Refractive Surgery (Instant Clinical Diagnosis in Ophthalmology)

Instant Clinical Diagnosis in Ophthalmology

Refractive Surgery

INSTANT CLINICAL DIAGNOSIS IN QPHTHALMOWGY

REFRACTIVE SURGERY Series Editors Ashok Garg MS PhD FI AO(Bel) FRSM FAIMS ADM FICA International and National Gold Medalist Chairman and Medical Director Garg Eye Institute and Research Centre 235-Model Town, Dabra Chowk Hisar-12500S

Emanuel Rosen MD Medical Director Rosen Eye Associates Harbour City, Salford Quays M503 BH

UK

In di a

Editors Frank Jozef Goes MD Medical Director Goes Eye Centre W Klooslaan 6 B 2050 Antwerp Belg ium

Jerome Jean Bovet MD Consultant Ophthalmic Surgeon FMH , Clinique de L'oei l 15, Avenue Du Boi s-de-Ia-Chapelle CH-1213,Onex Switzerland

Bojan Pal Ie MD Chief of the Corneal and Refractive Surgery Department Vision Care, Klinik Pallas, Louis Giraud Sir. 20 4600 Clten Switzerland

Yan Wang MD Professor Tianjin Medical University Director, Refractive Surgery and Vision Correction Centre, Tianjin Eye Hospital and Eye Institute, No.4, Gansu Road Tianjin 300020 Ch ina

8elquiz A Nassaralla MD PhD Consultant Ophthalmic Surgeon, Department of Cornea and Refractive Surgery , Goiania Eye Institute, GOiania, GO Brazil

Foreword Jorge L Alia

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PUbfisfJeq ..by

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USA Office 1745, Pheasant Run Drive, Maryland Heights (Missouri), MO 63043, USA, Ph: 001-6366279734 e-mail: [email protected]. [email protected] Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) © 2009, Editors All rights reserved. No part of this publication should be reproduced, stored in a retrieval system , or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the editors and the publisher. This book has been published in good faith that the material provided by contributors is original. Every effort is made to ensure accuracy of material , but the publisher, printer and editors will not be held responsible for any inadvertent error(s). In case of any dispute, all legal matters are to be settled under Delhi jurisdiction only. First Edition: 2009 ISBN 978-81-8448-452-6 Typeset at JPBMP typesetting unit Printed at Ajanta Offset & Packagings Ltd., New Delhi

Preface In modern day busy and fast life ophthalmologists are glued to their clinical

and surgical practice and have little time to read large volume books. The need of hour is to have pocket size ready recokners enriched with complete and upto-date information of the diseases in a comprehensive manner. At present very few quality ready reference books are available at an International level. After detailed research regarding the needs of ophthalmologists, we have developed a series of 10 Volume ready reference books termed as Instant Clinical Diagnosis in Ophthalmology. Th is series covers Oculoplastic and Reconstructive Surgery, Retina, Lens, Glaucoma, Refractive Surgery, Pediatric Ophthalmology, Strabismus, Anterior Segment diseases, cornea and Neurophthalmology. Present series has been designed to provide up-to-date information of concerned disease in a comprehensive and a lucid manner along w ith high quality clinical photographs in an easy to read format. International Masters of concerned subject have contributed chapters in this series covering Pathophysiology, clinical signs and symptoms, Investigations, differential diagnosis, treatment and prognosis in a simiplified manner. Present volume has been formatted with an aim to provide complete up-todate information about state-of-art Corneal Refractive Surgery and high tech Lenticular refractive surgery under one roof in a compreh ensive manner. Basic

optics and physiology of Refractive errors, advanced Surface Ablation procedures (PRK, Epilasik, Lasek, SBK), Lasik Surgery (Aspheric, customized and wavefront Presbyopic), Phakic rOLs (AC and PC Phakic IOLs, Multifocal lenses, ICL and customized IOLs), Presbyopic surgery lenses (Accommodating and Aspheric lenses) and complications have been covered beautifully by International panel of experts in this field. We are highly thankful to our publisher M/ s Jaypee Brothers Medical Publishers (P) Ltd. specially ShJitendar P Vij (CEO), Mr Tarun Duneja (Director of Publishing) and all staff members for their dedication and hard efforts put in the preparation of this high quality series of Instant Clinical Books. We hope this 10 volume set of ready reference pocket size books shall provide complete and useful clinical information to ophthalmologists all around the world and shall help them to accurately and precisely diagnose, treat and manage their clinical case confidently to the satisfaction and expectations of their valued patients. We also hope this ready reckoner shall serve as useful companion on every clinician's desk. Editors

Contents Section 1: Corneal Refractive Surgery 1. Refractive Errors of the Eye ......................................................................... 2 Grove fD, David Meyer (South Africa) 2. Basic Optics of Refractive Surgery ........................................................... 10 Yan Wang, Ming Liu, Kanxing Zhao, Lihua Fang, Feng Rao, fie Hou (China) 3. Pathophysiology of Various Refractive Errors Like Myopia, Hyperopia, Astigmatism, Accommodation and Presbyopia .............. 18 Ahmad K Khalil ( Egtjpt) 4. Orbscan .......................................................................................................... 24 Amar Agarwal, Nilesh Kanjiani, Athiya Agarwal, Sunita Aganval, Ashok Garg (India) 5. Photorefractive Keratectomy with Mitomycin C for High Myopia ........................................................................................... 36 Belquiz A Nassaralla, foao f Nassaralla fr (Brazil) 6. Photorefractive Keratectomy after Penetrating Keratoplasty ............ 42 Belquiz A Nassaralla, foiio f Nassaralla fl" (Brazil) 7. Phototherapeutic Keratectomy on Recurrent Corneal Erosions ....................................................................... 46 Belquiz A Nassara lla, folio f Nassaralla fr (Brazil) 8. Myopic Photorefractive Keratectomy Using Solid State Laser .......... 50 Nikolaos S Tsiklis, George D Kymionis, George A Kounis, Ioannis G Pallikaris (Greece) 9. Photorefractive Keratectomy for Residual Myopia following Radial Keratotomy .................................................................... 62 Belquiz A Nassaralla, foiio f Nassaralla fr (Braz il) 10. Recent Advances in Photorefractive Keratectomy ............................... 70 C Banu Casar (Turkey) 11. Painless EpiLASIK ...................................................................................... 80 Chu Renyuan, Zltou Xingtao, Wu Ying (Ch ina) 12. Wavefront-guided Photorefractive KeratectomyToday and the Future .................................................................................. 86 Weldon W Haw, Edward E Manche (USA) 13. Presby-EpiLASIK in Pseudophakic Eyes with the Wavelight Allegretto ................................................................... 92 Frederic Hehn (Fra nce)

xx Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) 14. EpiLASIK with Mitomycin C ................................................................... 110 D Ramamurthy, Chitra Ramamurthy (India) 15. One-shot Epithelium-rhexis: Personal Technique ............................. 118 Roberto Pinelli (Italy) 16. Surface Ablation after Laser In Situ Keratomileusis; Retreatment on the Flap ........................................................................... 126 Jeroen JG Beerthuizen (Netherland) 17. Wavefront Analysis and its Clinical Significance .............................. 130 Yan Wang, Lihua Fang, Boyan Li, Kanxing Zhao (China) 18. Wavefront LASIK ...................................................................................... 134 Mark Wevill, Emanuel Rosen (UK) 19. Aspheric Ablation with Nidek Platform ............................................... 148 S Bharti IIndia) 20. Costumized Excimer Laser Treatment Using the Wavelight Allegretto Eye Q Laser .......................................................... 156 Johan A de Lange (South Africa) 21. Advances EpiLASIK and LASEK ........................................................... 192 Bojan Fajic (Switzerland) 22. Wavefront Optimize and Astigmatism correction with the Allegretto Excimer Laser .......................................................... 202 Jerome Jean Bovet, Auguste Chiou (Switzerland) 23. Aberropia: A New Refractive Entity ...................................................... 214 Amar Agarwal, Nilesh Kanjiani, Soosan Jacob, Athiya Agarwal, Sunita Agarwal, Tahira Agarwal, Ashok Garg (India) 24. Topographic and Aberrometer Guided Laser ..................................... 226 Amar Agarwal, Sunita Agarwal, Athiya Agarwal, AS/10k Garg IIndia) 25. Refractive Change after RK ..................................................................... 236 Frank JozefGoes (Belgium) 26. LASIK Complications and Management .............................................. 242 Yan Wang, Wenxiu Lu, Kanxing Zhao, JinZing Yu, Jianmin Gao (China) 27. Cross-linking Plus Topography-guided PRK for Post-LASIK Ectasia Management .................................................... 258 A John Kanellopoulos (Greece) 28. PRK for Low to Moderate Myopia ......................................................... 270 Michael 0' Keefe, Caitriona Kirwan (Ireland) 29. LASEK Procedure with the Use of Mitomycin C ................................. 276 Iwona Liberek, Justyna Izdebska (Poland) 30. Transepithelial Cross-linking for the Treatment of Keratoconus ....................................................................... 286 Roberto Pinelli, E Milani (Italy) 31. Sub Bowman's Keratomileusis: Combining the Best of PRK and LASIK for Optimal Outcomes ................................................................ 292 Daniel S Durrie (USA)

Contents

xxi

32. cTEN™- Custom Transepith elial "No-touch, One-step, All-laser" Refractive and Therapeutic Ablations with the iVISTM suite .............................................................................. 312 Carlo Francesco Lovisolo, Charles Wm Stewart (Italy) 33. Astigmatism ................................................................................................ 330 Frank Jazef Goes (Belgium) 34. Customized LASIK for Presbyopia: PMLTM (Presbiopic Multifocal LASIK Technique) ........................................... 334 Roberto Pinelli (Italy) 35. Amblyopia .................................................................................................. 348 Frank JozefGoes (Belgium) 36. Laser Scleral Ablation for True Accommodation for Presbyopia ............................................................. 352 JT Lin (Taiwan) 37. Solid State Lasers for Refractive Surgery ............................................. 360 Emanuel Rosen (UK), Tarak Pujara (Australia) 38. Dry Eye after Refractive Surgery ............................................................ 394 Belquiz A Nassaralla, Joao J Nassaralla Jr (Brazil) 39. Corneal Biomechanical Properties ......................................................... 402 Jorge L Ali6, Mohamed H Shabayek (Spain) 40. Future of LASIK Surgery .......................................................................... 406 Arun C Gulani, Tracy Schroeder Swartz (USA)

Section 2: Lenticular Refractive Surgery 41. Refractive Management of Hyperopia ................................................. 416 Ahmad K Khalil (Egypt) 42. Restoration of Accommodation by Capsular Bag Refilling .............. 420 Okihiro Nishi, Kayo Nishi, Yutaro Nishi, Shiao Chang (japan) 43. Custom ICLs ............................................................................................... 430 Carlo Francesco Lovisolo (Italy) 44. Mini Incision IOL Implantation-Current Scenario .......................... 448 Roberto Bellucci, Simonetta Marselli (Italy) 45. Monofocal HOA Free IOL to Correct Secondary Presby-LASIK ..... 456 Frederic Hehn (France) 46. Man aging Intraoperative Floppy Iris Syndrome ................................ 470 David F Chang (USA) 47. Artisan, Toric Artisan an d Artiflex Phakic Intraocular Lenses ........ 478 Johan A de Lange (South Africa) 48. Orthok eratology ......................................................................................... 504 Antonio Calossi, Carlo Francesco Lovisolo (Italy) 49. Aspheric IO Ls (Wavefront Based IOLs) ............................................... 518 Sanjay Chaudhary (India)

xxii

Instal1t Clinical Diagl10sis ill Ophtllnllllology (Refractive SlIrgenJ)

50. Dual Optic Accommodative IOLs .......................................................... 528 GU Auffartll (Germany) 51. Anterior Chamber Phakic IOL with Angle Fixation ........................... 532 Juan C Rocco (Argentina) 52. Advacnes in Microphakonit for Refractive Lens Exchange (MIRLEX)-A New Technique ............................................................... 542 Arturo perez-Arteaga (Mexico) 53. Blue Light Filtering Intraocular Lenses ................................................. 554 Swati Piluljllele, Lalit Alok, Anand Aga rwal, Tanuj Dada (India) 54. Refractive Lens Exchange: Current Perspectives ............................... 560 T Howard Fine, Richard S Hoffman , Mark Packer, (USA ) 55. Advances in Optic Designs to Reduce PCO ......................................... 574 WoifBuehl, Oliver Findl (Austria) Index ...... ............... ............................... ... ...................................................... 583

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1 Refractive Errors ,. of the Eye Grove JD, David Meyer (South Africa)

INTRODUCTION

A refractive error (ametropia) is defined as failure of parallel light rays to focus on the retina w ith the eye in a non-accommodating state. Three conditions of ametropia are found , namely myopia, hypermetropia and astigmatism. Although not adhering to the true definition of ametropia, presbyopia (agerelated inadequacy of accommodation) is often included. MYOPIA Optical Principles

Parallel light ra ys focus anterior to the retina. Axial myopia - axial length too long for the optical power of the eye, e.g. posterior staphyloma, buphthalmos. Refractive (index) myopia -Optical power too strong for the axial length of the eye, e.g. keratoconus, nucleosclerosis, lenticonus, spherophakia. Clinical Signs and Symptoms Symptoms

Decreased ("blurred") vision for distant objects Asthenopia "Squinting" (piJ1hole effect). Signs

Decreased visua l ac uity Visual field - Contracted Ring scotoma An terior segment - Cornea might be slightly larger Anterior chamber deep Lens -Early cataract formation common abnormalities, e.g. spherophakia, lenticonus occasional phacodonesis. 2

Refractive Errors of the Eye

Fig. 1: Myopia- Parallel light rays ente ring the eye come to a point focus anterior to the retina

Fig. 2: Hype rmetropia- Parallel light rays entering the eye come to a point focus posterior to the retina

Sturm's conoid

Fig. 3: Astigmatism-The optical power of the eye varies in different meridians thus replacing a focus point with orthogonal focus lines (StOrm's conoid)

3

Ills tall t Clillical Diagl/osis ;" Opirtlralmologrj (Refractive SlIrgenj) Fundus: Disc -

Large Tilted Myopic crescent Choroidal crescent Tesselated Chorioretinal atrophy Lacquer cracks Coin hemorrhages Choroidal neovascu lar membranes

Fuch's spots Complications: Staphylomas - macula hole foveal retinoschisis Peripheral degenerations with retinal hole formation. Rhegmatogenous retinal detachment.

Physiological myopia - associated with nor ma l growth of th e refractive components of the eye resulting in mild to moderate nearsighted ness. Pathologic myopia -excessive growth of the axial length with normal growth of other componen ts of the eye resulting in severe nearsightedness. INVESTIGATIONS

Visual acuity - Near Distance

Pinhole test, Potential aguity (PAM) Refraction - Objective Subjective Visual fields Biomicroscopy - An terior segment and dilated fundus examination. Corneal topograph y Pach ymetry Anterior chamber depth analysis Wavefront aberometry. Differential Diagnosis

Hysteria Drugs - Anticholinesterase Pathologic myopia - Choroideremia Gyrate atrophy Diffuse choroida l atrophy Progressive bifocal chorioretinal atrophy. 4

Refractive Errors of the Eye

5

E "'c o

Decline in amplitude of accommodation

'~

'S;

ro

~ 10

'0 C

'0

"- 20

ro

~ 40

Presbyopia

o

10

20

30

40

50

60

70

Age in years

Fig. 4: Presbyopia- Difficulty or discomfort with near vision tasks due to age related reduction in accommodation amplitude and subsequently near point of clear vision

\

5

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) Treatment

Spectacles Contact lenses Surgical- Corneal surgery - Radial Keratotomy (RK) - Laser refractive - Laser-assisted in situ kera tomileusis (LASIK) Laser assisted sub-epithelial keratomileusis (LASEK) Photorefractive Keratectomy (PRK) - Onlays and Inlays - Epikeratoplasty - Intrastromal Ring Segments - Intraocular surgery - Phakic IOL - anterior chamber posterior chamber - Clear Lens Extraction with or without multifocal intraocular lenses. Prognosis

Physiological myopia - usually stabilized by the age of 21 years. Pathologic myopia - tends to progress with or without resultant complications. prognosis dependant on type and degree of pathology. HYPERMETROPIA Optical Principles

Parallel light rays focus posterior to the retina. Axial hypermetropia - Axial length too short for the optical power of the eye. Refractive hypermetropia - Optical power too weak for the axial length of the eye, e.g. aphakia, microphthalmos, cornea plana. Clinical Signs and Symptoms

Symptoms: Decreased (blurred) vision especially for near objects. Asthenopia Signs: Decreased visual acuity Anterior segment: - Cornea plana Anterior chamber might be shallow Fundus: Disc - Small Crowded Shot silk retina Vessels - Tortuosity Abnormal branching Types: Total: (hypermetropia under total cycloplegia) Latent - Disguised by ciliary muscle tone Manifest - Facultative - correctable by accommodation Absolute - remaining hypermetropia not correctable by accommodation. 6

Refractive Errors of tile Eye Investigations

Visual acuity

- Near - Dis tance

Pinhole tes t, PAM Refraction - Objective - Subjective - Cycloplegic Biomicroscopy - Anterior segment and dil ated fundus exa mination. Gonioscopy Corneal topography Pachymetry Anterior chamber depth analysis Wavefront aberometry. Differential Diagnosis

Drugs Tumors

- cycloplegics - Orbital - In traocular.

Macular edema Treatment

Spectacles Con tact lenses

Surgica l - Laser refractive - LASIK LASEK

PRK - Corneal surgery

- Onlays and Inlays - Thermokeratoplasty

- Intraoc ular surgery

- Phakic IOL

-

Keratophakia Epikeratoplasty Laser Cond ucti ve

- Anterior chamber - Posterior chamber

- Clear Lens Extrac tion Prognosis

Good prognosis with all modalities of treatment. Increased risk of angle closure glaucoma. Ea rly onset presbyopia.

7

Installt Clillical Diagnosis ill Opl.thall11ologlJ (Refractive SurgenJ! ASTIGMATISM Optical Principles

Optical power of the eye varies in different meridians thus rep lacing a focus point w ith orthogonal focus lines (Sturm's conoid). Regular as tigmatism - principal meridians 90° to each other. Oblique astigmatism - meridians not near 90° and 180°. Irregular astigmatism - principal meridians not at 90° to each other. Clinical Signs and Symptoms

Symptoms: Decreased vision. Asthenopia Signs: Diagnosed during objective or subjective refraction an d corneal topography. Simple astigmatism - one meridian = emmetropic other meridian ;:::: either myopic or hypermetropic

Compound astigmatism - both meridia either myopic or hypermetropic Mixed astigmatism -one meridian myopic and the other hypermetropic. Investigations

Visual acuity

- Near - Distance

Pinhole test, PAM Refraction - Objective - Subjective Biomicroscopy - Anterior segment and dilated fundus examination. Corneal topography Pachymetry Anterior chamber dep th analysis Wavefron t aberometry. Treatment

Spectacles Contact lenses Surgical - Laser refractive - Corneal surgery

8

LASIK, LASEK, PRK (wavefront guided) Transverse keratotomy Arcuate Keratotomy Thermokeratoplasty - Laser - Conductive Intraocular surgery - Toric Phakic 10L - anterior chamber - posterior chamber - ToricJOL during cataract surgery -

InstalltClinical Diagllosis ill Ophthall1lo1oglJ (Refractive SurgenJ) ASTIGMATISM Optical Principles

Optical power of the eye varies in different meridians thus replacing a focus point with orthogonal focus lines (Sturm's conoid). Regular astigmatism - principal meridians 90° to each other. Oblique astigmatism - meridians not near 90° and 180°. Irregular astigmatism - principal meridians not at 90° to each other. Clinical Signs and Symptoms

Symptoms: Decreased vision. Asthenopia Signs: Diagnosed during objective or subjective refraction and corneal topography. Simple as tigmatism - one meridian = ernmetropic other meridian = either myopic or hypermetropic Compound astigmatism - both meridia either myopic or hypermetropic Mixed astigmatism - one meridian myopic and the other hypermetropic. Investigations

Visual acuity

- Near - Distance

Pinhole test, PAM Refraction - Objective - Subjective Biomicroscopy - Anterior segment and dilated fundus examination. Corneal topography Pachyrnetry Anterior chamber depth analysis Wavefront aberometry. Treatment

Spectacles Contact lenses Surgical - Laser refractive - Corneal surgery

8

-

LASIK, LASEK, PRK (wavefront guided) Transverse keratotomy Arcuate Keratotomy Thermokeratoplasty - Laser - Conductive Intraocular surgery - Toric Phakic IOL - anterior chamber - posterior chamber - ToricIOL during cataract surgery

Refractive Errors of the Eye

Prognosis Regular astigmatism - Good prognosis with all modalities of treatment. Irregular astigmatism - Hard contact lenses or Keratoplasty required.

PRESBYOPIA Optical Principles Difficulty or discomfort of near vision due to age related reduction in accommodation amplitude.

Clinical Signs and Symptoms Symptoms: Decreased vision for near objects/ tasks. Asthenopia Signs: Decreased near visual ac uity. Decreased amplitude of accommodation.

Investigations Visual acuity

- Near - Distance Pinhole test, PAM RAFrule Refraction - Objective - Subjective Biomicroscop y - Anterior segment and dilated fundus examination. Corneal topography Pach ymetry Anterior chamber d epth analysis.

Differential Diagnosis Drugs - Parasympatholytics Tranquilizers Neurologic disorders - encephalitis closed head trauma.

Treatment Spectacles

- Reading . Multifocal/ progressive Contact lenses - Multifocal monovision Surgical - Laser refractive- LASIK - Corneal surgery - Intraocular surgery

- Monovision presby-LASIK - Thermokeratoplasty - Accommodative IOL Diffractive multifocal IOL Refractive multifocal IOL.

9

2 Basic Optics of Refractive Surgery Yan Wang, Ming Liu, Kanxing Zhao, Lihua Fang, Feng Rao, Jie Hou (China)

LIGHT, PHYSICAL OPTICS, GEOMETRICAL OPTICS

Light is a part of e lectromagnetic wave, and electromagnetic wave is a travelin g tran sverse wave of electric and magnetic fi eld. Physical optics views light as waves. Three principa l charac teristic of a wave are its wavelength, amplitude and frequen cy. Wavelength is determined by the distance between the nearest crests of the wave (A,). Amplitude is the maximum value attained by the electric field as the wave propagates (A ), determining the inten sity of the wave. Frequency is the number of wave crests tha t pass a fixed point per second. Geometrical optics conceives of ligh t as ra ys and en ables us to deal w ith the imaging properties of lenses and mirrors. REFLECTION, REFRACTION, DIFFRACTION, SCATTERING OF LIGHT

At the optical interface, the direction of the reflected ray bears a definite relation ship to the direction of the inciden t ray. 111e angle between the incident ray and th e norma l is known as the angle of incidence. The angle between the reflected ray and the normal is known as the angle of reflection . The law of reflection states as following: 1. The reflected ray lies in the sa me plan e with the incident ray and the surface normal; 2. The an gle of reflection equ als the angle of the incidence. As light passes from one transparent medium to another, its speed and bends are changed. The angle between the light ray and the normal is called the angle of refraction. The law of refraction consists of two parts: 1. The incident ray, surface normal and refracted ray lie in the same plane; 2. The an gle of incidence is related to the angle of refraction by the following formula: nj sine; = n, sine, Where: " i is the refractive index of the medium the light is leaving; OJ is the incident angle; II , is the refractive index of the medium the light is entering;O,is the refractive angle. 10

Basic Optics of Refractive SlIrgenj

1

A

_I

Fig . 1: Electromagnetic wave

n, n,

Fig . 2: Reflection and refraction

11

Instant Clillical Diagnosis ill Ophthalmology (Refractive Surgery) In the eye, the refraction shows the ability of the eye to bend light so that an image is focused on the retina. Diffraction is the slight bending of light as it passes around the edge of an object. All waves are subject to diffraction when they encounter an obstruction, an aperture or other irregularity in the merliurn. The mount of bending depends on the relative size of the wavelength of light and the object. The shorter the relative size, the less the diffraction is. Scattering of light occurs at irregularities in the light path, such as particles or inclusions in an homogeneous medium. Scattering caused by very small particles, such as the molecules in the atmosphere, is called Rayleigh scattering. Rayleigh sca ttering is generally very weak, and it varies according to wavelength, with greater at shorter wavelengths. The sky appears blue because blue light from the sun is scattered more than sunlight of longer wavelengths. Larger particles, such as dust in the air, scatter light more intensely and w ith less dependence on wavelength. ABERRATION, WAVEFRONT ABERRATION, CHROMATIC ABERRATION

In paraxial optics, all paraxial rays focus to a point. With nonpar axial rays,

the focus is not stigmatic. Deviations from stigmatic imaging are called aberrations.

A wavefront is a surface along the light path that contains all points of equal phase. Light from a point object will emit perfectly spherical wavefronts. When these wavefronts go through an optical system, the wavefront curvature is changed. If the optical system is perfect, the wavefronts that leave the exit pupil are also perfectly spherical; if the optical system is aberrated, the wavefronts that leave the exit pupil are also aberrated. The difference between the perfectly spherical wavefront and aberrated wavefront is wavefront aberration. Aberration that results in distortion of color is called chromatic aberration. There are two types of chromatic aberration. Longitudinal chromatic aberration is the inability of optical system to focus different wavelengths of light onto the exact same focal plane. Transverse chromatic aberration is caused by the optical system magnifying different wavelengths differently. EMMETROPIA, MYOPIA, HYPEROPIA, PRESBYOPIA

Emmetropia is the refractive state in which parallel rays of light from an object at infinity focus exactly onto the retina. The far point of the emmetropic eye is at infinity, and infinity is conjugate with the retina.

12

Basic Optics of Refractive SlIrgenJ

Fig . 3: Diffraction

Fig. 4: Chromatic aberration

Fig. 5: Emmetropia

13

Jllsta/lt Clinical Diagnosis ill Ophthalmol0:5lJ (Refractive SurgenJ)

In myopia, para llel light rays from an object at infinity con verge too soon and thus focus m front of the reti na, forming a blurred image on the retina. The far pomt of ti1e eye is in frontof the eye, between the cornea and optical infinity. In h yperoPIa, parallel hght rays from an object at infinity focu ses behind the retma. The vIrtual far point of the eye is behind the retina. Presbyopia is the gradual loss of accommodati ve response resulting from loss of elasticIty of the lens. Accommodative amplitude diminishes inexorably WIth age. It becomes a clinical problem when the remaining acco mmodate amplItude IS msuffi Clent for the patient to read and carry out nea r-vision ta sks.

CURVATURE, RADIUS OF CURVATURE At position s, the curvature is the magnitude of the change in w1ite tangent vector per W1i t change in distance along the curve, which is defined by: x:(s) = I dT~;s))1

Where, the vector T being a unit vector has no dimension; that is, it is W1affected by a lllliforn1 change in scale of aUcoordinates. s is a length; therefore dT - has the dimension of the reciprocal af a length, that is, of the reciprocal of

ds

a distance.

The radius of curvature is the reciprocal af curvature, which is a length. If the curvature is 0, a straight line, the radius of curvature is infinite, or wldefined .

Refractive surgery ma y involve altering the curvature of the cornea. Q-FACTOR, PROLATE, OBLATE

The curvature of an ellipsoid can be expressed as an asphericity quotient, called the Q-facta r. The Q-factor far a sphere is 0, the Q-factor for a prolate ellipsOid is negati ve and the Q-factor for an oblate ellipsOid is positive. OPTICAL AXIS, VISUAL AXIS

The human eye is not a centered optica l system. The optica l axes af the cornea and lens are not coincident (i.e. the centers of curva ture of their refracting surfaces do not all fall on one straight line). Nevertheless, we can define an approximation to the optical axis of the eye as the straigh t line that by best fit passes closest to all of the centers of curvature. The visua l axis is usually defined as the broken line that connects the fixation point with the fovea and passes through the nodal points.The fovea of the retina is not on even the approxin1ate optical axis of the eye. The visual axis of the eye extends from the fovea through the nodal point of the eye and out throug h th e cornea to an object, a poi.nt at "infinite" distance, such as a star. 14

Basic Optics a/Refractive SlIrgenJ

Fig. 6: Myopia

Fig . 7: Hyperopia

Aspherical surface

Spherical surface

Prolate shape

f\\

0=0 Radius (mm)

Oblate shape

~ 0<0

0>0

Fi g. 8: Q -fac tor

15

Illstallt Clillical Dingllosis ill OplttlwlmologtJ (Refractive SlIrgenJ) MTF, PSF

The modulation of an image is defined as modulation

Lmax - Lmin Lmax + Lmill

Where Lmax and Lmill are the nlaximum and minimum lunlinance of the

image, respectively. The modulation transfer function (MTF) is d efin ed as the modulation of the image M, divided by the modulation of the object M o' M. MTF= - '

Mo

Modulation transfer function is a quantity representing a relationship between the sample and result image. Consider a very small point of light. If the visual system had perfect optics, the image of this point on the retina wou ld be identical to the original point of light. However, the eye's optics is not perfect. So the point has a blurred image on the retina, and the relative intensity of the image is distributed across the retina, which is d efined as a function of d istance, called the po int spread fun ction (PSF).

16

Basic Optics of Refractive SlIrgenJ

Fig. 9: Visual axis and optical axis (a) Center of pupil , (b) Center of cornea , and (c) Visual axis

17

3 Pathophysiology of Various Refractive Errors Like Myopia, Hyperopia, Astigmatism, Accommodation and Presbyopia Ahmad K Khalil (Egypt)

18

Inability of the human eye to bring a focused image on the retina in various situations w ith subsequent blur and visual discomfort is the hallmark of various refracti ve errors. Hyperopia occurs \,,,hen the rays come to a focus behind the retina, myopia when the rays come to a focus in front of the retina. 111 astigm atism, rays come to differen t foc i due to difference in the power of the eye in diffe rent meridians, and in presbyopia, the eye is unable to bring rays emanating of near objects to focus on retinal level. The commonest cause of hyperopia is probably a shortened eye; eyes with short axial lengths. Flat keratometric readings and decreased refractive index of the lens are other causes. A combination of several factors often co-exist. In younger age, much of the hype ropia can usually be corrected by the patient's own accommodation, which ll1creases the effecti ve power of the eye brin ging incident rays to a focus on the retinal leve l (facultative hyperopia). With advancing age the accommodative effort cannot be sustained and symptoms of hyperopia with blurring and eyestrain become more and more manifest. Symptom atic h yperopia are trea ted by glasses, con tact lenses. As explained else were in this book, laser vision correction is useful for hyperopia degrees up to plus 6.0. Phakic lens implanta ti on and refractive lens exchange are suitable for higher degrees. Long axia l length, increased curvature of the cornea and increased refractive index of the lens are main causes of myopia. Blurring of distance vision is u niversal and proportionate to the degree of myopia. Patients with lower degrees of myo pia have the advantage of clear near vision, as the divergent rays from the near object come to focus on the retina with no need for accommodative effort or need for correction. This is an added ad van tage ll1 middle age, negating the ll1Cidents of presbyopia. Concave lenses in glasses or contacts help bring the raise to focus back on the retina laser vision correction is very useful in correcting myopia degrees

PatilOphysiologtj of Variolls Refractive Errors Like Myopia, Hyperopia

Focal point is behind the retina

Fig. 1: Hype ropia

Focal point

~~~:;:;;;!~i"-- is in fron t

of the retina

Fig. 2: Myopia

Multiple focal

~~~~~~"'-_ points· images -

on retina are blurry

Fig. 3: Astigmatism

19

Instal/t Clinical Diagnosis ill OplrtlralmologtJ (Refractive SlIrgenJ)

up to -10.0. Phakic lens implantation and refractive lens exchange are suitable for higher degrees. Difference in power in various axes is casused mainly by corneal curvature errors. Commonest cause is congenital curvature astigmatism. Others involve

keratocon us, scarred cornea, surgica lly induced, and lenticonus. [n simple astigmatism, the focus in one axis fa lls in the retina, and in front or behind the retina in the perpendicular axis. In compound astigmatism, both foci lie together in front or behind the retina, while in mixed astigmatism, one focus lies in fron t and the other behind the retina. H orizon tal corneal diameter (12 mm) is slightly larger than its vertical diameter (11.5 mm), with co-incide nt sli ght fla ttening of the horizontal meridian. This is caused by the continuous movement and slight pressure of the eye lids increasing the vertica l curvature in most subjects by about 0,12 D. Therefore, astigmatism associated with increased curvature of the vertical merid ian is called 'with the role astigma tism", expressed in horizontal lninus cylinder. Astigmatism can be treated with both glasses and hard contact lenses. Soft toric contact lenses are often less satisfactory because of the potential rotation-movement of the lens on the eye surface. Laser vision correction is usually very effective in ma naging asti gmatism not associated with other corneal pathology. Recently, toric ICLs began to be used satisfactorily. ACCOMMODATION AND PRESBYOPIA

The ability of a distance-corrected human eye to see at near depends on 2 components; true accommodation (o ptical change in power of the eye), and to a lesser extent; pseudo-accommod ation caused by increased depth of field (myopic astigmatism, vertical coma and other highe r order aberrations; HOAs and Pinhole vision) Theories of Accommodation

Along the centuries and up to this very moment, many theories have sprung out to explain the actions taken by the eye to change its power and bring images of near objects to proper focus on the retina. Theories involving changes in lens thickness, consistency, elasticity or changes in Ciliary muscle contracti lity or distribution of fibers, or changes in zonular fibers have been proposed. The most accep ted theories discussed in recent literature are the time honored Helmholtz theory and the new Schacher theory. Helmholtz Theory was proposed in the mid-nineteen th century, and with minor modifications, has stood the test of time. Developing modern techniques have 20 proven many of its constituents. Briefl y, contraction of the ciliary muscle

Pathophysiology of Various Refractive Errors Like Myopia, Hyperopia

Fig . 4 : Helmholtz theory of accommodation

Fig . 5: Schacher theory of accommodation

21

Installt Clinical Diagllosis ill Oplrthalmologtj (Refractive SlIrgenj) causes narrowing of the ciliary mu scle ring with relaxa tion of zonu lar fibers and subsequent decrease in the lens equatorial diame ter, an increase in lens

axial thickness, and the lens anterior and posterior central surfaces undergo an increase in curvature of the elastic lens increasing its power. Loss of accommod ation is mainly caused by senile hardening of the lens substance, preventing it from changing shape. In the mid 1990s, Schacher proposed his new theo ry of accommodation. He suggested that equatorial zon ules insert into the an terior cil iary muscle at the root of the iris, while an terior and posterior zonules insert into the posterior ciliary bod y. During ciliary mu scle con tracti on, it curls toward the sclera at the iris root increasing tension on the equatorial zonular fib ers (opposite ac tion to that in Helmholtz theory!), and releasing tension on the anterio r and posterior zonular bund les, causing flattening of the peripheral lens surfaces w hile increasing the central anterior and posterior lens surface curva tu res. Modern investigatin g techniques, however, like UBM, high resolution M RI have, however, proven severa l of the compone nts proposed by H elmholtz, like re lease of zonular tension during accommodation, lens equatorial movement away from sclera with accommodation. Zon ular fiber d istribu tion proposed by Schacher could not be demonstrated in humans. Failure of Accommodation ; Presbyopia

With growing age, the amplitude of true accommodation decreases, beginning early in life-in childhood or adolescence. Typically, between the ages of 38 and 43 years, these changes reach the stage at which accommodative loss is sufficien t to cause the blurred-vision symp toms of p resbyopia. The word presbyopia is based on a Greek word that means "aging eye". Incipient Presbyopia: It rep resents the earliest stage with nocturnal presbyopia (wider pupil with less dep th of foc us), distance blur fo llowing near work. This d istance blur is caused by a slowed response of the lensciliary body com plex during relaxa tion from near foc us (which has been attained with considerable effort). Typica lly, the patien t's history suggests a need fo r a reading additio n, but the patient perfo rms well visuall y on testing and, given the choice, ma y actuall y reject a near vision prescription. Functional Presbyopia: The age at which presbyopia becomes symptomatic varies. So m e patients are symptoma tic at an earlier age (premature p resbyo pia); others later than ex pecte d, largely d ue to va r ia tion s in environment, task requirements, o r nutrition. Absolute Presbyopia : As a result of the continuous grad ua l decline in 22 accommod ation, functional p resbyopia progresses to absolute presbyopia.

Pathophysiology of Various Refractive Errors Like Myopia, Hyperopia

Absolute presbyopia is the condition in which there is virtually no accommodati ve ability. SimjJar to accommodation, the etiology of presbyopia remains elusive in many aspects. There are theories incriminating the lens and its capsule, ciliary muscle and choroid, or changes in the geometry of zan ular fibers attachment. The lens has won the most theories and duly so for ca using presbyopia. Changes in its sagittal thickness, equator diameter, degree of anterior curvahu e, internal lens structure (decrease in nucleus ref index, increase in water soluble crystallins), Lens Biomechanics; (sclerosis), capsule thickness, and atrophy of the ciliary muscle have been proposed with various levels of evidence. [n the past decad e, refractive su rgeons have gone through various innovative approaches to tackle presbyopia, often calling it ' the last frontier" using various approaches; corneal approach (presby LASIK) playing on the theme of increasing pseudo-accommodation. Platforms are being developed by various researchers, and achieving reasonable success rates. Lenticular app roa ch invol ves impl anta tion of accommodative and pseudoaccommodative lenses. Scleral expansion surgery have also been tried based on the concept of Schacher in which lost accommodation is caused by equatorial expansion of the lens. Thls surgery, however, have met ve ry limited wd-long-term success so far.

