior chamber after use of dispersive viscoelastic solution (right). (E) Implantation of a posterior chamber intraocular lens in the capsular bag. (F) Removal of the viscoadaptive OVD using irrigationaspiration tip
FIGURE 16.3 Beside posterior chamber IOL fixation in the capsular bag, OVDs can also be used for implantation of the various phakic and aphakic IOL designs in the anterior chamber, ciliary sulcus, etc. Use of the OVD facilitated the implantation of the Artisan® IOL as shown in this photograph (Courtesy: Camil Budo, MD) The phaco tip being in a closed system, its vibrations are transmitted to the internal structures of the eye but viscoelastic provides a smothering shield against them. Irrigation and Aspiration The role of viscoelastic during this procedure is the protection of the endothelium. This is possible due to high adhesiveness. It remains where it is placed, without mixing with the cortex because of its low cohesiveness thus helping in easy removal of cortex.
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Capsular Bag Filling and IOL Implantation During IOL implantation, it is necessary to expand the capsular bag with a viscoelastic. It allows the surgeon to keep the bag well opened and formed thus allowing the easy IOL implantation. OVD is also helpful in correct positioning, centering and allowing for possible IOL rotation maneuvers (Figs 16.2E and F). Beside posterior chamber IOL implantation, OVD has also been used for implantation of other IOL designs (e.g. anterior chamber, iris fixated, artisan lenses, etc.) (Fig. 16.3).52 Cataract Surgery in Pediatric Patient Pediatric cataract surgery like the adult surgery has undergone major changes in recent years with the evolution of techniques including small incision and the development of modern IOLs. The main principle lies in the control of the very elastic nature of ocular tissues.42 It is difficult to perform a good capsulorhexis in the presence of high capsular elasticity. Moreover there is low scleral rigidity, greater intravitreal pressure that makes the capsulorhexis even more difficult, as the pressure tends to curve the capsulorhexis. But with the use of viscoelastic, e.g. Healon-GV® the effective push is in the opposite direction and hence completion of capsulorhexis can be done. In pediatric cases, the capsulorhexis must be started in the central portion and not towards the equator, in order to prevent radial extension. The high-density viscoelastic agents stabilize the posterior chamber and pushed back the vitreous face during the posterior capsulorhexis. During IOL implantation, the capsular bag is kept open and the anterior chamber is well formed thus ensuring easy and safe implantation of the IOL in the bag. These agents also help to dilate the pupil thus maintaining a good intraoperative mydriasis.55–57 OVDs like Healon-GV® can easily be removed at the end of the surgery including the position, which is behind the IOL due to its high cohesiveness thus preventing capsular blockade. Use of the OVDs in Glaucoma Surgery Viscocanalostomy Viscocanalostomy is a new surgical procedure for glaucoma therapy.45 Viscoelastics play an important role in this procedure. Figures 16.4A to F illustrates the surgical steps of Viscocanalostomy. Viscocanalostomy literally means “opening of the canal by means of viscoelastic substance”. This procedure is a non-penetrating and independent from external filtration. The advantages are decreased risk of infection, and decreased incidence of cataract, hypotony and flat anterior chamber as the anterior chamber is not opened, and moreover, with the absence of external filtration the bleb formation is
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FIGURES 16.4A TO F Surgical steps of viscocanalostomy. (A) Deep block construction incision. (B) Cutting the deep block in a single plane with a spoon blade. (C) Proximal to Schlemm’s canal there is a subtle change in the scleral fibers, from a crossing pattern to a tangential pattern, with an increased opacity. (D) Descemet’s window. (E) Cannulating Schlemm’s canal with three puffs of
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viscoelastic directed at the osteum. (F) Tight closure suture of the flap (Courtesy: Dr. med. Tobias Neuhann, MD, Munich, Germany) prevented and also the related discomfort with it. It minimizes the risk of late infections and is independent from conjunctival and episcleral scarring. Viscocanalostomy allows the aqueous to leave the eye, through Schlemm’s canal and episcleral veins thus restoring the natural outflow pathway. This procedure creates a bypass by which aqueous humor reaches Schlemm’s canal, skipping the trabecular meshwork. A chamber is produced inside the sclera, which is in direct communication with the Schlemm’s canal. There is also a communication through the Descemet’s membrane with the anterior chamber. The OVDs should have high pseudoplasticity to allow injection into Schlemm’s canal through a small needle and should have high viscosity at shear rate of zero to maintain the spaces as long as possible. Healon-GV® and Healon-5® are viscoelastics of choice for this procedure. OVDs for Intraocular Delivery of Dyes or Anesthetic Agents Researchers and vision scientists have been using OVDs as a vehicle to deliver capsular dyes for use during cataract surgery.1,25 Mixing these substances with the viscoelastic agent was attempted to prolong their effect and to limit the adverse effect on ocular tissues. Ciba Vision Corp. (Duluth, GA, USA), has recently proposed mixing an OVD with lidocaine. This was termed “viscoanesthesia” and was intended to prolong the anesthetic effect of intracameral lidocaine, as a complement to topical anesthesia. Also, the steps of intracameral injection of OVDs and of intracameral injection of lidocaine, as a complement to topical anesthesia, would be combined in only one step. In this chapter we will briefly address the use of OVDs for viscostaining and viscoanesthesia. Viscostaining of the Anterior Lens Capsule Various non-toxic ophthalmic dyes have been extensively used as diagnostic agents for the detection and management of different ocular disorders. Dyes such as fluorescein sodium, indocyanine green (ICG), and trypan blue have been increasingly used for enhancing visualization by staining intraocular tissues during the adult and pediatric cataract surgery and vitreoretinal surgery. Staining of ocular tissues by using ophthalmic dyes makes visual differentiation and manipulation of tissues easier. Enhanced viewing of ocular tissues can assist a surgeon’s ability to evaluate clinical structural relationships and may help attain surgical objectives with fewer complications. Uses of various capsular dyes for staining the anterior lens capsule in white, mature cataracts have been reported.31–37,46,53 The techniques originally reported for staining the anterior capsule using fluorescein sodium are: staining from above under an air bubble, as proposed by Nahra and Castilla27 and intracameral subcapsular injection of fluorescein sodium (staining from below) with blue-light enhancement. The first technique (staining
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under an air bubble) is currently used by most surgeons. One benefit is the staining of the peripheral anterior capsular rim, which is otherwise difficult to visualize during the phacoemulsification procedure. However, air in the anterior chamber makes it unsteady. Any instrument entering the eye will cause some air to escape, with a rise of the lens-iris plane. A small amount of high-density viscoelastic placed near the incision can prevent the air bubble from escaping the anterior chamber, thus minimizing the risk of sudden collapse. Also, with this technique, there is a progressive dilution of the dye by the aqueous humor. This may be a possible explanation for the fainter staining observed with this technique in recent clinical reports, without compromising its usefulness. Most of the drawbacks of this technique can be avoided by careful use of a viscoelastic solution to seal the incision site. Akahoshi1 proposed the “soft shell stain technique” for performing a CCC in white cataract cases. A small amount of viscoelastic (Viscoat®) was injected into the anterior chamber followed by high molecular weight viscoelastic material (Provisc®) to fill up the chamber completely. The author then injected ICG solution on the lens surface with a bent G27 viso cannula. The anterior capsule was uniformly stained in green and easily visualized while the cornea remained unstained. According to the author, the soft shell stain technique is extremely useful for CCC in white cataracts. Alternatively, the dye solution can be mixed with viscoelastic agents a technique known as “viscostaining of the anterior lens capsule”. Kayikicioglu and coworkers19 proposed a technique for limiting the contact of trypan blue to corneal endothelium by mixing the dye with a viscoelastic solution. These researchers mixed 0.4 percent trypan blue with 1 percent sodium hyaluronate in a 2 mL syringe. The dye, mixed in a viscoelastic solution, is injected onto the anterior lens capsule, which covers the anterior capsule without coming in contact with the corneal endothelium. Trypan blue mixed with sodium hyaluronate greatly increases the visibility of the anterior lens capsule without significantly touching the adjacent tissues. There is always a potential risk of corneal decompensation after intraocular use of self-mixed solutions; however, these authors used this technique without significant surgical and postoperative adverse effects. Use of OVDs in Topical Ophthalmic Anesthesia (Viscoanesthesia) Anesthetic techniques for cataract surgery have also advanced significantly. General anesthesia was preferred in past years, followed by various techniques of injectable anesthesia including retrobulbar, peribulbar, sub-tenon, and subconjunctival anesthesia. Due to marked improvements in surgical techniques, it is no longer essential to ensure complete akinesia of the eye and as a consequence, the technique of topical anesthesia has been popularized as “phaco anesthesia”. This includes eyedrops application, sponge anesthesia, eyedrops plus intracameral injection, and most recently gel application.15,40 Topical anesthesia is the preferred technique for the members of the American Society of Cataract and Refractive Surgery (ASCRS) in the United States (49%; range 37%–63%) according to a survey conducted by David Learning in 2000.21 It revealed that as high as 82 percent of the respondents using topical anesthesia preferred eyedrops in association with intracameral injection of lidocaine. We have recently completed some studies to evaluate the use of viscoelastic agents mixed with topical anesthetic solution (lidocaine). The aim of these studies was to evaluate the safety of this new solution (termed as viscoanesthesia) to intraocular
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structures.24,32,51 Our animal and experimental studies were divided into 3 parts. In Part I,24 we determined the toxicity of the viscoanesthetic solution to the corneal endothelium using a rabbit model. In Part II,51 we evaluated the toxicity of viscoanesthetic solutions to uveal tissues and retina in a rabbit model after performing phacoemulsification. Finally, in Part III,32 using postmortem human eyes, we evaluated and compared to currently available OVDs in regard to the surgical aspects such as injection and aspiration of the viscoanesthetic solutions. In brief, our experimental study demonstrated that addition of varying concentrations of lidocaine to sodium hyaluronate (Ophthalin Plus®) neither significantly altered its viscosity or consistency nor changed its removal time from the capsular bag. Our animal studies on viscoanesthesia (Part I, II) in rabbit eyes had suggested that viscoanesthetic solution with lidocaine concentrations up to 1.65 percent are non-toxic for the corneal endothelium, uveal or retinal tissues. Future clinical trails are necessary to address the issue of efficacy of viscoanesthetic solutions to provide prolonged topical anesthesia. Removal of the OVDs Several techniques have been reported in the literature for removal of the OVDs. These include: Rock and roll technique, two-compartment technique and bimanual irrigation/aspiration technique.4 Figures 16.5A to H are photographs from a human eye obtained postmortem (Miyake-Apple posterior view) showing the sequence of the experimental surgical technique of the removal of fluoresceincolored viscoelastic solutions (green color as viewed with oblique illumination) from the capsular bag using the rock and roll technique. An effective technique to remove Healon-5® is to create maximum turbulence to make it fracture into large pieces. This can be accomplished using rock and roll technique with standard I/A tip, 0.3 mm, with high settings; a flow rate of 25–30 ml/ min., and vacuum 350–500 mm Hg, depending on the type of pump. If a peristaltic pump is used the vacuum should be set towards the lower limit. A bottle height of 60–70 cm above the eye level. Figures 16.6A to C summarizes the removal technique of viscoadaptive agent, Healon-5®.
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FIGURES 16.5A TO H Gross photographs from a human eye obtained postmortem (Miyake-Apple posterior view) showing the sequence of the experimental surgical technique of the removal of fluorescein-colored viscoelastic solutions (green color as viewed with oblique illumination) from the capsular bag was documented by videotaping. (A) This figure shows the eye after capsulorhexis and
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removal of lens substance (cortex and nucleus) by phacoemulsification. Note the edge of the anterior capsulectomy (arrows). (B and C) Injection of fluorescein-colored viscoelastic solution (in this example, Ophthalin Plus®), with a 27 gauge Rycroft cannula through the orifice of the anterior capsulectomy. (D) Capsular bag completely filled with viscoelastic solution. (E) Same eye after insertion of a one-piece modified C-loop posterior chamber IOL in the capsular bag (arrows). (F) Viscoelastic solution removal with automated aspiration, set at 250 mm Hg (Alcon Legacy 20,000). (G) Final removal of viscoelastic substance. The surgeon reached behind the IOL optical edge to remove all the viscoelastic material. (H) Aspect after complete removal of the viscoelastic solution
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FIGURES 16.6A TO C Schematic photograph showing the one of the removal technique of viscoadaptive agent (Healon-5®), as recommended by the manufacturer. (A) The surgeon circle the I/A hand piece in the anterior segment at iris plane. (B and C) The surgeon gently rests the I/A handpiece on the anterior surface of the optic. Press gently on the IOL optic on one side and rotate the I/A handpiece directing the flow into the bag. Direct the handpiece port towards the equator of the capsular bag and stay in this
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position for a few seconds, and then repeat on the other side of the IOL optic until Healon-5® is completely removed. Finally sweep the anterior chamber including the angles and repeat the step if necessary (Courtesy: Pharmacia Inc. Peapack, NJ, USA)
FIGURES 16.7A AND B Schematic photograph showing an alternative removal technique of viscoadaptive agent (Healon-5®), as recommended by the manufacturer. (A) Start the removal directly after IOL implantation, while the anterior chamber is still filled with Healon-5® and before the IOL has been centered. Go behind the IOL optic without engaging the flow of the I/A tip (port up) and then start flow. Remove Healon-5® from the capsular bag first
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and ensure that lens has adequately centered. During removal of Healon5® from the capsular bag, the continuous flow of irrigation fluid keeps the bag inflated and reduces the risk of aspirating the capsular bag. While maintaining continuous flow remove the tip from behind the optic and place it on top of optic. (B) Continue the removal by circling the I/A tip at the iris plane, or on the optic surface, then make an additional sweep in the anterior chamber paying particular attention to angles (Courtesy: Pharmacia Inc. Peapack, NJ, USA) An alternative technique has been developed allowing the use of less turbulence, using a standard I/A tip, 0.3 mm, with effectual flow at 20–25 ml and vacuum 250–3000 mm Hg. The bottle height should be 60–70 cm above eye level. Figures 16.7A and B present the steps of removal technique of the viscoadaptive agent, Healon-5®, using another technique. We would like to emphasize that a careful and thorough removal of the OVDs from the capsular bag and the anterior chamber of the eye is must after the end of the surgery. This is important to avoid complications such as rise in intraocular pressure, crystallization of the IOL surface (see later).47 Studies have shown that complete removal of viscoelastic material from the capsular bag can be more difficult when some hydrophobic acrylic lenses are used because of the IOL’s tacky surfaces (Apple DJ, Auffarth GU, Pandey SK. Miyake posterior view video analysis of dispersive and cohesive viscoelastics, video presented at the Symposium on Cataract, IOL, and Refractive Surgery, Seattle, WA, April 1999). Complications of OVDs OVDs have many positive attributes but their drawbacks and complications must be given careful considerations. Some of the important complications are as follows: Increase in Intraocular Pressure Increase in intraocular pressure is the most important postoperative complication of OVDs. It was first noted with Healon®. The increase in pressure can be severe and prolonged, if the material is not thoroughly removed at the end of the surgery. The rise in
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pressure occurs in the first 6 to 24 hours and resolves spontaneously within 72 hours postoperatively.2,12 The rise in pressure is due to the mechanical resistance of the trabecular meshwork to the large molecules of the viscoelastic material, which decreases the outflow facility. Hence to decrease the incidence of this complication, many have advocated removing and aspirating the viscoelastic material from the eyes at the end of the surgery.16 Crystallization on the IOL Surfaces 29
Olson et al reported a physician survey, laboratory studies, and clinical observations of intraoperative crystallization on IOL surfaces. These authors sent a survey to all ophthalmologists in the states of Wyoming, Idaho, Montana, Utah, and Colorado (USA) asking whether crystallization on the IOL surface had occurred in any of their patients and what viscoelastics, IOLs, and other solutions were used. All returned surveys were tabulated and analyzed by standard statistical means. A sample of crystallization from an IOL submitted by a physician on a glass slide was analyzed to ascertain the relative elemental composition. During in vitro laboratory studies, BSS Plus® (Alcon Surgical, Fort Worth, Texas, USA) and BSS® (Alcon Surgical) were analyzed for precipitation. Healon-GV® (Pharmacia/Upjohn, Kalamazoo, Michigan, USA) and calcium chloride were combined in various solutions and examined for precipitate formation. Silicone IOLs were placed in different BSS® and BSS Plus® solutions with different viscoelastics and varying calcium concentrations. In seven patients, prominent crystallization on IOL surfaces was examined, photographed, and followed for up to 3 years. Results of this interesting survey showed that 206 surveyed ophthalmologists returned 181 surveys (88%) and reported 29,609 cataract surgeries with IOL implantation. In 22 eyes (0.07%) (22 patients) intraoperative crystallization was observed on the IOL surface during 1993. The survey indicated there was a correlation with BSS Plus® (chi-square=4.9, P=.0268) and silicone IOLs (chi-square=6.8, P=.0093). The analyzed sample submitted by one of the surgeons showed the cation to be calcium. The authors concluded that crystallization on the IOL surface during cataract surgery is a rare occurrence that may be associated with calcium as the cation. An osmotic gradient around the IOL is observed with increased calcium concentration. If encountered surgically, the lens should be exchanged in the operating theater after irrigating the anterior chamber with BSS® and completely filling the capsular bag with a low molecular weight viscoelastic.18,29 Since 1993 we received in our Center more than 9,000 IOLs explanted because of different complications. During gross and microscopic analyses of these lenses, it was not uncommon to find crystals on their surfaces, which exhibited some degree of birefringence (Figs 16.8A and B). Sometimes they had the typical fern-like appearance found after precipitation of viscoelastic or salt solutions. We believe those crystals correspond to precipitation of viscoelastic solutions used by the surgeons during the explantation procedure. These may crystallize on the surfaces of the IOLs sent to our Center in a dry state.
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FIGURES 16.8A AND B Crystallization on the IOL surfaces secondary to precipitation of the OVDs on the surfaces. (A) Light photomicrographs taken from the anterior surface of intraocular lenses, which were explanted because of different complications (including error in power calculation) and sent to our Center for analyses. A typical fernlike appearance of the crystals found on the surface of the lenses can be observed. Birefringence under polarized light is observed in the bottom picture. (B) Gross and light microscopic photographs taken from
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the posterior surface of a 3-piece silicone lens explanted because of opacification of the lens optic caused by a whitish deposit. The crystals found on the surface of the lens do not have a typical fern-like appearance, but exhibit birefringence under polarized light (bottom picture) Many lenses sent to our Center were explanted because of the presence of crystalline deposits on their optical surfaces. They caused significant decrease in visual function requiring lens esplantation/exchange (Figs 16.8A and B). Our analyses demonstrated that these deposits were also composed of multiple confluent small crystals, which sometimes did not assume a fern-like appearance, but rather an amorphous arrangement.54 Therefore, it could not be confirmed whether they were related to deposition/crystallization of viscoelastic material. Further studies are necessary to evaluate whether they may correspond to the crystallization of residual viscoelastics in an aqueous environment, late postoperatively. Most specifically, scanning electron microscopy coupled with a surface analysis technique such as energy-dispersive X-ray analysis could determine the elemental composition of the deposits observed on the surfaces of our explanted lenses. These observations highlight the fact that any viscoelastic agent should be thoroughly removed from the capsular bag and anterior chamber of the eye during cataract surgery. Capsular Block Syndrome or Capsular Bag Distension Syndrome Miyake and associate26 proposed a new classification of capsular block syndrome (CBS), a newly described complication of cataract-IOL surgery, to improve understanding of the etiology and provide effective treatment. Three groups of eyes with CBS were reviewed by these authors: eyes originally reported and diagnosed as having CBS; eyes experiencing CBS after hydrodissection and luxation of the lens nucleus; and eyes with CBS accompanying liquefied after-cataract or capsulorhexis-related lacteocrumenasia. These researchers noted that in all 3 groups, the CBS occurred in eyes with a capsulorhexis. It was characterized by accumulation of a liquefied substance within a closed chamber inside the capsular bag, formed because the lens nucleus or the posterior chamber IOL optic occluded the anterior capsular opening created by the capsulorhexis. Depending on the time of onset, CBS was classified as intraoperative (CBS seen at the time of lens luxation following hydrodissection), early postoperative (originally described CBS), and late postoperative (CBS with liquefied after-cataract or lacteocrumenasia). The etiology of the accumulated substance and the method of treatment are different in each type according to their study. These authors concluded that CBS is a complication of cataract/IOL surgery that can occur during and after surgery. Correctly identifying the type of CBS is crucial to understand the nature and effective treatment of this disorder. Recently use of high-density viscoelastic agents, such as Healon-GV®, has been found to be associated with complication of late CBS. Sugiura and associates49 analyzed the transparent liquid between the posterior lens capsule and the posterior chamber (PC) IOL
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in early postoperative capsular block syndrome and discussed the mechanism of posterior capsule distention. These authors evaluated 3 cases of capsular block syndrome presenting with transparent liquid in the distended capsular bag 1 day after cataract surgery. The transparent liquid material between the posterior capsule and PC IOL was aspirated and analyzed using high-performance liquid chromatography (HPLC). Also, sodium hyaluronate was diluted using a dialyzer to determine whether the aqueous humor was drawn into the capsular bag by an osmotic gradient across the capsule. Results of their study suggested that the elution time of the samples was almost the same as that of sodium hyaluronate 1.0 percent. The concentration of the samples ranged from 3.29 to 9.01 mg/mL by HPLC analysis. The sodium hyaluronate absorbed the physiological salt solutions through the dialyzer and expanded to 1.9 times its original volume. These results indicate that the main ingredient of the transparent liquid in capsular bags is sodium hyaluronate and that the distention is caused by aqueous humor being drawn into the capsular bag by an osmotic gradient across the capsule when the capsulorhexis diameter is smaller than that of the PC IOL and by viscoelastic material retained and trapped in the bag intraoperatively. Pseudo-anterior Uveitis The pseudo-anterior uveitis occurs because of the OVD’s viscous nature and also the electrostatic charge of the materials.28 The red blood corpuscles (RBCs) and inflammatory cells remain in the anterior chamber, thus giving it the appearance of uveitis. It spontaneously resolves within three days, requiring no treatment. Sometimes an intraocular hemorrhage gets trapped between the vitreous space and the OVD in the anterior chamber and mimics the appearance of vitreous hemorrhage.28 Summary and Conclusions The choice of a viscoelastic substance depends largely on the intended surgical use. At the present time, no single viscoelastic agent is ideal under all circumstances. For any particular surgical task, the surgeon should consider the multiple physicochemical characteristics of each viscoelastic material available as well as their desirable and undesirable clinical effects, then choose the most appropriate substance. As new materials are developed and as our knowledge of the physical properties, clinical effects, and surgical indications are better defined, the selection process for choosing the best product should improve.20 Widespread success in clinical situations has been achieved with pure hyaluronate and combination sodium hyaluronate chondroitin sulfate material. Although expensive, viscoadaptive agent-Healon-5®, has some distinct advantages. Methylcellulose possess special advantages of lower cost, no requirement of refrigeration, a larger quantity of the material per unit.
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References 1. Akahoshi T: Soft shell stain technique for the white cataract, presented at the ASCRS Symposium on Cataract, IOL, and Refractive Surgery, Boston, MA, May 2000. 2. Anmarkrud N, Begaust B, Bulie T: A comparison of Healon and Amvisc on the early postoperative pressure after extracapsular cataract extraction with implantation of posterior chamber lens. Acta Ophthalmol Scand 74:626–28, 1996. 3. Anna D: Healon 5, The world’s first Viscoadaptive. Ophthalmic Express 6:4, 1998. 4. Arshinoff SA: Rock and roll removal of Healon® GV (video). Presented at the American Society of Cataract and Refractive Surgery Film Festival; Seattle, WA; 1–5, 1996. 5. Arshinoff SA, Hofmann I: Prospective, randomized trial comparing Micro Visc Plus and Healon GV in routine phacoemulsification. J Cataract Refract Surg 24:814–20, 1998. 6. Arshinoff SA, Opalinski YAV, Ma J: The pharmacology of lens surgery: Ophthalmic viscoelastic agents. In Yanoff M, Ducker JS (Eds): Ophthalmology. Mosby-Yearbook: St Louis, 4:20.1–21.6, 1998. 7. Arshinoff SA: Dispersive and cohesive viscoelastics materials in phacoemulsification, Revisited 1998. Ophthalmic Practice 16:24–32, 1998. 8. Arshinoff SA: Dispersive-cohesive viscoelastic soft shell technique. J Cataract Refract Surg 25:167–73, 1999. 9. Arshinoff SA: New terminology: Ophthalmic viscosurgical devices. J Cataract Refract Surg 26:627–28, 2000. 10. Balazs EA, Freeman MI, Kloti R, et al: Hyaluronic acid and replacement of vitreous and aqueous humour. Mod Prob Ophthalmol 10:3–21, 1972. 11. Balazs EA: The development of sodium hyaluronate (healon) as a viscosurgical material in ophthalmic surgery. In Eisner G, (Ed): Ophthalmic Viscosurgery. Bern, Switzerland: Medicopia, 1–19, 1986. 12. Barren BA, Busin M, Page C, et al: Comparison of the effects of Viscoat and Healon on postoperative intraocular pressure. Am J Ophthalmol 100:377–84, 1985. 13. Cobo M, Beaty N: VITRAX? (sodium hyaluronate) in anterior segment surgery: A review and clinical study summary. Adv Ther 7:51–60, 1990. 14. Garg A: Viscoelastic substances and other surgical adjuncts. In Garg A, (Ed): Textbook of Ophthalmology. Jaypee Brothers, New Delhi, India, 126–38, 2001. 15. Pandey SK, Werner L, Apple DJ, et al: No anesthesia clear corneal phacoemulsification versus topical and topical plus intracameral anesthesia: Randomized clinical trial. J Cataract Refract Surg 27:1643–50, 2001. 16. Holzer MP, Tetz MR, Auffarth GU, et al: Effects of Healon 5 and 4 other viscoelastic substances on intraocular pressure and endothelium after cataract surgery. J Cataract Refractive Surg 27:213–18, 2001. 17. Hyndiuk RA, Schultz RO: Overview of the corneal toxicity of surgical solutions and drugs and clinical concepts in corneal edema. Lens Eye Toxic Res 9:331–50, 1992. 18. Jensen MK, Crandall AS, Mamalis N, et al: Crystallization on intraocular lens surfaces associated with the use of Healon GV. Arch Ophthalmol 112:1037–42, 1994. 19. Kayikicioglu O, Erakgun T, Guler C: Trypan blue mixed with sodium hyaluronate for capsulorhexis. J Cataract Refract Surg 27:970, 2001. 20. Larson RS, Lindstrom RL, Skelnik DL: Viscoelastic agents. CLAO J 15:151–60, 1989. 21. Learning DV: Practice styles and preferences of ASCRS members −2000 survey. J Cataract Refract Surg 27:948–55, 2001. 22. Liesegang TJ: Viscoelastics. Surv Ophthalmol 34:268–93, 1990. 23. Liesegang TJ: Viscoelastics. Int Ophthalmol Clin 33:127–47, 1993.
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24. Macky TA, Werner L, Apple DJ, et al: Viscoanesthesia Part II: Evaluation of the toxicity to ocular structures after phacoemulsification in a rabbit model. J Cataract Refract Surg 2002 (in press). 25. McDermott ML, Edelhauser HF: Drug binding of ophthalmic viscoelastic agents. Arch Ophthalmol 107:261–63, 1989. 26. Miyake K, Ota I, Ichihashi S, et al: New classification of capsular block syndrome. J Cataract Refract Surg 24:1230–34, 1998. 27. Nahra D, Castilla M: Capsulorhexis in no view cataract: Staining of the anterior capsule with 2% fluorescein, presented at the annual meeting of the American Academy of Ophthalmology, October 1996, Chicago, Illinois, USA. 28. Nirankari VS, Karesh J, Lakhanpal V: Pseudovitreous hemorrhage: A new intraoperative complication of sodium hyaluronate. Ophthalmic Surg 12:503–04, 1981. 29. Olson RJ, Caldwell AS, Jensen MK, et al: Intraoperative crystallization on the intraocular lens surface. Am J Ophthalmol 126:177–84, 1998. 30. Pandey SK, Ram J, Werner L, et al: Persistent pupillary membrane. Br J Ophthalmol 84:554, 2000. 31. Pandey SK, Werner L, Apple DJ, et al: Dye-enhanced pediatric cataract surgery. J Pediatr Ophthalmol Strabismus 2002 (in press). 32. Pandey SK, Werner L, Apple DJ, et al: Viscoanesthesia Part III: Evaluation of the removal time of viscoelastic/ viscoanesthetic solutions from capsular bag of human eyes obtained postmortem. J Cataract Refract Surg 2002 (in press). 33. Pandey SK, Werner L, Apple DJ, et al: Update on dyeenhanced cataract surgery. In Chang DF, (Ed): Hyperguide Online Textbook of Ophthalmology Thorofare, NJ, Slack, 2001, (http://www.ophthalmic.hyperguide.com/). 34. Pandey SK, Werner L, Apple DJ: Capsular dye-enhanced cataract surgery. In Nema HV, Nema N, (Eds): Recent Advances in Ophthalmology, Jaypee Brothers: New Delhi, India, 6:11–29, 2002. 35. Pandey SK, Werner L, Apple DJ: Staining the anterior capsule. J Cataract Refract Surg 27:647–48, 2001. 36. Pandey SK, Werner L, Escobar-Gomez M, et al: Dyeenhanced cataract surgery. Part I. Anterior capsule staining for capsulorhexis in advanced/white cataracts. J Cataract Refract Surg 26:1052–59, 2000. 37. Pandey SK, Werner L, Escobar-Gomez M, et al: Dyeenhanced cataract surgery. Part III. Staining of the posterior capsule to learn and perform posterior continuous curvilinear capsulorhexis. J Cataract Refract Surg 26:1066–71, 2000. 38. Poyer JF, Chan KY, Arschin SA: New method to measure the retention of viscoelastic agents on a rabbit corneal endothelial cell line after irrigation and aspiration. J Cataract Refract Surg 24:84–90, 1998. 39. Poyer JF, Chan KY, Arschin SA: Quantitative method to determine the cohesion of viscoelastic agents by dynamic aspiration. J Cataract Refract Surg 24:1130–35, 1998. 40. Ram J, Pandey SK: Anesthesia for cataract surgery. In Dutta LC, (Ed): Modern Ophthalmology. Jaypee Brothers: New Delhi, India, 325–30, 2000. 41. Ram J, Pandey SK: Indications and contraindications of phacoemulsification. In Dutta LC, (Ed): Modern Ophthalmology. Jaypee Brothers: New Delhi, India, 437–40, 2000. 42. Ram J, Pandey SK: Infantile cataract surgery: Current techniques, complications and their management. In Dutta LC, (Ed): Modern Ophthalmology. Jaypee Brothers: New Delhi, India, 378–84, 2000. 43. Saini JS, Pandey SK: Advances in techniques of penetrating keratoplasty. In Nema HV, Nema N, (Eds): Recent Advances in Ophthalmology, Jaypee Brothers: New Delhi, India, 4:37–51, 1998. 44. Silver FH, Librizzi JJ, Benedetto D: Physical properties of model viscoelastic materials. J Appl Biomater 5:227–34, 1994.
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45. Stegmann R, Pienaar A, Miller D: Viscocanalostomy for open angle glaucoma in black African patients. J Cataract Refract Surg 25:316–22, 1999. 46. Steinert RF: ICG dye aids in visualization of the anterior capsule. Ophthalmology Times, May 15, 1999. 47. Storr-Paulsen A: Analysis of the short-term effect of two viscoelastic agents on the intraocular pressure after extracapsular cataract extraction. Sodium hyaluronate 1% vs hydroxypropyl methylcellulose 2%. Acta Ophthalmol (Copenh) 71:173–76, 1993. 48. Strobel J: Comparison of space maintaining capabilities of Healon and Healon GV during Phacoemulsification. J Cataract Refract Surg 23:1081–84, 1997. 49. Sugiura T, Miyauchi S, Eguchi S, et al: Analysis of liquid accumulated in the distended capsular bag in early postoperative capsular block syndrome. J Cataract Refract Surg 26:420– 25, 2000. 50. Tetz MR, Holzer MP: Healon® 5 clinical performance and special removal technique (Two Compartment Technique). In Buratto L, Giardini P, Belluci R, (Eds): Viscoelastics in Ophthalmic Surgery. Thorofare, NJ, USA, Slack 401–04, 2000. 51. Trivedi RH, Werner L, Apple DJ, et al: Viscoanesthesia Part I: Evaluation of the toxicity to corneal endothelial cells in a rabbit model. J Cataract Refract Surg 2002 (in press). 52. Werner L, Izak AM, Isaacs RT, et al: Evolution and pathology of intraocular lens implantation. In Yanoff M, Ducker JS, (Eds): Ophthalmology. Mosby-Yearbook: St Louis, 2002 (in press). 53. Werner L, Pandey SK, Escobar-Gomez M, et al: Dyeenhanced cataract surgery. Part II. An experimental study to learn and perform critical steps of phacoemulsification in human eyes obtained post-mortem. J Cataract Refract Surg 26:1060–65, 2000. 54. Werner L, Shugar JK, Apple DJ, et al: Opacification, of piggyback IOLs associated to an amorphous material attached to interlenticular surfaces. J Cataract Refract Surg 26:1612–19, 2000. 55. Wilson ME, Trivedi RH, Apple DJ, et al: Ophthalmic viscosurgical agents (OVAs): A guide for the pediatric cataract surgeons. J Cataract Refract Surg 2002. 56. Wilson ME, Pandey SK, ThakurJ: Pediatric cataract surgery in the developing world. Br J Ophthalmol 2002. 57. Wilson ME, Pandey SK, Werner L, et al: Pediatric Cataract Surgery: Current Techniques, Complications and Management. In Agarwal S, Agarwal A, Sachdev MS, et al: (Eds): Phacoemulsification, Laser Cataract Surgery and Foldable IOLs. Jaypee Brothers Medical Publishers: New Delhi, India, 369–88, 2000.
Section III Phaco Steps 17. The Dynamics of Sutureless Cataract Incisions 18. Incisions 19. Capsulorhexis 20. Hydrodissection and Hydrodelineation
17 The Dynamics of Sutureless Cataract Incisions Samuel L Pallin History Prior to the advent of silk sutures, sutureless cataract incisions were the norm of necessity in ophthalmology but they were not self-sealing for obvious reasons relating to technique and instrumentation. Many advances in technique and technology have taken us through several stages in the evolution of modern cataract operations. The earliest mentions of self-sealing cataract incisions were made by Richard P Kratz in 19801 and by Louis J Girard in 1984.2,3 Dr Kratz viewed the scleral tunnel incision as an astigmatism-neutral method of entering the anterior segment and felt that the sutures which he routinely used provided a “belt and suspenders” secure closure. In 1980s, a mention was made by Jim Gills at a meeting in Atlanta, Georgia, USA, that a sutureless cataract closure should be possible. In March, 1990, Steven B Siepser described a radial transverse incision which admitted only foldable implants.4 This was a workable but technically difficult incision, and was potentially dangerous in inexperienced hands. A brief published report in Ocular Surgery News in March, 1990 quoted Michael McFarland5 who indicated he had developed a sutureless incision for foldable implants which was based on a series of relaxing incisions in the bed of a scleral tunnel. In April, 1990 a Chevron-shaped sutureless scleral tunnel incision (Fig. 17.1) was described by the author in a letter to the Editor of the Journal of Cataract and Refractive Surgery.6 The Chevron® incision was designed to admit not only foldable but rigid lenses as well, and was practical and easily adopted by cataract surgeons. Preliminary results with the Chevron® incision7 were presented at the
FIGURE 17.1 Artist’s depiction of the author’s Chevron® incision 1991 American Society of Cataract and Refractive Surgeons (ASCRS) meeting in Boston, Massachusetts. A similar incision called the Frown incision was widely
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popularized by Jack Singer. Dr. Singer initially closed with one suture and later adapted the Frown incision to sutureless cataract surgery.8 Sutured wounds were not all bad. Like all stages in the advancement of technology, they participated in a cascade of improvements to the field, not the least of which was the use of the operating microscope. It was the quest for finer sutures and better wounds that stimulated the transition to modern microsurgery in ophthalmology. The incision preferred by the majority of ophthalmologists in the United States today is the clear-corneal incision (Fig. 17.2). Most current incisions are designed to be suture free and self-sealing.9 It has become clear that the more corneal the placement of the incision, the certainty of self-sealing without sutures decreases. A scleral tunnel incision or a limbal tunnel incision in most hands will seal if the geometry is correct. Corneal incisions still require sutures in some cases because of the nature of corneal tissue which resists stretching, and because of the tendency of the incision to tear during implant insertion.10,11 According to Nick Mamalis,12 corneal incisions measured preand post- insertion of folded implants show a mean increase in internal width
FIGURE 17.2 Artist’s depiction of a corneal incision of 4.4 to 6.2 percent, depending upon whether forceps or injector insertion technique is used. Common Denominator Having come to this point in the history of the cataract incision, it is appropriate to see what might be the common denominator of self-sealing incisions. The earliest theory proposed was called the “corneal flap mechanism.” In this therapy, a layer of deep cornea seals from the interior against the wound creating a trap-door effect when the eye is reinflated. This was a popular theory to explain self-sealing incisions until April, 1995. In that year at the annual meeting of the ASCRS in San Diego, California, this author presented gonioscopic photographs (Fig. 17.3) showing insertion of an implant through the angle with a slit-like internal incision and no corneal flap.13 The incision was in fact self-sealing, as have been many others like it.
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Properties So, to what factors can we ascribe the self-sealing quality of a cataract incision? One theoretical principle which seems to stand the test of time is the so-called “square incisional geometry.” This means that the length of the tunnel must be equal to or exceed the width of the incision. In other words, a short tunnel with a long incision is less
FIGURE 17.3 Internal view through gonioscopic lens: 1—IOL haptic, 2— wound, 3—leading edge of optic, and 4—trabecular meshwork likely to be self-sealing than a long tunnel with a short incision. Square incisional geometry should be understood to be a general concept, a guideline, and not a strict rule for surgical planning. While the theoretical ideal of a self-sealing tunnel would be a figure in which length is equal to width, in the real world self-sealing incisions only strive to approach that configuration. Rarely does the length of the tunnel actually equal the width of the entry incision and more commonly is marginally smaller. But there is a definite relationship in which the probability that a given wound will be self-sealing is proportional to the successful approximation of square geometry. It is pertinent to discuss two incisions, one at either end of the tunnel: the first is the external entry wound to the tunnel, and the second is the internal communication between the tunnel and the anterior chamber. The reason for the importance of this distinction is that one can make an incision into becoming a self-sealing wound by making the external incision small and the internal incision larger. Lest the reader assume this configuration violates the square geometry rule, bear in mind that the tunnel is still nearly as long as the internal incision and longer than the external incision. In fact a smaller external incision is more reliably self-sealing than a larger external incision. Since a small incision presents an obstacle to the insertion of lens implants, the external incision can be made in a geometric shape which lends itself-to stretching and thus will admit a lens implant without difficulty (e.g. Chevron or Frown). The internal incision located in corneal territory does not lend itself to stretching and tearing can be dangerous. Therefore, the
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internal incision must be of a size to admit the chosen lens implant. So, the properties of the reliable self-sealing incision are • Square incisional geometry • Relatively short external incision, with a tunnel that flares to a larger internal incision • A geometric external incision shape which lends itself to stretching. Incisions which do not meet these criteria are subject to tearing or are problematic when required to be self-sealing. Given the above answers to the question, “What constitutes the essential elements of a self-sealing cataract incision?” One also might like to know what explanation we have for the fact that a pressurized sphere refrains from ejecting its contents through an incision to the atmosphere? In practical terms one can think about the globe as a double-walled structure, at least in the vicinity of the wound. For the purposes of a cataract incision, one wall is the roof of the tunnel and one is the floor of the tunnel. It is these two layers acting in a predictable manner when pressure is applied from within during reformation of the anterior chamber that results in closure of the wound. Visualize for example two latex balloons of the kind we see at children’s parties. One balloon is inserted inside the other balloon. One can make an incision in the outer balloon and then inflate the inner balloon and no air escapes. This is intuitively obvious. If on the other hand, one were to make an incision in the inner balloon as well but place that incision in a remote location away from the incision in the external balloon, and then inflate the internal balloon, one can imagine that the two disparate incisions would fail to communicate and inflation would still be viable. This mechanism is similar to what occurs in the globe after reinflation of the anterior chamber following cataract removal and lens implantation. The internal incision in the anterior chamber, whether it be in clear cornea or at the limbus, is remote from the external incision on the sclera, the limbus, or the cornea. The two incisions do not communicate directly. Communication can be forced by accessing the tunnel between them. When the internal pressure of the eye is re-established and the tunnel reacts to increased pressure from the interior as compared with ambient atmospheric pressure on the exterior surface of the globe, the tunnel collapses and the two incisions, in disparate locations, no longer communicate. The current popularity of clear-corneal incisions is understandable considering several advantages • Topical and intracameral anesthesia have been shown to be most effective in clearcorneal procedures.14,15 • Corneal incisions are usually located at the temporal aspect of the anterior segment which tends to counteract against-the-rule (ATR) astigmatism found in the elderly population most commonly.16,17 • The lack of the necessity to incise conjunctiva and cauterize blood vessels saves time and is esthetically pleasing to the surgeon. However, there are some disadvantages also to corneal incisions: • It is difficult to obtain square incisional geometry since a long tunnel through cornea presents a problem during manipulations in the anterior chamber.18,19 This phenomenon has been called “oarlocking” (Fig. 17.4).
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FIGURE 17.4 Artist’s depletion of an example of oarlocking • Since the tunnel in a clear-corneal incision cannot be very long, square geometry dictates the external incision be limited in length. Short external corneal incisions tend to tear when a lens implant is forced through an incision of marginal size.11,12,20,21 • Corneal tissue does not heal quickly, is not usually subject to fibrosis, and forms relatively weak adhesive bonds making the incisions less secure.11,22 • Corneal incisions depend for their integrity upon swelling of the lips of the incision initially. However, swelling is a transient phenomenon and the incision which appears to be self-sealing at surgery may be easily induced to leak in the postoperative period. According to Kurt Buzard, “It is by no means certain that the shift of the external opening of the incision toward the cornea [from the sclera] is beneficial, and in fact it is our contention that it is a negative development with disadvantages that are hidden by the smaller size routinely used for clearcorneal incisions.23 With respect to iatrogenic astigmatism—there is a controversy over whether a superior scleral tunnel incision or a temporal clear-corneal incision induces less astigmatism. If there is a difference, it appears to be a small one. But there is agreement over the fact that earlier stabilization occurs with scleral tunnel incisions.24–26 A few words about folding lens implants versus rigid implants—since small incisions in general and clear-corneal incisions in particular are favored based upon the premise that smaller and smaller incisions are preferable, it is necessary to regard the lens implant as the limiting factor in the tendency to decreasing size of incision. Bear in mind that the geometry of a lens implant is three-dimensional. One has to account for the diameter of the implant, but what is often forgotten is that one must also account for the thickness. For example, a planoconvex implant of 15 diopters might have a calculated central optical thickness of 0.64 mm. A 25-diopter similar lens would have a central thickness of 0.98 mm.27 Therefore if a very high-powered implant (for example, a +25 diopter lens) is folded or rolled, the thickness constitutes a significant part of the challenge in the insertion sequence. In other words, an incision which is sufficient in length to admit a 15-diopter implant which is folded, may not be sufficiently large to admit a 25diopter folded lens. As a result there is a law of diminishing returns in choosing folding lens implants over rigid implants solely for the purpose of making the incision smaller. It is possible to imagine that a rigid implant of say, 15 diopters may
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actually require a smaller incision than a very thick folded implant of 25 diopters. Add to this the fact that some soft lens materials have a lower index of refraction than the polymethylmethacrylate (PMMA) of hard implants. With a lower index of refraction, the foldable implant must be thicker than its hard counterpart of the same power. It is also true that the “smaller is better” dictum as applies to incisions has limitations. Transitioning from a large planned extracapsular incision to a small phacoemulsification incision does provide increased wound integrity and decreased iatrogenic astigmatism. But it is not clear that the same advantage applies, for instance, when the transition is from a scleral tunnel incision of 4.0 or 4.5 mm to a clear-corneal incision of approximately 3.2 mm (note—the author’s Chevron incision stretches from approximately 4.0 mm to more than 5.5 mm).7 Nevertheless, clear-corneal incisions and folded lens implants have become the most popular combination of choice by United States surgeons today.9 With the burgeoning numbers of clear-corneal procedures it is not surprising that some of these are subject to tearing during implant insertion and may require a suture for security more often than a scleral tunnel or limbal tunnel incision does. Conclusion In conclusion, it is proper to say that many variations of incisional design and incisional closure are viable and successful. Modern cataract incisions vary in geographic and anatomical location from superior to temporal and from scleral to clear corneal in position and location. There is agreement in two areas: (i) it is generally accepted that a smaller incision is better than a larger incision—this is true for reasons of wound integrity and the control of iatrogenic astigmatism, and (ii) there seems to be agreement among surgeons and patients that self-sealing incisions are preferred to sutured incisions. No doubt there will be continued progress in the area of wound construction and there is a plethora of solutions and more on the horizon with respect to management of astigmatism. Wound length, wound placement, tee-cuts, relaxing incisions, toric intraocular implants, and laser ablations in the photorefractive keratectomy (PRK) and in the LASIK configurations are available to modify astigmatism at the present time. Astigmatism historically has been the greatest stimulus to the exploration of cataract wound design. It is possible that with laser ablation and wavefront analysis the treatment of first order and higher order aberrations will be accomplished as a distinct and separate procedure making the astigmatism concern of very little significance in cataract wound design. The one challenge that will always attend cataract surgery is a secure suture-free closure. In this discussion a description of those principles which lead to reliable selfsealing closures is presented.
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References 1. Kratz RP, Colvard DM, Mazzocco TR et al: Clinical evaluation of the Terry surgical keratometer. Am Intraocular Implant Soc J 6:249–51, 1980. 2. Girard LJ, Hofmann RF: Scleral tunnel to prevent induced astigmatism. In Emery JM, Jacobson AC (Eds): Current Concepts in Cataract Surgery: Proceedings of the Eighth Biennial Cataract Surgical Congress Norwalk: Appleton-Century-Crofts 101–102, 1984. 3. Girard LJ: Origin of the Scleral Tunnel Incision (letter). J Cataract Refract Surg 21:7, 1995. 4. Radial Incision Helps Reduce Astigmatic Forces. Ocular Surgery News 1, 1990. 5. Surgeon Undertakes Phaco, Foldable IOL Series Sans Sutures. Ocular Surgery News 1, 1990. 6. Pallin SL: Chevron incision for cataract surgery (letter). J Cataract Refract Surg 16:779–81, 1990. 7. Pallin SL: Chevron sutureless closure—a preliminary report. Proceedings American Society of Cataract and Refractive Surgery Annual Symposium Boston, MA, 1991, and later published. J Cataract Refract Surg 17:706–09, 1991. 8. Singer JA: Frown incision for minimizing induced astigmatism after small incision cataract surgery with rigid optic intraocular lens implantation. J Cataract Refract Surg 17:677–88, 1991. 9. Learning DV: Practice styles and preferences of ASCRS members—1998 survey. J Cataract Refract Surg 25:851–59, 1999. 10. Ernest PH: Cataract incisions—rationale for the limbus. EyeWorld 2(9): 56, 1997. 11. Radner W, Amon M, Mallinger R: Diamond-tip versus blunt-tip caliper enlargement of clear corneal incisions. J Cataract Refract Surg 23:272–76, 1997. 12. Mamalis N:. Incision width after phacoemulsification with foldable intraocular lens implantation. J Cataract Refract Surg 26:237–41, 2000. 13. Pallin SL: Self-sealing versus corneal flap. Proceedings of the American Society of Cataract and Refractive Surgery Annual Symposium San Diego, CA. 1995 14. Gills J: The Use of Intraocular Xylocaine to Control Intraoperative Discomfort During IOL Surgery. Proceedings from the Fifth Annual Ocular Surgery News Symposium Cataract and Refractive Surgery (Suppl) 22, 1997. 15. Koch P: Anterior chamber irrigation with 1% unpreserved lidocaine for anesthesia for cataract surgery—a prospective sutdy of 400 cases. Proceedings from the Fifth Annual Ocular Surgery News Symposium Cataract and Refractive Surgery (Suppl) 32, 1997. 16. Fine IH: Corneal tunnel incision with a temporal approach. In Fine IH, Fichman RA, Grabow HB (Eds): Clear-Corneal Cataract Surgery and Topical Anesthesia Thorofare: Slack, 5–28, 1993. 17. Fine IH: Self-sealing corneal tunnel incision for small-incision cataract surgery. Ocular Surgery News 38–39, 1992. 18. Ernest PH, Lavery KT, Kiessling LA: Relative strength of scleral corneal and clear corneal incisions constructed in cadaver eyes. J Cataract Refract Surg 20:626–29, 1994. 19. Mackool RJ, Russell RS: Strength of clear corneal incisions in cadaver eyes. J Cataract Refract Surg 22:721–25, 1996 20. Kohnen T, Lambert RJ, Koch DD: Incision size for foldable intraocular lenses. Ophthalmology 104:1277–86, 1997. 21. Steinert RF, Deacon J: Enlargement of incision with phacoemulsification and folded intraocular lens implant surgery. Ophthalmology 103:220–25, 1996. 22. Ernest P, Tipperman R, Eagle R et al: Is there a difference in incision healing based on location? J Cataract Refract Surg 24:482–86,1998. 23. Buzard, KA, Febbraro, JL: Transconjunctival corneoscleral tunnel “blue line” cataract incision. J Cataract Refract Surg 26:242–49, 2000.
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24. Lyhne N, Krogsager J, Corydon L et al: One year followup of astigmatism after 4.0 mm temporal clear corneal and superior scleral incisions. J Cataract Refract Surg 26: 83–87, 2000 25. Olse T, Dam Johansen M, Bek T et al: Corneal versus scleral tunnel incision in cataract surgery: a randomized study. J Cataract Refract Surg 23:337–41, 1997. 26. Huang FC, Tseng SH: Comparison of surgically induced astigmatism after sutureless temporal clear corneal and scleral frown incisions. J Cataract Refract Surg 24:477–81, 1998. 27. Naeser K, Naeser EV: Calculation of the thickness of an intraocular lens. J Cataract Refract Surg 19:40–42, 1993.
18 Incisions Luis W Lu, Alejandro Espaillat Ana Claudia Arenas Francisco Contreras-Campos Introduction Intracapsular cataract extraction, popular during the 1970s, generally utilized a large corneal incision performed superiorly creating an against-the-rule astigmatism as a consequence. The switch to extracapsular cataract extraction (ECCE) with intraocular lens (IOL) implantation was a real improvement in the quality of vision, but did little to resolve the post cataract astigmatic errors due to the large incisions needed to introduce the IOL. With the introduction of phacoemulsification, and new foldable IOL designs, creating the correct small incision became crucial to determine the successful outcome of the procedure, and minimize the residual amount of astigmatism. The Limbal Incision In 1989, McFarland and Ernest introduced an incision architecture that allowed the phacoemulsification, and intraocular lens implantation without the need of suturing. Besides lengthening the “scleral tunnel”, as named by Girard and Hoffmann, this incision ended in a corneal entrance and a posterior lip, the so-called corneal lip, which acted as a one-way valve with self-sealing characteristics. Paul Koch described what he called the “incision funnel” indicating that there were certain characteristics of self-sealing incisions with respect to length and configuration, that imparted self-sealability as well as but also astigmatism neutrality. There are two aspect views of these incisions: sagittal and anteroposterior; and three components: the external incision, the intratissue tunnel and the internal incision. From the sagittal aspect, limbal incisions can be made in one of the following configurations varying between single-plane, grooved beveled and, triplane with a groove and a bevel. The external component may also be in one of the following theoretical configurations: the singlestep “stab” incision, as initially introduced by Howard Fine, and the two-step grooved incision by Charles Williamson, who felt that the wound should be larger on the outside than the inside, creating a trapezoid configuration. The sagittal shape, and the direction of the tunnel may also vary, but usually are made flat by blades advancing in a single plane. On the other hand, its anteroposterior configuration can be as a parallelogram.
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The third component of these incisions, the internal opening, may have a single-plane “Stab” or biplane “Steeped” sagittal shape. The anteroposterior aspect of the wound incision could be made limbus-parallel, tangential, or limbus antiparallel “corneal frown”. The limbal incision could be located superior, oblique or temporal. Superiorly located incisions, when not under the influence of sutures, are known to have an against-the-rule astigmatic effect. The oblique location, whether nasal or temporal, is advocated by some surgeons who prefer this site for ergonomic reasons as well as for greater wound stability. The temporal wound incision has been shown to be the most astigmatically neutral of these three locations, achieving stability almost immediately, and maintaining it for life.1,2 The limbal incision is very simple to perform making the maneuvers of entrance, and instrumental manipulation easy for the surgeon. It is used primarily by the surgeon in transition to phacoemulsification from the classic ECCE. The technique usually starts with a conjunctival peritomy, followed by a perpendicular limbal incision made with a metal or diamond blade, and an oblique entrance to the anterior chamber (Fig. 18.1). The length of the incision could be as small as 2.5 mm initially to keep a close system, and a deep anterior chamber during the phacoemulsif ication procedure, then it could be enlarged up to 6.0 mm, depending on the type of the IOL used.