23

4 Orbscan Amar Agarwal, Nilesh Kanjiani, Athiya Agarwal, Sunita Agarwal, Ashok Garg (India)

INTRODUCTION

Keratometry and corneal topography with placido disc systems were originally invented to measure anterior corneal curvature. Computer analysis of the more

complete data acquired by the latter has in recent years has been increasingly more valuable in the practice of refractive surgery. The problem in the placido disc systems is that one cannot perform a slit scan topography of the cornea. This has been solved by an instrument called the Orbscan that combines both slit scan and placido images to give a very good composite picture for topographic analysis. Bausch and Lomb manufacture this. PARAXIAL OPTICS

Spectacle correction of sight is designed only to eliminate defocus errors and astigmatism. These are the only optical aberrations that can be handled by the simplest theory of imaging, known as paraxial optics, which excludes all light rays finitely distant from a central ra y or power axis. Ignoring the majority of rays entering the pupil, paraxial optics examines only a narrow thread-like region surrounding the power axis. The shape of any smoothly rounded surface wi thin this narrow region is always circular in cross-section. Thus from the

paraxial viewpoint, surface shape is toric at most: only its radius may vary with meridional angle. As a toric optical surface has sufficient flexibility to null defocus and astigmatism, only paraxial optics is needed to specify corrective lenses for normal eyes. Paraxjal optics is used in keratometers and

two-dimensional topographic machines. RAYTRACE OR GEOMETRIC OPTICS

The initial objective of refractive surgery was to build the necessary paraxial correction into the cornea. When o utcomes are less than perfect, it is not just

because defoc us correction is in adequate . Typica lly, other aberrations (astigmatism, spherical aberration, coma, etc.) are introd uced by the surgery. These may be cau sed by d ecentered ablation, asy mmetr ic healin g, biomechan ical response, poor s urgical planning, and inadequate or 24 misinformation. To assess the aberrations in the retinal image all the light rays

Orbscatl

Fig . 1: Orbscan

Incident

Reflected

Fig. 2: Specular reflection. This is used in keratometers . This is angle dependent

25

InstantClillical Diagllosis in Oplttl/almologtJ (Refractive SlIIgenJ)

entering the pupil must properly be taken in acco unt using ray trace (or geometric) optics. Paraxial optics and its hypothetical toric surfaces must be abandoned as inadequate, w hich e linunates the need to measure surface

curvature. Ray trace optics does not require surface curvature, but depends on elevation and especially surface slope. The Orbscan uses ray trace or geometric optics.

ELEVATION Orbscan measure elevation, which is not possible in o ther topographic machines. Elevation is especially important because it is the only complete scalar measure of surface shape. Both slope and curvature can be mathematically derived fro m a single elevation map, but the converse is not necessarily true. As both slope and curvature have different values in different directions, neither can be completely represented by a Single map of the surface. Thus, when characterizing the surface of non-spherical test objects used to verify instrument accuracy, elevation is always the gold standard. Curva ture maps in corneal topog raphy (usually misnamed as power or dioptric maps) only display curvature measured in radial d irections from the map center. Such a presentation is not shift-invariant, which means its values and topograph y change as the center of the map is shifted. In contrast, elevation is shift-invariant. An object shifted with respect to the map center is just shifted in its elevation map. In a meridional curvature view it is also described. lbis makes e levation maps more intuitively understood, making diagnosis easier. To sumn1arize: 1. Curva ture is not relevant in ray trace optics.

2. Elevation is complete and can be used to derive surface curvature and slope. 3. Elevation is the standard measure of surface shape. 4. Elevatio n is easy to understand . The problem we face is that there is a cost in converting elevation to curvature

(or slope) and vice ve rsa. To go from elevation to curvature requires mathematical differentiation, which accentuates the high spatial frequency components of the elevation function. As a result, random measurement error

or noise in an elevation measurement is Significantly multiplied in the curvature resul t. The inverse o pe rationr mathematical integration used to convert curvature to elevation, accentuates low-frequency error. The Orbscan helps in

good mathematical integration. This makes it easy for the ophthalmologist to understand as the machine does all the conversion.

ORBSCANlANDII Previously, Orbscan I was used. This had only slit scan topographic system. Then the placido disc was added in Orbscan I. Hence, Orbscan II came into the 26 picture.

Orbscan

Incident

Scattered

Fig. 3: Back-scatter reflection. This is used in orbscan . This is omni-directional

\+- --1

Triangulate an edge point in camera object space (x, y, z) by mathematically intersecting the diffuse renected camera edge ray with the calibrated slit-beam surface.

Fig. 4: Direct triangulation

27

]IIstall tClillical Diagnosis ill Ophth almol0:5'J (Refractive Surgery) SPECULAR VS BACK-SCA TIERED REFLECTION

The keratometer eliminates the anterior curvature of the pre-corneal tear film. It is an estimate because the keratometer only acquires da ta w ithin a narrow 3 mm d iameter annulus. It measures the anterior tear-film because it is based on specular reflection, which occurs primarily at the air-tear in te rface. As the keratometer has very limited data coverage, abnormal corneas can produce misleading or incorrect results. Orbscan can calculate a variety of different surface curvatures, and on a typical eye, these are all different. Only on a properly aUgned and perfectly spherica l surface are the various curvatures equal. The ta bulated SimK values (magnitu des and associated meridians) are the only ones designed to give keratome ter- like measurements. Therefore, it only makes sense to compare kera tometry reading with SimK values. Orbscan uses slit-beams and back-scattered light to triangulate surface shape. The derived mathematical surface is then ray traced using a basic keratometer model to produce simulated keratometer (SimK) values. So it is the difficulty of calculating curvature from triangulated data, the repeatability of Orbscan I Si mK values is usually not as good as a clinica l keratometer. But when several readings of the same eye are averaged, no d iscernable systematic error is found.

So if one reading is taken and a comparison is made, the d ifference may be significant enough to make you believe the instrument is not working properly. So when the placido illuminator was added to Orbscan 11 to increase its anterior curvature accuracy, it also provided refl ected data similar to that obtained with a keratometer. This reflective da ta is now used in SimK analyses, resulting in repeatabilities similar to kera tometers and other placido based corneal topography instruments. Keratometry measures the tear-film, while slit-scan tr ian gu lation as embodied in Orbscan sees through the tear- film and measures the corneal surface directly. Thus, an abnormal tear film can produce significant differences in kerato metry but not in Orbscan II. Curva ture measures the geometric bending of a surface, and its natural uni t is reciprocal length, like inverse millinleters (l / mm). When keratometry was invented this wuamiliar Wlit was replaced by a d ioptric interpretation, making kera tometry values equi valen t on average (i.e. over the original population) to the paraxial back-vertex power of the cornea . As it has become increasulgly more important to distingu ish optical from geometric properties, it is now more p roper to evaluate keratometry Ul "keratometric di opters". The keratometric d iopter is strictly defined as a geometric unit of curvatu re with no optical significance. One inverse millimeter equals to 337.5 keratometric d iopters. 28

Orbscmt

Fig. 5: Beam and camera calibration in the orbscan

Fig. 6 : Ocular surface slicing by the orbscan slit

cornea reflex cornea reflex lens Limbus

Anterior iris

Fig. 7: Detai led orbscan examinat ion

29

Instant Clinical Diagnosis in OplttltalmologtJ (Refractive Surgery) IMAGING IN THE ORBSCAN

In the Orbscan, the calibrated slit, wh ich fa ll s on the cornea, gives a

topographical information, which is caprured and analyzed by the video carnera. Both slit beam surfa ces are determined in camera object space. Object space luminance is determined for each pixel va lue and framegrabber setting. Forty Slit images a re acquired in two 0.7-second periods. During acq uisition, involuntary sacca des typically move the eye by 50 microns. Eye movement is measured from anterior reflections of stationary slit beam and other light sources. Eye tracking data permits saccadic movements to be subtracted form the final topographic surface. Each of the 40 slit images triangulates one s]jce of ocular surface. Before an interpolating surface is constructed, each slice is regis tered in accordance with measured eye movement. Distance betw"een data

slices averages 250 microns in the coarse scan mode (40 slits limbus to limbus). So Orbscan exam consists of a set of mathematical topograph ic surfaces (x, y), for the anterior and posteriGf cornea, anterior iris and lens and backscattering

coefficient of layers between the topographic surfaces (and over the pupil). MAP COLORS CONVENTIONS

Color contour maps ha ve become a standard method for displaying 2-D data in corneal and an terior segment topogra phy. Although there are no wuversally standardized colors, the spectral mrection (from blue to red) is always orgm1ized in definite and intuiti ve way. Blue = low, level, flat, deep, thick, or aberrated. Red = high, steep, sharp, shallow, thin, or focused. ANALYSIS OF THE NORMAL EYE BY THE ORBSCAN MAP

The general quad map in the Orbscan of a normal eye shows 4 pictures. 111e upper left is the anterior float, which is the topography of the an terior surface of the cornea. The upper right shows the posterior float, wluch is the topography of the posterior surface of the cornea. The lower left map shows the keratometric pattern and the lower right map shows the pachymetry (thickness of the cornea). The Orbscan is a three-din1ensional slit scan topographic machine. If we were doing topography with a machine, which does not have slit scan imaging facility, we would not be able to see the topography of the posterior surface of the cornea. Now, if the patient had an abnormality in the posterior surface of the cornea, for example, as in primary posterior corneal elevation this would not be diagnosed. Then if we perform Lasik on such a patient we would create an iatrogenic keratectasia. The Orbscan helps us to detect the abnormalities on the posterio r surface of the cornea. Anothe r facility, wluch we can move onto once we have the general quad map, is to put on the normal band scale fil ter. If we are in suspici on of any abnormali ty in the general quad map then we put on the normal band scale filter. This highlights the abnormal areas in the cornea in orange to red colors. 30 The normal areas are all shown in green. This is very helpful in generalized screening in pre-operative examination of a Lasik patient.

Orbsca1l

OR8SCAN

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31

Instant Clinical Diagnos;s in OplrtlralmologtJ (Refractive Surgery) CLINICAL APPLICATIONS

Let us now understand this better in a case of a primary posterior corneal elevation. If we see the General quad map of a primary posterior corneal elevation we wi ll see the upper left map is normal. The upper right map shows abnormality highlighted in red. This indicates the abnormality in the posterior surface of th e cornea. The lower left ke ratometric map is normal and if w e see

the lower right map, which is the pachymetry map one will see slightly, thin cornea of 505 microns but still one calU10t diagnose the primary posterior corneal elevation only from this readi ng. Thus, we can understand that if not for the upper right map, which denotes the posterior surface of the cornea, one would miss this condition. The Orbscan can only diagnose this. Now, we can p ut on the normal band scale fil ter on and this will highlight the abnormal a reas in red. Notice in Figure 12 the upper right m ap shows a lot of abnorma li ty denoting the primary posterior corneal elevation . One can also take the three-dimensional map of the posterior surface of the cornea and notice the a lTIOlUlt of elevation in res pect to the normal reference sphere shown

as a black grid. In a case of a kera toconus all four maps show an abnormality, which confirms the diagnosis. If we take a Lasik patients topograph y we can compare the pre- and the post- Lasik. This helps to understand the pattern and amount of ablation done on the cornea . The picture on the upper right is the p re-operative topographic picture and the one on the lower right is the post-Lasik pictu re. The main picture on the left shows the difference between the pre- and post-Lasik topographic patterns. One can detect from this any decen tered ablations or any other complication of Lasik surgery. Corneal topography is extremely importan t in cataract surgery. The smalier

the size of the incision lesser the astig1l1atism and earlier stability of the astigmatism will OCCllr. One can reduce the ashgmatisnl or increase the astigmatism of a patien t afte r cataract surgery. The simple rule to follow is that-wherever you

make an incision that area will fiat ten alld wherever you apply sutures that area wili steepen. One can use the Orbscan to analyze the topography before an d after ca taract surgery. For instance in an Extracapsular cata ract extraction one can

check to see w here the astigmatism is most and remove those sutures. In a phaco the astigm atism will be less and in Phakon.it where the incision is sub 1.5 mm the as tigmatism will be the least. We can use the Orbscan to determine the anterior chamber depth and also analyze where one should place the incision when one is performing astigmatic keratotomy. The Orbscan can also help in a good fit of the contact lens with a fluoresce in pattern. SUMMARY

The Orbscan h as changed the wor ld of top ograph y as it gives us an understand ing of a slit scan three-dimensional picture. One can use this in 32 lmderstanding variolls conditions.

Orbscall DrAg-.1 Agarwal Eye Hospital CtMm-'

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Fig. 10: General quad map of a primary posterior corneal elevation. Notice the upper right map has an abno rmality whereas the uppe r left map is normal. This shows the anterior surface of the cornea is normal and th e problem is in the posterior surface of the cornea

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DrAgarwal Agarwal Eye HOlpli11ChInn.l

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Fig . 11 : Quad map of a primary posterior co rneal elevation with the normal band scale filter on . This shows th e abnormal areas in red and the normal areas are all green. Notice the abnormality in the upper right map

33

Instant Clinical Diagnosis ill Ophth alm ology (Refractive S/lrgery) P . Mah",lekshmi 00071 6 CD· 813.'02, 11 :" 5:4 1 AM

ORBseAN

Fig. 12: Three dimensional map of primary posterior corneal elevation. This shows a marked elevation in respect to a normal reference sphere highlighted as a black grid. Notice the red color protrusion on the black grid. This pictu re is' of the posterior sur1ace of the cornea

ORBseRN

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Fig. 13: General quad map of a keratoconus patient showing abnormality in all four maps

34

Orbscan

OABSCAN Differen ce - Anterior Elevati on 0.080 0.070 0 .060 0.050 0.040 0.030 0 .020

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Fig . 15: Pre- and postoperat ive photos of a Phakon it with a Thinoptx ro llable IOL

35

5 Photo refractive Keratectomy with Mitomycin C for High Myopia Belquiz A Nassaralla, Joao J Nassaralla Jr (Brazil)

INTRODUCTION

Excimer laser photorefractive keratectomy (PRJ<) is a common procedure for the treatmen t of low to moderate refractive disorders but because of the side effects it can generate, mainly slow vis ual recovery, discomfort in the early

postoperative period, corneal haze and possible regression of the refractive result, it was widely replaced by laser in situ keratom ileusis (LASIK). Unfortunately, in highly myopic eyes, especially in some p atients with insufficient corneal thickness, LASIK is associated with complications related to the flap and ectasia. In these cases, smaller abla tion zones have to be applied to correct the refractive error. Such a small ablation zone can lead to visual inconveniences slIch as impaired night vision \·" hen the pupil d ilates, halos,

blurred vision, an d ghost images. Therefore, in highly myopic eyes, it could be wiser to treat the refractive error by PRK, which has been infrequently reported to induce corneal tissue instability. However, in wOlmd healing after PRJ<, keratocytes in the corneal stroma are activated to proliferate. The collagen tissue produced by these keratocytes is much less organized than normal stromal tissue, shows matrix-free a reas and fibers with an irreguJar stereo-

spatial relatio nship, and is thought to be the cause of cornea l haze forma tion. To improve the results of PRJ<, attention has been focused on modulating the process of post-procedural wound healing. Corticosteroids are the most common prophy lactic treatment agai nst excessive haze formati on and

regression . Considering the poss ibl e severe side-effec ts of long-term corticosteroid treatment, it is desirabJe to find an alternative to prevent haze

and regression after PRJ<. Mitomyc in C (MMC), a potent an tip roliferative agent with alkylating properties, has been demonstrated to safely prevent cornea l haze following PRJ< and to p revent recurrence of haze following PRJ< and radial keratotomy (RJ<). MMC has also been found to induce the apoptosis of keratocytes and myofibrobJasts in a dose- and time-dependent manner. Since the use of higher concentrations and longer exposure times of MMC might lead to significant complications and ocular toxiC ity, establishing the lowest concentration and 36

duration of treabnen t that rema in effective in preventing subepithelial haze forma tion after PRJ<, is needed in humans.

Photorefrnctive Keratectomy with Mitomycin C for High Myopia

Fig. 1: Slit lamp photograph of the right eye of a 28-year-old woman with dense haze at 10 months after photo refractive keratectomy for

high myopia

37

Instnllt Clinical Diagnosis ill OphthalmologtJ (R efractive SllrgenJ) INVESTIGATIONS

Haze is characterized by subepithelial fibrosis caused by an abnormal wound healing res pon se confirmed by histologic studies that show epithelial hyperplasia, disruption of the corneal Bowman's layer, presence of newly formed type III disorganized collagen, vacuolization of keratocytes, and abnorma l acti vation of fibrocytes . Although conunon, the defini te etiology for corneal haze still remains obscure. It has been postulated tha t apoptosis occurs in keratocytes immediately after PRK, during which the activated migrating keratocytes from the remaining stroma produce increased amounts of disorga ni zed coll agen and cellula r matrix, severely reducing corneal h'ansparency and leading to regression after refractive surgical p rocedures. Some au thor s have demonstr ated that prop hylac ti c MMC 0.02 % intraoperatively in a single dose after PRK, for 2 minutes, effectively prevents haze formation after PRK in highly myopic eyes that were unsuitable for LASIK. The same authors also documented positive refractive and vis ual results over

a 6-month period and the absence of relevant corneal complica tions with this treatment. In a recent study we have concluded that PRK with a single intraoperative topical application of MMC 0.02% for 2 minutes is effective in treating residual myopia and preventing sub-epithelial haze formation in patients with undercorrection or regression following RK. Netto et al studied the effect of topical MMC used at different concentrations (0.002% and 0.02%) and for varying exposure times (12 seconds, 1 minute and 2 min utes) on corneal cells in situ and the efficacy of prophylactic and therapeutic MMC treatments on subepithelial corneal haze following PRK for high myopia in a rabbit model. 111ey concluded that when prophylactic MMC is used, it appears that 0.002% concentration for 12 seconds provides nearly the same efficacy in inhibiting subepithelial haze forma tion as 0.02% for 12 seconds, 1 minute or 2 minutes. Thorton et alcompared the safety and efficacy of lower dose MMC (0.002%) to that of the stand ard dose (0.02%) in eyes treated with PRKfor myopia. They concluded that standard concentration of topical MMC (0.02%) is more effective than low dose MMC (0.002%) in preventing postoperative haze following PRK for high myopia. The duration of MMC exposure appears to be less in1portant than its concen tration.

Wi th so many reports showing the reproducible effecti veness of Mitomycin C in reducing subepithelial corn ea l haze formation after PRK, topical prophylactic use of this drug has rapidly grown in refrac tive clinical practice. However, several questions regarding the 10ng-tern1 safety and efficacy of topical MMC treatment remain unanswered. Figures 2A to 2F a step-by-step PRK with MMC (0.02%) fo r high myopia. Reducing the d osage and exposure time to the lowest levels that remain effective in preventing subepithelial haze is probably better for corneal health. Until now, MMC 0.02% for 12 to 30 seconds appears to be the most safe and 38 effective dOSing.

PllOtorefractive Keratectomy with Mitomycin C for High Myopia

Fig. 2A: Microscopic view of the left eye of a 31 -year-old woman with high myopia (-7.75 -1.50 x 60°). A wire eyelid specu lum is used to expose the eye. Corneal epithelium is removed by mechanical scraping over the central cornea with a blunt spatula

Fig. 28 : Same patient as in Fig 2A. Residual surface epithelium is thoroughly removed using cellulose sponges. The patient is asked to fixate on the coaxial helium -neon light of the laser and the laser is centered over the entrance pupil

39

Installt Clinical Diagnosis in OplttltalmologtJ (Refractive SlIrgenJ)

Fig. 2C : Same patient as in Figures 2A and B. In this case, a Chiron Technolas 217 Z (Bausch and Lomb , Rochester, NY) excimer laser was used and the ablation performed in standard fash ion

Fig. 20: Same patient as in Figures 2A 10 C. Topical application of MM C (0.02%) is performed by placing a soaked Meracel sponge over the ablated stroma for 30 seconds

40

Photorefractive Keratectomy wit" Mitomycin C for High Myopia

Fig. 2E: Same pat ient as in Figures 2A 10 D. The corneal surface, conjunctiva, and fornices are vigorously irrigated with balanced salt solution (20 cc) to dilute and remove residual MMC

Fig. 2F: Same patient as in Figures 2A to E. At the end of the procedure,

one drop each of antibiotic and anti-inflammatory drugs are instilled into the inferior conjunctival cul -de-sac. A contact lens is placed in the operated eye and kept in place until the epithelial defect is completely healed

41

6 Photo refractive Keratectomy after Penetrating Keratoplasty Be/quiz A Nassaralla, Joiio J Nassaralla Jr (Ba rzi/)

INTRODUCTION

The visual recovery after penetrating keratoplasty (PK) is often adversely affected by important residual refractive errors, despite a clear graft. In particular, high astigmatism may prevent good postoperati ve visual acuity. Reducing post-P K refractive error, with or witho ut irregular corneal astigmatism, has been a challenge to corneal surgeons for a long time. Several techniques have been advocated to reduce post-PK astigmatism, including suture adjustment and selective suture removal. Frequently, if acceptable astigmatism is achleved, sutures are left in place for one or more years. H owever,

breakage often results, requiring suture removal. Additionally, there may be suttue-related complications including inflammation, infection, vascularization, epithelial erosion and ulceration. Incisional keratotomy and compression sutures have yielded fairly unpredictable results. The use of photorefractive keratectomy (PRJ() as a main stream refractive modality declined during the late 19905 and early 2000s due to the dramatic increase in laser in situ keratomileusis (LASJK). However, there has been a resurgence of interest in the PRK procedure, especially because of the increased number of post-LASIK ectasia cases and complications during the prepara tion of the cornea l flap (superficial keratectomy). Particularly, after penetrating keratoplasty, many patien ts have irregular or high astigmatism that may pred ispose to flap complications during the keratectom y. This would be specially true in very steep postoperative corneas where there is a large diffe rence in the flat and steep axis. Recent reports suggest that photorefractive keratectomy (PRK) is relatively safe and effective in reducing post-PKP refractive error. However, it still has limits. Post-penetrating keratoplasty PRJ( is associated with increased corneal scarring (haze). INVESTIGATIONS

Although rece nt technologies, such as flying spot lasers, that provide large and smooth ablations have reduced the stromal reaction that causes haze 42 formation, it conti nues to be the major complication after PRK. H aze is

PllOtorefractive Keratectomy after Penetrating KeratoplashJ

Fig. 1: Slit- lamp view of an eye before PRK with MMC 0.02% for high res idual ametrop ia (-7.00 -2.25 x 130°) after penetrating keratoplasty

Fig . 2: Same patient as in Fig. 1, 8 months after PRK with MMC 0.02% (for 30 seconds) for high residual ametropia after PK . No haze is observed

43

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery)

characterized by subepithelial fibrosis caused by an abnormal wound healing response confirmed by histologic studies that show epithelial hyperplasia, disruption of the corneal Bowman's layer, presence of newly formed type III disorganized collagen, vacuolization of keratocytes, and abnormal activation of fibrocytes . Although common, the definite etiology for corneal haze still remains obscure. It has been postulated that apoptosis occurs in keratocytes inunediately after PRK, during which the activated migrating keratocytes from the remaining stroma produce increased amounts of disorganized collagen and cellular matrix, severely reducing corneal transparency and leading to regression after refractive surgical procedures. To improve the results of PRK, attention has been focused on modulating the process of post-procedural wound healing. Among topical drugs evaluated to prevent or treat corneal haze, mitomycin C (MMC) has recently gained relevant interest. Mitomycin C, a potent antiproliferative agent with alkylating properties, inhibit the proliferation of fibroblasts and keratocytes. MMC inhibits DNA synthesis, preferentially affecting rapidly dividing cells, is fast-acting, and induces long-lasting suppression of keratocyte activity after a single dose. Some auth ors have demonstrated that prophylac tic MMC 0.02% intraoperatively in a single dose after PRK, effectively prevents haze formation after PRK in highly myopic eyes and after residual myopia after RK. A recent study has also shown good results of PRK with adjunctive topical MMC for refractive error after penetrating keratoplasty for keratoconus. Figure 1 (preop) and Figure 2 (post-op) show the case of a 51-year-old man who underwent PRK and a single intraoperative topical application of MMC 0.02% for 30 seconds, to treat high residual refractive error after penetrating keratoplasty for keratoconus. No haze was observed 8 months after surgery. Ultimately, technological advances in refractive surgery have led to two promising customized approach es: wavefront analysis and corneal topograph y. Wavefront analysis can detect optical aberrations that distort a ray of light as it passes through the entire optical system. This technology allows a better understanding of the impact that high order aberrations can have on visual performance. Custom laser ablation can then be performed with a small spot scanning laser equipped with a fas t eye tracker and a device linking the wavefront analysis data with the laser ablation. However, topography-guided PRK has achieved better results over wavefront-guided PRK when treating highly irregular corneas, as frequently occurs after penetrating keratoplasty. So, topography-guided PRK should be indicated in scarred or extremely irregular corneas with so much distortion 44 that wavefront measurement would be too rough for custom corneal ablation.

PlIO to refractive Keratectomy after Pelletrating KeratoplashJ PREOPERATIVE CONSIDERATIONS

The primary goal of PRJ( after penetrating keratoplasty is resol ution of sufficient ametropia to allow spectacle correction of the residual refractive error and the return to binocularity. If the patient is unable to wear spectacles or contact lenses, surgical treatment should be considered. An acc urate assessment of the patient's true refraction depends on the donor cornea re turning to its normal shape after suture removal. It is generally recommended that PRJ( not be performed for at least 12 months after the original transplant procedure. If extremely high amounts of astigmatism are present, relaxing incisions along the previous graft / host jWKtion, as tigmatic kera totomy incisions, or limbal relaxing incisions can be done prior to PRJ( in order to reduce the astigmatism. The cornea should be left to heal for 6 months to ensure refractive stabilization. If large amounts of tissue are ablated, the corneal thickness must be closely monitored. The risk of graft rejection mus t be considered whenever manipulation of a corneal transplant occurs. It is known that graft rejection can be induced by a procedure as simple as removing a corneal suture, so graft rejection induced by PRJ( is certainly not inconceivable. These patien ts should be treated with postoperative steroids. CONCLUSION

The use of PRJ( in corneal transplant as an enhancement or secondary operation markedly enhances the application of cornea l transplantation. The better w1derstanding of corneal wound healing and the adven t of mitomycin C as well has given surface ablation the advantage in performing on patients with previous PK. Customized ablation is an effective, safe, and stable option to trea t irregular astigmatism from various etiologies. A topograph y-linked excimer laser is a potentially excellent ap proach to irregular ametropia after keratoplasty.

45

7 Phototherapeutic Keratectomy on Recurrent Corneal Erosions Be/quiz A Nassaralla, Joao J Nassaralla Jr (Brazil)

INTRODUCTION

Recurrent corneal erosion synd rom e (RCES) was first desc ribed in 1872 by H ansen . It is a relatively comm on condition and may be classified as either dystrophic (dystrophic-RCES) where it occurs associated w ith an an terior corneal dystroph y, non-dystrophic (ndRCES) where it occurs following a sudden, sharp, abrading injury (fingernail, paper cut, tree b ran ch ), or unrelated to any pre-existing corneal disease or past h istory of trauma (idiopathic-RCES). The path ogenesis of recurrent corneal erosion is presumably related to the presence of abnormalities in the epithelial basemen t membrane with defective adhesion complexes (hemidesmosomes and anchoring fibrils). This results in poor adhesion between the basal epithelial cells, epithelial basement membrane, and Bowman's layer. Clinical Signs and Symptoms

Clinically, p atients experience recurrent episodes of acute symptoms of pain , tearing, redness and ph otop hobia u sually at night or upon first aw akening. Most patients recall minor trauma to the cornea or are diagnosed with a basem ent m embran e epithelial d ystrophy. Individual episodes m ay vary in severity and duration. Minor episodes usually last from 30 minutes to several hours and typically have an intact epithelial surface at the time of examination. More severe episodes may last fo r several days and a re often associated w ith greater pain, eyelid edema, decreased visual acuity, and photophobia. Physical examination during acute attacks reveals areas of eroded or loosely attached epithelium. After an interval varying from d ays to years, symptoms suddenly recur w ithout any obvious precipitating event. Differential Diagnosis

The key to make the disti nction between a posttraumatic erosion and a dys trophic erosion in a patient w ho h as no clear-cut his tory of sup erficial trauma lies in careful examination of the contralateral eye follo w ing maximal pup illa ry dilation. Occasion ally, subtle areas of loosely adherent epithelium 46 can be identified b y gentle pressure w ith a surgical sponge following the

Photo therapeutic Keratectomy on Recurrent Comea l Erosions

Fig. 1 : Slitlamp photo graph of the left eye of a 49-year -old woman with recurrent erosion secon dary to anterior basement membrane dystrophy . Areas of epithelial loss (positive staining) , lack of fluorescein over elevated epithelium (negat ive staining) and pooling of fluorescei n are seen . The patient responded well to clinica l t reatment with epilhelial scraping followed by eye patching with lubricants

Fig. 2: Slitiamp view of the same eye as in Figure 1 with a recurrent painfu l attack 5 months after the previous one. The patient was treated with ep ithelial debridement, anterior stromal micro puncture and eye patching with lubricants

Fi g. 3: Four months following anterior stromal micropuncture, the patient presented with another erosion in the same area that was previous ly treated. Examination demonstrated a large area of epithe lial defect. The patient underwent phototherapeutic keratectomy

47

Ills tallt Clinica l Diaguosis ill O phthalll1o lo:5'J (Refractive SurgertJ)

instillation of topical anesthetics. The presence of basement membrane changes in the unaffected eye implicates a primary basement membrane defect in the pat hogenesis, while the absence of such findings strongly sugges ts a posttraumatic etiology. Other clinical cond itions with associated abnormalities of the epithelial basement membrane include diabetes mellitus and d ystrophies of the stroma and Bowman's layer. Treatment

Treatment with epithelial scraping followed by eye patching w ith lubricants, hypertonic saline, antibiotic ointments, or therapeutic contact lenses, resolves symptoms in most cases. However, there is a small group of patients who suffer recurrent attacks at weekly or monthly intervals despite conventional treatments.

Several methods of surgical treatment have been shown to be helpful including epithelial basement membrane debridement, superficial keratectomy with a diamond burr, anterior stroma l micropuncture by sharp needles, and Nd :YAG laser. Although these method s have been used with good success, they ma y induce corneal sca rring and therefore are not appropriate near the visual axis. In 1983, Trokel and coworkers first reported the possibility of using the argon fluoride (ArF) excimer laser for the precise and controlled removal of corneal tissue without damage to the corneal stroma adjacent to the ablation zone. The objective of excimer phototherapeutic keratectomy (PTK) in patients with recurrent corneal erosions is to remo ve enough of the superficial part of Bowman's layer and provide a smooth new bed to permit formati on of a new basement membrane wi th adhesion complexes. The newly form ed adhesion complexes allow for better adhesion between the epithelium, the epithelial basement membrane, and Bowman's layer. By creating a large, shallow zone of ablation, this procedure can minimize the refractive effects, or it can be used to correct an associated myopic refractive error as well. Investigations

Histologic investigations performed on rabbit and monkey corneas after excimer laser photoablation have shown an increased accumulation o f hem ides-

mosomes and of type VI collagen, which is a major component of anchoring fibrils , alo n g the epithelia l b ase ment membrane as ea rl y as 7 days postoperati vely. The re-establishment of a nearly continuous anchoring fibril zone was evident at 12 weeks. In humans, undulations and excursions of epithelial cells, as large as 4 flm, into the corneal stroma were described following excimer laser abla tion. Such undulations would greatly increase the surface area of attachment. Indeed, in humans after excimer laser photoab lation, the epithelium appears to be firmly adherent to the underlying tissue and may be 48 very difficult to remove.

Photo therapeutic Keratectomy on Recurrent Comeal Erosions

Fig. 4: Laser ablation was performed to a depth of 5 micron using the Technolas 217 Z Excimer laser (Bausch and Lomb, Rochester, NY) . Photograph immediately after PTK

Fig. 5 : Slitlamp photograph 2 weeks after PTK . The patient has been followed for the fast two years with no recurrent erosion

Prognosis Reported success rates with PTK have va ri ed from 69 to 86%. Some patients may continue to have minor symptoms after PTK, but tend to respond well to treatment w ith lubricants. A small percentage of patients may require a second

PTK treatment to prevent further episodes. Recurrence rates are likely to be 49 higher when PTK is used for dys trophic RCES.

8 Myopic Photo refractive Keratectomy Using Solid State laser Nikolaos S Tsiklis, George 0 Kymionis, George A Kounis, loannis G Pallikaris (Greece)

INTRODUCTION

Myopic Photorefractive Keratectomy (PRK) using excimer laser systems of 193 nm wavelength have proved to be a safe and reliable procedure. Corneal photoablation using laser pu lses in the far UV region (190-220 nm) offers precise tissue removal with similar characteristics (ablation threshold, ablation rate and size of collateral damage zone). Two are the main sources of ultraviolet

radiation used in corneal photoablation; the ArF excimer laser (193 nm wavelength) and the fifth harmonic of the Nd:YAG laser which emi ts at the 213 nm wavelength. The current trends towards advanced modern corneal abla tions requires laser platforms with high pulse frequencies, small laser spot size and eye tracking system that can ensure accurate transfer of the energy on the cornea.

Recently, solid state lasers are gaining popularity in the refractive surgery community since they provide special technological features and many studies indicates tha t they can be used effectively as an alternative so lution to the traditional excimer laser systems. There are two solid state laser platforms available in the m a rket for refractive surgery: Pulzar Z1 laser system (Custom Vis) and LaserSoft (Katana Technologies GmbH). LASERS PRINCIPLES OF FUNCTION

Laser is a device that em its light through a specific mechanism which is described by the term laser as an acronym: Light Amplification by Stimulated Ernission of Radiati on. As a light source, a laser can have va rious properties,

depending on the purpose for which it is designed and calibrated. A typical laser emits light in a na rrow, low-divergence beam and with a well-defined wavelength which corresponds to a particular colollr if the laser is operating in the visible spectrllm . This is in contrast to a light source such as the incandescent light bulb, which emits into a large solid angle and over a wide spectrum of wavelength. These properties can be summarized in the tenn coherence which is the most important property of a laser light source. A laser consists of a gain medium inside an optical cavity, w ith a mean to 50 supply energy to the gain medium, and also of the gain medium pumping

Myopic PllOtorefractive Keratectomy Using Solid State Laser

Unique properties of laser radiation

Collimated beam directionality Spatial and temporal coherence Monochromatic well-defined wavelength

l

Fig. 1: The unique laser properties . Monochromat icity , Directionality and Coherence

Input coupler. .

.

m irro/.--1150% ren ectiveness

Optical cavity

couple r IlIiI~95%

reflecti eness..,

Ga in ~

Output

A .

m ~ ium

..

J •~7.J. . ,. . . ..

'-..,

I

, 1

Fig. 2: A laser cavity . Basic components of a Laser system

51

Illstallt Clinical Diagnosis in OphtlzalmologtJ (Refractive SurgeYlJ)

device. The gain medium is a material (gas, liquid, solid or free electrons) with appropriate optical properties. In its Simplest form, a cavity consists of tw o mirrors (input and output coupler wit h 100% a nd 95% reflecti veness accordingly) arranged such that light bOLmces back and forth, each time passing through the gain medium. Typically, one of the two mirrors, the output coupler, is partially transparent The output laser beam is emitted through th is mirror. The pumping device activates the ga in medium through various means depending on the type of the medium material. More often electrical discharge is being used for gas materials like excimer lasers or optical for solid mate rials like YAG lasers. Excilller lasers are gas gain medium lasers and are powered by a chemical reaction involving an excited dimer, or excimer, which is a short-lived dimeric molecule formed from hvo atoms, at least one of which is in an excited electronic state. The most typical excimer laser used in ophthalmology is the ArF at 193 nm wavelength.

Solid state lasers are laser which are using a solid material as gain medium which is optically pumped using a flash lamp or diodes lasers. Solid state laser gain materials are commonly made by doping a crystalline solid host with ions tha t prov ide the required energy states. For example, th e first working laser was a ruby laser, made from ruby (chrolllium-doped sapphire). NeodyllliulII is a common dopant in various solid state laser crystals, including yttrill11l alullliniulII ga rnet (Nd:YA G). These lasers can produce high powers of lOW (for clinical use) in pulsed mode (10 nsec pulse duration) in the illfrared spectrum at 1064 nm and is the most common used solid state laser in ophthalmology. The spo t size may be sized below 1mm and h as true Gaussian shape. The Nd:YAG laser is used as a m ea ns of correcting posterior capsl/lar opacification (after-cataract). Nd :YAG laser is used for periphe ral iridotolllY in patients w ith acute angle closure glaucoma, where it has s uperseded surgical iridectomy. Freql/ency-dol/bled Nd:YAG laser (532 nm) is used in place of argon laser for pan-retinal photocoagulation in patients with diabetic retinopathy. ACHIEVING THE FIFTH HARMONIC

Nd:Y AG solid state lasers have been introduced for use in the refractive su rgery during the last 5 years. In order to be used the proper ultra violet wavelength must be achieved. The principles of nonlinear optics ( LO) are being used fo r this purpose in order to obtain the fifth ha rmonic frequency from the initial wavelength of 1064 nm . Th is harmonic provides a wavelength in the far ultraviolet

NLO is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization P respond s nonlinearly to the electric field E of the light. This nonlinearity is typically only observed at very high light intensities such as those provi ded by pulsed lasers as the pulsed 52

Nd:YAG.

Myopic Pltotorefractive Kern tectomy Usillg Solid State Laser

1065 nm

Fig. 3: Non·Linear optics principles

co,

nm 308 nm

Ultraviolet

nm

Diode 680 nm

XeCI

,Visible light 400 nm

Nd: YAG 1064 nm

Infrared

750 nm

Fi g. 4: Common laser wavelength and the photonic spectrum

53

In stant Clinical Diagn osis in Ophthalmologtj (Refractive Sllrgenj)

Nonlinear optics utilizes a numbe r of optica l phenomena in order to create higher harmonic from the principle one. The most common method is the frequency-mixing processes. After creating second and third harmonic those frequencies are mixed together with the pri nciple in order to create higher harmonic like the fifth . Practically, frequency mixing is carried out by placing a special crystal in a laser beam under a well-chosen angle. These crystals have the necessary properties of being strongl y birefringent, hav ing specific crysta l symmetry and of course being transparent for and resistant against the

high-intensity laser light. CUSTOMVIS PULZAR Z1 SOLID STATE LASER

PULZARTM Zl is a solid state refractive laser that is designed specifically for custom surgery, permitting an accurate approach to correcting both standard and non-standard vision disorders. Also it is elim inating the need for toxic gases and storage and provides low ma intenance costs and do wntime.

( http: // www.customvis.com/) The waveleng th is 213 !Un and the pulse frequency is 300 H z. The system has a flying spot beam delivery system with spot diameter 0.6 mm and Gaussian profile prod ucing thus a clean and smooth ablated surface. This small spot size allows excellent customized ablation profiles as well as has more efficient tissue ablation due to closer to absorp tion peak of cornea l collagen. The solid state laser technology enables better p ulse to pulse stability which minimizes errors depending on time stability. It is free from hydration monitoring and the corneal hydration state is not any more a concern for the surgeon . Thus it is fr iendly wi th surface corneal fluid and overcorrection or lmdercorrections are not presented as often as they are with the use ofexcimer lasers. The small size and the Gaussian profile of the laser spot also reduce thermal effec t and collateral damage and thus improves patient comfort by minimising corneal haze and scarring . The latter in conjunction w ith the clinical observa tjons (a bsence of haze after surface treahnents) raise queries w hether mitomycin C is absolutely necessa rily after high attempted correc tions when using a solid sta te laser. For custo mized refractive surgery, a fundamental requirement is the fast

and accurate tracking teclmique in order to pOSition the laser spot precisely. The Pu lza r Zl is using two tracking systems. The ZTRAK is the main tracking system and is limbus based video eye tracking system. Most pupil tracking systems d o not compensate for pupil centre movemen ts d ue to the pupil diameter changes. The ZTRAK system along with the secondary GAZETRAK system provides the mos t efficient positioning of each laser pulse over the cornea. The GAZETRAK system is able to monitor the angle of patient's gaze and then changes the fixation target in tra-operatively in order to deliver the energy of each pulse accuratel y on the cornea. The Cyclorotation system finally is used to determine the patient s cyclorotation angle between the preoperatively 54 upright position and the supine position.1l1e treatment is appropriately rota ted to compensate any cycl orotation.

Myopic Photorefractive Keratectomy Usillg So lid State Laser

Fig . 5: The Custom Vis Pulzar 21 solid state laser system

Limbus

Conventional technology

1 ZTRAK technology

Fig. 6: ZTRAK limbus eye tracking system principles

55

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) Finally the system uses the TRACEY wavefront system and custom software, called ZCAD, which provides the laser with the ability to operate in full customize way. It uses information from pupillometry, refraction, topographic and wavefront data. The treatment plan is produced by inserting those data in the ZCAD software and the in the laser. Clinical Results

In our series, 115 consecutive patients (230 eyes) underwent primary bilateral myopic PRK with CustomVis Solid State Laser and completed one year followup. All procedures were performed in the Institute of Vision and Optics, University of Crete Greece. Mean patients age was 29.6 ± 7.13 years (range, 18 to 48 years) and the mean spherical equivalent error was -4.43 ± 1.81 D (range, -8.0 to -1.5 D of sphere and up to -4 D of cylinder). Table summarizes patients demographic and refractive data. All patients gave written informed consent in accordance with the institutional guidelines and the Declaration of Helsinki. At the one year follow up examination all post PRK eyes (100%) had uncorrected visual acuity (UCVA) 20/25 or better while 95% saw 20/ 20 or better. These results were far exceeds the FDA standards requiring only 50% of eyes to achieve UCV A of 1.0 or better and 85% to be 0.5 or better. No eye lost more than one best spectacle corrected visual acuity (BSCV A) line, while 50% of eyes gained one or more lines at the last follow-up after PRK. Changes in BSCVA during the follow-up examination are summarized in Figure 10. Mean preoperative spherical equivalent refraction (-4.43 ± 1.81 D) was reduced to -0.08 ± 0.20 D at one year postoperatively. All eyes were within ± 0.50 D of emmetropia. Refractive stability was obtained on the first postoperative month and remained stable during the follow-up period with no Significant changes between any interval (p>.05). Only 5% of eyes changed more than 0.50 D between 6m and the one year post-operative examination (Table 1). No eye had intra-operative or early or late postoperative complications. In all eyes epithelium healed in three to five days. Only three eyes had trace haze at 3 months post PRK and just one out of 230 eyes at the last follow-up examination. EXPERIMENTAL CORNEAL HISTOLOGY

Forty pigmented rabbits (40 eyes) underwent myopic PRK using CustomVis Pulzar Zl Laser System for the correction of -6 D at 5mm optical zone with O.5mm transitional zone. Rabbits were sacrificed immediately after the ablation and up to 12 months postoperatively. Light microscopy (LM) and Transmission electron microscopy (TEM) demonstrates smooth ablation surfaces in all samples with no edema, or 56 distortion of the adjacent corneal stroma, indicating absence of thermal damage.

Myopic Photo refractive Keratectom y Usillg Solid State Laser

Upright

Supine

Fig . 7: Cyclorora·tion correction for supine and upright pat ient position

Fig . 8: T he ZCAD custom iz ed proce ·

dure software

Uncorrected visual acuity bar graph 120%

100%

• Pre--op BSCVA EI 1 m Post-Op " 3mPos!~ c 6 m POS!-ep

~(:..°lo

nolo

,\)

,\)0°1 0

~ol ,\)

a 12m POSI..()p

~ 80%

i7

'0 60% #. 40%

1.0°10

20% 0%

0°1 10.0

0

,,01 0 12.5

Fig . 9: Cumulat ive UCVAa t 1,

I-ui I 16.0

20.0

25.0

30.0

Cumu lative Snellen visual acuity (20/20 )

40.0

3, 6 and 12 months atter

PRK

57

Instant Clinical Diagnosis in Ophthalm ologtJ (Refractive SurgenJ)

,

" ,. ~

'~

~

: / / Table 1: Patients Demographic and refractive data /

%

No of Eyes I Patients Sex (Male! Female)

230/ 11 5 55/60

Age (yrs) Mean ± SO Ra nge

29.6 ± 7.13 18-48

Preop Sphe re (D) Mean ± SO

-4 .13± 1.27

Range

-1.5 to -8. 0

Preop Cylinder (0) Mean ± SO Range

-1 .26 ± 0.87 o to -4.0

One year Postop Sphere (0) Mean ± SO Range

-0.04 ± 0.1 5 0.25 to -0.25

One year Postop Cylinder (0) Mean ± S D

-0.13 ± 0 .18

Range

o to -0.5

The upper stroma contained significant number of activa ted keratocytes with slight vacuolization while deeper stroma h ad normal structure of keratocytes and extracellu lar matrix in all postoperative exan1ma tions. Endothelial layer was intact an d end othelial cells appeared norm al in all samples, a crucial parameter for the safety of the proced ure. During th e entire 12 m onths of the study, n o sign of corneal mu tage n esis was seen, even th ou gh 213 nm wa velength is closer to absorption peak of DN A. The clinical course and the histopa thological findings w ere similar after photorefractive keratectomy using excimer laser sy stem. CONFOCAL MICROSCOPY ANALYSIS

Confocal microscopy was performed p re- and postoperatively (up to one year follow up) at 20 p atients (40 eyes) after PRK using C ustom Vis Pulzar Zl Solid State Laser system with a modified confocal scanning laser ophthalmoscope (HRT III Ros tock Cornea Module, Heidelberg Engineering) . Corneal images of post PRK trea ted corneas showed normal epithelial structure and regenerated subepithelial nerve plexus one year afte r the surgery. Increased scattering was observed at the ablation site, w hile keratocyte activation and abnormal scattering of the keratocyte's nuclei w as observed at the stromal layers immediately p oste rior to the ablation site. On the contrary, deeper stromal layers exhibit normal keratocyte activatio n and scattering of keratocyte's n uclei w ith an oval shape and norm al endothelium cells in sh ape and size. Repeated measures analysis of cell density variance did not indicate statistically significant differences in mean endothelial cell density between

58

Myopic PlIO to refractiv e Keratectomy Using Solid State Laser

Change in spectacle-corrected VA Bar graph 70%

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Stability of refraction in PRK

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Fig. 11 : Stability of intended correction during the tollow-up period after PRK

59

Instnllt Clillical Dingll osis in Oplltlrnlmologt) (Refractive SlI rgen)

Figs 12A and 8 : Rabbit corneal morphology immediately after PR K. light microscopy . Original magnification x 160 (A). Transmission electron microscopy , original magnification x

6600 (6 )

preoperatively and at any postoperati ve interval measurement. These results are in accordance with prev ious confoca l studies after PRK w ith excimer laser. CONCLUSION

Solid State Lasers seems to be the future in corneal refractive surgery. Custom Vis Pulzar Zl Laser System is a reliable, stable and robust laser pla tform with low main tenance costs, providing special characteristics essential for customized

corrections. Whether all the theo retical ad vantages of the solid state laser platforms as compared to the excimer laser systems ha ve any practical impact on corneal healing and the final vis ual or refractive ou tcome, still need to be 60 elucidated.

Myopic PllOtorefractive Keratectomy Usillg Solid State Laser

Fig. 13: Normal Descemet membrane and endothelium 8 months

after PRK on rabb it corneas. T ransmis sion electron mi cro scopy, original magni -

fication x 6600

Fi g s 14A to D: Confocal microscopy in PRK patients. Regenerated subepithelial nerve plexus 44 urn (A). Surface ablat ion site 54 urn (8) . Stromal layer immediately posterior to ablation site 69 urn (C). Deep stromal layer 405 urn (0)

61

9 Photo refractive Keratectomy for Residual Myopia following Radial Keratotomy Be/quiz A Nassaralla, Joao J Nassaralla Jr (Ba rzil)

INTRODUCTION

Radial kera totomy (RK) was at one time the most common surgica l procedure used to correct myopia, but the populari ty of this technique has markedly decreased since the advent of other technologies. Overcorrecti ons and w1dercorrections are among the mos t frequent sequelae of this procedtue. The lack of predictability is accentuated in severe myopia, often res ulting in undercorrection. Residual myopia after RK may also result because of a large optical zone, few incisions, shallow incisions, or unresponsiveness of the eye to RK. A number of patients with resid ual myopia after RK exist and need additional treatment. Figures lA to C Show slit-lamp photographs of patients who underwent a 4-cut, 8-cut, 16-cut radial keratotomy, respecti vely. Therapeutic strategies to correct residual m yo pia after RK include spectacles, contact lenses, and reoperations, including redeepening procedure, extending existing RK incisions, placing addi tional RK incisions, o r excimer laser trea tment.

Several investigators have reported the use of PRK fo r the treatment of residual myopia after previous RK. Although numerous early reports suggested that surface excimer laser ablations could be safely applied to corneas with previous RK, a series of subsequent studies indicated increased risk of haze formation, regression due to keratocyte ac tivation, dehiscence of the RK incisions d uring scraping of the epithelium, inegular astigmatism, and loss of best spectacle-corrected visual acuity (BSCVA). Probst and Machatp resented evidence that patients at greatest risk for haze formation include those with more than 8 RK incisions, an optical zone S 3.0 mm, preoperative corneal haze from the RK procedure, or increased splay of the RK incisions. Figure 2 shows a slit-lamp photograph of an eye with centra l corneal haze following PRK for the trea tment of resid ual myopi a after prev ious RK. After RK, the incisions can be seen for a long time and never completely heal. Patients wearing contact lenses may have deep vasculariza tio n, especially

62

in deep incisions. Epithelial ingrowth ma y also be found in the incisions.

PllOtorefractive Keratectomy for R esidllal Myopia

Figs 1 A to

c:

Post-AK sl it-tamp photographs of pat ients who underwent a 4·cut (A) , 8-cut (8 ), and 16-cut (C) radial keratotomy

63

[nstall t C/ill ical Diagllosis ill Oplltiza lmologtJ (Refractive SlIrgelY)

Figures 3A to 0 show slit-lamp photogra phs and corneal topographies of the right eye of a 42-year-old woman underwent RK p lus astigma tic keratotomy (AK) in 1991. Crossed incisions resulted in irregular astigmatism with resultant poor vision.

PREOPERATIVE CONSIDERATIONS

Before undergoing a retreatment procedure, the patient's symptoms should be carefully ex p lored and a complete ocular examination performed. Patients should und erstand that PRK will not improve the diurnal fluctuation that occurs from the inherent instability of the cornea in eyes previously treated with RK. PRK should only be attempted with a stable refraction for at least the last 6 months, and a corneal topograp hic pattern stable for two consecutive examinations in a 1 month interval Patients wearing contact lenses should discontinue use for at least 15 days before evaluation . Soft contact lenses should be discontinued for 15 days before PRK, and both hard and gas-permeable contact lenses should be discontinued for at least 1 month before PRK. Once residual refractive error is d etermined to be the cause of the patient's symptoms, a careful exanlination should include a measurement of uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCV A), manifest refraction, cycloplegic refraction, slit-la mp examination, pachymetry, and corneal topograph y. A loss of BSCV A must be explored cautiously, as the ch ance of optimal results will be increased in eyes wi th an intact BSCVA. Corneal topograph y is also useful in evaluating irregular astigmatism and / or decentered cen tral applanation as causes for 10s5 of or patient complaints of poor quality BSCV A. The mean preoperative K must be evaluated, because, excessive corneal flattening beyond 32-35 0 may resul t in poor postoperative quality of vision .

Pachymetry and preoperative calculation of the residual stromal bed are useful to determine whether full correction of residual refractive erro r can be

perfoffiled. Recently, aberrometers that can identify abnormalities through out the entire optical system with the use of wavefront technology, have become available. Like corneal aberrations, aberrations of the total eye increase following refractive surgery, including RK. Wavefront technology not only can measure these aberrations, but also can help to treat them with wavefront-guided laser vision

64

PllOtorefra ctive Keratectomy for Residual Myopia

Fig. 2: A slit-lamp photograph of an eye with central corneal haze following PR K for the treatment of residual myopia after previous RK

65

Instant Clinical Diagnosis in Opllthalm%gtj (Refractive Surgenj) correction. By clistomizing the laser ab lation, we can improve final visual acuity. Investigations

Although recent teclmologies such as flying spot lasers that provide large and smooth ablations have reduced the stromal reaction that causes haze formation, haze continues to be the major complication after PRK. To improve the results of PRK, attention has been focused on modul ating the process of postprocedural wound healing. Among topica l dr ugs evaluated to prevent or treat corneal haze, mitomycin C (MMC) has recently gained relevant interest. Some authors have demonstrated tl1at prophylactic MMC 0.02% intraoperatively in a single dose after PRK, for 2 minutes, effectively prevents haze forma tion after PRK in highly myopic eyes. The same authors also documented positive refractive and vis ual results over a 6-month period and the absence of relevant corneal complications.

Similar to these studies, and based on a cohort study with 12-month followup, we have recently shown that PRK with a single intraoperative topical application of MMC 0.02% for 2 minutes was effective in trea ting residual myopia and preventing sub-ep itheJiaJ ha ze formation in patients \,,'ith

undercorrection or regression following RK Figures 4A and B show slit-lamp photograph and corneal topography, respecti vely, of the right eye of a 45-yearold woman who underwent an 8-cut RK in 1990, for moderate myopia (-5.25 1.50 x 90"). She was undercorrected (-1.75 -0.75 x 165°) and underwent PRK with a single topical application of MMC 0.02 % for 2 minutes in 2003. No major side effects such as corneal edema, melting, perforation or haze were

observed, even five years after PRK/MMC. The efficacy and side effects of PRK with MMC after RK will be established with con tinued follow-up. To minimize complications, the lowest possible prophylactic concentration should be applied for the shortest effective period, ensuring minimal con1eal contact.

The better und erstanding of corneal wound healing and the advent of mitomycin C as well has given surface ablation the advanta ge in perforrning on patients with previous RK. CONCLUSION

Wavefront-guided PRK with topical mitom ycin C 0.02% is a good alternative for the correction of residual myopia after RK. The efficacy and predictability are inferior to that of virgin corneas that undergo PRK. Careful patient seJection will optim ize post-treatment results.

66

PllOtorefractive Keratectomy/or Residllal Myopia

Fig . 3 A : This sl il-Iamp photograph shows a combined rad ial (RK) and astigmatic (AK) keratotomy in the righ t eye of a 42 -year-old woman who underwent RK plus AK in 1991, Crossed incisions resulted in irregular astigmatism with resultant poor vision

Fig. 3 B : This photograph is a close-up of the same eye as in Fig. 3A. It shows the pronounced gaping that occurs at the intersection of incisions. The pronounced wound gaping pre-eludes the proper sequence of normal wound healing and resu lts in irregular astigmatism

67

Inst ant Clinical Diagnosis ill Ophthallllol0:5'J (Refractive SlIrgery)

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Fig. 3 C: Corneal topography map (8 and L Orbscn) of the same eye as in Figs 3A and B demonstrating a high irregular astigmatism (-13.6 x 26°) and excessive corneal flatten ing, '1 years after AK plus AK

ORBSCAN

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68

PlIO to refractive Keratectomy for Residllal Myopia

Fi g. 4 A : SIiHamp photograph of the right eye of a 45 -year-old woman who underwent an Bcui RK in 1990, for moderate myopia (-5.25 -1.50 x 90°). She was undercorrected (-1.75 0. 75 x 165°) and underwent PRK with a sing le topical application of MMC 0.02 % for 2 minutes, in 2003 . No corneal haze was noted during follow-up

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69

10 Recent Advances in Photo refractive Keratectomy C Banu Casar (Turkey)

INTRODUCTION

Photorefractive keratectomy (PRK) was first successfully applied ina n ormally sighted eye by Mc Donald in 1988. The use ofPRK as a main stream refractive modality declined during the late 1990s and early 21st century due to the dramatic increase in laser il1-situ keratomileusis (LASIK). However, there has been a resurgence of interest in the PRK procedure, especially because of the increased number of post-LASTK ectasia cases. In this chapter, recent advances in PRK such as mitomycin C (MMC) and ascorbic acid use, customized PRK (wavefront-guided, topography-guided, and Q factor cu stomized), PRK with solid state lasers and presbyopia treahnent with PRK are discussed. PRKWITH MMC Haze after PRK

H aze is characterized by subepithelial fibrosis caused by an abnormal wound healing response, confirmed by hi stologic studies that show epithelial hyperplasia, disruption of Bowman 's layer, presence of newly formed type III disorganised collagen, vacuoliza tion of keratocytes and abnormal activation of fibrocytes. Although common, the definite etiology of corneal h aze remains obscure. It has been postulated that apop tosis occurs in keratocytes immediately after PRK, w hen the activated migrating keratocytes from the remaining strOlna

produce increased amounts of disorganized collagen and cellular n1atrix, severely red ucing corneal tran sparenc y. It has been suggested, but not conclusjvely confirmed, that the development of postoperative corneal haze after PRK is associated with the removal of the epithelial basement membrane. There are likely many factors related to haze formation. These may include the depth of ablation, the smoothness of the stromal surface, and the time required for the closure of the epithelial defec t. The current genera tion of excimer lasers are characterized by sn100ther ablation profiles and reduced treatment times, 70 which may be associated with reduced risk of haze formation.

Recent Advances in Photo refractive Keratectomy

Hyperbola

Fig. 1: A conic section is the inte rsection of a plane with a cone . By changin g the angl e and location of intersection , a circle , ellipse, parabola , or hyperbola can be produced

71

Illstallt Cliu ical Diagnosis in Opllthalmo[0iJ'J (R efra ctive SlIrgenJ)

Clinically insignificant corneal haze is present in most eyes tha t h ave PRK and may last fo r 1 to 2 years after su rge ry. Clinicall y significant haze onl y occurs in a small percentage of eyes, usually less than 0.5 to 3%, d epending on the level of correction and other factors. Two types of haze are observed alte r PRK. The more common type of ha ze is the typical tra nsitory haze that is noted between 1 and 3 months after surgery. Th is type of haze is rarely associated w ith clinical symptoms and usuall y disappears within the first year after the surgery. The other type of haze (late haze) is much less conunon and is usually noted between 2 and 5 months after the procedure in an eye that has otherwise had a normal outcome after surgery. Late haze may severely compromise vision due to a marked decrease in transparency and regression of the refrac ti ve correctio n. Late ha ze, along wi th

the refracti ve regression associated with it, also resolves over time. Late haze usually persists longer than the more com mon type of earl y haze and in some cases may take more than 3 years to reso lve. Disappearance of haze is associated

with disappearance of myofibrob lasts and remodeling 01 disorga nized stromal collagen. Mitomycin C use as Prophylaxis and Treatment for Haze

Mitomycin C, a potent antiproliferative agent with alkylaling properties, inhibit the proliferation of fibrobl asts and kera tocytes. Mitomycin C inhibits DNA synthesiS, prelerentially affecting rapid ly dividing cells, is fast-acting, and induces long-lasting suppression of ke ra tocyte activity afte r a single dose. Mitomycin C is used prophylactically with PRJ< to prevent haze. MMC is also effecti ve for the treatment of haze after a previous PRK.1n this situation, the epithelium is d ebrided an d MMC is applied with out laser ablation. For the prophylaxiS of haze; MMC is used with: • Primary PRJ<, • PRJ< enhancemen ts after RK, PRK, and LASIK • PRK after LASIK flap complications such as button hole and irregular flaps • PRJ< after cornea l surgery such as penetrating keratoplasty. MMC with PRJ< could also be combined with phototherapeutic keratectomy (PTK) after LASIK flap compli cations such as button hole and epithel ial ingrow th. In all instances, MMC use was reported to lower haze rates. Azar and Jain suggested that mitomYCin C be applied with rings instead of disks, considering the h igher recu rrence of haze in the periphery of the cornea . 72

Rece1l t Adv ances in Photo refractive Keratectomy Su rgical Technique of PRK with MMC

The PRJ< proced ure is performed as usua l. Immed iately after laser treatment, a single topical application of MMC 0.02% by placing a soaked 8.0 mm diam~!er Merocell sponge over the ablated stroma for 2 minutes is performed . The sponge is then removed and the corneal surface, conjunctiva, and fornices are vigorously irrigated with balanced salt soluti on (20 cc) to dilute and remove residual MMC. Mitomycin C Side Effects

NfMC use w ith surgical in terventions other than PRK resulted in some seriolls complications. Following administration of MMC in pterygium surgery, visionthreatening complica tions such as seconda ry glaucoma, corneal edema, corneal perforation, iritis, photophobia, and, pain were reported. Thi s is why, some surgeons have expressed concern that mitomycin C added to the common decrease in fla p keratocyte density could, in some cases, result in late corneal melting or kera tectasia. In many studies of MMC use wi th PRJ<, no toxic or side effects were reported. However, Kymionis et al reported a patient with dry eye afte r bilatera l PRJ< with m itomycin C treatment in one eye. Fifteen months after surgery no impro vement was noted in that patient. In ano ther stud y w ith 1011 eyes undergoing PRK with MMC, delayed epithelial healing was noted in 2 eyes. The effect of MMC with PRJ< on cornea l endothelium was also in vestigated by various authors and no signi ficant di fference between the preoperative and postoperative endothelial cell density by specular microscopy was found. However, in one study of 18 eyes, the e nd othelial cell loss was statistically significant at one month and at three mo nths after PRJ< with MMC. ASCORBATE PROPHYLAXIS AFTER PRK

After PRJ<, the ascorbic acid levels of the tear fluid decreases significantly. Because ascorbic acid is the major scavenger of superoxide radicals in tears, topical ascorbic acid therap y was hypo thesized to help eliminate the harmful effect of free radicals from excimer laser surgery. Stojanovic e t al evaluated whethe r p rophylactic system ic ascorbic acid influences the average level of haze and the inc idence of late onset corneal haze after p hotorefractive keratectomy (PRJ<). One week, 1, 3, 6, and 12 months after surgery, the gro up sup plemented with oral ascorbate (201 eyes) showed less haze than the group withou t ascorbate supplementation (314 eyes). 73

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery)

However, routine prophylactic use of ascorbate can be recommended only after a random ized, prospective clinical trial substantia tes its efficacy. WAVEFRONT-GUIDED PRK

Wavefront sensors are instnunents designed to provide a quantitive analYSis

of the whole wavefront reflected (or projected) light enteri ng the eye and reaching the retina. The clinical investigation of these devices allowed a better understanding of the impact that high order abrrations can have on visual performance. Normal, virgin eyes usually have low, visually insignificant levels of high order aberrations. Eyes after corneal surgery (refractive or therapeutic) usually revea l an increase in high order aberrations. Wang et al perfonned

LASIK and PRK in 32 eyes with similar refractive powers. They found a l.69 fold increase in the PRJ< group and a l.43 fold increase in the LASIK group in overall higher order aberrations. At 3 months, the mean RMS value for higherorder (3rd to 6th) were signHicantly increased compared with the corresponding preoperative values for both LASIK and PRJ<. The fourth order aberrations, spherical like aberration, were dominant by a 2.64 fold in PRK and a 2.31 fold in LASIK. Different influences of the PRK group and LASIK group were shown in the various zernike components.TI,us, PRJ< and LASIK both h ave their own features. The difference between the two types of surgery may be correlated with the change of the corneal shape, the conversion of biodynamics, the healing of the cornea l cut, and re-structured corneal epithelium and/ or the stroma. Several authors have performed wavefront-guided PRK treatments in limited case series. Wavefront guided PRK is used for pri.mary treatments as well as

enhancements after previous refractive surgery including RK, PRJ<, and LASIK. All these studies concluded that wavefron t-supported PRK appears to be safe and effective for the treatment of myopia and astigmatism. Comparison between Standard PRK and Wavefront-guided PRK

Wavefront guided PRK was compared to the standard PRK by various authors. In one study, 28 eyes were treated with wavefront-guided PRK and 28 eyes with standard PRK using the same laser (Bausch and Lomb Teclmolas 217z). In another stud y, wavefront-guided PRJ< and conventional PRK on 30 eyes each we re performed with Asclepion Medi tec flying spot MEL 70 excinler laser. Both of these studies found that wavefront-guided PRJ< ind uced a smaller increase o f postoperative wavefront-error compared to conventional PRK and

concluded that wavefront-guided PRJ< is particularly indicated in eyes with higher preoperative RMS val ues. 74

Recent A dvances in PllOtorefra ctive Kemtectomy

Wavefront-guided PRJ( was also used to treat hyperopia. Nagyet al reported better results with wavefront-guided PRJ( (WASCA) than those achieved with traditional PRJ<. Comparison of Wavefront-guided PRK with Wavefront-guided LASIK

Panagopoulou and Pallikaris performed wavefront-g uided LAS IK and wavefront-guided PRJ( using Meditec MEL-70 G-scan excimer laser. They stated that W ASCA PRJ( revea led better outcomes than WASCA LASIK. TOPOGRAPHY-GUIDED PRK

Irreg ular corneal astigmatism has posed a challenge to refrac ti ve surgeons for a long time. Ultimately, technological ad va nces have led to two promising customized approaches: wavefront measurements and cornea l to pography.

Topography-guided treatment has seve ral advantages over wavefrontguided trea tment. First, as it is based on the corneal surface, it is theoretically possible to restore the nat ural aspheri c shape of the cornea . Second, by disregarding the aberrations that originate from the intraocular structures that change with age or accommodation, it concentrates on correcti ng the nonphysiological irregularities. Third, it can be used in patients with corneal scars, \...,here med ia opacities are present, as its measurement is based solely on the

su rface reflection. Fo urth, it can also be used in highly irregular corneas, which are beyond the limits of wavefront measuring devices, as the cornea contributes

two-third to the total dioptric power of a normal eye. And finally, topography maps are relativel y easy and intuitive to interpret, and lTIOst refrac ti ve s urgeons are more familiar w ith these maps than wi th wavefront maps.

The major d isadvantage of topograp hy-guided ablation comes from the same fac t tha t it igno res the rest of the intraocular structures, thus decreasing

the predictability of the refractive outcomes. The topography al one can serve for calcula ting the best-fit ideal anterior cornea l contour to reduce the corneal irregularities, but the newly achieved curvature may not be adequate for the particular eye, when the remainder of the intraocular structu res exert their effect on refraction.

In the literature, topography guided PRK was reported to provide successful res ults especially after previous refra ctive surgery (for enhancement, small hyperopic and myopic excimer laser optica l zones, decentration), for corneal scars (injury, postinfectious), and after keratoplasty. 75

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) Q FACTOR CUSTOMIZED PRK

The expression "aspheric surface" simply means a surface that is not spherical. However, this expression is commonly used to indicate the surfaces that can be described by the equation of a conic. In geometry, the conic curves have been given this n ame because they are generated by the section of a cone with a plane more or less tilted with respect to the base, and these include the circle, ellipse, parabola, and hyperbola. Each of these curves, if rotated on its axis of symmetry, creates a sphere, an ellipsoid, a paraboloid, and a hyperboloid, respectively. These solid figures are called conicoids. The typical corneal section is a prolate ellipse, consisting of a more curved central part, the apex, with a progressive flattening towards the periphery. The asphericity of the cornea usually is defined by determining the asphericity of the conicoid that best fits the portion of cornea to be described. If we accept this approximation, the profile of a meridian can be defined with two values only: • The apical radius (which is on the vertex of the conic), which can be expressed in terms of a circle w ith the same degree of curvature, • A shape factor, which represents the variation in curvature from the apex towards the periphery, which defines the degree of asphericity. This las t parameter can be defined in a number of different ways. Four different coefficients are used to express the shape factor of a conic, each one of which is used in a different way to quantify the same thing: the conic parameter p, the shape factor E, the eccentricity e, and the coefficient of asphericity Q. If one of these indices is known, the others can be calculated using the conversion formulas in Table 1. Table 2 Summarizes the Various Types of Conic Sections with the Corresponding Values of the Different Shape Factors

MyopiC PRK changes asphericity, increasing Q to an oblate value. The effect of reduction in the spherical aberration due to flattening is generally not sufficient to compensate for the increase in spherical aberration due to the substantial variatio n in shape obtained with the majority of the current ablation profiles. The opposite occurs w ith hyperopic treatments, as the current ablation profiles produ ce a hyper-prolate cornea. This variation in shape produces a negative spherical aberration, which usually is not compensated by the increase in positive from the increased curvature. Mastropaque et al performed a 6-month controlled trial to analyze ocular wavefront error and corneal asphericity (Q) in patients treated with aspheric profile ph otorefractive keratectomy (PRK) compared with patients having 76 conventional PRK to correct myopia and myopic astigmatism. In this study, 50

Recent Advances in PllOtorefractive Keratectomy Table 1: Formulas of conversion between various shape tactors of a conic section

p

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be 2

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Table 2. Different types of conical section with the corresponding values of the various coefficients of asphericity

H yperbola Parabola Prolate ellipse Circle Oblate ellipse Average normal cornea

p

Q

e

e'

<0 0 O1 0. 78

<-I -I -I0 -0. 22

>1 1 O<e<1 0 <0 0. 45

>1 ! 0< e 2 <1 0 <0 0. 22

p=conic parameter, Q= asphericity, e=eccentricity, e =illdex of nsphericity

77

Instant Clinica l Diagnosis in OplrtilaIJll ol0:5'J (Refractive Surgery) eyes were treated with aspheric profile PRK using the MEL 80 fl ying-spot excimer laser, and 24 eyes were treated wi th standard PRJ< using the MEL 70 flying-sp ot excirner laser. Postopera tive wavefront error increased in both groups. Six months after surgery, there was a s111aller increase in root mean square (RMS) of total higher-order aberrations and spherical aberration (59% and 106%, respecti vely) in the as phe ric p rofile PRK g rou p than in the conventional PRJ< group (94% and 136%, respectively). The aspheric profile PRJ< group showed more prolate corneal asphericities than the conventional grou p with increasing oblateness for higher attempted corrections. A higher percentage of patients with better low-contrast uncorrec ted visual ac uity and best corrected visual acuity was observed in the aspheric PRJ( g roup than in the conventional PRK group. They concl uded that aspheric profi le PRJ< might induce a smaUer increment of total wavefront error, related to a smaller increase in spherical aberration, and better maintain the physiology of the corneal surface than conventional treatment.

PRK IN THE TREATMENT OF PRESBYOPIA

Presbyopia is loss of accommodation by age. There are va r ious treatment options for presbyopia including spectacles, contact lenses (monovision or bifocal lenses) and refractive surgery. Surgical options fo r the treatment of presbyopia are still questionable in te rms of safety and/ or efficacy. Refractive surgery proced ures fo r the trea tmen t of presbyopia steepen cornea by means of excimer laser, the holmium:YAG laser, or rad iofrequency energy. Procedures that expa nd or relax the sclera, in tracorneal implan ts, m ul ti focal and accomn1od ati ve in traocular lenses are also used.

PRJ< has been used in the treatment of presbyopia by ind ucing monovision. Wright et al treated 21 myopic presbyopic patients with PRK. They ind uced monovision by undercorrecting the nondominant eye by 1.25 diopte rs for near vis ion and correcting the domi nant eye w ith em.metropia for distance vision.

Sixteen em me tropic patients who had PRK served as a control grou p. Monovision PRK patients had better near vision tha n control PRK patients, with mini.m al co mpromise in stereo acuity and overall high pa tient satisfaction. Apart fro m conventional mo novision (dorninant eye correc ted for distance),

crossed mo no vision (domina nt eye corrected for near) was also eva luated by Azar et aI, and repo rted to result in satisfacto ry visual outcomes.

78

RecentAdvances in Photorefmctive Kemtectomy PRK WITH SOLID STATE LASERS

During the pas t 10 yea rs, solid state lasers ha ve improved to become a reliable sou rce fo r treating organic and inorganic tissue materials. The ad vantage of solid-state lasers over excinler lasers is a considerable red uction of problems associated with excimer lasers, permitting a high pulse to stability, smaller spot size, and higher repetition rate. Due to absence of gas, solid-state laser nlaintenance costs are lower and noise level during opera tion is significantly less. Recentl y, Tsiklis et al and Roszkowska et al reported one yea r results of PRK fo r myo pia using a 213 run wavelength solid -state lase r (C ustom Vis and LaserSoft, respecti vely). They both conclu ded tha t PRK w ith solid state lasers is sa fe and e ffec tive (54,55) . Also, Anderson et al reported solid-state, neod ym ium:Y AG laser PRK in 3 patients with irregu la r asti g ma tism (Custom Vis). The laser's combination of a small spot, a fast pu lse rate, and ultrafast trac king/sca nning resulted in good results in those 3 patients with irregular as tigmatism. Yet, long term results with larger samples are necessary to establish the safety and efficacy of PRK with solid state lasers.

79

11 Painless EpiLASIK Chu Renyuan, Zhou Xing/ao, Wu Ying (China)

In excimer laser surgery, surface ablation has always been a kind of surgery

with high safety, high efficiency and high stability. PRK was the initial representative surgery. But advanced surface ablation with epi thelium being maintained has well developed since 1999 when it was first performed. There are two methods of epithelium sheet creation, physica l method with epikeratome and chemical method with ethanol. We have accumulated experience during the seven years' experimental and clinical researches of

advanced surface ablation. Our technique of pain less advanced surface ablation, LASEK /EpiLASIK is introduced as following.

SURGERY PROCEDURE Epi-trephine Assisted LASEK Technique

Epi-trephine (KN5000E) is a precise device for LASEK surgery. It is composed of a control panel, epithelial cutting rings and epithelial separating instruments. Placed with a medical silicon rubber washer inside the suction ring, the suction ring can firmly attract and fix eyeballs with different radius of cornea when the electric pump starts up. After topical anesthesia with eyedrops of 0.4% oxybuprocaine hydrochloride, the cornea is rinsed by balanced sal t solution. The surgeon places the suction ring on the cornea. Then start up the vac uum so as to fix the

eyeball. 20% alcohol solution is instilled into the ring for abo ut 15 seconds. The alcohol solution is then absorbed by the vacuum the trephine is used to delineate the margin of the epithelial sheet then the cornea is rinsed thoroughly. Remove the suction ring and detach the epithelial sheet gently using an epithelial spatula. Pay attention to the integrity of the epithelial sheet. The hinge is placed superiorly at 11 to 1 o'clock. After laser abla tion, the epi thelial sheet is gently repositioned with the help of BSS. Be sure not to overlap the epithelium or expose the stromal bed, especially at the peripheral region of epithelial sheet. A high-OK bandage contact lens is placed onto the cornea. Subsequently, a topical corticosteroid and antibiotic are instilled. The eyelid speculum is then removed carefully. The patient is examined with slit lamp biomicroscopy before dismissal.