FIGURE 18.1 Limbal incision. Oblique entrance to the anterior chamber Both limbal and clear corneal incisions heal by fibroblast response. The key is the timing of the healing process: 7 days for vascular origin (limbal) and 60 days for a vascular origin (corneal). Clear corneal incisions are also more subject to foreign body sensation than limbal incisions.1,2
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The Scleral Incision The scleral pocket incision was developed to provide a self-sealing and an astigmatically neutral incision.1,2 The incision size, and configuration are determined by the surgeon’s preference, and the chosen style of intraocular lens. The options for incision configuration include, linear shape or tangential to the limbus, smile shape or concentric to the limbus, and frown shape or opposite of the limbal curvature (Figs 18.2A and B). The frown configuration minimizes against-the-rule astigmatism, and is reportedly the most astigmatically neutral of these incision.3,4 A potential disadvantage of the frown incision is the difficulty in enlarging it, if conversion to ECCE is necessary. The technique usually follows the creation of a conjunctival flap with the base at the fornix, and blunt dissection of the sub-Tenon’s space with scissors. Mild cautery of the bleeding conjunctival and episcleral vessels is performed with high frequency bipolar diathermy. The globe is fixated, and the scleral incision is then made in three steps. The first step is to mark the lateral limits of the
FIGURES 18.2A AND B Smile (18.2A), and Frown (18.2B) configuration scleral tunnel incision
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scleral incision with calipers, followed by the creation of a vertical groove of a desired length and configuration, 40 to 50 percent scleral depth, using a microsurgical steel or diamond blade held perpendicular to the surface of the sclera. The second step is the creation of the scleral tunnel, with a rounded crescent blade, dissecting a lamellar flap anteriorly through the sclera, 1 to 2 mm into clear cornea. The dissection is carried forward to Descemet’s membrane at the anterior edge of the vascular arcade. The last step is the advancement of the scleral tunnel incision, aiming the tip of the keratome toward the center of the lens, dimpling the Descemet’s membrane of the cornea, before entering the anterior chamber creating a triplanar self-sealing incision. The scleral tunnel must extend into the clear cornea to avoid the prolapse of the iris, damage to the structures of the chamber angle, fluid loss and a flat anterior chamber, and to create a valve effect which will seal the wound at the end of the surgery. Some of the disadvantages of the scleral tunnel incisions are that it can surgically induce astigmatism, from the use of cautery to control bleeding conjunctival, and episcleral vessels,5,6 presents a difficult access to the anterior chamber with limited movement of the surgical instruments, and a difficult access to the lens nucleus, aspiration of the lens cortex, and IOL manipulation. The Clear Corneal Incisions The more advanced incision for phacoemulsification surgery is the clear-cornea incision. The indications for clear corneal cataract surgery have expanded significantly since the last few years. Initially the indications were limited to those patients on anticoagulants, with blood dyscrasias, patients with cicatrizing diseases such as ocular pemphigoid, or Stevens Johnson syndrome. However, the greatest advantage of the clear corneal incision has been the ability to do surgery with topical anesthesia. Another big advantage of clear corneal incisions is the tremendous safety with relative astigmatism neutrality, coupled with exceptional results. This is a bloodless, self-sealing, sutureless, and quick incision, best performed temporally, where the distance from the visual axis to the periphery is longer, and accessibility to the eye is optimal. This temporal approach includes also better preservation of pre-existing corneal configuration, and of the limbal zone at the 12 o’clock position in case of a future filtering surgery. It can also be used to reduce the patient’s natural astigmatism by approximately 0.50 diopters in that meridian.5,6 This type of incisions can be classified, after Fine, depending on: I-Location • Corneal tunnel incision: entry posterior to limbus, exit at the cornea-scleral junction. • Corneal tunnel incision: entry just posterior to the limbus, exit in clear cornea. • Clear corneal tunnel incision: entry and exit in the clear cornea. II-Architecture • Single plane no groove
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• Shallow groove<400 microns • Deep groove>400 microns III-Size and Planar Configuration • Single-plane incision 2.5 by 1.5 mm, rectangular tunnel • Two-plane incision 2.5 by 1.5 mm rectangular tunnel • Three-plane incision 2.5 by 1.5 mm rectangular tunnel plus perpendicular arcuate component. When making the incision, a decision must be made as whether to groove or not to groove, the external aspect to the incision. Non-grooved single-plane incisions utilize a 2.5 to 3.0 mm steel or diamond knife.7 First the anterior chamber is filled with a viscoelastic agent through the paracentesis site, giving the eye stability prior to entry into the anterior chamber. The globe is then fixated with a fixation ring or forceps to avoid creating conjunctival tears, hemorrhages, or corneal abrasions. The uniplanar incision is made inserting the blade in-and-out through the cornea at the surgical limbus, 1 mm anterior to the limbal vessels in the plane of the cornea until the shoulders, which are 2 mm posterior to the point of the knife, touch the external edge of the incision. After the tip enters the anterior chamber, the initial plane of the knife is re-established to cut through Descemet’s in a straight line configuration. A grooved, triplanar, self sealing, clear-cornea incision has three steps. The first step is the creation of an approximately 300 µm deep, perpendicular incision to the corneal surface, 1 mm anterior to the limbal vessels, using steel or preferably a calibrated diamond blade. The second step is the creation of a 1.75 to 2 mm stromal tunnel, parallel to the iris plane, dissecting the corneal stroma in a lamellar fashion. The third and final step is to downward tilt the keratome blade 30 degrees toward the visual axis, in order to penetrate the anterior chamber.8 The stability of the wound depends on the construction of the internal valve, the total width of the incision, and the length of the tunnel.9 Generally, the clearcorneal incision is limited to 4 or 5 mm in length in order to be self-sealing. The use of a foldable IOL that could be inserted through a 3 to 4 mm incision allows the surgeon to perform a purely corneal sutureless tunnel of 1.5 to 2.0 mm length, with minimal variation in the preexisting astigmatism.10 When properly created, the clear-cornea incision will seal by itself. This can be hastened by stromal hydration.11 Stromal hydration is best accomplished by the injection of fluid via syringe attached to a 27-gauge cannula tightly against the lateral wall of the deeper layers of the incision causing immediate opacification. All properly created incisions usually seal after 1 to 2 minutes, when the stroma opposes properly. In summary, one has to understand the rationale of clear corneal incisions: • Excellent access to the anterior chamber for proper capsulorrhexis performance, access to the cataract, and IOL placement. • Virtually bloodless incision. • Enables the formation of a self-sealing incision, resistant to deformation or leakage. • Variable incision architecture capable of eliminating pre-existing astigmatism. • Faster physical rehabilitation of the patient.
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• Being an anastigmatic incision, the refractive stability is almost perfect, enabling additional reading spectacles to be prescribed in a short period of time. • Faster healing with virtually no irritation, and redness.
The Side Port Incision A side port incision is a small paracentesis limbal incision 1 mm wide, and 0.75 mm long, usually created 90 degrees away from the main incision, using a 15–30 degrees metal blade, or a 1 mm diamond blade. The side port incision should always be used during phacoemulsification because it provides an access route for the introduction of viscoelastic, saline, anesthetics, and antibiotics to the anterior chamber. It can also be used to introduce additional instruments during the surgery to stabilize the globe, manipulate the lens nucleus, protect the posterior capsule, keep the iris in place, and facilitate the removal of the lens cortex, as well as the insertion of the IOL. The paracentesis incision is generally performed with the anterior chamber still closed, or with the chamber open but previously filled with a viscoelastic agent. The incision is performed through the clear cornea, just in front of the limbal vessels, tangential to the iris. The external end of the incision is usually larger than the internal wound, to facilitate the introduction of the surgical tools. When performed correctly the paracentesis incision is self-sealing. It is very important to avoid creating a paracentesis that is too narrow, wide, superficial, deep, anterior, or posterior, to facilitate the introduction of surgical instruments, and prevent fluid leakage, iris prolapse, and corneal folds. Relaxing Incisions Improved spherical and astigmatic outcomes are now well-recognized benefits of modern small-incision cataract surgery. The combination of limbal or corneal relaxing incisions with cataract surgery is fundamental to the current definition of “Refractive Cataract Surgery”, which has come to represent a reality for cataract patients. Over the past several years, great efforts have been made to study the astigmatic effects of various cataract incisions. By manipulating the size, location, and shape of the incisions, surgeons could tailor the astigmatic outcome according to the patient’s preexisting astigmatism. If a patient has enough pre-existing astigmatism to warrant reduction, modern astigmatic keratotomy may then be conservatively added to arrive at the desired cylindrical outcome. Arcuate astigmatic relaxing incisions (RIs) have proven to be extremely safe and reliable,12 and have been used since the early 1970s to reduce high pre-existing astigmatism in cataract surgery.13 The RIs can be made at the limbus (LRIs), or at the cornea (CRIs), depending on the amount of astigmatism. Although CRIs remain a powerful tool for correcting high astigmatism, they have a limited predictability, and often may result in overcorrection particularly in patients with lower amounts of preoperative astigmatism. Most surgeons prefer to use LRIs to correct the pre-operative astigmatism, because they are easy to perform, more comfortable for the patient, result in more regular corneal topographies with less corneal distortion, postoperative refractions
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are less variable, overcorrections are rare, and are effective in patients with low to moderate astigmatism, usually 3 diopters or less. To create a relaxing incision some surgeons advocate placing an orientation mark at the limbus at the 12 o’clock position before the patient is supine. The surgeon will then determine the amount, and axis of the corneal cylinder through corneal topography. The refractive cylinder is usually not considered in phakic patients, because any lenticular astigmatism would be removed by the cataract surgery, and cannot be included in the surgical plan. The LRIs are created using a diamond blade which incorporates an special preset 600-µm diamond microknife. The globe is fixated with a modified Fine-Thornton fixation ring, and the diamond blade is placed in the steep axis at the limbus just anterior to the palisades of Vogt, creating an incision of an appropriate length by visually following the degree marks on the metal ring. The number, and length of incisions are determined according to the various nomograms previously published.12–15 Astigmatic keratotomy, whether primary or associated with cataract surgery, is a simple, low-cost, and effective procedure. Following surgery, these incisions appear to heal quickly, and are nearly unidentifiable within several days leaving a long lasting effect on the patient’s quantity and quality of vision. Cataract surgery is a procedure which is in a constant evolution, and undoubtedly will continue to improve in the future. In the mean time, following the previous suggestions will help surgeons achieve a successful outcome of a phacoemulsification cataract extraction. References 1. Fine HI: Architecture and construction of a self-sealing incision for cataract surgery. J Cataract Refract Surg 17 (Supp):672–76, 1991. 2. Steinert RF, Brint SF, White SM, et al: Astigmatism after small incision cataract surgery: A prospective, randomized, multicenter comparison of 4 and 6.5 mm incisions. Ophthalmology 98:417–24, 1991. 3. Singer JA: Frown incision for minimizing induced astigmatism after small incision cataract surgery with rigid optic intraocular lens implantation. J Cataract Refractive Surgery 17(Supp): 677–88, 1991. 4. Koch PS: Mastering phacoemulsification: A simplified manual of strategies for the spring, crack and stop and chop technique. 4th ed. Thorofare, NJ: Slack, 19, 1994. 5. Long DA, Monica ML: A prospective evaluation of corneal curvature changes with 3.0 to 3.5 corneal tunnel phacoemulsification. Ophthalmology 103:226–32, 1996. 6. Ley land MD: Corneal curvature changes associated with corneal tunnel phacoemulsification. Ophthalmology 103: 867–88, 1996. Letter. 7. Fine IH: Self-sealing corneal tunnel incision for smallincision cataract surgery. Ocular Surgery News 1, 1992. 8. Williamson CH: Cataract keratotomy surgery. In: Fine IH, Fichman RA, Grabow HB, (Eds): Clear-Corneal Cataract Surgery and Topical Anesthesia. Thorofare, NJ: SLACK; 87–93, 1993. 9. Buratto LL: Phacoemulsification: Principles and Techniques. 1st ed. Thorofare, NJ: Slack, 41, 1998. 10. Albert DM: Ophthalmic Surgery: Principles and Techniques. 1st ed. Maiden, MA: Blackwell Science, 25(283):1999. 11. Mackool RJ: Current Personal Phaco Procedure. In Fine IH (Ed): Clear-Corneal Lens Surgery. Thorofare, NJ: SLACK; 239–50, 1999.
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12. Gills JP, Gayton JL: Reducing pre-existing astigmatism. In Gills JP, Fenzl R, Martin RG, (Eds): Cataract Surgery: The State-of-the Art. Thorofare, NJ: SLACK Inc; 1998. 13. Troutman RC: Management of pre-existing corneal astigmatism. In: Emery JM, Paton D, (Eds): Current Concepts in Cataract Surgery. St. Louis, Mo: CV Mosby; 1976. 14. Masket S, Tennen DG: Astigmatic stabilization of 3.0 mm temporal clear corneal cataract incisions. J Cataract Refract Surg 22:1451–55, 1996. 15. Nichamin LD: Intraoperative astigmatism. In Ford JG, Karp CL, (Eds): Cataract Surgery and Intraocular Lenses, a 21st Century Perspective. Ophth. Monographs 7, 2nd ed. AAO, LEO series. 2001.
19 Capsulorhexis Tobias Neuhann History “Cataract surgery has been developed to its ultimate state and any improvements from this date will be insignificant,” said one of the most renowned US ophthalmologists in 1962. Fortunately, this statement proved to be wrong throughout the four decades to follow until today and ophthalmological progress has continued to solve major problems and challenges managing both a multitude of different anatomic conditions as well as of material characteristics and designs of ophthalmic implants and devices. One of the major problems of the late 1970s and early 1980s was pupil capture of intraocular lenses due to sulcus implantation. This problem was seriously by the members of today’s ASCRS. As result of this discussion was favorising the idea of intraocular lens implantation into the capsular bag. The Simcoe loops (modified C-loop), a new design of that time, provided a considerable improvement in intracapsular centration compared to the generally used J-loops. However, the problem of decentration remained in 10–15 percent. Analyzing this decentration showed that disregarding targeted and correct endocapsular implantation tears of the anterior capsule originated, so that at least one loop luxated into the sulcus, thus mostly forming the precondition for later decentration. The Kelman Christmas-tree and also the Galand letter-box technique as well as the most frequently applied can-opener technique produced jagged edges which formed a locus minoris resistentiae, so that the logical conclusion was to develop a method to open the capsular bag in such a way that only smooth edges were created. Based on mutual experiences and observations my brother, Thomas E Neuhann, and myself were the first to describe the reproducible method of capsulorhexis.1 At the same time and completely independent of our development Howard Gimbel worked on the same idea, produced the same result and called his new technique continuous tear capsulotomy. In the attempt to find the most suitable and precise term for the new technique and to take the original terminological approach of both inventors into account Neuhann and Gimbel finally decided to call their mutual development “continuous curvilinear capsulorhexis” 2 the CCC. It has become the standard technique for planned anterior as well as posterior capsular opening. Taking into account that two independent developments had been made in the “Old” as well as in the “New World” and that this approach has remained the method of choice for opening all kinds of capsules until today shows that the CCC simply was the most logical conclusion summing up the experiences of the past (Fig. 19.1).3,4
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Needle Technique Using the needle technique, first an initial puncture of the anterior capsule within the central area to be removed is required. This puncture is then extended in a curve-shaped manner to the targeted eccentric
FIGURE 19.1 CCC with IOL in situ; clinical picture
FIGURE 19.2 Basic principle of the CCC
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FIGURE 19.3 The right and safe way to perform the CCC circle to be described. Either pushing starts the circular tear or pulling the central anterior capsule in either direction, while the flap to be created is gently lifted. The next step is to turn over the flap and apply the vectorial forces in tearing with the needle in such a way that a more or less concentrically opening originates. Once the full circle is almost completed the end will automatically join the beginning of the curve outside in (Figs 19.2 to 19.4).
FIGURE 19.4 Right and wrong approach to close the CCC
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Another option is to place the first puncture directly within the planned curvature and start the rhexis with a curved enlargement of this tiny hole. In this case the tear is brought around on both sides, until the ends finally join together as already described above.5 The needle technique can be performed using BSS or viscoelastics. In addition the below factors are essential for the success of the needle capsulorhexis: Needle 1. Although many different needles could theoretically be applied, only the 23 gauge needle is recommended. The lumen of this type of needle is just sufficient to produce a pressure exchange between the anterior chamber and the BSS irrigating bottle. 2. The metal of such a cannula offers just enough rigidity to provide the necessary resistance for difficult manipulations. Needles with higher gauge do not meet the described requirements, and this alone may cause a CCC failure—even though this fact is unfortunately not generally known. 3. A higher, i.e. positive pressure in the anterior chamber compared to the intracapsular pressure
FIGURE 19.5 Stellate burst created by a blunt needle is mandatory. This becomes especially noticeable with intumescent lenses, where the lens protein is hydrated resulting in a volume increase inside the capsular bag, which results in a considerable increase in the endocapsular pressure as a consequence. The necessary prerequisite for a successful capsulorhexis is a pressure of the anterior chamber that is greater than or equal to that inside the capsular bag. The pressure in the anterior chamber can be adjusted via the height of the infusion bottle. 4. The needle tip should be as sharp as possible, since a blunt needle will lead to stellate burst, which is more difficult to handle (Fig. 19.5).
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Forceps Technique The principle of the forceps capsulorhexis exactly follows the principle of the needle technique. In addition to the known Utrata forceps there are mini forceps that are similar in construction to the forceps developed for the posterior segment of the eye. The advantage of the mini forceps is that they can be inserted into the anterior chamber via a paracentesis, so that the incision is not exposed to needless strain (Figs 19.6A to C).5
FIGURES 19.6A TO C CCC performed with capsulorhexis forceps; clinical pictures
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Comparison of the Needle and Forceps Technique The forceps technique is easier to learn. For this reason it is also the most frequently applied capsulorhexis technique. However, applying the forceps technique, the use of viscoelastics is mandatory. The advantage of the needle technique is that it is economical, since it can be performed with application of BSS as well as viscoelastics and the cost of the needles is neglectable. To point out the difference between the needle and the forceps technique, the following example might be appropriate: To turn over a page of a book you can take the sheet between two fingers and turn it from one side to the other (this is what you do with the forceps), or you take a moistened finger, press the page a bit down and then turn it over (that is what you do with the needle; the counter hold is the cortex). With this in mind the consequences appear quite clear cut. I will always use a needle technique, the initial puncture peripheral or central, for the great majority of my cases. The forceps I will use in those situations where the needle—so to say—lacks the other branch. This is mainly the case in the presence of a liquefied cortex or in cases where a secondary enlargement of the capsulorhexis diameter is required.5 The Two-Step Needle Technique Today the two-step needle technique belongs to the past. Here, the capsule is first opened peripherally with the needle below the incision and the incision is enlarged in a curveshaped manner to the right and left applying the sharp edges of the needle accordingly, so that a larger flap is created. By bending the same needle now in such a way that the flap, which was transformed into an incision, is flipped around the tear is completed in the known way.5 Capsulostripsis This technique was invented by F.Rentsch and described by J.H.Greite at the 1995 ASCRS meeting (Fig. 19.7). This approach is specifically designed for difficult cases, where the intracapsular pressure exceeds that of the anterior chamber. With this method a vitrector with infusion sleeve is used to create an irregular opening in the anterior capsule. Experience shows that a guillotine-type cutter is preferable to a rotating system. To prevent the capsule from tearing, extremely slow motion is essential. The resulting opening in the capsule is a jagged, however, the rounded, mouse-bite-like cuts of the vitrector tip nevertheless produce a stable rim, because of the favorable distribution of forces of this series of mini arcs.
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FIGURE 19.7 Capsulostripsis opening and IOL in situ (Courtesy of JH Greite) This technique is rather time-consuming compared to conventional CCC performed by an experienced surgeon. On the other hand, it is easy to perform and provides a reliable alternative for hypermature or even milky cataracts without sufficient red reflex and other cases with difficult CCC, such as subluxated lenses or cataracts in children with elastic capsules.6–8 Diathermy Capsulotomy Another alternative method to create a circular and stable aperture of the anterior capsule that has been quite frequently discussed for some time is diathermy capsulotomy. In the attempt to create a circular rim in opening the capsule with this method mostly bridges remain that have to be cut with micro-scissors. To perform this technique, the use of viscoelastics is required. The method is especially recommended for intumescent cataracts, but a number of surgeons find it easier to perform than the CCC in general. However, even though the postoperative result may resemble that of a capsulorhexis, it should not be neglected that comparative studies demonstrated that the CCC is more stable and has a perfectly smooth edge, in contrast to the diathermy opening, which is marked by multiple irregularities and offers less stability and less elasticity. Hence, the application of diathermy in routine cataract surgery cannot be recommended.9–11 Capsulorhexis Size The author prefers a capsulorhexis that is somewhat smaller than the optic diameter of the IOL to be implanted. The CCC provides enough stability and elasticity to allow intraocular manipulations even with a smaller anterior aperture without any hazard. In fact, no study has ever been able to show that a larger CCC diameter relative to the IOL optic is more advantageous. Supporting this preference, comparative studies found that in
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addition a slightly smaller capsulorhexis diameter seems to reduce the postoperative opacification of the posterior capsule.12–14 When it comes to rhexisfixated IOL implantation, this type of IOL is completely excluded in the presence of an excessive rhexis diameter, for instance in case of damage of the posterior capsule, which is another reason why the rhexis size should be kept somewhat smaller than the lens optic. Furthermore, study results suggest that a smaller capsulorhexis size is likely to produce a smaller postoperative IOP as well as better effectivity of sharp edges of some IOL designs. Difficult Cases Small Pupil The fact that several different methods are available to intraoperative extend a narrow pupil has made capsulorhexis easier to perform in such cases. The generally applied measures in such cases are: • Removal of the pupillary membrane; • Bimanual stretching; • Removal of synechiae; • Iris hooks; • Pupil dilator. To perform a capsulorhexis in the usual way, first the pupil is extended using one of these methods. This is followed by creation of the CCC with needle or forceps. Pseudoexfoliation Syndrome, Uveitis und Pigmentosa With these patients often a thickened anterior capsule can be clinically observed, which is hard to tear. Another common finding in such cases is also a subluxated lens, which is only diagnosed intraoperative. An important aspect of surgery in such patients is to strictly refrain from a rather small capsulorhexis, as the result of this might be an undesired shrinkage of the anterior capsule. Capsules of Infants, Children and Juveniles Due to the high elasticity of the anterior capsule a smaller rhexis must be performed in such patients than is the case with adults. Here it must be taken into account that the rhexis opening still enlarges by 0.5 to 1.0 mm after completion of the rhexis. Regarding pediatric posterior capsulorhexis, the necessity of an accompanying anterior vitrectomy is controversially discussed. Here, in a number of cases a self-sealing closure provided by the IOL could be successfully achieved.15 A new method to create a CCC in infantile and juvenile capsules was recently described by Nischal.16 This new modification is called the two-incision push-pull capsulorhexis. Here, two stab incisions are made proximally and distally to the incision approximately 4.5 to 5.0 mm apart in the anterior capsule, thus outlining the diameter of
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the planned capsulorhexis. One end of the distal edge of the proximal anterior capsule stab is grasped using a fine capsulorhexis forceps and gently pushed toward the corresponding point of the distal stab incision and continued until halfway to the distal stab incision. A corresponding procedure is performed with the proximal edge of the distal anterior capsule stab incision until half a CCC has been created. An analogous procedure is performed on the other side, resulting is a complete capsulorhexis opening. This technique is specifically designed to meet the special conditions of the elastic pediatric capsule, because the tearing forces are always directed to the pupillary center, thus resulting in a curvilinear tear. The technique can be applied for the anterior as well as posterior CCC. Capsulorhexis in Calcified Capsules or Anterior Flaps These cases mostly require a completely individual CCC, where an additional application of Ong 01 Vannas scissors or comparable tools is required. Posterior Capsulorhexis A series of indications, such as large-scale capsular fibroses, damage of the posterior capsule17 or less frequent conditions like persisting arteria hyaloidea as shown by Greite at the 1990 ESCRS meeting may require a primary or secondary posterior capsulotomy. In the same way as the anterior CCC also the posterior capsulorhexis offers the preservation of a stable capsule. First the anterior capsulorhexis is performed using forceps or needle in the usual way and phacoemulsification or IOL explantation are carried out as preferred. The anterior segment is filled with viscoelastics to stabilize the posterior capsule. Then the posterior capsule is first only perforated and viscoelastics are injected prior to further manipulations. This instillation of viscoelastics behind the capsule is vital to prevent a vitreous prolaps. The posterior CCC can then be carried out with needle or forceps in the same way as an anterior CCC. In some cases a successive vitrectomy may be necessary to prevent the vitreous from invading the capsular bag via the posterior opening. The remaining tire-like capsular residue provides a stable and secure site for intraocular lens fixation.18 Gimbel especially recommends a posterior capsulorhexis in pediatric cataract surgery to avoid secondary membrane formation after cataract extraction.19 Capsulorhexis in the Presence of a Broken Posterior Capsule If ruptures of the posterior capsule occur intraoperative and cannot be transformed into a posterior CCC placement of the IOL in the ciliary sulcus with the known disadvantages of this fixation as listed below seems to be the only option. To avoid this, rhexis fixation of the IOL is the possible solution. The author at the 1991 ASCRS Film Festival first presented the applicable technique. The precondition for this method is an intact anterior capsulorhexis with a diameter that is smaller than that of the IOL optic. In rhexis fixation, the lens optic is manipulated behind the anterior capsulorhexis rim with a spatula, while the loops remain in the sulcus. This approach leaves the IOL optic securely positioned inside the capsule in a button-like manner (Figs 19.8 and 19.9). This method is also an
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option for pediatric surgery, where mostly a posterior capsulorhexis is performed as well to prevent secondary cataract formation.25,26 The only restriction using this method is the implied exclusion of plate-haptic IOLs. The advantages of this technique are: • No sunset or sunrise syndrome are possible; • Rotation and decentration are excluded; • The calculated lens power is effective because of the reliable location of the optic; • Iris chafing cannot occur; • Vitreous prolaps is prevented by stable endocapsular placement of the implant;
FIGURE 19.8 Principle of rhexis fixation of an IOL
FIGURE 19.9 Rhexis fixation of an IOL; clinical picture • Secondary cataract formation is avoided due to removal of the posterior capsule. Howard Gimbel described a variation of this technique in the middle of the 1990s. In his modified approach, he used the opened posterior capsule as support/fixation location in
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infantile or juvenile lens implantation, thus trying to prevent a vitreous prolaps calling this procedure capsular capture.19 Anterior and Posterior Capsulorhexis M.J.Tassignon works on that same topic to fixated IOLs on the capsulorhexis. Her technique is called “bag in the lens”. The IOL has no haptics but only a hinge of the IOL edge and is fixated while clipping the two capsular leaves in this edge hinge. Further clinical investigation is currently running to evaluate this very interesting IOL design and technique. Insufficient Red Reflex In cases of an insufficient or completely missing red reflex due to mature or hypermature cataract blue staining of the anterior capsule is now possible to increase the visibility for performance of the CCC. This method became very fast the recommended technique in such cases.20–24 Another option to deal with this problem is capsulostripsis instead of a capsulorhexis, as already described earlier in this chapter. Complications and Pitfalls There are three major potential intraoperative problems an ophthalmic surgeon may find himself confronted with performing the CCC: Discontinuity of the Capsulorhexis To avoid this complication the capsulorhexis should never be completed from inside out. But also stellate bursts originating from initial puncturing attempts with a blunt needle may destroy an intact capsular margin in the course of surgery to form a discontinuity which presents a most critical source for a radial tear down into the peripheral capsule. In the presence of such a discontinuity the entity of mechanical forces inside the capsular bag concentrate on this weakest point, and the only effective remedy is to repair the discontinuity immediately. If such a repair by transformation of the tear into a smooth edge is no longer possible, utmost care must be employed in the remaining intracapsular mani- pulations. Tear into the Zonula If a tear has already reached a zonular fiber, a conventional repair of the capsulorhexis is too hazardous, because it might result in further rupture right along the zonular fiber toward the equator. To cope with this critical situation two different approaches are available. One way is to follow the end of the respective zonula down to its origin, gently free it with the forceps and use this singled-out zonular fiber to tear a smooth-edged
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curve to unite with the otherwise intact capsulorhexis. The other and more risky approach is to firmly and briskly pulls the flap toward the center. Insufficient Capsulorhexis Size Realizing during the process of circular tearing that the capsulorhexis will be smaller than originally planned is not really an intraoperative problem. In such cases all the surgeon has to do is to direct the vector forces in such a way that the circle is not closed but rather proceeds further into the periphery. With this kind of spiral-shaped enlargement the CCC diameter can be increased to the desired size. Once the capsulorhexis is large enough the circle is closed in the usual way. Captured Viscoelastics If the anterior capsular rim adheres to the anterior IOL surface after implantation viscoelastics residues may be trapped behind the lens. Usually this problem does not occur if the viscoelastics are carefully removed. If it does, mostly the lens blocks the passage for the viscoelastics into the anterior chamber and at the same time allows the aqueous to invade the area behind the implant, thus pushing the IOL against the cornea. In such a situation an additional puncture of the peripheral anterior or—in comparably narrow pupils—posterior capsule is required to provide for a release of the viscoelastics into the anterior chamber or the vitreous, respectively. Disadvantages of the CCC As of the introduction of the CCC, a new problem was described over time, which is the capsular shrinkage syndrome or capsular phimosis.27 This complication is not known in any other capsulotomy technique and solely relates to the CCC. The genuine pathomechanism could not be clarified until today. Clinically this problem can be observed especially in patients suffering from Pseudoexfoliation syndrome (PEX), uveitis, retinopathy pigmentosa or subluxation in combination with PMMA or silicone IOL implantation. All these diseases have a considerably reduced number of zonula fibers in common. The fact that up to now this complication has not been described in patients suffering from these diseases in context with an acrylic IOL implantation allows the conclusion that a certain mechanical interaction of acrylic lens surface and capsule successfully prevents this problem, so that the acrylic IOL is presently the lens of choice in such cases. This, however, is not valid for low-water acrylics. A potential remedy to avoid the problem of capsular shrinkage is the insertion of a capsular tension ring.
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Discussion The development of the capsulorhexis definitely introduced a new age in small incision cataract surgery. This applies both for the development of new phacoemulsification techniques as well as for the important role phacoemulsification plays in modern cataract surgery in general. In addition, the CCC has opened the gate for the development of a multitude of new and refined foldable IOLs and implantation devices, because it was the first capsulotomy technique to offer a stable and reliable anterior capsular opening, so that today even a toric correction is possible with implantation of posterior chamber IOL. While capsulorhexis as a principle is well established, its technical performance is being refined and advanced. In this context I would like to stress once again that capsulorhexis in essence really is not a technical procedural detail but a fundamental surgical principle. Its theory needs to be well understood—then its technical details emanate as a logical consequence. In other words, you should be convinced that this anterior capsular opening is what you want to have. Also secondary surgery including intraocular lens exchange benefits from the specific properties of the capsulorhexis aperture. Intraocular manipulations in the anterior as well as posterior segment of the eye belonging to the realm of phantasy only two decades ago are feasible today; now that circular apertures at any required number and dimensions in both the anterior and the posterior capsule can be created securely and without taking the risk of tear originating from intraoperative manipulations. And what is more, the structural integrity of the capsule is not only maintained throughout the course of surgery but also postoperatively, thus forming the precondition for stable, safe and permanent IOL placement. From its invention 20 years ago the CCC has managed to form a reliable basis for all new developments of the ophthalmic market and no comparable technique to open the capsular bag has been invented ever since. In this way, the CCC occupies its place as one of the important milestones of ophthalmology. References 1. Neuhann T: Theorie und Operationstechnik der Kapsulorhexis. Klin Monatsbl Augenheilkd 190:542–45, 1987. 2. Gimbel HV, Neuhann T: Continuous curvilinear capsulorhexis (letter). J Cataract Refract Surg 17:110–11, 1991. 3. Assia EI, Apple DJ, Barden A et al: An experimental study comparing various anterior capsulectomy techniques. Arch Ophthalmol 109(5):642–47, 1991. 4. Krag S, Thim K, Corydon L et al: Biomechanical aspects of the anterior capsulotomy. J Cataract Refract Surg 20(4): 410–16, 1994. 5. Neuhann T: Capsulorhexis, Phacoemulsification, Laser Cataract Surgery and Foldable IOLs, In Agarwal S, Agarwal A, Sachdev MS, et al: (Eds): Jaypee Brothers Medical Publishers (P) Ltd: New Delhi 81–88, 1998. 6. Wilson ME, Bluestein EC, Wang XH et al: Comparison of mechanized anterior capsulectomy and manual continuous capsulorhexis in pediatric eyes. J Cataract Refract Surg 20(6):602– 06,1994.
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7. Wilson ME, Saunders RA, Roberts EL, et al: Mechanized anterior capsulectomy as an alternative to manual capsulorhexis in children undergoing intraocular lens implantation, J Pediatr Ophthalmol Strabismus 33(4):237–40, 1996. 8. Andreo LK, Wilson ME, Apple DJ: Elastic properties and scanning electron microscopic appearance of manual continuous curvilinear capsulorhexis and vitrectorhexis in an animal model of pediatric cataract, J Cataract Refract Surg 25(4):534–39, 1999. 9. Morgan JE, Ellingham RB, Young RD, et al: The mechanical properties of the human lens capsule following capsulorhexis or radiofrequency diathermy capsulotomy, Arch Ophthalmol 114:1110–15, 1996. 10. Krag S, Thim K, Corydon L: Mechanical properties of diathermy capsulotomy versus capsulorhexis—a biomechanical study. J Cataract Refract Surg 23:86–90, 1997. 11. Sugimoto Y, Kuho E, Tsuzuki S et al: Histological observation of anterior capsular edges produced by continuous curvilinear and diathermy capsulorhexis. J Jpn Ophthalmol Soc 100(11):858–62, 1996. 12. Ravalico G, Tognetto D, Palomba M et al: Capsulorhexis size and posterior capsule opacification. J Cataract Refract Surg 22(1):98–103, 1996. 13. Hollick EJ, Spalton DJ: Capsulorhexis size? Smaller seems better. J Cataract Refract Surg 2(5):12, 1997. 14. Cekic O, Batman C, Effect of capsulorhexis size on postoperative intraocular pressure, J Cataract Refract Surg 25(3): 416–19, 1999. 15. Gimbel HV, Chin PK, Ellant JP: Capsulorhexis, Ophthalmol Clin North Am 8(3):441–45, 1995. 16. Nischal KK: Two-incision push-pull capsulorhexis for pediatric cataract surgery, J Cataract Refract Surg 28:593–95, 2002. 17. Galand A, Van Cauwenberge F, Moossavi J: Le capsulorhexis posterieur chez l’adulte. J Fr Ophtalmol 19(10):571–75, 1996. 18. Sandler G: Pediatric Ophthalmology, Benefits seen to posterior capsulorhexis, anterior vitrectomy in children, http://news.eyeworld.org/October/08%20Kellan%20WZ.%20html.html. 19. Gimbel HV, DeBroff BM: Posterior capsulorhexis with optic capture—maintaining a clear visual axis after pediatric cataract surgery. J Cataract Refract Surg 20(6):658–64, 1994. 20. Fritz WL: Fluorescein blue, light-assisted capsulorhexis for mature or hypermature cataract, J Cataract Refract Surg 24(1):19–20, 1998. 21. Nahra D, Castilla M: Fluorescein-stained capsulorhexis, J Cataract Refract Surg, 24(9):1169– 70, 1998. 22. Melles GR, de Waard PW, Pameijer JH, et al: Färbung der Linsenkapsel mit Trypanblau zur Visualisierung der Kapsulorhexis bei Maturkataraktchirurgie, Klin Monatsbl Augenkeilkd 215(6):342–44, 1999. 23. Gotzaridis EV, Ayliffe WH: Fluorescein day improves visualization during capsulorhexis in mature cataracts, J Cataract Refract Surg, 25(11):1423, 1999. 24. Nodarian M, Feys J, Sultan G, et al: Utilisation du bleu trypan pou la realisation du capsulorhexis dans la chirurgie de la cataracte blanche, J Fr Ophthalmol 24(3): 274–76, 2001. 25. Behrendt S, Wetzel W: Vollständige Okklusion der Kapsulorhexisöffnung durch Vorderkapselschrumpfung. Ophthalmologe 91(4):526–28, 1994. 26. Neuhann T: When posterior capsule tears, use capsulorhexis for IOL fixation. Phaco and Foldables 4(6):1–3, 1991. 27. Sabbagh LB: Rhexis can hold IOL when posterior capsule breaks. Ocular Surgery News 3(3):1–10, 1992.
20 Hydrodissection and Hydrodelineation I Howard Fine, Mark Packer Richard S Hoffman Hydrodissection Hydrodissection of the nucleus in cataract surgery has traditionally been perceived as the injection of fluid into the cortical layer of the lens under the lens capsule to separate the lens nucleus from the cortex and capsule.1 With increased use of continuous curvilinear capsulorhexis2,3 and phacoemulsification in cataract surgery, hydrodissection became a very important step to mobilize the nucleus within the capsule for disassembly and removal.4–7 Following nuclear removal, cortical cleanup proceeded as a separate step, using irrigation and aspiration handpieces. Fine has previously described cortical cleaving hydrodissection,7 which is a hydrodissection technique designed to cleave the cortex from the lens capsule and thus leave the cortex attached to the epinucleus. Cortical cleaving hydrodissection usually eliminates the need for cortical cleanup as a separate step in cataract surgery by phacoemulsification, thereby eliminating the risk of capsular rupture during cortical cleanup. Technique A small capsulorhexis, 5 to 5.5 mm, optimizes the procedure. The large anterior capsular flap makes this type of hydrodissection easier to perform. The anterior capsular flap is elevated away from the cortical material with a 26-gauge blunt cannula (e.g., Katena Instruments No. K7–5150) prior to hydrodissection (Fig. 20.1). The cannula maintains
FIGURE 20.1 Placement of the cannula under the anterior
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capsulorhexis in one of the distal quadrants, elevating the capsule the anterior capsule in a tented-up position at the injection site near the lens equator. Irrigation prior to elevation of the anterior capsule should be avoided because it will result in transmission of a fluid wave circumferentially within the cortical layer, hydrating the cortex and creating a path of least resistance that will disallow later cortical cleaving hydrodissection. Once the cannula is properly placed and the anterior capsule is elevated, gentle, continuous irrigation results in a fluid wave that passes circumferentially in the zone just under the capsule, cleaving the cortex from the posterior capsule in most locations. When the fluid wave has passed around the posterior aspect of the lens, the entire lens bulges forward because the fluid is trapped by the firm equatorial corticalcapsular connections (Fig. 20.2). The procedure creates, in effect, a temporary intraoperative version of capsular block syndrome as seen by enlargement of the diameter of the capsulorhexis. At this point, if fluid injection is continued, a portion of the lens prolapses through the capsulorhexis. However, if prior to prolapse the capsule is decompressed by depressing the central portion of the lens with the side of the cannula in a way that forces fluid to come around the lens equator from behind (Fig. 20.3), the cortical-capsular connections in the capsular fornix and under the anterior capsular flap are cleaved. The cleavage of cortex from the capsule equatorially and anteriorly allows fluid to exit from the capsular bag via the capsulorhexis, which constricts to its original size, and mobilizes the lens in such a way that it can spin freely within the capsular bag.
FIGURE 20.2 Enlargement of capsulorhexis as seen following second cortical cleaving hydrodissection fluid wave placed in the opposite distal quadrant just prior to decompression of the capsular bag
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FIGURE 20.3 Return of capsulorhexis to its original size following decompression of the bag Repeating the hydrodissection and capsular decompression starting in the opposite distal quadran may be helpful. Adequate hydrodissection at this point can be demonstrated by the ease with which the nuclear-cortical complex can be rotated by the cannula. Hydrodelineation Hydrodelineation is a term first used by Anis8 to describe the act of separating an outer epinuclear shell or multiple shells from the central compact mass of inner nuclear material, the endonucleus, by the forceful irrigation of fluids (balanced salt solution) into the mass of the nucleus. Our technique uses the same hydrodissection cannula as previously described. The cannula is placed in the nucleus, off center to either side, and directed at an angle downward and forward towards the central plane of the nucleus. When the nucleus starts to move, the endonucleus has been reached; it is not penetrated by the cannula. At this point, the cannula is directed tangentially to the endonucleus, and a to-and-fro movement of the cannula is used to create a tract within the nucleus. The cannula is backed out of the tract approximately halfway, and a gentle but steady pressure on the syringe allows fluid to enter the “empty” distal tract without resistance. Driven by the hydraulic force of the syringe, the fluid will find the path of least resistance, which is the junction between the endonucleus and the epinucleus, and flow circumferentially in this contour. Most frequently, a circumferential golden ring will be seen outlining the cleavage between the epinucleus and the endonucleus. Sometimes the ring will appear as a dark circle rather than a golden ring. Occasionally, an arc will result and surround approximately one quadrant of the endonucleus. In this instance, creating another tract the same depth as the first but ending at one end of the arc, and injecting into the middle of the second tract, will extend that arc (usually another full quadrant). This can be repeated until a golden or dark ring verifies circumferential division of the nucleus.
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For very soft nuclei, the placement of the cannula allows creation of an epinuclear shell of any thickness. The cannula may pass through the entire nucleus if it is soft enough, so the placement of the tract and the location of the injection allow an epinuclear shell to be fashioned as desired. In very firm nuclei, one appears to be injecting into the cortex on the anterior surface of the nucleus, and the golden ring will not be seen. However, a thin, hard epinuclear shell is achieved even in the most brunescent nuclei. That shell will offer the same protection as a thicker epinucleus in a softer cataract. Hydrodelineation circumferentially divides the nucleus and has many advantages. Circumferential division reduces the volume of the central portion of nucleus removed by phacoemulsification by up to 50 percent. This allows less deep and less peripheral grooving and smaller, more easily mobilized quadrants after cracking or chopping. The epinucleus acts as a protective cushion within which all of the chopping, cracking and phacoemulsification forces can be confined. In addition, the epinucleus keeps the bag on stretch throughout the procedure, making it unlikely that a knuckle of capsule will come forward, occlude the phaco tip, and rupture. Completion of the Procedure After evacuation of all endonuclear material, the epinuclear rim is trimmed in each of the three quadrants (Fig. 20.4), mobilizing cortex as well in the following way. As each quadrant of the epinuclear rim is rotated to the distal position in the capsule and trimmed, the cortex in the adjacent capsular fornix flows over the floor of the epinucleus and into the phaco tip (Fig. 20.5). Then the floor is pushed back to keep the bag on stretch until three of the four quadrants of the epinuclear rim and forniceal cortex have been evacuated (Fig. 20.6). It is important not to allow the epinucleus to
FIGURE 20.4 Purchase of the epinuclear rim and roof in foot position 2, being pulled central to the capsulorhexis. The cortical layer is seen superior to the rim and roof of the epinuclear shell
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FIGURE 20.5 Following trimming of the initial purchase of the rim and roof in foot position 3, one can see the cortex flow over the floor and into the tip, removing it from that same quadrant
FIGURE 20.6 Repositing of the floor of the epinucleus after rim and roof of the epinuclear shell has been trimmed and the cortex has been evacuated from the third epinuclear quadrant flip too early, thus avoiding a large amount of residual cortex remaining after evacuation of the epinucleus. The epinuclear rim of the fourth quadrant is then used as a handle to flip the epinucleus (Fig. 20.7). As the remaining portion of the epinuclear floor and rim is evacuated from the eye, 70 percent of the time the entire cortex is evacuated with it (Fig. 20.8).9 Downsized phaco tips with their increased resistance to flow are less capable of mobilizing the cortex because of the decreased minisurge accom-
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FIGURE 20.7 Initiating the flipping maneuver of the residual epinucleus utilizing the fourth quadrant of epinuclear rim and shell
FIGURE 20.8 The capsular bag is clear of cortex, except for a single strang to the right following flipping and evacuation of the residual epinucleus panying the clearance of the tip when going from foot position two to foot position three in trimming of the epinucleus. After the intraocular lens is inserted, these strands and any residual viscoelastic material are removed using the irrigation-aspiration tip, leaving a clean capsular bag. If there is cortex still remaining following removal of all the nucleus and epinucleus, there are three options. The phacoemulsification handpiece can be left high in the anterior chamber while the second handpiece strokes the cortex-filled capsular fornices. Frequently, this results in floating up of the cortical shell as a single piece and its exit through the phacoemulsification tip (in foot position two) because cortical cleaving hydrodissection has cleaved most of the cortical capsular adhesions.
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Alternatively, if one wishes to complete cortical cleanup with the irrigation-aspiration handpiece prior to lens implantation, the residual cortex can almost always be mobilized as a separate and discrete shell (reminiscent of the epinucleus) and removed without ever turning the aspiration port down to face the posterior capsule. The third option is to viscodissect the residual cortex by injecting the viscoelastic through the posterior cortex onto the posterior capsule. We prefer the dispersive viscoelastic device chondroitin sulfate-hyaluronate [Viscoat]. The viscoelastic material spreads horizontally, elevating the posterior cortex and draping it over the anterior capsular flap. At the same time the peripheral cortex is forced into the capsular fornix. The posterior capsule is then deepened with a cohesive viscoelastic device [e.g., Provisc] and the IOL is implanted through the capsulorhexis, leaving the anterior extension of the residual cortex anterior to the IOL. Removal of residual viscoelastic material accompanies mobilization and aspiration of residual cortex anterior to the IOL, which protects the posterior capsule, leaving a clean capsular bag. Conclusions In summary, the lens can be divided into an epinuclear zone with most of the cortex attached and a more compact central nuclear mass. The central portion of the cataract can be removed by any endolenticular technique, after which the protective epinucleus is removed with all or most of the cortex attached. In most cases, irrigation and aspiration of the cortex as a separate step are not required, thereby eliminating that portion of the surgical procedure and its attendant risk of capsular disruption. Residual cortical cleanup may be accomplished in the presence of a posterior chamber IOL, which protects the posterior capsule by holding it remote from the aspiration port. References 1. Faust, KJ: Hydrodissection of soft nuclei. Am Intraocular Implant Soc J 10:75–77, 1984. 2. Neuhann T: Theorie und Operationstechnik der Kapsulorhexis. Klin Monatsbl Augenheilkd 190:542–45, 1987. 3. Gimbel HV, Heuhann T: Development, advantages, and methods of the continuous circular capsulorhexis technique. J Cataract Refract Surg 16:31–37, 1990. 4. Davison JA: Bimodal capsular bag phacoemulsification: A serial cutting and suction ultrasonic nuclear dissection technique. J Cataract Refract Surg 15:272–82, 1989. 5. Sheperd JR: In situ fracture. J Cataract Refract Surg 16:436–40, 1990. 6. Gimbel HV: Divide and conquer nucleofractis phacoemulsification: Development and variations. J Cataract Refract Surg 17:281–91, 1991. 7. Fine IH: The chip and flip phacoemulsification technique. J Cataract Refract Surg 17:366–71, 1991. 8. Anis A: Understanding hydrodelineation: The term and related procedures. Ocular Surg News 9:134–37, 1991. 9. Fine, IH: The choo-choo chop and flip phacoemulsification technique. Operative Techniques in Cataract and Refractive Surgery 1(2):61–65, 1998.
Section IV Phaco Techniques 21. Divide and Conquer Nucleofractis Techniques 22. Single Instrument Phacoemulsification through a Clear Corneal Microincision 23. The Use of Power Modulations in Phacoemulsification of Cataracts: The Choo Choo Chop and Flip Phacoemulsification Technique 24. Lens Quake Phaco 25. Supracapsular Phacoemulsification 26. New Non-laser Phacoemulsification Technologies
21 Divide and Conquer Nucleofractis Techniques Howard V Gimbel Ellen Anderson Penno Introduction Phacoemulsification, since its origin in the 1960s, has changed through the years and phacotechniques are still evolving. Besides the advantages of a smaller wound, phacoemulsification allows for the removal of even dense brunescent nuclei through continuous curvilinear capsulorhexis (CCC) openings. In the early 1980s, as phacoemulsification was being applied to more and more dense nuclei, the author developed in-situ nuclear fracturing techniques which added to the safety and efficiency of phacoemulsification.1–3 With the preservation of an intact capsular bag using CCC, fixation and centration of the intraocular lens (IOL), is ensured after safe and efficient inthe-bag phacoemulsification.3 The two-instrument nucleofractis technique was developed to facilitate subdivision of the nucleus into small pieces so that they could be removed more efficiently through the phacoemulsification handpiece and thus through a small cataract incision. The term derives from the Latin divide et impera, and nucleofractis comes from the prefix nucleo (nucleus) and the Greek suffix fractis (to fracture). Good nucleofractis skills can be learned by most ophthalmologists. Recent studies have demonstrated rates of vitreous loss by third-year resident surgeons learning nucleofractis techniques to be comparable to those found with standard extracapsular techniques.4–6 Because the fracturing procedure in divide and conquer places a stretching force on the anterior capsular opening, canopener-type capsulotomies are associated with an unacceptably high rate of peripheral capsular tears. This led to the development of the CCC, which provides a strong tearresistant border that maintains its integrity despite the stretching forces produced with nucleofractis.3,7,8 The basic technique of nucleofractis is founded on the anatomic relationship of the lens fibers and the lenticular sutures. During embryologic development lens fibers elongate and join, forming the two Y sutures, one anterior and one posterior. As more fibers are added, these sutures branch out into increasingly complex patterns.9 These radially oriented sutures create potential cleavage planes that are susceptible to fracturing. The lens epithelial cells lay down concentric layers of nuclear tissue that become more dense peripherally. These concentric layers resemble the lamellar organization of a treetrunk or an onion. Radial and lamellar zones form cleavage planes within the lens nucleus and may be split by instruments and divided into smaller and more manageable pieces for phacoemulsification.
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Divide and conquer nucleofractis can be viewed as four basic steps: (i) sculpting until a thin posterior plate of nucleus remains, (ii) fracturing of the posterior plate and nuclear rim, (iii) breaking away a wedge-shaped section of nuclear material for emulsification, and (iv) rotating the remaining nucleus for further fracturing and emulsification. All of the techniques described in this chapter represent variations on this theme. Which one is used depends on surgeon preference, density of the nucleus, degree of pupillary dilation, and whether or not an intact CCC is present. Down-Slope Sculpting Divide and conquer nucleofractis begins with sculpting until a thin posterior plate of nucleus remains. A variation from the traditional sculpting method involves nudging the lens inferiorly with the second instrument. With the lens nudged towards the 6 O’clock position, the surgeon can sculpt very deeply down the slope of the posterior curvature of the upper part of the capsule. This technique has thus been termed “down-slope sculpting”.10 The author first began using this nudging maneuver in small pupil cases out of necessity because of limitations of pupil size and capsular opening. The technique was then extended to almost all cases. It was found that down-slope sculpting greatly enhanced the speed and efficiency of the nucleofractis techniques and has increased the safety, because the sculpting is parallel rather than somewhat perpendicular to the posterior capsule. With traditional techniques, if the nucleus is broken through unexpectedly when sculpting a deep, long trench towards 6 O’clock, the tip is more perpendicular to the inferior portion of the posterior capsule because of its concavity and is directly perpendicular to the equatorial capsule. With down-slope sculpting, considerable nuclear material remains ahead of the tip at the end of each sculpting, pass (Fig. 21.1). Therefore, breaking through is unlikely with the “cushion” present. The risk of engaging the capsule is thus minimized.
FIGURE 21.1 Down-slope sculpting—the lens is nudged inferiorly by the second instrument and
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deep sculpting is done from just inside the continuous curvilinear capsulorhexis to the center of the lens: Then the tip will travel parallel to the concave slope of the posterior aspect of the nucleus and the posterior capsule Down-slope sculpting in the upper pole of the lens to just past the center reduces the chance of posterior capsule rupture with the phaco port. If the lens is nudged inferiorly by the second instrument and deep sculpting is done from just inside the continuous curvilinear capsulorhexis to the center of the lens, then the tip will travel parallel to the concave slope of the posterior aspect of the nucleus and the posterior capsule. Although the surgeon cannot visualize the tip when going “down-slope”, the depth of the sculpting is determined by visualizing the depth of the groove and translucency of the remaining tissue. Furthermore, with traditional sculpting techniques the deepest part of the sculpting inevitably ends up inferior to the center of the lens. If the surgeon rotates the lens 90° after sculpting each quadrant, then the nuclear material deep in the center or posterior pole of the nucleus may still impede complete fracturing to the center, and the sections will tend to hang together in the middle of the lens. However, with down-slope sculpting, complete and efficient fracturing and subsequent emulsification can be accomplished by sculpting deeply and fracturing through the entire posterior plate of the nucleus. The surgeon must be cautious when the CCC is small to avoid tearing the edge of the anterior capsule superiorly with the tip or the sleeve of the phaco instrument. In the author’s experience, small CCCs are most likely to occur in cases with poor visualization, such as when hypermature, white cataracts are present. Ordinarily, the risk is low because one is not sculpting much past the center when first beginning the trench. Care must also be exercised in displacing the nucleus within the capsular bag so that the whole bag is not displaced, and the upper zonular ligaments are not unduly stretched and broken. Adequate hydrodissection is essential to allow inferior nucleus displacement while minimizing stress to the upper zonular apparatus. Also, when tipping the handle of the phaco handpiece upto sculpt down towards the posterior pole, the surgeon must not push the tip posteriorly faster than the tip is chiselling its way through the lens material. The zonular ligaments may also be torn with such a maneuver. These risks are greatest in lenses with hard epinuclei and where the zonules are already weakened. Limiting sculpting to the superior part of the nucleus adds safety because of the reduced risk of contacting the posterior capsule and adds efficiency because of the rapidity with which the posterior pole of the nucleus is reached with the phaco tip. With instruments this deep in the nucleus, the fracturing can be effectively initiated and safely completed.
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The Fracture The fundamental principle underlying nucleofractis is the creation of fractures within the nucleus to facilitate the removal of the cataract through a small incision while causing the least possible trauma to the eye. If the nuclear rim is very hard or if the CCC is not intact, splitting the nucleus along a groove is achieved using a bimanual technique or a nuclear cracker. Regardless of the fracturing technique used, nucleofractis is facilitated by deep sculpting of the posterior pole of the lens nucleus. This will be discussed in more detail under “polar expenditions”. With the parallel instrument technique, a deep central groove is sculpted within the lens nucleus and the phaco probe is placed deep within the groove against the right-hand wall (for right-handed surgeons). A second instrument is placed in the groove against the other wall. The fracture is created by pushing the two walls away from each other. Alternatively, with a cross-handed technique, each instrument is placed against the opposite wall of the groove. With both the parallel instrument and cross-handed techniques, placing the two instruments as deeply as possible within the groove provides the most efficient application of the cracking force. An alternative fracturing technique involves creating a full diameter groove, aligning the groove midway between the main incision and moving the two instruments away from each other deep within the trench. The density of the lens and the preference of the surgeon will dictate the appropriate fracturing techniques necessary to achieve consistent and predictable results in nucleofractis. All fracturing techniques currently used by the author use the principles of deep sculpting followed by fracturing of the posterior plate of the nucleus and then the posterior rim. Once the initial fracture is achieved, rotation and additional fractures are used to break away wedge-shaped sections of the lens nucleus for emulsification.
FIGURE 21.2 The phaco tip is used in a lateral motion (nasal to temporal and back again) to sculpt the central nucleus quickly and deeply while maintaining constant visualization of the tip of the instrument. With a 30°
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Kelman tip, the removal of lens material is more efficient and easier to perform. However, this technique is also possible with standard straight tip phacoemulsification handpieces Phaco Sweep Another variation on the theme of sculpting is a technique the author calls “phaco sweep”.11 In traditional sculpting techniques, the phaco tip is moved from the superior to the inferior portion of the nucleus to create a groove. By using the phaco tip in a lateral motion (nasal to temporal and back again), the central nucleus can be sculpted quickly and deeply while maintaining constant visualization of the tip of the instrument. The author prefers to use a 30° Kelman tip to perform phaco sweep (Fig. 21.2). With this tip, the removal of lens material is more efficient and easier to perform. However, this technique is also possible with standard straight tip phacoemulsification handpieces. The engineers at Alcon Surgical explain this difference on the basis of a three-dimensional propagation of the ultrasound wave front from the bent Kelman tip. Standard handpieces tend to direct their ultrasound power primarily in the forward direction, somewhat limiting their cutting efficiency for this technique. As sculpting proceeds to deeper layers, the phaco tip is moved in a lateral sweeping motion. It is important to avoid occlusion of the tip during this
FIGURE 21.3 Phaco sweep—as sculpting proceeds to deeper layers the phaco tip is moved in a lateral sweeping motion. It is important to avoid occlusion of the tip during this procedure. The lens is stabilized inferior to the groove with a second instrument through the paracentesis
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procedure. The lens is stabilized inferior to the groove with a second instrument through the paracentesis (Fig. 21.3). After lateral sculpting is sufficiently deep, a horizontal fracture is created as described later in the “multidirectional divide and conquer” section of this chapter (Fig. 21.4). Phaco sweep is a variation of down-slope sculpting which enhances visualization of the phaco tip and results in increased safety for the removal of central nuclear
FIGURE 21.4 Phaco sweep—after the lateral sculpting is sufficiently deep, a horizontal fracture is created
FIGURE 21.5 Crater divide and conquer (CDC)—after adequate hydrodissection, a deep crater is sculpted into the center of the nucleus, leaving a dense peripheral rim that can later be fractured into multiple sections. It is important that the crater include the posterior plate of the nucleus, otherwise, fracturing of the rim will be much more difficult
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material. In addition, the motion of the probe remains parallel to the posterior capsule, diminishing the risk of its inadvertent rupture. Crater Divide and Conquer (CDC) Technique Divide and conquer nucleofractis phaco, described by the author was the first nucleofractis (two-instrument) cracking technique developed.1,12 It is still used for hard lenses and is now combined with the phaco chop for dense brunescent nuclei. The phaco chop technique will be discussed later in this chapter. After adequate hydrodissection, a deep crater is sculpted into the center of the nucleus, leaving a dense peripheral rim that can later be fractured into multiple sections (Fig. 21.5). The crater must include the posterior plate of the nucleus, otherwise, fracturing of the rim will be much more difficult. A shaving action is used to sculpt away the central nuclear material. When the central material is no longer accessible to the phaco probe, the lens should be rotated and additional central sculpting performed to enlarge and deepen the crater. The size of the central crater should be expanded for progressively denser nuclei. Enough of the dense material must be left in place, however, to allow the phaco
FIGURE 21.6 Crater divide and conquer (CDC)—rather than emulsify the sections as they are broken away the sections should be left in place within the rim to maintain the circular rim and the tension on the capsule. Leaving the sections in place also facilitates rotation and the progressive fracturing of the remaining rim probe and second instrument to engage the rim and fracture the lens into sections. The surgeon uses experience as a guide to determine how deeply the central crater should be sculpted. The peripheral nuclear rim stretches the entire capsular bag and acts as a safety mechanism to prevent the posterior capsule from suddenly moving anteriorly and being cut by the phacoprobe. For harder nuclei, small sections should be fractured
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from the rim. Rather than emulsify the sections as they are broken away, the sections should be left in place within the rim to maintain the circular rim and the tension on the capsule. Leaving the sections in place also facilitates rotation and the progressive fracturing of the remaining rim (Fig. 21.6). It is sometimes advisable to initially remove one small section to allow space for fracturing the other segments of the remaining rim (Fig. 21.7). If one small fragment is removed, the remaining segment can maintain capsular stretch and help to avoid rupture of the capsule. After the rim is fractured around
FIGURE 21.7 Crater divide and conquer (CDC)—it is sometimes advisable to initially remove one small section to allow space for fracturing the other segments of the remaining rim
FIGURE 21.8 Crater divide and conquer (CDC)—after the rim is fractured around the entirety of its circumference, each segment can then
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be brought to the center of the capsule for safe emulsification the entirety of its circumference, each segment can then be brought to the center of the capsule for safe emulsification (Fig. 21.8). One must be more cautious at this point because as more segments are removed, less lens material is available to expand the capsule, and the capsule will have a greater tendency to be aspirated into the phaco tip, especially if high aspiration flow rates are used (Fig. 21.9). Trench Divide and Conquer (TDC) Technique Recognizing the efficiency of fracturing maneuvers during CDC, the author stopped sculpting the right side of soft lenses after making the central trench
FIGURE 21.9 Crater divide and conquer (CDC)—as segments are removed less lens material is available to expand the capsule and the capsule will have a greater tendency to be aspirated into the phaco tip, especially if high aspiration flow rates are used
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FIGURE 21.10 Trench divide and conquer (TDC)—using the down-slope sculpting technique described earlier enables the phaco tip to remove more of the upper part of the nucleus during sculpting and to reach the posterior pole of the lens very early for effective fracturing and instead made a central fracture. Using the down-slope sculpting technique described earlier allows the phaco the tip to remove more of the upper part of the nucleus during sculpting and to reach the posterior pole of the lens very early for effective fracturing (Fig. 21.10). Then the left side is divided by fracturing, and also the right side. These variations were named “trench divide and conquer (TDC)” techniques.10,13,14
FIGURE 21.11 Trench divide and conquer (TDC)—using a 30° or 45° tip, the TDC technique begins with a shallow trench or trough sculpted slightly to the right of the center of the
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lens surface. The lens is stabilized with the spatula through the paracentesis Using a 30° or 45° tip, the TDC technique begins with a shallow trench or trough sculpted slightly to the right of the center of the lens surface. The lens is stabilized with the spatula through the paracentesis (Fig. 21.11). Then, nudging the loosened lens nucleus inferiorly with the second instrument, down-slope sculpting is performed very deeply to the posterior pole of the lens. Adequate hydrodissection is essential to downslope sculpting because then the nucleus is not attached to the peripheral cortex and capsule, and the nucleus can easily be displaced in the capsular bag. Placing the instrument tips deep in the center of the lens, fracturing is accomplished by pushing towards the right with the phaco tip as the cyclodialysis spatula is pushed to the left. This is accomplished in foot position two (irrigation/ aspiration only and no ultrasound power). The lens usually splits from the center to the superior and inferior rim of the nucleus if the instruments are held deep in the center. If the split does not readily extend to the equator inferiorly or superiorly, moving the instruments away from the center can produce the mechanical advantage necessary to extend the fracture through the nuclear rim. After this first crack has been obtained, the depth of the sculpted groove in the lens can be determined, and the surgeon can gauge how much deeper sculpting should be continued to facilitate
FIGURE 21.12 Trench divide and conquer (TDC)—keeping the probe deep in the tissue and close to the posterior cortex, the surgeon then burrows deeply into the hemisection and creates a second crack that intersects with the first, isolating a pieshaped section of nucleus further fracturing. In all but brunescent nuclei, usually three to five sculpting passes allow one to get deep enough into the lens to start fracturing.