80

Painless EpiLASIK

Fig. 1: Slit-lamp photo of one patient, 5 minutes after myopic epi·LASIK

Fig. 2: Patholog ic photo of an ep ithelia l sheet shows the entire basa l membrane

Fig. 3: Slit-lamp photo of one patient , one day after myopic epiLASI K

81

I1lsta1lt Clinical Diagllosis ill Ophthalmo[ogl) (Refractive SlIrgen)} Epi-LASIK Technique

Ep i- LASIK e pi keratome (KM-5000D), in vented and ma nufa ctured b y Department of Ophthalmology, Eye and ENT Hospital, Fudan University and Wuxi Kangming Medical Device Corp, is a precise device for EpiLASIK surgery. It is the unique rotational epikera tome used to create epithelial sheet in EpiLASTK. It is com posed of a control panel and epithelium separating system. Aft e r to pi ca l a n es thesia w ith eyedrop s of 0. 4% oxyb up roca in e hyd rochlorid e, the cornea is rinsed by balanced salt solu tion. The surgeon places the suction ring on the cornea. The size of the suction ring is chosen according to the curva ture o f the cornea. Then start up the vacuum so as to fix

the eyeball. When the vacuu m reaches the target level, the surgeon starts the automatic ep ikeratome. The epikeratome rotates anticlockw ise and creates a smooth epithelial sheet with reg ular border and hinge at superior 11 to 1 o'clock. It takes about 6 second in ave rage to make the epithelial flap. Remove the epikeratome slowly and place the epithelial sheet aside. After laser abla tion, the epithelial sheet is gen tly repositioned with the help of BSS. Be sure not to overlap the epithelium or expose the stromal bed, especially at the peripheral region of epi thelial sheet. A h igh-OK band age contact lens is placed on to the cornea. Subsequently, a topical corticosteroid and antibiotic are instilled. The eyelid speculu m is then removed carefu lly. The patient is examined with slit lam p biomicroscopy before d ismissal. Advantages of Rotational Epikeratome

The integrity, viability and stability of corneal epithelial sheet are the most importan t ele ments of a pa inless Epi-LASIK surgery. How to get the perfect epithelia l shee t is und ou b tedly a g rea t challenge to e ve ry d es igner of ep ikeratom es. Nowdays, there' re g ene rall y two d iffere nt d es igns of epikeratomes in the world, beeline design such as Mo ria epikeratome and ro tational d esign of KN5000D epikeratome (Wuxi Kangmi ng Medica l Device Corp. China). The beeline epikeratorne crea tes nasal hinged epithelial sheet, while the rotational one crea tes superior hinged epithelial sheet. The superior hinged sheet has the adva ntage of less movement w ith blinks, thus ass uring its stability . How ever, rotationally seperating corneal ep itheliunl is not as easy

as seperating corneal stromal flap . Un til now, KN5000D epikeratome is the only one that has settled this problem. How to asce rta in the integri ty and viability of corneal epithelial sheet is the key techniqu e of epikeratomes. KN 5000D rota t iona l epikera to me is 82 characterized with pressu re-free and flexible seperating design tl,at assures

Painless EpiLASfK

the integrity and viability of corneal epithelial sheet. During the seperating procedure, the corneal epithelium does not receive any possitive pressure from the seperator, so the epithelial sheet is perfect without any abnormalities such as tearing. The seperator is a dock-styled fl ex ible device, that is, sepe rating piece in the seperator is not rigidly connected, but w ith a suitable floating range. During the seperating procedure, the seperating pressure is flexibly adjusted as the seperator moves upward and downward on corneal surface~ thus settling the p roblem of damage to corneal stroma. The proced ure of creating corneal epithelial sheet by KN5000D epikeratome is the shortest, from 6 to 10 seconds, which is also important for a viable epithelial sheet. Comparing with KN5000D epikeratome, beeline epikeratom es are all pressure-relied and unflexible. The seperating procedure of beeline epikeratomes is much longer than KN5000D (30 seconds in average). POSTOPERATIVE MANAGEMENT Bandage Contact Lens

Bandage contact lens is used to cover the exposed corneal nerves and to prevent

the eyelids from scraping the cornea so as to reduce the pain after LASEK and Epi-LASIK. Decreased interference from the eyelids helps the stability of corneal epithelium, helps the healing process of epithelium and mean wh ile, prevents the detachment of epithelium layer from anterior stromal laye r. Disposable contact lens with Dk / t of 30x1O -9barrer/ mm is widely used as therapeu tic contact lens after LASEK, but because of its poor oxygen transmissibility, continuolls wearing usuall y causes hypoxia and edema of corneal epithelium. Consideri ng the s pecial condition after excimer laser corneal surgery, the therapeutic con tact lens ought to meet some special requirements in its basic curve and oxgen transmissibility. Idea l bandage con tact lens can fit the oblate shape of central cornea surface and provide the cornea with enough oxygen during the constant wearing period of 5 to 7 d ays. Good movem en t can prevent the contact lens from adhering to the corneal epithelium and improve the comfort of the eye. Therapeutic contact lens contains big basic curve to ensure the movement o f lens. Anterior corneal curvature turns smaller postoperatively so lens w ith big basic curve fits the ne\'v curvature better. But lens w ith too big movement sh ifts easily, which can not protect the epithelium. Wu has compared lens with different basic curve and suggests the lens with basic curve of8.7 m.m shows good movement, good centra l orientation and good tightness for postoperative trea tment of excimer laser surgery. Dk/ t value is another important factor of bandage contact lens to promote postoperative epithelial healing. Silicone hydrogel Contact lens with high 83

Il1stant Clin ical Diag1losis il1 Ophthalmologl) (Refractive SlI rgen))

Ok! t accelerates the corneal epithel ial healing and reduces th e applications related to anoxic. Wu reported significant less pain, less foreign body sense and milder epithelial edema using con tact lens with Ok! t of 86 x 1O- 9 barrer! mm than using mo nth-wearing contact lens. On postoperative day 3, corneal epithelium in 50% eyes with high Ok! t lens, 33% eyes with mon th-wearing contact lens have healed well enough to remove the lens. The bandage contact lens sh o uld be removed off in 5 to 7 days postoperative ly, depending on the h ea ling process of epithelium. If the epithelium has been renewed and no edema can be detected, the contact lens is safe to be taken off. Studies have showed th at cornea haze occurs at the place where epithelial defect or edema. Once there is spot of edema epitheli um, contact lens is recommended to remain for another 24 hours. Zholl has observed the epithelium healing process after LASEK and EpiLASlK and suggests that in eyes with epithelium healing delay, wearing contact lens longer can help to prevent the postoperative pain and cornea haze. EYE DROPS

While the bandage contact lens remains on cornea for the first 5 to 7 days after surgery, the patient is given topical corticosteroids (0.05-0.1 % dexamethasone eyedrops) to be used 6 times a day as a strike therapy to conquer the acute release of inflammation factors atthe first several days after the surgery. After the contact lens is removed, 0.1 % fluorometholone eyedrops is used 6 times a day for 5 days and then is reduced to 5 times a day for another 5 days. By then, the patient should have visual acui ty and refraction examined. According to the cornea transparency and refraction outcomes, the corticosteroid is adjusted and maintained for at least 3 months. The incidence of haze on the cornea after LASEK and Ep i LASTK is less, compared with PRK, howeve r, continual corticosteroids w iU, slow taper prevent the likelihood of stromal haze. Subjective symptoms such as visual blur or resid ual myopia and objective signs such as the presence of stromal haze serve to guide the postoperative course of topical corticosteroids. Since steroid may raise the intraocular pressure (lOP) in some patients, consta ntl y check of lOP is necessary during the period of using steroid. Topical antibiotics are recommended to be used 4 times a day for the first two postoperative weeks, unless there is any clue for infective LnfJammation. Nonsteroida l anti-inflammation d rugs inhibit epoxidase and stop the synthesis and release of prostaglandin so as to achieve the strong effect of diminishing inflammation and acesodyne. They are common ly ap p lied after PRK and LASIK to control the postopera tive reactivity. But indomethacin and 84 diclofenac sodi um are reported to ca use epithelium disso lution or to influent

Painless EpiLASIK

the epithelium healing. Verugno reported that among lour ki nds 01 NSAIDs such as indomethacin, dicJolen ac sodiu m, ketorolac and f1u rbi p rolen, f1urbiprofen has best eflect but least side-effect to control pain after pRJ(. Pranoprofen has the same effect and sa fety as f1urbiprofen. Wang combined pranoprofen and steroid to control the infl ammation reactivity after LASEK and found tha t pranoprofen can reduce the degree and period of postoperative uncomlor!. No severe side effect was reported. Topical NSAIDs such as pranoprolen and fl urbiprolen can be used 3 times a day lor the fi rst week if the patient complains of eye pain. ot like corticosteroid, NSAIDs don' t cause inh'aocular pressure to rise. So they can also serve as substitutes of corticosteroid to control the stromal proli feration and prevent corneal haze when the lOP has rise.

The in1porta nce of a strong tear layer on the cornea allows proper healing and best visua l outcome. Patients are advised a routine regiment of non preserved artjficial tears to maintain a smooth tear filnl over the cornea. Persistent dryness or surface irregularities secondary to tear defi ciencies are cause for considering punctal occlusion.

85

12 Wavefront-guided Photo refractive Keratectomy-Today and the Future Weldon W Haw, Edward E Manche (USA)

INTRODUCTION

Over the years, refractive surgeons have been driven to optimize results of keratorefracti ve su rgery. Radial keratotom y and fi rst generation excimer lasers treated spherical myopia by simply inpu tting the amou nt of myopia to be treated in experienced based algorith ms. The evolution of more complex technology has resulted in increasingly accurate and pred ictable results. Improved quality of results has also been driven by the emergence of both diagnostic and therape utic wavefront technology. Wavefront technology allowed the customization of the refracti ve p rocedure, minimized degradation of the quality of the vision (i.e. contrast sensitivity) that occurs with corneal refractive surgery, and has been instrumental in allowing us to come closer to achieving the possibility of "supernormal" vision for man y pa tien ts. WHAT IS WAVEFRONT TECHNOLOGY?

86

For many years, astronomers and mathemat icians realized the importance of using wavefro n t analysis to optimize the capture of images by the telescopic opticaJ systems from immense distances. It was until only recently w hen vision researchers adop ted this technology for use in optimizing the human optical systen1. The Hartmann -Shack wavefront sensor, used by astronomers to analyze ahnospheric aberrations above a telescope in real time was the first slich adopted technology. Since then vision researchers and refrac tive surgeons have become fluent in the language of wavefront optics. The imperfections of an optical system can be broken d own into its C0I11pOnents using wavefron t analysis. A plane wave of monochromatic light is distorted by optical aberrations as it passes through an op tical system (i.e. the eye). These distortions can be measured by evaluating this in formation in the form of a Zernike polynonual expans ion. The cumulative wavefront error can be subdivided into its individual components by a set of normalized Zemike polynomials that are best fit to the measured wavefron t error. The coefficient for each Zernike term demonstrates the component's relative contribution to the to tal root mean square (RMS) error. In most normal ametro pic eyes, lower order abe rration such as defocus (m yopia or hype ropia) is the dominant

Wavefrollt-gllided PllOtorefractive Keratectomy-Today and tile Fuhll'e

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4th~~~~~ Fig. 1: Zernike Py ramid. Low order aberrations include the first two top rows . (1st order aberrations include Tip and Tilt. 2nd order aberrat ions include Astigmatism and Defocus.) Higher order aberrations include any rows below the 3rd row. (3rd order aberration include Trefoil and Coma. 4th order aberration include Tetrafoil , Secondary astigmatism, and Spherical Aberration.) See text for detail

87

Instant Clinical Diagnosis in Ophthallllol0!5'J (Refra ctive SltygenJ)

aberration, fo llowed by astigmatism. Higher order aberrations (i.e. coma, spherical abe rration, trefoil, etc. .. ) usually constitute a small component (<10%) of the norma l eye's total aberrations. The amount of higher order aberrations can vary between individuals. In addition, pupil size is an important variable as higher order aberrations increase with increased pupil size. The benefits of correcting higher order aberrations are therefore maximized in younger patients who typica lly have larger pupils and under scotopic situatio ns (i.e. night driving). Although most ava ilable aberrometers measure to the sixth order, most refractive surgeons agree that measuring to the fourth order is probably all that is clinically re leva nt. At some po int, higher order aberra ti o ns cease to be

clinically significant as d iffraction and the density and hea lth of the retinal ganglion cells may limit an individual's ability to discriminate the q uality of images cast upon the retina. CUSTOM WAVEFRONT PRK

Despite the ability to measure aberrations beyond the 6th order and the ability to precisely deliver excirner laser ablations based on these measurements, the

outcomes of custom wavefront PRJ< are signilicantly limited by (i) the variable effects of the excimer laser on the cornea and (ii) the differences in healing that occurs during the postoperative recovery period following PRK. Corneal biomechanica l response to ablative surgery may Significantly affect outcomes, and should be taken into accou nt when planning customized procedures. The unpredictable hea ling response is a dynamic process that can occur even years after the refrac ti ve procedure. Studies have suggestive that this process plays a significant role in the interpersonal variability and refractive stabili ty of the procedure and can significantly impact the results of cus to m ablation . Unforh.mately, current algorithms do no t accurately predict the biomechanical response of the cornea for all individ uals. CLINICAL RESULTS

Several studies confirm the advantages of custom wavefront-g uided PRK over conventional PRK (Table 1). Wigled owska-Proienska evaluated 126 myopic or myopic astigmatic eyes of ll2 patients that underwent either wavefront-guided PRJ< or conventio nal PRJ< with the MEL 70 G-scan excimer laser system with two-year follow-up. Total higher-order root-mean square u1Creased by a factor of 1.l8 Ul the custom grou p versus l.60 for the conventional group. In addition there was a s ig nifican t increase in coma and spherical abe rration in the

conventi onal PRK group. The investigators concluded that custom PRK d emonstra ted ad vantages over conventional PRK incl udi ng improved uncorrected v isual acuity, spectacle corrected visual acuity, and a reduction in

88 the number of higher order aberra tions induced by the excimer laser.

Table 1: Summary of custom wavefront-guided PRK studies Study - Authors

Study Design

Investigator's Conclusions

Wigledowska-Promienska D, Zawojska I (2007)

126 eyes with myopia or myopic astigmatism undergoing custom PRK vs. conventional PRK with the MEL 70 G Scan excimer laser. Two-year follow-up.

Custom PAK reduced the number of higher order aberrations induced by the excimer laser and improved uncorrected and spectacle corrected visual acuity when compared to conventional PAK

Mastropasqua L. Nubile M, Ciancag lini M, Toto L, Ballone E (2004)

60 eyes of 60 patients randomized to wavefronlguided PRK vs. conventional PRK with the Asclepion Meditec flying spot Mel 70 excimer laser. 6 month follow-up.

Wavefront-guided PRK induced a smaller increase of postoperative wavefront error compared to conventional PA K, particularly in patients with higher preoperative higher order aberrations.

Nagy ZZ, Palagyi-Deak I, Kelemen E, Kovacs A (2002)

150 eyes of 104 patients with spherical myopia and myopic astigmatism treated with the Asclepion-Meditec MEL 70 G scan lase r. 6 month follow-up.

Wavefront supported PAK was efficacious, safe, and predictable. Best corrected visual acuity may be improved over results obtained with conventional PRK.

Mastropasqua L, Toto L, Zuppardi E, Nubile M, Carpineto P, Dl Nicola M, Ballone E (2006)

56 eyes of 56 patients with myopia randomized to receive wavefront-g uided PRK with the Zywave Bausch and Lomb Technolas 2Hz or conventional PRK. 6 month results.

Wavefront guided PAK is safe, effective, and induces less third order coma aberration as compa red to standard PAK. The use of Zyoptix wavefront guided PAK is particularly indicated in eyes with higher preoperative AMS values

Bahar I, Levinger S, Kremer I (2006)

40 eyes of 20 patients wi th suspected keratoconus underwent wavefront supported PAK with the Bausch and Lomb Technolas 217 z laser. All patients followed for a minimum of 40 months.

Wavefront supported PRK appears to be effective for the treatment of myopia and astigmatism in patients suspected keratoconus. Longer follow-up is needed to prove the safety of the procedure in this patient population.

30 eyes of 23 patients with myopic astigmatism underwent wavefront supported PRK with the Asclepion MEL 70 excimer laser. 12 months follow-up.

Wavefront supported PAK with the Asclepion MEL 70 laser was safe and effective . Daylight visual acuity and mesopic visual acuity outcomes remained stable over 1 year.

Dausch D, Dausch S, Schroder E.

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Instant Clinical Diagnosis ill Ophtlla!lIIo!ogJ} (Refractive SUI'gery)

Mastropasq ua et al evalua ted 60 eyes of 60 patients with myopic astigmatism randomized to receive custom PRK or conventional PRK with the MEL 70 excimer laser. Although wavefront error increased in both groups, at

six months, the custom PRK treated grou p demonstrated a smaller increase in the root-mea n-square compared to the conventional PRK (P 0.4 microns. The postoperative accuracy, uncorrected and best corrected visual were not statistically significant

between groups. Dausch et al treated 30 eyes of 23 patien ts with myopia less than -8.0 D (mean -3.76 D + / - 1.90 D) and cylinder less than -3.50 D (mean -0.81 + / -0.71 D) with wavefront supported PRK using the Asclepion MEL 70 excimer laser. Uncorrected visual acui ty was 20/16 or better in 47% (14 eyes) at 1 month, 67% (20 eyes) at 3 months, 77% (23 eyes) at 6 m onths, 90% (27 eyes) a t 9 months, and 83% (25 eyes) at 12 mon ths. 0 eyes lost more than 1 line of best corrected visual acuity (BSeVA) at 3, 6, 9, or 12 months. 13% (4 eyes) gained 2 or more lines of BSeV A at6, 9, and 12 months. BSeVA was 20 / 10 or better in 30% at 12 months. Visual acuity under low contrast was unchanged in 87% (26 eyes) at 12 months. Nagy et a l evaluated 150 eyes of 104 patients treated wi th wavefront supported customized PRK for myopia and myopic astigm atism using the Asclepion- Meditec MEL G-scan excim er laser. At 6 months, the mean postoperative visual acuity was better than 20/20 and the mean best spectacle corrected vis ual acuity was 20/16. The average spherical equi va lent on manifest refraction was -0.12 D. Pred ictability was excellent with 98.6% (148 of 150 eyes) of eyes being within +/ -0.50 D of intended correction and 100% within + / - 1.0 D ofintend ed correction. 8.2 % (11 of150) of eyes demonstrated a best spectacle corrected visual acuity (BSeV A) of 2 or more lines better than their preoperative BSeVA while no eyes lost 2 or more lines of BSCV A. The root mean square va lue for higher order aberrati ons increased 1.4 times following

PRK. Manche et al presented preliminary results on performing wavefront guided PRK in symptomatic h ighly aberrated eyes following previous keratorefractive su rgery using the VISX 54 excirner laser and the WaveScan Aberrometer. 25 eyes of 21 patients that had undergone previous keratorefractive surgery with LASIK (14 eyes), radial keratotomy (9 eyes), and PRK (2 eyes) were trea ted using a customized nomogralTI and adjunctive intraoperative applica tion of 0.02% mitomycin C. At 6 months, sphere had been red uced from -1.56 D +/ 1.09 D to -0.15 D +/ -0.42 D, astigma tism was reduced +1.18 D+/0-0.83 D to

90

Wavefrollt-gllided PlIO to refractive Keratectomy-Today alld tlte FlItllre

0.350 +/ - 0.35 D, a nd the spherical equivalent was reduced fro m -0.97D +/ 1.040 to +0.01D +/ -0.37 D. 61 % of eyes demonstrated an uncorrected visual acuity of 20/20 or better and all eyes had an uncorrected visual acu ity of 20 / 30 or better. 83% of eyes were within + / - 0.5 D of intended correction and 100% of eyes were wi thin + / - 1.0 D of intended correction. 23% of eyes gained one or mo re lines of best corrected visual acui ty. No eyes lost 2 or mo re lines of best corrected visua l ac ui ty. l1,ere was a small reduction of tota l higher order RMS values with a slight reduction in coma at the 6 month visit. No change was noted in trefoil or spherical aberra tion at 6 months. Dr Manche concluded that the procedu re improved uncorrec ted and best corrected visual acuity, d emonstra ted good pred icta b iIi ty and excelIent safety. LIMITATIONS

PRK has limita tions regardless of w hether conventional or custom wavefront

guided ablations are perfo rmed. Postoperati ve pain, potential for developing scarring and corneal ha ze, and slower v isual rehabili tation are liln ita tions

inherent withi n the PRK procedure. Also, although highe r-order aberrations increase in both LASIK and PRK, they are typically greater followin g LASIK possibly due to the generation of a LASTK flap . Uncomplicated lamella r flap creation is responsible for systematic chan ges in the cornea l topography and induction of higher order optical aberrations. Predictors of this response include stromal bed thickness, flap diameter, and total corneal pachymetry. ln addition, corneal surface healing following LASIK or PRK can result in overall smoothing of the corneal su rface as the epithelium thickens over divots and thins over

bumps. This may partially negate the acc uracy of micron and sub-micron wavefront tec hnology. In the future, inlproved methods of pharmacologically or biologically modulating the cornea's response to the excimer laser could help us realize the full potential of wavefro nt teclmology. SUMMARY

Custom wavefront-gu ided PRK dem onstrates promise in the correction ametropia. Avoid ing the mechanica l variations due to the creation of the lamellar flap (i.e. LASTK) has potential benefits when dealing with the micron level of acc uracy d e monstrated by wavefron t diagnostic and therapeutic modalities. In the future, we will have to reconcile with the biological variability resulting fro m interpersona l va riat io ns in corneal wo u n d healing.

Unfortunately, ad vances in the clinica lly available pharm acological and biological wound healin g modulation tec1miques have not kept pace with advances in wavefront tedU1ology. Despite this shortcomi.ng, custom w avefront

guided PRK has proven to be an importan t and valuable approach to managing patients 'with ametropia. 91

13 Presby-EpiLASIK in Pseudophakic Eyes with the Wavelight Allegretto Frederic Hehn (France)

INTRODUCTION

Presby-LASIK h as got no w a worldwide acceptance among ophthalmologists community. In some cases LASIK is not possible, then w e practice epiLASIK. PresbyLASIK in pseudophakic eye make sense to proof the truthfulness of the optical basement of this technique; and consequently the durability of the results in phakic patients. In this article we analyze the relationship between Q value asphericity and the amount of spherical aberrations. We observe what's happened during accommodation; propose 3 shapes of corneal presbyopia compensation, and finally gi ve some examples with topolink treatments. N atural eye is a hi-optic optical system with a variable axial myopic additional power due to the crystalli ne lens. Because evidently along visual axis (object to macula) the vision will be the more discrimina te with the best contrast sensitivity and MTF (modulation of transfer function) for the both near and far v ision. This bioptic system produces the best near and distant visual acuity, in using crystalline lens accommodation which can be achieve. Because Presby-LASIK cannot restore accommodation, it just can be a good compromise between near and distant vision. Na tural eye present some coma HOA due to the difference between visual axis (object to macula) and optical axis (apex of cornea to the center of crystalline lens). That's the reason wh y we are thinking that presby-LASIK teclmique does not increase the natural existent coma. Then to avoid to increase COlna presby-LASIK must be centered. Inspired of multifocal or bifocal soft lens for presbyopia, that gives good results in many cases, the therape utic choice w ill be to place distant vision in center or no t. Some authors have got good results with a small optical zone for near vision in the very center cornea. Relationship between Q Value Asphericity and Amount of Spherical Aberrations

The difficulty is to understand that, the Q value asphericity and the spherical abenations (SA) make change together, but they haven' t got the same 0 reference. Q value is due to the difference of keratometry between the center cornea and 92 the medium cornea (6.5 mm OZ). If keratometry increase from the central to the

Presby-EpiLASIK ill Pselldophakic Eyes w ith the Waveligh t A liegretto

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;;V

Probe

Fig . 2: Q value and SA relationsh ip

93

Instant Clin ical Diagnosis in Oplrtl"' llllo logtj (Refractive Surgenj)

perip heral cornea Q value is positive, and the cornea profile is called obla te. At the contra ry Q value is negative and the cornea profile is called h yper-prolate. [n no rmal cornea mean Q < 0 ( - 0.25) and SA >0 (0.25p). If the keratometry is constan t the cornea p rofile is spherica l Q ; 0, and SA »0 (lp or m ore). If Q value ; -0.55 then SA = O. These basements are checked up in the Fig ure 2. Q value is measured by the topograph, for instance the TOPO LYZER of Wavelight, it can give also the amOlmt o f SA d ue to the cornea . At the con trary the aberrometer like ANALYZER of wavelight , measure the to tal SA of the bo th corneal and crys tall ine lens. Generally negative SA occurred in the crystalline, and positive SA in the cornea, therefore the total amoun t of SA in yo ung peop le is often null. Why EpiLASIK is Necessary in Some Cases

It's well known that a thin cornea < 500 fl, has not to be treated by LASIK, according with the risk of pseudokera toconic corneal ectasia. But there are many publica tions about ectasia even in case of previous hyperopic eye, or sufficient resid ual stromal bed more than 250 ~l. 11,e last year it appea rs that biomechanical properties of the cornea have to be considered. Especially the cornea l hysterisis CH, \,vhich measures the comb ined elas ticity and viscosity of the cornea, with the ora machine. ORA ocular response anaJyzer is now a routine exa m in our office before p resby-LASIK. In considerations wi th others parameters: corneal thickness, topograp hy, If CH < 9 we practice an epiLASIK instead of a LASIK. We have choice the epilasik GEBAUER, because the procedure is very fast only 20 second s. The epilasik head present an ap planation plate and a special shape of one Single use blade. In fact the blade edge is not symmetrical. The angle of posterior face of the blade is mi nor than the anterior angle. That the reason why stromal in trusion is impossible, and multiple enhancements w ith epiLASIK afte r a p revious epiLASIK on the sa me eye are possible. Ep iLASIK creates a very thin epithelial flap, which need s a contact lens wearing, during 3 days to ensure his sta bil ity and healing. We must be careful with the management of the contact lenses, especiall y no wa ter must entry inside eyes to avoid acanthameoba infection. The second problem with epiLASIK is the ri sk of haze. Abo ut more than personal 500 cases we have got no haze grade 3 or 4 in myopic eyes, if enough steroid drops have been instilled (four times a day, during 8 weeks). At the contrary it remains a haze grade 3 or 4, in hyperopiCtreatment, as the shape of a concen tric ri ng in medium cornea . This haze ca n give regression and halos. That is the reason why we definitively treat hyperopic by LASIK or Femtosecond. 94

Presby-EpiLASIK ill Pselldophakic Eyes with the WavelightAllegretto

10Pec: ' •. 1 mmHg 10PII: 1$.611>n'1Hg

eH: 12.2 rnrnHg

----

CRF : 12.01'ft11'Hg

eel:

".

Af'9nohlter - -

foWMle<ea -

Fig. 3: Ocular response analyzer

Fig . 4 : EpiUft: asymmetrical blade avoid stromal injuries

95

In stallt Clinical Diagll osis ill OphthalmologJJ (Re/mctive SlllgenJ) Interest of using a Spherical Aberration Free IOL to Correct Presbyopia in Pseudophakic Eye If we are using the B and L akreos adapt JOL, Q value of this TOL is -0.55 then it creates no SA. Therefore, the crysta lline implantation does not modify the corneal rebuilt sh aping for presbyopia compensation. A pseudophakic eye with this kind of IOL, give us a pure human corneal model, to well understand wha t exactly presby-LASIK does. Secondl y Presby-LASIK in p seudophakic eye make sense to proof the truthfu lness of the optica l basement of this technique; and consequently the durab ili ty of the results in phakic pa tients. And we are thinkin g that: when our patients would have been cataract surgery, they would keep the results of their previous presby-LASIK. Monofocal IOL give a good distant vision (DV). But the patient, due to the natural multifocali ty of the cornea, can have also an intermed iate vision (iv) : that's ca]]ed the depth of focus. By a modification of the SA of the cornea it w ill be possible to increase the depth of foc us until patient will be ab le to read without glasses.

What Happens with Q Value and SA During Accommodation The augmentation of anterior curvature of the crystalline lens give a myopic shift with an increasing of Z2,0 zernike polynoma : without myopia no n ear v ision possible. But in concern of HOA only spherical abe rra tion e12 o r Z4,0 ha ve significan t modification accord ing to a study (2). Th ese autho rs demonstrate tha t during accommodation the variation of spherical aberration are always nega ti ve, and most interestin g point is that variation is precisely and linea rly correla ted to the amount of acconunodation in u sing a Hartmannshak aberrome ter system. Varia tion of SA = -0.0435 pm/ diopter. Therefore 3 diopters of accommodation correspond to a variation of - 0.130 pm in SA. Presby-LASIK tedmique must simula te accommodation in creating a myopic zone and also negative spherical aberra tion. We have verified this fact in using our w avelight aberrometer system a nd obtain exac tly the sam e results: we place our 16 yea rs old son behind aberrometer and present to him myopic lens to turn him to hyperopia and force him to accommodate; we re la te these resu lts in Figures 7 and 8. Then presby-LASIK mus t mine natural accommodation with Q va lue negative, idea ll y Q = -l.00 And increasing negative spherica l aberration. The variation between preap and postop SA h as to be /', SA = - 0.130 J.l for 3 Diopters of accommodation. Then we ha ve to p ass from a prolate cornea to a hyperprolate cornea; h yperprolate cornea = pseudoaccommodative cornea. Three profiles of cenh·ed presby- LASIK w hich can give Q = - 1.00 1. Distant vision in cen tral cornea:The centered presby-LASIK teclmique with distant vision in the center give a very good distan t vision and a useful aptiona I nea r and in termed iate vision . The d ifficul ties rema in the necessi ty

96

Presby-EpiLASIK ill Pselldophakic Eyes with the WavelightAllegretto

Pseudophakic monofocal = DV

Pupil

Fig. 5:

Increasing MF cornea iv--+ nv

Fig. 6 : Figs 5 and 6 : Corneal multifocality can give intermediate and nea r vision in pseudophakic eyes

97

Instant Clinical Diagnosis in OplztltalmoloS'J (Refractive SurgeJy) to get high luminance for reading a book. The goal of presby-LASIK is not to completely erase spectacles but to decrease the pa tient's glasses depende ncy. Figures 10 and 11 show ideal presby-LASIK profile. This way give excellent d istant vision and an optional useful near and intermediate vision. We practice at first a hyperopic trea tment of + 3.00 d iopters on a large 6.5 or 7.0 mm OZ to get a good near vision. Second ly we performed a myopic treatment of - 3.00 on a small OZ depending on pupil size to get a very good vision in central cornea as naturally it is. We measure also our results in using the TOPOLYZER topograph of wavelight. We are using the very prec ise allegretto waveli ght, argon fluor excimer laser, with a little fly ing spot of O.S mm diameter and a high speed delivery system of 400 Hz, and eye tracker so. This first presby-LASIK approach gives an alUlular ring in medium cornea for near vision.

This profile is useful in case of small pupil, and for myopic eye. In myopic eye you ha ve just to make a myopic treatment on a small OZ. It is very tissue saving, but the very oblate profile, can give some halos. 2. Near visi011 in central cornen: We make exactly the contrary; like SOlne authors do (1); at first myopic treatment and secondly hyperopic treatment. That is the best of because, that is given large OZ. It is a good compromise for emmetropic and hyperopic eyes. The resulting shape is a continuous hyperprolate shape. Nea r vision will be excellent, but distant vision cou ld be poorer. This technique is perfect for large pupil. 3. Direct Q vallie adjllstment with F-CAT: In the F-CAT program allegretto we can choice a Q value target. If we choice the Q value; - 1.00, the results are the sames that the second technique. But the real useful OZ will be sma ller, and we must be careful to compensate the hyperopic shift induced by this treatment. For a constant OZ of 6.50 mm, each variation of - 0.1 of Q value induce ap proximately + 0.13 hyperopic shift. 4. Preferentiall1lllltifocality could be a good comprol1lise: Each eye see the both dista nt an d near vision without glasses but the dominant eye get a better distant vision than near vision, and the dominated eye can get a better near visio n than distant vis ion. In this example right eye is treated ,'vith the first teclUlique: distant vision in central cornea, the left eye is treated with near v ision in central cornea. It results an excellent binocular distant, near and intermediate vision, w ith a good defocus curve, as we can see in the next chapter about clinical example.

98

Presby-EpiLASIK in Pselldoplzakic Eyes with the WavelightAllegretto - - - - - - - -- --

- - - - - - - - -- - - - - - -

'" SA is proportional to accommodation Cheng H Hoamett JK Apopu\;Jtlon "Iud)! on changc~ In w ...·o OIbcrrnt.ons with aec.ornmodallon Colloyo 01 oplomety Unlvcro.1y of Houston, Houston TX n204-2020, USA J Vis 2004 Ap r 16 4(41 272-8ll

0.35

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-

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-

-

---

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Stimulated accommodation Analyzer + Aberroscopic lens

- --

-

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3 Diopters = -0.130 J.lm SA

Fig . 8 Figs 7 and 8: During crystalline accommodation SA decrease of -0 .130 11 for 3 dioplers

99

IllstalltClinical Diag llosis in Ophthal1l1ologtj (Refracti ve SlIrgenj) Clinical Examples

We show results in two examples of pseudophakic patients with monofocal IOL. 1. Distant vision in centml cornea : The first patient is a 53 years old man has got hydrophilic STABIBAG IOl TECH laboratories in the both eyes. In this case we remark some irregularities in the topographic map due to the fact in this first case s tudying we have not ever practiced a previous A-CAT (a berrometric customized ablation treatment) treatment to make sure to get a free HOA eye before performing presby-lAS1K. The second point is that this patient gets in monocular vision very good results on the defocus curve. That is a proof of very good dep th of focu s with this technique as so good than wi th MF 10 l it is. 2. Near vision in celltml cornea: The both eyes have got a corneal excentricity = 1.00 tha t means Q value = - 1.00 This patient previously enm1etropic, obtained an excellen t results with 20/ 20 j1 uncorrected binocular vision. T-CAT IS THE CLUE

Topolink can compensate the angle kappa. Angle kappa is due to the difference between visual axis (object to macula) a nd the center of the pupi l. This angle is calculated by the topograph. The topolyzer wavelight gives the both angle kappa and the d ynamic pupillometry which can help surgeon to adapt the OZ of the trea tment with the pupil size in mesopic and photopic conditions, especially in case of presby-LASIK. The visual axis, crosses the cornea at a point which is approximately the point of fixation of the patien t. In the case of a topographic measurement, we consider that the point of fixation, is the center of the ve ry center ring of the machine. If Angle kap pa it is more than 100 J.I, the laser treatment, even U1 case of a spherical trea tment can induce the both coma and astigmatism . Then we have to consider Angle kappa espeCially in hyperopic eye, with often nasal fixation, enhancement for decentration, and d ual treatment like presby-LASlK. Secondly presby-LAS1K occurred generally U1 older patient than in lASIK; it will be not logical to treat crystallille abe rrations. Because after the crys talline lens extraction reveal some others new, HOA. Then it is preferential to modify only the cornea and do not compensate the crystallille aberrations. Finally in case of pseudophakic eye, the wavefront da ta are often not ava ilable, because there a capula r fib rosis, and pupil dis torsion, and a lot of reflexion of the laser ray. Then often wavefront meas urement are not va lid in case of pseudophakic eye. Therefore we have three reasons to use only T-CAT treatment for presbylASlK o r presby-EpilAS1K ill the both phakic and pseudophakic eyes. 100

Presby-EpiLASIK ill Pselldophakic Eyes w ith the Wavelight A llegretto

Fig. 9: Hyper-prolate corneal shape looks like lens accommodation

101

Instant Clinical Diagnosis in OphthalmologtJ (Refractive SlIrgery) CONCLUSION

Presby-lASIK cou ld be logically compensate presbyopia in emrnetropic pseudophakic eye witi, rnonofocal IOl, like the MF TOl do. The centered presbyl ASTK technique with distant vision in the center give a ve ry good distant vision and a useful optional near and intermediate vision. A t the contrary near vision in the center give only a useful distan t vision . That's the reason why,

preferential mu lti focality could be a good compromise. The goa l of presbyl ASlK is not to completely erase spectades but to decrease the patient's glasses dependency. T-CAT treatment is the clue for presby-LASIK or presby-EpilASIK in the both phakic and pseudophakic eyes. Presby-LASIK seems to get as so good results as Multifocal IOL , especially in terms on in termediate vision and defocus curve. Is presby-LASIK will become a non-penetrative alternative of the dea r lens exchange? I

102

Presby-EpiLASIK ill Pselldophakic Eyes with the Wavelight Allegretto

Ideal presbylasik profile

Q<0

A natural concept

Near visio

Fig. 10

Ideal presbylasik profile

Q <0

A natural concept

Fig. 11 Figs 10 and 11: Distant viSion in central cornea isa natural shape

103

Instant Clinical Diagnosis in Ophthalmoloi51} (Refractive Surgery)

. - . - -.

Fig. 12

1

\ 20/20

i ~

I + 3.00 /I - 3.00

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J3 Fig. 13

Figs 12 and 13: Distant vision in central cornea is exceUenl , but near vision is on ly useful

104

Presby-EpiLASIK ill Pselldophakic Eyes with the Wave/igM Allegretto

Fig . 14

- 3.00 11 + 3.00

16/20

J1

Fig . 15 Figs 14 and 15: Near vision in central cornea is excellent. but distant vision is only useful

105

Instant Clinical Diagnosis in Opll t/w[mo[oSlj (Refractive SlIIgenj)

Fig. 16

Fig. 17 Figs 16 and 17: 11 Q value decrease , OZ decrease also

106

Presby-EpiLASIK ill Pselldopiwkic Eyes with the Wavelight A llegretto

R

L + 3.00 II - 3.0 0

IRIS

Fovea

I 20/20 I

J3

~

16/20

I

J1

FIg. 18: Preferential multifocality could be a good compromise

Fig. 19: Bilateral distant vision in center

107

InstantClinical Diagnosis in OphthalmologtJ (Refractive Surgery) ~

M

53 years old

Pseudophakic

<;,

Good distant vision,J

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NATIONS VISION

Fig . 21 : Bilateral near vision in the very central cornea

108

1

Good depth of focus -;

V~

I

6

Good near vision

\

Presby-EpiLASIK ill Pselldophakic Eyes w ith the Wave/igl.tAl/egretto

Fig. 22 : Angle kappa

109

14 EpiLASIK with Mitomycin C o Ramamurthy, Chitra Ramamurthy (India) Corneal Refractive surgery has evolved through the last couple of decades. The rad ial keratotomy introduced by Fyodorov in 1980's fo llowed by 1990's era of photorefractive keratoto my had their period of glo ry. However inconsistency in the predicted outcome, the discomfort in PRK, the regression which followed were the limiting features. The need of the hOllr was a constant, predictable v isual outcome and Lasik

emerged a winner in late 1990's with safety and reproducibility. With improved understand ing of the bugbears inherent in lasik over the ensuing years, the occurrence o f microkeratome induced complications, the rare occurrence of DLK and the growing awareness of probable ectasia, a rejuvenation of surface

ablations occurred. This was also the period of growing awa reness of the wound remodeling and the corneal biomechanical response. Resurfacing of surface ablations was initiated by the LASEK procedure with alcohol induced separation of the basement membrane of the cornea. This was followed upon by a more refined EpiLASIK procedure described by Pallikaris in 2003. The reasons for res II rgellce of surface ablations are: 1. Conservation of corneal tissue by creating thinner flaps of 45 to 601-1 thickness depend ing on the thickness of the epitheli um in that individual. 2. Feasability to plan larger optic zones corresponding to the mesopic pupil measurement.

3. Theearlier broad beam lasers and central island formation which brought disrep ute to PRJ( gave way to sophisticated laser ablation profiles with distinctive ly improved visual ou tcome fo r surface trea tment. 4. Thinner corneas, steep K's with expectant microkeratome cOlnplications were more idea l for surface ab lations.

5. Post flap complica tions with lasik could undergo enhancements with surface treatments with improved safety profile. 6. Wavefront ablations wa s found to perform better with surface ablations through various studies conducted and th e cornea l biomechanical response wa s more predictable in surface procedures.

110

7. Contrast sensitivity recovered faster than in lasik. Recovery from dry eye status was again speedier.

EpiLASIK w ith M itomycin C

Dissection in Epilasik

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Deseemet membrane Endothelium

Fig. 1: The red arrow indicates the plane of cleavage for EpiLASIK

Fig. 2: Moria Epi K

111

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) HISTOLOGICAL FINDINGS

Transmission electron microscopy of the ha rvested epithelial sheets showed minimal evidence of trauma in the basal epithelial cells, the intracellular organelles and intercellular desmosomal connections as well as the hemidesmosomal connections w ith the basement membrane appeared closer to normal with only focal disruptions. Alcohol assisted epithelial separations take place within the basement membrane affecting its integri ty. The intact basement membrane has been found to be important to control the fibro tic activation of keratocytes and faster epithelial wo und healing. To this end, Epilasik with the clean cleavage at the level of basement membrane faired better over LASEK. PRINCIPLE OF EPILASIK

A blw1t epikerotome moves on the eye providing a clean cleavage between the basement membrane and Bowman's layer, lifting an epithelial sheet of 50 - 60~ followed by surface laser ablation requisite for the refractive error. Procedure

leepacks need to be placed on either eye for 15 minutes prior to the procedure. This preoperative step contributes significantly in lessening the pain component following the surgery. The operative eye is prepared w ith three drops of topical propacaine hydrochloride (applied every 5 minutes before the procedure) and povidone iodine and is covered w ith a sterile drape. The epikeratome unit needs to be checked for all its parameters including vacuum build u p and a trial run prior to the procedure. The cornea could be marked wi th the usual markers as in all corneal refractive procedures for a proper flap alignment. Different epikeratomes are presently available in the market. The popular epikeratomes are the Amadeus, Moria, Centurion and Nidek. The Amadeus epikeratome allows a consistent flap diame ter 01 9.0mm, variable hinge width of 1.0, 1.1 and 1.2 mm, 11,000 rpm with an ad vance rate of 3-5 nun /sec and a vacu um build up of 21.5 inch/ Hg The epikeratomes include a blunt plasti c separator instead of the blade in the LASIK microkeratome which have different angles of entry and slide along a path 01 least resistance. A speculum is placed on the eye and copiously irriga ted with chilled BSS or saline. Anesthetic drops are reapplied. The epikeratome assembly is placed on the eye and the vacuum built up. Following adequate vacuum build up Signal and cross check with applanation tonometer, the epikeratome is rW1 on its trac k by pressing on the foot peda l. The assis tant should continuously irrigate with chilled BSS throughout the forwa rd and reverse reill. This crucial 112

EpiLASIK with Mitomycin C

~"" ~ 'J .. 20.11-01

~

........