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Either before the first fracture or immediately afterward, the Down-slope technique may be used to sculpt the majority of the upper part of the lens. Keeping the probe deep in the tissue and close to the posterior cortex, the surgeon then burrows deeply into the left hemisection and creates a second crack that intersects with the first, isolating a pieshaped section of nucleus. In soft nuclei, this is usually performed about 60° from the first fracture, but in hard nuclei, the crack is shortened to about 30° away (Fig. 21.12). The isolated pie-shaped section can then either be emulsified or left in place as the next crack is made in a similar fashion (Fig. 21.13). The remaining right section of nucleus is then maneuvered with the second instrument and brought to the midpupillary zone. A final split is made after impaling the tip with a short burst of ultrasound, pushing with the phaco tip towards the 6 O’clock position while stabilizing the upper portion (Fig. 21.14). The piece can then be fractured into halves or thirds and emulsified as they are fractured. Alternatively, the right hemisection may be rotated to the left side and fractured in a way similar to the first hemisection.
FIGURE 21.13 Trench divide and conquer (TDC)—the isolated pieshaped section can then either be emulsified or left in place as the next crack is made in a similar fashion
FIGURE 21.14 Trench divide and conquer (TDC)—a final split is made
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after impaling the tip with a short burst of ultrasound, pushing with the phaco tip toward the 6 O’clock position while stabilizing the upper portion. The piece can then be fractured into halves or thirds and emulsified as they are fractured Rather than utilizing grooves to start the fractures, the surgeon simply needs to get the instruments deep into the center of the lens to fracture through the naturally occuring radial fault lines of the lens. Except in brunescent nuclei where notches are sculpted in the nuclear rim so that the spatula has a wall to push against, the principal advantage of the technique is that pregrooving the nucleus for subsequent fracturing is completely unnecessary.
FIGURE 21.15 Multidirectional divide and conquer (MDC)—the phaco sweep technique is initiated with small lateral movements of the phacotip at the bottom of the previously formed groove. The Kelman tip works very well for this side-to-side movement to create a deep groove horizontally. The phaco tip is then used to stabilize the upper portion, while the spatula pushes inferiorly against the wall, creating a horizontal fracture
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Multidirectional Divide and Conquer (MDC) Technique Down-slope multidirectional nucleofractis is begun by debulking the superior part of the lens. The phaco sweep technique is initiated with small lateral movements of the phaco tip at the bottom of the previously formed groove. The Kelman tip works very well for this side-to-side movement to create a deep groove horizontally. The phaco tip is then used to stabilize the upper portion while the spatula pushes inferiorly against the wall, creating a horizontal fracture (Fig. 21.15). This horizontal fracture is a combination of separation, and shearing. The second instrument pushes towards 6 O’clock and the phaco tip pushes down and away so that these opposing forces result in the splitting of the nucleus as the horizontal fracture.
FIGURES 21.16 TO 21.18 Multidirectional divide and conquer
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(MDC)—Multidirectional nucleofractis occurs when the phaco tip is used to engage the inferior hemisection and multiple pie-shaped sections are fractured using the second instrument to stabilize the nucleus. The multidirectional fracturing is accomplished without rotating the lens Multidirectional nucleofractis occurs when the phaco tip is used to engage the inferior hemisection and multiple pie-shaped sections are fractured using the second instrument to stabilize the nucleus (Figs 21.16 to 21.18). The sections are brought into the central pupillary zone for safe emulsification. The multidirectional fracturing is accomplished without rotating the lens. With the natural fault lines in the lens, this can be accomplished very easily without the chopping technique through the use of two-instrument separation. The fracturing is enhanced by not only separation but again by shearing (pushing down on one segment and away on the other) so that the separation is in two planes. The superior hemisection is rotated inferiorly and emulsified in a similar fashion. Alternatively, the superior section is nudged inferiorly with the spatula and the phaco tip is burrowed into the bulk of the nucleus, which is fractured without rotation. Phaco Chop Kunihiro Nagahara first introduced the phaco chop technique in 1993 at the annual meeting of the American Society of Cataract and Refractive Surgery (ASCRS) in Seattle, Washington. This technique also uses the lamellar structure of the nucleus to create radial fractures in the lens. The phacoemulsification probe is directed into the central core of the nucleus until occlusion of the port occurs. A modified lens hook is then inserted just beneath the anterior capsular leaflet at the 6 O’clock position just adjacent to the phaco probe, but extending to the equator of the lens. The tip is drawn centrally from the equator of the lens towards the phaco tip. This chop must encompass at least half of the anteroposterior diameter of the lens. The two instruments can then be used in a standard bimanual technique to complete the fracture. The nucleus is rotated slightly after the first chop and the procedure is repeated until pie-shaped wedges are created throughout the lens. These wedges can then be aspirated into the center of the capsular bag for safe emulsification. While the phaco chop technique can reduce phacoemulsification time significantly, this technique poses a persistent threat to anterior capsular integrity. Traversing the chopping instrument through the cortex towards the equator ensures that the anterior capsule remains anterior to the chopping instrument. The risk to capsular integrity with the phaco chop technique is greatest for surgeons with limited experience.
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FIGURES 21.19 AND 21.20 Crater divide and conquer (CDC) variation using phaco chop—in this modified technique the central nucleus is sculpted away. Rather than fracture the remaining nucleus by traditional nucleofractis techniques, the chop maneuver is used to split and than separate the nuclear rim using shearing forces. Creating a central crater provides a space where rim segments can be easily maneuvered following the chop As discussed earlier, the author has incorporated this phaco chop technique into the crater divide and conquer method for dense brunescent nuclei.15 It can be difficult to separate the nuclear rim in very hard lenses. In this modified technique, the central nucleus is sculpted away as described earlier (see “Crater Divide and Conquer” section). However, rather than fracture the remaining nucleus by traditional nucleofractis techniques, the chop maneuver is used to split and then separate the nuclear rim using shearing forces (Figs 21.19 and 21.20). Creating a central crater provides a space where rim segments
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can be easily maneuvered following the chop. Fracturing is thus made easier and zonular and capsular stress is reduced. The use of the chop technique is safer in the presence of anterior capsular tears because stretching of the capsule is reduced. For soft and moderately soft nuclei, the chop technique does not offer sufficient added efficacy to offset the increased risk of capsular tears. Steve Arshinoff recently presented his “slice and separate” modified phaco chop technique at the 1997 annual meeting of the American Society of Cataract and Refractive Surgery. This method is designed to be used for moderately dense nuclei. Dr Arshinoff describes impaling the nucleus and using a phaco chopper to slice across the nuclear part of the lens from anterior to posterior, passing by the phaco tip. The nucleus is then rotated 15° to 20°, and the same maneuver is repeated on the distal half. After the second slice, the segment is vacuumed out and the procedure is repeated—slice and vacuum—until the nucleus is removed. The slice maneuver is always started in the lens center, and the posterior capsule remains protected by the remaining nuclear and cortical material. Dr. Arshinoff emphasizes the need for good hydrodissection for success in this technique and notes that the slice and separate technique is difficult to perform on very soft nuclei due to difficulty in stabilizing the lens. Polar Expeditions Regardless of the fracturing technique used—crater divide and conquer (CDC), trench divide and conquer (TDC), or multidirectional divide and conquer (MDC)—the key is to sculpt nuclear material away centrally, leaving a thin layer of epinuclear material. Deep sculpting to the posterior pole of the lens facilitates the fracturing of the nucleus because it provides for safe and efficient segmentation and removal of the nuclear segments by taking advantage of the natural fault lines of the lens. Deep sculpting also allows one to obtain the mechanical advantage required to effectively fracture through the entire lens. Sculpting should be deep enough to be right through the nucleus into the epinucleus. The bent Kelman tip facilitates this deep sculpting. The expedition to the posterior pole can be accomplished with forward sculpting or phaco sweep lateral sculpting to thin the posterior plate before fracturing is attempted.16 Once a thin posterior plate is achieved, the segments fracture very easily with the twohanded technique. In a brunescent lens, the phaco chop instrument is used to fracture segments in the crater chop so that the segments are smaller and more easily managed. In trench divide and conquer (TDC) nucleofractis, polar sculpting is limited to a central trough or trench. This works best in a very soft nucleus where one has to maintain most of the nucleus which is firm enough to fracture. The nucleus is nudged slightly inferiorly and stabilized with the second instrument. Then the polar expedition for the posterior pole of the lens begins. The trench has to be wide enough to allow the phaco sleeve to get down into the nucleus. Once deep enough, the fracture is obtained with the two instruments. The segments are broken away, similar to the other nucleofractis techniques. Once the fracture is through the posterior plate of the lens, the fractured segments fracture completely without being tied together at the apices, and small segments are easier to manage than large segments. Only low-ultrasound power is necessary for these small nuclear segments to be emulsified.
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In multidirectional divide and conquer, downslope sculpting towards the posterior pole is used initially. The upper part of the nucleus is removed, and then with phaco sweep, polar expedition involves sculpting of the posterior pole before the horizontal fracture. The lens is stabilized and nudged inferiorly, and the sculpting is done with forward passes until one is deep in the lens. Then phaco sweep is used to delicately sculpt through the deepest part of the nucleus to the epinucleus before the horizontal fracture is made. The Small Pupil The most important goal in small pupil cataract surgery is to limit serious surgical complications. Relatively complication-free surgery in small pupil cases can be achieved with phacoemulsification techniques. These techniques also help to attain other goals such as the use of a small incision, the minimal use of pupil enlarging surgery and certain verification, of in-the-bag placement of a posterior chamber intraocular lens. The placement verification, long-term stability, and centration can be virtually assured by obtaining and maintaining a continuous curvilinear capsulorhexis opening in the anterior capsule.17 The lens nucleus, even though dense and large, can be fractured into small segments and removed by emulsification through relatively small capsule openings, small pupil openings, small scleral incisions and small conjunctival incisions. These are important considerations in many glaucoma patients who have small pupils from longterm miotic therapy and who have had or may in the future require filtering surgery The author developed the down-slope sculpting method, as described earlier in this chapter, in small pupil cases to quickly reach the posterior pole of the nucleus for efficient fracturing. The lens is nudged inferiorly, using a second instrument and the phacotip sculpts down the concave posterior capsule towards the posterior pole as described earlier, parallel to the capsule as opposed to perpendicular to it. Once the pole is reached, the two-instruments are held deep in the center. The spatula pushes inferiorly while the phaco tip pushes superiorly to create a horizontal fracture. The two instruments are repositioned to create a vertical fracture. The fractured segments can remain in the bag to stabilize it or be removed piece by piece. The second instrument holds back segments, while other segments are emulsified in the center of the lens. As well, the spatula brings nuclear material to the phaco tip to be emulsified. The phaco tip itself, stays mainly in the center of the lens. Small pupil cases demonstrate the distinct advantage of nucleofractis techniques in that the phaco tip does not have to be put under the iris or under the small openings in the capsule. As such there is little risk of iris or capsule flowing unexpectedly with the lens material into the tip of the phaco port. One should use a lower flow when the pupil is small. This may reduce efficiency, but certainly increases safety. Again, epinuclear material is brought to the phaco port using the second instrument. The phaco port itself does not go searching for this material in a small pupil case. Intumescent Lens The nucleus in an intumescent lens can be safely and efficiently fractured and phacoemulsified using the down-slope sculpting technique.18 In intumescent cases with
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primary, small capsulorhexis openings, the nucleus is nudged inferiorly with a second instrument. The upper portion of the nucleus is then sculpted using the down-slope sculpting technique. The nudging maneuver allows the phacotip to get very deep into the nucleus for subsequent fracturing. The phaco tip should be maintained centrally to avoid stress on either the small capsulorhexis rim or a can-opener margin. Mechanical stress to the ring of the can-opener with the use of the phaco handpiece, or by a second instrument, should be avoided. This is another instance in which down-slope sculpting nucleofractis is advantageous for safe emulsification, because the phaco tip always stays in the center of the lens. The second instrument is used to rotate, maneuver, and help fracture the nuclear rim. The depth of the sculpting is quite easy to gauge in an intumescent lens due to the whiteness of the nucleus and the red reflex exposed during fracturing. In doing phacoemulsification out near the periphery or up near the capsule in the epinucleus, a low flow and low vacuum should be used so that a sudden breakthrough with a high flow and high vacuum can be avoided. This will avoid engaging the equatorial capsule with the phaco tip. The intumescent lens is usually easy to fracture and quite often the lens will fracture spontaneously just with the attempt at rotation. Capsular Tension Rings Since phacoemulsification and continuous curvilinear capsulorhexis were developed, it has become possible to remove a cataract through a small incision and implant an intraocular lens (IOL) into the capsular bag. The centration and stability of the IOL inthe-bag is critical for maintaining excellent visual outcome. In some situations, placing an IOL in the capsular bag may be insecure, as in the case of a traumatic cataract with broken or loose zonules. To manage this situation, many anterior segment surgeons (including the first author) prefer to use phacoemulsification if possible, even if the capsular bag cannot be used for IOL placement. A sutured posterior chamber IOL (PCIOL) or an anterior chamber IOL (AC-IOL) may be placed after phacoemulsification is completed. Sutured fixation of a PC-IOL significantly increases surgery time and axial tilt of the IOL often occurs postoperatively. Implantation of an AC-IOL may be associated with postoperative corneal pathology, chronic cystoid macular edema, or secondary glaucoma. In 1991, Hara et al introduced an equator ring for maintaining the circular contour of the capsular bag after cataract removal.19 Following their work, different types of rings of varied material were developed. Cionni and Osher reported on four cataract surgery cases with extensive zonular dialysis managed with endocapsular rings.20 The results showed that the ring facilitated phacoemulsification and PC-IOL in-the-bag implantation. In January 1995, the author began using a polymethylmethacrylate (PMMA) capsular tension ring (Morcher GMBH, Germany) to manage patients with zonular dialysis requiring cataract surgery (Fig. 21.21).21
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FIGURE 21.21 Polymethylmethacrylate (PMMA) capsular tension ring (Morcher GMBH, Stuttgart, Germany) type 14 (dimensions 12.5 ×10.0 mm) A capsular tension ring may have potential benefits for cataract surgery patients with zonular dialysis—a capsular tension ring appears to enhance safety and efficacy during the phacoemulsification and PC-IOL implantation, it may help to avoid vitreous herniation, it maintains the circular contour of the capsular bag, it may reduce IOL decentration, and it may inhibit lens epithelial cell proliferation on the posterior capsule by compression, which may reduce the incidence of secondary cataract. Clinically, cataracts with loose zonules or broken zonules are commonly seen which present a challenge for surgeons when performing phacoemulsification and PC-IOL implantation. The capsular tension ring provides an alternative means to manage this situation. Challenges to Topical Anesthesia in Small-Incision Cataract Surgery The use of topical anesthesia in cataract operations requires that surgeons learn new techniques and adapt to challenges not faced with the use of local or general anesthesia.22 The transition to topical anesthesia means that surgeons cannot use some of the techniques that have been entirely safe on the immobilized eye. Under topical anesthesia, one cannot rely on the patient’s fixation or on voluntary immobilization of the eye, and persistent ocular movements on a regular or irregular basis may occur. In some circumstances, the globe must be immobilized with a second instrument. The author began using topical anesthesia for cataract surgery in 1993, specifically because of a case involving a very myopic eye with an axial length of 36.3 mm. In this case, it was felt that the risks of using peribulbar or even pin-point anesthesia were too high. The patient was relatively co-operative and communicative and fixated well. The author became convinced that topical anesthesia in long eyes adds an element of safety, reducing or eliminating the risks of the local anesthetic. Topical anesthesia introduces new challenges to cataract surgery. A learning curve presents itself with changes in surgical technique, and modifications must be made in
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reflex and habit that have evolved while doing surgery with peribulbar anesthesia surgery. Two-handed cataract extraction techniques are relatively advantageous in topical anesthesia cases, particularly because the second instrument—at almost 90° from the first—helps to stabilize the eye against unwanted movements in both the vertical and horizontal directions. In general, the learning curve involves modifications to almost every stage of cataract surgery. The eye must be stable even before the paracentesis is done. If an eye is not very quiet, it is valuable to use a ring to stabilize the eye while making the paracentesis. Next, the eye needs to be stabilized with forceps during the incision. The surgeon cannot afford any sudden movements (particularly when using diamond knives) of an eye anesthetized only topically. Scleral incisions under topical anesthetic must be made with the eye stabilized with forceps (unlike clear corneal incision where the eye is stabilized by a ring), grasping and regrasping the sclera before continuing with dissection. Sometimes, with local anesthesia, when the incision is being made, the grasp on the sclera is released and reapplied in a different place when the blade is in the tunnel. In eyes under topical anesthesia, the author advocates that the blade be removed from the tunnel before the forceps are released and the sclera be grasped at another location before the blade is reentered. One should never release the eye with the second instrument unless the sharp instrument is taken away first, because if the eye moves unexpectedly with only the sharp instrument in the tunnel, the sclera could be inadvertently cut. Another area of concern is the injection of viscoelastic. One cannot simply insert the cannula into the eye to inject viscoelastic, because the eye can move before the surgeon has an opportunity to fill the chamber. Any sudden movement may cause a tear to the anterior or posterior capsule. It is best to hold the eye while injecting viscoelastic. Furthermore, instead of inserting the viscoelastic cannula directly perpendicular to the eye, insert it so that it approaches the eye tangentially so that the side of the cannula is pushing or nudging the side of the wound. Any sudden movement of the eye towards the cannula will push the side of the cannula rather than allow the cannula to puncture the capsule unexpectedly. Some extremely nervous patients do not agree to topical anesthesia even after sedation. In patients with language barriers we now bring an interpreter or family member into the operating room. When faced with communication difficulties with extremely deaf or demented patients, we sometimes opt for a local anesthetic. However, nonverbal communication for instructions allows surgery to be done under topical anesthesia in many cases. Topical anesthesia appears to be the growing trend in cataract surgery. It avoids the potential risks of damage to vessels, globe, and nerves that exist when a needle is used. Surgeons who use topical anesthesia should already be experienced in phacoemulsification. A surgeon in the transition to phacoemulsification should probably not consider topical anesthesia until confident with phacoemulsification first. Initially, a surgeon should use topical anesthesia only on routine unchallenging cases. At the outset, surgeons should avoid using topical anesthesia on uncooperative patients or with patients who have difficulty in communicating. As one becomes more experienced and more confident, topical anesthesia can be used in more challenging cases. Cases in which local or general anesthesia is preferred will always exist, and these include patients who are
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unable to co-operate, have extremely small pupils, or very dense or subluxated lenses, and those requiring more complex surgery or delicate dissection. Summary Each of the nucleofractis techniques described in this chapter are variations of four basic steps: (i) sculpting to obtain a thin posterior plate of nucleus, (ii) fracturing the posterior plate and nuclear rim, (iii) breaking away wedge-shaped sections of nuclear material for emulsification, and (iv) rotating the nucleus for further fracturing and emulsification. The techniques of continuous curvilinear capsulorhexis, down-slope sculpting, phaco sweep and polar expeditions are refinements which add efficacy and safety to the divide and conquer nucleofractis techniques. The surgeon should be familiar with the variety of nucleofractis techniques described and be able to modify the surgical strategy as dictated by specific patient characteristics and intraoperative events. References 1. Gimbel HV: Divide and conquer nucleofractis phacoemulsification—development and variations. J Cataract Refract Surg 17:281–91, 1991. 2. Gimbel HV, Ellant JP, Chin PK: Divide and conquer nucleofractis. Ophthalmol Clin North Am 8(3):457–69, 1995. 3. Gimbel HV, Neuhann T: Development, advantages, and methods of the continuous circular capsulorhexis technique. J Cataract Refract Surg 16:31–37, 1990. 4. Cruze OA, Wallace GW, Gay CA et al: Visual results and complications of phacoemulsification with intraocular lens implantation performed by ophthalmology residents. Ophthalmology 99:448–52, 1992. 5. Noecker RJ, Allinson RW, Snyder RW: Resident phacoemulsification experience using the in situ nuclear fracture technique. Ophthalmology 25:215–21, 1994. 6. Pearson PA, Owen DG, Van Meter WS et al: Vitreous loss rates in extracapsular cataract surgery by residents. Ophthalmology 96:1225–27, 1989. 7. Gimbel HV, Neuhann T: Continuous curvilinear capsulorhexis (letter). J Cataract Refract Surg 17:110, 1991. 8. Neuhann T: Theorie und operationstechnik der kapsulorhexis. Klin Monatsble Augenheilkd 190:542–45, 1987. 9. Hogan M, Alvaradd J, Weddell J: Histology of the Human Eye. Philadelphia: WB Saunders 1971. 10. Gimbel HV: Down slope sculpting. J Cataract Refract Surg 18:614–18, 1992. 11. Gimbel HV, Chin PK: Phaco Sweep. J Cataract Refract Surg 21:493–96, 1995. 12. Gimbel HV: Divide and Conquer. (Video) Presented at the European Intraocular Implant Lens Council meeting 1987. 13. Gimbel HV: CCC and nucleus fracturing. Ophthalmol Clin North Am 4:235, 1991. 14. Gimbel HV: Evolving techniques of cataract surgery—continuous curvilinear capsulorhexis, down-slope sculpting and nucleofractis. Semin Ophthalmol 7:193–207, 1992. 15. Gimbel HV: Nuclear phacoemulsification—alternative methods. In: Steinert RF (Ed) Cataract Surgery: Technique, Complications, and Management Philadelphia: WB Saunders 148–81, 1995.
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16. Gimbel HV, Austin A: ‘Polar expedition’ technique expedites phaco. Ocular Surgery News 15(9): 27–32, 1997. 17. Gimbel HV: Nucleofractis phacoemulsification through a small pupil. Can J Ophthalmol 27(3):115–19, 1992. 18. Gimbel HV, Willerscheidt AB: What to do with limited view—the intumescent cataract. J Cataract Refract Surg 19: 657–61, 1993. 19. Hara T: Endocapsular phacoemulsification and aspiration (ECPEA—recent surgical technique and clinical results. Ophthalmic Surg 20:469–75, 1989. 20. Cionni RJ, Osher RH: Endocapsular ring approach to the subluxated cataractous lens. Cataract Refract Surg 21:245–49, 1995. 21. Gimbel HV, Sun R, Heston JP: Management of zonular dialysis in phacoemulsification and IOL implantation using the capsular tension ring. Ophthalmic Surgery and Lasers 28(4):273– 81, 1997. 22. Gimbel HV: Challenges of topical anesthesia in small incision cataract surgery. Ophthalmic Practice 14(3):123–24, 1996.
22 Single Instrument Phacoemulsification through a Clear Corneal Microincision Robert M Kershner Introduction An increasing number of surgeons have adopted phacoemulsification as the preferred method for cataract removal, since its introduction as a method of cataract removal over one-quarter of a century ago, The advantages of removing a cataract through a small incision have been recognized by surgeons the world over. Phacoemulsification has made it possible to abandon suture closure, utilize smaller incisions, replace injection anesthesia with topical anesthesia, and improve our ability to correct refractive error with cataract surgery.1 Today’s new techniques of topical anesthesia, clear corneal cataract surgery, and injection of elastic intraocular lenses through small incisions have placed new constraints on the ability of the surgeon to perform phacoemulsification. Introducing the phacoemulsification tip through a small clear corneal refractive microincision limits access to the cataract and can restrict the surgeon’s ability to manipulate the lens within the capsular bag. As a result of the challenge and demands of smaller incision cataract surgery, surgeons have adopted several new approaches to the strategy for phacoemulsification. All methods of cataract removal have essentially one goal in common—to take a large anatomic structure (the lens) and dismantle it into smaller pieces for ease of removal through an incision smaller than the overall size of the lens. Whether one adopts a divide and conquer technique, a quadrantic phacoemulsification method, a chip and flip, or a stop and chop method, the goal remains the same. One can either mechanically divide the cataract into segments and remove the individual segments, or chip away at the larger structure and remove it piece by piece. Many surgeons use two incisions through the cornea, and two instruments for phaco: one for the phaco tip and one for a sideport lens manipulating instrument. The author does not believe that a second-handed instrument is necessary for effective and efficient phacoemulsification of the cataract. There are distinct advantages of maintaining the phaco incision as one incision. Placing an additional incision in the eye is not only unnecessary, but it increases the likelihood of incisional leaks, an additional portal for infection, synechiae and encourages excessive instrumentation of the eye. We learned to drink a glass of milk as children by holding onto the glass with two hands. As adults, we can learn to hold a glass with one hand, freeing up the other hand for other needs. So, it is with phacoemulsification.
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Single Incision Phacoemulsification: The Four-step Keyhole Technique Early in its development, phacoemulsification was performed entirely through a single incision. This single incision or single instrument phacoemulsification technique has previously been called a “one-handed” phaco technique. The name is a misnomer, however, as two hands are required to successfully perform phaco. They just do not each require their own incision! The maneuvers of lens rotation and segmental removal of the cataract can be performed with a single hand on the instrument, thus, freeing the left hand for manipulating the eye, stabilization of the globe, retrieval of instruments, or to hold the phacoemulsification handle and tubing. It is important that the surgeon adopt an efficient method of phacoemulsification through today’s small corneal microincisions. The single instrument phaco technique is elegant, more efficient, easier to learn, and less traumatic to the eye. The time is right, as we enter the next millennium, to take a new look at an old technique—the single incision or single instrument phacoemulsification method that the author calls the keyhole technique.6 Incision Construction The clear corneal microincision has placed new demands on the surgeon for evacuating the cataract through a single small corneal incision. These incisions can be very unforgiving—they must not be distorted, torn or heated during the procedure without creating profound refractive effects for the eye. Incision construction is critical to a successful phacoemulsification procedure. The incision needs to be accurately sized for the size of the phacoemulsification tip to be used. Today’s microincision corneal procedures utilize an incision of 2.5 mm or smaller that must accommodate a micro phaco tip. The clear corneal refractive microincision technique has been described elsewhere.1–3 Following fabrication of the clear corneal incision with a diamond keratome, the anterior chamber is entered, and a viscoelastic placed to deepen the chamber. Capsulorhexis is performed using the technique of onestep capsulorhexis with a cystotome/forceps which the author developed in 1984.4,5 In early phacoemulsification methods, it was important to maintain the position of the cataractous lens within the capsular bag to stabilize it. Following the introduction of capsulorhexis, it was found that the limited access into the capsular bag created difficulties for the surgeon in rotating the lens for emulsification and removal. To facilitate these maneuvers, hydrodissection must be performed to cleave the strong cortical attachments between the lens capsule and the cortex of the cataract. By slipping a curved 27-gauge cannula through the incision and positioning it beneath the subincisional anterior lens capsule, a fluid wave can be created across the posterior lens. This maneuver prematurely loosens the cortex beneath the incision making it easier to remove with irrigation and aspiration later in the procedure.
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Phacoemulsification Parameters It is preferable to use a phacoemulsification machine whose individual parameters are controllable by the surgeon. When utilizing a peristaltic pump, the factors of flow rate, rise time, vacuum and phacoemulsification power can be set to the individual needs of the surgeon. By setting the flow rate, the surgeon can control how rapidly the fluid moves into the eye and out of the aspiration port. This is important in cooling the phacoemulsification tip during brief bursts of phaco power. The faster the flow rate, the quicker the rise time, and the more fluid which is utilized during aspiration. The vacuum level can also be set by the surgeon. Under normal conditions, the vacuum level is zero until the aspiration port of the phacoemulsification tip is occluded, when it will reach the maximum preset. As soon as the occlusion is broken, the vacuum will return to zero. Phacoemulsification power should be set to a reasonable level which allows the surgeon adequate control with the phaco pedal. The author will rarely use phaco powers above 30 to 40 percent maximum. For most cataracts, the author uses a vacuum level of between 150 and 200 mm Hg and a flow rate of approximately 20 to 50 rpm of the peristaltic pump (4–6 cc/minute). The higher the height of the infusion bottle, the greater the pressure head of fluid within the eye. With single incision phacoemulsification, a higher head of pressure is required. This maintains the chamber, and allows the delicate maneuvers with the phaco tip without danger of collapsing the capsular bag or injuring the corneal endothelium. Phacoemulsification tips are available in zero degree, 15 degree, 30 degree, and 45 degree angulations. For most purposes, a 30 degree angulated tip is most effective for soft to medium cataracts. Hard cataracts should be removed using a 45 degree tip which has a sharper cutting edge but less occludability. Step 1: Central Sculpting When performing central sculpting, occlusion of the phacoemulsification tip rarely occurs. Therefore vacuum levels can be quite low (less than 20 mm Hg). In fact, vacuum levels of zero for central sculpting work quite well. Low flow rates are required during the central sculpting maneuver. The goal of central sculpting is to remove the densest, hardest part of the nucleus at the beginning of the procedure when it is easiest to do so. The lens is kept entirely within the capsular bag. Using the phacoemulsification tip, gentle sculpting of the central nucleus is carried out (Fig. 22.1). Many surgeons wonder how far and how deep they should sculpt? Fortunately, there is a way to measure within the eye when performing phacoemulsification. The phaco tip is approximately 1 mm in width, and therefore three phaco tip width is approximately 3 mm deep. The average cataractous lens is at least 4.5 mm in anterior/posterior thickness, therefore one would have to place the phaco tip at least 3 to 4 tip width deep until the posterior capsule is encountered. With gentle aspiration and emulsification, the central nucleus can be safely and completely removed without damaging the posterior capsule. In soft lenses, the author suggests keeping the emulsification furrows narrow and shallow to leave enough cortical rim to be removed in the second and third steps. With hard, more mature cataracts, wide sculpting of the central dense nucleus and sculpting deep up to the level of
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the posterior capsule is necessary to allow the cortical rim to be opened and removed. When removal of the central nucleus is completed, attention is then directed to removing the cortical bowl.
FIGURE 22.1 Step 1: Central sculpting of the cataractous nucleus
FIGURE 22.2 Aspiration of two clock hours of cortical rim—the keyhole technique
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Step 2: Creating an Inferior Notch: The Keyhole Method Once central sculpting is completed, the surgeon is left with a cortical bowl. To remove the cortical bowl, an inferior notch must be aspirated to release the tension on the cortical ring of the cataract (Fig. 22.2). Low-power phacoemulsification and a higher vacuum is required to adequately aspirate and remove two clock hours of cortical rim. By gently placing the phacoemulsification tip at the edge of the lens capsule, the cortex can be aspirated into the tip and the vacuum level will rise. A small section of the rim can be aspirated and pulled into the center of the pupil. Here it is in the deepest portion of the chamber and furthest from the lens capsule, capsular rim, iris and endothelium. This is the triangle of safety which is an imaginary triangle bordered by the corneal incision at the apex and the east and west edges of the pupil. Only within this region should emulsification be performed (Fig. 22.3). Step 3: Removal of the Cortical Rim Using the phacoemulsification tip as a fulcrum, the remaining cortical rim can be gently rotated counterclockwise. The rotational maneuver is
FIGURE 22.3 The triangle of safety— that region bounded by the incision and the east and west margins of the pupil where the anterior chamber is deepest and the furthest distance from the phacoemulsification tip to the corneal endothelium and the posterior capsule. The safest zone in which to perform phacoemulsification
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performed as follows: the tip is gently embedded into the cortical rim at a convenient location (usually 3 O’clock), the tip is brought to the center of the lens within the triangle of safety along with the rim of cortical cataract and gently emulsified (Fig. 22.4). Consecutive low levels of emulsification power are applied until each individual quadrant is removed. Step 4: Removal of the Nuclear Plate Following complete removal of the cortical rim, a small flat section of posterior nucleus remains. The phacoemulsification tip is turned over (bevel down) and placed flat against this plate. Using very low levels of aspiration, the remaining nuclear plate is elevated off the posterior capsule and removed (Fig. 22.5). Low power levels are used at this the final stage of cataract removal. To enhance followability, the surgeon can select pulsed phaco mode. This prevents excessive pushing away of the final piece when emulsification is engaged. Avoid the tendency to chase the final piece around the chamber—
FIGURE 22.4 Step 3—Removal of the cortical rim patience is rewarded if the surgeon waits for the piece to come to the tip. Before removing the phacoemulsification tip, check on either side of the incision for any loose remaining pieces of nucleus, which should be removed prior to completing the phacoemulsification procedure.
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FIGURE 22.5 Step 4—Removal of the nuclear plate Conclusion The single instrument phacoemulsification procedure is quick, requires only one incision, one instrument and is less traumatic to the eye. The benefits of this technique are less induced astigmatism, more rapid visual recovery, better uncorrected visual acuity and a happier patient.1 Any difficulties encountered when using a single instrument technique are quickly overcome when the surgeon performs all of the maneuvers of central sculpting, aspiration of cortical rim, nuclear rotation and removal of the nuclear plate using just one instrument—the phacoemulsification tip alone. The single incision or single instrument approach to phacoemulsification paves the way to a fully integrated microincision refractive cataract procedure. With less portals into the eye, the procedure is amenable to topical anesthesia. Suturing is no longer required. Bandaging is unnecessary. The single microincision allows injection of onepiece elastic intraocular lenses without enlarging the incision. The patient’s refractive status can therefore be taken into account when correcting both spherical and astigmatic error simultaneously with one procedure. By using a single incision, implantation of a toric or multif ocal intraocular lens is facilitated. This translates into immediate visual recovery for the patient, without glasses. The ultimate goal of outpatient cataract surgery is less intervention with better visual results and more rapid visual rehabilitation. As our techniques to remove a cataract and implant an intraocular lens evolve toward smaller and smaller incisions, the single instrument method of phacoemulsification will become appealing to more and more surgeons. References 1. Kershner RM: Clear corneal cataract surgery and the correction of myopia, hyperopia and astigmatism. Ophthalmology 104(3):381–89, 1997. 2. Kershner RM (Ed.): Refractive Keratotomy for Cataract Surgery and the Correction of Astigmatism Thorofare: Slack, 1994.
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3. Kershner RM: Keratolencticuloplasty—arcuate keratotomy for cataract surgery and astigmatism. J Cataract Refract Surg 21:274–77, 1995. 4. Kershner RM: One-step forceps for capsulorhexis. J Cataract Refract Surg 16:762–65, 1990. 5. Kershner RM: Embryology, anatomy and needle capsulotomy. In Koch PS, Davison JA (Eds): Textbook of Advanced Phacoemulsification Techniques Thorofare: Slack, 35–48, 1991. 6. Kershner RM: Sutureless one-handed intercapsular phacoemulsification—the keyhole technique. J Cataract Refract Surg 17(suppl):719–25, 1991.
23 The Use of Power Modulations in Phacoemulsification of Cataracts: The Choo Choo Chop and Flip Phacoemulsification Technique1 I Howard Fine, Mark Packer Richard S Hoffman Introduction In the late 1980’s, as phacoemulsification was increasing in popularity, the desire on the part of most phacoemulsification surgeons was for increased power availability in order to address increasingly hard cataracts. In the 1990’s this became available, as did other very important technical innovations like high vacuum tubing and cassettes, microprocessor controls integrated with central onboard computers, and downsized tips with better holding power and increased followability. In the late 80’s and early 90’s, we described two endolenticular phacoemulsification techniques, chip and flip2 and chop and flip phacoemulsification3 in which we utilized pulse mode for the removal of nuclear material. In doing so, we recognized decreased chattering and increased holding power of the nuclear material. More recently, multiple modulations in the delivery of power have become available which allow for dramatic reductions in the total amount of ultrasound energy delivered into the eye. In addition, the Allergan systems provide occlusion mode phaco allowing for different parameters of percent power, vacuum levels, and aspiration flow rate on tip occlusion compared to an unoccluded tip. The Alcon Legacy has a bimodal option allowing linear aspiration flow rate or vacuum in foot position 2. More recently we described the use of burst mode4 and bevel down chop techniques.5 The Choo Choo Chop and Flip Phacoemulsification Technique The choo choo chop and flip phacoemulsification technique is designed to take maximum advantage of various new technologies available through the Alcon 20,000 Legacy6 (Alcon Surgical Inc., Ft Worth, TX), the AMO Diplomax7 (Allergan Medical Optics, Irvine, CA), the Allergan Sovereign (Allergan Medical Optics, Irvine, CA), the Mentor System (Mentor, Santa Barbara CA), the Storz Millennium (B and L Surgical, St. Louis, MO), and the Staar Wave (Staar Surgical, Monrovia, CA) phacoemulsification systems. These technologies include high vacuum cassettes and tubing, multiple programmable features, as well as new tip designs. The result is enhanced efficiency, control, and safety. The procedure is done as follows:
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A side-port incision is made to the left with a 1 mm-trifaceted diamond knife after which the anterior chamber is irrigated with 1/2 cc preservative-free xylocaine. Utilizing the soft-shell technique described by Steve Arshinoff,8 Viscoat (Alcon Surgical Inc) is placed into the anterior chamber angle distal to the side port through the side-port incision. It fills the anterior chamber but allows the eye to remain relatively soft. Provisc is instilled on top of the center of the lens capsule under the Viscoat. Provisc (Alcon Surgical Inc) forces the Viscoat up against the cornea, creating a soft shell which helps stabilize the anterior chamber and protect the endothelium. Additionally Provisc, which is a cohesive viscoelastic, decreases any tendency for iris prolapse during the hydro steps. Following construction of a temporal 2.5 mm× 2 mm clear corneal incision, cortical cleaving hydrodissection9 is performed in the two distal quadrants followed by hydrodelineation. After the two hydro steps, the nucleus should rotate easily within the capsular bag. The Mackool/Kelman aspiration bypass microflare tip on the Legacy is introduced bevel down to aspirate the epinucleus uncovered by the capsulorhexis, and is then turned bevel up. Alternatively on other systems a MST chop series SP tip (Microsurgical Technologies, Redmond, WA) or a 30 degree standard bevel down tip is used throughout endonuclear removal. The Fine/Nagahara chopper (Rhein Medical, Tampa, FL) is placed in the golden ring by touching the center of the epinucleus with the tip and pushing it peripherally so that it reflects the capsulorhexis. The chopper is used to stabilize the nucleus by lifting and pulling toward the incision slightly (Fig. 23.1),
FIGURE 23.1 Stabilization of the nucleus during lollipopping for the initia chop after which the phaco tip lollipops the nucleus in either pulse mode at 2 pulses/second or 80 millisecond burst mode (Diplomax). Burst mode is a power modulation that utilizes a fixed percent power (panel control), a programmable burst width (duration of power), and a linear interval between bursts. As one enters foot position 3, the interval between bursts is 2 seconds; with increasing depressions of the foot pedal in foot position 3 the interval shortens until at the bottom of foot position 3 there is continuous phaco. In pulse mode, there is linear power (%) but a fixed interval between pulses, resulting at 2 pulses/sec in a
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250 millisecond pulse (linear power) followed by a 250 millisecond pause in power followed by a 250 millisecond pulse, etc. However, in both of these modulations with tip occlusion, vacuum is continuous throughout the pulse and pause intervals. With the energy delivered in this way, we minimize ultrasound energy into the eye and maximize our hold on the nucleus as the vacuum builds between pulses or bursts. Because of the decrease in cavitational energy around the tip at this low pulse rate or in burst mode, the tunnel in the nucleus in which the tip is embedded fits the needle very tightly and gives us an excellent hold on the nucleus, thus maximizing control of the nucleus as we score and chop it (Fig. 23.2) in foot position 2.
FIGURE 23.2 Completion of the initial chop The Fine/Nagahara chop instrument is grooved on the horizontal arm close to the vertical “chop” element with the groove parallel to the direction of the sharp edge of the vertical element. In scoring the nucleus, the instrument is always moved in the direction the sharp edge of the wedge-shaped vertical element is facing (as indicated by the groove on the instrument), thus facilitating scoring. The nucleus is scored by bringing the chop instrument to the side of the phaco needle. It is chopped in half by pulling the chopper to the left and slightly down while moving the phaco needle, still in foot position 2, to the right and slightly up. Then the nuclear complex is rotated. The chop instrument is again brought into the golden ring (Fig. 23.3), the nucleus is again lollipopped, scored, and chopped with the resulting pie-shaped segment now lollipopped on the phaco tip (Fig. 23.4). The segment is then evacuated utilizing high vacuum and short bursts or pulse mode phaco at 2 pulses/second (Fig. 23.5). The nucleus is continually rotated so that pieshaped segments can be scored, chopped, and removed essentially by the high vacuum assisted by short bursts or pulses of phaco. The short bursts or pulses of ultrasound energy continuously reshape the pie-shaped segments which are kept at the tip, allowing for occlusion and extraction by the vacuum. The size of the pie-shaped segments is
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FIGURE 23.3 Stabilization of the nucleus prior to commencing the second chop
FIGURE 23.4 Pie-shaped segment adherent to the phaco tip following completion of the second chop customized to the density of the nucleus with smaller segments for denser nuclei. Phaco in burst mode or at this low pulse rate sounds like “choo-choo-choo-choo”; ergo the name of this technique. With burst mode or the low pulse rate, the nuclear material tends to stay at the tip rather than chatter as vacuum holds between pulses. The chop instrument is utilized to stuff the segment into the tip or keep it down in the epinuclear shell.
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FIGURE 23.5 Mobilization of the first pie-shaped segment
FIGURE 23.6 Scoring of the second hemi-nucleus After evacuation of the first hemi-nucleus, the second hemi-nucleus is rotated to the distal portion of the bag and the chop instrument stabilizes it while it is lollipopped. It is then scored (Fig. 23.6) and chopped. The pie-shaped segments can be chopped a second time to reduce their size (Fig. 23.7) if they appear too large to easily evacuate. There is little tendency for nuclear material to come up into the anterior chamber with this techni-que. Usually, it stays down within the epinuclear shell, but the chop instrument can control the position of the endonuclear material. The 30-degree beveldown tip facilitates occlusion, as the angle of approach of the phaco tip to the endonucleus through a clear corneal incision is approximately 30 degrees. This allows full vacuum to be quickly reached which facilitates embedding the tip into the nucleus for chopping and allows mobilization of pie-shaped segments from above rather than
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FIGURE 23.7 Mobilizing the final quadrant necessitating going deeperinto the endolenticular space as is necessary with a bevel-up tip. In addition, the cavitational energy is directed downward toward the nucleus rather than up toward the endothelium. Following evacuation of all endonuclear material (the 30 degree tip is turned bevel up) (Fig. 23.8), the epinuclear rim is trimmed in each of the three quadrants, mobilizing cortex as well in the following way The distal rim and roof are purchased in foot position 2. Upon occlusion, the roof and rim are drawn central to the capsulorhexis and then foot position 3 is entered. This results in mobilization of the roof and rim and clearance of occlusion. As each quadrant of the epinuclear rim is trimmed, the cortex in the adjacent capsular fornix flows over the floor of the epinucleus and into the phaco tip. Then the floor of the epinucleus is pushed back to keep the capsular bag on stretch and the epinucleus is rotated to bring a new
FIGURE 23.8 The epinuclear shell being rotated for trimming quadrant of roof and rim to the distal position. This is repeated until three of the four quadrants of epinuclear rim and forniceal cortex have been evacuated. It is important not
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to allow the epinucleus to flip too early, thus avoiding a large amount of residual cortex remaining after evacuation of the epinucleus. The epinuclear rim of the fourth quadrant is rotated to the distal position, (i.e. nasally) and then utilized as a handle to flip the epinucleus (Fig. 23.9) As the remaining portion of the epinuclear floor and
FIGURE 23.9 Flipping of the epinucleus
FIGURE 23.10 Empty capsular bag following flipping of the epinucleus rim is evacuated from the eye, 70 percent of the time all of the cortex is evacuated with it (Fig. 23.10). Continuing with the soft-shell technique, the capsular bag is filled with Provisc and Viscoat is injected into the center of the capsular bag to help stabilize the anterior chamber and to blunt the movement of the foldable IOL as it is implanted into the eye. If the cortex was incompletely mobilized during epinuclear removal, Viscoat (rather than Provisc) is instilled first to viscodissect the cortex into the capsular fornix and drape some of it on top
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FIGURE 23.11 Viscodissection of residual cortex prior to IOL implantation
FIGURE 23.12 Viscodissection of residual cortex prior to IOL implantation of the capsulorhexis (Figs 23.11 and 23.12). Provisc is then injected into the bottom of the bag, forcing the Viscoat anteriorly. The foldable IOL is then implanted. Residual cortex is evacuated with residual viscoelastic, the posterior capsule being protected by the optic of the IOL. Mobilization of Viscoat is greatly facilitated as it is encased within the much more highly cohesive Provisc and less time is necessary to evacuate residual viscoelastic.
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Summary The choo choo chop and flip technique utilizes the same hydro forces to disassemble the nucleus, but substitutes mechanical forces (chopping) for ultrasound energy (grooving) to further disassemble the nucleus. High vacuum is utilized as an extractive technique to remove nuclear material rather than utilizing ultrasound energy to convert the nucleus to an emulsate that is evacuated by aspiration. This technique maximizes safety and control as well as efficiency in all cases, and allows for phaco of harder nuclei in the presence of a compromised endothelium. This technique facilitates the achievement of two goals: minimally invasive cataract surgery and maximally rapid visual rehabilitation. References 1. Fine IH: The choo-choo chop and flip phacoemulsification technique, Operative Techniques in Cataract and Refractive Surgery, 1(2), 61–65, 1998. 2. Fine IH: The chip and flip phacoemulsification technique, Journal of Cataract and Refractive Surgery, 17(3):366–71, 1991. 3. Fine IH: Crack and flip phacoemulsification technique, Journal of Cataract and Refractive Surgery, 19(6):797–802, 1993. 4. Fine IH: Chop and flip phaco with high vacuum and burst mode, Clinical Education Videotapes, American Academy of Ophthalmology, 1997. 5. Fine IH: Bevel down chop and flip phaco with Arshinoff soft shell technique, Clinical Education Videotapes, American Academy of Ophthalmology, 1997. 6. Fine IH: Choo choo chop and flip with the soft-shell technique is safer and more efficient, Phaco and Foldables, 1997. 7. Masket S, Thorlakson R: The OMS Diplomax in endolenticular phacoemulsification. In Fine IH (Ed): Phacoemulsification: New Technology and Clinical Application, Slack, Inc., Thorofare, NJ, 1996. 8. Arshinoff S: Dispersive-cohesive viscoelastic soft shell technique, Journal of Cataract and Refractive Surgery, 25:167, 1999. 9. Fine IH: Cortical cleaving hydrodissection, Journal of Cataract and Refractive Surgery, 18(5):508–12, 1992.
24 Lens Quake Phaco Jack A Singer Introduction Lens quake phaco utilizes a hexagonal or diamond-shaped phaco tip to induce a disturbance in the lens nucleus, which simulates a miniature earthquake called a lens quake. The lens quake can be propagated along nuclear fault lines that run from the ysutures to the equator and posterior pole. Using this method, the nucleus can be cracked from the center to the periphery without the need to place a sharp chopping instrument near the equator of the lens. TIPS The Lens quake phaco cobra tip (Figs 24.1A to C) from surgical design has a modified hexagon shape, a 15-degree curve, a 15-degree bevel that faces up when the curve is pointing up, and a circular lumen (Fig. 24.2), which promotes occlusion. The hexagonal shape permits lens quake propagation without tilting or zonular stress, which can occur with a round phaco tip. Also, the additional mass in the head of the cobra tip focuses additional cavitation inside the tip that enhances the efficiency of both lens quake inducement and segment removal. Mastel Precision Instruments can supply non-cobra hexagonal Lens quake phaco tips for various other phaco systems. However, the additional mass in the head of the cobra tip focuses additional cavitation inside the tip that enhances the efficiency of both lens quake inducement and segment removal. The author has used the Storz Osher nucleus manipulator for years and finds it ideal for lens quake phaco. It has two blunt finger-like projections that can be used for a variety of maneuvers. However, any nucleus manipulator that provides a firm grasp on nuclear material will work. A sharp chopper is unnecessary but can be used for lens quake phaco.
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FIGURES 24.1 A TO C Hard-Rock Lens quake tip, with double 15-degree bevel for enhanced cutting and gripping
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FIGURE 24.2 Singen Lens quake tip with external hexagonal shape and circular internal lumen Mechanism We are all familiar with the annular structure of a tree. Similarly, the human lens is composed of annular concentric layers of radial fibers, beginning with the fetal nucleus, which becomes the hard adult nucleus through the addition of radial fibers throughout life (Figs 24.3A to C). These radial lens fibers join at the anterior and posterior y-sutures, which are encountered at times during central sculpting or during slit lamp examination of the lens. These are natural fault lines in the lens corresponding to these radial layers that are added through life. So, the lens not only has concentric layers but also has radial cleavage planes, which can be used for lens quake propagation. When the phaco tip is advanced into the center of the nucleus and is occluded, vacuum energy and the wedge shape of the tip induces stress and strain near the y-sutures resulting in lens quake induction. Techniques In order to perform lens quake phaco, set your machine at a low flow rate of 3 to 5 cc/minute and a vacuum limit of 200 mmHg. Rotate the infusion sleeve 90 degrees so that the infusion stream is
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FIGURES 24.3A TO C Mechanism of lens quake phaco
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FIGURES 24.4A TO C Hard-rock lens quake tip, with double 15-degree bevel for enhanced cutting and gripping directed sideways when the phaco tip bevel is sideways. Clean up the anterior cortex and epinucleus inside the anterior capsulotomy for better visibility. Next, orient the phaco tip bevel sideways so that the points of its hexagon are facing up and down, and the flat areas are facing sideways. Then, place the tip just inside the capsulorhexis at an angle pointing towards the center of the nucleus and place your nucleus manipulator in a stand-by position about 90 degrees away (Figs 24.4A to C). Using U/ S, drive the tip into the nucleus at a slow pace, switching between foot switch positions 3 and 2 as needed but do not go into position 1. When the top of the hexagon is
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completely buried, begin leveling off the entry angle and continue advancing until the port is at the central nucleus with its bottom point at half nuclear depth. Mute the U/S and stay in foot switch position 2 holding the phaco tip still while the vacuum builds. One of the most common causes of lens quake inducement failure is releasing the vacuum after the tip is placed into position and occluded. After the phaco tip is driven into position and vacuum is allowed to build, place the second instrument into the nucleus directly above the stationary phaco tip until it touches the tip. Now, hold it there for a second or two until you see a crack forming just in front of the tip. This is the induced lens quake! A simple manipulation will propagate the lens quake to the posterior pole and to the equators. We need to mimic a strike-slip fault in which blocks of earth slide past each other horizontally during an earthquake in order to induce lens quake propagation in the lens nucleus. Slide the nucleus manipulator downward along the side of the stationary phaco tip and then move the phaco tip slightly forward and the nucleus manipulator slightly backward to produce a strike-slip fault, sliding the nuclear segments past each other horizontally. This will induce complete propagation of the lens quake to the posterior pole and to the equators. While sliding the nuclear segments past each other horizontally, the lens and phaco tip can be rotated into position for the subsequent lens quakes, which is performed in a similar fashion on each heminucleus. Lens quake phaco can be used on any nucleus that is sufficiently firm enough to crack, and should not be used on soft lenses due to the risk of aspirating lens material distal to the tip down to and including the posterior capsule. Summary In summary, lens quake phaco is a significant advance in phaco efficiency and safety, which utilizes a hexagon-shaped phaco tip and high vacuum to induce a lens quake near the y-sutures. A simple manipulation that mimics earthquake movements will propagate the lens quake to the posterior pole and to the equators.
25 Supracapsular Phacoemulsification Aamir Asrar Introduction Since Kelman1–8 first introduced phacoemulsification improvements have been made not only with the instruments9–11 but in the technique also.12–21 Phacoemulsification is now the preferred choice of surgery for all types of cataracts, even the ones previously considered to be pure extracapsular cataract extraction cases (ECCE). Divide and conquer20 is still the favored technique for most of the phaco surgeons, as it is quite comfortable to perform if the cataract is straightforward, but becomes much more difficult with complicated cases as in weak zonules and small pupils. With the introduction of David Brown’s,23 Phaco Flip and Jack Kearney’s, Supracapsular Technique, phacoemulsification entered into a new era. William F Maloney’s,24–28 contribution to this technique has been remarkable. History of Supracapsular Phacoemulsification The procedure of phacoemulsification has undergone great deal of change since it was first introduced1,6–24 in 1967. This progress has been stepwise with the improvements made in phaco machines, intraocular lenses (IOLs), and instrumentation, leading to change in our techniques, thus making the whole procedure much safer and predictable to a greater extent. William F Maloney has explained this whole process of evolution very well by classifying it into different generations in the phacoemulsification era.24–26 • First generation (1967–1977) Anterior chamber • Second generation (1977–1987) Posterior chamber • Third generation (1987–1997) Endocapsular • Fourth generation (1997–2007) Supracapsular (?). Changes that evolved each decade have been related with the availability of the supporting equipment. With the introduction of larger capsulorhexis the idea of Supracapsular phacoemulsification evolved. Introduction of new generation phacoemulsification machines has further helped this technique of phacoemulsification. It is still a bit early to say if this really is going to be the Supracapsular phacoemulsification decade.