:.:..~

Fig. 3: Amadeus Epi keratome holders and separators

Fig. 4: Copious ch illed BSS irrigating the track during Epi keratome run

113

Instant Clinical Diagnosis in Opl1tl1alll1olol5l} (Refractive SlIrgen})

measure sign ificantl y a lleviates pain in the postoperative p e ri od. The microkeratome pushes the thin epithelial sheet creating a nasal h inged flap. The epikera tom e is lifted off the eye and the thin flap gently n udged to the periphery. The laser pa rameters fed in the laser machine for the requisite correction is activated, the usual preca utions for centered treatment applied and the surface ablation is performed. After laser ablation, mitomycin C a t 0.02% concentration is applied w ith a merocoel sponge for a duration of 12 sec. The concentration of 0.02% is arrived by a simple dilution measure. 2 mg of mitomycin is mixed w ith 5 ml of sterile water. 2.5 ml of this reconstituted mixture is discarded. The rema ining 2.5 ml is fur ther dilu ted with 2.5 ml of sterile wa ter. From this final reconstituted 5 ml soluti on, 1 ml is taken in a syringe to wet the merocoel which is p laced on the stromal bed. Different exposure times is suggested by different surgeons but a la rge r consensus fa vors 0.02% nlitomycin concentration. Application of mitomycin has been accep ted to significantl y reta rd the cytokine induced in flammatory cascade in the tear film . The exposed surface is then copiously w ashed to remove any remnant of mitomycin. A blunt cannula is then used to gently reposit the thin rolled up epithelial flap opposed to the nasa l hinge. The epithelium is found to extend beyond the epithelial gutter because of the mechanical stretch induced by the cut. The periphery of the flap should be stroked smoothly to remove all the fold s. The epithelial flap shou ld be given adeq ua te time to settle on the underlying stroma. A bandage con tact lens (preferably 8.6 - 8.7 mm diameter) is gentl y placed on the eye and aga in given sufficient time to settle on the flap gently nu dgin g the air bubble awa y under the BCL. The speculum is removed once the flap integrity is checked and BCL is left in place. INTRAOPERATIVE COURSE

The sequence of events may not be smooth in all situa tions. The fl ap may get torn or a buttonhole ma y present. Attempts to salvage the flap, if fail ed, allows remova l of the flap in toto and gently scraping any epithelial tags. Remo val of this thin flap is no quanda ry as in a Lasik fl ap. Su rgeons at different centres have studied the results w ith and w ithou t the flap and the final visual outcome is comparable. Rarely, a stromal incursion could occur (as low as 1% incidence) because of high vacuum and the procedure needs to be aborted. POSTOPERATIVE TREATMENT

As re-epithelialization progresses, the separa ted epithelial sheet shrinks in the central part and has a hazy appearance. 114

EpiLASIK with Mitomycin C

Fig. 5: The thin epithelial flap is nudged to the nasal periphe ry

Fig. 6: Merocoel sponge soaked with mitomycin placed on the stromal bed

115

Installt Clinical Diagnosis ill Ophthalmol0:5'J (R efractive Surgery)

The presence of the epithelial fla p itself is lmderstood to ac t as a bandage contact lens preventing the marked in flammator y cascad e of cytokine production. However the epithelium tend s to die out with the new epithelium migrating in from the periphery rep lacing the separated epithelial sheet. Significant epithelial haze is seen in the first 3 days tiLl a newly synthesized transparent epithelial sheet is laid d own. The time of epithelial healing ranges from 3 to 5 days. The patient is started off on a postoperative regime of frequent topical steroids coupled with fourth generation fluoroquinolones for the first couple of weeks. The topical steroids a re gradually tapered off over the 6 weeks. Presence of a mild subepithelial haze may warrant continuation of s teroid drops upto 3 months w ith comp lete clearing of the haze. Artificial tear substitutes are maintained for 6 weeks or longer. The bandage contact lens is removed after 5 da ys by which time th e epithelial healing is complete. Mild analgesics are indicated for 3-5 days. Different studies favo r the usage of vitamin c (500 mg - BD dosage) over the 6 weeks period. Clinical Deductions

The present generations ofepikeratomes are very safe involving intact epithelial flaps. The 60 ~ thin flap expand the range of correc tion leaving significant residual stroma l bed. However, as of, now, mild to moderate myopes do perform favourably w ith epi procedures. The visual outcome is comparable to Lasik after the initialS days. The wow effect of Lasik, however, is missing. The superficial lamellar fibres show a more predictable biomechanical response then in the thicker flaps . Wavefront ablation performs better as the flap induced aberra tions of a thick Lasik flap are obviated. The initial corneal thickness of 480 - 500 ~ and the residual bed of 300 + ~ is a safe limit as of today. CONCLUSION

TIle armamentarium of refractive surgery, at the present day scenario, provides varying options for differing corneal parameters. The final onus falls on the

surgeon to a nalyse the preset criteria and adopt a rational approach providing the requisite customized treatment with optimal visual outcome. The future awaits for a customized biomechanical wound response to be tailored to our h'eahnent stra tegy.

116

EpiLASIK with Mitomycin C

Fig. 7: Bandage CL placed on the reposited epithelium

Fig. 8: Damaged epithelial flap could be discarded

Fig. 9: As reepithelia lization progresses, the separated epithelial sheet shrinks in the central pa rt and has a hazy appearance

117

15 One-shot Epithelium-rhexis: Personal Technique Roberto Pinelli (Italy)

INTRODUCTION

The surface ablation technique through excimer laser is a procedure in use since long time. In the last 25 years this technique has h ad an evolution and many surgeons in the world gave their contribute to develop different sub-techniques of surface ablation. The most important issue is to remove regularly the epithelium and obtain a smooth surface in order to perform excimer laser in a safe and effective way. Questions

1. H ow to remove the epithelium in order to obtain a regular surface and perform the excimer laser and obtain a pure abla tion without central islands or irregularity? 2. H ow to manage the post-operative phase? 3. Is the post-operative pain rela ted to the removal of the epithelium? 4. The re-epithelialization depends on the technique? At the beginning of this procedure, the most common technique was to remove the epithelium ll1echanically with surgical instruments: different spatulas to remove the epithelium were designed b y a lot of surgeons but the problem of the technique is the timing of this maneuver and the elegance of this delicate part of the surgery. Alcoholic solution is another technique which is able to separate the epithelium from the Bowman' s melnbrane and consequently to relTIOVe it more easily. Once that the epithelium is treated with the alcoholic solution, the problem is how to remove it: aga in it is possible to remove it with more soft instruments, not necessarily surgicaL EDiLASIK and LASEK are two techniques able to remove the epithelium and then, after the ablation, to put the epithelium again in its natural position. Description

In our experience at Istituto Laser Microchirurgia Oculare, Brescia (Italy), surface ablation is around 10% of the procedure, being the 90% of our corneal procedure 118 the thin-flap LASIK.

One-shot Epithelium-rhexis: Personal Technique

Fig. 1: The metal ring surgical instrument is applied on the cornea

Fig . 2: The alcoholic solution is adm inistered on the cornea with a metal ring surgical instrument

119

Instant Clinical Diagnosis in Ophthalm ologtJ (Refractive Surgery)

Our favourite approach to surface ablation, called "Epithelium-rhexis ASA" (Advanced Surface Ablation) is to remove the epithelium with a maneuver that we call "epithelium - rhexis". This technique is very similar to the Capsulorhexis Technique in the cataract surgery. As you can see in the images we usually use a dry merocel after 25 seconds application of alcohol solution on the epithelium and we detach epithelium with one circular induced maneuver in order to have only one single approach to the epithelium and less trauma. If we are able to remove the epithelium circularly in one n1aneuver we will have not only less problems but even an optical zone around 8 mm read y to the ablation with a perfect smooth surface. The epithelium detachment from Bowman's membrane is very crucial in this technique; after the alcohol solution treatment the epithelium is more soft and once broken the epithelium membrane with the merocel we can choose a clockwise movement or an anticlockw ise movement (it depends on the surgeon's attitude), and in one circular shot we can remove the epithelium at 8 mm optical zone. As you can see by the figures and in the CD-rom the maneuver is relatively simple and clean. An interesting question can be: why we remove the epithelium at 8 mm optical zone and we do not go to the limbus? In our experience we compared one eye (8 mm optical zone disepithelialization treated) with another (10 mm optical zone of disepithelialization) and as far as transparency of the cornea, visual acuity post laser excimer and absence of haze is concerned, we can observe that the refractive result was in the two eyes very similar. The eye treated with 8 mm optical zone epithelium-rhexis was significantly better as far as less pain for the patient and more fast re-epithalialization: 3 days only compared to the 5 days of the collateral eye with the disepithelialization at 10 mm optical zone. We think that touching the cornea with the merocel and not with a surgical instruments we cause less trauma to the epithelium : less surgery in the classic meaning of the word is giving to the eye less microtraumas and consequently less complain as far as pain is concerned. The proced ure to epithelium-rhexis and the surface ablation is in our Institute always bilateral and in topical anesthesia. To perform a correct epithelium-rhexis very important are: • the quality of the alcoholic solution; • the timing of preparing the solution; • the concentration of alcohol in the solution (with BSS - balanced salt 120 solution, we use 20% solution of alcohol).

One-shot Epithelium-rhexis: Personal Technique

Fig. 3: The epithelium-rhexis is performed with mera-cell in an anti-clockwise movement

Fig . 4 : "One -shot" epithelium-rhexis is totally performed

121

Instant Clillical Diagnosis ill OplttlwlmologtJ (Refractive SlIrgery)

The patient is prepared before with three drops of Propacaine and three drops of Tetracaine in each eye at the fo llowing intervals of time: • 10 minutes before surgery • 5 minutes before surgery • some seconds before the surgery. The alcoholic solution is administered on the cornea with a metal ring (E. Janach sri, Como -Italy), a surgical instrument, actually very easy to find in the surgical instruments market. After we drape the eye lashes (the upper and not the lower eyelashes). After the classical bilateral epithelium-rhexis ASA ( in the CD-rom you can see all the maneuvers) we put in the eye some drops of Oftacilox (SA AlconCouvreur NV- 2870 Puurs - Belgium) and then the soft contact lens. After the excimer laser abla tion, a soft con tact lens is enough to protect the ablation, and contact lenses after a bilateral treatment are removed usually on day 4th postoperatively. Second eye is performed immediately after the first eye just operated. Finally we cl,eck the both operated eyes at the slit lamp in the consultation room in order to be sure that the con tact lenses are in the proper position. When the patient will come back to the Institute, on day 4th postoperatively, we remove the two contact lenses, and we check the complete re-epitilelialization of the cornea. After a learning course, which can be different from surgeon to surgeon, usually no t more than 10 hours, this teclulique can be easily performed by every refractive surgeon.

It is easy, simple and well accepted by tile patients.

lil the last five years of use of this teclmique no haze was detected in our patient, no problems of re-epithelialization and no central is lands were observed on the surface of the cornea and the new epithelium was extremely reg ular. Also the satisfac tion questionnaire of the patient reported as high satisfaction level very close to LASIK procedure. So the patients are accepting this teclmique of Advance in Surface Ablation with grea t confidence. We started to perform this techniq ue five years ago beca use the classical mecha nical epithelial removal was not well accepted by the patients although the v isua l acuity postoperative was extremely positi ve: th e satisfaction question naire of th is patient by th e classical surface ab la ti on w ithout epithelium-rhexis was very different from the satisfaction questiolU1aire of

122

LASIK procedure; now the sati sfaction questionnaires of LASIK procedure

One-shot Epithelium-rhexis: Personal Technique

Fig. 5: Afte r the laser ablation , a contact lens is applied

Fig. 6: Specu lum removed. At this point the surgery is over

123

Instant C/ittical Diagttosis in OphthalnwlogtJ (Refractive Surgery)

and of Advanced in Surface Ablation Technique through epithelium-rhexis are very close. In our Institute the popularity of this surface technique is very high and also the patient' s reaction to it: when we decide for this technique, generally due to the pachymetry < 500 microns (which is the limit of our thin flap LASIK and our Advances in surface Ablation Teclmique) results are very positive. Patient selection of one-shot-epithelium-rhexis compare to the LASIK thin flap technique is substantially focused on the visual defect and the pachymetry: • If the pachymetry is < 500 microns we decide for Advanced in Surface Ablation Technique; • If the visual defect is from - 0.5 to -60 of myopia, with or without as ti gm atism and from + 0.5 to + 3 of h yperopia, w ith or without astigmatism, as far as myopic population, and we have> 500 microns we switch to thin flap LASIK Technique; • In hyperopia also, when we have central pachymetry of > 500 microns, we switch to thin flap LASIK Teclmique. • Phakik IOL' s also, and their implantations, are covering the population ACO with higher visual defects in presence of an anterior chamber (minimum3mm). "Epithelium-Rhexis ASA " Technique Different phases: 1.

T he patient is prepared before with three drops of Propacaine and three drops of

Tetracaine in each eye at the following intervals of time: 10 minutes before surgery • 5 minutes before surgery ~

2.

some seconds before surgery Alcohol solution is administrated on the cornea

3.

Upper eyelashes are draped

4. 5.

7.

Epithelium is removed with one circular maneuver by using a dry merocel Excimer laser ablation is pertormed Some drops of Oftacilox are administered in the eye and then a soft contact lens is inserted Both operated eyes are checked at the slit lamp

8.

On 4th day postoperatively the contact tenses are removed

6.

124

One-shot Epithelillm-rhex is: Personal Technique CONCLUSION

We will see in the next years what will be the destiny of the surface ablation bein g thinner and thiJuler the flap of the LASIK and growing the implantation of Phakik IOL. But we think that the surface abla tion with soft and nice epithelium-rhexis ASA technique is reducing the pain and giving to the eyes of our patients bri ll iant and visual acuity and the regular absence of hazes still remains an issue and an option for OU f patients. In the CD-rom you can see all the maneuvers of this technique, from the begiJUling of the surgery to the end and in the box you will see a summary of the most important phases in order to pe rform a correct epithelium-rhexis in one shot and in order to obtain a perfect advanced disablation.

125

16 Surface Ablation after laser In Situ Keratomileusis; Retreatment on the Flap Jeroen JG Beerthuizen (Netherland)

The most common complication of laser il1 situ keratomileusis (LASTK) is postoperative overcorrection or undercorrection. Such residual ametropia can be bothersome to a patient and laser re trea tment can be considered. There are

different ways to retreat a post-LASIK cornea. The flap can be relifted, even years after the original LASIK p rocedure, although this might be challenging at times. It is also possible to recut a new flap, although this is less safe and effective than a relift. In both p rocedures, the underlying stromal bed is being treated and the amount of residual stroma should be sufficient to p revent ectasia. Disadvantages regardin g safety include an increased chance of epithelial ingrowth after a relift and the risk for diffuse lamellar keratitis and flap striae. To avoid problems with residual stromal thickness, ablation can also be p erformed on the tmdersid e of the fla p or on the surface of the flap. Surface ablation options include intra-epithelial or subepithelial photorefractive keratectomy (PRK) and laser-assis ted subepithelial keratectomy (LASEK). Subepithelial PRK j LASEK w ill be discussed in this chapter. Surface ablation has additional adva ntages. Superficial abnormalities such as map-dot-fingerprint lesion s are likely to benefit from a superficial approach. Microstriae in the flap tend to smooth en out after surface ablation, whichrnight improve quality of vision. Patients in need of a hyperopic retreatment 'with a small flap can be treated without the need of recutting a larger flap. FLUthermore, wavefront-guided treatment of flap-induced higher-order aberrations is more

logical when the flap is left in place. Finally, patients with a history of postLASIK dry-eye syndrome are better off wi thou t a relift. The biggest disadvantage of surface ablation retreatment is the chance of developing haze. Carones et al found severe haze in 14 of 17 eyes after PRK retreatment for regressed myopic LASIK. The average amount of corrected myopia in tha t study was -2.48 ± -0.74 D (range -1.50 to -3.75). 111e wound reaction was much more aggressive than expected and seemed to be related to

126

Swfaee Ablatioll after Laser In Si tu Keratomileusis; Retreatmellt 011 tile Flap

Fig . 1: Severe haze after PRK on the flap

127

Instant Clinica l Diagnosis in Ophthalmology (Refractive Surgery) the lamellar cut. It is hypothesized that app lying laser energy to a stromal area with previously actived keratocytes, which can be found arow1d the flap interface, leads to an exaggerated wound-healing response. This would imply that the combination of flap thickness and amount of ablated flap stroma relates to the chance of developing haze. Problems with severe haze have not been seen after PRK treatrnentof patients with LASIK flap complications and PRK retreatment after complicated LASIK. In more recent studies, good results regarding safety and efficacy were fOW1d for correcting low amounts, less than -1.50 D and -2.00 D respectively, of residual ametropia. Caution should be ta ken with hyperopic corrections. In both studies, no Mitomycin-C (MMC) was used. The use of MMC might be considered in treating higher amounts of residual ametropia if surface ablation is still preferred. TECHNIQUE

The epitheliW11 is trephined with the LASEK flap hinge opposite to the LASIK flap hinge. Application of 20% ethanol for 20 to 30 seconds is advisable to suffiCiently loosen up the epithelium. After rinsing away the ethanol, a LASEK flap can be created by moving epithelium away from the LASIK flap hinge. By moving in that direction, changes of accidentally dislocating the LASIK flap are extremely low . lNhen the epithelium is removed and Bm,vn1an' 5 membrane dried, the appearance of microstriae is very common, also in eyes that did not shm,v microstriae preoperatively at the slitlamp. Laser ablation can be performed

in the usual manner. After the abla tion, the cornea is rinsed with chilled balanced salt solution (BSS) and th e e pithelial flap is either repositioned or removed. A bandage contact lens is placed on the eye. Postoperative medications and follow -up visits are the same as fo r a regular surface ablation .

128

Surface Ablation after Laser III Situ Keratomileusis; Retreatmellt on the Flap

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129

17 Wavefront Analysis and its Clinical Significance Yan Wang, Lihua Fang, Boyan Li, Kanxing Zhao (China)

THE CONCEPT OF THE WAVEFRONT ABERRATION

Wavefront aberration, which is originated from Physical Optics, is defined as the difference between the actual aberrated wavefront and the ideal wavefront. It is illustrated in Figure l. METHODS OF DESCRIBING WAVEFRONT ABERRATION

Wavefront map, which can display d istortions in phase on the differe n t positions of the pupil, is considered the most visualized mode to describe the wave aberration of the human eye. This wa y is similar w ith the corneal topography. Wavefront aberration map can be also reconstructed w ith mathematica l fun ctions, such as Taylor polynomia ls, Zernike polynomials and Fourier transform polynomials. 111e comm on use for fitting ,-v ave aberrations is the Zernike p o lynom ial eq uatio n s ince Ze rn ike aberrations have several

advantages. The Zernike polyno mial is a set of basis functi ons and each function has a coefficient the relative va lu e of which corresponds to the an10unt of that particular aberration. In addition, the Zemike polynomials area complete set of polynomials that are orthogona l over a circular pupil, and then the variance is directly given by the sum of the square of the Zernike coefficients. Formally, it has the form k

W( p , B) =

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130

Wavefront AI/alysis al/d its C/il/ical Significance

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131

Instant Clinical Diagnosis in Ophtlralmologtj (Refractive Surgery) THE SIGNIFICANCE OF ZERNIKE ABERRATIONS

The Zernike term with n=O is referred to piston (z~ ).It does not induce image distortion. The Zernike terms with n=l are referred to tilts including vertical tilt (Z,-' ) and horizontal tilt (Z: ). They only make the whole wavefront tilt relative to its original position. The Zernike terms w ith n::::2 are referred to second-order aberration . The

central term is defocus ( Z~ ). On either side of it are the astigmatisms including oblique astigmatism (Z - 2) and with-/ against-the-rule astigmatism ( Z 2) . 2

2

The Zernike terms with n::::3 are referred to third-order aberration including vertical coma ( Z;' ), horizontal coma (Z~) , obligue trefoil (Z;3 ) and horizontal trefoil ( The Zernike terms with n=4 are refe rred to fourth-order aberration. The middle one of these is called spherica l aberration (Z~ ) . Spherical aberration is defined as the difference between the focalization of light from the margin of the entrance pupil and that of light from the central portion. The Zernike terms with n=5 are referred to fifth-order aberration. The middle two tenns are defined as second horizontal coma (Z~) and second vertical coma ( Z ; l), respecti ve ly. The other fO llr terms are not specific definition in the classical aberrations.

Z: )

INTERACTION AMONG WAVE ABERRATIONS

I. Interactio" among wave aberratio"s for the complete eye: Mathema tical independence of the Zernike modes does not mean their inopact on visual performance is independent. Acuity varies significantly depending on which modes are mixed and the re lative value of each mode. II. Interaction between cornea and len s for specifiC terms of aberrations: The wavefront aberrations produced by the internal optics (primarily the crystalline lens) offset, or compensate for, the aberrations produced by the cornea to reduce ocula r wavefront aberrations. This effect is illustrated in Figure 3. The spherical aber ration (Z ~) is well compensated regardless of refractive

error. Also horizontal coma (Z~) is found well compensated. Clinical Examples

Figures 4A to C show three wavefront maps of high-order aberrations for the real eyes after refractive surgery. The total RMS in Figures4A to C is l.13, l.03 and 0.91 ,U In, respectively. 111e most components of high-order aberrations are trefoil (A), coma (B), and spherica l aberration (C), with RMS being 0.41, 0.88 and 0.82 ~m, respectively. Figure 5 d emonstrates point spread function (PSF) for the eyes correspond to Figu re 4. 132

Wav efront Ana lysis and its Clinical Significance

+ Cornea

Internal

Tota l

Fig . 3 : The compensatory mechanism of the wavefront between cornea and lens

Trefoil (RMS o0.41 )

Coma (RMSo O.88)

Spherical aberration (RMSoO.82 )

Figs 4A to C: (A) Trefoil (RMS = 0.4 1) Wavefront maps of (S) Coma (RMS = 0.88) highorder aberrations for postoperative (C) Spherical aberration (RMS = 0.82) eyes

Trefoil

Coma

Spherical aberration

Fi g. 5 : PSF for the high-order aberrations of the real eye corresponding to Fig . 4

133

18 Wavefront lASIK Mark Wevifl, Emanuel Rosen (UK)

INTRODUCTION

LASIK has proved effective in reducing refractive errors, but it is known to cause higher order aberrations (HOA's), specifically spherical aberrations and coma. Patients may have reasonable Snellen visual acuity yet may con1plain about debilitating visual synlptoms s lich as nig ht vision disturbances and

ghosting. Therefore, quantifyin g and improving quality of vision after LASIK has become important. Contrast sensitivity testing has been helpful, but more recently wavefront measurements have been used to assess higher order

aberrations (HOAs). The link between HOAs and visual symptoms is the subject of ongiong studies, but spherical abe rra ti ons have been linked to starbursts.

Wavefront-guided ablations can red uce u nwa nted side effects of LASIK especially in low light conditions, red uce enhancement rates, improve the

quality of vision of patients who are dissatisfied with the result of U1eir treatment, reduce fear of LASIK and offer patien ts excellen t vision . The sources of image blur in the human eye are diffract ion, aberrations and scatter. Scatter is relevan t in the ageing eye. Diffra ction is significant w ith

small pupils, is less significant with larger pupi ls, but cannot be eliminated. But aberrations can be modified . The goal o f Wavefron t-guided LASIK (Wg LASIK) is to correct all optical aberra tions o f the eye, which reduce vis ual quality leaving only the spatial resolution of the neuroretina as the lin1iting factor for Optimtffi1 vision . In other words the concept of "supervision" may be achievable. Knowledge and technology are progressing rapidly and there are already a number of benefits of Wg LASIK. ADVANTAGES OF WAVEFRONT GUIDED LASIK

Wg LASIK can be directed to reduce o r eliminate all or certain HOA's and it can be customized to the individ ual eye. Among the benefits are the poten tial to in1prove the quantity of vision (e.g. the Snellen visual acuity), and the quality (e.g. contrast sensitivity). Wg LASIK m ay also reduce post-LASIK n ight-vision problelTIS, w hich are frequently caused by an i.ncrease in aberrations. Stud ies

have shown increases in pre-existing H OA's after standard LASIK, reductions in HOAs after Wg LASIK and studies compa ring standard versus Wg LASIK 134 have shown the benefits of Wg LASIK. H owever there is limited evidence that

W avefrollt LASIK Pre: Wavefront maps: Total aberrations

HOA's

Post:

Total aberrations

HOA's

Fig . 1 (eonld .. .)

135

Instant Clinical Diagnosis in Ophthalmology (Refractive SurgenJ)

136

Wg LASIK consistently outperforms con ventional laser in sit1l keratomileusis that incorporates broad ablation zo nes, smoothing to the periphery, eyetrackers, and other technological refinements. It is evident that wavefrontcustomized ablation holds a promising future and merits ongoing investigation. Figures 1 and 2 illustrate the potential benefits of Wg LASIK (Data courtesy of the Kirkwood-Fyfe Clinic, Aberdeen, Scotland). Preoperatively the patient had low myopia with refractions of -1.5 DS (6 / 6) in the right eye and -2.25 DS (6 / 6) in the left eye. He had Standard LASIK in the right eye with an Alcon Ladarvision 4000 laser. He complained postoperatively of poor vision, which is reflected in the increase higher order aberrations in the postoperative data in Figure 1. Therefore, his left eye treatment was delayed until Wg LASIK (Ladarwave) was available. Three months after treatment of his left eye and a year after treatment of his right eye his refractions were +0.50 / - 0.25 x 44 (6/ 6) in the right eye and 0.00 DS (6/4) in the left eye. His HOAs and point spread function in the left eye were reduced, subjective visual quality and best corrected Snellen acuity had improved, and the patient was happy with the result. This is an isolated case report and does not represent the experience of all Standard or Wg LASIK patients . Studies have shown that HOAs can increase in eyes that have received Wg LASIK, particularly eyes with low amounts of preoperative HOA's. In addition, comparison of the efficacy of different laser platforms has shown differing degrees of improvement, with some showing improvement in all HOA's and others showing improvement only in some HOA's. This may indicate a need to improve the algorithm. Therefore, there are limitations to the effectiveness of standard and Wg LASIK w hich contribute to good or poor outcomes with either procedure. Patients who are dissatisfied with the ou tcome of their LASIK may require repeat surgery to achieve a satisfactory visual outcome. Reoperation rates for primary myopic keratorefractive surgery range from 5.5 to 8.3%. Wavefront technology can measure and trea t optical aberrations that could not be addressed previously with standard refractive surgery and, as such, offers an additional method for enhan cement in patients who had not achieved satisfactory outcome with traditional keratorefractive surgery. A number of studies using different laser platforms and Wg LASIK have claimed better results with wavefront-guided enhancement compared to standard LASIK enhancement. Studies have shown improved efficacy, predictability, and safety, a decrease in aberrations, expanded optical zones and improved subjective symptoms of glare and halos with Wg LASIK. H owever once again there are differences in outcomes with different platforms and a study by Jin showed conventional LASIK retreatment was superior to wavefront-guided LASIK retreatment in both efficacy and safety. Therefore there are limitations that

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137

Instant Clinical Diagnosis in Ophthalmologtj (Refractive Surgery) affect the efficacy of enhancements and further study is required to consistently deliver better results with Wg LASIK compared to standard LASIK. Wavefront data capture is more difficult in highly aberrated eyes. Some post LASIK eyes have significant HONs, and in these eyes topographically guided treatments, or perhaps an initial treatment with th e fluid masking technique may be more beneficial. More study is required to optimize QutcOlnes of these complex treatments.

LIMITATIONS OF WAVEFRONT GUIDED LASIK

To acheive supervision a number of limitations of current wavefront data capture and delivery systems have to be overcome. There are many factors that affect the amount of postoperative aberrations present after Wg LASIK. The flap cut, the flap lift, and the subsequent biomechanical and postoperative healing responses of the cornea, dynamic eye movements that occur during the ablation, constant offset errors of ablation centration and the efficiency of a laser pulse when striking differ,ent areas of the cornea play roles. Inhomogeneities in the cornea, fluctuati'"ons in the laser's intensity, and changes in humidity and other factors affect the ac tual ablation profile applied to the cornea for each individual eye. A study by Buhren and Kohnen showed that the overall change in H OAs using the Zyoptix 3.1 system was a result of simultaneous increases and reductions in HOAs. Various factors determined the net effect. The wavefrontguided algorithm had a strong effect on the reduction of H OAs. Larger pupil diameters reduced the p redictability of HOA reduction. The benefits of the wavefront-guided algorithm were minimised by the induction of spherical aberrations and coma. It follows that the high er the attempted spherical error correction and the smaller the optical zone, the higher the amount of induced spherical aberration and coma is induced. Age, preoperative cylinder and right or left eye did not correlate with induced changes. LASER FACTORS

Laser factors including hot or cold spots in the laser beam, inaccurate registration or tracking can also playa role. Hersch et al developed a mathematical model of the change in asphericity of the cornea when undergoing laser ablation . They concluded that the angle of incidence of the laser beam across the ablation area causes the change in spherical aberration. Therefore changes in laser algorithms are need ed, which deliver more ablation to the 138 peripheral optical zone, preserving the p rolate shape of the cornea. In addition,

Wavefront LASIK Pre: Wavefront maps: Total aberrations

HQA's

Post:

Fig, 2 (eonld ... )

139

Inst ant Clinica l Diagnosis in Ophthalmology (Refractive Surgery) to correct other aberrations w ith wavefron t treatments, fluence variability across

the optical zone has to be considered . BIOMECHANICAL ISSUES

Biomechanical effects of the flap and wavefront-guided laser ablation induce postoperative optical aberrations that are not explained by the ablation profile. These effects are dependant on man y fac tors incuding the type of procedure (surface treatment, femtosecond LASIK or microkeratome LASIK), depth and diameter of ablation and corneal h ysteresis. Corneal hysteresis refers to the integrity and elasticity of the cornea, which is difficult to measure and varies from patient to patient. There are 2 m ain components of the biomechanical response of the cornea to laser refractive surgery, namely structural instability and biomechanical remodelling of the anterior surface. Structural instability or increased distensibilty of the cornea is important in terms of the risk of developing post LASIK ectasia. Ectasia produces a number of higher order aberrations including coma. The biom echanical remodelling produces central fla ttening accompanied by mid peripheral steepening and thickening caused by severing of circumferential tension bearing lamellae. This produces a hyperopic shift and probable spherical aberration. The creation of the LASIK flap alone can modify the eye's optical characteristics in low-order aberrations and HOAs. A significant increase in HOAs was found in Hansatome LASIK patients compared to an IntraLase group. This may have significant clinical implications in wavefront-guided LASIK treatments, which are based on measurements made before flap creation. Better UCYA and manifest refractive outcomes after LASIK with the femtosecond laser compared to the Hansatome have been noted. This may be the result of reduced postoperative astigmatism and trefoil and ma y have clinical significance for wavefront-guided treatments. Therefore the corneal biomechanical response to ablative surgery m ay significantly affect outcomes, and should be taken into account when plalU1ing customized procedures.

ROLE OF THE PUPIL

The pupil plays an important role in the quality of vision after laser refractive surgery. Diffraction through the pupil causes image blur. Also postoperative aberrations can be caused by the static offset of a wavefront-guided ablation due to pupil shift. Shifts in pupil center location can occur between preoperatively aberration measurements of the dilated pupil and when the 140 Wg LASIK is done with an undilated pupil. On some laser platforms wave

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Fig. 2: Left eye pre and post wavefront-guided LAS IK

141

Instant Clinical Diagnosis in Ophtltnlmologtj (Refractive Surgery) aberration measurements are performed in dilated eyes to obtain the maxi_ffitun

amOllnt of aberration data for to op timize vis ion in scotopic condition s

postoperatively. Wg LASIK is usually performed in eyes with undilated pupils under photopic lighting conditions because it is more comfortable for the patient, easier for the surgeon to center the ablation and some trackers may track an undilated pupil better. Because wavefront-gu ided LASIK treatments typically use the center of the undilated pupil as a reference point for treating the cornea, any differences in pupil center location between the pharmacologically dilated and normal undilated conditions will result in a static decentration of the wavefront-guided ablation profile on the cornea and the creation of aberrations. Reports of typical shifts in pupil center location between natural and pharmacologically dilated pupil conditions show wide variability. Most investigators fowld that pupil center location shifted in the superotemporal d irection when going from a natural, undilated condition to a pharmacologically dilated condition (cyclopentolate 1'Yo). Therefore, a potential source of the coma induced after wavefront-guided LASIK could be due to a decentration of the customized ablation. Ablation should also occur at the same pupil diameter and light levels as the wldilated wavefront data to ensure correct registration of the center of the optical zone. If this is not done, the incorrect offset may be applied and there is the potential to induce aberrations. A study fOlUld that measuring aberrations over a Neosynephrine-dilated pupil and treating them over an undilated pupil typically resulted in a shift of the wavefront-guided ablation in the s upero-tempo ral direction and an induction of higher-order aberrations. Methods referencing the aberration measurement and treatment with respect to a fixed feature on the eye (such as the limbus) w ill reduce the potentialfor inducing aberrations due to shifts in p upil center. The issue of p upil diameter and optica l zone with respect to higher order aberrations, visua l quality and night vision dis turbances is controversial. A number of good papers have been written on the subject and reviews of the literature have been published. A brief summary of some current thought on the subject is as follows. THE OPTICAL ZONE

The optical zone (OZ) is defined as the area of the treated cornea that has the full intended correction. Prog ressively higher degrees of spherical equi valent correction are associated with a progressive red uction in the effective optical zone. Approaches to improve optical quality after LASIK included the introduction of flying-spot lasers, which made the treatment of moderate and higher myopias with OZ diameters larger than 6 mm possible. Algorithms 142

Wavefront LASIK w ere introduced to include a transition zone to connect the OZ to the Wltreated cornea. La ter wavefron t-guided treatment algorith ms were developed . Although very large OZ d iameters are desirable, th eir usefulness is lim ited because of the higher ablation d ep ths required , w hich carry the risk for iatrogen ic keratectasia. Discrepancy between pupil and OZ diameter is considered one reason for optical disturbances such as halos or starbursts and loss of contrast sensitivity afte r refractive corneal surgery. Light rays passing the pup il through the peripheral untrea ted cornea and degrading the reti na l image quality induce these phenomena. Although the effect of large pupils and small OZ diameters on retinal image quality h as been shown theore tically, it cou ld be confirmed by few clinical studies. The fact that most studies could not show preoperative scotopic pupil diameter (PO) to be predictive for loss of con trast sensiti vity and subjecti ve symptoms raised further controversy concerning the role of PO in refractive surgery. However fhe concepto! fractional clearance (FC) is useful to better unders tan d the complex issue of the role of pupil diameter in quality of vision after LASIK. FC is the ratio of fhe programmed O Z diameter (in mm) to the scotopic p upil diameter. TIms, FC values smaller than 1 indicate an O Z smaller fhan PO an d vice versa. Buhren's stud y sh owed that the higher the FC, the higher the amount of induced H OA, and this was independent of the absolute HOA, pupil, a nd O Z size values. Results of some other studies of night-vision d isturbances could be explained by this find ing. Treating an eye with FC less th an 1, does not m ean that a high amoun t of H OA w ill be in duced. Thus, as already observed by Sch allhorn et al a large p u pil is not th e only risk factor for visual symptoms after corneal refractive surgery, even if there is an Fe less than 1. Because higher myopic corrections are assoc iated w ith higher levels of HOA induction, these eyes should be more su sceptible to visual symptoms, pa rticularl y ifFC is less than 1. Postoperative H OA's especiall y sphe r ical aber rat io n th e refore reduces with pupi l constriction. Visual disturbances prevailing at la rger mesopic or scotopic PDs can be reduced with mild miotic drugs (e.g. brimonidine tartrate) or induction of accommodative miosis by nlyopic overcorrection. Another aspect is a possible infl uence of the Stiles-Crawford effect: an FC of 0.9 migh t ha ve more impact in a 5.0 mm pupil than in a 7.0 m m pupil, as in the latter case in w hich th e unablated area is located outside th e por tion of the pupil that is considered visually important by the Stiles-Craw ford effec t. No upper limit for an FC value causing no symptoms can be given. Therefore the ratio betvveen the planned OZ and the scotopic p up il di ameter (FC) should be considered before treatment. Ablations a t FC less th an 1 sh o uld be avoided at least in higher myopic patients, whereas OZ diam eters tha t ove rl ap the pupil by 15% or more could help minimize the difference between p reoperative and postoperative 143

Instant Clinical Diagnosis in Ophthalmologt) (Refractive Surgen)) HOA However, the benefit fro m very large OZ diameters must be seen criticall y, as a large OZ requires more tiss ue to be abla ted. CORNEAL WOUND HEALING

Corneal \·v ound healing Inakes important contributions to the Qutcon1€S of both traditional excimer laser ablation procedures and custom corneal ablations and reduces the predictability of keratorefractive surgery in SOn1€ patjents. Tn addition, wound healing makes imp ortant contributions to some complications of PRJ<, LASEK or LASTK, including haze and diffuse lamellar keratitis. Detailed characterization of the wound healing cascade that occurs following refractive procedures is fundan1ental to pharmacological and molecular approaches for controlling or normalizing the response to surgery, thereby reducing biological diversity in variables such as epithelial hyperplasia and stromal remodeling that often ten d to mask attempts at custom ablation. DECENTRATION

Decentration of the ablation due to poor patient co-operation w ith poor fixation on the fixation target, pupil shift, a slow or no tracker can cause HOAs in conventional and Wg LASIK. One major diffi culty in centering an y ophthalmic procedure is thatthe alignment cannot be completely controlled by the surgen. He or she relies on the co-operation of the patient, \vho is asked to fixate on a target during the lneasurement and the surgical procedure. Eccentricities of 0.5 to 1.0 mm ma y occur in a small percentage of cases. Decentrations of more than 1.0 mn1, how ever, are rare. Mrochen and coauthors demonstrated that decentrations as sn1all as 0.2 n1m significantly increase wa vefront aberrations and, therefore, dimin ish the optica l quality of the retinal image. Active eye tracking during photoablation h as bee n shown to help pre vent gross decentrations from eye movelnents and is necessary for scanning-spot excimer lasers, in w hich the precise overlapping of adjacent ablations is crucial for the predictability of the correction. Active eye-tracking systems are intended to compensate for dynanuc intraoperative eye movements, but constant alignment errors that are maintained during the treatment also cause decentrations. To correct spherocylindrical errors and higher-order aberrations up to the 6th Zernike order and to achieve the d iffraction limit in 95% of the nonnal eyes with a 7.0 mm pupil, alignment of wavefront-guided treatments have to be performed with a lateral p recision of 0.07 mm or better. With smaller pupil sizes, alignment is less critical and an accuracy of 0.2 mm or better would result in the same optical qua li ty in 95% of the normal eyes w ith a 3.0 mm 144 pupil. Ablation zone decentration may be caused b y an initially disp laced

Wavefront LASIK treatment or by intraoperative fixa tion errors and can cause seriolls, visually

disabling side effects such as halos, glare, and d iplopia. Alignment errors can happen constantly or randomly. Constant offset e rrors occur because of displacement of the treatment rela tive to the reference co-ordinate system. Such a displacement might occur due to cen ter of p upil shi fts between dilated data capture and undilated trea tments as di scused above. Inaccura te laser calibra tion and constant eccentric gaze (eye roll) not compensated for by the eye tracker can also cause constant alignment errors. Random decentrations are due to eye movements such as drifts and tremors and can be prevented by fast, active intraoperative eye tracking. Clinically an eye with a 7mm pupil would probab ly not have a decrease in optical quality with customized refracti ve surgery if the lateral alignment error did not exceed 0.45 nun. In 90% of the eyes, even an accuracy of 0.8 mm or better would have been sufficient to achieve the same goal. Besides lateral shifts and axial movements, torsional misalignment of the ablation, i.e. a rotation of the ablatio n pa ttern arou nd the longitudinal axis of the eye m ight occur due to cyclotorsion of the eye between the sea ted (data cap ture position) and the supine (treatment) position or a slight lateral tilt of the patient's head. The degree of torsional ali gnment accuracy required to avoid degrading ideal optical corrections below certai n specified levels was studied by Mrochen et al in the case of spherocylindrical only and spherocylindrical plus HOA wavefront-guided refracti ve corrections. Wg Lasik with classic spherocylindrical procedures and a 7.0 mm pupil demonstrated stricter requirements for torsional alignment than standard treatments when trying to correct HOAs up to the 6th Zernike order, especially in eyes with a small original cylinder. To achieve the di ffraction limit in 95% of the measured normal eyes with a 7.0 nun pupil, alignment of wavefront-guided treatments would have to be performed with a torsional precision of approximately 1 degree or better. As alignment becomes less critical in sma ller pupils, the same optical quality would result in 95% of the 3.0 nun pupils providing an accuracy of 3 degrees or better. Clinically a wavefront treated eye's optical quality would probably not be d egrad ed compared to the preoperative state if the torsional alignmen t error did not exceed 15 degrees. Tn 90% of the examined eyes, an accuracy of 25 deg rees or better would have been sufAcient to achieve the same goal. Smith and Talamo did not find a statistically significant difference between torsional meaSll renlents in the seated and the supine posi tio ns, although they observed cyclotorsion up to 16 degrees in some patients. Clinical trials presented by SMI (SensoMotoric Instruments GmbH) show a mean and stand ard deviation for ocular torsion of2. 8 ± 3.6 degrees, with a maxim um of9.4 degrees. 145

Inst ant Clinical Diagnosis in Opht/lalmologt) (Refractive Surgery) Further clin ical trials are need ed to cla rify the amou nt of ocular cyclotorsion and lateral head tilt to be expected in refrac tive surgery. TEAR FILM

Campbell assessed the effect of the tea r film on wavefron t data capture in a stud y. Tea r flow changes in an eye with a high amount of abe rration d ue to an u nsuccessful LASIK procedure we re sinlUlated to show that while tear fluid causes changes in the tear / air surface, the change when expressed in terms of unwanted aberrations is below th at whi ch wou ld cause any image degradation. Results of the li ve video technique on a cornea w ith an irregular surface 4 days after photo refractive kera tecto my show that irregularities in the tea r film surface immediately after a blink a re not smoothed to any extent in the time before the nex t blink. Therefore tea r film dynam ics will not erase the effects of ablative corrections for higher order aberrations. Diffe rent method s of detec tion of wave abe rration namely Tscherning, Hartmann-Schack, scanning slit skiatoscopy and ray tracing methods may also have varying degrees of accuracy in di fferent pre- and postoperative eyes. Analysis of the data by Zernicke or Fourier a nalysis may also have its own uniq ue adva n tages, and the relative benefits of each are still unknow n. Accommoda tion can also affect the da ta capture and must be eliminated by the aberron1eter.

CONCLUSION

Refractive surgery is one of the most innovative and evolving fields in ophthalmology. With the ad vent of customized ablation, a change in paradigm has been established : the primary goa l of refractive surgery is not only to eliminate spectacles but also to imp rove or at least prevent deterioration of the optical performance of the eye. Wavefron t-guided refractive surgery has, as a ne',,' goal. to correct or at least min imize all o ptica l aberrations of the eye, and consequently to improve or preserve v isual performance, especially under scotopic conditions. To achieve this goal more consistentl y imp rove ments in each aspect of Wg LASIK is necessary. Clin ical in ves tiga tio n conn ecting wavefront data with subjective symp toms and functional results as well as rob ust wavefront-derived metrics are needed to answer the optimum OZ to pupil ra tio. Although there is progress in research, no " th reshold value" of HOA RMS or single Zernike parameter leading to synl ptoms or un acceptabl~ quality of vision has been d efined. Proced ures must be developed to ensure that the ini tia l placement of 146 the co-ordina te system used in the trea tment coincides exactly with the reference

Wavefront LASIK

system set up in the measureme nt. Fast trackers which can track in the x,y,z axes and acti vely track torsional changes w ill allow more accurate ablations. Some d egree of some higher order aber rations ma y enhance vision; therefore a greater lmderstanding of the ideal wavefront map of the hum an eye is also required. Improved d ata capture with better d ata ana lysis resulting in better wavefront data being generated for the shot profile and further improvements in minimizing accommodative effects w ill improve outcomes. And finally a better understanding and customisation of treatment according to ind ividual eye's biomechanica l characteristics w ill imp rove Wg LASIK results. But theoretically and as demonstrated in man y studies, Wg LAS1K is the way forward .

147

19 Aspheric Ablation with Nidek Platform S Bharti (India)

A nannal cornea has a curve w hich is steeper in the center and flatter peripherally is called a prolate shape. In most cases the cornea is flattened centrally after the laser treatment and becomes oblate. The oblate cornea has increased higher order spherical aberrations and produces symptoms like reduced contrast, ghost images, blurring, etc and though the patient can read 6/ 6 , the quality of vision is typically unsatisfactory. Maintaining the natural aspheric profile of the cornea after laser ablation is the focus of scientists and industry tod ay. Spherical aberrations induced after excimer laser ablation of cornea are responsible for the decreased quality of vision more so the night vision disturbances including glare, haloes and reduced contrast sensitivity alon g w ith poor visual performance. Paolo Vinciguerra MD theorized that a reduced optical zone size along w ith a large transition zone reduces the amoun t of induced spherical aberrations thereby reducing these symptoms. The advantages of this interesting ablation profile is reduction in optical zone is markedly tissue saving and the smooth blending of this optical zone into a large transition zone effectively creates a near natural corneal shape and a large optical zone. This has been observed in human eyes treated w ith this ablation profile. Aspheric treatment is a unique Nidek algorithn1 that treats cornea in such a way that prolate shape is maintained and introduction of spherical aberrations is minimized . The Nidek aspheric profile has given a new dimension to the understanding of the visual symptoms after excimer laser ablation. The ablation algorithms in NA VEX platform reduces the abrup t diopteric change and sudden curvature changes in the corneal surface are thus smoothened into a aspheric flattening more or less like in the normal cornea. The over three year results of this treatment profile are very pron1ising showing largely maintained or improved contrast sensitivity and patient's subjective quality of vision in photopic and scotopic conditions. THE NIDEK ADVANCED VISION EXCIMER LASER SYSTEM (NAVEX)

The Navex system comprises of tlu·ee components :(1) The OrD Scan to measure refactiv e error and for topography, aberrometry and scotopic / photopic 148 pupillometry. (2) 111e Final fit software to create the ablation laser shot data

Aspheric Ablation with Nidek Plaifonn

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Fig. 2: The OPD scan aberrometer principle

149

Instant Clinical Diagllosis in OphthalmologtJ (Refractive Surgery)

wi th Final Fit software and (3) The Excimer laser system EC-5000 CXIlJ for the predetermined treabnent on the cornea . The OPO Scan

The OPO scan features a non visible light for m easurement of refractive and wavefront components. This eliminates the pupil size induced accomlTIodation

changes. It measures 1440 points on the cornea which is highest in the available technology today giving a high range of -20 to +20 at a very high resolution. The OPO Scan (Optical path differe nce scanning system) is a autorefractor, Keratometer, Topographer, Aberrometerand Pupillometer in one. It is a scanning slit refractometer which works on p rincip le of skiascopy. It is a specialized autorefraction system coupled w ith topography. The topography system is used to confirm the centration o f the skiasco py system and to correl ate information on corneal shape changes before and after surgery.The resulting information can be used with Nid ek EC 5000 excimer laser which has a larger area scam1jng slit as well as sma Iter area ablation capabilities to perform customized ablation. The OPO scan uses skiascopic information by projecting light from an infrared LED through a projecting lens and chopper wheel having slit apertures. The chopper wheel creates sli t shaped light bundles. The projecting system rotates 180 degrees across both hemimeridians thus covering 360 meridians. TI,e slit rays go onto the re tina and are reflected back and then go through the receiving lens a nd ape rture stop to a group of photodetectors that receive the light signal. The LED and photodetectors are conjugate with the cornea . The aper ture stop is conjugate to the retina when the eye is emmetropic. Both the projecting system and receivu'g system rotate arou nd an optical axis synchronously to measure the refraction at each one degree meridian. The cen ter of aper ture is also the cen ter of photodetectors, which is

the optical axis of the equipment and is ve ry close to the optical axis of the eye. In myopia the apertu re stop is in front and in hyperopia beillild the retina. The principles are described elsewhere. The OPO sca n measures the time difference between the center of cornea and each of the p hotodetectors. The time difference is proportional to the refractive power. The re tin oscopic autorefractive system

does not assume that the eye is symmetric. The OPO Software

The OPO scan captures the AR (autorefrac tion) entire eye wafefront data with mesopic pupil size before the placido lights become on. TIlen the placido is on and the topography with photopic pup il image, the corneal wavefront and iris pattern recognition is captured. Th is complete data is then stored for analysis with OPO station and for crea tion o f Jaser ablation shot data with fina l fit software. The topographic map display has options of eye image map, axial map 150

(axial curvature), instantaneous map (the local curvature), refractive map (local

AspizericAblation with Nidek Platfom.

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151

Instant Clinica l Diagn osis in Ophthalmology (Refractive SlIrgenj)

corneal refracti on), OPO map (the tota I wavefront), internal OPO (wavefront except corneal), wavefront Zernike map, visual acuity simulator, corneal profile classifier, PSF (point spread function) map, and MTF (modular transfer fimction) map. The Final Fit

Final fit software is loaded on a stand alone pc. This software is the interface between OPD scan aberrometer and the EC5000 excimer laser. The softwa re after the measurements fro m the OPO scan splits the d ifferent components of errors (The spherical, cylindrical and irregularity com ponents) and creates the shot d ata of operator's choice. The so ftware allows a ablation simulato r displaying the preoperative and simulated postoperative maps of anyone or multiple views discussed above. The final fit allows selection of d ifferent profiles, d ifferent zone sizes and different nomogram selections fo r the shot data creation for excimer laser ablation. The nomograms allow the surgeo n to titra te resul ts for the best res ults. A SI00-Cl11-S30 nomogram means sph erical ablation set to 100% va l ue, cylindrical ablation set to I II % val ue and a sphere to cylinder shift of 30% to compensate for the coupling effect in astigmatism correction. The NAVEX

152

The NA VEX has three main methods: (1) OATZ (Optimized aspheric transition zone) - This keeps the cornea more prolate tha n the normal laser software and is used for for eye with little or no spherica l aberrations, (2) CATZ (Customized aspheric transition zone) - This is used in eyes w ith irregular corneas from previous eye surgery, injury or disease and (3) OPO CAT (OPO guided aspheric transition zone) - It is full wavefront guided aspheric treatment for correction of smaller irregularities in the virgin eyes. This is useful in eye with high level of higher order aberrations. Most of the normal eyes are benefited with OATZ and if the higher order aberrations are Significant, the OPD CAT is the profile of choice. During CATZ and OPD CAT it is important to have "registration" of eye so that smaller irregular aberrations are corrected (ablated) at the correct place over the cornea. The iris registration software lines up the laser with the unique markings on the iris which are unique to every individual. This is just like a bar code arranged in a cicle and this alignment ensures that the eye is not twisted out of alignment. The use of aspheric ( OATZ, CATZ, OPD CAT) treatment algorithms for excimer laser reduce the curvature grad ient and increases the effective optical zone postoperatively. Analysis of ind uced wavefront root mean square change was lower with aspheric treatment with Nidek as compared to the conventional

Aspheric A blatioll w ith Nidek Platfonn

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Fig. 6: The NAVEX aspheric ablations

-6D Postoperative Simulation: Conventiomll vs. OA Tz

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153

Instant Clinical Diagnosis in OplltiialmologtJ (Refractive SlIrgenJ)

treatment. The conventional trea tm ent had more oblate corneal profile and sma ller effective optical zones. The Ablation Profiles

The normal cornea is aspheric and the steeper central zone blends impe rceptibly into the flatter periphe ral cornea. The blending ca n be appreciated on a instantaneous map. There are seven profiles available for ablation in the fina l fit software. The profiles no. 4, 5, 6 and 7 are aspheric profiles and resul t into producing prolate cornea post ablation. The aspheric treatment centered at the line of sight (LOS) w ith oriline active eye tracking w ith 200Hz tracker and active torsion error correction produces a prolate cornea with peripheral curva ture blending like in a virgil1 eye w ith Nidek NA VEX platform which in turn produces excellent quality vision.

154

Aspheric Ablation with Nidek Platform

Fig . 8: The normal cornea with the aspheric profile blending conti nuously (left) and simulated map of the same after ablation with aspheric profile 7 (right)

Fig . 9: The simulated postoperative profile of same cornea after ablation with profi le 5 (left) and with profile 1 (right)

155

20 Customized Excimer Laser Treatment Using the Wavelight Allegretto Eye Q Laser Johan A de Lange (South Africa)

WHAT IS CUSTOMIZED EXCIMER LASER TREATMENT? It is individualized Exeimer Laser treatlllent based on maps and data of the particular

eye it is treating. Previously all eyes were treated with a standard ablation pattern, and the only variable was the refractive error.

This means that all eyes with a similar refraction [e.g. -3.00 or any other value] received a similar treatment irrespective of other differences between different eyes. When doing customized excimer laser treatment, each eye is regarded as totally unique and is examined thoroughly to determine its unique refracti ve qualities. These qualities are then used to develop a customized ablation pattern to treat this eye with the excimer laser. THE LASER

The laser is called the Wave light Allegretto Eye-Q [400 Hz] . It is one of the Wavelight family of Excimer Lasers. Wavelight also produce the Allegretto Wave 200 Hz as well as the Concerto 500 Hz excimer lasers Qualities of the Allegretto Eye-Q [400 Hz] • It is an Argon fluoride excimer laser with a • Wavelength of 193 11m. • The laser has a nitrogen purged beam path which is responsible for very stable energy levels. • It has a scanning spot which functions at 400H z. The high speed prevents corneal stromal dehydra tion and also reduces the risk of fluids seeping into the treatment area. In addition, the shorter treatment time minimizes the stress for the patient and therefore improves patient cooperation. • The spot size is 0.95 micron and has a Gaussian shaped beam profi le. This beam profile leads to a smoother ablation than other laser systems 156 with a tophat shaped beam profile.

Customized Excimer Laser Treatment

Fig. 1: Allegretto eye·Q [400Hz] excimer laser

Fig. 2: Gaussian beam profi le

157

Instant Clinical Diagnosis in Ophthalmology (Refractive SurgenJ) • The laser also features an excellent tracker with an active video based closed loop tracker. The tracker controls the laser. If tracking is interrupted the laser will not fire. • The tracker follows the pupil and is faster than the fastest saccade the eye can make. It tracks at 200-250 H z • The tracker uses 3 infrared lights to follow the pupil. Even if 2 of these are obstructed by surgeon or d rapes, th e tracker will still function well. • Illumination of the eye is provided by a cold light source to prevent interference of the light source w ith the infrared tracking lights. • The laser also has a cross line projector w h ich helps the surgeon to align the patient's eye and to verify the correct rotational position. This is particularly helpful in high as tigmatism an d complex custom ablations. • The laser comes with a la ptop computer i_nto which all data is introduced to treat the patient. This includes refractive data for the standard ablation as well as complicated wavefront or topograph y maps. • Included in the sys tem is also a patien t bed which has an x- y-z system and is electrically operated. • The system has the usual m icroscope, a footswitch, as well as a slit lamp and a video camera with monitor for training purposes. The Allegretto Eye-Q [400] has 5 different treatment programs: 1. Standard Treatmen t. Also called Wavefront Optimized. 2. Custom QTreatment. Also known as F-CAT. 3. T-CAT. Topograph y guided using the Placido-disc based Topol yzer. 4. Oculink. This is the new topography guided treatment using the Oculyzer. 5. A-CAT. This is Wavefront Guided treatm ent using the Analyzer. These w ill be discussed la ter in this chapter. TREATMENT PRINCIPLES Corneal Asphericity

An integral p art of the philosophy is the emphaSiS placed on corneal asphericity. Corneal asphericity is described w ith a Q -value. A cornea which is perfectly spherical will ha ve a Q -value of zero. lf the peripheral cornea is less spherical [flatter] than the central cornea the Qvalue is < 0 [negative]. This is also described as a prolate cornea. In cases where the peripheral cornea is more spherical [steeper1than the central cornea it will have a positive Q-value of > O. This is an oblate cornea. A prolate corneal shape produces better contrast sensitivity as well as better night vision than an oblate cornea. Therefore, all the treatment profiles aim to make the cornea more asp herical [prolate] w ith the per ipheral cornea flatter 158 than the central cornea [bulle t shaped].

Customized Exdmer Laser Trea tmellt

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Figs 3A and 8 : (A) Ablation with Gaussian beam profil e and (9) Smooth surface postoperative

159

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) REQUIREMENTS FOR CUSTOM ABLATION

l. Data: Either Wavefront data or Topographical data must be available.

The process of data accumulation is an extremely important requirement for accurate customized ablation. Obtaining different maps and data will be discussed later.

2. Scanl1 ing Spot: The excimer laser must have a scanning spot sn1all enough to treat the data differences on the maps which were obtained with wavefront or topography techniques. The scanning spot has been referred to when discussing the lase r. 3. Tracker: To utilize the scanning spot effectively, the laser must have an excellent tracker, which has been discu ssed. 4. The Eyetrackillg: The system must not only follow the eye but also prevent decentration and compensate for cyclotorsion. Optokinetic eyetracking is utilized to compensate for cyclotorsion and decentratiol1.

Optokinetic eye tracking to compensate for cyclotorsion and decentration. Decentration ll1ay be linear or torsional. Di fferent factors can cause decentration of ablation.

Improper head alignment [causing cyclotorsion], movement from sitting to supine p osition [causing cyclotorsion], saccadic eye movements, pupil shift, eye rolling, as well as technical misalignment of the laser beam, can all cause decentration and cyclotorsion: a. Improper head alignment Improper head alignment can cause cyclotorsion of significant degrees. b. Movement from sitting to supine position can cause cyclotorsion. In 1995 Smith and Talamo reported no significant difference in ocular torsion between seated a nd supine position of the body . Chernyak published a 51 eye study in which he reported an average of 2 degrees of cyclotorsion between seated and supine position [highest was 9.5°] There are 3 ways to deal w ith cyclotorsion: Prevent it, [Wavelight], monitor the degree of cyclotorsion [Wavelight, Alcon], or re-adjust treatment profile to the degree of cyclotorsion.[ Alcon, VIS-X, Zeiss] - Preven ting C1Jclotorsion : Optokinesis is a neuronal response of the eye to spatial clues of an image. The vestibular ocular reflex [VORl automatically rotates the eye to compensate for possible head rotation. The square shape created by the Allegretto illumination lights stimulates the VOR and rotates the eye to the correct position, preventing cyclotorsion. This is very effective and 160 probably the most important factor in the p revention of cyc1otorsion.

Custom ized Excimer Laser Treatment

t?

Figs 4A and B: (A) Ablation with Tophat beam profile and (8) Surface post-op less smooth

161

Instant Clinical Diagnosis in Ophthalmology (Refracti ve SurgenJ)

- Monitor oJelotorsion: This is the conventional a pproach. Th e li mbus is marked at 3 and 9 0' clock positions w ith ink and a marker. These marks are aligned with the cross line projector fro m the laser and the eye position is controlled with head movement. - Re-adjust treatment profile to the degree of cyclotorsion. Iris registration is done by VIS-X. c. Saccadic eye movements Since the introduction of h igh speed trackers even the fastest saccadic eye movements can be followed. The Allegretto Wave featnres the most advanced eye tracking system in the m arke t that uses 200-250Hz sampling rates and has a response time of only 4-6 milliseconds. Pupils of up to 7 mm can be followed and the system can even track nystagmus patients. d. P upil shift The center of mos t pupils move to a di ffe rent location when the pupil constricts or dilates . This can cause misplacement of the ablation. This problem can be exacerbated w hen using d ifferent types of trackers for the examination than for the treatmen t. Wavelight uses the same eyetracking technology in the wavefront analyzer as in the laser system. This minimizes errors. In addition it is recommended to use the same pupil size for exalnma tion as for the treatment. For wavefront guided treatm ent the eye should be measured and treated with a large pupil and for topography guided cases it is best to measure and treat w ith small pupil. e. Eye rolling All eye trackers available today can only function w hen the patient cooperates and contil1llOlIsiy fixates on a target light. When the patients loses fixation, eye rolling occurs for which the eye tracker calu10t compensate. The shorter the treatment time the better th e patient w ill be able to cooperate. The Allegretto Wave is the second fastest laser available today, second only to the Wavelight Concerto [500H z] f. Technical misalignment of laser beam This can cause substantial decentration. Allegretto uses 2 methods to ensure accurate aligmnent. An eyetracker target test is conducted on every treatmen t day to align the eyetracker and the fixation test is conducted before every treatm ent. 162

Customized Excimer Laser Treatment Gaussian beam profile

Flat (Tophat) beam profile

n

~llnFr

. . ': . . "-LL/ ,

.

. -yn-r ':. ,"

.

Fig. 5: Gaussian beam profile gives smoother ablation than Tophat beam profi le

Fig. 6: Patient un der laser with tracker lights visible

163

Instant elillical Diagnosis in OplrtlralmologrJ (Refractive Surgery)

The Wavelight Allegretto is designed such a way that it utilizes the principles of optokinetic eye tracking maximally. Therefore the results achieved in custom ablation and high astigmatism a re very good. THE DIFFERENCE BETWEEN WAVEFRONT GUIDED AND TOPOGRAPHY GUIDED CUSTOM ABLATION

Two basic types of (listonl ablatj on are ava ilable; Wavefront guided and

Topography- guided. It is important to understand this difference. The difference is in the DATA. How is the data obtained and which anatomical structure is exam ined.

Wavefront data is data of the total optical system of the eye. It includes optical aberrations caused by all tile media of the eye; e.g. cornea, anterior chamber, lens and vitreous. It is obtained by the use of a wavefront. A converging wavefront of 168 rays

of light is directed in to the eye and is defl ected by the m edia on its way to the fovea. Before reaching the fovea itis focused and then diverges again to produce an image on the fovea. Using a parax ial ape rture system the aberrated image

on the fovea is photographicall y record ed. The anal yze r measures the aberrations of the light rays that were reflected. These aberrations are then compared to the perfect wavefront of ligh t rays that were directed into the eye. The differences between the perfect wavefront projected into the eye and the reflected wavefro nt rep resent the aberrations of the eye. The new aberra ted wavefront data is registered and converted into a treatnlent platform.

Topography data is data which is based only on the cornea. Topography data is obtained with the use of more than one technology, the Topolyzer as well as the Ocul yzer. The Topolyzer uses a placido disc to p roject placido rings onto the cornea. The reflected altered height da ta image is captured by a CCO camera and sen t to the computer which compares this to a perfect image calculating the aberration of the cornea.

164

The Owlyzer is based on the Scheimpfl ug principle and uses a rotating camera to photograph the cornea and an terior segment. Only the corneal data is currently used to treat the eye. The corneal data obtained by anyone of these instru ments will be used to o·eat the eye. Once the data is accumulated, the trentment for either technique is done on the comea.

Customized Exdmer Laser Treatment

Fig. 7: Cross line projector in action

Q < -

1

Q =· 1

-1 < Q < 0 Q=O Z axis

Yaxis Fig. 8: The fam ily of conic sections of asphericity Q , with vertex at the origin and radius (R) constant

165

Instant Clillical Diagnosis ill Ophthalmology (Ref m ctive SlIrgenJ) Confu sion between wavefron t guid ed and topography guided custom ab lation o ften arises beca use many sim ilar iti es exist between the tw o techniques. Both are based on ma ps, both treat the cornea, and both can be done w ith LASIK as well as Advanced Surface Ab lati on [ASA]. INDICATIONS FOR CUSTOM ABLATION

General Indications When it is possible to achieve significantly be tter vision with ClIstom abla tion than wi th standard treatment, it follows logica lly that custom ablation should be th e treatment of choice.

Any aberratioll which prevents the eye from achieving 1.0 [20120} BSCVA preoperatively shollld be all illdication to consider ClIstom ablatioll. Any corneal shape wh ich cannot be treated with the Standard treatment should be considered for custom abla tion. This includes previous RK, PKP, sma ll optical zones and decentered opti ca l zones. Eyes with large pupils are problematic and may have poor night vision if highe r order aberrations [HOA's] are not trea ted. Th us they should be considered for cllstom abla tion. H ighe r order aberrations [HOA's] w ill ca use poor contrast vision as well as poor night vision and should be treated to im prove contrast sensitivity and overall visu al function . HOA's have more effect when the pupil is wide. Most p rimary LASIK patients [>90%] ca n be trea ted successfully with the Stan dard [Wavefront Optimized] progra 111 . Indications for the Standard or Wavefront Optimized [WFO] Treatment

The WFO treatment is also desc ribed as the Standard Treatment Strictly spoken WFO trea tment is also custom ized treatment because it is adjusted according to the pa tient's refraction as well as the patient's K-readings. Most eyes with no Significant aberrations and normal pupil sizes can be very successfully treated with the Wavefront Op timized [WFO] treatment. Various studies have demonstra ted that the patients treated with the WFO ablation will have better n.ight vision as we ll as better contrast sensitivity than pa tients treated with conventional excimer laser trea tment. Indications for Custom Q Treatment [F-CAT]

Some surgeons will do Custom Q [F-CAT] for all primary eyes, because they 166 believe it is ideal to give every patien t the ad va n tage of maximum asphericity.

Customized Excimer Lase,. Treatment 50

Population distribution of 0 values

40

•~ 30

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10

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Fi g . 9 : Popu lat ion distribution of values Q (for 176 ey es ) (The mean shape of the human cornea PM Kiely, G Smith and LG carney optica acta , 1982, Vo l. 29. No.8. 1027-40)

Population distribution of asphericity values Q (for 176 eyes)

.... ,-.,-- - - - - - - .- •......

f,

...........

.....

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~I

Fi g . 10 : Sche · mat ic represe ntation of an ablat ion creat i ng a prolate cornea. The red line depicts the p reoperat ive co rnea and the black line the postoperative prolate cornea

Fi g . 11 : Sche-matic representati o n of an ablat ion creating an obJate cornea . The red line dep icts the preoperat ive cornea and the black li ne the postoperative ob late cornea

167

Instant Clinical Diagnosis in OplttltalmologtJ (Refractive SurgenJ)

Eyes with large mesopi c pupil s are pron e to have poor nightvision postoperative and can be very successfully treated with the Custom Q program. Custom Q treatment with little or no refractive change is a good option for enhancement treatment in patients with good snellen acuity who still complain of poor vision.

111ese patients may have 1.0 [20/ 20] VA after recent LASlK but are not satisfied with their night vision and / or their contrast sensitivity. After the Custom-Q enhancement treatment, they w ill achieve better contrast sensitivity as well as

better nightvision and they will experience better subjective quality of vision. Indications for T-CAT: These eyes usually cannot be corrected to 20/20 BSCV A pre-operatively because of significa nt lowe r and higher order aberrations of the cornea. The most common and impo rtan t indications in this group include:

Previous penetrating keratoplasty [PKP]. Previous radial keratotomy [RK] Small optical zones after previous LASIK. Decentered optical zones after previous refracti ve surgery. Any irregu lar corneal astigmatism. T-CAT ca n also be used to create asphericity in primary LASIK treatments. T-CAT Following Previous PKP

These eyes can be treated with LASIK or ASA [ad vanced su rface ablation] When there is no contra-indica tion, it is better to do LASIK because of the rapid, pa infree recovery. T-CAT LASlK fo r PKP has a few problems: Firstly it is difficult to obtain good maps, mainl y because the peripheral donor cornea is often so distorted tha t the topolyzer carmot measure the peripheral cornea. This, in turn, reduces the tota l information available to the surgeon and prevents the use of the T-CAT. Secol1dly we have the induced myopia after T-CAT willch has to be anticipated and pre-empted. The patient should be forewarned abou t this myopia and the patient should be expecting a second laser treatmen t 3-6 months after the first treatment to compensate for the induced myopia. Thirdly , some transplanted corneas ha ve a slight haze even if the transplant was otherwise successful, and this will also red uce the fina l visual acuity. T-CATafter Previous RK

These are some of the most difficult eyes to treat w ith T-CAT mainly because it is extremely difficult to get good maps of the peripheral cornea. Reason being 168 that the RK-cuts have so distorted the peripheral cornea that good readings are

Customized Excimer Laser Treatme1lt

Fig . 12: Patient view of tracker and lights

Fig, 13 : Decentered ablation as a result of eye rolling. The patient did not manage to fixate on the fixation light during surgery

169

Illstant Clinical Diagnosis ill Ophthalmolo?;!) (Refractive Surgery)

often impOSSible with the placid o d isc based Topolyzer. 1f good maps are obtained it is easy to treat these eyes. Once again it is mandatory to get good repeata ble maps of the cornea. Once this is done the most impo rtant other problem is to precalculate the induced myopia and to compensa te fo r it. The TNT [Topography Ne utralisa tion Test] is performed to do this. 1f the TNT is successful the patient will have emmetropia post-operative. If not, the eye will be myopic and will require another treatmen t after about 3 months to correct the residual myopia. Indications for Oculink Ablation Based on the Oculyzer

It is very sim ilar to the indications for T-CA T, b ut the Oculyzer should be so much better than the Topolyzer that it should re nder the Topolyzer obsolete. We repeat indications [same as for T-CATI again: Previous PKP Previous RK Sm all optical zones after previous LASIK. Decentered optical zones. Any irregular corneal astigm atism. Indications for A-CAT

The A-CAT is Wavefront guided Lasi k based on the wavefront analyzer data. The ma in advantage of A-CAT is that it will correct for lenticular as well as corneal aberrabons. Off course this w ill have certain disadvantages too, because

len ticular aberrations may change as the patien t becomes older. Another important hmc tion of A-CAT is that it will correct most HOA 's as well as lower order refractive errors. [Obtai ning Maps for custom ablation for d iscussion of HOA's] Correcting of HOA's only gives a small im p rovement of snellen VA because snellen VA is measured at high contrast levels with relatively small pupils. Correcting HOA's has more effect on contrast sensitivity and night v ision than

on snellen acuity. HOA's are usually situated peripherally and only have significant effect on vision at lower levels of illumina tion w hen the pupils are relatively wide. A-CAT is usually indica ted for: Eyes with exceptionally wide p upils. Patients with poor con tras t sensitivity and known poor night vision. Enhancement Lasik for eyes w ith small residual refractive errors. 170 Eyes with known abnorma l amoun ts of higher order aberration.

Customized Excimer Laser Treatment

.'...... .'

-,~-

::::: : : ...........

',.',.,

,::~~:"::'

....

Fig. 14: demonstrates a wavefront entering an eye. On the left is the perfect grid of rays and on the right is the aberrated wavefront as photog raphed by the camera

Fig. 15: Shows the decentered optical zone after previous RK. Note the poor quality of the superior nasal area of the map. This is quite a common finding in previous RK eyes and is caused by the severe irregularities of the RK incisions

171

Instant Clinical Diagnosis in Ophtlra lmologtJ (Refractive SlIrgenJ)

A-CAT can also be done for primary Lasik, if the surgeon elects to do it. The reason it is not done regularly is that it takes a lot longer than standard wavefront optimized treatment. OBTAINING MAPS FOR CUSTOM ABLATION TREATMENT Measuring Technique

During the measurement of any Topographical or Wavefront map a number of requirements must be met. 1. Good patient cooperation. 2. Pe rfect patient head posi tion and s tabi li ty of the head during measurements. 3. An excellent tear film is important. Artificial tears without preservative

4. 5. 6. 7. 8.

can be used. Accurate alignment of the eye and visual axis. Management of the position of the brow, nose or other possible obstructing factors. For Wavefront measurements the pupil must be dilated. For Topolyzer it is better to have a small p upil. Peripheral map data is importan t and care should be taken to acquire enough peripheral da ta.

DIFFERENT MAPS Topolyzer Maps

The Topolyzer maps the cornea . It onl y evaluates the cornea and is inherently different from the wavefront maps. Th e Topoly zer uses a placido disc to project placid o rings onto the cornea. 22000 points are sampled on the reflected ring pattern. The Topolyzer measures slope which is converted to height da ta. It combines keratom etric and topographic measuring methods in a single unit. The reflected altered image is captured by a CCD camera and sent to the computer which calculates the topography of the cornea. This produces a topographical map which is shown on the computer screen. Topolyzer data becomes more inaccurate the further peripherally it is measured. In addition, no useful da ta is obtained inside the central placido disc ring projected onto the cornea . The ring projections of the placido disc can be obscured by the nose, brow and eye lashes. To avoid this, the patient's head should be well positioned and 172 the tearfilm must be good.

Customized Excimer Laser Treatment

.~

.... A:

I

(i) (i) G>

&

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Fig. 16: Shows 4 maps of the same eye. Lower left is the diffe-rence map to compare the individual maps with each other to choose the best maps

Fig. 17 : A·CAT ablation map

173

In stant Clinica l Diagnosis in Opl1t1wlmologtj (Refractive SlIrgenj)

The Topolyzer maps are compared to each other and the best maps are chosen and exported to the laser laptop. The laser uses this data to do a customized treatment of the cornea.

Topolyzer maps are necessary to do T-CAT Topolyzer measurements must be done to deternline eccentricity values which are required to do Custom Q trea tment. When doing Custom Q [F-CAT] treatment, the maps are not exported to the laser laptop. Only the eccentricity values are used in the treatnlent.

Waverfront analysis evaluates all the media of the eye. In this respect it is significantly different from Topolyzer which onl y measures the cornea. Wavefront analysis is performed w ith the Waveligh t Allegro Analyzer. The Analyzer has an integrated p up il-detecti ng eye tracking system, allows 100 micron x-y deviation and 200 lllicron deviation on the z-axis. Figure Image on Ana lyzer screen during testing A pupil size of at least 6 mm, but preferably 7 mm, is required to allow registration of periphera l aberra tions . Autofogging is possib le and the instrunlent does an accurate autore frac tion. The Analyzer works on the Tscherning principle which projects a square shaped, bundle of low intensity laser light thro ugh a 10 nun corneal area onto the fovea. These 168 rays are deflected by the aberrations of the media and defocused on the cornea.

The defocused grid on the cornea is photograp hed by a CCO camera. The deflection pa ttern is then compared to the d ata of a perfect wavefront and the deviations of the aberra ted wa vefron t [wavefron t aberrations] can be calculated. This is done automatically and instantaneously by the computer. Wavefront maps are prod uced by the analyzer. These maps can be evaluated using Zernike polynomials up to the 6th orde r. Zernike polynomials 1 to 5 are lower orde r aberrations and are grouped under Zernike rad ial order 0 to 2. Polynomials 6 to 20 are called higher o rder aberra tions [HOA 's] and are grouped under Zernike radial order 3 to 5. The most important HOA's are those which are centrally located. As can be deducted from the picture they are HOA 7 and 8 [Coma] as well as HOA 12 [spherica l aberration] . Wavefront aberrations are recorded in R.MS va lues. RiY15 is the Root Mean Squa re of the positive or nega tive deviations of the patient's wavefront from the perfect wavefront. It means that the RMS va lue represents the mean deviation of the wavefront from the perfect wavefron t n1easured in micron. 174

Customized Excimer Laser Treatm ellt

Fig. 18: Topolyzer

Fig. 19: It is an example of a good Topolyzer map of a normal cornea with -2. 40 of astigmatism

175

Insta nt Clinical Diagnosis in Ophthalmology (Refm ctive Su rgery) RMSg represents the total RMS value of the wavefront of an eye. RMSh is the total HONs of the eye. How to calculate RMS? • Measure all the deviations from the perfect wavefront • Some values will be positive and others will be negative. • Calculate the square of each value individually. • Find the average off all these sq uared numbers . • Calculate the root of the average. This is the RMS value. A number of wavefront maps sho uld be obtained for each eye. They must be compared and care must be taken to detenn ine that the maps are very similar and reproducible. If wavefront maps show significant variation, they carmot be regarded as accurate and cannot be used to treat the patient. Oculyzer Map

This is new technology and was recen tly launched by Wa velight. It is based on the Penta cam made by Oculus. A Sheimpflug camera rotates around the eye and takes [usually] 25 pictures of the anterior segment in about 2.5 seconds. More or less pictures can also be used but 25 give the required results. The Oculyzer maps are better than those of the Topolyzer because it uses the rotating calnera and not a static placido disc. It is 3 dimentional, has more data points, also records the posterior corneal surface as w ell as corneal pachyn1etry; it giv es excellent data on the central cornea and it can also record peripheral aberrations of the cornea significantly better than the Topolyzer. Unfortunately it is not perfect. In o rder to produce maps of the anterior segment it must have good quality p ictures of the corneal apex as well as the pupil. In some cases with very flat corneas and peripheral bulging, e.g. after PKP, it may not be possible to obtain OClllyzer maps.