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What is Supracapsular Phacoemulsification? In Supracapsular phacoemulsification, the nucleus is maneuvered out of the capsular bag through a 5 to 6 mm capsulorhexis in such a way that it finally lies in a upside down position above the anterior capsule, i.e. in the Supracapsular space, where it can be emulsified. There are many variations to this technique. Surgical Technique Patient Selection As with any other surgical procedure in order to achieve good results and to gain confidence, patient selection is of importance. However, with experience any patient suitable enough to undergo phacoemulsification surgery, Supracapsular approach can be utilized. The author has used this procedure in difficult cataract cases (pseudoexfoliation, small pupil, unstable capsulorhexis, etc.) and found it safer and as effective. Anesthesia There is no specific preference for any type of anesthesia.29–44 The author always lets the patient decide regarding the type of anesthesia they feel comfortable with. The procedure may require less time and can easily be done under topical anesthesia. Incisions Site and type of incision is mainly surgeon’s preference.45–52 The author prefers a corneal incision but he alters the site and type according to the needs and requirement of the surgery. Paracentesis incision for the side-port instrument is placed 2 O’clock hours left of the main incision (for-right-handed surgeon and reverse for the left-handed surgeons). If placing an anterior chamber maintainer, the author prefers infratemporal position in the case of superior incision and is placed infranasally if temporal incision is made. Viscoelastic There is no actual indication that this procedure is effected by any specific sort of a viscoelastic.53,54 The author has used various types of viscoelastic for this procedure (mainly—Viscoat by Alcon, Healon by Pharmacia & Up John, Provisc by Alcon Fig. 25.1) but have not found any significant difference between them. Viscoelastics are used during phacoemulsification for the following main advantages • Keep the anterior chamber formed during capsulorhexis
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• Protection of corneal endothelium • Stabilize the anterior capsule during capsulorhexis • Insertion of IOL • Flip the nucleus out of the bag.
FIGURE 25.1 Viscoelastic with cannula
FIGURE 25.2 Cystotome on a viscoelastic syringe In addition to the one mentioned above there are many other uses, that make viscoelastic an integral part of eye surgery. Capsulorhexis After the introduction of the continuous curvilinear capsulorhexis (CCC)55–57 in the mid to the late 80s its advantages were soon evident to the cataract surgeons. As the capsulorhexis was 3 to 4 mm in size the nucleus could not be taken out of the bag and had to be emulsified in it. All the techniques developed during this stage were keeping in mind the limits imposed by the capsular bag. As the surgeons enjoyed the advantages58–60 of CCC, at the same time the restrictions61–62 and the problems of doing phacoemulsification in the bag started becoming more evident. With the introduction of a larger capsulorhexis of 5 to 6 mm in diameter it was easier to flip the nucleus out of the bag, allowing us to emulsify the nucleus in the supracapsular space away from the capsular bag restriction. The author normally starts the capsulorhexis, after injecting the viscoelastic in the anterior chamber, by making a flap in the anterior capsule with the help of a cystotome on a viscoelastic syringe (Fig. 25.2). Once the flap is lifted the whole capsulorhexis of 5
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to 6 mm (Figs 25.3 and 25.4) diameter is completed with the help of a Utrata forceps (Fig. 25.5). The cystotome can also be used to complete the whole capsulorhexis from start to finish. Hydrodissection/Hydrodelineation Hydrodissection or hydrodelineation is done with the help of a 26 G-hydrodissection cannula
FIGURE 25.3 5 to 6 mm capsulorhexis
FIGURE 25.4 5 to 6 mm capsulorhexis
FIGURE 25.5 Utrata forceps
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(Fig. 25.6)63,66–69 on a 3- or 5 CC-syringe filled with balanced salt solution (BSS). For hydrodissection the author injects small amount of fluid (Fig. 25.7) under the capsule first at 4 O’clock and then at 7 O’clock and looks for the fluid wave to pass under the nucleus and it is considered completed when he can see the sommer ring (golden ring) or the tilt in the nucleus. For hydrodelineation,64,65 the author places the cannula between the epinucleus and the nucleus. For supracapsular phacoemulsification the author does not find any special advantage of hydrodelineation over hydrodissection. They both work well for him. Rotation of the Nucleus It is important to free the nucleus from any adhesion with the lens cortex so that it lies freely in the capsular bag, as this makes it easier to flip it out of the bag. Presence of a golden ring around the nucleus or a small tilt in the nucleus is an indicator
FIGURE 25.6 26-G Hydrodissection cannula on a balanced salt solution (BSS) syringe
FIGURE 25.7 Injection of BSS under the anterior capsule to achieve hydrodissection
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FIGURE 25.8 Direction for rotation of the nucleus
FIGURE 25.9 Direction for rotation of the nucleus following hydrodissection that the nucleus is lying free in the bag. It can be confirmed by using the hydrodissection cannula to rotate the nucleus70 taking care not to push it towards the vitreous and not to force it in any direction (Figs 25.8 and 25.9). Another important point while carrying out nuclear rotation is to keep the tip of the cannula in view as it might pass through the lens rupturing the lens capsule. Once the nucleus lies free in the bag supracapsular phacoemulsification can be started. There are many variations to this approach. The author has mentioned the one that he used and found safe and effective. Phaco-hemi Flip Phacoemulsification71 is started with the standard settings (low aspiration and ultrasound power) on the phaco machine. Nuclear sculpting is done in the area of capsulorhexis along an imaginary line extending from the site of incision vertically downwards (Fig.
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25.10). Once the sculpting is completed to half the thickness of the nucleus it is rotated by 90 degrees (Fig. 25.11). Keeping the phaco probe and the side-port instrument (nucleus rotator) in the sculpted groove of the nucleus (Fig. 25.12), it is cracked into two halves by moving the instrument in the opposite direction (Fig. 25.13). Then the settings on the phaco machine are changed, by increasing the vacuum to 200 mmHg
FIGURE 25.10 Sculpting of the nucleus
FIGURE 25.11 Rotation of the nucleus by 90 degrees and raising the bottle to the maximum height. The author keeps both the instruments (phaco probe and the nucleus rotator) in the eye. Now the two nuclear fragments are arranged in the bag so that the smaller one is away from the site of incision. The phaco probe is brought near the superior edge of the nucleus and the smaller piece of the
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nucleus fragment is engaged in the phaco tip by only utilizing the vacuum. The nucleus rotator is taken
FIGURE 25.12 Insertion of the instruments and their placement in the nuclear groove
FIGURE 25.13 Cracking the nucleus by moving the instruments in the opposite direction to the base of the nuclear fragment (Fig. 25.14). Now with a bimanual motion, i.e. utilizing the rotatory movement of the nucleus rotator to sweep the inferior surface of the lens fragment over the posterior capsule and at the same time helped with the vacuum of the phaco instrument the nuclear fragment is flipped out of the bag into the pupillary plane (Figs 25.15 to 25.17). The nuclear fragment being smaller than the size of the whole nucleus can easily be emulsified in the iris plane (Figs 25.18 and
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FIGURE 25.14 Placement of instruments for flipping the nucleus out of the bag
FIGURE 25.15 25.19). The other nuclear piece in the capsular bag keeps the bag formed and the posterior capsule away from the phaco probe. Flipping of the other piece and its emulsification in the iris plane follows this. Phaco Flip David Brown,23,25 introduced this supracapsular phacoemulsification technique, and so was the
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FIGURE 25.16
FIGURE 25.17 FIGURES 25.15 TO 25.17 Maneuver of flipping the nucleus out of the bag actual birth of the new generation supracapsular phacoemulsification. After completing the basic steps mentioned above one can proceed with this technique (Fig. 25.20). The nucleus is depressed at the superior equator. This can be done with the help of a viscoelastic cannula, spatula, hydrodissection cannula or a nucleus rotator. As the capsulorhexis is large the depression on the nucleus in such a way causes the nucleus to move out of the bag. This maneuver is continued so that the nucleus flips
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FIGURE 25.18 Final position of the nuclear segment in the pupillary plane before starting emulsification
FIGURE 25.19 Emulsification of the nucleus in the pupillary plane completely and lies almost facing upside down. Emulsification of this nucleus can now be started by bringing the phaco probe tip at the level of the iris plane in the pupillary area. Nucleus is engaged from the posterior side and emulsification started. The phaco probe is kept static in this position and the nucleus is fed into the tip with the help of a sideport instrument. This whole process is very fast with effective utilization of ultrasound energy. With the develop-
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FIGURE 25.20 Phacoflipemulsification of the nucleus from down under ment of new generation of phacoemulsification machines, more reliance on vacuum can achieve the end point quickly. Tilt and Tumble Phaco Tilt and tumble phaco has been described by Richard L Lindstrom in a recently published textbook74 “Clear Cornea Lens Surgery” by Howard Fine published by Slack Incorporated. After completing the CCC, hydrodissection is performed by placing the hydrodissection cannula under the anterior capsule approximately 180° from the site of incision. BSS is injected until a fluid wave is seen. The hydrodissection is continued which causes the nucleus to tilt out of the bag. The nucleus can also be tilted out of the bag by retracting the anterior capsule at 7:30 O’clock position. If the nucleus does not tilt out of the bag at the superior edge then it can always be rotated to face the site of incision. Otherwise the inferior half of the nucleus is depressed which causes the superior edge of the nucleus to tilt out of the bag. Viscoelastic is injected anterior and posterior to the nucleus to protect the cornea, iris and posterior capsule. Nucleus is kept in this position supported by the nucleus rotator and can be emulsified using high vacuum (Fig. 25.21). Once half of the nucleus is emulsified the half left can be tumbled upside down
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FIGURE 25.21 Tilt and tumble phaco and can now be emulsified by a direct approach on to the posterior surface of this fragment. The whole nucleus can also be emulsified without tumbling the last fragment. This has also been described as a transitional step from endocapsular to supracapsular phacoemulsification procedure. Supracapsular Quick Chop Phaco William F Maloney introduced supracapsular quick chop phacoemulsification.24–28 In this procedure he tilts the lens early during hydrodissection by continuing it even after the fluid wave is seen (Fig. 25.21). If not successful, one can repeat hydrodissection after nuclear rotation. He advises to convert it into an endocapsular approach if the lens fails to tilt. Once a lens tilt is achieved the process to flip the nucleus can be carried out further, by depressing the posterior half of the tilted nucleus with a hydrodissection cannula (Fig. 25.22) and then gently sweeping the posterior equator of the nucleus over the posterior capsule, till the superior equator lies just pass the midline (Fig. 25.23). Now viscoelastic is injected as needed (Fig. 25.24) and at the same time the viscoelastic cannula continues to flip the nucleus so that it finally lies in a horizontal position but only upside down (Fig. 25.25). With the help of the same cannula the nucleus is moved into the posterior chamber, i.e. between the iris and the anterior capsule outside the capsular bag (Fig. 25.26). The tip of the phaco probe is extended 1.5 to 2.00 mm beyond the irrigation sleeve (Fig. 25.27) as this will act as safeguard to deeper penetration. He also advises to use 100 percent linear phaco power with slow pulse mode of 2 to 4 pulse/second. Introduce the phaco tip (Fig. 25.28) and the quick chopper into the anterior chamber. The phaco probe is buried deep into the central nucleus up to its sleeve and then maintaining the
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FIGURE 25.22 Flipping of the nucleus out of the bag following hydrodissection
FIGURE 25.23 Sweeping the lens over the posterior capsule with the hydrodissection cannula
FIGURE 25.24 Nucleus almost lying past midline
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FIGURE 25.25 Viscoelastic used to complete the flipping of the nucleus aspiration to stabilize the nucleus till the nuclear chop is completed. Quick chopper is buried into the nucleus just above the phaco tip (Fig. 25.29). Now the nucleus is separated vertically by briskly depressing the nucleus straight down accounting for 80 percent displacement and elevating the embedded phaco tip accounting for the remaining 20 percent of the vertical displacement (Fig. 25.30). This causes the division to appear in the center of the nucleus (Fig. 25.31). Now the phaco tip and the quick chopper are separated laterally causing a complete break in the nucleus. Nucleus is rotated by 90 degrees. The separation can now be confirmed
FIGURE 25.26 Nucleus being placed in the posterior chamber above the anterior capsule
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FIGURE 25.27 Introduction of phaco tip into anterior chamber with sleeve drawn posteriorly again by moving the two halves in opposite direction with the chopper and the phaco tip. The second chop is done on the inferior half of the nucleus. By placing the phaco tip in the middle wall, exposed in the crack. Machine settings are kept the same as initially. The chop is repeated in the same fashion as the first one. First by vertical and then by horizontal separation of the two instruments causing division of the nucleus fragment. Soft lenses are divided into four but for the harder ones may need further disassembly into smaller pieces (Figs 25.32A and B). As there is no
FIGURE 25.28 Aim the tip of the probe towards the center
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FIGURE 25.29 Phaco tip and the chopper tip buried in the center of the nucleus capsular bag to keep the nuclear pieces organized it is better to evacuate them as soon as liberated (Figs 25.33 and 25.34). For emulsification of the nuclear pieces the phaco tip extension is shortened to 1 mm and the settings on the machine are changed to traditional linear phaco power control with higher aspiration flow. WF Maloney has advised an aspiration flow setting of 160 mmHg for supracapsular quadrant removal. Once the nucleus is out of the bag the usual techniques for endocapsular phacoemulsifica-
FIGURE 25.30 Opposite direction movement of the instruments to achieve a crack in the nucleus
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FIGURE 25.31 Appearance of division in the center of the nucleus tion18,22,69,70 can also be used like cracking, chopping, sculpting or manual prechopping, etc (Figs 25.35 to 25.40). Other Variations Bruce Wallace Dr Wallace begins sculpting the nucleus in the bag. Completes a classic criss-cross pattern. Then flips the nucleus outside the bag so that it lies in an upside down position. The criss-cross pattern is still visible from the inverted side. This can be used as a landmark for chopping and completing the sculpting and emulsification.
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FIGURES 25.32A AND B Completion of second chop Irrigation, Aspiration and IOL Insertion Once all the nuclear fragments are emulsified irrigation and aspiration can be started. It is important to remove all the soft lens matter and then to clean the capsule properly. This should not only be done in the obvious visible areas of the capsule but the author prefers to clean the cells from the remaining anterior capsule and the equator. Polishing of the posterior capsule is also essential. Once convinced that no more polishing is required the lens can be introduced in the bag.
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FIGURE 25.33 Division of nucleus in four and start of their emulsification
FIGURE 25.34 Emulsification of each fragment independently Advantages Emulsifying the nuclear fragments in the supracapsular space protects the posterior capsule from rupture. The author found that phaco hemiflip could be performed easily in small pupils without the need of stretching the iris, using iris clips, sphincterotomy or any other damaging procedures to the iris. At the same time the zonules are not damaged to the same extent as if the phacoemulsification is done in the bag.
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FIGURE 25.35 Splitting of the nucleus
FIGURE 25.36 Separating the nucleus pieces further by lateral movement of the instruments Protection of posterior capsule Once the nucleus is flipped out of the bag it can be emulsified in the iris plane or in the posterior chamber above the capsular bag, away from its restrictions. This leads to less pressure and danger to rupture of the posterior capsule.75–79 Emulsification is helped by the use of higher vacuum, which normally is not used in the bag, as chances of catching the capsule in the phaco tip are minimal. Less zonular damage Small amount of manipulation is done in the bag, which prevents any
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FIGURE 25.37 Splitting of nucleus further into four quadrants
FIGURE 25.38 Emulsification of each fragments
FIGURE 25.39 Removal of fragments individually
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FIGURE 25.40 Final outcome damage to the zonules.80,81,86 Emulsification performed outside the bag in the supracapsular space prevents damage to the zonules. Effective utilization of ultrasound energy Since the nucleus is easily approachable in the supracapsular space and in the upside down position the use of ultrasound energy is utilized very effectively. At the same time it is helped by the added high aspiration flow rate, which keeps the nucleus near the phaco tip. High volume surgery For high volume phaco surgeons this is an effective way of doing surgery, as the average time required for supracapsular phaco is less than that of the endocapsular approach. Advantages of larger capsulorhexis Larger capsulorhexis is the key for a supracapsular phacoemulsification. Other than allowing one to flip the nucleus out of the bag it has following main advantages. • Prevents IOL decentration. • Prevents capsular phimosis.82,83 • Good retinal view following phacoemulsification. • Easy access to the equator of the capsule for removal of cells thus preventing posterior capsule opacification.
Supracapsular Phacoemulsification in Difficult Cases Difficult cases are the test of endurance for any procedure. The credibility and efficiency of a procedure can be honored by its effectiveness in difficult cases. The author has used these techniques in cases like small pupil, pseudoexfoliation, vitrectomized eyes, hard nucleus, white cataracts and others and found these procedures very effective with excellent results. Pseudoexfoliation In a pseudoexfoliation84–87 case, the surgeon is always concerned about the status of the zonules. Excessive manipulation of the lens in the bag can lead to damage of the zonules.
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This damage can be significant enough to cause a dislocated or dropped nucleus or unstable bag at the end of surgery not suitable enough to support an IOL. Capsule tension rings are a good option but they also have their limits. With supracapsular phacoemulsification there is little amount of manipulation in the bag and once the nucleus is removed out of the bag no further pressure is exerted on the zonules. Small Pupil Phacoemulsification in small size pupils88–93 is always a challenge. Mainly because it is difficult to achieve a good size capsulorhexis and then it is difficult to do sculpting and aspiration of soft lens matter under the iris. One can use iris hooks, stretching of the iris, or sphincterotomy for such eyes to increase the pupillary diameter. The author always does phaco hemiflip procedure for such cases. To have good pupillary aperture the author tries to dilate the iris by stretching but if this does not work then he does the following procedure. Lifting the flap of anterior capsule towards the paracentesis incision with the help of a cystotome starts the capsulorhexis. Then introduce a Sinskey hook from the paracentesis incision and Utrata forceps through the main incision. Pull the iris to the paracentesis side with the help of a Sinskey hook exposing 5 to 6 mm zone of the capsule. Once this area is exposed hold the flap of the capsule with the help of Utrata forceps held in the other hand. Now start rotating the flap to attain capsulorhexis in 5 to 6 mm zone of the anterior capsule, exposing that area of capsule by dragging iris toward the periphery. Once pass the 6 O’clock position when it is required to push the iris then to pull it away the author uses the Y-shaped instrument as he finds Sinskey hook to be a sharp instrument for this purpose. The capsulorhexis continues in the same fashion as to expose with the side-port instrument and tearing of the flap with Utrata forceps. Once the capsulorhexis is completed phaco hemiflip can be started by just burring the phaco tip in the center of the nucleus to create groove almost two-third of the thickness of the nucleus then it is divided and flipped out of the bag as discussed before. As it is half the size of the whole nucleus it can fit in the pupillary plane where it can be emulsified easily. Aspiration of the lens cortex can also be done with the same exposure technique as used for doing capsulorhexis. Vitrectomized Eyes94–97 As there is no support of the vitreous the posterior capsule is quite flabby and the dynamics in the anterior and posterior segment are very different than in the normal eye. With this technique the lens is out of the bag in the early stages and the posterior capsule does not come in the way of the phaco probe. On occasions, the author has used an anterior chamber maintainer in these eyes which makes phacoemulsification very easy. It is important to note that the pressure in the anterior segment should not be increased to an extent that the bag ruptures. The author has seen people using posterior segment infusion but he thinks this is really not required.
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Hard Nucleus These types of nuclei are not difficult with supracapsular approach as a high aspiration flow rate can be used to help the emulsification of the nucleus. Low Endothelial Cell Count Cornea The author prefers to use a phaco flip technique in these cases. As his average percentage of endothelial cell loss with this technique is 7.00 percent.98–112 The main reason for less endothelial cell loss (ECL) is that • The pieces are smaller than the whole nucleus and can be emulsified in the pupillary plane. • Less instrumentation required as compared to the cracking technique as one does not need to insert and reinsert different instruments. • Less operation time is required. • Less ultrasound time, as most of the time high vacuum is assisting.
New Generation Phaco Machines and Supracapsular Phacoemulsification The new generation phaco machines have provided us with a new dimension of phacoemulsification. With the availability of high aspiration flow rate supracapsular phacoemulsification is much simpler, more effective and safer. This is especially important for the high volume phaco surgeons. Supracapsular phacoemulsification is a step forward in the phacoemulsification technique. Flipping the nucleus out of the bag not only allows easy approach to the nucleus but as it is in the supracapsular plane there is less chance of rupturing the posterior capsule and damaging the zonules. At the same time, the posterior surface is directly approachable which allows effective utilization of ultrasound energy. All these factors help to make it not only a safer and effective technique but quicker too. References 1. Kelman CD: Phacoemulsification and aspiration—a new technique of cataract removal—a preliminary report. Am J Ophthalmol 64(1):23–35, 1967. 2. Kelman CD: Phacoemulsification and aspiration—a progress report. Am J Ophthalmol 67(4):464–77, 1969. 3. Kelman CD, Brooks DL: Ultrasonic emulsification and aspiration of traumatic hyphema—a preliminary report. Am J Ophthalmol 71(6):1289–91, 1971. 4. Kelman CD: Phacoemulsification and aspiration—a report of 500 consecutive cases. Am J Ophthalmol 75(5):764–68, 1973. 5. Kelman CD: Phacoemulsification in the anterior chamber. Ophthalmology 86(11):1980–82, 1979.
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6. Kelman CD: History of phacoemulsification. In Little JH, Emery JM (Eds): Phacoemulsification and Aspiration of Cataracts. St Louis: CV Mosby.5–7, 1979. 7. Kelman CD: The history and development of phacoemulsification. Int Ophthalmol Clin 34(2):1– 12, 1994. 8. Kelman CD: In tune with the father of phacoemulsification. J Cataract Refract Surg 23(8):1128– 29, 1997. 9. Hoh H, Fischer E: Erbium laser phacoemulsification—a clinical pilot study. Klin Monatsbl Augenheilkd 214(4):203–10, 1999. 10. Tunc Z: Laser phacoemulsification with the Paradigm Photon Laser—surgical technique and first results. J Fr Ophthalmol 22(1):39–40, 1999. 11. Neubaur CC, Stevens G Jr: Erbium: YAG laser cataract removal—role of fiberoptic delivery system. J Cataract Refract Surg 25(4):514–20, 1999. 12. Lee SY, Tan D: Changing trends in cataract surgery in Singapore. Singapore Med J 40(4):256– 59, 1999. 13. Thatte S, Raju VK: Phacosandwich technique. J Cataract Refract Surg 25(8):1039–40, 1999. 14. Gonglore B, Smith R: Extracapsular cataract extraction to phacoemulsification—why and how? Eye 2(Pt 6):976–82, 1998. 15. Kohlhaas M, Klemm M, Kammann J et al: Endothelial cell loss secondary to two different phacoemulsification techniques. Ophthalmic Surg Lasers 29(11):890–95, 1998. 16. Garcia AS, Limao AM, Sampaio AM et al: Chop and rechop. J Cataract Refract Surg 24(2):147–48, 1998. 17. Lampe Z, Vamosi P, Berta A: Changing concept and modern techniques in cataract surgery Acta Chir Hung 36(1–4):184–85, 1997. 18. Fine IH, Maloney WE, Dillman DM: Crack and flip phacoemulsification technique. J Cataract Refract Surg 17:797–802, 1993. 19. Fine IH: Chip and flip phacoemulsification technique. J Cataract Refract Surg 17:366–71, 1991. 20. Gimbel HV: Divide and conquer nucleofractis phacoemulsification—development and variations. J Cataract Refract Surg 17:281–91, 1991. 21. Arnold PN: Nuclear flip technique in small pupil phacoemulsification. J Cataract Refract Surg 17(2):225–27, 1991. 22. Koch PS, Katzen LE: Stop and chop phacoemulsification. J Cataract Refract Surg 20:566–70, 1994. 23. Brown D: Phaco flip, course presented at the Symposium on Cataract, IOL and Refractive Surgery, Seattle, Washington, 1996. 24. Maloney WF, Dillman DM, Nichamin LD: Supracapsular phacoemulsification—a capsule-free posterior chamber approach. J Cataract Refract Surg 23:323–28, 1997. 25. Maloney WF: For more and more surgeons phaco is on its way out…out of the capsular bag, that is. Ocular Surg News, 1997. 26. Maloney WF: Supracapsular phaco—the next generation? Ocular Surg News, 1996. 27. Maloney WF: Supracapsular and quick chop phaco combines safety, efficiency. Ocular Surg News, 1998. 28. Maloney WF: Supracapsular phaco and its larger continuous curvilinear capsulorrhexis may allow for more efficient cataract surgery. Ocular Surg News, 1999. 29. Findl O, Dallinger S, Menapace R et al: Effects of peribulbar anesthesia on ocular blood flow in patients undergoing cataract surgery. Am J Ophthalmol 127(6):645–49, 1999. 30. Gillart T, Barrau P, Bazin JE et al: Lidocaine plus ropivacaine versus lidocaine plus bupivacaine for peribulbar anesthesia by single medical injection. Anesth Analg 89(5):1192–96, 1999. 31. Schwarz EC, Gerdemann M, Hoffmann R et al: Strabismus and diplopia as complications after cataract surgery with IOL implantation. Ophthalmology 96(10):635–39, 1999.
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32. Anders N, Heuermann T, Ruther K et al: Clinical and electrophysiologic results after intracameral lidocaine 1% anesthesia: a prospective randomized study. Ophthalmology 106(10):1863–68, 1999. 33. Nociti JR, Serzedo PS, Zuccolotto EB et al: Ropivacaine in peribulbar block—a comparative study with bupivacaine. Acta Anaesthesiol Scand 43(8):799–802, 1999. 34. Brown SM, Brooks SE, Mazow ML et al: Cluster of diplopia cases after periocular anesthesia without hyaluronidase. J Cataract Refract Surg 25(9):1245–49, 1999. 35. Eke T, Thompson JR: The National Survey of Local Anaesthesia for Ocular Surgery: I—survey methodology and current practice. Eye 13(Pt 2):189–95, 1999. 36. Yepez J, Cedeno de Yepez J, Arevalo JF: Topical anesthesia for phacoemulsification, intraocular lens implantation, and posterior vitrectomy. J Cataract Refract Surg 25(8):1161–64, 1999. 37. Edge R, Navon S: Scleral perforation during retrobulbar and peribulbar anesthesia—risk factors and outcome in 50,000 consecutive injections. J Cataract Refract Surg 25(9):1237–44, 1999. 38. Warwar RE, Bullock JD: Globe rupture after peribulbar anesthesia. J Cataract Refract Surg 25(7):880–81, 1999. 39. Bellucci R: Anesthesia for cataract surgery. Curr Opin Ophthalmol 10(1):36–41, 1999. 40. Rigal-Sastourne JC, Huart B, Pariselle G et al: Diffusion if lidocaine after intracameral injection. J Fr Ophthalmol 22(1):21–24, 1999. 41. Winder S, Walker SB, Atta HR: Ultrasonic localization of anesthetic fluid in sub-Tenon’s, peribulbar, and retrobulbar techniques. J Cataract Refract Surg 25(1):56–59, 1999. 42. Rous SM: Simplified sub-Tenon’s anesthesia: miniblock with maxiblock effect. J Cataract Refract Surg 25(1):10–15, 1999. 43. Johnston RL, Whitefield LA, Giralt J et al: Topical versus peribulbar anesthesia, without sedation, for clear corneal phacoemulsification. J Cataract Refract Surg 24(3):407–10, 1998. 44. Roman SJ, Chong Sit DA, Boureau CM et al: Sub-Tenon’s anaesthesia: an efficient and safe technique. Br J Ophthalmol 81(8):673–76, 1997. 45. Rainer G, Menapace R, Vass C et al: Corneal shape changes after temporal and superolateral 3.0 mm clear corneal incisions. J Cataract Refract Surg 25(8):1121–26, 1999. 46. Vass C, Menapace R, Rainer G et al: Comparative study of corneal topographic changes after 3.0 mm beveled and hinged clear corneal incisions. J Cataract Refract Surg 24(11):1498–504, 1998. 47. Vass C, Menapace R, Rainer G: Corneal topographic changes after frown and straight sclerocorneal incisions. J Cataract Refract Surg 23(6):913–22, 1997. 48. Huang FC, Tseng SH: Comparison of surgically induced astigmatism after sutureless temporal clear corneal and scleral frown incisions. J Cataract Refract Surg 24(4):477–81, 1998. 49. Simsek S, Yasar T, Demirok A et al: Effect of superior and temporal clear corneal incisions on astigmatism after sutureless phacoemulsification. J Cataract Refract Surg 24(4):515–18, 1998. 50. Kohnen T, Dick B, Jacobi KW: Comparison of the induced astigmatism after temporal clear corneal tunnel incisions of different sizes. J Cataract Refract Surg 21(4):417–24, 1995. 51. Fine IH: Corneal tunnel incision with a temporal approach. In Fine IH, Fichman RA, Grabow HB (Eds): Clear Corneal Cataract Surgery and Topical Anesthesia. Thorofare: NJ Slack 5–26, 1993. 52. Fine IH: Architecture and construction of a self-sealing incision for cataract surgery. J Cataract Refract Surg 17(Suppl):672–76, 1991. 53. Schmidl B, Anterist N, Mester U: Corneal endothelial protection in phacoemulsification of high risk eyes with cornea guttata. Intraindividual comparison of 2 viscoelastic substances of different viscosity and molecular size. Ophthalmology 96(6):382–86, 1999. 54. Lehmann R, Brint S, Stewart R et al: Clinical comparison of Provisc and Healon in cataract surgery. J Cataract Refract Surg 21(5):543–47, 1995. 55. Gimbel HV: Two-stage capsulorhexis for endocapsular phacoemulsification. J Cataract Refract Surg 16(2):246–49, 1990.
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56. Gimbel HV, Neuhann T: Continuous curvilinear capsulorhexis (letter). J Cataract Refract Surg 17:110–11, 1991. 57. Gimbel HV, Neuhann T: Development, advantages and methods of the continuous circular capsulorhexis technique. J Cataract Refract Surg 16:31–37, 1990. 58. Tahi H, Fantes F, Hamaoui M et al: Small peripheral anterior continuous curvilinear capsulorhexis. J Cataract Refract Surg 25(6):744–47, 1999. 59. Andreo LK, Wilson ME, Apple DJ: Elastic properties and scanning electron microscopic appearance of manual continuous curvilinear capsulorhexis and vitrectorhexis in an animal model of pediatric cataract. J Cataract Refract Surg 25(4):534–39, 1999. 60. Luck J, Brahma AK, Noble BA: A comparative study of the elastic properties of continuous tear curvilinear capsulorhexis versus capsulorhexis produced by radio-frequency endodiathermy. Br J Ophthalmol 78(5):392–96, 1994. 61. Assia EI, Apple DJ, Tsai JC et al: The elastic properties of the lens capsule in capsulorhexis. Am J Ophthalmol 111(5):628–32, 1991. 62. Cochener B, Jacq PL, Colin J: Capsule contraction after continuous curvilinear capsulorhexis— poly(methyl methacrylate) versus silicone intraocular lenses. J Cataract Refract Surg 25(10):1362–69, 1999. 63. Gimbel HV: Hydrodissection and hydrodelineation. Int Ophthalmol Clin 34(2):73–90, 1994. 64. Anis AY: Understanding hydrodelineation—the term and the procedure. Doc Ophthalmol 87(2):123–37, 1994. 65. Beyer RW: Distinguishing hydrodissection and hydrodelineation. Ophthalmic Surg 24(2):135, 1993. 66. Brierley L: Hydroexpression of the nucleus. J Cataract Refract Surg 19(5):666–67, 1993. 67. Allarakhia L, Pearce JL: A new cannula for nucleus hydrodissection. Ophthalmic Surg 20(4):296–97, 1989. 68. Ayaki M, Ohde H, Yokoyama N: Size of the lens nucleus separated by hydrodissection. Ophthalmic Surg 24(7):492–93, 1993. 69. Shephered JR: In situ fracture. J Cataract Refract Surg 16:436–40, 1990. 70. Maloney WF, Grindle L: Textbook of phacoemulsification. Fallbrook, CA, Lasenda, 1988. 71. Fine IH: Cortical cleaving hydrodissection. J Cataract Refract Surg 18(5):508–12, 1992. 72. Braverman SD: Braverman-Bechert nucleus rotator. J Cataract Refract Surg 18(4):410–11, 1992. 73. Asrar A, Flitcroft I, Tormey P: Phaco-Hemiflip—a suitable technique for small pupil and weak zonules. Ocular Surgery News 17(11):28, 1999 74. Lindstrom RL: Tilt and tumble phacoemulsification technique. In Fine HI (Ed): Textbook of Clear Corneal Lens Surgery. Slack Inc, 1999. 75. Meng YA, Wang YF, Liu XM: Management of posterior capsule rupture and vitreous loss during IOL implantation. Chung Hua Yen Ko Tsa Chih 30(3):174–76, 1994. 76. Mulhern M, Kelly G, Barry P: Effects of posterior capsular disruption on the outcome of phacoemulsification surgery. Br J Ophthalmol 79(12):1133–37, 1995. 77. Koch PS: Managing the torn posterior capsule and vitreous loss. Int Ophthalmol Clin 34(2):113–30, 1994. 78. Traianidis P, Sakkias G, Avramides S: Prevention and management of posterior capsule rupture. Eur J Ophthalmol 6(4):379–82, 1996. 79. Osher RH, Cionni RJ: The torn posterior capsule—its intraoperative behavior, surgical management, and long-term consequences. J Cataract Refract Surg 16(4):490–94, 1990. 80. Saber HR, Butler TJ, Cottrell DG: Resistance of the human posterior lens capsule and zonules to disruption. J Cataract Refract Surg 24(4):536–42, 1998. 81. Mackool RJ, Sirota MA: Intracapsular foldable posterior chamber lens implantation in eyes with posterior capsule tears or zonular fiber instability. J Cataract Refract Surg 24(6):739–40, 1998.
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82. Hayashi H, Hayashi K, Nakao F et al: Anterior capsule contraction and intraocular lens dislocation in eyes with pseudoexfoliation syndrome. Br J Ophthalmol 82(12):1429–32, 1998. 83. Sugimoto Y, Takayanagi K, Tsuzuki S et al: Postoperative changes over time in size of anterior capsulorhexis in phacoemulsification/aspiration. Jpn J Ophthalmol 42(6): 495–98, 1998. 84. Breyer DR, Hermeking H, Gerke E: Late dislocation of the capsular bag after phacoemulsification with endocapsular IOL in pseudoexfoliation syndrome. Ophthalmology 96(4):248–51, 1999. 85. Fine IH, Hoffman RS: Phacoemulsification in the presence of pseudoexfoliation: challenges and options. J Cataract Refract Surg 23(2):160–65:1997. 86. Gimbel HV, Sun R, Heston JP: Management of zonular dialysis in phacoemulsification and IOL implantation using the capsular tension ring. Ophthalmic Surg Lasers 28(4):273–81, 1997. 87. Dosso AA, Bonvin ER, Leuenberger PM: Exfoliation syndrome and phacoemulsification. J Cataract Refract Surg 23(1):122–25, 1997. 88. Kadonosono K, Ohno S: New iris retractor for pupil dilatation during anterior vitrectomy: double-hook iris retractor. Ophthalmic Surg Lasers 30(3):241–43, 1999. 89. Novak J: Flexible iris hooks for phacoemulsification. J Cataract Refract Surg 23(6):828–31, 1997. 90. Masket S: Avoiding complications associated with iris retractor use in small pupil cataract extraction. J Cataract Refract Surg 22(2):168–71, 1996. 91. Federman JL, Anand R: Surgical dilation of the pupil during pars plana vitrectomy. Ophthalmic Surg 20(1):46–48, 1989. 92. Eckardt C: A modified technique of pupillary stretching. Dev Ophthalmol 14:32–36, 1987. 93. Yuguchi T, Oshika T, Sawaguchi S et al: Pupillary functions after cataract surgery using flexible iris retractor in patients with small pupil. Jpn J Ophthalmol 43(1):20–24, 1999. 94. Katsu Y, Ogino N, Kumagai E: Posterior chamber lens implantation concurrent with vitrectomy for proliferative diabetic retinopathy. Nippon Ganka Gakkai Zasshi 95(1):86–91, 1991. 95. Grusha YO, Masket S, Miller KM: Phacoemulsification and lens implantation after pars plana vitrectomy. Ophthalmology 105(2):287–94, 1998. 96. McDermott ML, Puklin JE, Abrams GW et al: Phacoemulsification for cataract following pars plana vitrectomy. Ophthalmic Surg Lasers 28(7):558–64, 1997. 97. Kang YH, Lee JH: Phacoemulsification and posterior chamber intraocular lens implantation after scleral buckling, vitrectomy, or both. Ophthalmic Surg Lasers 29(1):23–27, 1998. 98. Asrar A: Effect of site of incision on corneal endothelial cell following phacohemiflip surgery. Presented in Irish Academy of Medicine Ophthalmology faculty meeting in Dublin, Ireland. Nov 1999. Bourne WM, Kaufman HE. Endothelial damage associated with intraocular lenses. Am J Ophthalmology 81:482–85, 1976. 99. Bourne WM, Kaufman HE: Cataract extraction and the corneal endothelium. Am J Ophthalmology 82:44–47, 1976. 100. Waltman SR, Cozean CH Jr: The effect of phacoemulsification on the corneal endothelium. Ophthalmic Surg 10(1):31–33, 1979. 101. Beesley RD, Olson RJ, Brady SE: The effects of prolonged phacoemulsification time on the corneal endothelium. Ann Ophthalmol 18:216–22, 1986. 102. Zetterstrom C, Laurell CG: Comparison of endothelial cell loss and phacoemulsification energy during endocapsular phacoemulsification surgery. J Cataract and Refract Surg 21:55– 58, 1995. 103. Sugar J, Mitchelson J, Kraff M: The effect of phacoemulsification on corneal endothelial cell density. Arch Ophthalmol 96:446–48, 1978. 104. Beesley RD, Olson RJ, Brady SE: The effects of prolonged phacoemulsification time on the corneal endothelium. Ann Ophthalmol 18:216–22,1986. 105. Binder PS, Sternberg H, Wickman MG et al: Corneal endothelium damage associated with phacoemulsification. Am J Ophthalmol 82:48–54, 1976.
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106. Kaufman E, Katz JI: Endothelium damage from intraocular lens insertion. Invest Ophthalmol 15:996–1000, 1976. 107. Mc Carey BE, Polack FM, Marshall W: The phacoemulsification procedure. I—the effect of intraocular irrigating solution on corneal endothelium. Invest Ophthalmol 15: 449–57, 1976. 108. Matsuda M, Kinoshita S, Ohashi Y et al: Comparison of the effects of intra-ocular irrigating solution on the corneal endothelium in intra-ocular lens implantation. Br J Ophthalmol 75(8):476–79, 1991. 109. Craig MT, Olson RJ, Mamalis, Olson RJ: Air bubble endothelial damage during phacoemulsification in human eye bank eyes—the protective effects of Healon and Viscoat. J Cataract Refract Surg 17:21–26, 1991. 110. Hoyashi K, Nakao F, Hayashi F: Corneal endothelium cell loss following phacoemulsification using the small port-phaco. Ophthalmic Surg 25:510–13, 1994. 111. Lane SS, Naylor DW, Kullerstrand LJ et al: Prospective comparison of the effects of Occucoat, Viscoat and Healon on Intra Ocular Pressure and endothelial cell loss. J Cataract Refract Surg 17:21–26, 1991. 112. Dick HB, Konen T, Jacobi KW: Long term endothelial cell loss following phacoemulsification through a temporal clear corneal incision. J Cataract Refract Surg 22(1):63–67, 1996.
26 New Non-laser Phacoemulsification Technologies I Howard Fine, Mark Packer Richard S Hoffman Introduction New technology brings challenges and opportunities to the anterior segment surgeon. The drive towards less traumatic surgery and more rapid visual rehabilitation after cataract surgery has spawned various modalities for reducing incision size and decreasing energy utilization. Although ultrasonic phacoemulsification allows for relatively safe removal of cataractous lenses through astigmatically neutral small incisions, current technology still has its drawbacks. In ultrasonic phacoemulsification piezoelectric crystals convert electrical energy into mechanical energy which emulsifies the lens material by means of tip vibration. Ultrasonic tips create both heat and cavitational energy. A conventional phaco tip moves at ultrasonic frequencies of between 25 KHz and 62 KHz. The amount of heat generated is directly proportional to the operating frequency. In addition, cavitational effects from the high frequency ultrasonic waves generate even more heat. Because of the liberation of heat, phacoemulsification needles have required an irrigation sleeve for cooling. This irrigation sleeve carries heat away from the tip and necessitates an incision size larger than the tip alone would require. Nevertheless, standard ultrasonic phacoemulsification with an irrigation sleeve still carries with it the potential for thermal injury to the cornea in case of diminished flow. Flow and aspiration problems may be caused by compression of the irrigation sleeve at the incision site, kinking of the sleeve during manipulation of the handpiece, tip clogging by nuclear or viscoelastic material and inadequate flow rate or vacuum settings.1 Heating of the tip can create corneal incision burns.2 When incisional burns develop in clear corneal incisions, there may be a loss of self-sealability, corneal edema, and severe induced astigmatism.3 Cavitational energy results from pressure waves emanating from the tip in all directions. Although increased cavitational energy can allow for phacoemulsification of dense nuclei, it can also damage the corneal endothelium and produce irreversible corneal edema in compromised corneas with pre-existing endothelial dystrophies. Reduction in average phaco power and effective phaco time has been correlated with improved patient outcomes after cataract surgery.4 Low power phaco technology will have an important advantage in minimizing intraoperative damage to ocular structures and maximizing the level and rapidity of visual rehabilitation of the patient. The last decade has given rise to some of the most profound advances in both phacoemulsification technique and technology. Techniques for cataract removal have
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moved from those that use mainly ultrasound energy to emulsify nuclear material for aspiration to those that utilize greater levels of vacuum and small quantities of energy for lens disassembly and removal. Advances in phacoemulsification technology and fluidics have allowed for this ongoing change in technique by allowing for greater amounts of vacuum to be safely utilized, while power modulations that have allowed for more efficient utilization of ultrasound energy with greater safety for the delicate intraocular environment.5 Elimination of the frictional heat produced during ultrasound phacoemulsification and reduction of the power required for cataract extraction represent important steps towards the goal of atraumatic surgery. The sonic phacoemulsification system (Staar Wave, Staar Surgical) demonstrates another new approach to elimination of heat and the danger of thermal injury to the cornea. Modification of ultrasound energy through refinement of power modulation offers yet another route leading to elimination of heat and reduction of incision size (White Star, Allergan). The introduction of innovative oscillatory tip motion in coordination with power modulation permits further reduction of average phaco power and effective phaco time (NeoSonix, Alcon). Other new modalities under investigation, which promise low-energy, non-thermal cataract extraction, include vortex phacoemulsification (Avantix, Bausch and Lomb) and Aqualase (Alcon), a fluid-based cataract extraction system. Sonic Phacoemulsification Sonic technology offers an innovative means of removing cataractous material without the generation of heat or cavitational energy by means of sonic rather than ultrasonic technology. Its operating frequency is in the sonic rather than the ultrasonic range, between 40 Hz and 400 Hz. In contrast to ultrasonic tip motion, the sonic tip moves back and forth without changing its dimensional length. The tip of an ultrasonic handpiece can exceed 500 degrees Celsius, while the tip of the Wave handpiece in sonic mode barely generates any frictional heat. In addition, the Sonic tip does not generate cavitational effects and thus fragmentation, rather than emulsification or vaporization, material takes place. The same handpiece and tip can be utilized for both sonic and ultrasonic modes. The surgeon can alternate between the two modes using a toggle switch on the foot pedal when more or less energy is required. The modes can also be used simultaneously with varying percentages of both sonic and ultrasonic energy. We have found that we can use our same chopping cataract extraction technique in sonic mode as we utilized in ultrasonic mode with no discernable difference in efficiency. The Staar Wave also allows improved stability of the anterior chamber with coiled SuperVac tubing, which increases vacuum capability to upto 650 mmHg (Fig. 26.1). The key to chamber maintenance is a positive fluid balance between infusion flow and aspiration flow. When occlusion is broken, vacuum previously built in the aspiration line generates a high aspiration flow that can be higher than the infusion flow. This results in anterior chamber instability. The coiled SuperVac tubing limits surge flow resulting from occlusion breakage in a dynamic way. The continuous change in
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FIGURE 26.1
FIGURE 26.2 Postocclusion surge comparison chart
FIGURE 26.3 Postocclusion surge comparison chart direction of flow through the coiled tubing increases resistance through the tubing at high flow rates such as upon clearance of occlusion of the tip (Figs 26.2 and 26.3). This effect only takes place at high flow rates (greater than 50 cc/minute). The fluid resistance of the Super Vac tubing increases as
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FIGURE 26.4 NeoSonix™ handpiece a function of flow and unoccluded flow is not restricted (personal communication, Alex Urich, Staar Surgical).6 The Staar Wave combines important innovations in phacoemulsification technology, which satisfy the demands of non-thermal, low power cataract extraction. Neo Sonix Phacoemulsification NeoSonix technology (Alcon) represents a hybrid modality involving low frequency oscillatory movement that may be used alone or in combination with standard high frequency ultrasonic phacoemulsification (Fig. 26.4). Softer grades of nuclear sclerosis may be completely addressed with the low frequency modality, while denser grades will likely require the addition of ultrasound. In the NeoSonix mode, the phaco tip has a variable rotational oscillation upto two degrees, at 120 Hz. As with sonic phacoemulsification, this lower frequency does not produce significant thermal energy and so minimizes the risk of thermal injury. The Legacy may be programed to initiate NeoSonix at any desired level of ultrasound energy. Thus, the surgeon may utilize the low frequency mode to burrow into the nucleus for stabilization prior to chopping by setting the lower limit of NeoSonix to zero percent phaco power. This approach works best with a straight tip, which acts like an apple corer to impale the nucleus. Alternatively, NeoSonix may be initiated as an adjunct to ultrasound at the 10 or 20 percent power level. We have found NeoSonix most efficacious at 50 percent amplitude with a horizontal chopping technique in the AdvanTec burst mode at 50 percent power, 45 ml/minute linear flow and 450 mmHg vacuum. A 0.9 mm microflare straight ABS tip rapidly impales and holds nuclear material for chopping. During evacuation of nuclear segments the material flows easily into the tip, with very little tendency for chatter and scatter of nuclear fragments. With refinement of our parameters, we have found a 57 percent reduction in average phaco power, and an 87 percent reduction in effective phaco time, compared with the data we previously published with the Legacy system.7 NeoSonix has permitted further reduction in the application of ultrasonic energy to the eye when used in conjunction with ultrasound, and allowed nonthermal cataract extraction when used alone. It represents an important new modality in phacoemulsification technology.
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White Star Technology White Star (Sovereign, Allergan) represents a new power modulation within ultrasonic phacoemulsification that virtually eliminates the production of thermal energy. Analogous to the ultrapulse mode familiar to users of carbon dioxide lasers, White Star extrapolates pulse mode phacoemulsification to its logical limit. As the duration of the energy pulse is reduced it eventually becomes less than the thermal relaxation time of ocular tissue. Thus, it is theoretically impossible to produce a corneal wound burn. White Star technology sets the stage for bimanual cataract extraction with the Sovereign phacoemulsification machine. The absence of thermal energy obviates the need for an irrigation sleeve on the phaco tip, thus permitting reduction of incision size and allowing irrigation through a second instrument, such as an irrigating chopper, placed through the side-port. With an incision size for cataract extraction less than 1 mm, the challenge becomes production of intraocular lenses capable of insertion through such microphaco incisions. Olson8 and Packard9 have reported exciting results using a 21-gauge irrigating chopper and a 21-gauge bare phaco needle with the bimanual technique. Olson’s study of cadaver eyes has demonstrated that thermal injury does not occur even in the absence of aspiration with 100 percent power for three minutes. Packard reported an absence of wound burns with excellent surgical ease and efficiency via sub-2 mm incisions. The White Star technology demonstrates important advantages in improved safety and efficiency of cataract extraction, whether used in standard fashion or with the microphaco technique. Avantix Vortex phacoemulsification involves placement of a tiny rotary impeller inside the capsular bag through a 1 mm capsulorhexis. The impeller rotates at 60 kHz and causes expansion of the capsular bag with rotation of the nuclear complex, thus allowing extraction of the cataract from a nearly intact lens capsule. Expansion of the capsular bag minimizes risk of capsular rupture. The tiny circular capsulorhexis is constructed with a round diathermy instrument, thus reducing the technical demands of such a surgical feat. The irrigation/aspiration tube containing the rotary impeller is placed over the capsulorhexis while hydrodissection is performed with gentle irrigation. The tube is then inserted into the capsular bag through the 1 mm capsulorhexis prior to initiation of rotation, thus completely isolating the anterior chamber from the activity of cataract extraction. Nuclear material is effectively removed from the capsular bag with vortex action, after which cortex is actually stripped away and extracted. The advantages of leaving nearly the entire capsular bag in situ following cataract extraction will not be realized until an injectable artificial crystalline lens becomes available and the problem of capsular opacification is eliminated. Okahiro Nishi and others are currently investigating these devices, and may soon have a prototype available.10
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Aqualase Research at Alcon has led to the development of a fluid-based cataract extraction system. Another nonthermal modality, Aqualase employs pulses of balanced salt solution at 50 to 100 Hz to dissolve the cataract. This modality may potentially demonstrate advantages in terms of safety and prevention of secondary posterior capsular opacification. Still early in its development, Aqualase represents an innovative and potentially advantageous modality for cataract extraction. Conclusion Since the time of Charles Kelman’s inspiration in the dentist’s chair (while having his teeth ultrasonically cleaned), incremental advances in phacoemulsification technology have produced ever-increasing benefits for patients with cataract. The modern procedure simply was not possible even a few years ago, and until recently prolonged hospital stays were common after cataract surgery. The competitive business environment and the wellspring of human ingenuity continue to demonstrate synergistic activity in the improvement of surgical technique and technology. Future advances in cataract surgery will continue to benefit our patients as we develop new phacoemulsification technology. References 1. Sugar A, Schertzer RIO: Clinical course of phacoemulsification wound burns. J Cataract Refract Surg 25:688–92, 1999. 2. Majid MA, Sharma MK, Harding SP: Corneoscleral burn during phacoemulsification surgery. J Cataract Refract Surg 24:1413–15, 1998. 3. Sugar A, Schertzer RM: Clinical course of phacoemulsification wound burns. J Cataract Refract Surg 25:688–92, 1999. 4. Fine IH, Packer M, Hoffman RS: Use of power modulations in phacoemulsification. J Cataract Refract Surg 27: 188–97, 2001. 5. Fine IH: The choo choo chop and flip phacoemulsification technique. Operative Techniques in Cataract and Refractive Surgery 1:61–65, 1998. 6. Fine IH, Hoffman RS, Packer M: The Staar Wave in Kohnen T (Ed). Modern Cataract Surgery Update. Dev Ophthalmol. Basel, Karger, 2002, vol 34 (in press). 7. Fine IH, Packer M, Hoffman RS: Use of power modulations in phacoemulsification. J Cataract Refract Surg 27: 188–97, 2001. 8. Olson RJ, Soscia WL: Safety and efficacy of bimanual phaco chop through two stab incisions with the Sovereign. XIII Congress of the European Society of Ophthalmology, Istanbul, 3–7, 2001. 9. Packard R: Evaluation of a new approach to phacoemulsification: bimanual phaco with the Sovereign system rapid pulse software. XIII Congress of the European Society of Ophthalmology, Istanbul, 3–7, 2001. 10. Nishi O, Nishi K: Accommodation amplitude after lens refilling with injectable silicone by sealing the capsule with a plug in primates. Arch Ophthalmol 116(10):1358–61, 1998.
Section V No Anesthesia Cataract Surgery 27. No Anesthesia Cataract Surgery with the Karate Chop Technique 28. No Anesthesia Cataract Surgery 29. No Anesthesia Cataract Surgery: Comparision Between Topical, Intracameral and No Anesthesia 30. Ocular Anesthesia for Small Incision Cataract Surgery
27 No Anesthesia Cataract Surgery with the Karate Chop Technique Athiya Agarwal, Sunita Agarwal Amar Agarwal Introduction On June 13th, 1998 at Ahmedabad, India the first no anesthesia cataract surgery was done by the authors (Amar Agarwal) at the Phako and Refractive Surgery conference. This was performed as a live surgery in front of 250 delegates. This has opened up various new concepts in cataract surgery.1–4 In this surgery the technique of karate chop was used. For high refractive errors, clear lens extraction with phacoemulsification is a very good alternative. In such cases, if necessary one can implant an IOL. This technique is very useful in hypermetropes, as LASIK does not give excellent results in such cases. The most commonly done refractive surgery in the world is not PRK or LASIK it is cataract surgery. This is why this chapter will discuss phacoemulsification techniques for removal of cataract as well as clear lens extraction. Nucleus Removal Techniques Since the introduction of phacoemulsification as an alternative to standard cataract extraction technique, surgeons throughout the world have been attempting to make this new procedure safer and easier to perform while assuring good visual outcome and patient recovery. The fundamental goal of Phaco is to remove the cataract with minimal disturbance to the eye using least number of surgical manipulations. Each maneuver should be performed with minimal force and maximal efficiency should be obtained. The latest generation Phaco procedures began with Dr. Howard Gimbel’s “divide and conquer” nuclear fracture technique in which he simply split apart the nuclear rim. Since then we have evolved through the various techniques namely four quadrant cracking, chip and flip, spring surgery, stop and chop and phaco chop. Clear lens removal by phacoemulsification is a very good alternative to manage refractive errors. In these cases, as the nucleus is soft one can use only Phacoaspiration to remove the nuclei, rather than use ultrasound power.
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Karate Chop Unlike the peripheral chopping of Nagahara or other stop and chop techniques we have developed a safer technique called “Central Anterior chopping” or “karate chop”. In this method the phaco tip is embedded by a single burst of power in the central safe zone and after lifting the nucleus a little bit (to lessen the pressure on the posterior capsule) the chopper is used to chop the nucleus. In soft nuclei, it is very difficult to chop the nucleus. In most cases, one can take it out in toto. But if the patient is about 40 years of age then one might have to chop the nucleus. In such cases we embed the phaco probe in the nucleus and then with the left hand cut the nucleus as if we are cutting a piece of cake. This movement should be done three times in the same place. This will chop the nucleus. Soft Cataracts In soft cataracts, the technique is a bit different. We embed the phaco tip and then cut the nucleus as if we are cutting a piece of cake. This should be done 2–3 times in the same area so that the cataract gets cut. It is very tough to chop a soft cataract, so this technique helps in splitting the cataract. Agarwal Chopper We have devised our own chopper. The other choppers, which cut from the periphery, are blunt choppers. Our chopper is a sharp chopper. This is a 28 gauge chopper made by Gueder (Germany). It has a sharp cutting edge. It also has a sharp point. The advantage of such a chopper is that you can chop in the center and need not go to the periphery. In this method by going directly into the center of the nucleus without any sculpting ultrasound energy required is reduced. The chopper always remains within the rhexis margin and never goes underneath the anterior capsule. Hence, it is easy to work with even small pupils or glaucomatous eyes. Since we don’t have to widen the pupil, there is little likelihood of tearing the sphincter and allowing prostaglandins to leak out and cause inflammation or cystoid macular edema. In this technique we can easily go into even hard nuclei on the first attempt. Our Karate Chop Technique Incision Ours is a modification of the Nagahara chop. The important feature is that we don’t chop the periphery. A temporal clear corneal section is made. If the astigmatism is plus at 90 degrees then the incision is made superiorly.
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First of all, a needle with viscoelastic is injected inside the eye in the area where the second site is made (Fig. 27.1). This will distend the eye so that when you make a clear corneal incision, the eye will be tense and one can create a good valve. Now use a straight rod to stabilize the eye with the left hand. With the right hand make the clear corneal incision (Fig. 27.2). When we started making the temporal incisions, we positioned ourselves temporally. The problem by this method is that, every time the microscope has to be turned which in turn would affect the cables connected to the video camera. Further the theater staff would get disturbed between right eye and left eye. To solve this problem, we then decided on a different strategy. We have operating trolleys on wheels. The patient is wheeled inside the operation theater and for the right eye the trolley is placed slightly obliquely so that the surgeon does not change his or her position. The surgeon stays at the 12 o’clock position. For the left eye the trolley with the patient is rotated horizontally so that the temporal portion of the left eye comes at 12 o’clock. This way the patient is moved and not the surgeon.