TREATMENT PROGRAMS The Wavelight Allegretto has 5 differen t programs: The first is the Standard treatment program. [Wavefront Optimized1 Three programs are based on topography data. They are T-CAT, Oculink, as well as Custom Q [only partially]. In addition Wa velight also has a Wavefront-guided program w hich is based on data from the Wavefront Analyser. A discussion of the 5 programs will follow.

176

Cu stomized Excimer LaserTreatnlent

Fig. 20: Topotyzer map of small optical zone

Fig. 21 : Topolyzer map of keratoconus eye

177

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) Standard Treatment Program In all excilner laser treabnents the laser beam hit the peripheral cornea more obliquely than the central cornea. This means the periphery will receive less energy per surface area and thus less abla tion. The peripheral laser rays will also be reflected off the cornea more than the central rays and this will cause even less peripheral ablation To compensate for these factors, the Wavefront Optimized [WFO] program has been developed.

This software program uses the so-called Wavefront Optimized ablation pattern. This pattern is a standardized algorithm based on previously accumulated wavefront ablation data. Basically the Wavefront Optimized ablation pattern gives more peripheral treatment than treatment programs of the past. This creates a more as ph erical corneal shape [prolate] with central steepening and peripheral flattening [bullet shaped1. As a result the patient will attain better night vision as well as better contrast sensitivity than 'with less peripheral ablation. Custom Q Program [F-CAT]

This program can only be used in conjw1Ction with the Topolyzer.The Topolyzer is used to n1easure the eccentricity values as well as the K-readings of the preoperative cornea. These eccentricity values are fed into the computer which will calculate the Q values of the cornea before surgery. The aim of the CustomQ program is to adjust the Q-values of the patient's cornea to more aspherical values. To achieve this, the laser wi ll apply even more laser treatment to the peripheral cornea than the Standard WFO program.With this treatment the peripheral Q-value of the cornea can be modified to the specific requirements of the patient. The ideal Q value aimed for is regarded as being -0.43. This is a debatable value and may be adjusted in future. It is probably better to individualise the Q-value for each patient. This will also fit in better with the concept of "Customized" Treahnent. [The normal Q-Value of the peripheral cornea in a 20-year-old patient is about -0.27]. Another advantage of the Custom Q treatment is that it allows the entry of treatment data with a mixed prefix e.g. +5.00/-2.50 D. The module will automatically calculate the correct and most tissue saving conversion and treat accordingly. This minimizes conversion errors "'.vhen treating mixed 178 as tigmatism .

Customized Excimer Laser Treatme1lt

Fig. 22: Wavefront analyzer maps

Fig. 23: The allegro analyzer

179

Instant Clinical Diagnosis ill OphthalmoloiJIJ (Refractive SlirgenJ)

Other features include: optical zones are adjustable in O.lmm steps; the transition zones are adjustable in O_lmm steps; the correction is adjustable in 0.10 steps. Some surgeons do all standard LASIK treatments with the Custom Q program. T-Cat Treatment

T-CA T is the abb reviation of Topography linked Custom Ablation Treatment This treatment is based on corneal data only. Hus data is obtained from the Topolyzer. The T-Cat is regarded as a corneal repair station. It creates a rotationally symmetrical smooth cornea, but does not repair the refraction accurately. Many corneas end up too convex [myopic] and will require another treatment to rectify the refraction. However, because the T-CAT has smoothened the cornea, the BSCV A will improve compared to the preoperative va lue and this already is a significant improvement. T-CAT after Previous Penetrating Keratoplasty [PKP]

Some surgeons will proceed by cutting a Lasik flap without doing Lasik. The rationale for tlLis is that the PKP wOlmd has unpredictable fibrotic forces pulling on the wound. After cutting this flap the astigmatism wil change immediately. This will change the refraction, and th e surgeon who continues to laser immediately, will be treating the preoperative refraction, wlLich has changed a few seconds ago with the cut, and is no longer the refraction . TlLis, of course, will give sub-optimal results. After a perio d of six weeks the new refraction should be stable.This can be tested clinically. Once the eye is stable it should be measured and mapped again before laser treatment can be d one. Then the flap can be lifted and the excimer laser treatment can commence. T-CAT After Previous RK

As mentioned before it can be very difficult to obtain good Topolyzer maps. If good maps are obtained it is easy to treat these corneas v.,ith lasik. Contrary to some warnings it is sa fe to cut the Lasik flap and also to do the laser treatment. Although the periphe ral flap may separate on the previous RJ( lines, it can easily be replaced afte r the Laser and usu ally heals without a problem. In some eyes this dehiscence of the previous RK incisions ma y lead to epithelial ingrowth which is very d ifficult to treat. Nevertheless the surgeon could replace the flap first and give the eye a chance to heal before conSidering m ore drastic actions. 180

Customized Excimer Laser Treatment

Order

Aberration Tilt

Defocus (Sphere)

astigmatism Corm a 3-foil Spherical aberr. astigmatism 4-foil Fig. 24: Schematic representation of Zern ike polynom ials

Z1

1st Order

Z3 ~ 2nd Order 3rd Order 4th Order

Z

5th Order

ZS

<

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l z19AJZ 20

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6th Order

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Fig. 25 : Three dimensional representation of Zern ike polynomials

181

Instan t Clin ical Diagnosis ill Oplltl, aI11lo[ogtj (Refractive SlI rgery)

The refractive result after the T-CAT lasik for previous RK is usually myopic. A stable method to produce a plan o refraction after T-CAT has ye t to be developed. A postopera tive UCVA of 0.8 can be regarded as a good result. The corneal instability which follows a fter RK is retained afte r the Lasik but it does improve a little bit, probably d ue to the circumferential Lasik flap scar. Since previous RK cuts were often made in such a way as to leave only a 3 mm clear zone, the paracentral and central irregularities of these corneas that are not removed by T-CAT, w ill con ti n ue to have a negati ve effect on the patient's vision. The Topolyzer does not captu re data within the cenh'al placido disc ring of the cornea and trea tment of the central cornea may not be perfect. T-CAT for Other Indications

Small or decentered optica l zones as well as other corneal aberrations can be treated very successfull y w ith T-CA T. Obtaining good maps is the most important factor. Once this has been achieved th e data ca n be used to do a lasik or ASA . As with other T-CAT treatme nts, res idual myopia is the most important challenge. Oculink Treatment Program

A comprehensive 3D optical an alysis of the cornea, anterior chamber, iris surface and anterior lens is done by the Oculyzer. This data is utilized to produce comp rehensive maps. These maps are ave raged and then exported to the laser's computer. The treatment is d one in a similar way as a T-CAT. A-CAT [Wavefront Analyzer Guided Custom Ablation Treatment]

182

A-CAT is the excimer laser trea tment based on w avefront d ata, ""hkh means this is wavefront guided treatmen t. A-CAT is used for patients w ith la rge p upils as well as retreatments and patients w ith excessive Higher O rde r Aberrations [HOA's]. The Analyzer wo rks on the Tscherning Prin ciple as d escribed earlier in thi s chapter. Until recently the registering of good maps were difficult. The system has been upgraded in 2006 and we exp ect significant improvement in the future. The anal yzer measures the whole wavefront including the refractive error up to a pupil size of 7 ml11. The wavefront data can be evalua ted on the screen at dilferent pupil sizes. It is very importan t to compare the wavefront refracbon shown at a pupil size of 4 mrn w ith the clinical refraction. A normal subjecti ve refraction is usua lly measured w ith a pu p il size of 4.0 to 4.5 mm.

Customized Excimer Laser Tren.tmellt

Fig . 26 : It is a wavefront map illustrating horizontal coma

Laser beam

...... +-- Original shape of cornea

• • •

Full energy Lower fluence Decreasing flue nee

Fig. 27: Illustrates variation in laser energy appl ied to the cornea in different locations

183

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery)

The maps obtained are exported to the laser and used to do wavefront guided custom ablation under a lasik flap or as part of an ASA. RESULTS Results of Wavefront Optimized [or Standard] Treatment It is simple and quick and gives excellent results. Some authors have published

UCVA of 20/20 or better in 96% of trea ted eyes. In addition it results in good mesopic vision as well as good contrast sensitivity. For most patients [more than 90%] it is absolutely adequate and effective. The average amount of ind uced HOA's was only 12%, which is very low. Results of Custom Q treatment [F-CAT]

This program aims to create more corneal aspherici ty than preoperati ve and in doing so shapes a prolate cornea by ablating even more peripheral cornea than the Standard program. Theoretically it should yield even better results than the wavefront Optimized treatment, particularly for night vision and contrast sensitivity. Very good results have been published for this modality. Results of Wavefront Guided Treatment [A-CAT]

With the Wavefront Analyzer a number of wavefro nt maps are taken. The best of these maps are combined to create a map to export to the laser. This data is used to do the A-CAT treatment. The main challenge is to obtain good maps because the analyzer is not very robust. Once good maps are available the results are very good . The system has recently been upgraded and excellent results are expected in the near future. Wavelight is the only company to date that has effectively demonstra ted its ability to reduce higher order aberrations, especially trefoil. T-CAT Results

184

The T-CA T program is a powerful tool and should not be used without proper training. It can induce complex irregular astigmatism if not used correctly. Results are dependant on the patient selection, the accuracy of the maps, the calculation of the postoperative myopia and the quality of the surgery. Patient selection has alread y been discussed under indications. The accuracy of the maps is crucial. If it is not possible to get good repeatable maps, one should not try to d o a T-CAT. Any map which has an AA [analyzed area] of less than 60% should not be used to treat a patient.

Customized Excimer Laser Treatment

Fig. 28: Example of a Typical T-CAT profile

Fig , 29: T-CAT profile afte r PKP with 7,0 dioptres of astigmatism

185

In stant Clinical Diagnosis ill OpiltiJalllloioglj (Refractive SlIrgenj)

The calculation of the postoperative myopia has been a problem since the advent ofT-CAT. T-CAT removes more tissue than the Standard program because most often the surgeon will endeavour to improve the eye's asphericity. To do this he must change the Q-value to -0.43 or even more. 111is module will remove much more peripheral corneal tissue than the Standard ablation . This ablation pattern is similar to a hyperopic ablation and will induce some myopia. Currently we have 2 methods with w hich to precalculate the induced postoperative myopia. Both methods are reasonably accurate but not yet perfect. Centration of the treatment is ve ry important. To summarise, results are highly dependen t on the surgeon's mastery of this modality. COMPLICATIONS OF CUSTOMIZED ABLATION General Complications

Any of the complications of Lasik and Advanced Surface Ablation [ASA] can OCCUI,

but will not be discussed here.

Complications of Standard [WFOl Ablation

Over- o r undercorrectio n: This is probably nomograln - or refraction-related. If th e refraction data is not accura te, o ne cannot expect an accurate result.

Every laser has its own nomogram. This should be calculated and used meticulously to ensure accurate results .

Decentration: Because the tracker follows the plpil a decen tration of treatment on the cornea can occur if the patien t d oes not fixate on the green fixation light during surgery. See discussion on decentration, cyclotorsion and optokinetic eyetracking . Ro tation of cylind er: Because the patien t is supine, excyclotorsion may occu r

and may cause misplacement of the cylindrical correction. Marking the limbus preoperative and using the cross line projector may prevent this error.

The laser also has 4 orange colored lights around the fixa tion light to stimulate the vestibular ocular refl ex to orientate the patient's visual cortex and to prevent excyclotorsion d uring surgery.

Inad equate asphericity: Patients with large pupils may need more asphericity than wha t the Standard program provide a nd ma y still end up with poor night vis ion and poor contrast sensitivity postoperative. They would have been better

off with a Custom Q or other trea tment. Complications of Custom Q Ablation

Over or undercorrec ti o n. As with Sta ndard ablation

186

Decentration . See Standard ablation Rotation of cylind er. See standard a blation.

Customized Excimer Laser Treatment

Fig. 30: T·CAT profile after previous RK

Fig. 31; Typical A·CAT wavefront guided treatment profile

187

Instant Clinical Diagnosis in OphthalmologtJ (Refractive SlIrge1Y)

Induced Myopia . Because peripheral ablation is significantly increased, some m yopia may be induced. The nomogram should be adapted to prevent this. Complications of A-CAT

Over or undercorrection. The wavefront analyzer often measures more myopia than the clinical refraction. Care should be taken to determine tl1e refraction accura tely preoperatively, even when this is slightly different from the wavefront refraction. The clinical refraction is usually measured with a pupil size of 4 to 4.5 mm. When using the wavefront refraction the surgeon must use the refraction from the analyzer as measured with a 4 mm pupil. It needs to be emphasized that the analyzer will show d ifferent refractive values for every pupil size. By selecting a specific pupil size [4 mm], the refraction for that par ticular pupil size will be show n on tl1e computer screen. Decentration . See Standard ablation Ro tation of cylinder. See standa rd ablation. Complications ofT-CAT

Induced Myo pia: This has been comp rehensively d iscussed earlier in this chap ter. It is adequate to say that T-CAT induces myopia and that the surgeon as well as the patient should be aware of tl1e fac t tl1at a second treahnent may be necessary to compensate fo r the ind uced myopia. Decentration: See Standard ablation Rotatio n of abl ation: Not only the cylinder, but the whole ablation may be rotationally misplaced due to the fac t that excyclotorsion may take place when a patient is in the supine position. Corneal thinn ing: T-CAT ablates more cornea l tissue than any other program and the corneal pachymetry should always be kept in mind before proceeding w ith a T-CAT. LASIK vs ADVANCED SURFACE ABLATION combined with customized ablation

Advanced Surface ablation includes PRK, Epi lasik and Lasek. This debate is not over yet. Lasik with Custom Ablation It has been proven that higher order aberrations increase after conventional

lasik, even as much as 200%. This is main ly ca used by the biomechanical effect of cutting the rigid lamellar structure of the cornea. The corneal stromal fibers peripheral to the cut will retract somewhat and develop some edema . The central cornea is effectively thin ner than before the cut and will bulge slightly forward. This will induce some myopia. Even in the best cases the lamellar tension in the fla p is never aga in as good as it was before cutting the flap. This 188 will obviously have an effect on the visual outcome.

Customized Excimer Laser Tl'eatmellt

..

Common names Piston Tip, Tilt (Prism)

Radial order

0

2

Astigmatism (3,5), Oefocu s(4)

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16

17

20

Reflection

Elliptical in the penphery. Ablative power is Ios\ in several way~ light is being reflected The ellipse covers a larger area. resulting in a lower energy denSity. The lower ablation rate causes a spherical aberration resulting in poor night vision. The allegretto algorithm compensates for thiS.

plane wavefront

19

A circular beam is being projected on the cornea

Normal ablation

Parallel beam

"

Fig . 32 : Three dimensional pictorial direc tory of zernike modes 0 10 20

Reduced ablation, low f1u ence

Fig. 33A: Elliptical in the periphery . Ablative power is lost in several ways light is being reflected . The ellipse covers a larger area, result ing in a lower energy dens ity . The lower ab lat ion rate causes a spherical aberration resulting in poor night vision. The allegretto algorithm compensates for th is

Converg~ng beam

spherical wavefront

Fig. 33B: The relation ship between the wavefront and light rays. The light rays travel perpendicular to the wavefront at all pain ts

189

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) The effect of these lactors are reduced wh en doing customized ablation. Many publications have shown that h e visu al results of lasik with custom ablation are truly excellent. Advanced Surface Ablation [ASA] with Custom Ablation

ASA have very little effect on the tensile strength of th e corneal fibers and induces very few higher order aberrations . Visual results are excellent. The main disadvantages of ASA are still the pain and the relatively slow

recovery_ For tha t reason the decision to do lasik or ASA is not made on the visual results only. The fact that lasik is painfree and h as a quicke r recovery time still m akes lasik the treatment of choice for most excimer laser custom abla tion cases. A recent publication has compared 10 years visual results betw een Lasik

and PRK and the results were very similar. The fact that there has been many advances in both techniques over the last 10 years m ust also be taken into consideration. However this study did not m easure the H ONs in the different groups but was based solely on UCVA and BCV A. For me the answer is very simple: In eyes where there is no contraindication to lasik, I will prefer lasik every time because of the painfree and rapid recovery. However, in a number of eyes, contraindications to Lasik are present and then Advanced Surface Ablation [ASA] should be done. Indications for ASA with customized ablation. • Cornea too thin fo r Lasik. • It has to be mentioned that ASA can be done 011 a previoll s Lasik fla p in cases where the cornea is too thin lor enhancemen t lasik. This is definitely controversial but a nu mbe r of these cases have been reported where no other option was feasible and the results were very good. • Forme Fruste keratoconus. • Surface scarring of the cornea which can be removed with ASA. Customized ablation with the Wavelight Allegretto Eye Q 400 is well developed and effective, More than 90% of eyes can be treated with the wavefront optimized program. The other p rograms can be used to treat complicated cases as explained. Results are gra tify ing . The boundaries of refractive surgery continue to expand and many cases previously untreatable are now curable.

190

Customized Excimer Laser Treatment

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Fig. 330: The wave aberration , illustrated in gray is the difference between the ideal wavefront and the aberrated wavefront Fig s 33A to D: Wavefront optimized profile

191

21 Advances in EpiLASIK and LASEK Bojan Pajic (Switzerland)

Photorefracti ve keratectomy (PRK) was the 1110stcommonly performed surgical procedure until the introduction of laser in sitll keratomileusis (LASIK) in the mid nineties. While PRJ( is safe and effective, the risk of corneal haze, especially in high myopia, is significant. Postoperati ve pain and slow visual rehabili tation are other limiting factors in PRJ<. LASIK has minimal postoperative pain, faster visual recovery, less regression, and no ha ze even in high myopia. However, cations (free cap, incomplete flap, button-holes and lost flaps), interface related complications (epithelial ingrowth, deep lamellar keratitis and interface debris), flap-related corneal biomechanical instabil ity and iatrogenic keratectasia have

been reported. Lase r epithelial keratom ileusis (LASEK) and EpiLASIK may combine the advantages of PRK and LASIK while avoiding the disadvantages of both. It avoids all of the flap-related complica tions and reduces the risk of keratectasia associated with LASIK. In addition, it has relati vely faster recovery periods with slightly less pain and haze than PRK. LASEK and EpiLASIKmay be considered in patients with low to moderate myopia and myopic astigmatism, thin corneas with no signs of keratocon us, extrem keratometric values (such as steep or flat corneas), deep set eyes and small palpebral fissure, ecurrent erosio syndrome, dry eyes and for patients who are predisposed to tralUna, such as military personnel and athletes. METHODS Patients

A total 01140 eyes of 70 patients were matched. In the right eye a LASEK and in the left eye a PRK treatment was done. All patients were 27 years of age and had between - 0.5 a nd - 6.0D SE of myopia with up to - 4.0D of astigmatism. Examination

192

Preoperative evaluation included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCV A), manifest and cycloplegic refractions,

Advances in EpiLASIK and LASEK

Fig. 1: Human eye

Epithelium Basement me'mt"a nel -~

Bowman layer level

Stroma

-

•

Fig. 2: Porcin eye

193

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) ocular dominance, slit-lamp examina tion, keratometry, tonometry, pachymetry, computerized videokeratography (Orbscan II), mesopic pupil size measuremen t u sing a pupillometer, and d ilated fundus examin ation. Surgery Procedures

LASEK and EpiLASIK surface are techniques in refractive surgery of surface ablation, it is said, that the epithelium is separa ted from th e cornea . Surgery Procedure LASEK

After topical anesthesia and lid speculum application, a semi sharp circular w ell is used to administrate 20% alcohol is used for 25 to 35 seconds on corneal surface. Prior to alcohol exposure, positioning m arks were used to mark the corneal surface. The margins of the delineated area were freed using a hockey kn ife and leaving up to three clock-hours of intact margins for hinge. The loosened epithelium was then p eeled back using a Merocel sponge. After standard laser ablation, the epithelial sheet was gently repositioned using in tennittent irrigation. The epith elium was ca refully realigned using the preplaced positioning marks and allowed to d ry for three to five minutes. A combination of antibiotics and stero ids eye drops was applied, followed by placing a bandage contact lens to reduce the mechanical frictio n b y the eyelid and to reduce postoperative pain. EpiLASIK Surgery Procedure

The separation of epithelium in the EpiLASIK technique is done mechanically with a keratome. The epithelium is separated from the cornea just over the Bowman's Layer. The Flap thickness is given from the thickness of the patient's epithelium, not from the Blade H older. The h uman epithelium thickness is about 40-50 mm. The pig ep ithelium is abou t 50-70 mm. Comparison of the Different Techniques

The ad vantages of the LASEK/EpiLASIK technique comparison to LASIK is no flap related complications, 100 mm extra microns available for performing the correction, more versa tile fo r thin. The di sadvantage are that in average patients have more pain during the first 5 days p ostoperative, it is more difficult to handle a surface abla tion fl ap than a Lasik Flap and the visual recovery need more time. Surface ablation d oes n ot substitute the LASIK. It is a complementary method to LASIK. 194

Adv ances in EpiLASIK and LASEK

Basement membrane

Bowman 's membrane

Fig . 3: Basement membrane with least resistance

Bowman's layer Corneal stroma

Fig. 4: Epi-tome: blunt separator

195

Instant Clinical Diagnosis ill OphthalmologtJ (Refractive SlIrgenJ)

EpiLasik is similar to 'standard ' LASEK, except no alcohol is applied . Epiflap is made with a keratome-like equipment. Cleavage of epithelial basal cells from Basement membrane is perfor med along plane of least resistance. Epitome is similar to microkeratome, but blwll separator is used instead of a sharp blade. The forward speed is more slow. A suction unit is proposed of 8.5 mm for a k-read ing over 45 0 , 9.0 mm for a k- read ing between 42 and 45 D, and 9.5 mm for a k-reading below 42 D. [ n the study epithelial separa tion was do ne with Amadeus U Epikeratome (AMO). Data Analysis

Statistical anal ysis was performed using SPSS 14.0 software. Paired-samples t tests, independent samples t tests, and Chi-squa res were applied. A P-value of less than 0.05 was considered statistically sign ificant. RESULTS

The mean age was 35 yea rs (wi th a range of 21 to 69 years) . 35 patients (50%) were male and 35 (50%) were fem ale. The differences of preoperative visual and refractive values between LASEK and PRJ( were not statistically significant for mean spheres, cylinders, spherical equiva lents, and BSCV A. The mean p reoperative sphere was -1 .81 ± 0.83 0 fo r LASEK and -1.92 ± 1.18 0 for PRJ( (P = 0.27). The mean preoperative cylinder was-0.55 ± 0.71 D for LASEK and - 0.92 ± 0.79 D for PRJ( (P = 0.39). The mea n follow-up period was fo r all patients 6 months. Efficiency

93% of patients had an UCV A of 0.5 or better at one month, where 73% had 0.8 or better. At three months respectively at six months, 90% respectively 100% of eyes examined had UCV A of 0.8 or better in the LASEK eyes. 93% of patients had an UCVA of 0.5 or better at one month, where 86% had 0.8 or better. At three months respectively atsix monti,s, 82% respectively 100% of eyes examined had UCV A of 1.0 or better in the PRK eyes. Predictability

For all LASEK and PRJ( eyes, the mea n postoperative spherical equivalent was 0.04 ± 0.28 D. for LASEK and - 0.13 ± 0.5 D for PRK. 93% respectively 100% of LASEK-treated eyes were within ± 0.50 D at one months respec tively three months of the intended correction com pared with 94% respectively 93% for 196 PRK.

Advances in Ep iLASIK and LASEK

Fig . 5: Suction unit choice regarding K·reading for surface ablation

Fig. 6: Amadeus II epikeralome (AMO)

197

Instant Clinical Diagnosis in Ophthalmology (Refractive SurgenJ) Safety

At six months the safety index w hich is the ratio of mean postoperative BSCV A to mea n preoperative BSCV A w as 0.98 for LASEK and 1.02 for PRK. Relevant h aze was seen in the LASEK eyes in 2 cases and in the PRK eyes in 8 cases, what is statistically significan t. DISCUSSION

Several reports have investigated the safety, efficacy, predictability, and stability of LASEK. Azar and associates fo und that all p atients had an UCVA of 0.5 or better at one week, where 64% had 0.8 or better. At one months, 92% of eyes examined h ad UCVA of 0.8 or better. Taneri et al reported that approximately 95% of the eyes were ±1.0 D of emmetropia after four weeks . At one year not loss of BSCV was present. Par tal et al Found that 66% an d 98% of the eyes had postoperative UCV A of 1.0 or better and 0.5 or better, respectively. Claringbold found that the UCV A was 0.5 or better in 83.8% of eyes at day 4. At two weeks, all eyes were completely epithelialized, an d the UCV A was 0.5 or better in 91.8% of the eyes. In a large series, Anderson et al fOlmd that patients w ith a preoperative SE between 0 and 6.0D had better UCVA at three months than those with a preoperative SE between 6.1 an d 12.00. Clinically significant haze was observed in 1.6% of eyes. In our study we observed, where one eye was treated with PRK and the oth er w ith LASEK technique, that the reepithelialisation time was significan t longer in the LASEK eye than in the PRK eye. Further there was more pain in the LASEK eye compared with PRK. The reason could be in the alteration of a lcohol wi th the conjunctiva and in the induction of apoptosis of epithelial cells by alcohol. The incidence and degree of corneal haze formation were compared following laser subepithelial keratomileusis (LASEK) and epithelial laser in situ keratomileusis (EpiLASIK), and examined its correlation with tear film transforming growth factor-betal (TGF-betal) levels. Less corneal haze was noted after EpiLASIK than LASEK. A positive correlation between corneal haze and tear fluid TGF-betal levels on the first postoperative day suggests a possible mechanism for the ob serv ed d iffe rence . Prophylac tic use of intraoperative MMC in LASEK significantly decreases haze in cidence. EpiLASIK is a safe and efficient meth od to correct m yopia with the advantage that it has only mild symptoms and mild haze. At higher attempted corrections, LASEK-treated eyes showed less ke ra tocyte apoptosis, myofibroblast transformation, and up-regulation in the synthesis of chondroitin sulfate than PRK-treated eyes. These diffe rences ma y account for better visual acuities and 198 less stromal haze in higher a ttemp ted corrections in LASEK-treated eyes.

A dv an ces in EpiLASIK and LASEK

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199

Instant Clinica l Diagnosis in Ophtlra lmologtj (R efractive SJlrgenj)

Reduced subepithelial stromal tissue deposition was observed in LASEKtreated eyes compared with PRK-treated eyes. Postoperative preservation of the epithelial basement membrane and survival of epithelial cells in LASEK and possibly in epithelial laser in situ keratomileusis may contribute to this phenomenon. An advantage of LASEK over PRK is the reduction of postoperative haze. The basal epithelial cells of the separated epithelial d isks showed minimal trauma and edema. Specimens obtained using 15% and 20% alcohol concentrations showed formation of cytoplasmic fragments of the basal epithelial cells, enlargement of the intercellular spaces, and extensive discontinuities in the basement membrane, w hich was excised at the level of the lamina lucida . Mechanica l separation did not affect the normal cell morphology of the excised epithelial d isks. Transmission electron microscopy of the specimens proved the manual technique is less invasive to epithelial integrity than LASE K using either alcohol concentration. Recovery of corneal sensitivity began 1 month after LASEK and was completed by 3 months in eyes treated for low-moderate myopia and at 6 months in eyes with high myopia . The depth of ablation during surgery affected the recovery of corneal sensitivity. The greater decrease in the number of subbasal nerve fibers in the LASIK group compared with the LASEK group ma y relate to the greater decrease in corneal sensitivity. The pattern of corneal nerve regeneration and the recovery of corneal sensation after LASEK did not differ g rea tly from that after photorefractive keratectomy in previous studies. EpiLASIK-treated eyes had faster rehabilitation of corneal sensitivity and tear function than LASIK-treated eyes. Histological examination of specimens in four eyes showed that 24 hours after mechanical separation the epithelial cells' morphology was close to normal. EpiLASEK appeared to be a safe and effective treatment for the correction of myopia and myopic astigmatism. Most patients achieved postoperative visual acuities comparab le to those w ith laser in situ keratomileusis and photorefractive keratec tomy. There was a low incidence of haze and pain postoperatively. Keratocy te density in the an terior retroablation area recovers

during the first year afte r LASEK for the correction of myopia, but does not go back to preoperative values. Laser in situ keratomileusis and LASEK did not significantly affect the RNF L thickness parameters postoperatively. Acknowledgments I thank for distinct suppo rt of Dr Gerhard Youssefi, Anton H ilger (Technolas) and Dr Anton Wirthlin, Fritz Meyer (Ziemer ophthalmology) for personal and technical advice.

200

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201

22 Wavefront Optimize and Astigmatism Correction with the Allegretto Excimer Laser Jerome Jean Bovet, Auguste Chiou (Switzerland)

The term, "wavefront-optimized", describes the unique ablation profil e and proprietary algorithms incorporated into the AllegrettoRexcimer laser. One of the most irU10vative features of the laser excimer Allegretto R is the way it incorporates wavefront optimization in rendering proper treatment. It is the only vision-correcting laser system that takes into account the starting curvature radius of the cornea being treated. The laser excimer Allegretto R is specifically designs to preserve the most normal curvature characteristics (and thereby optimize visual quality) as a consequence of treatment. In earlier laser systems (treating nearsightedness), the optical zone, or area of correction, was centered on the front of the cornea; the result was a flattened circular area that ended w ith an abrupt ed ge, causing wlwanted side effects like poor night vision, glare, and halos. Laser trea tment patterns (ca lled algorithm s) then evolved to apply peripheral trea tment in a blend zone around the optical zone. There is a problem that arises, however, in treating the peripheral cornea w ith older laser systems. All prior laser systems are designed to be calibrated on flat plastic test surfaces. However, the cornea is curved, and when treating on the downslope of the d omed surface (everywhere but the top dead center of the dome), some laser energy is scattered rather than being absorbed by the target tissue. This problem becomes more pronounced the more peripheral the laser aims from "straight down ", In order to fully understa nd the significance of wavefront-optimization, it is first necessary to consider the idea l pre and postopera tive shape of the cornea. NORMAL CORNEAL SHAPE AND ASPHERICITV

202

The natural shape of the human cornea is asp heric with a prolate shape or higher in the center (where the optical power is less in the corneal periphery).

Wavefrollt Optimize andAstigmatislIl Correction

Fig . 1: Allegretto wave exci mer system ove rvi ew

Fig . 2 : Allegretto laser beam distribution

Fig . 3 : Ga uss ian prof il e

203

Instant Clinical Diagnosis in Ophthalmology (Refractive SllrgertJ) In a normal preoperative eye, corneal steepness decreases from the central cornea to the periphery with progressive peripheral flattening. All refractive laser systems utilize a light beam (whether broadbeam or scanning spot) that is fixed in one position, striking parallel through the axis and perpendicular to the central cornea. When laser pulses hit the center of the cornea, they are fully absorbed. But in the corneal periphery, the laser beam m eets the cornea at an incline due to the cornea's curved shape. Changing the angle of incidence w ill alter the round spot into a larger, elliptical shape, thereby distributing laser energy over a larger surface. The photoablative effect, therefore, decreases, causing a reduction in effective peripheral ablation At an optical zone of 8 mm, the effective energy (energy over a surface) used for corneal tissu e ablation at the periphery is reduced by as much as 20% compared w ith the ablation at the central cornea. Most laser systems flatten centrally to create an oblate cornea. This oblate shape causes spherical aberration, which degrades the quality of vision, and increase the spherical aberration. SPHERICAL ABERRATION

A type of optical aberration resulting from failure of a lens (or optical system) to form a perfect image of a monoch romatic, on-axis point source object. Spherical aberration is a form of 'higher-order' aberration. A lens can be perfectly spherical in curvature, but that does not mean that parallel light rays entering near the center of the lens will intersect the lens axis at the same point behind the lens as rays entering from more peripheral points. The differences in where these rays intersect determines the amount of spherical aberration. When rays from a point on the ax is passing through the outer lens zones are focused closer to the lens than rays passing the central zones, the lens is said to ha ve negative spherical aberration; jf the outer zones have a longer focal length than the inner zones, the lens is said to have positive spherical aberration. Spherical aberration can be corrected by lenses with aspheric design. WAVEFRONT OPTIMIZED TECHNOLOGY

The Allegretto system, by design, applies extra pulses to the peripheral cornea in order to compensate for the angle of the laser beam. In this manner, the laser anticipates and corrects for any cosine offset issues. In addition, the laser treatment is specifically designed to preserve the naturally aspheric sh ape of the cornea to a degree that older lasers simply could not achieve. This compensation produces a smooth, cleanly sculpted optical surface. 204

Wavefro11t Optimize and Astigmatism Correction Ga ussian abl ation profile

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Fig . 6: The eye tracker

205

Ill stallt Clillical Diagnosis ill Ophtlwlmologtj (Refractive SlIrgery) In earlier laser correction systems, th e "optical zone," or area of correction, was centered on the front of the cornea; the result \vas a flattened circular area

that ended with an abrup t edge, ca using unwanted side effects like poor nigh t vision, glare, and halos. Un derstanding that the cornea is a sp he re, the laser excimer uses a proprietary treatment that is adjusted to the patient's individual cornea l cu rvature. To overcome the in d uctio n o f spherical aberrations resulting from

reflection and reduced photoablative effect beyond the central cornea, the laser applies additional pulses in the periphe ry of the cornea to precompensate for

these energy losses. Tn this manner, the spherical shape of the cornea is preserved. This compensation, combined w ith the incredibly small, Imm size of the lase r, produces a smooth, effective optical zone that produces what can only be described as high performa nce vision. The wavefront- optimized algori thm ta kes into consideration each patient's

p reoperative keratometry val ue (or co rnea l steepness). The desired pos toperative aspheric contour is lnaintained, even in the outer areas of the cornea,

resulting in a large, true optical zone. Due to the additional peripheral ablation, the actual blend zone is minim ized. CLINICAL IMPLICATIONS Clinical studies have shown that con ven tio nal laser surgery results in a s ignificant induction of higher ord er aberrati ons. The most significant increase

in the type of higher order aberration following refractive surgery occurred for spherical aberrations.

Aberrations describe a distortion of light through an optical system; spherical aberrations are li ke concentric rings of power. If the normal corneal asphericity is changed, it will result in induced spherical aberrations.

Clinical Results (from the FDA Whe n it was approved in 2003 shown the following statistics:At one year after treatment, more than 93% of patients said they saw at least as well or better than they had w ith glasses or contacts before treatment.

More than 98% of patien ts achieved 20/40 vision one year after treatment. Nearly 60% of near-sighted patie nts achieved 20/16 vision after one year oftreatment. Both near- and far-sighted patients reported an inlprovement in their reaction

to bright lights and night d riving glare afte r treatments. In addition, nearsighted patients reported an improvement in sensitivity to light. 206

Wavefrollt Optimize alld Astigmatism Correction Eye tracker display

Detected pupil (white area)

Fig. 7: The eye tracker Threshold value

Fig. 8: The eye tracker (Three illumination elements with large of incidence to reduce the effect of scattered I R light)

Small ab lation spot (Cross-section of an ablation)

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mm

spots Cornea (top view)

2 mm spots

11 mm Diameter

Fig. 9: Ablation

207

Illstall t Clinical Diagllosis in Ophtlwll11ologlJ (Refractive SlIrgenJ)

Predictable results are the norm for the treatment. More than 90% of patients achieve refraction within 1 diopter of the ir target correction.

The procedure has a total re-treatment rate of less than 5% of patients. ASTIGMATISM

Is an affliction of the eye, where vision is blurred by an irregularly shaped cornea . 111e cornea, instead of being shaped like a sphere, is ellipsoidal (like an egg) and reduces the cornea 's ability to focus light. Astigmatism is a refractive error of the eye in which there is a difference in degree of refraction in different meridians (i.e. the eye has different foca l points in different planes). For example, the image may be clearly focused on the retina in the horizontal (sagittal) plane, but not in front of the retina in the ve rtical (tangential) plane. TYPES OF ASTIGMATISM Based on Axis of the PrinCipal Meridians

Regular astigmatism - principal merid ians are perpendicular With-the-rule astigmatism - axis lies between 0 and 30 o r 150 and 180 degrees Against-the-rule astigmatism - axis lies between 60 and 120 degrees Oblique astigmatism - axis lies between 30 and 60 or 120 and 150 degrees Irregular as tign1atisn1- principal merid ians are not p e rpendicular Axis is always recorded as an angle in degrees, between 0 and 180 degrees in a countre-clockwise direction. 0 and 180 lie on a horizontal line at the level of

the center of the pupil, and as seen by an observer 0 lies on the right of both eyes. Although it is unproven, there remain proponents of the theory that astigmatism allows a greater pallet of colors to reach the brain. Based on Focus of the Principal Meridians Shnple astigmatism

Simple hyperopic astigmatism - retina coincides with first focal line Simple m yopic astigmatism - retina cou1Cides with second focallu1e Compound astigmatism Compow1d hyperopic astigmatism - botJ, foca l lines are in front of the retina Compound myopic astigmatism - both focal lines are behind the retina Mixed astigmatism - foca l lines are on both sides of the retina (straddlu1g the rern1a). Photo refractive Excimer Laser Astigmatic Correction

The excimer laser corrects simple myopia by applyi ng a greater amount of 208 laser energy to the central cornea than to the peripheral cornea. This technique

Wavefront Optimize and Astigmatism Correction

200

100

50

o .~ ·50

10 B

"'. 100

B

10 Fig . 10: Myopique ablation profile

Indu ces flattening on short axis

-

-

Induces flattening on short axis

, Figs 11 A an d B: Myopic and astigmatism ablation

209

Instant Clinical Diagnosis in Ophthalmology (Refractive SurgenJ) can be accomplished by opening and closing a circular aper ture through which the laser light passes or by using a scanning lase r to direct pulses primarily to the central cornea. This results in the centra l stromal tissue receiving more ablation than the peripheral cornea, the reby creating a convex surface. Hyperopic corrections can be achieved by a process in which tissue in the peripheral area receives m ore laser energy than that in the central area. Myopic astigmatic corrections are achieved by applying the laser energy in an elliptical pattern along the central part of the flat merid ian, thereby flattening the steep axis . Alternatively, hyp eropic astigmatic correction is ach ieved by applying the laser energy preferentially in the periphery, steepening the flat axis . "Mixed astigmatism is particularly challenging for doctors to treat because it requires that both a myopic and hyperopic treatment be applied to the cornea, often in two consecutive treatments. The new ap proval for the ALLEGRETTO WAVE will enable ophthalmologists to provide one treatment while conserving m ore corneal tissue in comparison to other available approaches ." Mixed astigma tism or irregular as tigma tism describes the lUleq ua I eu rva ture of the cornea in which one principal m eridian is myopic and the other is hyperopic. Mixed astigma tisln causes distorted vision at both near and far distances because of the way in w hich distortions occur on different portions of the eye's surface. Wavefront-guided Laser Vision Correction

Recent advances in techniques used to ga ther refractive data a11m'v for correction of not on ly m yopia, hyperopia, and as tigm atism but also higher order aberrations. This w avescan digital technology was originally developed for astrophysics to reduce atmospheric distortions when viewing distant objects in space through high-powered telescopes. By applying wavescan analysis, coma, trefoil, quadrafoil, higher order spherical aberration, and astigmatism can be corrected. These higher order aberrations are visually significant fo r man y patients. The LASIK or PRK or LASEK p rocedure does not change but rather the method of mapping the visual imperfection s (optical aberra tion s) is different. Zernike polynomials are used to provide a convenient m athema tical expression o f the aberration content in the optical wavefront, resulting in more precise measurements than with sta ndard methods. The wavefront aberrations are then transferred into an ablation profile that is applied using variable beam or scalm ing spot technology. Variable spot sizes are used to remove corneal tissue with an excimer laser. 111is translates to decreased subjective p erception of halos and glare, espeCially in mesopic cond itions, along with increased v isual acuity in low-contrast conditions. 210

Wavefront Optimize aIJd Astigmatism Correction

Induces steepening along short axis (horizontal)

() Induces steepening along short axis (horizontal)

Figs 12A an d B: Hyperopic and astigmatism ablation

Induces central flattening

Fig. 13: Mixed astigmatism ablation

211

Instant Clinical Diagnosis in OphthalmologtJ (Refractive SurgenJ!