FIGURE 27.1 Eye with cataract. Needle with viscoelastic entering the eye to inject the viscoelastic. This is the most important step in no anesthesia cataract/clear lens surgery. This gives an entry into the eye through which a straight rod can be passed to stabilize the eye. Note no forceps holds the eye
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FIGURE 27.2 Clear corneal incision. Note the straight road inside the eye in the left hand. The right hand is performing the clear corneal incision. This is a temporal incision and the surgeon is sitting temporally
FIGURE 27.3 Rhexis being done with a needle
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Rhexis Capsulorhexis is then performed through the same incision (Fig. 27.3). While performing the rhexis it is important to note that the rhexis is started from the center and the needle moved to the right and then downward. This is important because today concepts have changed of temporal and nasal. It is better to remember it as superior, inferior, right or left. If we would start the rhexis from the center and move it to the left then the weakest point of the rhexis is generally where you finish it. In other words, the point where you tend to lose the rhexis is near its completion. If you have done the rhexis from the center and moved to the left, then you might have an incomplete rhexis on the left hand side either inferiorly or superiorly. Now, the phaco probe is always moved down and to the left. So every stroke of your hand can extend the rhexis posteriorly creating a posterior capsular rupture. Now, if we perform the rhexis from the center and move to the right and then push the flap inferiorly then if we have an incomplete rhexis near the end of the rhexis it will be superiorly and to the right. Any incomplete rhexis can extend and create a posterior capsular tear. But in this case, the chances of survival are better. This is because we are moving the phaco probe down and to the left, but the rhexis is incomplete up and to the right. If you are a left handed person start the rhexis from the center and move to the left and then down. Hydrodissection Hydrodissection is then performed (Fig. 27.4). We watch for the fluid wave to see that hydrodissection is complete. We do not perform hydrodilenation or test for rotation of the nucleus. Viscoelastic is then introduced before inserting the phaco probe. Karate Chop—Two Halves We then insert the Phaco probe through the incision slightly superior to the center of the nucleus (Fig. 27.5). At that point apply ultrasound and see that the phaco tip gets embedded in the nucleus (Fig. 27.6). The direction of the phaco probe should be obliquely downwards toward the vitreous and not horizontally towards the iris. Then only the nucleus will get embedded. The settings at this stage are 70 percent phaco power, 24 ml/minute flow rate and 101 mmHg suction. By the time the phaco tip gets embedded in the nucleus the tip would have reached the middle of the nucleus. We do not turn the bevel of the phaco tip downwards when we do this step, as the embedding is better the other way. We prefer a 15-degree tip but any tip can be used.
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FIGURE 27.4 Hydrodissection
FIGURE 27.5 Phaco probe placed at the superior end of the rhexis
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FIGURE 27.6 Phaco probe embedded in the nucleus. We started from the superior end of the rhexis and note it has got embedded in the middle of the nucleus. If we had started in the middle then we would have embedded only inferiorly that is at the edge of the rhexis and chopping would be difficult Now stop phaco ultrasound and bring your foot to position 2 so that only suction is being used. Now lift the nucleus. When we say lift it does not mean lift a lot but just a little so that when we apply pressure on the nucleus with the chopper the direction of the pressure is downwards. If the capsule is a bit thin like in hypermature cataracts you might rupture the posterior capsule and create a nucleus drop. So when we lift the nucleus the pressure on the posterior capsule is lessened. Now, with the chopper cut the nucleus with a straight downward motion (Fig. 27.7) and then move the chopper to the left when you reach the center of the nucleus. In other words, your left hand moves the chopper like a laterally reversed L. Remember do not go to the periphery for chopping but do it at the center Once you have created a crack, split the nucleus till the center. Then rotate the nucleus 180 degrees
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FIGURE 27.7 Left hand chops the nucleus and splits like a laterally reversed L, that is downwards and to the left and crack again so that you get two halves of the nucleus. In brown cataracts, the nucleus will crack but sometimes in the center the nucleus will still be attached. You have to split the nucleus totally in two halves and you should see the posterior capsule throughout. Karate Chop—Further Chopping Now that you have two halves, you have a shelf to embed the probe. So, now place the probe with ultrasound into one-half of the nucleus (Fig. 27.8). You can pass the direction of the probe horizontally as now you have a shelf. Embed the probe, then pull it a little bit. This step is important so that you get the extra bit of space for chopping. This will prevent you from chopping the rhexis margin. Apply the force of the chopper downwards. Then move the chopper to the left so that the nucleus gets split. Again, you should see posterior capsule throughout so that you know the nucleus is totally split. Then release the probe, as the probe will still be embedded into the nucleus. Like this create three quadrants in one-half of the nucleus. Then make another
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FIGURE 27.8 Phaco probe embedded in one-half of the nucleus. Go horizontally and not vertically as you have now a shelf of nucleus to Embed. Chop and then split the nucleus three halves with the second-half of the nucleus. Thus, you now have 6 quadrants or pieshaped fragments. The settings at this stage are 50 percent phaco power, 24 ml/minute flow rate and 101 mmHg suction. Remember 5 words—Embed, Pull, Chop, Split and Release. Pulse Phaco Once all the pieces have been chopped, take out each piece one-by-one and in pulse phaco mode aspirate the pieces at the level of the iris. Do not work in the bag unless the cornea is preoperatively bad or the patient is very elderly. The setting at this stage can be phaco power 50–30 percent, flow rate 24 ml and suction 101 mmHg. Remember—It is better to have striate keratitis than posterior capsular rupture. Cortical Washing and Foldable IOL Implantation The next step is to do cortical washing (Fig. 27.9). Always try to remove the subincisional cortex first, as that is the most difficult. In Figure 27.10 note the cortical aspiration complete. Note also the rhexis margins. Note also that everytime the left hand has the straight rod controlling the movements of the eye. If necessary use a bimanual irrigation aspiration technique. Then inject viscoelastic and implant the foldable IOL. We use the plate haptic foldable IOL (Fig. 27.11) with large fenestration’s generally as we find them superior. Take out the viscoelastic with the irrigation aspiration probe (Fig. 27.12).
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Stromal Hydration At the end of the procedure, inject the BSS inside the lips of the clear corneal incision (Fig. 27.13). This will create a stromal hydration at the wound. This will create a whiteness, which will disappear after 4–5 hours. The advantage of this is that the wound gets sealed better. No PAD, S/C Injections No subconjunctival injections or pad are put in the eye. The patient walks out of the theater and goes home. The patient is seen the next day and after a month glasses prescribed.
FIGURE 27.9 Cortical aspiration completed. Note the straight rod in the left hand which helps control the movements of the eye
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FIGURE 27.10 Eye distended with viscoelastic. Note the rhexis margins No Anesthesia Clear Lens Extraction In cases of clear lens removal’s, the same technique is followed. No anesthesia is used. If one is not good
FIGURE 27.11 Plate haptic foldable IOL with large fenestrations being implanted
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FIGURE 27.12 Foldable IOL in capsular bag. Viscoelastic removed with the irrigation aspiration probe then it is advisable to use a parabulbar anesthesia (pin-point anesthesia) rather than a peribulbar
FIGURE 27.13 Stromal hydration done and the case completed block. The reason is that in such cases one could perforate the globe with the needle. Once the patient is draped, the syringe with viscoelastic is taken and the viscoelastic
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injected inside the eye using a 26 gauge needle. Then the temporal clear corneal incision is made. If the astigmatism is + at 90 degrees then a superior incision is made. The rhexis is then done using a needle. This is followed by hydrodissection. The phaco probe is passed into the eye and using phaco aspiration the soft nucleus removed. One does not have to use ultrasound, as the nucleus in such cases is very soft. This is followed by cortical aspiration. Depending on the biometry a foldable IOL is implanted in the eye. If the patient has high myopia and an IOL is not required then an IOL is not implanted. The authors have realized that chances of retinal detachment do not increase just because the eye is aphakic. The authors prefer to keep one eye emmetropic and the other slightly myopic to about 1 to 1.5 D so that the patient can see without glasses for distance and near with both eyes open. Compared to LASIK this is a very good alternative, as LASIK does not help much in hyperopes and in high myopes (powers above −15 D). Phacodynamics of the Phaco Chop Technique We should take full advantage of the phaco machines capability thereby decreasing physical manipulation of the intraocular tissues. In this phaco chop technique, we use a vacuum of 101 mm Hg, about 70 percent phaco power and the flow rate is 24 ml/minute. In this phaco chop technique, the most important is the vacuum, which needs to be sufficient to stabilize the nucleus while the chopper is splitting it. If the action of the chopper is dislodging the vacuum seal on the phaco tip, it is said that the vacuum can be raised from 120 to 200 mm Hg. After embedding the phaco needle with mild linear ultrasound power in foot switch position 3, it is important to raise the pedal back to foot switch position 2, while the vacuum builds up. This is because the purpose of ultrasound was to completely embed the aspiration port into the nucleus to obtain good vacuum seal. In foot switch 3, there is risk of adverse heat build up because the occluded tip prohibits any flow of cooling. Also, when manipulating the nucleus by pulling with the embedded tip, the vacuum seal is likely to be compromised by the vibrating needle if it is in foot switch position 3. Advantages The phacoemulsification procedure has been proved to be reasonably safe to the endothelium. As compared to the “divide and conquer” technique, this phaco karate chop technique eliminates the need for trenching thereby producing significant reduction in phaco time and power consumed which in turn decreases endothelial cell damage. Even with increased density of cataract, there is a less pronounced increase in phaco time. Here we utilize the “Chop” to divide the nucleus by mechanical energy. It is safe and effective in nuclear handling during phacoemulsification. In conventional chop, the disadvantage is that the chopper is placed underneath the anterior capsule and then pulled towards the center. This can potentially damage the capsule and the zonules. In phaco chop, we don’t go under the rhexis, the vertical element of the chopper remains within the rhexis margin and is visible at all stages. Hence very
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easy to work with even in small pupils or glaucomatous eyes. The stress is taken by the impacted phaco tip and the chopper rather than transmitting it to the fragile capsule. By going directly into the center of the nucleus with the phaco tip and not doing any sculpting, we don’t need as much ultrasound energy as is usually required. It is safe and easy to perform and we don’t have to pass as much balanced salt solution (irrigating fluid) through the eye. Disadvantages This technique demands continuous use of the left hand and hence requires practise to master it. Topical Anesthesia Cataract/ Clear Lens Surgery All cases done by the authors were previously done under topical anesthesia. Four percent xylocaine drops was instilled in the eye about 3 time’s 10–15 minutes before surgery. No intracameral anesthesia was used. It is not advisable to use xylocaine drops while operating. This can damage the epithelium and create more trouble in visualization. No stitches and no pad are applied. This is called the—No injection, no stitch, no pad cataract surgery technique. Now the authors have shifted all their cases 100 percent to the no anesthesia technique. No Anesthesia Cataract/ Clear Lens Surgery We had been wondering whether any topical anesthesia is required or not. So we then operated patients without any anesthesia. In these patients no xylocaine drops were instilled. The patients did not have any pain. It is paradoxical because we have been taught from the beginning that we should apply xylocaine. This is possible because we do not touch the conjunctiva or sclera. We never use any one-tooth forceps to stabilize the eye. Instead what we use is a straight rod which is passed inside the eye to stabilize it when we are performing rhexis etc. The first step is very important. In this we first enter the eye with a needle having viscoelastic and inject the viscoelastic inside the eye. This is done in the area of the side port. Now, we have an opening in the eye through which a straight rod can be passed to stabilize the eye. The anterior chamber should be well maintained and the amount of ultrasound power used very less. If you tend to use the techniques like trenching then the ultrasound power generated is high, which in turn generates heat. This causes pain to the patient. If you follow these rules one can perform o anesthesia cataractor clear lens extraction surgery. It is not necessary to do this, as there is no harm in instilling some drops of xylocaine in the eye. The point that there is always a discussion which anesthetic drop to use. It does not matter. The technique, which you perform, should not produce pain to the patient.
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Conclusion As in any other field, progress is inevitable in ophthalmology more so in refractive surgery. We have started to look on refractive surgery as a craft and should constantly try to improve our craft and become better every day. By this, we will be able to provide good vision to more people than any one dared dream a few decades ago. It also goes without saying that we are and will be forever grateful to all our patients because without their faith, we would never have had the courage to proceed. Keeping this in mind, we hope and wish that the effectiveness and the advantages of this “No Anesthesia Clear Lens Extraction Technique” be realized and practiced thereby making the technique of phacoemulsification safer and easier providing good visual outcome and patient recovery. References 1. Agarwal S, Agarwal A, Mahipal S Sachdev, et al: Phacoemulsification, Laser Cataract Surgery and Foldable IOL’s; (2nd ed); Jaypee Brothers; Delhi, India, 2000. 2. Agarwal A, Agarwal S, Agarwal A: No anesthesia cataract surgery with the karate chop technique; In Amar Agarwal’s Presbyopia: A Surgical Textbook; Slack Incoporated USA; 177– 85, 2002. 3. Agarwal A, Agarwal S, Agarwal A: No anesthesia Cataract and clear lens extraction with Karate chop; In Agarwal’s Phako, Phakonit and laser Phako: A quest for the best; Highlights of Ophthalmology Panama; 113–20, 2002. 4. Agarwal A, Agarwal S, Agarwal A: No anesthesia Cataract and clear lens extraction with Karate chop; In Boyd-Agarwal’s Lasik and beyond Lasik; Highlights of Ophthalmology Panama; 451– 62, 2001.
28 No Anesthesia Cataract Surgery Tobias Neuhann Introduction As we all know, the surface of the human eye is highly sensitive. A quick approach, a dust particle, a gust of air to dry out the ocular surface—the eyelids will close immediately in a protective reflex. To operate an eye without any anesthesia? The mere idea seems to be absurd. However, disregarding all that we know, it is possible. On June 13, 1998, Amar Agarwal successfully performed the first no anesthesia cataract operation during the Phaco and Refractive Surgery conference in Ahmedabad, India, in front of an audience of 250 persons, applying the karate chop technique.1,2 On the occassion of the 1999 ASCRS convention in Seattle, live surgery was performed in India by Sunita Agarwal, Amar Agarwal and Mahipal S Sachdev and communicated via satellite to the meeting in Seattle. All these operations were performed under NO ANESTHESIA. The cataracts were removed through a sub 1 mm incision by Sunita Agarwal and Amar Agarwal using a technique called PHAKONIT. Sunita Agarwal demonstrated laser phacoemulsification, while Mahipal S Sachdev performed high vacuum phacoemulsification.3 In the 1999 Indian Intraocular Implant and Refractive Surgery conference, I had the opportunity to personally attend live no anesthesia cataract surgery by Amar Agarwal. He kindly offered me the to perform a live no anesthesia cataract operation, myself. It was a fascinating experience, and even during the operation itself, it was hard to believe that it was really possible. Back in Munich, I successfully operated two patients under the age of 40 using this astounding new method—both upon their own request. Fourteen other cases followed. However, the specific preconditions of this particular group of patients will be discussed lateron in this chapter. Incision Without any anesthesia, naturally the incision is much more critical than in routine cataract surgery under topical (retrobulbar, parabulbar or surface anesthesia) or even general anesthesia.4 The entire procedure is only possible if neither the sclera nor the conjunctiva are touched. In addition, no one-toothed forceps is used to stabilize the eye. Instead, a straight rod is inserted into the eye to guarantee a stable position during the operation.
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The first step is essential. A side port is created with a diamond and viscoelastic is injected. This incision is then used to insert a straight rod to stabilize the eye. This is followed by a clear corneal incision.1,2 Capsulorhexis The capsule is opened using capsulorhexis, like in any routine cataract surgery. The capsulorhexis can be performed alternatively using the needle or the forceps technique. The needle technique first requires an initial puncture of the anterior capsule within the central area to be removed, which is then extended in a curve-shaped manner to the targeted eccentric circle to be described. The circular tear is started by either pushing or pulling the central anterior capsule in either direction, while the flap to be created is gently lifted. The next step is to turn over the flap and apply the vectorial forces in tearing with the needle in such a way that a more or less concentrical opening originates. Once the full circle is almost completed the end will automatically join the beginning of the curve outside in (Fig. 28.1). It is also possible to place the first puncture directly within the planned curvature and start the rhexis with a curved enlargement of this tiny hole. With this approach, the tear is brought around on both sides, until finally the ends join together.5 Advantages of the needle technique are that it is economical, since it can be performed with
FIGURE 28.1 The ideal capsulorhexis application of BSS as well as viscoelastics and the cost of the needles is neglectable. The following factors are essential for the success of the needle capsulorhexis: I highly recommend the use of a 23 gauge needle, because the lumen of this type of needle is just sufficient to produce a pressure exchange between anterior chamber and BSS irrigating bottle and the metal of such a cannula supplies just enough rigidity to provide the necessary resistance for difficult manipulations. A higher, that is positive pressure in the anterior chamber compared to the intracapsular pressure is mandatory. This becomes especially noticeable with intumescent lenses, where the lens protein is hydrated resulting
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in a volume increase inside the capsular bag, so that also the endocapsular pressure is considerably increased. Only if the anterior chamber pressure is greater than or equal to that inside the capsular bag can a successful capsulorhexis be performed. The pressure in the anterior chamber can be adjusted by varying the height of the infusion bottle. In addition, the needle tip should be as sharp as possible, since a blunt needle may create stellate burst (Fig. 28.2).5 The forceps technique is easier. For this reason it is also the most frequently applied capsulorhexis technique, which, however, can only be performed after viscoelastic instillation. The principle of the forceps capsulorhexis exactly corresponds to the principle of the needle technique. In addition to the
FIGURE 28.2 Stellate burst known Utrata forceps there are mini forceps which are similar in construction to the forceps developed for the posterior segment of the eye. The advantage of these newly designed forceps is that they can be inserted into the anterior chamber via a paracentesis, so that the incision is not exposed to needless strain.5 To point out the difference between the needle and the forceps technique, the following example might be appropriate: To turn over a page of a book you can take the sheet between two fingers and turn it from one side to the other (this is what you do with the forceps), or you take a moistened finger, press the page a bit down and then turn it over (that is what you do with the needle; the counterhold is the cortex). With this in mind the consequences appear quite clear cut. I will always use a needle technique, the initial puncture peripheral or central, for the great majority of my cases. The forceps I will use in situations where the needle—so to say—lacks the other branch. This is mainly the case when liquified cortex is apparent or secondary enlargement of the capsulorhexis diameter is necessary.5
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Phacoemulsification Techniques A variety of phacoemulsification techniques has been developed with the aim to disintegrate the nucleus in the safest and most efficient way. When Howard Gimbel introduced his divide and conquer technique, it was adopted enthusiastically by ophthalmologists throughout the world.6 For many years after, divide and conquer remained the outstanding technique for all nuclei hard enough not to be simply aspirated, until Nagahara presented his new technique, phaco chop, the big brother of divide and conquer. Other than in divide and conquer, the nucleus is no longer divided with the phaco tip, but with a second instrument, the “chopper”, so that hardly any manipulations with the tip itself were necessary any longer, thus reducing the risk to damage the sensitive intraocular structures with the tip to a minimum.7 The phaco chop technique has remained one of the most efficient methods in phacoemulsification until today. The advantages are obvious. The lens can be divided up mechanically into 4, 6 and 8 or more pieces. In this process, the originating forces counteract, since the force exerted by the chopper is directed against the phaco tip. The result is that all force vectors go centrally, so that there is no hazard for the lens capsule or the corneal endothelium. The phaco chop technique is especially suitable for mature cataracts or cataracta nigra, where mostly weak zonulas are found. A beneficial side effect for the surgeon is the ease of work, because the nucleus can always be rotated into the most favorable position. However, an important aspect of phaco chop is that it is only a technique for experienced surgeons, whereas beginners should start with divide and conquer to develop a feeling for the consistency of the nucleus to stay on the safe side. For the first chopping attempt, a medium nuclear sclerosis should be selected. To understand the mechanism of phaco chop, you have to consider the anatomic structure of the nucleus, where the crystalline lens fiber runs from one side of the equator towards the opposite side through the center of the nucleus. As a logical consequence, the natural cracking direction follows the lens fiber. As is usual in modern cataract surgery, the capsule is opened with the CCC and hydrodissection is carried out. Then the epinucleus is aspirated inside the CCC with weak phaco energy. For your first chop, you have to catch the lens with your phaco tip at the 12 hours position, advance the phaco tip until you have firm hold of the nucleus and then insert the chopper into the space between the equator and the capsule at the 6 hours position. As the chopper is gradually brought closer to the tip, the nucleus will crack into two halves. Then the nucleus is rotated 90° and the inferior heminucleus is cracked into quadrants applying the same principle. If the nucleus is relatively soft, the quarters can be aspirated and emulsified with the phaco tip. In this process, the tip opening should remain in the center of the lens capsule not to increase the hazard of damaging either the posterior capsule or the corneal endothelium unnecessarily. When aspiration and emulsification of the inferior heminucleus are completed, the superior heminucleus is rotated 180° and disintegrated accordingly. In the case of harder nuclei, a subdivision of the nucleus into 8 or more pieces may be required to exclude that residual fragments escape into the anterior chamber and damage the corneal endothelium with their sharp edges.
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Experience in phacoemulsification shows that it is beneficial to reduce the overall phaco time and power to the necessary minimum. An additional advantage of the phaco chop technique is that here the nuclear matter is first aspirated and then emulsified. In this way, the entire phaco energy is used for emulsification of the nucleus, the aspiration volume concentrates on the nucleus, and less phaco energy and time are required, thus reducing strain for the incision as well as for the corneal endothelium. The initial phaco chop technique has been modified several times by different ophthalmologists including Nagahara, its inventor. He uses his karate chop technique,7,8 which was also applied in the first live no anesthesia cataract surgery by Amar Agarwal,1,2 for cases with poor mydriasis to be able to perform the whole phacoemulsification procedure within the range of the pupil or the CCC. Other than in the initial phaco chop technique, karate phaco chop goes from the anterior pole to the posterior pole of the crystalline lens. For hard nuclei with a thin epinucleus and the typical dual structure of soft periphery and hard core Nagahara suggests the crater phaco chop technique. To be able to grab hold of the hard core of the nucleus with the phaco tip, first a crater is excavated providing enough space for easy insertion of the tip. My personal method of choice is the quick-chop technique when performing no anesthesia cataract surgery because of the above mentioned advantages, such as stressand pain-free intraocular manipulations. Intraocular Lens Implantation Using no anesthesia cataract surgery, I recommend an implantation of a soft, foldable silicone or acrylic IOL to be able to make use of the advantages of small incision surgery, especially under the aspect that a clear corneal incision is inevitable, because the sclera as well as the conjunctiva must not even be touched. For both intraocular lens families, acrylic as well as silicone, a large variety of IOL models and types from the different manufacturers is available in the market. In this way it is easy to find a lens to meet the specific requirements of the individual patient. As one of the newest developments, even a foldable toric IOL can be implanted using a ring-haptic-fixation with a specific indented capsular tension ring (*Acri.Clip) (Figs 28.3 and 28.4).9 Foldable IOLs can be implanted with forceps or with an injector, which is mostly the easier alternative. No Anesthesia Clear Lens Extraction At the Agarwal eye hospitals in Chennai and
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FIGURE 28.3 Ring-haptic fixation; computer animation
FIGURE 28.4 Ring-haptic fixation; clinical case Bangalore, India, clear lens extraction—also without anesthesia—is applied for the surgical treatment of high refractive errors as an alternative to PRK or LASIK, especially in hyperopic or high myopic patients (more than −15 D). Depending on the specific case, an IOL is then implanted or, in cases of extremely high myopia, the patient is left aphakic. The operation follows the same procedure as no anesthesia cataract surgery. For less experienced surgeons, a parabulbar anesthesia is recommended instead of a peribulbar block to avoid the hazard of globe penetration with the needle.1,2 Specific Precautions in No Anesthesia Cataract Surgery Experience shows that it is beneficial to cover the cornea with HPMC 2.4 percent to reduce the surface sensitivity of the eye. In addition, it is essential to maintain the moisture of the cornea throughout the operation.
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It is important, not to inform the patient prior to the operation to exclude the danger of increased sensitivity caused by the patient’s fear of pain. In addition, it is very important to exclude any sharp or pointed instrument, such as Colibri forceps. However, the use of diamond knives is appropriate. Furthermore, utmost care with the eyelid is required, because it is experienced as highly disturbing by the patients. During phacoemulsification, it is very important to only apply low amounts of ultrasound power to avoid the origination of heat, which would be painful for the patient. In addition, the anterior chamber should be well maintained throughout the procedure.1 Recent Cases Recently, I operated two female patients with a history of allergic shock. In both cases, a severe allergic reaction to anesthetics administered during treatment by their dentist had occurred. In these patients, there was a high probability of allergy against the CAINgroup, thus forming an indication for no anesthesia cataract surgery. One of the patients had been looking desperately for a possibility to have cataract surgery performed despite her allergy. Both patients were highly motivated, and surgery could be performed without any problems. As a new step in the procedure, I applied very cold BSS solution in the area of the limbus immediately prior to the incision to decrease the ocular sensitivity. Discussion No anesthesia cataract surgery is a surprising new development in our highly refined techniques in ophthalmic surgery that have been achieved to date. Without any doubt, the mere existence of this new option is very exciting and also might be very helpful in cases with specific indications. However, in my opinion, the different preconditions of the patient goods in different areas of the world need to be briefly discussed. As we all know, a series of amazing phenomena exists in India. Which other country on earth has been able to produce individuals who are able to stick knives and sabres through their bodies and faces and pull them out again without a drop of blood dripping down and without any wound remaining? On the other hand, documentations of almost unbelievable practices also exist from other areas in the world, like in parts of Africa, where trepanation is performed without any anesthesia, too, and the patients maintain not to feel too much pain when their skulls are opened without any anesthetic relief. On this basis, the no anesthesia approach should be further investigated in terms of its introduction in suitable countries, also taking into account the poverty in large parts of the world, where no anesthesia cataract surgery might be a step into the right direction to improve health care for the population by lovering the costs of treatment. Generally, in the Western World this method is only suitable for especially old patients, where the surface sensitivity of the eye is already considerably reduced or for highly motivated patients. In my own practice, I operated a total of 18 patients without anesthesia to date. All of these patients had a particular mental attitude in common, which
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enabled them to undergo this kind of procedure, and which considerably differs from that the majority of the population in any of our industrialized countries. All of these patients asked me to perform no anesthesia cataract surgery, while the larger majority especially of the younger patients rather tend to consider the advantages of general or topical anesthesia, instead, and would not even dream of having an operation performed without any anesthesia. In this way, the special motivation of my 18 cases formed the only possible basis for this new approach. No anesthesia cataract surgery is a highly fascinating new alternative. It is certainly not designed for routine practice. However, it remains an excellent method for patients with specific indications, where our common forms of anesthesia are not possible, for example in hemophilics. References 1. Agarwal A, Agarwal S, Agarwal A: No anesthesia cataract/clear lens extraction. Refractive Surgery New Delhi: Jaypee Brothers Medical Publishers (P) Ltd, 487–98, 2000. 2. Agarwal A, Agarwal S, Agarwal A: No Anesthesia Cataract Surgery. Phacoemulsification, Laser Cataract Surgery and Foldable IOLs New Delhi: Jaypee Brothers Medical Publishers (P) Ltd, 139–43, 1998. 3. Azim Siraj A: Dr Agarwal’s Homepage Volume II, No 2: Issues Conference and Seminars: 1999. 4. Lang GK: Operative Therapy. Augenheilkunde Georg Thieme Verlag, Stuttgart: 190–93, 1998. 5. Neuhann T: Capsulorhexis. Phacoemulsification, Laser Cataract Surgery and Foldable IOLs New Delhi: Jaypee Brothers Medical Publishers (P) Ltd, 81–88,1998. 6. Gimbel HV, Anderson PE: Divide and Conquer Nucleofractis Techniques. Phacoemulsification, Laser Cataract Surgery and Foldable IOLs New Delhi: Jaypee Brothers Medical Publishers (P) Ltd, 97–109, 1998. 7. Nagahara KB: Phaco Chop—Development and Recent Advances. Atlas of Cataract Surgery London: Martin Dunitz Ltd, 98–109, 1999. 8. Agarwal A, Agarwal S, Agarwal A: Karate Chop. Phacoemulsification, Laser Cataract Surgery and Foldable IOLs New Delhi: Jaypee Brothers Medical Publishers (P) Ltd, 144–54, 1998. 9. Neuhann T: New Foldable IOLs. Atlas of Cataract Surgery London: Martin Dunitz Ltd, 169–80, 1999.
29 No Anesthesia Cataract Surgery: Comparison Between Topical, Intracameral and No Anesthesia Suresh K Pandey Liliana Werner, Amar Agarwal Introduction Ophthalmic surgeons have witnessed a significant evolution in surgical techniques for cataract extraction in the 20th century.1 The most remarkable advance is, of course, the considerable decrease in the size of the wound incision. Small-incision cataract surgery using phacoemulsification through clear corneal self-sealing incisions avoids cauterization, suturing and intraocular pressure (IOP) fluctuations. Moreover, this is faster, more controlled and less traumatic when compared with conventional largeincision extracapsular cataract extraction (ECCE). With the advent of the “phaconit” technique, today it is possible to remove the cataract through a 0.9 mm incision.2 The evolution in surgical techniques for cataract extraction is summarized in Table 29.1. Anesthetic techniques for cataract surgery have also advanced significantly (Table 29.2).3,4 General anesthesia was preferred in past years, followed by various techniques of injectable anesthesia including retrobulbar, peribulbar, sub-Tenon, and subconjunctival anesthesia. Due to marked improvements in surgical techniques, it is no longer essential to ensure complete akinesia of the eye and as a consequence, the technique of topical anesthesia has been popularized as “phaco anesthesia”.5–22 This includes eyedrops application, sponge anesthesia, eyedrops plus intracameral injection, and most recently gel application.5,7,11–15,18–21,23,24 Topical anesthesia is the preferred technique for cataract surgeons in the USA (37%; range 22–63%) according to a survey conducted by David Learning in 1998.25 It revealed that as high as 76 percent respondents using topical anesthesia preferred eyedrops in association with
TABLE 29.1 Evolution of techniques for cataract surgery Technique
Year Author/Surgeon
Couching ECCE* (inferior incision) ECCE* (superior incision) ICCE** (tumbling) ECCE with PC-IOL***
800 Sushruta 1745 Daviel 1860 von Graefe 1880 Smith 1949 Ridley
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ECCE with AC-IOL**** 1951 Strampelli Phacoemulsification 1967 Kelman Foldable IOLs 1984 Mazzocco Capsular surgery 1992 Apple/Assia Accommodating IOLs 1997 Cummings/Kamman Phakonit 1998 Agarwal *ECCE: extracapsular cataract extraction **ICCE: intracapsular cataract extraction ***PC-IOL: posterior chamber intraocular lens ****AC-IOL: anterior chamber intraocular lens
TABLE 29.2 Evolution of anesthetic techniques for cataract surgery Technique
Year Author
General anesthesia Topical cocaine Injectable cocaine Orbicularis akinesia
1846 ? 1885 Koller 1884 Knapp 1914 Van Lint, O’Briens Atkinson Hyaluronidase 1948 Atkinson Retrobulbar (4% cocaine) 1984 Knapp Posterior peribulbar 1985 Davis and Mandel Limbal 1990 Furata and coworkers Anterior peribulbar 1991 Bloomberg Pinpoint anesthesia 1992 Fukasawa Topical 1992 Fichman Topical plus intracameral 1997 Gills No anesthesia 1998 Agarwal Cryoanalgesia 1999 Gutierrez Carmona Xylocaine jelly 1999 Koch, Assia
intracameral injection of lidocaine. In a recent, prospective, randomized, double-masked clinical trial, Gillow et al26 evaluated the efficacy of supplementary intracameral lidocaine in routine phacoemulsification under topical anesthesia. There was no significant relationship between the use of intracameral lidocaine and either intraoperative or postoperative pain scores. The authors concluded that the routine use of intracameral lidocaine as a supplement to topical anesthesia did not have any clinically useful role. Clear corneal phacoemulsification has the advantage of avoiding touching any superficial sensitive ocular tissue (other than the peripheral cornea) during the surgery. Preserved ocular motility can be used to improve the operating conditions by optimizing the red reflex and wound access. Compared to regional anesthetic techniques such as peribulbar anesthesia, the topical approach does not increase the vitreous pressure, and there is no effect on the optic nerve blood flow. Postoperative recovery is quicker,
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postoperative pain is reduced, and the patient may prefer this technique. Recently, various authors reported their experience concerning topical anesthesia.11–13,15,18–21 However, neither injectable nor topical anesthetics are completely safe, injectable techniques of these agents can lead to various complications which can be non-sightthreatening, sight-threatening and very rarely, life-threatening.3,4,6,8,27 Topical anesthesia prevents these complications but it can lead to corneal epithelial, corneal endothelial, and/or retinal toxicity, mostly due to the preservatives in the anesthetic solutions.28–32 Moreover, topical anesthetic agent and its vehicle may serve as reservoir of microbial contamination with the potential for causing an infection. Some of these agents (e.g. proparcaine) can lead to allergic and idiosyncratic reactions. Manifestations of such reactions include periocular swelling, erythema, and the typical rash of contact dermatitis. Further, preoperative instillation of some of the topical anesthetics (e.g. lidocaine) may cause burning and stinging sensations and multiple applications sometimes lead to mild haziness of the cornea during the surgical procedure. There is a potential for cumulative toxicity on account of need for administration of several doses. Recent reports suggested that cataract surgeons should be aware of the potential for endothelial injury if anesthetic agents are injected into the eye.30–32 This is not surprising because the intraocular concentration of the anesthetic agent after intracameral injection can be 250 times higher than the concentration after topical application.32 Complications associated with topical anesthesia are summarized in Table 29.3.
TABLE 29.3 Side effects and complications of topical ocular anesthetics 1. Alteration of the stability of lacrimal and tear films 2. Delayed healing of the epithelium in presence of epithelial defects 3. Toxicity to the corneal endothelium secondary to preservative benzalkonium 4. Surface keratopathy 5. Retinal and macular toxicity
The modern cataract surgical procedures are currently so well defined and quickly performed that we can question whether the topical anesthesia represent a dead end or if it is possible to perform the surgery without using it. Indeed, one of the major advances documented in the last decade of the 20th century is the performance of cataract surgery without using topical anesthesia.34 This was first done by Amar Agarwal (AA), in June, 1998. Interestingly, this happened as an accident. A case of posterior polar cataract was scheduled for an ECCE in the early 1998, under pinpoint anesthesia (preferred by the surgeon: AA) rather than topical anesthesia. At the last moment, the surgeon decided to perform the surgery using phacoemulsification instead of ECCE. In the middle of the surgery, he came to know that he was performing it without anesthesia. To his surprise, the patient was lying comfortably without pain. Since then, more than 5,000 cataract surgeries have been performed using this technique. We recently completed a collaborative study on no anesthesia cataract surgery in comparison to topical and topical plus intracameral anesthesia. The aim of the study was to avoid the use of topical anesthesia during cataract surgery and to evaluate the efficacy of this technique. We also compared the comfort of the patient and the stress for the surgeon during the surgery in the three groups.
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Randomized Study Patients Seventy-five patients were enrolled in this prospective, randomized, double blind study. Informed consent was obtained from the patients after explaining in detail the outline of the study, which was reviewed and approved by the ethics committee of the hospital. All patients were randomized to one of the three groups: group I—no anesthesia, 25 patients; group II—topical anesthesia, 25 patients; group III—topical plus intracameral anesthesia, 25 patients. The patients included in the study were between 38 and 79 years of age. The density of the cataracts varied from grade 2 to 4 (Emery-Little classification).35 Excluded were patients with barrier to communication or cooperation during surgery (extreme anxiety, language and/or hearing impairment, mental retardation, dementia, Parkinson’s disease, very young, etc). Monocular patients and those with hard, mature cataracts (grade 5 Emery-Little classification), shallow anterior chamber(s), pupil(s) less than 5 mm in diameter (when fully dilated), and inability to understand a visual analog pain scale were also excluded. The patients were prepared for cataract surgery without preoperative (or intraoperative) sedation. The pupils were preoperatively dilated using phenylephrine (5%), cyclopentolate (0.5%) and tropicamide (1%) eyedrops. Nonsteroidal antiinflammatory drugs (NSAIDs) were not used. Anesthetic Techniques Patients in group I received, while still in the preoperative area, two drops of balanced salt solution (BSS® Alcon, Forth Worth, TX) every 5 minutes three times, beginning 10 to 15 minutes before the procedure. After the corneal endothelium was coated with viscoelastic, before performing the capsulorhexis, an intracameral injection of BSS® via a 25-gauge Rycroft cannula (Beaver and Visitec Products, Bidford on Avon, England) was performed. Patients randomized to group II received lidocaine (4%) eyedrops preoperatively, and an intracameral injection of BSS®, as described above. Patients in group III received both, preoperative 4 percent lidocaine eyedrops and intracameral injection of preservative-free lidocaine (1%), using the same methods as in the other 2 groups. The protocol established for the supplemental anesthesia for breakthrough pain during the surgery, if it should occur, was as follows: if the patient was in pain, two additional drops of lidocaine (4%) would be placed in the eye. If the pain persisted, a peribulbar or retrobulbar block would be used. Surgical Technique All cataract surgical procedures in this study were performed in a referral institute of South India by the same surgeon (AA). A wire speculum was placed and the patients were asked to look down. No superior rectus sutures were used in any group. Patients were informed that they would be aware of the sensation of touch and would be able to move their eyes. First of all, viscoelastic (Healon®, Pharmacia and Upjohn, Uppasala,
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Sweden) was injected into the anterior chamber using a needle through the area where the second (paracentesis) site was made. This was important in order to distend the eye to create a good self-sealing corneal valve. A straight rod was then used to stabilize the eye (with the left hand) at the 2 O’clock position for the right eye and at the 10 O’clock position for the left eye. With the right hand, a 3.2 mm groove was made in clear temporal cornea using a diamond knife. During the entire surgical procedure care was taken to avoid grasping of the conjunctiva or sclera by tooth forceps. The globe was stabilized by the straight blunt rod during the entire surgery. A 5.0 to 5.5 mm wide capsulorhexis was performed using a 26-gauge bent needle cystotome. Hydrodissection was performed with BSS®. Nuclear emulsification (Alcon, Master 10,000, Fort Worth, TX) was performed with Karate chop technique using less ultrasound power. The capsular bag was filled with viscoelastic. Foldable one-piece plate hap tic PCIOL lenses were then implanted (STAAR Surgical Co, Monrovia, CA). Intracameral miotics were not used in any of the patients. The viscoelastic was removed from the anterior chamber and the capsular bag by irrigation. The corneal incisions were secured by performing stromal hydration. The operating microscope light was kept at its lowest level and gradually increased in intensity. The level was up to the usual operating levels after hydrodissection and the patient was encouraged to fix the eye toward the microscope light during the surgery. No subconjunctival injections or an eyepad was applied at the completion of the surgery. Parameters Assessed After the surgery, the patients were taken to the postoperative area where vital signs were obtained. There, one constant observer also collected patient assessment responses. Questions were presented to the patients in a standardized written form. Each patient was shown a 10-point visual analog graphic pain scale with numeric and descriptive ratings where 0 represented no pain and 10 represented severe, “unbearable” pain.35 They were asked to grade the level of discomfort or pain during the surgery and postoperatively, on separate scales. If the patient was unable to see the scale or read the accompanying text, the scale was described and verbal score was obtained. They were also asked to differentiate “pain” or “discomfort” from “touch” or “movement” sensation. The degree to which the patients were bothered due to ability to move their eyes, sense of touching their eyes and by the operating microscope light was also assessed. This was graded as “not at all” (0), “not very much” (1) and “very much” (2). If the surgeon was bothered by the patients’ eye movement, it was also graded as “not at all” (0), “not very much” (1) and “very
TABLE 29.4 Characteristics of the patients included in each group *Group I **Group II ***Group III Number of cases 25 25 25 Average age 59.66±9.54 56.80±9.35 60.00±10.17 Males/females 18/7 15/10 14/10 Nuclear density 2.50±1.10 2.64±0.90 2.28±0.79 Operating time (min) 8.25±1.78 8.88±2.24 8.38±1.70
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Race (% non-white) 100 100 * No anesthesia ** Topical anesthesia *** Topical and intracameral anesthesia
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100
much” (2). Stress for the surgeon during the surgery (from 0–2) and total surgical time (minutes) were also noted. The patients were kept in the recovery area for a minimum of 30 minutes. The surgeon also completed a questionnaire on the surgical conditions, complications and need for supplemental anesthesia. Comparison of various parameters between the three groups was performed using analysis of variance (ANOVA). A P value inferior to 0.05 was considered statistically significant. Results A total of 75 patients were recruited into the study. No patient refused to take part. Patient data are listed in Table 29.4. There was no significant difference in age and density of cataracts of the patients from the three groups (Figs 29.1A and B). Therefore, the patients included in the study were comparable. The average surgical time was 8.25±1.78 minutes for the no anesthesia group (group I), 8.88±2.24 minutes in the topical anesthesia group (group II) and 8.38± 1.70 minutes in the topical plus intracameral anesthesia group (group III). The surgical time was slightly higher in the topical anesthesia group when compared to the no anesthesia or topical plus intracameral anesthesia groups, but this difference was not significant (P=0.3562—Fig. 29.1C). No patients in any group required supplemental anesthesia.
FIGURE 29.1A
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FIGURE 29.1B
FIGURE 29.1C The results from the questionnaires are summarized in Table 29.5. The mean score of intraoperative pain (scale from 0 to 10) in the no anesthesia group was slightly superior than in the topical and topical plus intracameral groups. However, this difference was not statistically significant (P=0.6101—Fig. 29.1D). In other words, there was no significant difference in the subjective sensation of pain during
FIGURE 29.1D
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FIGURE 29.1E
FIGURE 29.1F
FIGURE 29.1G
FIGURE 29.1H
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FIGURE 29.1I FIGURES 29.1A TO I Graphs showing the results of the parameters assessed in the randomized study cataract surgery either with or without topical anesthesia. The mean score of patient discomfort due to the microscope light was slightly higher in the no anesthesia group, but this difference was again not statistically significant (P=0.2115—Fig. 29.1E). Patient discomfort due to ability to move the eyes had a significantly higher mean score in the no anesthesia group (P=0.0235—Fig. 29.1F) when
TABLE 29.5 Parameters (and scores) evaluated in the three groups Group I* (N=25)
Group II** (N=25)
Group III*** (N=25)
P value
Pain (0–10) 1.54±1.84 1.44±1.04 1.16±1.17 0.6106 Discomfort due to microscope 0.20±0.41 0.04±0.20 0.16±0.37 0.2115 light (0–2) Discomfort due to ability to move 0.25±0.44 0.40±0.20 0.40±0.20 0.0235**** the eye (0–2) Discomfort due to sense of touch 0.37±0.64 0.20±0.40 0.28±0.45 0.0629 (0–2) Surgeon’s discomfort during 0.30±0.57 0.12±0.33 0.28±0.45 0.158 surgery (0–2) Stress for surgeon during surgery 0.40±0.58 0.08±0.27 0.16±0.37 0.0206**** (0–2) *—No surgery, **—Topical anesthesia, ***—Topical and intracameral anesthesia, ****— Statistically significant (P<0.05)
compared to the two other groups. Regarding patient discomfort due to sense of touching the eyes the mean score was higher in the no anesthesia group. However this difference was not statistically significant (P=0.0629—Fig. 29.1G). Concerning surgeon discomfort
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due to the ability of the patients to move the eyes, the difference between the three groups was also not statistically significant (P= 0.1580—Fig. 29.1H). However, the stress for the surgeon during the surgery was significantly greater in the no anesthesia group when compared to the topical or topical plus intracameral group (P =0.0206—Fig. 29.1I). In summary, the only two parameters that differed significantly in the 3 groups were patient discomfort due to ability to move the eyes and stress for the surgeon during the entire surgical procedure. Current Study/Experience of Other Surgeons This is the first randomized, double-masked, controlled trial comparing three techniques, namely no anesthesia, topical anesthesia and topical plus intracameral anesthesia. The use of either topical anesthesia or topical anesthesia combined with intracameral lidocaine was not associated with significantly lower intraoperative and early postoperative pain scores. Assessments of other parameters in the 3 groups besides the pain scores revealed that only patient discomfort due to ability to move the eyes and stress for the surgeon during the procedure were significantly different. No anesthesia cataract surgery has been currently performed by other surgeons in various countries. Dr Francisco J Gutierrez-Carmona performed no anesthesia cataract surgery on 50 patients in Spain.37 He used cooled balanced salt solution in the operating eye and termed this technique as “cryoanalgesia”. The experience of Dr Tobias Neuhann from Germany concerning no anesthesia cataract surgery performed on 30 cases is also interesting (Neuhann T, personal communication). He performed it mostly on patients over 50 years, but interestingly some of the patients less than 50 years of age also asked for the no anesthesia technique. This is due to a trend of “no medical treatment”, which is common in very selective group of peoples in Germany. The use of 2 percent hydroxypropylmethyl cellulose (HPMC) to cover the cornea, helped in avoiding corneal dryness during the surgery. Although motivation is important, according to Dr Neuhann’s experience no anesthesia cataract surgery works better in older patients. Dr Keiki R Mehta from India also performed more than 450 cases using this technique (Mehta KR, personal communication). The need for supplemental anesthesia in his series was about 10 to 12 percent. He believes that the limbus is a watershed area for tactile sensations and therefore the corneal sensitivity in the peripheral cornea is significantly lower than the central cornea (see below: anatomical factors). Other surgeons currently performing this technique include Drs Oman Almullah (USA), Mohan Rajan (India) etc. No Anesthesia Cataract Surgery: Why Does it Work? It seems surprising that cataract surgery can be performed through one of the most sensitive structures (cornea) without using any anesthesia. The precise explanation for this fact is still unknown to us. However, we can advance some hypotheses related to surgical factors and anatomical factors.
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Surgical Factors The skill and experience of the surgeon is one of the most important factors for the no anesthesia cataract surgery. While using this technique, it is important to avoid grasping the conjunctiva or sclera with tooth forceps. The surgeon should use a straight and relatively blunt rod to stabilize the eye during the entire procedure. Also, the use of a clear corneal incision avoids the use of cautery, necessary to achieve hemostasis with scleral tunnel incisions. In addition, gradual increase in the microscope luminance, minimization of the iris-lens-diaphragm movement and iris manipulations are important factors for topical as well as no anesthesia techniques. The phaco power should be used minimally to avoid excessive heating of the phaco tip, which in turn can produce pain. Anatomical Factors The cornea is supplied by the medial and lateral long ciliary nerves, which are branches of the trigeminal nerve. It is sensitive to touch, pain and temperature.38 However, there are marked topographical variations in the corneal sensitivity. Besides the diurnal variations, corneal sensitivity also varies according to age, sex and race.38–40 The central part of the cornea is the most sensitive. There is an overall reduction in the corneal sensitivity from the center to the periphery. The superior part of the cornea is the least sensitive, probably because of a decreased concentration of acetylcholine. Concerning the diurnal variations, corneal sensitivity is the lowest in the morning and highest in the evening. This decreased sensitivity in the morning must be attributed to the reduction in oxygen tension at the epithelium surface when the eye is closed.39 Corneal sensitivity remains practically unchanged from 10 to about 50 years of age. Beyond that age, the decline is significant reaching a half beyond 65 years of age. The precise mechanism is not clear, however, some authors relate it to the formation of arcus senilis and to a decreased concentration of acetylcholine. In females, corneal sensitivity decreases during the premenstrual and menstrual periods. The role of racial factors should not be underestimated.40 It was documented during contact lens fitting and many studies confirmed that corneal sensitivity in non-white (dark-brown eyed: Indians, Chinese, and Negroes) peoples is 4 times less than in white (blue-eyed: Caucasians) peoples. As reported by Michel Millodot in 1975, this phenomenon is obviously relevant to the wearing of contact lenses.40 It may also have some bearing on problems of anesthesia as it is possible that different quantities of anesthetics may be needed according to eye color. This is similar to the clinical fact that more ocular drugs are needed for people with dark rather than light-pigmented irises to obtain the same effect (for example, cycloplegia). The reason for this is not known, although it may be related to the amount of melanin pigment present in the iris. Since the cornea does not contain any pigment, however, it is not easy to explain the diminution of corneal sensitivity with darker pigmentation of the iris. It is not known whether the thickness of the cornea varies with eye color. It has been shown that thicker corneas, as a result of edema, are less sensitive than normal corneas. It is also unknown whether nerve supply density varies widely among these different peoples. Another possibility is that the difference in sensitivity arises in the central nervous system and not at the periphery The difference in tactile sensitivity may also be relevant to understand that the practice of
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acupuncture may be more acceptable in China than it is in countries inhabited by blueeyed people. Finally, recent studies have documented that frequent exposure to ultraviolet rays (between 280 and 310 nm) may give rise to a loss in corneal sensitivity, as high as 73 percent.38 Also, decrease in temperature can lead to reduction in corneal sensitivity, which have been documented up to nine folds.38 Thus, no anesthesia cataract surgery works due to atraumatic surgical techniques in suitable patients by a very experienced and confident surgeon. The speed and dexterity of the surgeon are paramount to the successful use of this technique, as it is the proper patient selection. Incision and manipulations through the least sensitive (superior) part of the cornea are probably the most important factors. Further decrease in corneal sensation due to the dark iris of patients in India, and aged patients exposed to ultraviolet rays probably accounted for the results obtained in our study. As mentioned earlier, the reasons for the racial variations are still unknown. However, the differences may be important in adapting the technique for more sensitive corneas in white patients, as did Dr Francisco Gutierrez-Carmona’s in Spain by using cooled balanced salt solution (“cryoanalgesia”) for corneal desensitization.37 Conclusion In conclusion, we demonstrated that cataract surgery could be performed without the use of anesthetic agents. The advantage is that it avoids any toxicity associated with topical and/or intracameral anesthetic solutions. However, it is certainly not suitable for every cataract surgeon or every patient and its real benefits have to be measured carefully, in a case-by-case basis. References 1. Linebarger EJ, Hardten DR, Shah GK et al: Phacoemulsification and modern cataract surgery. Surv Ophthalmol 44:123–47, 1999. 2. Agarwal A, Agarwal S, Agarwal A: Phakonit and laser phaconit: lens removal through a 0.9 mm incision. In Agarwal A (Ed): Textbook of Ophthalmology Slack Inc: Thorofare 2:2000 (in press). 3. Greenhalgh D: Anesthesia for cataract surgery. In Yanoff M, Ducker JS (Eds): Ophthalmology Mosby-Yearbook: St Louis 21.5–21.6, 1998. 4. Ram J, Pandey SK: Anesthesia for cataract surgery. In Dutta LC (Ed): Modern Ophthalmology Jaypee Brothers: New Delhi 325–30, 2000. 5. Koch PS: Anterior chamber irrigation with unpreserved lidocaine 1% for anesthesia during cataract surgery. J Cataract Refract Surg 23:551–54, 1997. 6. Patel BCK, Burns TA, Crandall A et al: A comparison of topical and retrobulbar anesthesia for cataract surgery. Ophthalmology 103:1196–1203, 1996. 7. Gills JP, Cherchio M, Raanan MG: Unpreserved lidocaine to control discomfort during cataract surgery using topical anesthesia. J Cataract Refract Surg 23:545–50, 1997. 8. Zehetmayer M, Radax U, Skorpik C et al: Topical versus peribulbar anesthesia in clear corneal cataract surgery. J Cataract Refract Surg 22:480–84,1996.
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9. Manners TD, Burton RL: Randomized trial of topical versus sub-Tenons local anaesthesia for small-incision cataract surgery. Eye 10:367–70, 1996. 10. Roman S, Auclin F, Ullern M: Topical versus peribulbar anesthesia in cataract surgery. Cataract Refract Surg 22: 1121–24, 1996. 11. Crandall AS, Zabriskie NA, Patel BCK et al: A comparison of patient comfort during cataract surgery with topical anesthesia versus topical anesthesia and intracameral lidocaine. Ophthalmology 106:60–66, 1999. 12. Masket S, Gokmen F: Efficacy and safety of intracameral lidocaine as a supplement to topical anesthesia. J Cataract Refract Surg 24:956–60, 1998. 13. Martin RG, Miller JD, Cox CC III et al: Safety and efficacy of intracameral injections of unpreserved lidocaine to reduce intraocular sensation. J Cataract Refract Surg 24: 961–63, 1998. 14. Garcia A, Loureiro F, Limao A et al: Preservative-free lidocaine 1% anterior chamber irrigation as an adjunct to topical anesthesia. J Cataract Refract Surg 24:403–06, 1998. 15. Tseng HS, Chen FK: A randomized clinical trial of combined topical-intracameral anesthesia in cataract surgery. Ophthalmology 105:2007–11, 1998. 16. John T: Simplified anesthesia technique for scleral tunnel phacoemulsification. J Cataract Refract Surg 24:1562–65, 1998. 17. Pham DT, Scherer V, Wollensak J: Sponge-Oberfldchenandsthesie in der Kataraktchirurgie (bie skleralem Tunnelschnitt). Klin Monatsbl Augenheilkd 209:347–53, 1996. 18. Gills JP, Cherchio M, Raanan MG: Unpreserved lidocaine to control discomfort during cataract surgery using topical anesthesia. J Cataract Refract Surg 23:545–50, 1997. 19. Koch P: Anterior chamber irrigation with unpreserved lidocaine 1% for anesthesia during cataract surgery. J Cataract Refract Surg 23:551–54, 1997. 20. Carino NS, Slomovic AR, Chung F et al: Topical tetracaine versus topical tetracaine plus intracameral lidocaine for cataract surgery. J Cataract Refract Surg 24:1602–08, 1998. 21. Garcia A, Loureiro F, Limao A et al: Preservative-free lidocaine 1% anterior chamber irrigation as an adjunct to topical anesthesia. J Cataract Refract Surg 24:403–06, 1998. 22. Claoue C: Simplicity and complexity in topical anesthesia for cataract surgery (editorial). J Cataract Refract Surg 24: 1546–47, 1998. 23. Koch PS: Efficacy of lidocaine 2% jelly as a topical agent in cataract surgery. J Cataract Refract Surg 25:632–34, 1999. 24. Assia EI, Pras E, Yehezkel M et al: Topical anesthesia for lidocaine gel for cataract surgery. J Cataract Refract Surg 25:635–39, 1999. 25. Learning DV: Practice styles and preferences of ASCRS members—1998 survey. J Cataract Refract Surg 25:851–59, 1999. 26. Gillow T, Scotcher SM, Deutsch J et al: Efficacy of supplementary intracameral lidocaine in routine phacoemulsification under topical anesthesia. Ophthalmology 106:2173–77, 1999. 27. Davis DB, Mandel MR: Anesthesia for cataract extraction. Int Ophthalmol Clin 34:13–30, 1994. 28. Rosenwasser GOD: Complications of topical ocular anesthetics. Int Ophthalmol Clin 29:153– 58, 1989. 29. Maloney WF: Intraocular lidocaine causes transient loss in small number of cases. Ocul Surg News 14:32, 1996. 30. Werner L, Legeais JM, Obsler C et al: Toxicity of xylocaine to rabbit corneal endothelium. J Cataract Refract Surg 24: 1371–76, 1998. 31. Liang C, Peyman GA, Sun G: Toxicity of intraocular lidocaine and bupivacaine. Am J Ophthalmol 125:191–96, 1998. 32. Judge AJ, Najafi K, Lee DA et al: Corneal endothelial toxicity of topical anesthesia. Ophthalmology 104:1373–79, 1997. 33. Behndig A, Linden C: Aqueous humor lidocaine concentrations in topical and intracameral anesthesia. J Cataract Refract Surg 24:1598–1601, 1998.
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34. Agarwal A, Agarwal A, Agarwal S: No anesthesia cataract surgery with karate chop. In Phacoemulsification, Laser Cataract Surgery and Foldable IOLs. Slack Inc: Thorofare 145–53, 1998. 35. Emery JM, Little JH: Phacoemulsification and Aspiration of Cataracts; Surgical Techniques, Complications, and Results. CV Mosby: St Louis 45–48, 1979. 36. Scott J, Huskisson EC: Graphic representation of pain. Pain 2:175–84, 1976. 37. Gutierrez-Carmona FJ: Phacoemulsification with cryoanalgesia: A new approach for cataract surgery. In Agarwal A (Ed): Text Book of Ophthalmology Slack Inc: Thorofare 2:2000 (in press). 38. Millodot M: A review of research on the sensitivity of the cornea. Ophthal Physiol Opt 4:305– 318, 1984. 39. Millodot M: Do blue-eyed people have more sensitive cornea than brown-eyed people? Nature 8:151–52, 1975. 40. Millodot M: Diurnal variation of corneal sensitivity. Br J Ophthalmol 56:844, 1972.
30 Ocular Anesthesia for Small Incision Cataract Surgery Samuel Masket Introduction Traditional methods of local ocular anesthesia for cataract surgery have employed injection of anesthetics to the periorbital region. It is well recognized that regional infiltration can produce ocular anesthesia, ocular akinesia, orbicularis akinesia, and varying degrees of amaurosis. However, recent trends strongly indicate that only ocular anesthesia is necessary for routine small incision cataract surgery The 1997 American Society of Cataract and Refractive Surgery member survey for the year 1996 suggests that roughly 15 percent of surgeons employ non-injection anesthesia (topical with or without intracameral agents) routinely.1 Nevertheless, the great majority of surgeons continue to use anesthetic injections with some degree of risks, that include damage to the globe, optic nerve, and periocular structures, and central nervous system (CNS) toxicity including brainstem anesthesia, apnea, and death. Very rarely, the patient may sustain bilateral ocular anesthesia as a result of anesthetic spread through the cavernous sinus. Moreover, with anesthetic injection, there is the potential for cosmetic blemish of the lids and conjunctiva. It is worth noting that patients often rate the quality of their cataract surgery by how the eye looks as well as how the eye sees during the early postoperative period. The risks of periorbital anesthetic injections are of some consequence, in that the overall occurrence rate for retrobulbar hemorrhage is in the vicinity of 1 percent of all cases, the likelihood increases with long needles and intraconal injection.2 Furthermore, ocular penetration and optic nerve damage are not terribly rare. The risks of those maloccurrences increase in patients who are uncooperative for injection, those with high myopia, those with prior scleral buckling surgery, and when the injections are administered by non-ophthalmologists. Additionally, no needle types, injection sites, or injection styles are immune to the risk for damage to the globe or other orbital structures.3–5 Another issue regarding the blind passage of sharp needles into the orbit concerns those patients on anticoagulant medications or those with naturally occurring coagulopathies. It should be obvious that these patients are at greater risk for periocular hemorrhage with needle injection, but often the medical necessity for anticoagulation dictates that patients remain on treatment during the perioperative period. Often, the systemic risk to cessation of anticoagulant treatment is greater than the risk of intraoperative bleeding. Indeed, the published guidelines for cataract surgery in the United Kingdom suggest that cataract surgery should proceed up to an INR (International
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Normalized Ratio) of 4.0 for patients taking Coumadin. It is evident that non-injection forms of local anesthesia are safer for anticoagulated patients. Additional consequences of periocular anesthetic include an inability of the patient to move the eye during and after surgery. While it was once considered essential that the eye be fully still for safe surgery, it is now recognized that purposeful eye movements, on command, can benefit the progress of surgery. As an example, in cases with narrow palpebral fissures, the eye can be moved to facilitate incisions, etc. A further consequence of regional anesthetic infiltration is amaurosis. As a result, the patient cannot see to fixate a target. However, with topical/intracameral anesthesia, the patient can be asked to follow a light source or other visual target to help fixate the globe in a satisfactory position for surgery. Movement away from periocular injection toward topical methods of ocular anesthesia is natural, given the overall changes in small incision cataract surgery that have progressed to outpatient surgery with methods that allow for immediate ambulation, rapid return to a full lifestyle, and stable optical results of surgery within days.6 The immediate use of the eye after cataract surgery is possible only with topical/intracameral methods and is in keeping with the concepts of modern surgery. Topical anesthesia resurfaced in this decade as a useful tool after Fichman’s suggestion regarding the use of tetracaine 0.5 percent applied to the eye as the only anesthetic for cataract surgery.7 Other agents, such as bupivacaine and lidocaine have been popularized because of a reduced tendency to cause corneal epitheliopathy and to have a longer period of action as compared with tetracaine. However, patients are not universally comfortable with topical anesthesia as the only agent. Many surgeons employ small amounts of intravenous, oral, or sublingual sedation as an adjunct. However, in 1995 Gills suggested the routine use of intracameral non-preserved lidocaine in addition to topical anesthesia with or without systemic sedation,8 although the concept had been mentioned earlier by Fichman who considered intraocular tetracaine for use in difficult case situations. Safety and efficacy of intracameral lidocaine has been further established by Koch9 and Masket with Gokmen in separate studies.10 In the latter investigation, approximately 40 percent of more than 300 patients receiving only topical anesthesia required intraoperative conversion to a deeper level of local anesthesia, whereas fewer than 1 percent of 300 cases receiving intracameral lidocaine had need for an additional local anesthetic method. In the same study, safety was measured by comparing the degree of corneal edema on the first postoperative day between the two groups, a reduced likelihood for corneal edema was associated with the use of intracameral nonpreserved lidocaine hydrochloride 1 percent, but this finding may be related to the use of chop style phacoemulsification for the latter group. Nevertheless, based upon the early postoperative appearance of the cornea, nonpreserved lidocaine is seemingly nontoxic although Koch reports reduced contrast sensitivity and visual acuity in the first few hours after surgery. Other methods to provide ocular anesthesia for cataract surgery without the risks of blind pass, sharp needle orbital injection have evolved during the same era as the movement to topical anesthesia. Posterior sub-Tenon’s infiltration employs a blunt
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FIGURE 30.1 Blunted reusable cannula for sub-Tenon’s (parabulbar) anesthesia. (Courtesy Rhein Medical, Tampa, Florida) cannula (Fig. 30.1) to place local anesthesia directly in the retrobulbar space. A conjunctival button hole incision, performed under topical anesthesia, is necessary for the cannula to gain direct access to the sub-Tenon’s space. This method was suggested as an alternative to sharp needle orbital injection,11 and has been further popularized by Greenbaum as a primary method for cataract anesthesia. He coined the term “parabulbar” anesthesia to describe the concept.12 Additionally, the method may be used for surgeons in transition to topical/intracameral anesthesia and is very useful to convert from topical methods in cases where complications occur, surgery is prolonged, or if the patient is otherwise in need of a deeper level of anesthesia. As long as the cataract incision is selfsealing, the parabulbar infiltration may be given at any time during the surgery. Varying with the nature of the agent used for infiltration, parabulbar anesthesia may provide complete ocular akinesia and amaurosis. Other alternatives include anterior subconjunctival injection given diffusely or only focally in the region of the incision, socalled “pin-point” anesthesia.13 It is evident that traditional ocular anesthesia for cataract surgery, utilizing sharp needles passed blindly through the skin of the lids or the conjunctiva engenders risks (Table 30.1) that are avoidable with topical/intracameral or other recently developed means for local anesthesia. However, in addition to the greater safety associated with newer anesthetic systems, topical and topical/intracameral methods avoid the need for patching and allow the patient the use of the eye immediately following surgery in the overwhelming majority of cases. Advantages, therefore, include safety, improved cosmesis, ability to use the eye immediately following surgery, and the ability to move and fixate the eye during surgery in response to the surgeon as an aid to the procedure (Table 30.2).
TABLE 30.1 Risk of injection anesthesia • Damage to optic nerve • Retrobulbar hemorrhage • Ocular penetration/perforation
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• Central nervous system anesthesia • Apnea • Unintended bilateral ocular anesthesia • Damage to extraocular muscles/diplopia • Aesthetic blemish
TABLE 30.2 Advantages of topical/intracameral anesthesia • Avoids pain, blemish and risk of injection anesthesia • Allows immediate useful vision after surgery • Eliminates need for patch after surgery • Reduces anxiety and/or heavy sedation associated with injection anesthesia • Compatible for patients on anticoagulants • Patients can aid surgeon by moving eye for favorable exposure
TABLE 30.3 Contraindications to topical/intracameral anesthesia Relative • Language barrier • Anticipated difficult surgery • Poorly cooperative patient Absolute • Total deafness • Coarse nystagmus
Varying with the experience of the surgeon, certain conditions may contraindicate the use of topical/intracameral anesthesia (Table 30.3). Given the ability to move the eye, the patient can aid in the surgery or create significant obstacles, cataract surgery under topical/intracameral anesthesia is, by necessity, interactive. Poor patient cooperation is a relative contraindication, as is the inability of the surgeon and patient to adequately communicate in the same language. Often, an interpreter or bilingual family member can be present in the operating theater in order to facilitate surgery without need for injection anesthesia. However, absolute congenital deafness with speaking difficulty is an absolute contraindication, since the patient may become disoriented under the surgical drapes and cannot be expected to communicate by the usual means of lip reading or sign language, patients of this nature often require general anesthesia. Ocular conditions may also act as relative or absolute contraindications, cataracts too dense to allow fixation on the microscope light, potentially complicated surgery (preoperative zonulysis, etc.), and nystagmus are common examples. Nevertheless, the huge majority of patients may safely experience small incision cataract surgery under topical/intracameral anesthetic with very limited sedation.
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Methods The author prefers the use of lidocaine HCl 4.0 percent nonpreserved for topical anesthetic. It is long acting and nonmucogenic (previous experience with 0.75% bupivacaine HCl suggests that it causes undesired mucus production.) Intracameral anesthesia is achieved with unpreserved lidocaine HCl 1.0 percent. Some surgeons advocate diluting the intracameral agent with balanced salt solution (BSS) solution in order to raise the pH and reduce the mild discomfort associated with anterior chamber instillation. 1. Administer topical proparacaine HCl 0.4 percent to initiate anesthesia with little sting. Administer dilating agents (cyclopentylate or tropicamide and phenylephrine 2.5%), topical antibiotics, a topical non-steroidal anti-inflammatory drug (NSAID), and lidocaine HCl 4.0 percent four times at five minute intervals prior to surgery. 2. After the patient is brought into the theater, several drops of the 4.0 percent lidocaine are administered prior to the sterile “prep”. The latter begins with instillation of two drops of half strength Betadine solution (not Betadine scrub) directly to the operative eye. At this time, very small amounts of intravenous sedation may be given, depending upon the mental and medical status of the patient, the anxiety of the surgeon, and the observations of the anesthetist or equivalent. The author generally asks that 0.5 mg to 1.0 mg of midazolam HCl be administered IV. 3. During the draping process communicate with the patient about the operative process. Tell them that they will feel slight pressure from the lid speculum and that they will need to fixate on the light of the microscope. Tell them that requests to look up, down, etc. should be achieved by moving the eye and not the head. Reassure them that they will feel no pain. 4. Begin surgery with the microscope light at low levels of illumination, sufficient only to perform a paracentesis. Place 0.2 cc of nonpreserved lidocaine HCl in the anterior chamber and follow that with the viscoelastic of choice. The anesthetic will be washed out as the viscoagent fills the chamber if the lip of the sideport is depressed as the viscoelastic is injected. Slowly increase the microscope light and perform the clear corneal incision. Continue with routine surgical procedure. 5. Generally, no further anesthesia is necessary. However, in situations with prolonged surgery or very sensitive patients, additional intracameral anesthetic may be administered for complaints of “pressure” or intraocular pain. For surface discomfort, the conjunctiva may be swabbed with a pledget of any sterile topical anesthetic, but care should be taken to avoid placing the agent near or in the incision if it contains preservatives. Additionally, small increments of intravenous sedation can be added as may be (rarely) necessary. 6. In the very unlikely case that the patient cannot tolerate the microscope light even at low illumination and continues to squeeze the lids against the speculum, additional doses of IV medicine could be given until the intracameral anesthetic is administered. In author’s observations, once the eye has received the intracameral agent, all lid squeezing and signs of anxiety or discomfort abate rapidly. However, in extreme situations or should an operative complication occur that will significantly prolong
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surgery, one can stop surgery, given a self-sealing incision, pressurize the eye to normal, and administer deep sub-Tenon’s local anesthetic with a blunt cannula (Fig. 30.1) through a conjunctival buttonhole entry in the superior or inferior nasal quadrant. Prior to incising the conjunctiva, a pledget of local anesthesia may be placed on the area for a few moments. The cannula should reach the retrobulbar space with ease if the buttonhole opening includes Tenon’s capsule. Only 2.0 cc of local agent is necessary, given direct access to the muscle cone. Relative amaurosis will be achieved in a matter of seconds, and, with strong local agents, akinesia can be established in a few minutes. References 1. Learning DV: Practice styles and preferences of ASCRS members: 1996 survey. J Cataract Refract Surg 23:527–35, 1997. 2. Cionni R, Osher R: Retrobulbar hemorrhage. Ophthalmology 98:1153–55, 1991. 3. Duker JS, Belmont JB, Benson WE et al: Inadvertent globe perforation during retrobulbar and peribulbar anesthesia. Ophthalmology 98:519–26, 1997. 4. Hay A, Flynn HW Jr, Hoffman JI et al: Needle penetration of the globe during retrobulbar and peribulbar injections. Ophthalmology 98:1017–24, 1991. 5. Grizzard WS, Kirk NM, Pavan PR et al: Perforating ocular injuries caused by anesthesia personnel. Ophthalmology 98: 1011–16, 1991. 6. Masket S, Tennen DG: Astigmatic stabilization of 3.0 mm temporal clear corneal cataract incisions. J Cataract Refract Surg 22(10):1451–55, 1996. 7. Fichman RA, Fine IH, Grabow HR: Clear-corneal Cataract Surgery and Topical Anesthesia Thorofare: Slack Inc. 1993. 8. Gills JP, Cherchio M, Raanan MG: Unpreserved lidocaine to control discomfort during cataract surgery using topical anesthesia. J Cataract Refract Surg 23:545–50, 1997. 9. Koch PS: Anterior chamber irrigation with unpreserved lidocaine 1% for anesthesia during cataract surgery. J Cataract Refract Surg 23:551–54, 1997. 10. Masket S, Gokmen F: Efficacy and apparent safety of intracameral lidocaine as a supplement to topical anesthesia. J Cataract Refract Surg 1998 (in print). 11. Stevens JD: A new local anaesthesia technique for cataract extraction by one quadrant subTenon’s infiltration. Br J Ophthalmol 76:670, 1992. 12. Greenbaum S Anesthesia in cataract surgery. In Greenbaum S (Ed): Ocular Anesthesia, Philadelphia: WB Saunders, 1–55, 1997. 13. Fukasaku H, Marron JA: Pin-point anesthesia—a new approach to local ocular anesthesia. J Cataract Refract Surg 20:468, 1994.
Section VI Phakonit 31. Phakonit 32. Microphaco: Concerns and Opportunities 33. Ultrasmall Incision Bimanual Phaco Surgery and Foldable IOL 34. Corneal Topography in Phakonit with a 5 mm Optic Rollable IOL 35. Phakonit with the Acritec IOL
31 Phakonit Amar Agarwal Athiya Agarwal, Sunita Agarwal History On August 15th 1998 the authors (Amar Agarwal) performed the first 1 mm cataract surgery by a technique called Phakonit.1,2 Since Charles Kelman started phacoemulsif ication, various new modalities have developed which have made this technique more refined. One problem still persists which is the size of the incision. The normal size of the incision is 3.2 mm. With time and more advances in phaco machines and phaco tips this reduced to 2.8 mm and then to 2.6 mm. The authors (Amar Agarwal) performed this technique for the first time in the world on August 15th 1998. It was performed without any anesthesia. No anesthetic drops were instilled in the eye nor was any anesthetic given intracamerally. The first live surgery in the world of Phakonit was performed on August 22nd 1998 at Pune, India by the authors (Amar Agarwal) at the Phako and Refractive surgery conference. This was done in front of 350 ophthalmologists.1,2 In 1999 a live surgery of Phakonit under no anesthesia was telecast live via satellite from India by the authors to Scattle USA to the ASCRS 99 conference. The problem with this technique was to find an IOL, which would pass through such a small incision. Then on October 2nd 2001 the authors (Amar Agarwal) did the first case of a Phakonit Reliable IOL. This was done in their Chennai (India) hospital. The lens used was a special lens from Thinoptx. This was a Reliable IOL, which was implanted after a Phakonit procedure, and as it was a rolled IOL it was called the Thinoptx Rollable IOL. This lens uses the Fresnel principle and was designed by Wayne Callahan (USA). It is manufactured by the company Thinoptx. The first Rollable IOL was implanted by Jaino Hoyos (Spain). The authors (Am A) modified the lens to a 5 mm optic to make it pass through a smaller incision. The lens goes through a sub 1.5 mm incision. Principle The problem in phacoemulsification is that we are not able to go below an incision of 3 mm. The reason is because of the infusion sleeve. The infusion sleeve takes up a lot of space. The titanium tip of the phaco handpiece has a diameter of 0.9 mm. This is surrounded by the infusion sleeve which allows fluid to pass into the eye. It also cools the handpiece tip so that a corneal burn does not occur.3 The authors separated the phaco tip from the infusion sleeve. In other words, the infusion sleeve was taken out. The tip was passed inside the eye and as there was no
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infusion sleeve present the size of the incision was 1.2 mm. In the left hand an irrigating chopper was held which had fluid passing inside the eye. The left hand was in the same position where the chopper is normally held; i.e.; the side port incision. The assistant injects fluid (BSS) continuously at the site of the incision to cool the phaco tip. Dr DP Prakash (India) used a 0.8 mm phaco needle with a 21 gauge irrigating chopper and demonstrated through a digital caliper the incision in this case would be a sub 1 mm incision. Terminology The name PHAKONIT has been given because it shows phaco (PHAKO) being done with a needle (N) opening via an incision (I) and with the phako tip (T). It is also because it is phaco with a Needle Incision Technology. Synonyms 1. Bimanual phaco 2. Micro phaco 3. Micro incision cataract surgery.
Technique of Phakonit for Cataracts Anesthesia All the cases done by the authors have been done without any anesthesia. But the technique of Phakonit can be done under any type of anesthesia also. In the cases done by the authors no anesthetic drops were instilled in the eye nor was any intracameral anesthetic injected inside the eye. The authors have analyzed that there is no difference between topical anesthesia cataract surgery and No anesthesia cataract surgery. They have stopped using anesthetic drops totally in all their hospitals. Incision In the first step a needle with viscoelastic is taken and pierced in the eye in the area where the side port has to be made. Then a special knife to create an incision is made (Fig. 31.1). The viscoelastic is then injected inside the eye. This will distend the eye so that the clear corneal incision can be made. Now a temporal clear corneal incision is made. The problem here is that the diamond knives are all 2.6 mm or larger. Since our aim is to make only a 1.2 mm opening these diamond knives are not sufficient. So a special blade is used (Fig. 31.2). This creates an opening of 1.2 mm. When this incision is made it should be done in such a fashion that a clear corneal valve is made. The authors have devised a keratome of 1.2 mm which they now use. This keratome creates a good valve.
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This keratome and other instruments for Phakonit are made by Microsurgical Technology (USA) and Gueder (Germany).
FIGURE 31.1 A 26 gauge needle with viscoelastic making an entry in the area where the side port is. This is for entry of the irrigating chopper
FIGURE 31.2 Clear corneal incision made with the keratome (1.2 mm). Note the left hand has a straight rod to stabilize the eye as the case is done without any anesthesia. These instruments are made by Microsurgical Technology (USA) and Gueder (Germany)
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Rhexis The rhexis is then performed. This is done with a needle (Fig. 31.3). In the left hand a straight rod is held to stabilize the eye. The advantage of this is that the movements of the eye can get controlled as one is working without any anesthesia. Hydrodissection Hydrodissection is performed and the fluid wave passing under the nucleus checked. Check for rotation of the nucleus.
FIGURE 31.3 Rhexis started with a needle Phakonit After enlarging the side port a 20 gauge irrigating chopper connected to the infusion line of the phaco machine is introduced with foot pedal on position 1. The phaco probe is connected to the aspiration line and the phaco tip without an infusion sleeve is introduced through the incision (Fig. 31.4). Using the phaco tip with moderate ultrasound power, the center of the nucleus is directly embedded starting from the superior edge of rhexis with the phaco probe directed obliquely downwards towards the vitreous. The settings at this stage is 50 percent phaco power, flow rate 24 ml/min and 110 mmHg vacuum. When nearly half of the center of nucleus is embedded, the foot pedal is moved to position 2 as it helps to hold the nucleus due to vacuum rise. To avoid undue pressure on the posterior capsule the nucleus is lifted a bit and with the irrigating chopper in the left hand the nucleus chopped. This is done with a straight downward motion from the inner edge of the rhexis to the center of the nucleus and then to the left in the form of an inverted L shape (Fig. 31.5). Once the crack is created, the nucleus is split till the center. The nucleus is then rotated 180° and cracked again so that the nucleus is completely split into two halves.
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The nucleus is then rotated 90° and embedding done in one-half of the nucleus with the probe directed horizontally (Fig. 31.6). With the previously described technique, 3 pie-shaped quadrants are
FIGURE 31.4 Phakonit irrigating chopper and phako probe without the sleeve inside the eye
FIGURE 31.5 Phakonit started. Note the phako needle in the right hand and an irrigating chopper in the left hand. Phakonit being performed. Note the crack created by karate chopping. The assistant continuously irrigates the phaco probe area from outside to prevent corneal burns
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FIGURE 31.6 Phakonit continued. The nuclear pieces are chopped into smaller pie-shaped fragments created in one-half of the nucleus. Similarly 3 pie-shaped fragments are created in the other half of the nucleus. With a short burst of energy at pulse mode, each pie-shaped fragment is lifted and brought at the level of iris where it is further emulsified and aspirated sequentially in pulse mode. Thus the whole nucleus is removed (Fig. 31.7). Note in Figure 31.7 no corneal burns are present. Cortical wash-up is to be done with the bimanual irrigation aspiration technique (Figs 31.8 and 31.9). Many doctors like Jorge Alio (Spain), Richard Packard (UK), F Vejanaro (Columbia), Randall Olson (USA) have devised their own instruments for Phakonit.
FIGURE 31.7 Phakonit completed. Note the nucleus has been removed and there are no corneal burns
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FIGURE 31.8 Bimanual irrigation aspiration started
FIGURE 31.9 Bimanual irrigation aspiration completed
FIGURE 31.10 Anti-chamber collapser (air pump) in phakonit
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Anti-chamber Collapser One of the real bugbears in Phakonit when we started it was about the problem of destabilization of the anterior chamber during surgery. This was solved to a certain extent by using an 18 gauge irrigating chopper. A development made by us (SA) was to use an anti-chamber collapser4,5 which injects air into the infusion bottle (Fig. 31.10). This pushes in more fluid into the eye through the irrigating chopper and also prevents surge. Thus we were not only able to use a 20 gauge on 21 gauge irrigating chopper but also solve the problem of destabilization of the anterior chamber during surgery. This increases the steady-state pressure of the eye making the anterior chamber deep and well maintained during the entire procedure. It even makes phacoemulsification a relatively safe procedure by reducing surge even at high vacuum levels. Thus this can be used not only in Phakonit but also in Phacoemulsification. Surge When an occluded fragment is held by high vacuum and then abruptly aspirated, fluid rushes into the phaco tip to equilibrate the built up vacuum in the aspiration line, causing surge. This leads to shallowing or collapse of the anterior chamber. Different machines employ a variety of methods to combat surge. These include usage of noncomplaint tubing,4 small bore aspiration line tubing,4 microflow tips,4 aspiration bypass systems,4 dual linear foot pedal control4 and incorporation of sophisticated microprocessors4 to sense the anterior chamber pressure fluctuations. The surgeon dependent variables to counteract surge include good wound construction with minimal leakage5 and selection of appropriate machine parameters depending on the stage of the surgery.5 An anterior chamber maintainer has also been described in literature to prevent surge, but an extra side port makes it an inconvenient procedure. Another method to solve surge is to use more of phacoaspiration and chop the nucleus into smaller pieces. Technique A balanced salt solution (BSS) bottle is used (Fig. 31.10). The bottle is kept at a height of about 65 centimeters above the operating field. The automated air pump, which is similar to the pump used in fish tanks to supply oxygen to the fish, is utilized to forcefully pump air into the irrigation bottle at a continuous rate. The air pump is connected to the BSS bottles through an IV set. A millipore air filter is used between the air pump and the infusion bottle so that the air pumped into the bottle is sterile. Sterile air is pumped into the infusion bottle, pressurizing it to force fluid into the anterior chamber, thereby neutralizing surge and maintaining a deep anterior chamber through out the procedure. Discussion Surge is defined as the volume of the fluid forced out of the eye into the aspiration line at the instant of occlusion break. When the phacoemulsification handpiece tip is occluded, flow is interrupted and vacuum builds up to its preset values. Additionally the aspiration
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tubing may collapse in the presence of high vacuum levels. Emulsification of the occluding fragment clears the block and the fluid rushes into the aspiration line to neutralize the pressure difference created between the positive pressure in the anterior chamber and the negative pressure in the aspiration tubing. In addition, if the aspiration line tubing is not reinforced to prevent collapse (tubing compliance), the tubing, constricted during occlusion, then expands on occlusion break. These factors cause a rush of fluid from the anterior chamber into the phaco probe. The fluid in the anterior chamber is not replaced rapidly enough to prevent shallowing of the anterior chamber. The maintenance of intraocular pressure (steady-state IOP) during the entire procedure depends on the equilibrium between the fluid inflow and outflow. In most phacoemulsification machines, fluid inflow is provided by gravitational flow of the fluid from the balanced salt solution (BSS) bottle through the tubing to the anterior chamber. This is determined by the bottle height relative to the patient’s eye, the diameter of the tubing and most importantly by the outflow of fluid from the eye through the aspiration tube and leakage from the wounds. The inflow volume can be increased by either increasing the bottle height or by enlarging the diameter of the inflow tube. The intraocular pressure increases by 10 mmHg for every 15 centimeters increase in bottle height above the eye.5 High steadystate IOPs increase phaco safety by raising the mean IOP level up and away from zero, i.e. by delaying surge related anterior chamber collapse. Air pump increases the amount of fluid inflow thus making the steady-state IOP high. This deepens the anterior chamber, increasing the surgical space available for maneuvering and thus prevents complications like posterior capsular tears and corneal endothelial damage. The phenomenon of surge is neutralized by rapid inflow of fluid at the time of occlusion break. The recovery to steady-state IOP is so prompt that no surge occurs and this enables the surgeon to remain in foot position 3 through the occlusion break. High vacuum phacoemulsification can be safely performed in hard brown cataracts using an air pump. Phacoemulsification under topical or no anesthesia6 can be safely done neutralizing the positive vitreous pressure occurring due to squeezing of the eyelids. Thinoptx Reliable IOL Thinoptx the company that manufactures these lenses has patented technology that allows the manufacture of lenses with plus or minus 30 dioptres of correction on the thickness of 100 microns. The Thinoptx technology developed by Wayne Callahan, Scott Callahan and Joe Callahan is not limited to material choice, but is achieved instead of an evolutionary optic and unprecedented nano-scale manufacturing process. The lens is made from off-the-shelf hydrophilic material, which is similar to several IOL materials already on the market. The key to the Thinoptx lens is the optic design and nanoprecision manufacturing. The basic advantage of this lens is that they are Ultra-Thin lenses. Thinoptx has made a special lens for Phakonit which has a 5 mm optic.
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Lens Insertion Technique The lens is taken out from the bottle. The lens is then held with a forceps (Fig. 31.11). The lens is then placed in a bowl of BSS solution that is approximately body temperature. This makes the lens pliable. Once the lens is pliable it is taken with the gloved hand holding it between the index finger and the thumb. The lens is then rolled in a rubbing motion. It is preferable to do this in the bowl of BSS so that the lens remains rolled well.
FIGURE 31.11 The phakonit thinoptx reliable IOL when removed from the bottle
FIGURE 31.12 The reliable IOL inserted through the incision
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FIGURE 31.13 The reliable IOL in the capsular bag The lens is then inserted through the incision carefully (Fig. 31.12). One can then move the lens into the capsular bag (Fig. 31.13). The natural warmth of the eye causes the lens to open gradually. Viscoelastic is then removed with the Bimanual irrigation aspiration probes (Fig. 31.14). The tips of the footplates are extremely thin which allow the lens to be positioned with the footplates rolled to fit the eye.
FIGURE 31.14 Viscoelastic removed using bimanual irrigation aspiration probes Roller Thinoptx have devised a special injector to implant the Reliable IOL after Phakonit. The advantage of this roller is that it not only rolls the lens but also inserts the lens inside the eye.
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Topography We also perfomed topography with the orbscan to compare cases of phakonit and phaco and we found that the astigmatism in phakonit cases is much less compared to phaco (Figs 31.15 to 31.18). Stabilization of refraction is also faster with Phakonit compared to phaco surgery. Laser Phakonit Laser Phakonit uses laser energy (coupled with ultrasound energy in hard nuclei) to remove the nucleus. This technique was started first time in the world by the authors (Sunita Agarwal). The laser machine used is the Paradigm Laser Photon. In these cases, two ports are used. One port has fluid (BSS) flowing through an irrigating chopper of 20 gauge and in the other hand is the phaco probe without a sleeve. In the center of the phaco probe is passed the laser probe. The diameter of the phaco probe is 900 microns. The laser probe reduces the orifice opening to 550 microns. Thus the nucleus can be removed through a very small opening.
FIGURE 31.15 Phako foldable and phakonit thinoptx IOL. The figure on the left shows a case of phako with a foldable IOL and the figure on the right shows phakonit with a thinoptx reliable IOL
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FIGURE 31.16 Phako foldable IOL orbscan results. The figure on the left is the preoperative orbscan. The figure on the right is the one day postoperative orbscan. Note the difference between the two orbscan pictures. This is the site where the clear corneal temporal incision was made Three-Port Phakonit Another technique by which one can perform Phakonit is to use an anterior chamber maintainer. The authors started this technique. They call it three-port phakonit. Just as a three port vitrectomy, here also we have three ports, hence the name- Three-Port Phakonit. There are pros and cons in every technique. The problem in three-port phakectomy is that it is too
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FIGURE 31.17 Phakonit thinoptx reliable IOL orbscan results. The figure on the left is the preoperative orbscan. The figure on the right is the one day postoperative orbscan. Note the similarity between the two orbscan pictures. This shows the minimal astigmatism created even on one day postoperative
FIGURE 31.18 Phakonit thinoptx reliable IOL orbscan results. The
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figure on the left is the preoperative orbscan. The figure on the right is the one day postoperative orbscan. Note the similarity between the two orbscan pictures. This shows no astigmatism created even on one day postoperative. Do note the astigmatism preoperative is 0.8 d and postoperative on day one is 0.7 d cumbersome. Surgeons prefer to have two ports only. Some surgeons prefer three ports as an anterior chamber maintainer is present in the eye and thus the anterior chamber is always formed. At present it is easier to perform Phakonit using a 20 gauge irrigating chopper with the anti-chamber collapser. AC Stability in Phakonit One of the real bugbears in Phakonit when we started it was about the problem of destabilization of the anterior chamber during surgery.1–5 This was solved to a certain extent by using an 18 gauge irrigating chopper. Another solution would be to raise the bottle to the roof which is not very practical. The main problem in Phakonit was that the amount of fluid entering the eye through the irrigating chopper was not equal to the amount of fluid exiting the eye through the sleeveless phaco needle. With better methods as discussed below on AC stability one can use a 21 gauge irrigating chopper. Solution Different surgeons have tried different methods to solve this problem of anterior chamber stability. The various methods are1. Air pump or Anti-chamber collapser 2. Anterior Vented Gas Forced Infusion System (VGFI) of the Accurus Surgical System 3. STAAR Surgical’s disposable Cruise Control device 4. Well designed irrigating choppers from Duet (Microsurgical Technology). The anterior vented gas forced infusion system (AVGFI) of the Accurus Surgical System in the performance of phakonit This was started by Arturo Pérez-Arteaga from Mexico. The AVGFI is a system incorporated in the Accurus machine that creates a positive infusion pressure inside the eye; it was designed by the Alcon engineers to control the intraocular pressure (IOP) during the anterior and posterior segment surgery. It consist of an air pump and a regulator who are inside the machine; then the air is pushed inside the bottle of intraocular solution, and so the fluid is actively pushed inside the eye without raising or lowering the bottle. The control of the air pump is digitally integrated in the Accurus
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panel; it also can be controlled via the remote. Also the footswitch can be preset with the minimal and maximum of desired fluid inside the eye and go directly to this value with the simple touch of the footswitch. Arturo Pérez-Arteaga recommends to preset the infusion pump at 100 to 110 cm H2O; it is enough strong irrigation force to perform a microincision phaco. This parameter is preset in the panel and also as the minimal irrigation force in the footswitch; then he recommends to preset the maximum irrigation force at 130 to 140 cm H2O in the foot pedal, so if a surge exist during the procedure the surgeon can increase the irrigation force by the simple touch of the footswitch to the right. With the AVGFI the surgeon has the capability to increase even more these values. Cruise Control The Cruise Control is a disposable, flow-restricting (0.3-mm internal diameter) device that is placed in between the phaco handpiece and the aspiration tubing of any phaco machine. The goal is very similar to that of the flare tip (Alcon): combining a standard phaco tip opening with a narrower shaft to provide more grip with less surge. This has been popularized by David Chang (USA) for phakonit surgery. STAAR Surgical introduced this disposable Cruise Control device, which can be used with any phaco machine.
FIGURE 31.19 Phakonit knives. The one on the left is the Agarwal sapphire phakonit knife made by Huco (Switzerland). The one on the right is the one made by Microsurgical Technology
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FIGURE 31.20 Duet system. These are the handles of the Duet system (Microsurgical Technology). The irrigating choppers and bimanual irrigation aspiration sets can be interchanged with the handles
FIGURE 31.21 Two designs of irrigating choppers. The one on the left has a larger opening for fluid so that AC stability is more. This has been designed by Larry Laks (Microsurgical Technology). The one on the right has two openings on the sides (Gueder— Germany) Duet System Larry Laks (USA) created the Duet system (Micro-surgical Technology-MST). The advantage of this was a whole bimanual phaco set for Phakonit. The Duet system has
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phakonit knives also (Fig. 31.19) and also handles on which various irrigating choppers can fit (Fig. 31.20). The Microsurgical Technologies (MST) 20 gauge Duet irrigating choppers provide the best inflow of comparable
FIGURE 31.22 Clear corneal incision made with the microsurgical technology knife
FIGURE 31.23 Phakonit being done with the Agarwal sharp irrigating chopper from Microsurgical Technology devices. The MST shaft design gives an impressive inflow rate of 40 cc/min at 30 in of bottle height and is available with an assortment of interchangeable chopper tips. This whole design was created by Larry Laks. The idea was to have the opening in the irrigating choppers larger (Fig. 31.21). The clear corneal incision can be created with the
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MST knife (Fig. 31.22) and then Phakonit started using the Agarwal sharp MST irrigating chopper (Fig. 31.23).
FIGURE 31.24 Bimanual irrigation aspiration started using the Duet system (MST)
FIGURE 31.25 Bimanual irrigation aspiration completed
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TABLE 31.1 The differences between phako and phakonit FEATURE
COAXIAL PHAKO
INCISION SIZE AIRPUMP HAND USAGE
>3 MM NON MANDATORY SINGLE HANDED PHAKO POSSIBLE NON DOMINANT HAND LAST TO ENTER & ENTRY & EXIT FIRST TO EXIT CAPSULORHEXIS NEEDLE OR FORCEPS IOL FOLDABLE IOL ASTIGMATISM TWO UNEQUAL INCISION CREATE ASTIGMATISM STABILITY OF LATER THAN REFRACTION PHAKONIT
BIMANUAL PHAKO (PHAKONIT) SUB 1.4 MM MANDATORY TWO HANDS (BIMANUAL) FIRST TO ENTER & LAST TO EXIT BETTER WITH NEEDLE ROLLABLE IOL TWO EQUAL ULTRA SMALL INCISIONS NEGATE THE INDUCED ASTIGMATISM EARLIER THAN PHAKO
Once Phakonit is completed the Bimanual Irrigation aspiration set from the Duet system is used (Fig. 31.24) and the cortical aspiration completed (Fig. 31.25). Summary There are various problems, which are encountered, in any new technique and so also with Phakonit. With time these will have to be solved. The differences between phako and phakonit are shown in Table 31.1. The important point is that today we have broken the 1 mm barrier for cataract removals. This can be done easily by separating the phaco needle from the infusion sleeve. As the saying goes— “We have miles to go before we can sleep”. References 1. Agarwal S, Agarwal A, Sachdev MS et al: Phacoemulsification, Laser Cataract Surgery and Foldable IOLs (2nd ed). Jaypee Brothers: Delhi, 2000. 2. Boyd BF, Agarwal S, Agarwal A et al: Lasik and Beyond Lasik; Highlights of Ophthalmology; 2000, Panama. 3. Ronge LJ: Clinical Update; Five Ways to avoid Phaco Burns; February 1999. 4. Fishkind WJ: The Phaco Machine: How and why it acts and reacts? In: Agarwal’s Four volume Textbook of Ophthalmology. Jaypee Brothers: New Delhi, 2000. 5. Seibel SB: The fluidics and physics of phaco. In: Agarwal’s et al: Phacoemulsification, Laser Cataract Surgery and Foldable IOLs (2nd ed). Jaypee Brothers: New Delhi; 45–54, 2000. 6. Agarwal et al: No anesthesia cataract surgery with karate chop. In: Agarwal’s Phacoemulsification, Laser Cataract Surgery and Foldable IOLs (2nd ed). Jaypee Brothers: New Delhi, 217–26, 2000.
32 Microphaco: Concerns and Opportunities Randall J Olson Introduction Microphaco is a concept I define as completing cataract surgery through two stab incisions of 1.5 mm or less in size. True, microphaco in my mind however, is two stab incisions of no more than 1.0 mm. Microphaco can have as its energy source ultrasound, laser or sonic energy. While certainly not a new subject, removing soft lenses such as in pediatric cases through two stab incisions has a very long track record; it is just recently that there has been interest and enthusiasm in this approach. With the predominant power source for cataract removal being ultrasound, the concern about wound burn has been substantial and that has been one of the major sources for emphasis on laser or sonic energy to try to remove a cataract by microphaco. The obvious first question one must ask prior to considering microphaco is the big one, “why do we need to consider a change”? Certainly our present cataract surgery through 2.5 to 3.0 mm incisions is well entrenched with great success and excellent postoperative results. Astigmatism change is minimal and the wounds are required to insert the present intraocular lenses. Simply removing a cataract through a smaller incision for no obvious net gain makes no sense. Progress is only progress if, indeed, doing something new adds to either the safety or the quality of our results. In the past I felt that microphaco was unlikely to be advantageous; however, a series of issues have convinced me that this is a subject worthy of serious consideration. It is certainly obvious in very complicated cases where there have been an expulsive choroidal hemorrhage, that the smallness of the incision would be protective for the eye. In the present day, where we maintain positive pressure for most of the procedure, such complications are exceedingly rare and that in and of itself would not be reason enough to make a change. A second advantage, however, has to do with the ease of switching from one wound to the other in regard to using our aspiration (phaco) needle. Certainly complicated cases, either preoperatively complicated or complicated by the surgery, may result in difficulty completing the procedure safely due to the position of the complication. If our safe zone is right in the middle of our complicated area then switching the aspiration needle to the opposite wound produces an entirely new safe zone. This certainly has been understood as an advantage in regard to irrigation/aspiration. In present phacoemulsification techniques there are those who put in two stab incisions so they can do bimanual irrigation/ aspiration such that they can switch wounds and obviate any subincisional cortex problem and at the same time use the two instruments to manipulate removal of the cortex in a way that is simpler and safer than the standard coaxial approach. For me this was still not enough reason for me to want to proceed on this venture. The main reason I moved into microphaco was the realization of what a problem irrigation is presently for us in traditional phacoemulsification. We have wrapped irrigation around our phaco aspiration needle to make sure that we have a cooling source
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to avoid wound burn and to have plenty of irrigation to maintain the chamber. Certainly this has been very good in the prevention of wound burn, which is a very uncommon event, and also does a good job of maintaining the chamber. Irrigation surrounding aspiration has necessitated wounds of at least 2.5 mm and it is unlikely, due to the law of diminishing returns that we can go much smaller than that as long as we maintain a coaxial approach to our irrigation and aspiration. The problem is irrigation maintains our chamber but otherwise is not a positive force. Let me explain. First of all some of the irrigation as it flows around the phaco needle is immediately aspirated and therefore does no practical work. This is very similar to an arterial-venous shunt in which the blood does nothing for the tissue just as shunted irrigant does nothing for our cataract surgery. Also, we have more flow than we need creating increased turbulence, which can be seen as lens fragments spinning and bouncing. Air bubbles and lens particles can damage the endothelium by this turbulence. Furthermore, irrigation pushes nuclear fragments away right when we want to have the particles come to our phaco tip. This is quite apparent, clinically, as you watch nuclear fragments being buffeted and even pushed away by irrigation until you can finally move the phaco tip and find that aspiration vortex that sucks the particle back in. Larger fragments are often, besides being repulsed by the ultrasound, also pushed away by irrigation and all of this creates inefficiency. The other factor about irrigation is that when it is separated from irrigation it can be a positive force. You can use it to open the fornix so free nuclear fragments automatically flow to our phaco because this is the only exit if our wounds are tight. All of these irrigation advantages combined, if appropriately utilized in our microphaco technique, should significantly decrease the amount of fluid necessary and improve our efficiency and safety. These reasons in combination were the major impetus for me wanting to move forward in microphaco. Prior to feeling comfortable with microphaco, it was critical to go to the lab to feel safe about this approach. My standard phacoemulsification technique being phaco chop has been ultrasound-assisted aspiration. Therefore to prove that microphaco was safe we, in a series of eye bank eyes, mounted a thermister right in the wound for continuous temperature monitoring. With continuous ultrasound we determine how long it would take to create a wound burn. Indeed, 100 percent power with aspiration and irrigation separated created wound burn; however, it took several minutes and is only a minor concern. Our next phase, which was clamping the aspiration line, certainly increased the problem, however, it still occurred at 80 percent power and it took approximately one minute of continual power. Interestingly, when we did a pulse mode at 50 milliseconds (6 per second), we actually found less time was necessary in creating wound burn showing that just decreasing the energy alone may not be the answer. We still have not figured out exactly why this result (which was consistent with several eyes) occurred, but think it may be some type of harmonics which induces greater tissue energy buildup and a burn.1 These results left us cautiously optimistic that microphaco was safe if you used minimal amounts of ultrasound. Our original wounds were quite leaky and we recognize the room for error is even less trying to produce tight wounds. We cautiously started with microphaco and it was only when we realized that White Star (a new Allergan technology) could potentially diminish the risk of wound burn that we decided to
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duplicate our experiments using White Star with a duty cycle of one-third on and twothirds off. White Star is a technology in which the ultrasound vibration can be turned off and on at levels of a millisecond or less. Previously such fine control had never been available, and therefore, there is an infinite number of modalities that can be used. Largely, an off cycle with very brief on cycles (about 20% on) enhances our ability to hold onto nuclear fragments and to remove them without chatter. It was also found that sculpting could be enhanced by this (usually 50% on and 50% off) with less energy utilized. Clearly, microchatter must occur in that particles are repulsed by ultrasound and then brought back by aspiration. This resulting in an inefficient use of energy which is obviated with White Star with very brief pulses of energy such that when the repulsion occurs the energy is off and energy is back on again when the item is aspirated. With all types of techniques used by a multitude of surgeons, the total energy utilized has been substantially less as one side benefit. With microphaco we were mainly interested in claims of minimal energy heat transference. By putting a microthermister in the wound we repeated our eye bank studies and found that with 100 percent energy we never could get the temperature above 28°C, even after three minutes of continual energy! The temperature plateaued and we were confident that twenty minutes would not have made any difference. The second step was to block all aspiration that we found previously tremendously increased the risk of wound burn, and we certainly have found the same thing clinically. Even with aspiration blocked, the temperature never went above 32°C after three minutes of continual energy. We took this to the final stage in which we eliminated irrigation and just put a bare phaco needle in the wound. Even in this situation with 100 percent energy it took 29 seconds before we finally got a temperature elevation in the wound2! This technology is incredibly forgiving and now we have an ultrasound variant that gives us the flexibility of ultrasound and the elimination of wound burn risk. White Star ultrasound, therefore, became our focus for microphaco. This has since been duplicated in a clinical study where wound temperature averaged 30°C.3 We considered laser and sonic energy but were disappointed in the results of others,4–6 that showed they took longer to remove the cataract and neither modality was particularly effective in very hard nuclei. Our clinical experience with White Star was that it was equally efficacious on the hardest of nuclei as regular ultrasound and, therefore, we felt that we had the best of all worlds with lack of concern about wound burn. Our clinical work has now proceeded for over one year with multiple issues discovered. It has been an interesting experience and I think that it would be best for me to categorize our experiences and concerns with each step of the procedure. Initial Incisions Certainly making two stab incisions should be no problem, however, the size of the incision is particularly important. If the incisions were created too large, the leak is too great and maintaining the anterior chamber is a big problem (Fig. 32.1). Furthermore, nuclear fragments come to the wound and not to our phaco needle obviating a major microphaco advantage. We have moved to 21 gauge technology largely because we
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found this worked perfectly with our diamond blade, which makes an incision 0.8 mm wide. This results in a very tight incision but not too small that we can’t insert our instruments. The tightness of the wound helps maintain the anterior chamber and keeps lens fragments going to the phaco needle. For a
FIGURE 32.1 A large leak around the irrigating chopper (a rush of fluid can be seen above the chopper) results in anterior chamber shallowing and difficulty completing the procedure 20 gauge, the incision should be 1.0 to 1.1 mm and for 19 gauge between 1.3 and 1.4 mm. We found even 0.1 mm too large can result in difficulty with maintaining the anterior chamber and let too much flow around the instruments. The incision size is critical, too small and the wound is torn and tends to leak at the end of the procedure. Location is also important in that we found we should insert the intraocular lens not through either incision, which will be discussed later. We kept them, therefore, at least 45° apart and left them between parallel to the iris surface and perpendicular to the eye and no longer than 1 mm. The length is critical in that the incisions being tight will oarlock our instruments and if they are too long can make the surgery more difficult. Also, anything other than almost parallel to the iris surface makes the incisions too long. Capsulorhexis Those who perform needle capsulorhexis will find microphaco incisions to be extremely simple such that a cystotome or bent tip needle works just fine. I prefer using forceps, and I had a difficult time finding forceps that work through a 21 gauge incision. Most small microincision forceps were too big. Finally, a 21 gauge forcep, while tight, was acceptable in completing my needle capsulorhexis
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FIGURE 32.2 A 23 gauge capsulorhexis forceps by ASICO makes work through a 0.8 mm incision a simple task incision. A 23 gauge microcapsulorhexis forcep is now available from ASICO that will easily go through any of these incisions. The tip was originally too sharp and would cut the capsule easily; however, the latest modification has been a joy to work with (Fig. 32.2). The capsulorhexis should be similar in size and shape to whatever you normally do. However, I have been making my capsulorhexis smaller to make sure that it overlaps the edge of the intraocular lens which is optimal for prevention of after-cataract formation. This means the capsulorhexis should be well-centered and approximately 5 mm in diameter. Hydrodissection/Delineation Making sure that the nucleus will rotate is even more critical in microphaco than in regular phaco. Because the instruments are relatively tightly controlled by the incision, it is more difficult to manipulate the nucleus, therefore, free rotation is critical. I have found the Chang cannula where the tip can be impaled in the nucleus extremely helpful in guaranteeing easy rotation. The other problem with hydrodissection and hydrodelineation is the smallness of the incision and making sure there is egress of fluid such that positive pressure is not produced to the point that the capsule or zonules are broken. Breaking the capsule or zonules is much easier to do than you might imagine, particularly with very high viscosity viscoelastics such as Healon 5. I make the fluid burst minimal and short but rapid. Irrigate as you go in so that there is a fluid egress channel around the cannula. Anterior Chamber Maintenance This continues to be a major problem with microphaco. Irrigation through a 21 gauge cannula requires unimpeded flow in order to maintain the chamber. Wounds that are too
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large leak too much and a stable chamber is very problematic. Furthermore, the cannula openings must be as large as possible with a single open end, the best option, which also best utilizes irrigation as a positive directable force. Unfortunately, it also leaves little strength on the end to mount a tip for chopping, etc. The second option we have used is two oval holes as large as possible and as far forward as possible on each side of the cannula to guarantee adequate flow. The cannula must be very thin walled and utilize a large hollow handle in which the irrigation line can be directly inserted. Furthermore, I put the irrigation bottle on an IV pole to raise it as high as possible. Dr. Agarwal has pressurized the line to try to enhance anterior chamber maintenance. Our experiments with the bottle at normal height showed large fluctuations in the intraocular pressure up to 55 mmHg. My concern is that a constantly pressurized line could result in extremely high pressures that may be dangerous to the optic nerve or could push the lens back if it is trapped by the iris and causes zonular damage. The solution to this would be an irrigation line that has positive pressure assistance to maintain the pressure level at no less than 22 mmHg. I am sure such a pressurized system will be available soon. Whatever instrument you use, and I have seen many proposed lately that clearly will not maintain enough flow to maintain the chamber, should be tested. It is simple to set the bottle at your working height and if you don’t have at least 40 ml of fluid flow in one minute at free flow, then reconsider using that instrument!
FIGURE 32.3 “Oar-locking” by a tight wound makes use of the irrigating chopper on the left hemi-nucleus a difficult task. Nucleus rotation is critical here Nucleus Removal Nucleus removal using White Star with microphaco is no different than any other techniques you may have used. My preference is vertical or horizontal chop and divide and conquer works well. There are, however, some notable differences with which you must become accustomed. The first is already mentioned and that is the oarlocking, which makes movement of the irrigation instrument and the aspiration needle somewhat
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more difficult (Fig. 32.3). It is important to use the utility of the two instruments such that between the two, all areas of the chamber can be covered. Simple irrigation will move nuclear fragments to the safe zone. The importance of nucleus rotation will become apparent once you start removing the nucleus. The second difficulty has to do with the weight of the instrument, which is noticeably heavier and stiffer due to the irrigation line. It will not feel as manipulable as second instruments you have used. My experience is this only takes a little time to get used to and is not a major problem. All of these issues are compounded very much if there is not good anterior chamber (AC) maintenance, and I am convinced in talking to others that AC stability is the biggest problem they are running into and not the actual nucleus removal technique. Microphaco is tailor-made for vertical chop. In vertical chop it is important to move the sleeve back as far as possible. One of the first things you will find about microphaco is that the sleeve mechanically blocks all penetration and that with the absence of the sleeve your cutting will be much faster and much better. At first this was a little shocking and I am sure if the surgeon is not careful you could easily penetrate the nucleus (fortunately, I have not done this in nucleus removal to date). With vertical chop in microphaco, the phaco needle easily cuts into the nucleus with no sleeve to block it. Taking an irrigating chopper with a classical approach in the capsular fornix or lodged in the nucleus can result in loss of flow with AC shallowing. Such is never necessary with vertical chop in which the irrigating openings are always above the nucleus. I feel microphaco vertical chop will come to be the superior technique. Bimanual Irrigation and Aspiration Having two instruments has already been seen by many as a distinct advantage. The irrigating instrument and irrigation flow can open the capsular fornix and retract the iris, making aspiration a snap. Subincisional cortex is removed by switching the two instruments, which also works in creating a new safe zone should there be a problem (Figs 32.4A and B). Cortex removal is two-handed, and again the problem is anterior chamber maintenance. If you have a 20 gauge incision to start with and then use 21 or 23 gauge bimanual irrigating/aspirating instruments, you will not maintain the chamber because your leak is too great. Your irrigation/ aspiration instruments should be the same size as your original phaco instruments. Intraocular Lens Insertion Neoptics has a lens that has been put through a 1.5 mm incision. Other approaches will take advantage of microphaco-type incisions. At present, however, the majority of microphaco surgeons are enlarging the wound to insert an intraocular lens. There are multiple ways to put the lens in; however, I found that making a totally
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FIGURES 32.4A AND B Switching the irrigating and aspirating instruments from the regular position (A) to an aspiration right position (B) eliminates the sub-incisional cortex problem separate incision for the lens was best in that it was easiest to seal this wound (Fig. 32.5). This does create some difficulty for final irrigation and aspiration such that you can either use a typical coaxial system to remove the viscoelastic or, if you want to continue the bimanual approach, then you must hydrate your intraocular lens wound or you will get too much leakage from this wound and you will have difficulty in maintaining the anterior chamber. Closure of Microphaco Wounds This has turned out to be a problem in microphaco and, in particular, when I made my intraocular lens wound centered on one of the two stab incisions. It
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FIGURE 32.5 If a regular foldable implant is to be used, I make a separate incision with a diamond keratome to facilitate wound closure turns out that microphaco by putting our instrument through a very small and tight wound results in stretching of the tissue and they tend to continue to leak. I had great difficulty in getting these to seal and had to put a suture through several, which occurrence had been exceedingly rare in the past. It turns out hydration of the edges of the wound does not effect the original stretching that was in the center of the wound and this was the reason I encountered difficulty. By making a separate intraocular lens wound and never having manipulated or stretched it with phacoemulsification steps allowed spontaneous sealing to occur even more often than usual. The two stab incisions, however, will not spontaneously seal. I aggressively stromal hydrate both stab incisions and found that getting a 19 gauge wound to seal was very difficult while it was much easier with a 21 gauge wound. If it continues to leak, stromal hydration directly in the center, either posteriorly or anteriorly, may work. Usually stromal hydration does the trick. If it does not, invariably this is an incision where you had to work to force the instrument in (usually the irrigating instrument) and therefore stretched the wound. Understanding this problem is important in instrument development. An additional approach I have found successful is to make the stab incision on the edge of the phaco wound so that stromal hydration closes this wound more easily. In talking to others however, getting the wounds to close is clearly a disadvantage. We will develop technology to obviate this issue. Making the original incisions large enough so that you don’t have to stretch them is not effective due to the anterior chamber maintenance problem secondary to the leak. Maintaining positive fluid flow in the face of some leaking will certainly help the anterior chamber maintenance problem but not the problem of nuclear particles coming to the wound and not to the phaco tip. In summary, microphaco is a technique that is evolving and to take advantage of the newer, smaller intraocular lenses that will be coming soon everyone will have to move to microphaco. It is slightly more difficult; however with experience, success is achievable. Twenty-one gauge technology has made it a little slower due to the smallness of the phaco needle bore; however, 20 gauge technology is just as fast as regular phaco. The irrigation advantages I have found to be real with basically the same sense of speed using
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one-third less irrigation. White Star will safely work with the densest cataracts as another significant advantage. As this technology evolves not only will it take advantage of the new intraocular lenses that can go through such small incisions, it may also prove to be safer with the irrigation advantage, the opportunity to switch wounds and by obviating the need to chase lens fragments with the ultrasound needle. In the meantime stay tuned to an interesting and evolving approach to cataract surgery. References 1. Soscia W, Howard JG, Olson RJ: Bimanual phacoemulsification through two stab incisions: A wound temperature study. J Cataract Refract Surg 28:1039–43, 2002. 2. Soscia W, Howard JG, Olson RJ: Microphacoemulsification with White Star: A woundtemperature study. J Cataract Refract Surg 28:1044–46, 2002. 3. Donnenfeld ED, Olson RJ, Solomon R, et at: Efficacy and Wound Temperature Gradient of White Star Technology Phacoemulsification Through a 1.2-mm Incision. J Cataract Refract Surg; submitted 4. Kanellopoulos AJ: Laser cataract surgery. Ophthalmology 108:649, 2001. 5. Dodick JM: Laser phacolysis of the human cataractous lens. Dev Ophthalmol 22:58–64, 1991. 6. Alzner E, Grabner G: Dodick laser phacolysis: Thermal effects. J Cataract Refract Surg 25:800– 03, 1999.
33 Ultrasmall Incision Bimanual Phaco Surgery and Foldable IOL HiroshiTsuneoka Introduction The increasing use of phacoemulsification and aspiration (PEA) and the advent of foldable intraocular lenses (IOLs) have been accompanied by dramatic advances in the field of cataract surgery. Some ophthalmologists even suggest that this technology may be reaching its peak, with fewer developments to be expected in the future. However, a number of problems remain to be resolved. One of these problems involves the need for further improvement in postoperative visual acuity. Although the availability of IOLs has increased the likelihood of a good outcome, numerous problems remain regarding lack of accommodation, glare, deterioration in contrast sensitivity, and changes in color perception. A second problem is the need for less invasive surgery. At present, cataract surgery can be performed through an incision of 3–4 mm, and surgical procedures are under development which will make it possible not only to remove the clouded lens through an ultrasmall incision of approximately 1.0 mm, but also to insert the IOL without enlarging that incision. Ultrasmall-incision cataract/IOL surgery requires not only improved techniques for lens extraction, but also the development of IOLs which can be inserted through these ultrasmall incisions. Many companies are currently working to develop IOLs which can be inserted through an incision of less than 2 mm, and a number of these products are expected to be on the market soon. Regarding lens extraction, considerable attention has been directed in recent years to new emulsification and aspiration techniques using the erbium YAG laser and the neodymium YAG laser. This technology provides numerous advantages, including the absence of heat generated during phacoemulsification and minimal invasiveness of the cornea of the capsular bag, and is expected to drive the next generation of cataract surgery technology. However, it is not yet widely used because it currently takes longer than phacoemulsification for nucleus removal. Recently AJ Kanellopoulos and JM Dodick have reported on the results of bimanual laser phaco surgery using a Q-switched neodymium YAG laser.1 They state that by improving laser surgery equipment and surgical techniques it is possible to dramatically reduce operating time, and that a dehydrated and folded acrylic IOL can be inserted through an incision of 1.6 to 1.8 mm after YAG laser surgery. However, in contrast to the PEA equipment which is in wide use today, laser phaco machines still have considerable room for improvement before the technology will be fully matured, so we expect that it will be some time yet before these
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procedures become widely available. There is also some question about how well this new IOL material will stand up over years of use. Since 1999 we have been studying the use of PEA, a mature technology with highly reliable equipment, for lens extraction through an ultrasmall incision. We have used this equipment to perform basic research on lens extraction through an incision of 1.4 mm or less,2 and have also developed a new type of foldable acrylic lens which can be inserted through these incisions. The present article will address ultrasmall incision cataract surgery using surgical equipment, surgical techniques, and IOL materials which are widely available today. Basic Research on Ultrasmall Incision Cataract Surgery Using Phaco Machines Use of the Sleeveless Phaco Tip Enables Ultrasmall Incision Cataract Surgery In ordinary PEA, the pahco tip is equipped with an infusion sleeve. In order to reduce incision size, it has been necessary to decrease the outer diameter of the infusion sleeve. Phaco machines in current use require an incision of at least 2.6 mm even when using a thin phaco tip. In order to successfully utilize surgical incisions of less than 2.0 mm, the infusion sleeve must be removed to leave the sleeveless phaco tip, with infusion provided through a side port. In order to use the sleeveless tip safely it is necessary to ensure that adequate infusion is provided through the side port, that the phaco tip does not overheat during emulsification and aspiration, and that there is no deformation of the incision due to movement of the tip. History of PEA Using a Sleeveless Phaco Tip In 1984, Hara and colleagues began using a sleeveless phaco tip in intracapsular phacoemulsification and aspiration for lens refilling.3 The technology attracted considerable attention, particularly in the United States, but procedures for lens emulsification and aspiration at that time were quite difficult and no suitable lens refilling material was available, so the method was never widely adopted. Fifteen years later, in 1999, we began working with bimanual PEA using a sleeveless phaco tip in order to reduce incision size during cataract surgery. We first performed basic research to make sure that the surgery would be safe, determining the feasibility of bimanual nucleofractis with infusion through a side port, establishing methods for ensuring adequate infusion flow volume, and investigating techniques to prevent thermal burn and deformation at the incision site. We then applied these findings in a clinical setting to develop procedures for lens extraction through a 1.2 to 1.4 mm incision.2 Prior to this, in 1998 A Agarwal and colleagues reported4 successful lens extraction through a 0.9 mm incision using the Phakonit method with a sleeveless phaco tip. Under this method thermal burn is avoided by providing external irrigation of the incision through which the ultrasound probe is inserted.
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At almost the same time P Crozaf on reported the successful use of a sleeveless 21 gauge Teflon-coated tip for minimally invasive bimanual PEA through a 0.9 mm incision. Crozafon felt that thermal burn could be prevented by coating the phaco tip with Teflon, which has poor thermal connectivity. In 2001 R Olson reported the feasibility of PEA through a 1.0 mm incision using the new PEA machine, Sovereign (Allergan), with White Star software. Olson found that tip heating could be minimized by setting the machine for pulse mode so that ultrasound was generated for extremely short intervals. In our ultrasmall incision cataract surgery we use a relatively large incision of 1.2 to 1.4 mm. We find that when the incision is slightly larger than the phaco tip, the tip can be cooled by the leakage of infusion solution through the incision, and the extra space also prevents deformation at the incision site due to tip movement. Problems Related to PEA with a Sleeveless Tip Major problems when using a sleeveless tip for PEA include thermal burn at the incision site because of overheating of the phaco tip, and destabilization of the anterior chamber due to inadequate infusion flow. Also, the necessity of providing infusion through the side port means that the traditional nucleofractis hook cannot be used. Many surgeons have been particularly concerned that ultrasound waves through the sleeveless tip could cause a sudden rise in tip temperature, resulting in thermal burn at the incision site, and that the sleeveless phaco tip would, therefore, be unfeasible for emulsification of hard nuclei where the tip is sometimes fully occluded. To resolve these concerns, we measured incision site temperature in postmortem porcine eyes during phacoemulsification with full occlusion of the phaco tip. Our experiments confirmed the absence of thermal burn when using a 20 gauge sleeveless phaco tip through an incision made by a 19 gauge microvitroretinal (MVR) blade. We also modified a 20 gauge infusion cannula and inserted it through a side port created with a 20 gauge MVR. The cannula modifications ensured adequate infusion flow, stabilizing the anterior chamber, and also made it possible to use the infusion cannula as a nucleofractis hook. This allowed us to safely emulsify and aspirate nuclei with conventional bimanual nucleofractis techniques, and enabled us to confirm the feasibility and safety of PEA through an incision of 1.2 to 1.4 mm using familiar techniques and widely available surgical equipment.2 Avoid Thermal Burn and Injury at the Incision Site: Widen the Incision by 1 Gauge We believed that if the incision was made slightly wider than the outer diameter of the phaco tip, the tip would be satisfactorily cooled by the leakage of infusion solution through the incision, preventing thermal burn at the incision site. To test this hypothesis we measured temperature at the incision site in postmortem porcine eyes during phacoemulsification. The PEA device used in our experiments was the Alcon Legacy 20000® with a 20 gauge Kelman phaco tip (manufactured by Alcon Laboratories, Inc). Temperature at the incision site was measured with a sheathed thermocouple Model TSC-K0.3 manufactured
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by Toa Electric Co, Ltd, and a thermometer Model AR5757-F00 manufactured by Chino Co, Ltd. We created a corneal incision in the postmortem porcine eye using a 19 gauge (1.4 mm) MVR. We also used the MVR to create a tunnel in the cornea above the incision and parallel to it. We inserted the thermocouple electrode of the thermometer through that tunnel, and performed 3 measurements of temperature elevation at the corneal incision during ultrasound oscillation with the phaco tip fully occluded (Fig. 33.1). We used a clamp to close the aspiration tube so that aspiration pressure was 0 mmHg during ultrasonic wave generation. We inserted a sleeveless 20 gauge Kelman microtip through the 19 gauge incision and a 20 gauge infusion cannula through the corneal side port. The phaco tip was pressed against the incision, and ultrasound waves were generated continuously for 2 minutes at 80 percent US power. Our results showed a mean temperature elevation of 8.4°C. At no time during the procedure did the temperature at the incision site exceed 40°C, and no thermal burn was observed (Fig. 33.2B).
FIGURE 33.1 Method for measuring temperature at the incision site. The thermocouple is inserted into a tunnel created in the cornea above the incision site, and temperature at the incision site is measured with US in operation
FIGURES 33.2A AND B Using a thermometer to measure temperature at
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the incision site in postmortem porcine eyes. Phaco machine setting: Aspiration port occluded (aspiration pressure: 0 mmHg). US power: 80%, US duration: 2.0 min continuous. (A left) A 20 gauge Kelman U/S tip with the infusion sleeve was inserted through a 3.0 mm incision, and US were operated. Temperature at the incision site rose only slightly while the tip was kept from pressing on the incision wall. But, once the tip was pressed against the incision wall during US operation, the temperature at the incision site rose significantly and a thermal burn developed. (B right) A 20 gauge Kelman U/S tip without the infusion sleeve was inserted through a 19 gauge incision, and US were operated. Temperature did not rise at the incision site even when the tip was pressed against the incision, and no thermal burn developed When the phaco tip is not fully occluded in PEA, the tip lumen and outer wall are bathed in infusion solution, so that even when friction develops there is a sufficient flow of infusion solution to cool the tip. However, in phacoemulsification with full occlusion the infusion solution is ordinarily unable to circulate within the phaco tip, so the amount of infusion solution in contact with the outer wall of the tip is limited to the volume of solution passing through the incision site. During fully occluded nucleofractis with a phaco tip equipped with an infusion sleeve, there is a decrease in the volume of infusion solution flowing around the tip. If the tip should press against the incision wall under these circumstances, the infusion solution may not provide sufficient cooling to compensate for the friction heat generated by the tip and sleeve. This can result in the development of thermal burn at the incision site (Figs 33.2A and 33.3A). However, when using a sleeveless phaco tip in an incision which is slightly larger than the tip itself, there is still considerable leakage of infusion solution through the incision site even during fully occluded phacoemulsification when the tip may be moved in multiple directions and pressed against the incision in order to emulsify the nucleus. This leakage of infusion solution provides sufficient cooling of any friction heat which may develop between the tip and the surrounding tissue, making it possible to emulsify and aspirate the nucleus
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without the occurrence of thermal burn and without resorting to Teflon-coated phaco tips or ultrasonic wave-control technology (Fig. 33.3B). By implementing this technique, thermal burn is less likely to occur when using a sleeveless tip than when using a tip equipped with the infusion sleeve. When we perform bimanual PEA, one of the main points in our surgical technique involves the use of an incision which is 1 gauge larger than the outer diameter of the phaco tip. This means that the incision for a 20 gauge phaco tip is made using a 19 gauge (1.4 mm) MVR, and for a 21 gauge phaco tip we used a 20 gauge (1.2 mm) MVR. The slight space between the phaco tip and the incision wall prevents deformation and injury at the incision site due to movement of the phaco tip. Tools for Successful Bimanual PEA: The 20 Gauge Irrigating Chopper (Fig. 33.4) The goal of bimanual PEA is to remove the nucleus through the smallest incision possible. In addition, it is desirable to use only a single corneal side port,
FIGURES 33.3A AND B Flow dynamics of infusion solution around the phaco tip when the opening of the tip was closed during occlusion mode. (A left) Emulsification and aspiration following insertion of a sleeved phaco tip through a 3.0 mm incision. Because the sleeve is deformed by contact with the incision, leakage volume through the incision is low. During phaco tip fully occluded in PEA, the flow of infusion solution around the phaco tip within the infusion sleeve is also low. When the phaco tip pressed against the incision wall, friction heat develops
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between the tip and the sleeve. Because there is insufficient infusion solution flowing around the tip to provide cooling, the heat is transmitted to tissues at the incision site. Thermal burn develops at the incision. (B right) Emulsification and aspiration following insertion of a sleeveless 20 gauge phaco tip through a 19 gauge (1.4 mm) incision. Because the phaco tip is not deformed by passage through the incision, there is space between the tip and the incision. Thus, the maximum possible volume of infusion solution is available to flow around the tip, providing cooling for any friction between the tip and the incision tissue. No thermal burn develops at the incision site and to make that port as small as possible also. Creating a third incision for the nucleofractis hook would run counter to the objectives of this surgical technique. With that in mind, we experimented with a bend in the tip of the infusion cannula. This resulted in the production of hooked infusion cannulae having nearly the same shape as conventional nucleofractis hooks. The Tsuneoka Irrigating Hook and the Tsuneoka Irrigating Chopper are manufactured by American Surgical Instruments Corporation (ASICO). When using the infusion cannula as a hook or chopper, considerations of intraocular operability dictate that instrument size not exceed 20 gauge. However, an ordinary cannula having a 20 gauge outer diameter would have an inner diameter of only 0.6 mm, making it difficult to guarantee
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FIGURE 33.4 The 20 gauge irrigation cannula with nucleofractis hook. A cannula was prepared having an outer diameter of 0.9 mm and an inner diameter of 0.7 mm, with large aperture at the tip. The cannula walls were made thinner to ensure adequate flow of infusion solution. This cannula, manufactured by ASICO Co, Ltd, is an essential tool for use in the procedure described here adequate infusion volume. With the infusion bottle at a height of 110 cm, an inner diameter of 0.6 mm would permit a flow volume of only 38 mL/min. This is not enough to sustain anterior chamber depth during surgery. We thus reduced the thickness of the infusion cannula wall to yield an inner diameter of 0.70 mm. The modified cannula provides a flow rate of 50 mL/min when the infusion bottle is raised to 110 cm. The hook at the tip of this cannula is shaped to provide excellent operability during emulsification and aspiration. Stable anterior chamber depth is maintained during PEA, and the hook works well in a variety of nucleofractis procedures. Equipment for Safer Bimanual PEA: The GFX Unit and VGFI Tubing (Fig. 33.5) In order to safely perform this surgery, it is important to increase the depth of the anterior chamber during emulsification and aspiration. In cases where destabilization of anterior chamber depth occurs during PEA even with the infusion bottle elevated to 110 cm or higher, it is advisable to increase the flow rate by applying pressure to the infusion bottle. During lens extraction we use a GFX fluid-gas exchanger, manufactured by Alcon Laboratories, Inc, with vented gas forced infusion (VGFI) tubing. Applying a pressure of 10 mmHg
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FIGURES 33.5A AND B GFX (Gas Fluid Exchange) equipment and VGFI (Vented Gas Forced Infusion) tube an air pump of GFX equipment (A) creates pressurized air, and VGFI tubing (B) delivers it to the infusion bottle. Fluid from the infusion bottle creates the same pressure and improves anterior chamber stability of patient eye. Infusion flow rate can be automatically controlled with the GFX air pump without raising or lowering the bottle to the infusion bottle has the same effect as raising the bottle an additional 13 cm, and makes it possible for us to increase the infusion flow to the specific extent required. Agarwal and colleagues5 also use the technique of applying pressure to the infusion bottle in order to stabilize anterior chamber depth.
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Clinical Results of Ultrasmall Incision Cataract Surgery Using PEA Results from our experiments indicated that thermal burn could be prevented by obtaining
FIGURE 33.6A A temporal corneal incision is made using a 19 guage MVR sufficient leakage through the incision, and that a hooked infusion cannula (the Tsuneoka Irrigating Hook, manufactured by ASICO) can be used to emulsify and aspirate nuclei by bimanual nucleofractis while maintaining stable anterior chamber depth. In October 1999 we began applying these procedures to ultrasmall incision phaco surgery in human patients. Procedures for Ultrasmall Incision Bimanual Phaco Surgery6 After the eye is anesthetized, we make an incision from the temporal clear cornea into the anterior chamber. We use a 19 gauge MVR blade for a 20 gauge small tip or a 20 gauge blade for a 21 gauge microtip (Fig. 33.6A). The incision is approximately 0.9 mm in length. We also create the infusion side port at a desirable location on the clear cornea, using a 20 gauge MVR blade (Fig. 33.6B). Sitting at the patient’s head, the surgeon positions the side port at eleven O’clock for the left eye or at one O’clock for the right eye. Injecting a viscoelastic material into the anterior chamber, we use a 26 gauge needle to perform continuous curvilinear capsulorrhexis (CCC) with a diameter of approximately 5.0 mm, and then initiate hydrodissection. In order to prevent an abrupt rise in anterior chamber pressure, it is important to press the base of the hydrodissection
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FIGURE 33.6B A side port for irrigation is made at 1 O’clock in the right eye using a 20 gauge MVR needle firmly against the lower side of the incision so that excess fluid can leak out of the incision while injection is in process. We insert the Tsuneoka Irrigating Hook through the side port and the sleeveless phaco tip through the temporal corneal incision, and emulsify and aspirate the lens while using the tip of the cannula for nucleofractis (Fig. 33.6C). When we are working on the right eye we hold the irrigating hook in the left hand and the ultrasound probe in the right hand, and when working on the left eye we do the reverse, with the irrigating hook in the right hand and the ultrasound probe in the left hand. We use bimanual nucleofractis when emulsifying and aspirating the nucleus. Depending on nucleus hardness, we use choose between the divide and conquer, quick chop (karate chop), or crater divide and conquer methods (Fig. 33.6D). Safe PEA requires that stable anterior chamber depth be maintained during surgery to prevent collapse of the anterior chamber, and that scattering of nuclear fragments be avoided. In order to maintain anterior chamber depth, a careful balance must be maintained between the settings for side port infusion and for phaco tip aspiration. We adjust the height of the infusion bottle to provide a side port infusion flow rate of at least 50 mL/min when using a 20 gauge phaco tip, and an infusion flow rate of 40 mL/min for a 21 gauge phaco tip. It is also important to set the parameters of the PEA
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FIGURE 33.6C A 20 gauge sleeveless phaco tip is inserted into the anterior chamber through a 19 gauge incision and a 20 gauge Tsuneoka irrigating hook is inserted through a 20 gauge side port
FIGURE 33.6D PEA is performed using bimanual nucleofractis technique machine appropriately, particularly the values for aspiration flow rate and maximum aspiration pressure. The settings used at our institution are shown in Table 33.1. Infusion flow may not keep up with aspiration flow if aspiration is continued when there are no nuclear particles to be captured by the aspiration port on the phaco tip. Surgery can be performed more safely if aspiration is turned off when it is not needed. Prevention of nuclear fragment dispersion is an important point for improving PEA safety. It is important to turn the ultrasound power as low as is feasible in order to reduce the extent of endothelial injury from nucleus “kick”. Great care must also be taken when using the nucleofractis hook to handle nuclear fragments.
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TABLE 33.1 Parameters used by phaco machine type Size of phaco tip Legacy 20000 (Alcon) Sovereign (Allergan) 24000 (Nidek)
20 gauge
Pulser (Optikon)
21 gauge
20 gauge 20 gauge
Flow rate
Maximum aspiration pressure
25 ml/min 28 ml/min 23 ml/min 30 ml/min
Height of irrigation bottle
250 mmHg
120 cm
280 mmHg
100 cm
200 mmHg
100 cm
300 mmHg
90 cm
FIGURE 33.6E Residual cortex is aspirated using a sleeveless I/A tip or 23 gauge bimanual I/A tip through the side port FIGURE 33.6 Ultrasmall incision (1.4 mm) bimanual phaco surgery Aspiration of the residual cortex through an ultra-small incision can be performed using a sleeveless I/A tip or a 23 gauge aspiration cannula through the side port (Fig. 33.6E). In cases where it is difficult to remove endothelial fragments below the incision line, the positions of the infusion cannula and the aspiration tube can be reversed so that this procedure can be performed safely and effectively.
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Perioperative and Postoperative Results Results of Surgery Since October 1999, ultrasmall incision PEA surgery has been performed at the Jikei University School of Medicine Hospital by 3 surgeons on 757 eyes. Mean operating time is 8 minutes 42 seconds, comparable to the time required for conventional cataract IOL surgery by PEA. Approximately 90 mL of infusion solution is required per surgery, slightly more than that for conventional procedures. Both operating time and amount of infusion solution increase with greater nucleus hardness. Incidence of Perioperative Complications Among the patients studied, posterior capsular rupture occurred without vitreous prolapse in 3 eyes (0.4%), and with vitreous prolapse in 6 eyes (0.8%). However, none of these incidents of posterior capsular rupture were caused by use of this technology, and all were treated successfully with uneventful recovery. Nuclei having a hardness of grade 4 or above (Emery-Little classification) were encountered in 37 eyes. No thermal burn developed in any of these cases, even though the use of ultrasound was prolonged. Postoperative Course Slight iris injury developed in 6 eyes (0.8%) which showed preoperative shallow anterior chamber and in 6 eyes (0.8%) with small pupils. There were no other notable postoperative complications. Postoperative follow-up was continued for at least 3 months in 312 eyes. Greater nuclear hardness was associated with higher rates of reduction in endothelial cell density (4.1±12.3% for nuclei of hardness grade 1 or 2, 10.8±16.0% for grade 3, and 16.8±12.6% for grade 4 and above). However, none of these results differed greatly from those for conventional techniques. IOL Insertion through an Ultrasmall Incision New IOLs for Use with Ultrasmall Incisions In current cataract surgery even though the cataract can be removed through an incision of 1.2 to 1.4 mm, there are no commercially available IOLs which can be inserted through such a small incision, so at present the incision must be enlarged to 2.8 to 4.1 mm before the IOL can be inserted. However, several companies are developing acrylic soft lenses which are thinner than the current commercially available foldable IOLs, and in the near future we can expect to see the marketing of IOLs which can be inserted through an incision of 1.4 mm or less. At present Kanellopoulos and colleagues have reported the insertion through a 1.6 mm incision of a dehydrated acrylic IOL manufactured by Acri Tec GmbH (Germany), and
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Agarwal and colleagues have reported insertion through a 0.9 mm incision of a hydrophilic acrylic IOL manufactured by ThinOptX, Inc (USA). I have also experimented with the ThinOptX IOL, but the lens is difficult to roll, and we believe that an insertion system needs to be developed in order to enable the routine insertion of this lens through incisions of predetermined size. Also, it remains to be seen whether these new ultrasmall incision IOLs will provide satisfactory visual performance, and whether they will maintain satisfactory long-term stability within the eye. Techniques for Inserting Currently Available IOLs through Smaller Incisions (Fig, 33.7) By modifying the commercially available Alcon injector and cartridge (Monarch IIC), we have succeeded in inserting Alcon acrylic soft lenses having an optic diameter of 5.5 mm (the AcrySof
FIGURE 33.7A The initial corneal incision is widened to 2.2. mm
FIGURE 33.7B AcrySof® SA30AL is inserted through a 2.2 mm incision
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SA30AL and MA30BA) through a 2.2 mm incision (Fig. 33.7A). We set the AcrySof® SA30AL (Fig. 33.7B) or MA30BA (Fig. 33.7C) in the Monarch IIC cartridge, place the cartridge loaded with the IOL into the injector, and press the plunger forward while ensuring that the pressure is applied to the optic portion of the lens. During insertion, the front tip of the cartridge is inserted into the corneal incision so that it presses against the incision wall. The cartridge tip does not enter the anterior chamber. Immediately before inserting the lens, we instruct the patient to look steadily in the direction of the incision. With the
FIGURE 33.7C AcrySof® MA30BA is inserted through a 2.2 mm incision
FIGURE 33.7D The final incision size is measured using Tsuneoka ultrasmall inner caliper cartridge tip elevating the inner edge of the corneal incision and pressing down on the outer edge, we slowly press the injector plunger forward. With a hook inserted through the side port, and making sure that the eye is not turned inward toward the nose, we continue to press the plunger forward without decreasing the downward pressure of the
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cartridge on the incision, until the entire optic is within the anterior chamber. When using the single piece SA30AL lens, we insert the trailing loop into the eye along with the optic, but when using the three-piece MA30B A lens we leave the trailing loop outside the eye when we withdraw the cartridge,
FIGURE 33.7E The incision self-seals easily FIGURE 33.7 The acrylic foldable IOL of which optic diameter is 5.5 mm (AcrySof® SA30AL or MA30BA) is inserted using the injector
FIGURE 33.8 5.5 mm optic acrylic IOL is implanted through 2.2 mm incision and then use an instrument such as a hook to insert the trailing loop into the capsular bag. After verifying the final incision width with a Tsuneoka micro incision inner caliper (Fig. 33.7D), we aspirate the viscoelastic material and allow the incision to self seal.
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The AcrySof® MA30BA and SA30AL lenses, currently the most widely used hydrophobic acrylic lenses in the world, are normally inserted through an incision of 3.0 mm or above. Our method makes it possible to insert these lenses through a 2.2 mm incision (Fig. 33.8), which increases the significance of ultrasmall incisions for lens removal. In our experience this lens removal surgery can be most effectively performed by bimanual PEA using a sleeveless phaco tip. References 1. Kanellopoulos AJ, Dodick JM, Brrauweiler P: Dodick photolysis for cataract surgery. Ophthalmology 106:2197–2202, 1999. 2. Tsuneoka H, Shiba T, Takahashi Y: Feasibility of ultrasound cataract surgery with a 1.4 mm incision. J Cataract Refractive Surg 27:934–40, 2001. 3. Hara T, Hara T: Clinical results of phacoemulsification and complete in-the-bag fixation. J Cataract Refractive Surg 13: 279–86, 1987. 4. Agarwal A, Agarwal A, Agarwal S et al: Phakonit: Lens removal through a 0.9 mm corneal incision. J Cataract Refractive Surg 27:1548–52, 2001. 5. Agarwal S, Agarwal A, Sachdev MS, et al: Air pump to prevent surge. In: Agarwal Set al (Eds): Phacoemulsification, Laser Cataract Surgery and Foldable IOLs (2nd ed). Jaypee Brothers: New Delhi, 2000. 6. Tsuneoka H, Shiba T, Takahashi Y: Ultrasonic phacoemulsification using a 1.4 mm incision: Clinical results. J Cataract Refractive Surg 28:81–86, 2002.
34 Corneal Topography in Phakonit with a 5 mm Optic Reliable IOL Amar Agarwal, Soosan Jacob Athiya Agarwal, Sunita Agarwal Introduction Cataract surgery and intraocular lenses (IOL) have evolved greatly since the time of intracapsular cataract extraction and the first IOL implantation by Sir Harold Ridley1. The size of the cataract incision has constantly been decreasing from the extremely large ones used for ICCE to the slightly smaller ones used in ECCE to the present day small incisions used in phacoemulsification. Phacoemulsification and foldable IOLs are a major milestone in the history of cataract surgery. Large postoperative against-the-rule astigmatism were an invariable consequence of ICCE and ECCE. This was minimized to a great extent with the 3.2 mm clear corneal incision used for phacoemulsification but nevertheless some amount of residual postoperative astigmatism was a common outcome. The size of the corneal incision was further decreased by Phakonit2–4 a technique introduced for the first time by one of us (Am.A), which separates the infusion from the aspiration ports by utilizing a sleeveless phaco probe and an irrigating chopper. The only limitation to thus realizing the goal of astigmatism neutral cataract surgery was the size of the foldable IOL as the wound nevertheless had to be extended for implantation of the conventional foldable IOLs. Rollable IOL With the availability of the ThinOptX® reliable IOL (Abingdon, VA, USA), that can be inserted through sub-1.4 mm incision, the full potential of Phakonit could be realized. A special ultrathin 5 mm optic rellable IOL was designed by one of us (Am.A) to make the incision size smaller. Surgical Technique Five eyes of 5 patients underwent Phakonit with implantation of an ultrathin 5 mm optic reliable IOL at Dr Agarwal’s Eye Hospital and Eye Research Center, Chennai, India. The name PHAKONIT has been given because it shows phacoemulsification (PHAKO) being done with a needle (N) opening via an incision (I) and with the phaco tip (T). A specially designed keratome, an irrigating chopper, a straight blunt rod and a 15
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degree standard phaco tip without an infusion sleeve form the main prerequisites of the surgery. Viscoelastic is injected with a 26 gauge needle through the presumed site of side port entry This inflates the chamber and prevents its collapse when the chamber is entered with the keratome. A straight rod is passed through this site to achieve akinesia and a clear corneal temporal valve is made with the keratome (Fig. 34.1A). A continuous curvilinear capsulorhexis (CCC) is performed followed by hydrodissection and rotation of the nucleus. After enlarging the side port a 20 gauge irrigating chopper connected to the infusion line of the phaco machine is introduced with foot pedal on position 1. The phaco probe is connected to the aspiration line and the phaco tip without an
FIGURE 34.1A Clear corneal incision made with a specialized keratome. Note the left hand has a straight rod to stabilize the eye
FIGURE 34.1B Agarwal’s Phakonit irrigating chopper and sleeveless phaco probe inside the eye infusion sleeve is introduced through the main port (Fig. 34.1B). Using the phaco tip with moderate ultrasound power, the center of the nucleus is directly embedded starting from the superior edge of rhexis with the phaco probe directed obliquely downwards towards
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the vitreous. The settings at this stage are 50 percent phaco power, flow rate 24 ml/min and 110 mm Hg vacuum. When nearly half of the center of nucleus is embedded, the foot pedal is moved to position 2 as it helps to hold the nucleus due to vacuum rise. To avoid undue pressure on the posterior capsule the nucleus is lifted slightly and with the irrigating chopper in the left hand the nucleus chopped. This is done with a straight downward motion from the inner edge of the rhexis to the center of the nucleus and then to the left in the form of an inverted L shape. Once the crack is created, the nucleus is split till the center. The nucleus is then rotated 180° and cracked again so that the nucleus is completely split into two halves. With the previously described technique, 3 pie-shaped quadrants are created in each half of the nucleus. With a short burst of energy at pulse mode, each pie-shaped fragment is lifted and brought at the level of iris where it is further emulsified and aspirated sequentially in pulse mode. Thus the whole nucleus is removed. Cortical wash-up is then done with the bimanual irrigation aspiration technique.
FIGURE 34.1C The reliable iol inserted through the incision
FIGURE 34.1D viscoelastic removed using bimanual irrigation aspiration probes
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The lens is taken out from the bottle and placed in a bowl of BSS solution of approximately body temperature to make the lens pliable. It is then rolled with the gloved hand holding it between the index finger and the thumb. The lens is then inserted through the incision carefully (Fig. 34.1C). The teardrop on the haptic should be pointing in a clockwise direction so that the smooth optic lenticular surface faces posteriorly. The natural warmth of the eye causes the lens to open gradually. Viscoelastic is then removed with the bimanual irrigation aspiration probes (Fig. 34.1D). Figure 34.1 shows different steps of the surgery.
FIGURE 34.2 Comparison of pre- and postoperative BCVA
FIGURE 34.3 Mean astigmatism over time Topographic Analysis and Astigmatism The preoperative best corrected visual acuity (BCVA) ranged from 20/60 to 20/200. The mean preoperative astigmatism as detected by topographic analysis was 0.98 D±0.62 D (range 0.5 to 1.8 D). The postoperative course was uneventful in all cases. The IOL was well-centered in the capsular bag. There were no corneal burns in any of the cases. Four eyes had a best-corrected visual acuity of 20/30 or better. One eye that had dry ARMD showed an improvement in BCVA from 20/200 to 20/60. Figure 34.2 shows a comparison of the pre-and postoperative BCVA. The mean astigmatism on postoperative day 1 on topographic analysis was 1.1±0.61 D (range 0.6 to 1.9 D) as compared to 0.98 D±0.62 D (range 0.5 to 1.8 D) preoperatively. The mean astigmatism was 1.02±0.64 D (range 0.3 to 1.7 D) by 3 months postoperatively. Figures 34.3 and 34.4 shows mean astigmatism over time. Figures 34.5A and B show a comparison of the astigmatism over the pre- and postsurgical period.
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Discussion Cataract surgery has witnessed great advancements in surgical technique, foldable IOLs and phaco TIME EYES MEAN Std. Dev. MINIMUM MAXIMUM PREOP. 5 POD 1 5 POD 7 5 POD 30 5 POD 90 5
0.98 11 1.12 1.08 1.02
0.62 0.61 0.58 0.62 0.64
0.5 0.6 0.5 0.5 0.3
1.8 1.9 1.7 1.8 1.7
FIGURE 34.4 Table showing pre- and postoperative mean astigmatism
FIGURE 34.5A Comparison of preand postoperative day 1 cylinder
FIGURE 34.5B Comparison of 1 day postoperative and 3 months postoperative astigmatism technology. This has made possible easier and safer cataract extraction utilizing smaller incision. With the advent of the latest IOL technology which enables implantation through ultrasmall incisions, it is clear that this will soon replace routine phacoemulsification through the standard 3.2 mm incisions. The ThinOptX® IOL design is based on the Fresnel principle. Flexibility and good memory are important characteristics of the lens. It is manufactured from hydrophilic acrylic materials and is available in a range from −25 to +30 with the lens thickness ranging from 30 µm up to 350 µm. One of the authors (Am.A) has modified the lens further by reducing the optic size to 5 mm to go through a smaller incision. The lens is now undergoing clinical-trials in Europe and the USA. In this study, no intraoperative complications were encountered during CCC, phacoemulsification, cortical aspiration or IOL lens insertion in any of the cases. The
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mean phacoemulsification time was 0.66 minutes. Previous series by the same authors showed more than 300 eyes where cataract surgery was successfully performed using the sub-1 mm incision.3 Our experience and that of several other surgeons suggests that with existing phacoemulsification technology, it is possible to perform phacoemulsification through ultrasmall incisions without significant complications.2–6 In a recent study from Japan, Tsuneoka and associates6 used a sleeveless phaco tip to perform bimanual phacoemulsification in 637 cataractous eyes. All cataracts were safely removed by these authors through an incision of 1.4 mm or smaller that was widened for IOL insertion, without a case of thermal burn and with few intraoperative complications. Furthermore, ongoing research for the development of laser probes7,8 cold phaco, and microphaco confirms the interest of leading ophthalmologists and manufacturers in the direction of ultrasmall incisional cataract surgery (Fine IN, Olson RJ, Osher RH, Steinert RF. Cataract technology makes strides. Ophthalmology Times, December 1, 2001, 12–15). The postoperative course was uneventful in all the cases. The IOL was well-centered in the capsular bag. There were no significant corneal burns in any of the cases. Final visual outcome was satisfactory with 4 of the eyes having a BCVA of 20/30 or better. One eye that had dry ARMD showed an improvement in BCVA from 20/200 to 20/60. Thus the lens was found to have satisfactory optical performance within the eye. In our study, the mean astigmatism on topographical analysis was 0.98± 0.62 D (range 0.5 to 1.8 D) preoperatively, 1.1±0.61 D (range 0.6 to 1.9 D) on postoperative day 1 and 1.02 ± 0.64 D (range 0.3 to 1.7 D) by 3 months postoperatively. Figures 34.5A and B showing a comparison of the pre- and postoperative astigmatism indicate clearly that Phakonit with an ultra-thin 5 mm reliable IOL is virtually astigmatically neutral. Figures 34.6A and B depicting the topography comparison in different surgical periods show clearly the virtual astigmatic neutrality of the procedure and stability throughout the postoperative course. There is an active ongoing attempt to develop newer IOLs that can go through smaller and smaller incisions. Phakonit ThinOptX® modified ultrathin rollable IOL is the first prototype IOL which can go through sub-1.4 mm incisions. Research is also in progress to manufacture this IOL using hydrophobic acrylic biomaterials combined with squareedged optics to minimize posterior capsule opacification.
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FIGURES 34.6A AND B Topographical comparison during different surgical periods
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Conclusion Phakonit with an ultrathin 5 mm optic reliable IOL implantation is a safe and effective technique of cataract extraction, the greatest advantage of this technique being virtual astigmatic neutrality. References 1. Apple DJ, Auffarth GU, Peng Q, et al: Foldable intraocular lenses: Evolution, clinicopathologic correlations, complications. Thorofare, NJ, Slack, Inc., 2000. 2. Agarwal A, Agarwal A, Agarwal S et al: Phakonit: Phacoemulsification through a 0.9 mm corneal incision. J Cataract Refract Surg 27:1548–52, 2001. 3. Agarwal A, Agarwal A, Agarwal A et al: Phakonit: Lens removal through a 0.9 mm incision. (Letter). J Cataract Refract Surg 27:1531–32, 2001. 4. Agarwal A, Agarwal S, Agarwal A: Phakonit and laser phakonit: Lens removal through a 0.9 mm incision. In: Agarwal S, Agarwal A, Sachdev MS, et al: (Eds): Phacoemulsification, Laser Cataract Surgery and Foldable IOLs. New Delhi, India: Jaypee Brothers Medical Publishers (P) Ltd, 204–16, 2000. 5. Tsuneoka H, Shiba T, Takahashi Y: Feasibility of ultrasound cataract surgery with a 1.4 mm incision. J Cataract Refract Surg 27:934–40, 2001. 6. Tsuneoka H, Shiba T, Takahashi Y: Ultrasonic phacoemulsification using a 1.4 mm incision: Clinical results. J Cataract Refract Surg 28:81–86, 2002. 7. Kanellpoupolos AJ: A prospective clinical evaluation of 100 consecutive laser cataract procedures using the Dodick photolysis neodymium: Yittrium-aluminum garnet system. Ophthalmology 108:1–6, 2001. 8. Dodick JM: Laser phacolysis of the human cataractous lens. Dev Ophthalmol 22:58–64, 1991.
35 Phakonit with the Acritec IOL Amar Agarwal History On August 15th 1998 the authors (Amar Agarwal) performed the first 1 mm cataract surgery by a technique called PHAKONIT.1,2 Today companies have started manufacturing IOL’s that can pass through ultra-small incisions of 1.5 mm or less. One such IOL is the Acri. Lyc IOL made by the Acritec company (Berlin, Germany). Terminology The name PHAKONIT has been given because it shows phaco (PHAKO) being done with a needle (N) opening via an incision (I) and with the phako tip (T). This shows phaco done with Needle Incision Technology. Incision In the first step a needle with viscoelastic is taken and pierced in the eye in the area where the side port has to be made (Fig. 35.1). A special keratome (Micro Surgical Technology, USA) is then used to create an incision of 1.2 mm (Fig. 35.2). The viscoelastic is then injected inside the eye. Rhexis The rhexis is then performed. This is done with a needle (Fig. 35.3). In the left hand a straight rod is held to stabilize the eye. The advantage of this is that the movements of the eye can get controlled as one is working without any anesthesia. Hydrodissection is performed and the fluid wave passing under the nucleus checked.
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FIGURE 35.1 A 26 gauge needle with viscoelastic making an entry in the area where the side port is. This is for entry of the irrigating chopper
FIGURE 35.2 Clear corneal incision made with the keratome. Note the left hand has a rod to stabilize the eye as the case is done without any anesthesia. These instruments are made by Katena (USA)
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FIGURE 35.3 Rhexis started with a needle Phakonit After enlarging the side port a 20 gauge irrigating chopper connected to the infusion line of the phaco machine is introduced with foot pedal on position 1. The phaco probe is connected to the aspiration line and the phaco tip without an infusion sleeve is introduced through the incision (Fig. 35.4). Using the phaco tip with moderate ultrasound power, chopping of the nucleus is done (Fig. 35.5). The whole nucleus is finally removed (Fig. 35.6). Note in Figure 35.6 no corneal burns are present. Cortical wash-up is done with the bimanual irrigation aspiration technique (Figs 35.7 and 35.8). Acritec IOL The Acry.Lyc IOL is manufactured by the Acri.Tec company in Berlin, Germany. This lens is a sterile foldable intraocular lens made of hydrophobic acry late. The intraocular lens consists of highly purified biocompatible hydrophobic acrylate with chemically bonded UV-absorber. It is a single piece foldable IOL like a plate-haptic IOL. The lens is
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FIGURE 35.4 Phakonit irrigating chopper and phako probe without the sleeve inside the eye
FIGURE 35.5 Phakonit started. Note the phako needle in the right hand and an irrigating chopper in the left hand. Phakonit being performed. Note the crack created by karate chopping. The assistant continuously irrigates the
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phaco probe area from outside to prevent corneal burns
FIGURE 35.6 Phakonit completed. Note the nucleus has been removed and there are no corneal burns
FIGURE 35.7 Bimanual irrigation aspiration started
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sterilized by autoclaving. The lens comes in a sterile vial, filled with water and wrapped in a sterile pouch.
FIGURE 35.8 Bimanual irrigation aspiration completed Lens Loading Technique To remove the IOL one should open the Medipeel pouch at the defined spot. The lens vial or bottle (Fig. 35.9) is then taken out and placed on the sterile tray. The lens is like a plate haptic IOL (Fig. 35.10). The next step is to prepare the injector (Fig. 35.11). First of all the injector tip is fitted with a sponge tip (Figs 35.12 and 35.13) which comes with the cartridge. This will prevent the injector tip from damaging the lens while inserting it inside the eye. The lens is then taken out from the bottle/vial. The lens is then held with a forceps. The lens is then placed in the cartridge (Fig. 35.14). Viscoelastic is injected in the cartridge and once the flanges of the IOL are in the groove of the cartridge the cartridge is closed and then inserted in the injector (Fig. 35.15). Once the cartridge is fixed onto the injector the injection of the lens is done by the spongy tip (Fig. 35.16) till one can see the lens coming into the nozzle of the cartridge (Fig. 35.17). Lens Insertion Technique After the Phakonit procedure is completed, the incision is increased to 1.5 mm. Then the tip of the
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FIGURE 35.9 The Acri. Lyc foldable IOL in the sterile vial
FIGURE 35.10 The Acri. Lyc foldable IOL cartridge is kept at the site of the incision (Fig. 35.18). Remember the cartridge is not inserted inside the anterior chamber. Now, the lens is gradually inserted through the incision (Fig. 35.19).
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FIGURE 35.11 The Acri. Tec injector
FIGURE 35.12 The soft spongy tip being fixed onto the tip of the Acri. Tec injector
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FIGURE 35.13 Tip of the injector with the spongy tip. This will prevent any damage to the lens when inserting the lens
FIGURE 35.14 The Acri. Lyc IOL placed in the cartridge
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FIGURE 35.15 The cartridge fixed onto the injector
FIGURE 35.16 The tip of the injector with the spongy tip ready in place to push the IOL
FIGURE 35.17 The IOL coming out into the nozzle of the cartridge
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FIGURE 35.18 The tip of the nozzle of the cartridge is at the incision site but not inside the anterior chamber
FIGURE 35.19 The IOL inserted through a 1.5 mm incision
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FIGURE 35.20 The IOL being inserted inside the bag One can watch the lens unfolding inside the capsular bag. The inferior haptic goes into the bag (Fig. 35.20) and the superior haptic is gradually tucked inside the capsular bag. Viscoelastic is then removed with the Bimanual irrigation aspiration probes (Fig. 35.21).
FIGURE 35.21 Viscoelastic removed using bimanual irrigation aspiration probes
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Summary With the advent of Phakonit the size of the incision has drastically reduced. Now with more companies moving into manufacturing ultra-small incision IOL’s which can pass through 1.5 mm incisions or less the advantage of Phakonit becomes even more. With time more surgeons will move into this technology thus benefiting more patients. References 1. Agarwal S, Agarwal A, Sachdev MS, et al: Phacoemulsification, Laser Cataract Surgery and Foldable IOL’s (2nd edn) New Delhi: Jaypee Brothers, 2000. 2. Boyd BF, Agarwal S, Agarwal A, et al: Lasik and Beyond Lasik; Highlights of Ophthalmology; Panama, 2000.
Section VII Laser Cataract Surgery 36. Laser Phaco Cataract Surgery 37. Erbium-YAG Laser Cataract Surgery 38. Cataract Surgery with Dodick Laser Photolysis
36 Laser Phaco Cataract Surgery Sunita Agarwal J Agarwal, T Agarwal Introduction From the time of its inception in 1949 with Meyer Schwickerath in Germany the concept of lasers has caught the imagination of child and adult alike, scientist and the public in general. Science fiction movies are made with the concept of the laser as the ultimate weapon against all evil. Little wonder then as eye surgeons we are always trying to better the techniques of cataract removal over the years, thus today with lasers we find ourselves equipped with one more wonderful tool in the armamentarium of the operating room. We are in the midst of a paradigm shift in cataract surgery today. We must either become a part of the shift or we will be blind-sided by it. Today, one of the latest developments in ophthalmology is the laser cataract surgical system. The laser cataract surgery system would entail less trauma and better rehabilitation of the patient. History Cataract the bane of old age has been known as a disease process to human civilization for many years. Earliest records of its treatment were carried out by Sushruta 500 BC the famous Indian surgeon who practiced a form of medicine called Dhanvantri. He used a needle with no anesthesia, through a bloodless route entered the eye through the cornea and dislodged the cataract. The needle would stick into the cataract like a lollipop and small movement of the cataract to and fro would break its zonular attachments. Then the cataract would be made to fall into the deep vitreous. This saved many a eye in that era and times, however many fell prey to the adversities of the posterior segment. Yet today we have come a full circle by bringing in the concept of no anesthesia, bloodless, painless, laser phaconit (needle surgery) cataract surgery. This idea of couching traveled the silk route into the Arab world and reached the far corners of Europe. However somewhere along the 11th century an Arabian scientist Ammar came up with the methodology of removing the cataract enbloc out of the eye. Thus, started the road of intracapsular cataract and extracapsular cataract extraction. For many years the cataract would need to be rippend before the surgeon would go to remove it. Somewhere along the last two centuries sutures came into being and cataract surgery became more and more safe where the eye and life were concerned. However it was the
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remarkable discovery by Sir Harold Ridley of PMMA pieces of plastic broken from the windshield of planes, lying insert in the eyes of pilots of the Royal Air Force during the Second World War. This led him to believe and rightly so that pieces of plastic could be permanently placed in the eye to replace the lost condensing power of the eye. Thus started the saga of intraocular lens in 1949. However it was the conception of the ultrasound power by Charles Kelman in 1970 that made it really possible to make cataract surgery as atraumatic experience as we see it today. It was also this ideology, which made industry look around and give us the foldable intraocular lens. With the last two decades research into the idea of lasers removing cataracts grew stronger and stronger. We had some surgeons carrying out Nd: YAG laser capsulotomy preoperatively over a slit lamp delivery and then taking the patient immediately to the operation theater to remove the cataract and replace with an intraocular lens. Around the latter part of the 80s a few patent applications were accepted for laser cataract surgery per se. Here Dr. Eichenbaum created history by teaming up with Paradigm Laser Photon and bringing out the first commercially available laser cataract surgery system.
FIGURE 36.1 Laser photon machine from paradigm (USA) It was the author’s (SA) good fortune to acquire such a machine way back in 1995 and with continuous efforts from the parent principal company and the experience handed over through patients, evolution of this methodology for cataract surgery has increased ever more. Laser Cataract Surgery At the time when I first got the laser photon machine from Paradigm (Fig. 36.1) all I could see was it was a powerful machine. The laser fiber optic actually could burn a hole in steel, thus I wondered if such a machine can make a hole in steel a cataract tissue would be child’s play for it.
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However, there were many barriers to this thinking and soon I realized that evolution of a better system was needed. The fluidics which make such an important part of cataract surgery today was in its infantile phase. We were actually holding vacuum levels at less than 100 mm of Hg and this was not fast enough to remove cataract tissue. The major problem that all high-energy source have is, even though they may disintegrate the tissue instantaneously they also have the repulsion to push away the piece from the aspirating porthole. Combating this element with another physical capacity of the laser being heat was another ball game altogether. Nd: YAG laser was carried to the tip of the probe through a fiberoptic and instilled inside the suction arena with a sleeve outside bringing in the fluids. The laser has the capacity to ablate solid tissue on coming into contact, to about 20 microns tissue space. However a small part of the tissue around this area of action would get caseated due to the high protein content, slow aspiration rate and high temperatures. This caseating mass would then plug the aspirating porthole and the surgery would have to wait till the mass was deluged. This kind of method continued for sometime until I realized this was not going to be effective enough. Another aspect of laser cataract surgery is due to the probe fashioned in the manner of a spoon. With the aspiration in the deep part of the spoon, occlusion was next to impossible. We had learned till then the cataract was to be divided and conquered, if occlusion was not possible then divide and conquer was not possible. So started our road of incorporating the laser with the ultrasound. The patents for this probe were filed that same year, because we had understood this was the wonderful link between ultrasound and lasers. This became the method of choice for tackling hard and soft cataracts alike. Today we are slowly moving away and away from ultrasound because we understand the endothelial damage in an already compromised cornea. Thus the increased interest in the laser that can remove the cataract with the ease of an irrigation aspiration handpiece yet the power of the ultrasound vibrating needle. We have much better fluidic control, our aspiration rates can touch 350 to 400 mm of Hg, and this allows the cataract to get sucked in before it has time to caseate on the tip. The laser is much better centered in the probe allowing all the laser energy to be targeted along the cataractous tissue. We have developed newer technologies for cataract removal without having to subject the cataract into a divide and conquer routine we are able to remove the cataract with a carouselling technique “Like each temple to its own deity and each monastery to its own monk so is each technique to its own master.” From the words of Jackie Chan, this relates so to in our advanced laser phaco techniques, where each surgeon has their own techniques. Pioneers For decades now we have known benefits of the ultrasound energy. Incorporated with Dr Kelmans path breaking in roads of using this energy for the removal of cataracts has indeed reduced rehabilitation of the cataract patient.1–7
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Four top ophthalmologists have been working independently on the system of developing a laser to help in cataract removal. The first has been Dr Daniel Eichenbaum from USA. It has been basically due to Dr Daniel Eichenbaum and Paradigm that the laser cataract removal system could be started. They have developed a machine called the Laser Photon. This laser photon uses the Yag laser for cataract removal. The second ophthalmologist Dr Jack Dodick introduced the use of the Yag: YLF laser for surgical cataract removal. A laser beam is a fiber-optically directed toward a titanium mirror target. The reflection produces waves of optical breakdown power, resulting in photoablation of the surface down to any depth desired. Succeeding generations of instrumentation for this technique have been modified and refined. The probes are getting thinner and thinner compared to a phacoemulsification tip. The third ophthalmologist is Dr Michael Colvard. The Erbium laser is being used by Michael Colvard to ablate ocular tissue and its advantage is that it has maximal absorption in water. When properly directed and mirrored, as in Dodick’s approach, the laser beam is kept away from the posterior pole and the retina. Safety seems to be built into reflected laser ablation, allowing ablation without thermal injury. In Colvard’s technique, the laser beam is placed directly in contact with the nucleus of the cataract for nonpercusssive cutting. By directing the beam much as one would use an eraser to wipe over the surface, the tip of the beam is directed over the ablation zone, causing optical breakdown just at the beam’s tip. The nuclear material is then removed with irrigation and an IOL is implanted.
FIGURE 36.2 Sunita Agarwal’s laser phaco probe The fourth ophthalmologist was from India—Dr Sunita Agarwal who designed a new probe which incorporates laser and ultrasound in the same pico second (Fig. 36.2). In 1995 we acquired our first laser machine for cataract surgery. Soon we realized the potential of capitalizing on both the energy sources together, something not thought of by any cataract surgeon at that time. And we developed a probe now capable of utilizing at the same pico second laser and ultrasound energies.
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Instrumentation An ordinary phaco unit would contain three functional elements, the phaco power delivered through a vibrating titanium needle of 900 microns diameter, aspiration through the needle, and irrigating fluid pump into the eye through a silicon sleeve. The laser unit consists of a key switch screwed into the laser head unit that allows the laser light to pass through a glass fiberoptic delivery and the aiming beam is also passed through the same system. This fiber is of 380 microns in diameter. The laser phaco probe developed by Sunita Agarwal is patent pending as the idea of incorporating laser with ultrasound in the removal of cataracts was first developed by us and after going through many experimentations and variations we
FIGURE 36.3 Comparison between a phaco probe and the laser phaco probe
FIGURE 36.4 Comparison between other companies’ and Sunita Agarwal’s laser phaco probe now plough the laser fiberoptic through the phaco probe making any phaco probe into a SA (Sunita Agarwal) laser phaco probe (Fig. 36.3).
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The instrumentation is thus in two parts. One is the Phaco part that most of us are accustomed too, and the second is the laser part. These may come from the same machine or from two different machines. The Sunita Agarwal Laser Phaco Probe All probes used before this (Fig. 36.4) were thus designed that used laser or ultrasound in the innermost circumferential ring, with aspiration and irrigation flowing on the outer ring. This was modified by special intermediary equipment that would allow that phacoemulsification machine to still function with a laser fiberoptic delivery system in its midst. Around this is the ultrasound waves pounding along with irrigation and aspiration flowing on the outside. Thus the whole system consists of a four-function probe. The use and utilization of both energy sources makes it easier for the cataract to be blasted out of the eye in shorter time span, with less energy sources used in the eye. The machine we used was the laser photon machine. Anatomy of Dr Sunita Agarwal Laser Phacoemulsification Probe The author has designed this patent pending SA laser phaco probe and it utilizes both, the laser to a maximum extent and ultrasound to a lesser extent for cataract removal. This probe can be developed by passing the laser fiberoptic through the aspiration end of a regular phaco probe. This version of the laser phaco probe gives the advantage of using the laser, ultrasound, irrigation and aspiration. Based on the ablation power of the laser of water containing tissues four main have been evaluated of which Nd: YAG has the lowest capacity for water absorption. It has been further qualified with being near perfect in effect and holds its place in the industry for over two decades. The laser beam is focused onto grades of high tensile glass fiberoptic which carry the same and release it on the cataractous tissue on contact and hence the name contact laser. The laser photoablates 20 microns of cataractous tissue on contact and liquefies a further 200 microns cataractous tissue around it. Comparison Let us compare the phaco probe with the laser phaco probe. There is a slight embarrassment to outflow using the laser fiberoptic (Fig. 36.6) in comparison with a phaco probe. This is because the phaco probe is of 900 microns. The laser probe is 380 microns. This is placed inside the phaco
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FIGURE 36.5 Phaco incision
FIGURE 36.6 Laser phaco incision probe. So we get only 520 microns of space left. Still the cataract is removed faster and much more safely. The laser has the capacity to photoablate 20 microns of tissue space in contact and another 200 microns is liquefied reducing the solid cataract into liquid and gas. The incision size is thus reduced as the phaco handpiece gets hot and can burn the corneal tissue (Fig. 36.5). We are able to perfom laser phaco in an incision of 2 mm (Fig. 36.6). The phaco incision in the cornea can get ragged with corneal burns. This rarely occurs in laser phaco as the phaco energy used is comparatively very small (Fig. 36.7). As the needle held in the hand is not vibrating anymore it can reach further into the eye without any complications of iris capture or posterior capsule capture. Moreover, the laser is ineffective
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FIGURE 36.7 Comparison of incision between phaco and laser phaco
FIGURE 36.8 Laser phaco probe 500 microns away from the posterior capsule and can be used very close to the capsule. The laser used is an ND: YAG with fiberoptic delivery and only the cataractous tissue needs to be removed thus leaving behind an epinucleus and cortex that can be easily aspirated. Laser Photon In the Laser Photon (Fig. 36.8) pulsed laser energy is used to vaporize and aspirate the lens material out of the eye (Table 36.1). The most important feature of the Laser Photon is its containment of laser energy. The probe is so designed that energy used to emulsify the cataract is contained in a photovaporization chamber. The energy used to remove the cataract does not expose the contents
TABLE 36.1 Paradigm photon laser phaco system specifications Laser system Type
Specification Nd: Yag q-switched
Laser phaco cataract surgery
Wavelength Mode structure Pulse duration Burst mode Pulse interval Energy (max) Energy selector Cone angle Aiming beam Ultrasonic system Ultrasonic capsule probefrequency Ultrasonic phaco probefrequency Ultrasonic phaco probe-stroke General system Fluidics Smartpac reusable cassette system Vitrectomy cutter Bipolar diathermy Programmable Display and indicators Cooling Weight Overall dimensions Power requirements
529
1064 nanometers Fundamental temoo Less than 4 nano seconds One, two or three pulses per burst 20 microseconds 20 ml per pulse 0.5 to 20 ml variable 16 degrees HENE—intensity variable to 5 mw Specification 40 KHz 40 KHz 5 to 90 micron linear variable Specification Peristaltic paraflow vacuum system Automated, programmable Irrigation pole Pneumatic guillotine—50–70 cuts per minute On demand 100 surgeon case programs Video crt and computer touch panel. Audio prompts for all surgical operations Air quiet laminar flow base 175 lbs (79.4 kg) 21w-26d-53h inches 100–240 vac 20 a 50/60 Hz
of the eye to this energy. This gives the laser cataract removal system an advantage over conventional phacoemulsification systems, with which the ultrasonic energy can vibrate throughout the anterior chamber and involve other ocular tissues. The laser cataract surgery entails this specially designed probe that combines fluid handling and systems controls of ultrasonic cataract systems, now fortified with the laser energy from a solid state pulsed laser. All three major features of the system irrigation, aspiration and laser are simultaneously transmitted through a precise location in the eye through a single small incision. The laser is capable of ablating high water containing tissues without pigmented chromophore. This is done causing thermal injury. Its capability of performing these functions through smooth cutting makes utilization inside the eye very favorable. Most ocular tissues are very high in their water content and the laser acts best in these surroundings. Also its high absorption by the cataractous lens makes its unwanted transmission and scatter of laser energy to adjacent and underlying tissues more controlled and precise. The laser energy is generated through a solid state crystal and its care and service come down to a minimum. The laser is air cooled and does not require any special
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installation practices. Hence it can be transported easily to the end user facility with no untoward engineering practices. In-built The laser photon machine has an in-built: 1. Laser, 2. Phacoemulsification system, 3. Vitrectomy system and 4. Diathermy.
Uses The laser cataract system is used for many purposes: 1. To do a capsulorhexis: This can be done with the help of the laser. One can get a neat round rhexis even in cases of mature cataracts. 2. To remove the nucleus: A combination of laser and aspiration helps remove the nucleus. This is aided by the technique of nuclear chopping. If the cataract is very hard a combination of laser followed by emulsification can be done to make the cataract removal through a 3 mm incision. 3. To remove cyclitic membranes: In such cases even a vitrectomy is difficult as the membrane does not get removed with the help of the vitrectomy probe. But with the help of the laser one can create a central opening in these membranes. 4. To create an opening in glaucoma cases. This is less traumatizing than other routine anti-glaucoma surgeries. 5. To make an inferior iridectomy in cases when vitrectomy is completed and one has to inject silicone oil. In such cases, we normally make the iridectomy with the vitrectomy probe which can by mistake convert a small iridectomy to a complete iridectomy. But with the laser photon one good controlled iridectomy can be created.
Surgical Procedure The technique is basically the same as in normal phacoemulsification procedures—the only difference being that here instead of ultrasound power one uses the laser energy and very rarely the ultrasound energy also. In the first step a needle with viscoelastic is injected inside the eye to distend the eye. Then a clear corneal incision is done with a diamond knife The rhexis can be done with the laser also. We prefer to do it with a needle. After hydrodissection, the laser phaco probe is passed through the incision, with the phaco chopper in the other hand through the side port opening. The nucleus is circumferentially removed and gradually aspirated out, followed by cortical aspiration, implantation of a foldable IOL and stromal hydration. In stromal hydration the BSS or
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saline is injected at the lips of the clear corneal wound hydrating the cornea and making it white. This helps make a better wound closure. Advantages • There is no corneal burns or ragged edges at site of the incision as only minimal ultrasound is used in laser phaco as compared to phacoemulsification. • A smaller incision is enough than that used for Phacoemulsification for cataract removal. • The titanium needle has a diameter of 900 microns. After threading the laser fiberoptic of 380 microns through the phaco probe, only 520 microns of space is left inside the titanium needle for the rest of the lens material to be removed. But inspite of this embarrassment in space the cataract extraction takes less time than a regular phacoemulsification. • The laser is ineffective 500 microns away from the posterior capsule and can hence be relied upon while working close to the posterior capsule. • Capsulorhexis can be safely and neatly performed with the laser. • This laser has been used in performing laser sclerotomy in cases suffering from glaucoma, to remove cyclitic membranes and to perform iridectomy.
How Small Will Our Incisions Go Today, with more and more new technology, the Laser Photon will get better and better. It will make the incision size smaller and smaller so that the astigmatism amount becomes much less. By 2000 AD lasers will have become a major force in cataract removal. Foldable IOLs have definitely come to stay and they will improve day by day. Today with the Reliable IOLs the lenses are going through 1 mm incisions. Any ophthalmologist who wants to put large lenses in large incisions is bucking the tide of history. Small incisions offer the best chance for most rapid, stable visual rehabilitation of the cataract patient at the least cost, including time of impaired vision following surgery, the need for follow-up care, the attendance of relatives to take care of them to the doctor and the like. It is unclear as to how small will our incisions go—perhaps down to 0.1 mm. With laser phakonit the size has gone to the sub 1 mm incision level. In laser phaconit the laser probe is passed through the titanium tip and the sleeve of the phaco probe is removed. Increasingly, sophisticated laser equipment is capable of giving us better utilization of energy. With the advent of the lasers, the size of the incisions will decrease. Conclusion Lasers would revolutionize cataract surgery. This is the modality by which one can go real small in the incision. With this, new techniques and instruments will allow us to put IOLs through these small incisions.
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What the human mind can achieve as it marshals the basic and clinical sciences will continue to amaze us. Look how far we have come regarding IOLs and just imagine how far we will go and can go. References 1. Thornton SP: IOL’s, knives and lasers: A new commitment to the cataract patient. Proceedings of Ocular Surgery News Symposium, 15:3, 1994. 2. Daniel Eichenbaum: Phaco is easier to do with the new laser system. Ophthalmology Times, 19(13), 1994. 3. Daniel Eichenbaum: New laser phaco. Eye Care Technology, 1994. 4. Jack M Dodick: New laser phaco. Eye Care Technology, 1994. 5. Vance M Thompson: A perspective on balancing the knife with the laser. Ocular Surgery News, 11(13):1993. 6. Daniel Eichenbaum: Laser probes for cataract surgery. Ophthalmology World News, 1995. 7. Daniel Eichenbaum: First computer-aided laser cataract removal system ready for clinical trials. Ocular Surgery News, 13(9): 1995.
37 Erbium-YAG Laser Cataract Surgery Demetrio Pita-Salorio Guillermo L Simon Castellvi Jesús Costa-Vila, Marc Canals-lmhor JR Fontenla, J Laiseca Introduction Most North American and European surgeons agree today that ultrasonic cataract surgery, when possible is the safest and the one with the shortest visual recovery. Very soon ocular surgeons worldwide will be able to use the upmost of laser technology for cataract surgery. In the authors’ hands the first European erbium-yttrium aluminum garnet (Er-YAG) laser prototypes have shown to be effective, and, as they have been developing the first European prototypes, they have found that Er-YAG laser surgical approach to cataracts slightly differs from that of classical ultrasonic phacos. Brief History of European Laser Cataract Surgery The idea of substituting ultrasounds for another kind of energy is not new. Many have been the lasers under research for cataract surgery. Some are still under development, others—like ultraviolet lasers—were abandoned years ago due to their mutagenic and carcinogenic side effects. Alternatives to ultrasonic emulsifiers for cataract surgery include various instruments and lasers, with different wavelengths of laser energy. The wavelengths currently under investigation for opacified crystalline lens removal include the following (Table 37.1). To date, the pursuit of the appropriate wavelength has centered around the neodymium: yttrium aluminum garnet (Nd: YAG) and the Erbium: YAG.
TABLE 37.1 Wavelengths under investigation for opacified crystalline lens removal • 1,064 nm neodymium: yttrium aluminum garnet (Nd: YAG) • 1,047 nm neodymium: yttrium lithium fluoride (ND: YLF) • 1,053 nm with picosecond pulses • 2,940 nm (Er: YAG) • 193 nm, 248 nm, 308 nm, and 351 nm ultraviolet laser wavelengths (excimer lasers)
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FIGURE 37.1 Aesculap Laser. Picture shows the first prototype of Erbium: YAG laser for cataract surgery we developed in the early nineties. It was made by the German AesculapMeditec™ in Heroldsberg, according to our first specifications. This first prototype did not—and still does not in 1998—incorporate an irrigating/aspirating system in the same instrument. An external I/A system has to be purchased separately to perform cataract surgery The development of the European Er: YAG phaco laser started in 1992, when Professor Pita-Salorio suggested the use of this kind of laser for cataract surgery to AesculapMeditec™ (Fig. 37.1). Aesculap-Meditec™ owned an Er: YAG used for glaucoma surgery (for ab externo fistulizing surgery—laser sclerostomy). Months later, the first prototype of laser built to our specifications—with the obvious first technical limitations—was given to us, and we started the development of laser that was due to be a new tool for cataract surgery. We performed some in vitro studies, with human cataractous lenses (eye bank lenses), to study the tissular effects of this kind of laser on human crystalline lens. The first prototype did not have I/A system, only a fiberoptic and different tips for laser
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FIGURES 37.2A AND B Pictures show the first generation of tips at high magnification—some were straight, others bent, with different diameters. The fiberoptic core had also different diameters, and slightly protruded from the metal sleeve, easing the contact with the lens material (arrow) application on the eye (Figs 37.2A and B). This laser forced two-handed surgery, with the laser tip in one hand and the I/A system in the other (through a paracentesis). After checking the usefulness of the laser to ablate cataracts, we started the first in vivo studies with human volunteers. The fiberoptics proved to be extremely fragile, and the tips bulky, uncomfortable to manage and not perfectly designed. Aesculap-Meditec™ protected and improved the fiberoptics and made the second generation of tips (Fig. 37.3) to design (with I/A, through an external I/A system, we used the Storz Premiere™ phaco I/A system). We soon found new problems—we observed an energy loss throughout the fiber. Day after day, the energy loss increased inside the fiberoptic, until the
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FIGURE 37.3 Picture shows the first and second generation of laser tips for the early Aesculap-Meditec Er: YAG MCL-29 Phacolase. The first generation (top) did not incorporate I/A system in the handpiece, while the second generation (bottom) handpiece incorporated the possibility of using an external I/A system the way we are used to with ultrasonic phacos. Nevertheless, a separated I/A system had to be purchased fiber became useless. New fibers had to be designed. At this time, we suggested to make a new instrument combining the laser and the I/A system—nobody would buy a laser without an I/A system! But Aesculap-Meditec™ did not manufacture it, and they still have not achieved. When Aesculap-Meditec™ relocated to the former East Germany in 1996, employees who decided to remain in the West formed Wavelight Laser Technology™. Following the split, Wavelight™ focussed on developing a new laser phaco system with the benefit of incorporating past experience. Wavelight engineers came up with the Adagio™, that produces pulse energy of 100 mJ and 100 Hz. It incorporates a conventional I/A system in the same instrument. This system provides the possibility to work with smaller tips. Why Er: YAG? The Reason to Choose the Er: YAG Unlike other wavelengths, the Er: YAG boasts the highest absorption of energy in water of any laser
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FIGURE 37.4 Graph depicting Er: YAG as the highest absorber of energy in water of any laser (Fig. 37.4). This means maximum protection for the high water content ocular tissues— energy is absorbed by the water of crystalline lens, and there is a reduced thermal effect on other ocular tissues. But Er: YAG is not only under investigation for ophthalmic use—many are the fields in medicine where Er: YAG is being investigated (Table 37.2). FDA approval is a reality for cosmetic skin surgery. Pulsed laser energy is used to vaporize and photofragment (emulsify) high water contents lens material out of the eye. Every pulse caused rapid localized heating and vaporization, and creates a bubble at the tip of the fiber. The size of the bubble depends on the pulse energy and is about 1 mm at 1 mJ. The shape of the bubble has multiple lobes. In other words, tissular water contents absorb this laser wavelength as heat—when temperatures
TABLE 37.2 Current other investigational uses of Er: YAG lasers • Dentistry—cosmetic dentine destruction, cavity preparation, caries removal, pits and fissures • Trauma/orthopedics—osteolysis of bone tumors • Digestive surgery*—destruction of gallstones • Cosmetic surgery—photodermolysis, dermabrasion • Dermatology—destruction of superficial skin tumors • Vascular surgery—angioplasty • ORL—tympanoplasty * FDA approved
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FIGURE 37.5 Mechanism of tissular damage are higher than 100°C, vaporization of tissue water occurs. The liquid water changes into gas (vapor), with a dramatic volume expansion that leads to tissular damage because of the formation and collapse of vapor cavities—it is what we call vaporization (Fig. 37.5). This laser-induced vaporization is accompanied by the formation of acoustic transients (pressure waves) that also produce mechanical damage to the tissue. Unwillingly, at the same time, the proteins of the lens coagulate, progressively increasing lens hardness, and making tissular lens photoemulsification more difficult as surgery progresses. One of the vital points to lessen this problem is to use the laser in a pulsed mode. Every pulsed mode has an effective energy (at the beginning of the pulse) and an uneffective energy at the end of the pulse, i.e. wasted as a thermic increase without tissular damage. The higher the frequency, the more effective will be the laser. But too much frequency leads to an enormous energy amount that dehydrates and cooks lens tissues. Correctly balancing energy and frequency are extremely important. Tissular Effects In 1995, to evaluate the tissular effects of the new experimental European erbium: YAG (Er: YAG) phaco laser on the human cataractous crystalline lens, we ruled a first in vitro trial with a limited number of human eye bank crystalline lenses, to determine the mechanism of damage and the utility of the European Er: YAG phaco laser to emulsify cataractous lens cortex and nucleus. We show and discuss the tissular effects of this laser, as observed through electron scanning microscope, at increasing energy levels, both in aerial medium and underwater (like in real surgery). Twenty human eye bank cataractous crystalline lenses underwent laser effect in two groups (in aerial medium and underwater), at different increasing energy levels. After perpendicular laser irradiation, each lens was preserved in a glutaraldehyde solution and sent to our ocular morphology investigation unit to be processed and examined under electronic scanning microscope. Laser application time was set in all cases to 3 seconds, frequency was set in all cases to 10 pulses per second (10 Hertz). Laser application was directly perpendicular to the lens, at its center.
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Results We briefly show and discuss the tissular effects of this laser, as observed through electron scanning microscope, at increasing energy levels, both in aerial medium (Figs 37.6A to E) and underwater {(Figs 37.6F and G) in real surgery}. Group A: Eye Bank Lenses, in Aerial Medium 1. Energy level: 10 mJ (10 Hz, 3 seconds) (Fig. 37.6A) 2. Energy level: 20 mJ (10 Hz, 3 seconds) (Fig. 37.6B) 3. Energy level: 30 mJ (10 Hz, 3 seconds) (Fig. 37.6C) 4. Energy level: 80 mJ (10 Hz, 3 seconds) (Fig. 37.6D) 5. Energy level: 100 mJ (10 Hz, 3 seconds) (Fig. 37.6E) Group B: Eye Bank Lenses, Underwater (Under BSS, Like in Real Surgical Conditions) The scanning electron micrographs show an Er: YAG crater at 20 mJ (3 seconds of irradiation at 10 pulses per second), with the European Er: YAG laser (Fig. 37.6F). Observe that the borders of the crater show clear exfoliative tissular disruption (similar to Nd: YAG laser effect), while deep smooth crater walls are due to tissular ablation (similar to excimer laser effect). 1. Energy level: 10 mJ {(10 Hz, 3 seconds) (Fig. 37.6A)}
FIGURE 37.6A Lens anterior capsule has been disrupted, and only superficial lens cortex has been damaged. This picture confirms23–25 that, in air, Er: YAG laser has a very short penetrating effect over crystalline lens at this energy level, and may be used for anterior circular continuous capsulotomy
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2. Energy level: 20 mJ {(10 Hz, 3 seconds) (Fig. 37.6B)}
FIGURE 37.6B Anterior capsule and cortex have been damaged. The central round crater shows the point where laser tip contacted the lens. Its walls are razor sharp. Laser tissular damage has spread far (1–2 mm) from the contact point, showing that in aerial conditions laser collateral effects may not be so circumscribed as postulated by other authors. The linear cotton fiber is an undesired artifact from the operating room 3. Energy level: 30 mJ {(10 Hz, 3 seconds) (Fig. 37.6C)}
FIGURE 37.6C Er: YAG laser disruptive effect can be clearly observed—it seems as if a group of small explosions (the different pulses) had occurred inside the lens. The image is similar to that obtained by
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Nd: YAG laser irradiation over a human crystalline lens. The picture on the right shows laser effects at greater magnification We also observe a localized thermal effect (protein coagulation). Our phaco laser system easily emulsifies lens cortex and nucleus—the higher the energy, the better the effects. We were the first to notice that Er: YAG laser tissular effects were different in air than underwater. Tissular destructive mechanism varies according to the medium where it acts—in 4. Energy level: 80 mJ {(10 Hz, 3 seconds) (Fig. 37.6D)}
FIGURE 37.6D Tissular disruption has destroyed superficial lens cortex and anterior capsule. Tissular damage is greater than before. It seems as if laser destruction was due to the first laser pulse—other pulses have damaged in depth 5. Energy level: 100 mJ {(10 Hz, 3 seconds) (Fig. 37.6E)}
FIGURE 37.6F Underwater, like in real surgical conditions, the crater is
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much deeper than the obtained in aerial medium. Mass loss is much higher underwater than in air—the European Er: YAG works much better with a film of water between lens and cataract tip
FIGURE 37.6E Er: YAG laser disruptive effect can be observed in superficial lens layers—observe that the borders of the crater show clear exfoliative tissular disruption. In deep, smooth crater walls are due to tissular ablation. The deepness of the crater increases with energy level. In 3 seconds, at 100 mJ we reach one-third of lens thickness aerial medium, disruption prevails over ablation. Underwater, in surgical conditions, ablation prevails over disruption. In vitro Er: YAG ablation does not confirm to a linear model—the European Er: YAG laser “mass loss versus fluence” curve is still to be stated. The penetrating effects over crystalline lens increase with energy levels, either in air or underwater. Under certain conditions (high energy levels, in aerial conditions), the extent of surrounding tissue damaged may not be as
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FIGURE 37.6G Note the smooth walls of the crater, showing no tissular disruption, though clear-cut tissular ablation limited as previously stated. Fortunately, this seems less important under real surgical conditions (underwater). To obtain the best result with this laser, there must be a small quantity of aqueous humor (or irrigating balanced solution) between the laser tip and lens surface—the laser energy is better absorbed, and destroys lens tissue, because of vaporization and acoustic effects. If laser acts on a dry crystalline lens, there is more thermal damage with coagulation and necrosis of the target (tissular disruption). Er: YAG thermal damage depends on the tissular absorption coefficient, which varies with water contents of the tissue, and the presence or not of a small quantity of water between laser tip and the lens. The lens tissue absorption coefficient of Er: YAG increases from 439+/−151 cm−1 in ambient air to 12.800+/−400 cm−1 in water—for this last value, cavitation phenomena with bubble formation are added to heat production, producing more tissular damage. Adagio™ by Wavelight™ Laser Technology GmbH Today, we use the Adagio™, a laser final prototype made in Erlangen-Tennenlohe, in Germany by Wavelight™ Laser technology GmbH (Figs 37.7A to C and Table 37.3). In our clinical research, we use the serial number 1002–1–009. This phaco laser integrates in one instrument an erbium: YAG laser system, a peristaltic vacuum system, and a diathermy unit. A special tip allows circular continuous laser capsulotomy The same instrument, with different tips allows cataract surgery, iridectomy, vitrectomy (?) and antiglaucomatous ab externo laser sclerostomy. With the Adagio™, pulsed laser energy is used to vaporize and photofragment (emulsify) high water contents lens material out of the eye. With the newly designed probes, irrigation, aspiration and laser are simultaneously transmitted to a precise location in the eye through a single small incision. Adagio™ has an integrated water cooling and does not require any special installation practices.
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Fiberoptic Design Because Er: YAG can be transmitted by fiberoptics, it has a great potential for intraocular procedures. The best kept secret of this laser is the material, the fiberoptic and the tip fiber are made of. As laser energy is being absorbed by water, we could not use quartz because it has too high a water content. Instead, we use a fluoride/zirconium based fiberoptic (Figs 37.8 and 37.9). The first fibers were extremely fragile (and expensive): new fibers are more resistant, though not cheaper.
FIGURES 37.7A TO C Pictures show the handpieces we are currently using for cataract surgery with the
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Wavelight™ “Adagio” phaco laser system—the handpiece incorporates a laser fiber (see detail, in red), an irrigating port through the silicone sleeve and an aspirating port parallel to the fiberoptic
FIGURE 37.8 Figure shows a continuous long-term test of the durability of NIR fibers made of zirconium fluoride. It proved that these fibers, which fail easily when transmitting 800 mJ of input energy,1 survive much longer at a lower energy level of 600 mJ2. To do this test, the free-running laser produced pulses of 500 microseconds at 10 Hz (picture taken from “improved Erbium Laser Parameters” by Klaus Vogler and Max Reindl, in Biophotonics InternationalNovember/December 1996. Page 41)
FIGURE 37.9 Close examination of the distal end face of a 600
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micrometer-core zirconium fluoride fiber reveals significant damage at the surface. The utility and resistance of these fibers have improved in the last few years. (Picture taken from “Improved Erbium Laser Parameters” by Klaus Vogler and Max Reindl, in Biophotonics InternationalNovember/December 1996. Page 41) Cataract Surgical Procedure The initial approach to cataract surgery is much similar to classical ultrasonic phaco technique. The main difference is that instead of mechanical ultrasonic energy, laser energy is used. Surgery can be performed under local (retro or peribulbar, topical or intraocular) or general anesthesia. Wide
TABLE 37.3 Wavelight Laser Technology GmbH “Adagio” phaco laser system specifications Laser system
Specifications
Type Wavelength Pulse duration Pulse energy Pulse frequency Usual working parameters Maximum output Radiation transmission Laser class Aiming beam Safety standard
Solid state/Erbium: YAG 2940 nm 50–150 microseconds up to 100 mJ (panel or linear, pedal controlled) up to 100 Hz (panel or linear, pedal controlled) 20–60 mJ and 20–50 Hz
Power Handpiece General system Fluidics
Diathermy
2W (100 mJ) Fluoride based fiber 4 diode laser (635 nm), continuous wave, 1 mW max IEC 601/IEC 825, Medical device law EU conformity declaration 93/42/EEC Foots witch (4 positions: rest, irrigation alone, I/A, I/A+laser) combined laser-I/A, autoclavable different fiber tips (anterior capsulotomy, vitrectomy, sclerostomy) Specifications Peristaltic paraflow vacuum system Premiere DPX 100 (Storz Instrument Co. St. Louis, USA) Aspiration range: 0–40 ml/min Vacuum range: 0–500 mn Hg (linear) Yes
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Display and indicators Video CRT and Computer touch panel Power connection 100/230 V, 50/60 Hz max. 3.2 kW Cooling Integrated water cooling Weight 65 kg Dimensions 102×40×75 cm3
FIGURE 37.10 Wide mydriasis is preferable, though not essential. It allows better surgical view. We have noticed that pupil tends to contract as laser progresses mydriasis is preferable, though not essential (Fig. 37.10). We prefer a slightly side-incision (temporal) approach to ease surgical maneuvers with the laser tip. A clear corneal single plane 2.5-mm incision is made, being the gateway for laser phacoemulsification and for foldable IOL implantation. Smaller incisions will soon be able with new phaco laser tips. After the incision has been completed, viscoelastic (any of the currently used substances) is injected to fill the anterior chamber, and thus protect corneal endothelium from shockwave damage. Performing a clear-cornea paracentesis in the opposite side is preferable for better rotation and positioning of nuclear fragments. Capsulorhexis may be performed either using a cystitome (30 G bent needle, the classical way), the
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FIGURE 37.11 When capsulorhexis is performed with the special capsulorhexis laser tip, it is less regular than mechanical capsulorhexis with the cystitome or the Utrata forceps
FIGURE 37.12 A special capsulorhexis laser tip has been designed to allow continuous circular laser anterior capsulotomy Utrata’s forceps, or a specially designed laser capsulorhexis tip (Fig. 37.11). This laser tip allows circular continuous laser capsulotomy (capsulorhexis) even in cataracts without red reflex (Fig. 37.12). One important point to ease surgery is performing a wide capsulorhexis—this will allow luxation of the superior pole of the dissected nucleus and cortex to better and faster fragment it with the Er: YAG laser. The goal is to use the lowest possible energy levels, to make phaco laser a safe technique. Hydrodissection and hydrodemarcation of the cortex and nucleus follow, with balanced salt solution (BSS) and a 27 gauge anterior chamber cannula. Up to now there are no surgical differences with ultrasonic phacoemulsification technique. Whatever technique you are using, good nuclear rotation is essential.
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In soft cataracts, where Er: YAG laser works at its best, you can proceed the same way you do in ultrasonic phacoemulsification—a divide and conquer technique may be used, with very high aspiration levels to attract the cortex and nuclear masses to the tip. Nevertheless we prefer performing complete nuclear phacofragmentation-aspiration, starting at high frequency (50–60 Hz) and low-energy levels (20–30 mJ)—superior cortex is ablated and aspirated, and nucleus fragmented and aspirated by the laser energy. We direct the laser beam over the cortex and nucleus as we would use an eraser to wipe over a surface. The laser tip is directed as perpendicular as possible over the ablation zone, producing optical breakdown at the beam’s tip. As a result, we obtain a tough posterior cortical shell, that can be luxated to the pupillary area with the manipulator, cut, fragmented and aspirated with the laser, at lower frequency (20–30 Hz) and higher energy (40–50 mJ). Working in the pupillary area, never in the anterior chamber, far from the posterior capsule, we avoid posterior capsule breaks. Sometimes, it will be advisable to inject some viscoelastic under the corticonuclear shell, to lift it and allow easier and safer laser manipulation. Touching the tip of the laser with the manipulator is not dangerous for the tip. Our in vitro trials showed that laser energy (thermal and acoustic laser effect) is not only limited to the end of the tip as we first thought, but can go 1 to 2 mm away from it, endangering the posterior capsule. Nevertheless, posterior capsule break arises when the capsule is directly touched by the laser at work. We suggest you to work as far away as possible of the posterior capsule—this is not difficult with a sealed incision and good intraocular pressure (25 mmHg) obtained by the I/A system that pushes the capsule backwards. Due to hydrodemarcation, nuclear mobility may make removal difficult because of the tendency to move away from the laser phaco tip. To avoid this, a nuclear manipulator may be used through the
FIGURE 37.13 Superior pole luxation eases emulsification, since laser better attacks the cortex from the equator of the lens paracentesis, to stabilize the masses. Do not forget that this laser is not effective without a close contact of the mass to be ablated and the laser phaco tip. Without this contact, laser energy is wasted as undesirable heat and Shockwaves in the anterior chamber.
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For all kind of cataracts, specially when the nucleus is hard, laser phaco chopping may be specially difficult if the rhexis line is not clearly seen. That is why we perform a wide capsulorhexis, as wide as possible. After good rotation of the nucleus, we perform luxation of the superior pole of the lens contents (Fig. 37.13). The superior pole may be cut with the laser through an equatorial approach, in the pupillary area. If necessary, you can inject some viscoelastic under the cortex to ease this luxation (viscoexpression). The nucleus is split into small pie-shaped pieces and gradually aspirated out. We prefer a twohanded technique, which makes surgery easier and faster, though one-handed is also possible if you are not stressed by time. Luxating the superior pole to pupillary area avoids nuclear movement and zonular stress, making surgery easier.
FIGURE 37.14 Picture shows Adagio Er: YAG laser at work—notice that the early tips had a metal sleeve instead of the today’s blue silicone sleeve
FIGURE 37.15 IOL lens insertion does not differ from ultrasonics Wide capsulorhexis allows safe rotation of the nucleus (by reducing the effects of friction), allows superior pole luxation, and has the advantage of less future capsular bag retraction, though it has the disadvantage of slightly more unstable IOL positioning.
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Cortex remnants are aspirated using a standard I/A probe, followed in the end with the insertion of a posterior IOL, preferably foldable IOL. We either use silicone lenses, acrylics or hema with polymethyl-methacrylate (PMMA) rigid haptics (Fig. 37.14). The ideal foldable or injectable, and stable IOL has yet to be invented. Even with a complete rhexis and whatever method is used to remove the nucleus, a break may result. Even so, using Adagio™ phaco laser we find that rhexis breaks enlarge less in proportion to what happens with ultrasonic phaco in similar cases (Fig. 37.15). Frequency and Energy: Vital Parameters A no vice will experiment some difficulty in balancing frequency and energy levels. The correct management of both parameters is essential to avoid “cooking” lens proteins and dehydrating lens material. In summary, we can say that hard nucleus need low frequency and high energy soft cataracts need high frequencies and low energy levels. Personal experience allows better balancing of both parameters. Both can be controlled on the computer touch panel. If the laser mode (energy and frequency) is set to panel control, the full preset power will be reached as soon as the pedal reaches the “laser position” (I/A+laser). Adagio™ laser can also be set to linear control, which gives progressively more laser energy and/ or frequency as the pedal is progressively depressed. The foot pedal has also reflux control that reverses flow, so that fluid (capsule or iris) will flow out of the aspiration port. The AdagioR Er: YAG laser seems well suited to cut the high water-content structures of the eye, specially the cataractous soft crystalline lens. Nevertheless, far more research is necessary until this laser might be widely used for intraocular cataract surgery. Postoperative Evolution Typical postoperative aspect and evolution does not differ from that of an ultrasonic phacoemulsification for an uncomplicated surgery. Mild corneal edema at the incision is seen if manipulation is excessive, the energy dissipation in the incision area being negligible. Minimal postoperative inflammation and endothelial cell loss are the rule for uncomplicated surgery The endothelial cell loss seems very similar to that of our first ultrasonic phacos, and should improve as we get experienced with this new tool (Fig. 37.16). Complete results of our studies are still awaited.
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FIGURE 37.16 Postoperative aspect of uncomplicated patients treated with the Erbium: YAG Wavelight Adagio system does not differ at all from that of patients treated with ultrasounds. Nevertheless, we have observed a mild increase of the intraocular pressure the first days after surgery. This IOP increase was common in patients that underwent the first ultrasonic cataract surgeries
FIGURE 37.17 IOP rise Mild to moderate intraocular pressure rise is common a couple of days after surgery (Fig. 37.17). Postoperative medication may be necessary in patients with advanced glaucomatous optic nerve damage. Short-term follow-up of our first patients has revealed no adverse effects or extraordinary complications. In our clinical study with volunteer patients, we also perform corneal topography, before surgery and three months after surgery. Preliminary results seem to show that
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there are no special topographic changes that might be attributable to Er: YAG. Corneal topographic changes do not differ from that of ultrasonics. Anterior Chamber Temperature Since Er: YAG laser use in human eyes still raises some safety concerns, we are also checking temperature rise in anterior chamber. For an uncomplicated surgery of about 10 to 15 minutes, temperature rise is lower than 10°C, and should suppose no special danger for endothelium, as it reverses after a few minutes. I/A system minimizes temperature rise, as it permanently cleans and refreshes anterior chamber. At the energy levels we use (20–60 mJ), there is actually no need for cold BSS. As we are planning to increase energy levels in a close future in order to be able to deal with harder nuclei, the use of cold BSS will probably become necessary. Conclusion The Er: YAG phaco laser works at its best with soft and middle-soft cataracts, yet has some important difficulty with middle hardness and hard nuclei (Table 37.4). Nevertheless we are sure laser will soon be a major force in cataract removal. The incision size is getting smaller and smaller, minimizing postoperative astigmatism. To new small-incision surgeons, it has the advantage of a shorter learning curve. Experienced surgeons will have to slightly modify their phaco technique, and will be satisfied to use a modern new tool that may achieve cataract surgery in a safer and easier way. Initially dismissed as being unsafe and not effective enough, we believe that through perseveration, Er: YAG phaco laser improvements will develop into a procedure that will gain worldwide acceptance as a safe effective method of removing cataracts (see Chart 37.1). But there is still a long way to go, a lot of work to be done.
TABLE 37.4 Advantages and disadvantages of Er: YAG Advantages • Effectively removes cataractous lens cortex and nucleus (in soft and middle hardness nuclei) • Best absorption under water • Safe and easy to learn does not directly damage adjacent tissues less thermal damage endothelial cell loss not worse than ultrasound • Many potential different ophthalmic uses (cataract, glaucoma, retinal and
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vitreous surgery, cosmetic surgery) Disadvantages • “Slow”—ablation mass smaller than other techniques (ultrasound, Ho: YAG laser?) • Not risk free (posterior capsule break, IOP rise) • “Fragile” and “perishable” fiberoptics • Still some technical problems to be solved • Expensive? • Does not work properly with hard nuclei
Further Reading 1. Agarwal S: Laser can be used to ablate cataracts. Ocular Surgery News (International ed) 8(9):1997. 2. Bath PE: Laserphaco—an introduction and review. Ophthalmic Laser Ther 3(2):75–82, 1988. 3. Bath PE, Kar H, Apple DJ et al: Endocapsular excimer laser phakoablation through a 1-mm incision. Ophthalmic Laser Ther 2(4):245–48, 1987. 4. Bath PE, Mueller G, Apple DJ et al: Excimer laser lens ablation (letter). Arch Ophthalmol 105:1164–65, 1987. 5. Bonnie SR, Puliafito CA: Erbium: YAG and Holmium: YAG laser ablation of the lens. Lasers Surg Med 15:74–82, 1994. 6. Borkman RF: Cataracts and photochemical damage in the lens. Ciba Found Symp 106:88–109, 1984. 7. Brown S: The multipurpose 1053 picosecond laser. Presented at the American Society of Cataract and Refractive Surgery (ASCRS) Annual Meeting, 1990. 8. Cleary SF: Laser pulses and the generation of acoustic transients in biological material. In Wolbarsht ML (Ed): Laser Applications in Medicine and Biology New York: Plenum Press, 3:175–219, 1977. 9. Cleary SF, Hamrick PE: Laser induced transients in the mammalian eye. J Acoustic Soc Am 46:1037–44, 1969. 10. Colvard DM: Erbium: YAG laser removal of cataracts. Presented at the American Society of Cataract and Refractive Surgery (ASCRS) Annual Meeting, 1993.
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CHART 37.1 Wavelight Adagio™: Er-YAG laser cataract surgery
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11. Dodick JM: Laser phacolysis of the human cataractous lens. Dev Ophthalmol 22:58–64, 1991. 12. Dodick JM, Christiansen J: Experimental studies on the development and propagation of shock waves created by the interaction of short Nd: YAG laser pulses with a titanium target—possible implications for a Nd: YAG laser phacolysis of the cataractous human lens. J Cataract Refract Surg 17(6):794–97, 1991. 13. Dodick JM, Sperber LTD, Lally JM et al: Laser phacolysis of the human cataractous lens. Arch Ophthalmol 111:903–04, 1993. 14. Ebran JM, Buisson JP, L’Huillier JP et al: Absorption cristallinienne du laser Er: YAG (French with English summary). Ophthalmology 3(9):265–72, 1995. 15. Jean B, Kriegerowsky M, Bende T: Correction of myopia with Er: YAG laser fundamental mode photorefractive keratectomy. J Ref Surg 5:392, 1995. 16. Kelman CD: Phacoemulsification and aspiration-a new technique of cataract removal, a preliminary report. Am J Ophthalmol 64(1):23–35, 1967.
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17. Kochevar IE: Cytotoxicity and mutagenicity of excimer laser radiation. Lasers Surg Med 9(5):440–45, 1989. 18. Li Zhao-zhang, Code JE, Van de Merwe WP: Er: YAG laser ablation of enamel and dentin of human teeth—determination of ablation rates at various fluences and pulse repetition rates. Laser in Surg and Med 6(12):625, 1992. 19. Li Zhao-zhang, Reinisch L, Van de Merwe WP: Bone ablation with Er: YAG and CO2 laser— study of thermal and acoustic effects. Lasers in Surg and Med 1(12):79, 1992. 20. Maguen E, Martinez M, Grundfest W et al: Excimer laser ablation of the human lens at 308 nm with the fiber delivery system. J Cataract Refract Surg 15:409–14, 1989. 21. Margoli TI, Farnath DA, Destro M: Erbium-YAG laser surgery on experimental vitreous membranes. Arch Ophthalmol 107:424–28, 1989. 22. Marshall J, Sliney DH: Endoexcimer laser intraocular ablative photodecomposition (letter). Am J Ophthalmol 101(1):130–31, 1986. 23. Muller-Stolzenburg N, Muller GJ: Transmission of 308 nm excimer laser radiation for ophthalmic microsurgery—medical, technical and safety aspects. Biomed Tech (Berlin) 34(6):131–38, 1989. 24. Muller-Stolzenburg N, Stange N, Kar H et al: Endocapsular cataract surgery using the excimer laser at 308 nm (in German with English abstract). Fortschr Ophthalmol 86(6):561–65, 1989. 25. Nanevicz T, Prince MR, Gawande A A et al: Excimer laser ablation of the lens. Arch Ophthalmol 104:1825–29, 1986. 26. Parel JM, Simon G and the members of the accommodation club: Phaco-Ersatz 2001—update. Anales del institute Barraquer 25:143–51, 1955. 27. Pellin MJ, Williams GA, Young CE et al: Endoexcimer laser intraocular ablative photodecomposition (letter). Am J Ophthalmol 104:118–22, 1986. 28. Peyman GA, Katon N: Effects of an Erbium: YAG laser on ocular structures. Ophthalmol 10:245–53, 1987. 29. Peyman GA, Kuszak JR, Weckstrom K et al: Effects of XeCl excimer laser on the eyelid and anterior segment structures. Arch Ophthalmol 104:118–22, 1986. 30. Pita-Salorio D, Simon G: Cirugia laser de la cataract. Course at the Faculty of Medecine. Spain, Santiago de Compostela, 1996. 31. Pita-Salorio D, Simon-Castellvi G, Canals-Imhor M et al: Er: YAG laser tissular effects on human cristalline lens. Proceedings of the XIth Congress of the European Society of Ophthalmology, Budapest (Hungary), 1997. 32. Pita-Salorio D, Simon G: Chirurgie des cataractes au laser Er: YAG—premieres impressions French with English summary. Ophthalmoloy 11:264–67, 1997. 33. Pita-Salorio D, Simon G: Poster presented at the Aesculap-Meditec booth. American Academy Meeting 1995. 34. Pita-Salorio D, Simon G: Er: YAG laser tested in ten eyes. Ocular Surgery News (International ed) 7(2):1996. 35. Pita-Salorio D, Simon G et al: Erbium: YAG laser cataract surgery. Course. Presented at the American Society of Cataract and Refractive Surgery (ASCRS) Annual Meeting 1998. 36. Puliafito CA, Steinert RF: Laser surgery of the lens—experimental studies. Ophthalmology 90(8):1007–12, 1983. 37. Puliafito CA, Steinert RF, Deutch TF et al: Excimer laser ablation of the cornea and lens— experimental studies. Ophthalmology 92:741–48, 1985. 38. Trentacoste J, Thompson K, Parrish RK II et al: Mutagenic potential of a 193 nm excimer laser on fibroblasts in tissue culture. Ophthalmology 94:125–29, 1987. 39. Tsubota K: Application of Erbium: YAG laser in ocular ablation. Ophthalmologica 200(3):117–22, 1990.
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40. Visuri SR, Pristowsky JB, Walsh JT: Er: YAG laser ablation of pairie dog gallbladder epithelium for the prevention of gallstones. Laser Surg Med 4(15):358, 1994. 41. Wang Kang-sun, Li Qi, Lan Zhi-lin: Comparison of Er: YAG and excimer laser corneal ablation in rabbits. Lasers Light Ophthalmol 2:69,1994. 42. Wetzel W, Häring G, Brinkmann R et al: Laser sclerostomy ab externo using the erbium: YAG laser. German J Ophthalmol 2:1–4, 1993. 43. Wetzel W, Scheu M: A new application system for laser sclerostomy ab externo. Laser Light Ophthalmol 5(4):193–98, 1993. 44. Williamson WA, Aretz HT, Weng G: In vitro decalcification of aortic valve leaflets with the Er: YAG laser, Ho: YAG laser, and the cavitron ultrasound surgical aspirator. Laser in Surg and Med 4(13):421, 1993.
38 Cataract Surgery with Dodick Laser Photolysis Jorge L Alio Valerio De Iorio Introduction The possibility of cataract removal using a laser system has been investigated in the last 15 years as an alternative to the present ultrasound phaco system introduced by Kelman in 1967.1 The first presentation of the idea of laser cataract removal was done by Jack Dodick at the American Academy of Ophthalmology’s 1989 annual meeting2 and in 1991 he performed his first case using a pulsed 1064 nm Nd: YAG laser.3,4 The technique was presented as an alternative of the ultrasound phacoemulsification. As a matter of fact, even if the effectiveness of the ultrasound phacoemulsification with all degree of nuclear density is well known, this technique is not free of drawbacks, complications such as burns at the wound, the potential damages of the endothelial cells, of the iris, the mechanical trauma due to the turbulence of the fluids and the nuclear fragments specially of hard cataracts and the always present risk of posterior capsule breaks.5 Technical Fundamentals of Laser Photolysis System Up to now only two solid-state laser system are available for cataract removal: The neodymium: yttrium aluminum garnet (Nd: YAG) laser, and the erbium: YAG (Er: YAG) laser.5 The systems using the Nd: YAG laser are divided in: (i) direct acting system (Photon, Paradigm Medical Industries, Salt Lake City, UT), and (ii) indirect acting system {(Dodick laser lens ablation device, ARC laser GmbH, Germany) Fig. 38.1}. The Nd: YAG laser principle has been used for
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FIGURE 38.1 Dodick’s ARC laser system
FIGURE 38.2 View of the titanium target inside the laser tip many years in YAG capsulotomy and is based on the generation of plasma and shock waves. Specifically the laser-pulsed energy is transmitted from the source by a Quartz fiber of 300 µm through the handpiece, stopping 1.3 mm in front of the Titanium target inside the tip (Fig. 38.2). This target acts as a transducer converting light energy into mechanical energy (shock waves). As soon as the light strikes the titanium target, an optical breakdown (plasma formation) and shock waves result which disrupts the nuclear material held at the mouth of the aspirating port. In this way there is no light leakage potentially dangerous for the retina, corneal endothelium and for the eyes of the surgeon.6–9
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FIGURE 38.3 Laser phaco lysis handpiece and two port side irrigation cannula On the bases of recent studies, comparing the heat produced at the US phaco tip and at the laser phaco lysis tip, it has been proved that the laser system produces no clinical significant heat in respect to what happens in the US phaco system,10 for this reason there is no need of a cooling system. The previous model of handpiece, that included besides the Quartz fiber and aspiration line the infusion line, now is formed only by Quartz fiber and aspiration (Fig. 38.3). In this way the purpose of reducing both the handpiece dimensions and the diameter of the tip and obviously the incision size is reached. Consequently, the surgical approach has been modified from unimanual to bimanual configuration, in which the infusion connected with a conventional I/A phaco system, better with Venturi-based pumps is introduced through a second paracentesis.11 Actually the diameter of the tip is 1.2 mm and the wound size to implant a foldable IOL has to be enlarged up to 3.4 mm. Selection of Patients and Indications Up to this moment the cataract density that we are able to treat range from +1 to +3. The hard cataract of more than +3 or +4 and harder, for the moment remain treatable in our hands, only with the US phacoemulsification. We found that an optimal elective indication nowadays of Dodick’s laser photolysis is for lens refractive surgery. Considering the very delicate way of working of this device, other excellent indications are subluxated cataractous lenses and post-traumatic cataracts of not high density, zonular laxity and some congenital cataracts. Anesthesia • Topical anesthesia: Generally, the laser photolysis, can be done using topical anesthesia 0.75 percent bupivacaine plus 2 percent lidocaine 2 drops every 5 minutes before surgery, with supplemental intracameral preservative-free 1 percent lidocaine diluted
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1:1 in balanced salt solution (BSS). Additionally we can use to add sedation with 1 mg ½ of Dormicum and 0.5 mg of Limifen, upon patient needs. However, we may prefer to use other anesthesia options in order to eliminate intraoperative eye movements, especially in young anxious patients and according to the surgeon’s preference. • Peribulbar anesthesia with 8 cc of 0.75 percent, bupivacaine and 2 percent lidocaine plus Tiomucase to help the diffusion in the orbit: Special attention should be taken in the anesthesia of high myopic eyes with posterior staphyloma. Mild venous sedation is used when necessary, specially to decrease the pain sensation during the injection of the anesthetic solution. In this case we use 1 mg per kg of Propofol EV. • Retrobulbar anesthesia has been abandoned in our hands, specially in the elongated myopic eye, due to the risk of globe perforation. • General anesthesia is not necessary unless requested as in very young patients. • Sub-tenonian anesthesia with blunt Fukasaku cannula (Katena, products. Inc. Denville; New Jersey, USA. Ref. K7–4002) of 1 percent lidocaine, provides an alternative option specially with sclerocorneal approach in high myopes. Then a light compression with the Honan balloon is applied for 5 minutes, 15 minutes before surgery.
FIGURE 38.4 First paracentesis with a 1.4 mm calibrated blade at 2 O’clock position Surgical Technique with Dodick Laser Phacolysis: Our Experience We have operated 45 patients with this device with cataract density of +1/+3, and all except the first five cases, under topical anesthesia. We perform first two watertight paracentesis in clear cornea 90° apart, at 10 and 2 O’clock with 1.4 mm blade (V-Lance Knife, Alcon Surgical, Fig. 38.4) followed by the injection of 1 percent lidocaine preservative-free diluted 1:1 in BSS. Two different viscoelastic solutions are used in the anterior chamber, first Viscoat (Alcon Cusi’, Barcelona, Spain) to protect the endothelium, then Celoftal (Alcon Cusi’, Barcelona, Spain) to increase volume in the
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anterior chamber (AC). A 5.5 mm continuous curvilinear capsulorhexis (CCC), is performed with Condon capsulorhexis forceps (John Weiss, Milton Keynes, England. Ref. 0101566), which is the only one that we have found effective through the watertight incision (Fig. 38.5). After the hydrodissection of the cortex and nucleus with a flat cannula, we introduce first the irrigation cannula with two-port side, at 2 O’clock incision, then the phaco laser tip at 10 O’clock incision. The laser lysis of the cataract can be described as “touch, pulse, aspiration”.11 In fact the ablation of the nucleus begins applying
FIGURE 38.5 Continuous curvilinear capsulorhexis (CCC) with Condon forceps through the 1.4 mm incision lightly the probe on the anterior surface of the cataract then a pulse of laser is delivered at the lower laser set power with vacuum level of 250 mm Hg using the Venturi pump of the Accurus device (Alcon Ref. 8065740238): and the fragment is aspirated (Figs 38.6A and B). We have found less effective the peristaltic pump used previously in our initial cases. The nucleus is cracked after creating a deep initial groove, as soon as is possible. When all the nucleus is aspirated, we insert at 10 O’clock position the aspiration cannula decreasing the vacuum till 100 mmHg and we finish to clean the cortex remnants (Fig. 38.7). After the injection of a dispersive cohesive viscoelastic solution like methylcellulose Celoftal (Alcon Cusi’, Barcelona, Spain) in the capsular bag, we enlarge the 10 O’clock incision up to 3.2 mm and we implant a foldable IOL (Figs 38.8A and B). The procedure terminates with the aspiration of the viscoelastic solution using specific I/A cannula (Geuder, GmbH, Heidelberg, Germany. Ref. G-32774; G-32769) in continuous irrigation and hydrating the two wound with BSS (Figs 38.9 and 38.10). The reason why we perform two watertight incisions is because this procedure utilizes high vacuum, so it is necessary to work in a closed pressurized surrounding, the only drawback is the needs to screw a bit the tips into the incision.
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FIGURE 38.6A Laser lysis and aspiration of the nucleus
FIGURE 38.6B Aspiration of cortical material Usually with +1/+2 density cataracts, 40 to 100 pulses are sufficient to complete the procedure, while with +3 density we use about 300 to 400 pulses. The bottle of BSS is fixed 75 cm high from the patient’s head. If placed at a higher level, the excessively high intraocular pressure (IOP), may induce initial vagal response to the patient due to the induction of oculo-vagal reflex.
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FIGURE 38.7 Cleaning of the cortical cells with the aspiration cannula
FIGURE 38.8A Implantation of a foldable IOL with Buratto IOL folder forceps, after enlarging the incision up to 3.2 mm Transition from Phacoemulsification The transition from the US phacoemulsification to the photolysis system is easy, the surgeon has only to be customized on working in a pressurized anterior chamber. Converting into Phacoemulsification If for any reason the surgeon has to interrupt the photolysis technique, for instance when the nucleus is harder than what he expected, before entering with the phaco tip, he has first to enlarge the 10 O’clock incision up to 3.2 mm, then to avoid the anterior chamber collapse due to the excessive
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FIGURE 38.8B Implantation of an injectable acrylic IOL, after enlarging the incision up to 3.2 mm
FIGURE 38.9 Aspiration of viscoelastic solution with I/A cannulas outflow of fluidics, has to stitch the 2 O’clock paracentesis. In this way, it is possible to complete the operation as the usual phacoemulsification. Cataract Surgery and Clear Lens Extraction in High Myopia with Photolysis Laser System: Our Technique In high myopic patients, in whom we implant a non-foldable IOL, the AL-3 (Domilens, Chiron Vision, Lyon, France) we use a scleral approach.
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FIGURE 38.10 Hydration of the two incisions with BSS solution This lens for its concavoconvex shape, seems to maintain better the anatomical relations between the posterior capsule, the vitreous, and the retinal periphery, decreasing in this way the risk of retinal detachments,12 more frequent after clear lens extraction, specially in the high myopic patients, and the posterior capsular opacification (PCO). After preparing the patients with topical anesthesia, we perform a superior limbal conjunctival peritomy, and we insert the Fukasaku cannula (Katena, Products Inc. Denville; New Jersey, USA. Ref. K7–4002) for a sub-Tenon anesthesia with 1 percent lidocaine. A 7 mm Frown incision with a 45 blade is done 2 mm from the limbus (Fig. 38.11 A), then with a crescent knife we create a scleral tunnel 1 mm towards the cornea in order to create an anastigmatic incision (Fig. 38.11B). The procedure continues as usual creating two side ports of 1.4 mm at 10 and 2 O’clock, injection of viscoelastic solutions, CCC with the Condon forceps, hydrodissection, laser photolysis, at that point we open the anterior chamber with a 3.2 mm knife and widening the incision with a crescent knife before IOL implantation (Figs 38.12A to C). Even if the sclerocorneal incision should be self-sealing, because of the abnormal consistency of the high myopic sclera, we prefer to use a continuous 10–0 nylon suture to avoid an against-the-rule (ATR) postoperative astigmatism due to the dehiscence or disinsertion of the sclera, finally we complete the procedure aspirating the viscoelastic solution, hydrating the incisions and
FIGURE 38.11A Frown incision 2 mm from the limbus
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FIGURE 38.11B Creation of a sclerocorneal tunnel, to introduce a polymethylmethacrylate (PMMA) IOL after Dodick’s photolysis in a high myope closing the conjunctival peritomy with diathermy or with one drop of adhesive (ADAL-2 TM, Medical Inc., Alicante, Spain). Postoperative Medication • Dexamethasone alcohol 0.1 percent (Maxitrol, Alcon Cusi’, Barcelona, Spain), prednisolone acetate 1 percent (Pred Forte, Allergan SA, Madrid, Spain) 3×per day per 3 weeks. • Tobramycin eyedrops are used for 3 days at postoperatively. • Diclofenac eyedrops are used for 1 month.
FIGURE 38.12A View of: aspiration cannula, a new infusion cannula provided of a hook for chopping the
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harder nucleus and the two-port side infusion cannula
FIGURE 38.12B Enlarged view of the three cannulas Complications We can just aspect some generic complications in common with the US phacoemulsification technique. Endothelial Cell Count Long-term specular microscopy follow-up of the endothelium preoperatively and postoperatively will be required to document that the rate of endothelial cell loss does not exceed that of
FIGURE 38.12C Enlarged view of the tip of the new infusion cannula
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traditional ultrasound phacoemulsification. In this regard Dodick referred that in his last series of cases, he found that the endothelial cell loss ranged from 0 to 6 percent, and no change in corneal thickness following the procedure occurred.5 Posterior Capsule Rupture In our experience we had only two cases of capsular breaks due to the use of the highlaser power setting used in soft cataracts. Generally no specific postoperative complications happened to our cases, anyway we cannot refer any about other surgeon’s experiences. No other complications were observed. Corneal edema, even minimal, was never observed at the slit-lamp examination, even at the early postoperative period. Advantages and Disadvantages This system appears to be safer for the corneal endothelial cells, for the posterior capsule, and the iris. Practically no heat production is produced and there are no corneal burns. The ergonomic shape of the handpiece gives to the surgeon a more comfortable way of working. Moreover we emphasize the low energy and the low fluidics used, the stability of the anterior and posterior chamber during the procedure, the quietness if compared to the traditional phacoemulsificator device and most important of all the “minimal” incision surgery (less than 2 mm), VS the “small” incision surgery (more than 2 mm). The procedure itself has low cost, considering the quartz fiber, the handpiece and the disposable titanium target. For the moment only the laser system has high cost. Technically the only limitation is the hard cataract. Future Trends The big target pursued by all the surgeons to perform a cataract operation with the “Minimal” incision, seems finally to be catch, and the old dream of injecting a malleable, clear polymer trough a small capsulotomy, capable of accommodation, brings to our memory the Phacoersatz idea.13 Now the biggest effort has to be done by the company interested on inert polymer that could really mimic the human lens and its characteristic accommodation ability. We can imagine that the new kind of IOLs, could be liquid, injectable and made of silicone, hydrogel or collagen.11 Summary More than 20 years have passed since Kelman introduced the US phaco system,1 till Dodick presented his first laser phacolysis cataract extraction.2–4 From that moment different types of phaco lasers have been tried. Actually only two-laser system are used for this purpose: (i) the Nd: YAG laser, and the Er: YAG laser. Our personal experience is referred to the Dodick laser photolysis device. The undoubted advantages (Table 38.1) of this technique are: the minimal incision, the safety for the endothelium, the very low
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rate of posterior capsular rupture, no heat production at the tip and consequently no corneal burns, the very delicate and controllable way of cataract removal, the minimal or practically absent intra/postoperative complications and the safe and fast learning curve. The main technical limitation is represented by the high-density cataracts. Today the most important indication seems to be the surgical treatment of high degree of refractive errors through clear-lens extraction and IOL implantation (phaco refractive cataract surgery). Our experience with high myopic patients, seems to confirm the suitability of this device in order to avoid any complications in treating this particular kind of eyes.12 Because of the safety of this technique, other indications could be—subluxated lens, zonular laxity, post-traumatic cataracts and congenital cataracts. Now, to make use properly of the advantages brought by this “Minimal incision surgery”, we must wait for the technical improvements in the development of new IOLs materials. References 1. Kelman CD: Phacoemulsification and aspiration—a new technique of cataract removal, a preliminary report. Am J Ophthalmol 64:23–35, 1967. 2. “Use of Neodymium-YAG laser for removal of cataracts is reported”. Ophthalmology Times 1:1989. 3. “First Laser Phacolysis proves a success”. Ophthalmology Times, 1991. 4. Dodick JM, Sperber LTD, Lally JM et al: Nd: YAG laser phacolysis of human cataractous lens—a case report. Arch Ophthalmol 111:903–04, 1993. 5. Aasuri MK, Basti S: Laser cataract surgery. Current Opinion in Ophthalmology 10:53–58, 1999.
TABLE 38.1 Dodick’s photolysis laser system: settings (Prof. Jorge L. Alio’, Instituto Oftalmologico de Alicante) Cataract hardness from 0 to Soft clear 5+ lenses
1+
2+
3+
Frequency Laser power
1×sec Low energy
1×sec Low energy
3×sec High energy
Vacuum power (Venturi pump) 250 mmHg Vacuum Mean number of pulses to finish 10 pulses the cataract
250 mmHg Vacuum 40 pulses
2–3×sec High>Low energy 250 mmHg Vacuum 100 pulses
400 mmHg Vacuum 300–400 pulses
6. Dodick JM: Laser phacolysis of the human cataractous lens. Dev Ophthalmol 22:58–64, 1991. 7. Dodick JM, Lally JM, Sperber LTD: Lasers in cataract surgery. Current Opinion in Ophthalmology 4(1):107–09, 1993. 8. Dodick JM, Cristiansen J: Experimental studies on the developement and propagation of shock waves created by the interaction of short Nd: YAG laser pulses with a titanum target—possible implications for Nd: YAG laser phacolysis of the cataractous human lens. J Cataract Refract Surg 17:794–97, 1991. 9. Lewin PA, Bhatia R, Zhang Q et al: Characterization of optoacoustic surgical devices. IEEE Transaction on Ultrasonics, and Frequency Control 43(4):1996.
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10. Alzner E, Grabner G: Dodick laser phacolysis: termal effects. J Cataract Refract Surg 25:800– 03, 1999. 11. “Laser Lens Lysis—a new approach to very small incision cataract surgery” Cataract and Refractive Surgery Euro Times, 6:1997. 12. Dorothy SP Fan, Dennis SC Lam, Kenneth KW Li: Retinal complications after cataract extraction in patients with high myopia. Ophthalmology 106:688–92, 1999. 13. Haefliger E, Parel JM, Fantes F et al: Accommodation of an endocapsular silicone lens (phacoersatz) in non human primate. Ophthalmology 94:471–77, 1987.