Clinical results of wavefront-guided LASIK to correct myopic astigmatism by Mrochen et al showed that, in a group of 35 eyes tested, 93.5% of eyes were at an uncorrected visual acuity level of 20/20 or better at 3 months. This teciu1010gy has also been helpful in the treatment of mixed astigmatism, as repor ted by Maloney. CONCLUSION

AliegrettoRexcimer lase r also fea tures a w1ique approach to corneal sculpting. The normal curvature of a healthy cornea is prolate. The laser not only treats the cornea centrally, but also peripherally. The laser uses proprietary nomog rams to adjust the asphericity of the cornea to perform a prolate ablation based on the an terior curvature readings. This prolate curvature, in part, accounts for the excellent q uality of vision during the day and night. The wavefront optimize offers a trea tment that incorporates wavefront principles to patients with nearsigh tedness, fa rsightedness and as tigmatism . Every procedure is tailored to the patients' cornea l curvature an d refraction with the intention to preserve the natura l aspheric cornea shape and to maintain

or improve quality of vision and visual acuity.

212

Wavefront Optimize and Astigmatism Correction

Central ablation depth

~r,,90 '

Optical zone Ablation zone

....." ,,-.t-If-j- Cornea preoperation

Cornea postoperation

;I 0°, i

Ablation depth

. i

i

90·'-'-.JL~2 .. ~~.~ ' =.2.~;-"--,

Ablation depth

Fig, 14 : Myopique ablation profile

213

23 Aberropia: A New Refractive Entity Amar Agarwal, Nilesh Kanjiani, Soosan Ja cob, Athiya Agarwal, Sunita Agarwal, Tahira Agarwal, Ashok Garg (India)

INTRODUCTION

The next evolution to come on to the visual science scene in refractive ocular itnaging is the aberrometer, the O rbscan an d wave front analysis. This

technology is based on astrophysical principles, which as tronomers use to perfect the images impinging on their telescopes. Dr Bille, the Director of the Institute of Applied Physics at the Uni versity of Heidelberg first began work in this field while developing this specific technology for astronomy applications in the mid-1970's. For perfect imaging, astrophysicists have to be able to measure and correct the imperfect higher-orde r aberrations or vvavefront distortions that enter their telescopic lens system from the galaxy. To achieve this purpose, adaptive optics are used wherein deformable mirrors refo rm the distorted wavefront to a11m,,' clea r v isualization of celestial objects. Extrapolating these same principles to the human eye, it was tho ug ht that renwval of the wavefront

abe rrations of the eye migh t finally yield the long awaited and much desired ultimate goal of "super vision", So far, the only parameters that could be modified to obta in the optical correction for a given patients refractive e rror were the sphere, cylinder and axis even though this does not g ive the idea l optical correction many a tiln es. This is because the current modes fo r correcting the optical aberrations of the eye do not reduce the higher order aberra tions. The ideal optical system should be able to correct the optical aberra tions in such a way that the spatial resolving ability of the eye is limi ted only by the limits imposed by the neural retina, i.e. receptor diameter and receptor packing. Thus, there may be a large grou p of patien ts whose best corrected visual acu ity (BCVA) may actually improve significantl y on removal of the optical aberrations. These optical aberrations are contributed to by the eye's entire optical system, i.e. the cornea, the lens, the vitreous and the retina. This study was conducted to determine the existence o f a hitherto unidentified entity \.vhich ,,,'e label as "aberropia" w here in patients with best corrected visua l 214 acui ty of,<; 6/ 9 (0.63), corneal topogra phy no t accounting fo r the lack of

Aberropia: A New Refractive Entin}

Comparison of preoperative BCVA and postoperative UCVA in aberropic patients 1.6

V ;

,

-

1.4

u a I

--

1.2

E q u u ;

I~

,

PREOP BCVA

POSTOP UCVA

-

-

-

-

I- -

-

-

-

I- -

-

-

-

-

-

a

;

t

y

n

,d ,

1

v

~ 0.8

I-

n t

I-

-

-

-

-

-

-

-

-

, ,

0.6

-

-

I-

04

m a

0.2

I

0 2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Number of patients

Fig. 1: Preoperative BCVA versus postoperative UCVA

Comparison RMS values preoperative and postoperative aberropia 6

I_

5

a n d

a

PRE OP RMS

I

[] POSTOP RMS

5

,

r

d 3

d

e v

i

2

a t

i

1

0

llli,nL J.

n 0 l110 2111 Z200 Z221

mo

--.

IJII 2310 l331 Ij.l() 2400 2420 z.t21 14-l0 2441

Z~10

Z511 ZS30

Z~1

2550 ZS!>l

Rool mean square val ues

Fig. 2: RMS va lues preoperative and postoperative

215

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) improvement in BeV A and w ith no o ther kn own cause for decreased vision improved by :2: two Snellen lines after refractive correction of their wavefront aberrati on .

Materials and Methods

16 eyes of 10 patients were included in this retrospective study carried out at the Dr. Agarwal's Eye Institute, India between May to December 2002. Only patients who had visual acuity less th an 6 /9 (0.63) prior to the procedure and whose visual acuity improved by more than or equal to two lines after the procedure were included in the study. N one of these patients had any other known cause for decreased vision and their corneal topography did not account for the lack of improvement in BeyA. The rou tine patient evaluation including uncorrected (Uey A) and best corrected (BeY A), slit lamp examination, applanation tonometry, manifest and cycloplegic refractions, Orbscan, aberrometry, corneal pachymetry, corneal diameter, Schirmer test and indirect ophthalmoscopy had been performed for all the patients. Patients wearing contact lenses had been asked to discontinue soft lenses for a minimum of 1 week and rigid gas permeable lenses for a minimum of 2 weeks before the preoperative examination and surgery . Informed consent was obtained form all patients after a thorough explanation of the procedure and its potential benefits and risks. The Zyoptix procedure was then perfor m ed using the Bausch and Lomb Technolas 217 Z machine. The param eters used were: wavelength 193 nm, fluence 130 m) / em and ablation zone diameters between 4.8 mm and 6 mm. The Hansatome (Bausch and Lomb) w as used in all the eyes. Either the 180 pm or the 160 pm plate was used in all the eyes. The aberrometer and the Orbscan, which checks the corneal topography, are linked and a zylink created. An app ropriate software file is created which is then used to generate the laser treatment file. Postoperatively, the patients underwent complete examination including Uey A, Bey A, slit lamp examin ation, Orbscan and aberrometry. The mean follow-up was 37.5 days. For statistical analysis, the Snellen acuity was converted to the decimal notation. Continuous variables were described with mean, standard deviation, minimum and maximum values.

216

Resu lts: 16 eyes of 10 patients satisfied the inclusion criteria. The mean age of the patients was 29.43 years (range 22 to 35 years). 6 patients were females and 4 were males. The mean preoperative pupil diameter measured on aberrometer was4.69 nun and mean postoperative pupil diameter measured on aberrometer was 4.53 mm.

Table 1; RMS values pre laser Patient

Z IIO

Z III

Z200

Z221

Z220

Z3 11

Z310

Z331

Z330

Z400

Z420

Z42 1 Z440

Z44 1

Z5 10

Z5 11

Z530

Z53 1

Z550

4.055

-6.131

0.299

-0.113

0.725

-0.44

o.em

-0.03

0.102

-1.719

6.COS

-0.273

0.022

-0.353

0.275

0.092

0.002

-0.088

0.118

0.435

-0.658

·0.444

-0.567

-0.779

0.514

-0.155

029

.().006

0.Q\6

0.529

-0.123

-0.886

0.156

~.09

0.004

-0.128

Z 55 1

-0.233

0.100

0.131

0.fJZl

-0.048

-0.04 1

0.052

0.009

-9999

-0. 145

0.199

-0.013

-0.006

O.Q\ 1

0.034

·0.039

0.042

0.042

-9999

-0.089

0.043

-0.202

-0.053

-0.052

-0.057

-0.04

-0.001

0.13

0.111

-9999

-0.9 1

0.124

0. 124

-0.431

-0.222

0.074

-0.04

0.001

-0.063

-0.14 1

0.119

-9999

-0.084

-0.072

0.<Xl5

-0.009

-0.044

O.(X)!

-0.031

0.01

-0.005

o.cm

-0.041

-9999

Z6

No

..,.'"

~

o

o

-5.77

2

o

o

-4.323

3

o

o

-1 1.8

4

o

o

-12.46

5

o

o

-6.535

6

o

o

-7.887

0.185

1.704

7

o

o

-4.28

0.187

2.571

8

o

o

-10.4

0.502

9

o

o

-17.15

10

o

o

-16.78

"

o

o

12

o

o

13

o

o

14

o

o

15

o

o

-4.955

16

o

o

-4.367

0.414

0.44 1

0.197

0.365

0.197

0.107

-0.155

-0.002

0.123

0.CQ6

-0.001

0.049

0.00

0.032

-9999

0.cX)7

.().089

0.356

0.125

0.585

0.101

-0.002

-0.17

-0.062

-0.077

0.100

0.001

-0.104

-0.022

0.029

-9999

-0.587

-0.007

-0.331

0.165

-0.126

-0.054

-0.071

0.03]

-0. 11 8

-0.128

0.003

0.017

·0.007

-0.026

0.003

-0.052

-9999

-0.414

-1.217

0.093

-0. 106

0.343

-0.18

-0.254

0.009

0.002

0.001

-0.025

0.007

-0.022

-0.007

-0.042

0.C07

0.04

-9999

-0.162

.().637

0.122

-0.159

0279

02

-0.181

0. 115

0.007

-0.002

0.042

-0.034

-0.028

0.021

-0.043

-0.006

-0.017

-9999

-4.513

2.916

4.001

'().634

'()205

0.4n

0.44

0.094

0.377

0.058

-0.201

0.101

0.133

-0.147

0.003

0.011

-0.055

0.118

-9999

·5.736

-1.50 1

5.195

-1.126

0.32

0.865

-0.254

0.218

0.479

0. 122

-0.253

-0.045

0.099

-0.025

0.012

-0.006

-0.05

0.11

-9999

· 15.46

1.005

>754

0.378

0443

0200

0.458

0.643

-0.003

0.00

0.407

-0.006

-0.02 1

0.00

0.033

0.032

0..239

0.149

-9999

-15.26

-0.557

2.865

-0.26

-0.059

0.107

0. 122

0.168

0.025

-0.256

-0.003

0.257

0.007

O.ffi l

0.136

-0.061

-0.11 4

0.124

-9999

0.735

0.383

-0.401

0009

0.62

-0.494

-0.676

0.391

0. 163

-0.421

·0.264

0.039

-0.261

·0.079

0.241

0. 103

-0.067

-9999

-0.195

-0.238

0.2l!

0.11

-0.11 2

0.084

-0.022

-0.061

0.013

-0.018

-0.063

O.Q()cI

0.063

0.044

~.02

'().04

0.021

0

-9999

;..
]

?-

;..

~ ~

::.0

~

"

~ ;;-

'"~ ~­

~

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) The mean preoperative spherical equivalent was - 4.940 (range -12.50 to - 1.5 D). The mean spherical equivalent at 1 month postoperative period was - 0.16 ± 0.68 0 (range -1.0 to 1.5). Mean preoperative sphere was -4.95 0 (range -12.50 to -0.75 0 ) and the mean postoperative sphere was - 0.13 ± 0.68 o (range-1 to 1.5) at 1 month. The mean preoperative cylinder was -1.34 0 (range 0 to - 3.50). The mean postoperative cylinder was -0 .08 ± 0.24 0 (range o to - 0.75 D) at one month. Postoperatively, at the end of first month, 70% of the patients were within ± O.SD and 90% were within ± lD of emmetropia. Preoperatively mean RMS (Root Mean square) values were: Z 200 Defocus -9.22, Z 221 Astigmatism 0.12, Z 220 Astigmatism 1.02, Z 311 Coma -D.041, Z 310 Coma -0.04, Z 331 Trefoil 0.23, Z 330 Trefoil 0.016, Z 400 Spherical aberration - 0.054, Z 420 Secondary as tigmatism 0.103, Z 421 Secondary astigmatism 0.029, Z 440 Quadrafoil-D.103, Z 441 Quadrafoil -0.021, Z 510 Secondary coma 0.025, Z 511 Secon da ry coma - 0.015, Z 530 Secondary trefoil 0.0049, Z 531 Secondary trefoil -0.00219, Z 550 Penta foil 0.023, Z 551 Pentafoil 0.046. Postoperative mean RMS values were: Z 200 Defocus -D .429, Z 221 Astigmatism 0.07, Z 220 Astigmatism -D.07, Z 311 Coma 0.149, Z 310 Coma -0.079, Z 331 Trefoil-0.102, Z 330 Trefoil - 0.004, Z 400 Spherical aberration0.179, Z 420 Secondary astigmatism 0.015, Z 421 Secondary astigmatism 0.031, Z 440 Quadrafoil 0.019, Z 441 Qua drafoil - 0.069, Z 510 Secondary coma -0.008, Z 511 Secondary coma 0.008, Z 530 Secondary Trefoil -0.002, Z 531 Secondary Trefoil - 0.014, Z 550 Pentafoil 0.006, Z 551 Pentafoil 0.026. RMS pre and post laser showed a reduction in the higher order aberrations (Tables 1 and 2). 6.25% patients achieved 6/9, 31.25% patients achieved;:>. 6/ 6 (1.00),37.50% achieved a BCVA of 6/5 (1.25) and 25% achieved a BCVA of 6/4 (1.6) Figure 4 shows the preoperative Orbscan picture of a patient showing no abnormality. Figures 5A an d B shows the aberrometer maps of the right eye and left eye of a patient in which we can see the aberrations reduced post laser.

Discussion Zyoptix is the new generation of excimer laser used for the treatment of refractive disorders. Until recently, refractive disorders were treated with standard

teclmiques, which took into consideration only the subjective refraction. Zyoptix technique on the other hand, takes in to account the patient's subjective refraction, ocular optical aberrations and corneal topography, with the latter not only for the diagnosis, but also for the therapeutic treatment, in order to design a personalized trea tment based on the total structure of the eye. The wavefront technology in Zyop tix uses the H artmann Shack aberrometer based on the Hartmann-Shack princip le demonstrated by Liang et al to measure the eye's wave aberration. This wavefront sensor has been improved by increasing 218

the density of samples taken of the wavefront slope in the pupil. All H artmann-

.

__ ..· ,~~.?\.~tSl{~'%\~~ .~t~'%fF;WI .D.~. ,/*'If&~W . ..~~."%'! W .-%0~ ~.i< _ -~.-~. Table 2 : RMS values post laser ,:§ft..f%;tVf.Z~[f!iJ~~.~~¥AYi~~1~~";#J4~.>~<'$'f%'fu"0,fh%yg,~{~ ·" f!t~ ~ "_,_"_",_,."w,."-,,,'i$."'~:./fi!j;,,._n,~~.\~~,,,I:;~&\}~~'!i..~'i'\;"~'S'"",:iiw.~t:~%.~~*t,~~,'Wi.->i:-;1l ~~

i&""*',--::m;:;~%'.'<."",;"",\"""~,,,,:_~~,,,,,,W>.,~_ •.. ," ". '. ""';>:'''''''_~~l(.l('''·''''''''''''~''':·'.~·~_=M '';·'M''''';~~;·;''''''~·'.~".'''',{m..'<S..'''''''''3.'''·'--''~'''~&':'''~;_''~''V,·:·'''''·:''''&:;\~~'r~

.,:': "

Pal.No. ZI10

Z,II

Z200

Z221

Z220

Z311

Z310

Z331

Z330

Z400

Z420

Z421

Z440

Z441

Z510

Z511

Z 530

Z 53 1

Z550

Z551

Z6

o

o

-0.022

0.74

· 1.294

0.117

-0.067

0.14 1

0.052

-0.063

.0.076

0.1

0.054

-0.037

-0.028

a.e)J1

0,(00

0,007

0.013

0.003

·9999

o

o

-0508

0.12

0.194

-0.085

0,039

-0.12

-0.016

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

o

o

-1.398

-0.606

0.697

-0.558

-0.351

0.841

0.345

-0.39

0.392

0.036

-0,303

-0.038

-0.001

0.103

-0.066

-0.105

·0.021

0.137

-9999

o

o

-2.05

-0.499

-0.375

-0.027

-0.269

-0.534

-0.269

-0.56

0.114

0.058

0.236

-0.161

0.034

-0.083

0.004

0."'"

om

-0.077 ·9999

o

o

0.229

0.1

-0.123

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

6

o

o

-0_036

-0.17

0.425

-OJJ02

0.069

-0.045

-0.042

-0.342

-0.032

0.094

0.075

-0.05

0068

0.03

0.004

-0.014

0.012

0.002

-9999

7

o

o

0.687

0.128

-0.028

-0.117

-0.043

0.062

0,008

-0.178

0.179

0.024

-0.045

0.055

0.013

0.Q16

·0.034

-0,013

-0,013

0.059

·9999

2

4

'" ~

'"

;..

c-

~?. ;..

~

:>:l

8

o

o

·2.164

0279

-0.696

-0.25

-0.398

-0.147

-0.128

-0.581

-0.238

0.02

0.032

·0.088

·0.129

o.em

-0.029

0.W7

0.009

0.059

-9999

9

o

o

-0.296

o.w

-0.311

0,156

-0.206

0.129

-0.116

-0. 105

-0.045

·0.043

-0.1

-0.1

.,."

-9999

-9999

-9999

-9999

-9999

-9999

10

o

o

0.109

0241

-0.503

0.233

-0.119

-0.16

-0.204

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

11

o

o

0.034

-0.092

0.076

0.013

-0.03

-0.067

0.003

-9999

-9999

·9999

·9999

-9999

-9999

-9999

-9999

-9999

-9999

·9999

·9999

12

o

o

0.187

0.001

0.004

-0.097

0.015

0.067

0.035

·9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

-9999

·9999

-9999

13

o

o

-0,701

0,291

0.596

2.161

0.349

-1 .062

-0.201

-0.428

-0.013

0.204

0258

-0.636

-O'c)82

0.113

0.009

·0.239

0.062

-9999

-9999

14

o

o

·0.638

0.004

0.391

0.517

·0.328

-0.336

0.188

-0.118

-0.077

0.003

0.157

0.004

·0.006

-0.025

0.004

0,018

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Instant Clinical Diagnosis ill Ophthalmology (Refractive Sllrgery) Shack devices are outgoing testing devices in that they evaluate the light being bounced back out through the optical system. A narrow laser beam is focused onto the retina to generate a point source. The out coming light rays which experience all the aberrations of the eye pass through an array of lenses which detects their deviation. The wavefront deformation is calculated by analyzing the direction of the light rays using this lenslet array. Parallel light bea ms indicate a good wavefront and non-parallel light beams indicate a wavefront w ith aberrations, which does not g ive equidistant focal points. This image is then captured onto a ccd camera and the wavefront is reconstructed . The data is explained mathematically in three dimensions with polynomial functions. Most investigators have chosen the Zern ike method for this analysis although Ta ylor series can also be used fo r the same purpose. Data from the wavefront map is presented as a sum of Zernike polynomials each describing a certain deformation. At any point in the pupil, the wavefront aberration is the optical path difference between the actual image wavefront and the ideal spherical wavefront centered at the image point. Any refra ctive error which cannot be corrected by sphero-cylindricallens combinations is referred to by physicists as higher order aberrations, i.e. comma, spherical aberration, chromatic aberration. The Zernike Polynomials, which describe ray points, are used to obtain a best fit toric to correct for the refractive error of the eye. The points are described in the x and y coordinates and the third dimension, height, is described in the z-axis. The local refractive correction of each area of the entrance pupil can be determined by calculating from the wavefront polynomial the corresponding local radii of curvature and hence the required spherocylindrical correction. Thus each small region of the entrance pupil has its own three parameters that characterize the local refractive correction: sphere, cylinder and axis. The global aberrations of the entire optical system including the cornea, lens, vitreous and the retina are thus measured. The great advantage of wavefront analysis is that it can describe these other aherra tions.

The first order polynomial describes the spherical error or power of the eye. The second order polynomial describes the regular astigmatic component and its orientation or axis. Third order aberrations are considered to be coma and

fourth order aberrations are considered to be spherical aberration. Zernike polynomial descriptions for wavefront analysis typically go up to the tenth order of expression. The first and second orders describe the morphology of a no rmal straight curve. More local maximum and minimum points require

220

higher orders of the polynomial series to describe the surface. No rmal eyes exhibit spherical and coma aberrations in addition to exhibiting defocus and astigmatism. Ideally, the difference in the magnitude of the local refractive correction of eac h area of the en trance pup il s hould not exceed 0.25 D. Lowe r spherocylindrical corrections are generally associated with lower wavefront aberrations. These observations regard ing va riation in local ocular refraction

A berropia: A New Refractive EI1 tin)

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221

Instant Clinical Diagllosis in Ophthalmology (Refractive Surgery) along different meridians are also confirmed by Ivanoff and Jenkins. Van den Brink also commented on the change in refraction ac ross the pupil. Clinically significan t changes of at least 0.25 0 in one or both components of the spherocylindrical correction might normally be expected for decentrations of abou t 1 mm. Rayleigh's quarter wavelength rule states that if the wavefront aberration exceeds a quarter of a wavelength, the quality of the retinal image will be impaired significantl y. Thus the aberration in eyes starts to become significan t when the pupil diameter exceeds 1-2 mm. Thus it is not possible to correct the entire wavefront aberration with a single spherocylindrical lens. As conventional refractive procedures such as Lasikalso reduce only the second order aberrations, the visual ac uity w ill still be lim ited by aberrations of third and higher order aberra tions. These patients are likely to undergo tremendous improvement in their BCVA after correction of their aberrations by Zyoptix. in the Zyoptix system, the aberrometer and the orbscan, which checks the corneal topography, are linked and a zylink created. An appropriate software file is created which is then used to generate the laser treatment file. The truncated gaussian beam shape used in Zyoptix combines the advantages of the common beam shapes, i.e. flat top beam a nd the gaussian beam, creating a maximized smoothness and mininlized thermal effect. Thus Zyoptix gives a smoother corneal su rface, reducing glare and increasing visual acuity. The larger optical zones reduce haloes. Zyoptix also causes a reduction of the ablation depth by 15-20 % and a reduced enhancement rate. [n a patient with higher order aberrations, lasik does not remove the higher order aberrations and the pOint-spread function is a large blur. Zyoptix on the other hand, performs customized ablation and removes the higher order aberrations thus minimizing the wavefront deformation. The point-spread function is therefore a small spot of light. In our study, the mean preoperative spherical equivalent improved from -4.78 D to -0.16 D ± 0.68 and the mean preoperative cylinder improved from -1.34 D to -0.08 D ± 0.24. The aberra tions were reduced drastically in all the eyes and the BCY A improved in all cases by 2 two li nes. Reduction of the aberrations of the eye can thus result in an improved BCY A postoperatively. Improving the optics of the eye by removing aberrations increases the contrast and spatial detail of the retinal image. Reduction of higher order aberrations may not improve high contrast acuity much more in eyes where spherocylindricallenses alone improve the BCV A to 6/ 3 (2.00) or better. In contrast, in otherwise normal eyes where the BCY A is limited to 6/9 (0.50) or 6/ 6 (1.00) due to optical aberrations, reduction of higher order aberrations should improve visual acuity. Realization of the best possible wlai ded visual acuity may be limited at the cortical, retinal and the spectacle, corneal, or implant level. All maculae may not be able to support 6/ 3 (2.00) vision. insufficient cone denSity or sub-optimal orientation of cone receptors or a sub-optimal Stiles-Crawford profile of the 222 macula may make 6/ 3 (2.00) vis io n impossible. Clinical or sub-clinical

Aberropia: A New Refractive Ell tin}

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223

Instant Clinical Diagnosis in OphthalmologIj (Refractive Su rgenj) amblyopia ll1ay make achievement of super vision impossible. But in spite of this, there may be a certain patient population who have the potential for an improved BeVA on removal of their \,vavefront aberrations. The corneal topography does not account for the decreased preoperative visua l acuity in these patients, neither do they have any other identifiable cause for the decrease in acuity except for an abnormal wavefront. It is important that this subgroup of patients are identified and their optical aberrations neutralized so that they are not deprived of the opportunity to gain in their BeV A. Wavefront sensing technology, at present, does not in most cases define the exact locale of the pathology causing the aberration. Hence, clinical examination and other refractive tools, such as corneal topographic Inapping, along with sound clinical judgment is required for proper understanding of the eye and its individual refractive status. Also, wavefront aberrations may not relnain static. Numero us authors have sho,vn that ocular optical aberrations probably remain constant between 20 and 40 years of age but increase after that. Aberrations also ch ange during accommodation and may be affected by mydriatics. Thus, the patient should be informed about these possibilities while taking the consent for the procedure. Long-term studies are required to detennine the stability of the postoperative refraction, residual aberrations and changes in BeV A if any. The question of magnification facto r improving visual acuity does not arise as these patients preoperatively did not improve with contact lenses. Further the refractive error in some of these patients was not very large. CONCLUSION

Tn conclusion, removal of the wavefront aberration may extend the benefit of an improved BeV A to patients with an abnormal wavefront. The subgroup of patients vl'ith higher order aberrations, normal corneal topography and no other knm,v n cause for decreased vision may thus benefit immensely with \vavefront guided refractive surgery. Customized refracti ve surgery tailor-made for these individual patients, aimed a t neutralizing the wavefront aberrations of the eye is safer, more predictable, provides better visual acuities and reduces the incidence of w1satisfactory outcon1es. Further studies are required to assess the long-term outcomes. Till nm,v, when we discuss refractive errors we discuss about spherical and a cylindrical correction. But in todays world we have to think of a third parameter \vhich is the aberrations present in the eye which can be anyvvhere in the optical media. These can be corrected in the corneal level by the laser treatment.

224

Aben'opin:A New Refrnc tive E/ltih}

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225

24 Topographic and Aberrometer Guided laser Amar Agarwal, Sunita Agarwal, Athiya Agarwal, Ashok Garg (India)

INTRODUCTION

Since as early as middle of 19th century it has been known that the optical quality of human eye suffers fro m ocula r errors (aberrations) besides the commonly known image errors such as myop ia, hyperopia and asigmatism. In early 1970's Fyodorov introdu ced the ante rior radial incisions to flatten the central cornea to correct myop ia. Astig matic keratotomy , Keratomileusis and Keratophaki3, Epikeratopha ki a and currently Excimer Laser have been used to manage the various refractive errors. These refractive procedures correct lower order aberrations such as sphe rical and cylindrical refractive errors however higher order aberrations persist, w hich affect the quality of vision but may not significantly affect the Snellen visual acuity . Refractiv e corrective p rocedures are known to ind uce aberrations. It is the subtle dev iations from the id eal optical system, which can be corrected by wavefront and topography gu ided (customized ablation) LASIK procedures. ABERRATIONS

Optical aberration custom iza tion can be corneal topography guided which measures the ocular aberrations detected by corneal topography and treats the irregularities as an in tegra ted part of the laser treatment plan. The second m ethod of optical aberra tion customization n1easures the wav efront errors of the entire e ye and treats based on these measurelnents. Wavefront analysis can be done either using How land's aberroscope or a Hartmann Shack wavefront sensor. These techniques measure all the eye's aberrations including second-order (sphere and cylindrical), third -order (coma- like), fourt h-order (spherical), and higher order w avefront aberrations. Based on this information an ideal ablation plan can be formulated w hich treats lower order as well as higher order aberrations. ZYOPTIX LASER

226

Zyoptix TM (Bausch and Lomb) is a system for Personalized Vision Solutions, which incorporates Zyvvave ™ HartrnalU1 Shack aberrometer coupled \vith

Topographic and Aberrometer Guided Laser

FIg. 1: Hartmann shack aberrometer

Fig. 2: Zywave projects low-intensity HeN e infrared light into the eye and use the diffuse reflection from the retina

227

b,stallt Clillical Diagnosis ill Ophthalmology (Refractive Surgery) Orbscan ™ II z multi-dimensional device, which generates the individual ablation profiles to be used with the Teclmolas® 217 Excimer Laser system. Thus this system utilizes combination of wavefront anal ysis and corneal topography for optical aberration customization.

ORBSCAN The Orbscan (BA USCH and LOM B) co rn eal topograph y sy stem uses a scanning optical slit scan that is fund am entally different than the corneal topography that analyses the reflected images from the anterior corneal surface. The high-resolution video camera ca p tures 40 light slits at 45 degrees angle projected through the cornea similarly as seen during slit lamp exan1inatiol1. The slits are projected on to the an terior segm ent 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 crea te a topographic Inap . This technique provides more information about an terior seglnent of the eye, such as anterior and posterior corneal curvatu re an d corneal thickness. It in1proves the diagnostic accuracy and it has passive eye-tracker frOln fralne to frame, 43 fran1es are taken to ensure accu racy. It is easy to interpret and has good repeata-

bility. Three different maps are ta ken, and the one featuring the least eye rnovelnents is used. The maximum movements considered acceptable are 200 p.

ABERROMETER ZywaveTIvl is based on Hartmann - Shack aberrometry in \,v hich a laser diode (780 nm) gene rates a laser beam tha t is focused on the retina of the patient's eye. An adjustable collimation system compensates for the spherical portion of the refractive error of the eye. Laser diode is turned on for approximatel y 100 milliseconds. The light reflected fro m the focal poin t on the retina (source of wavefront) is directed through an a rra y of small lenses (lenslet) generating a grid like pattern (array) of focal points. The position of the focal points are detected by Zywave™ Due to de via tion of the points from their ideal position, the w avefront can be reconstruc ted . Wavefron t display show s (a) higher orde r aberrations (b) predicted phoropte r refraction (PPR) calculated for a back vertex correction of 15 mm. (c) Simulated point sp read function (PSF). Zywave™ examinations are done with (a) single exa mi nation with undilated pupil (b) five examinations with dila ted pupil (mydriasis) non-c ycloplegic, using 5% Phenylephrine drops. One of these five measurements, which matched best with the manifest refraction of the undila ted p upil, is chosen for the treatment.

ZYLlNK Information gathered fro m Orbscan and Z ywa ve are then translated into treatment plan using ZylinkTM software and copied to a flopp y disc k. The 228 floppy disc is then inserted into the Technolas 217 system, fluence test carried

Topographic alldAberrometer Gllided Laser

Fig. 3: Schematic illustration of the Bausch and Lomb Zywave aberrometer. A low-intensity HeNe infrared fight is shone into the eye; the retlee-ted light is focused by a number of small lenses (Ienslet-array), and pictured by a CeO-came ra. The capture image is shown on the bottom left

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229

II/stal/t Clil/ical Diagllosis ill Ophtha lmologtJ (Refractiv e SlIrgery) out and a Zyopitx treatmen t card was inserted. A standard LASIK procedure is then performed with a superiorly hinged flap. A HansatomeT>1 rnicrokeratome is used to create a flap. Flap thickness varied from 160).1111 to 200 ).1111. A residua l stromal bed of 250 ).lm or more is left in all eyes. Optical zone varied from 6 mm to 7 mm depending upon the pupil size and ablation required. Eye tracker is kept on d uring laser ab lation. Postoperatively all patients are followed up for at least 6 months. RESULTS

We did a study comprising 150 eyes with myopia and compolmd myopic astigmatism. Preoperatively, the patients underwent comeal topography wi th Orbscan II z ™ and wavefront ana lysis with Zywave ™ in addition to the routine pre-LASrK work up. The results were assimilated using Zylink T", and a customized treatment plan was form ula ted. LAS IK was then performed with Technolas® 217 system. All the patients were fol lowed up for at least six months. Mean preoperative Be VA (in deci mal) was 0.83 ± 0.18 (Range 0.33- 1.00). Mean postoperative (6 mo nths) BeVA was 1.00 ± 0.23 (Ran ge 0.33-1.50). Difference was statistically significa nt (p = 0.0003). Out of 150 eyes that underwen t customized ab lation, 3 eyes (2%) lost two or more lines of best spectade corrected visual ac ui ty (BSeVA) . Safety Index = Mean postoperati ve BSeVA/Mean preoperative BSeVA = 1.20. Mean preoperative UeVA was 0.06 ± 0.02 (Range 0.01-0.50). Mean postoperative UeVA was 0.88 ± 0.36 (Ran ge 0.08 - 1.50). Difference was statistically Significant (p = 0.0001). Efficacy index =Mean postoperative uev A / Mean preoperative uev A = 14.66. Preoperatively, none of the eyes h ad ueVA of 6 \6 or more and one eye (0.66%) had Ue VA of 6/ 12 or more. At 6 months post-operatively, 105 eyes (69.93%) had UeVA of 6\6 or more and 126 eyes (83.91 %) had UeVA of 6/ 12 or more. Mean preoperative spherical equiva lent was -5 .25 0 ± 1.68 0 (Range - 0.87 0 to -15 0). Mean postopera tive sphe rical equivalent (6 months) was - 0.36 0 ± 0.931 0 (Range - 4.25 0 to +1.25). Difference between the two was statistically significant (p < 0.05). 132 eyes (87.91 %) were within ± 1.000 of emmetropia willie 120 eyes (79.92%) were within ± 0.050 of emmetropia. 1 eye (0.66%) was overcorrected by > 0.5 0 and 1 eye (0.66%) was overcorrected by >10. The mean pupil d iameter was 5:1 mm ± 0.62 mm. Preoperatively, 95 eyes (63.27%) had third order aberrations.42 eyes (28%) had second order aberration alone, while 13 eyes (8.65%) had fo urth and fifth order aberrations. Postoperatively, 60 eyes (40%) had third order aberration.75 eyes (50%) had second order alone while 15 eyes (10%) had hig her order aberrations.

230

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231

Instant Clinical Diagnosis in OphthalmologJ) (Refractive SlIIogel1)) DISCUSSION Hartnlann - Shack w avefront sensor was first used by Liang and colleagues to detect ocular aberrations. They applied an adaptive optics deformable mirror to correct the lower and higher order aberrations of the eye. They reported a 6 tilnes increase in contrast sensitivity to hi gh spatial frequency w hen the pupil was large. This study demonstrated that correction of higher order aberrations could lead to supernormal vision in normal eyes. Figures 8 to 10 show v arious aberrations . In our series, using Zyoptix and Teclul01as 217 system, which is wav efront and corneal topography guided, w e yielded results that are comparable to standard LASIK procedure. In a series of 347 eyes, McDonald et al reported a postoperative refraction of -0.29 ± 0.45 D (-0.36 ± 0.93 D in our series) w ith standard LASIK. 57% of the eyes in their series had postoperative UCVA of 6/ 6. In our study, 70% of the eyes had UCVA of 6/ 6, six months postoperatively. Higher order aberrations were red uced postoperatively in our study. 1l1irdorder aberration (coma) was most com mon in our series, foll owed by secondorder (defocus and astigmatism) and fo urth-ord er (spherical aberration). Postoperatively, after 6 months, there was considerable decrease in third-order and fourth -order aberrations. While most of the eyes had only defocus and astigmatism (i .e. second -order aberration). A slight increase in fourth-order aberration (spherical) was noted. Spherical aberration is known to increase after LASIK. Roberts has reported that cornea changes its shape in response to ablation and this change, along with wound healing effects have to be taken into account before custOlnized correction can nullify higher-order aberrations. Roberts and coworkers suggest tha t increase in spherical aberrations following LASIKmay be caused by a biomechanically induced steepening and thickening that ma y occur in mid periphery of the cornea. MacRae and cow orkers have reported that simply creating a LASIK flap increases higher-order aberrations in unpredictable manner. They suggest that improved results can be obtained using a surface ablation such as PRK or LASEK, or by doing a two-stage LASIK, with the second stage adjusting fo r the aberration created by the flap and initial ablation. Scotopic visual complaints have been the bugbear of LASIK proced ures, ranging from mild annoyance to server optical disability. N ight-time starbursts, reduced contrast sensitivity and haloes are the Inost common cOll1plaints. Spherical aberration that is induced durin g LASIK may account for this scotopic complaints. Pupil diameter is another factor that is important. When pupil diameter is large, as in young patients, dim light vision is improved after customized correction. In our series, 11 % of the patients complained of haloes around light at night and difficult night driving. In dim light, the mean pupil 232 diameter in these patients was 4.2 mm while it was 5.9 mm in other patients.

Topographic and Aberrometer Gllided Laser

Fig. 8: Second order sphe re

Fig . 9: Second order ast igmatism

233

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) Smaller pupi l diameter an d induced higher-order aberration may account for these scotopic visual complaints. 25% of the patients in our series reported improvement in bright light vision, wh ile 40°;{) showed improvement in dim light vision. A similar improvement was n oted by Cox and co-workers (p resentation by Cox IG at Zyoptix Alliance meeting, 2002 reported in Ocular Surgery News, July 2002 volume 13, number 7).ln our series, treatment optical zone ranged from 6 mm to 7 mm. Treatmen t ,·vith larger optical zones and transition zones as compared to conventional LASIK may be p ossible since entire corneal topography and not just th e central cornea overlying pupil along with wavefron t ablation in dilated pupil are considered during treatment. This may induce lesser spherical aberration post-LASIK and account for impro ved scotopic vision . Though we did not measure contrast sensiti v ity and glare acuity postoperatively, our results suggest improved quali ty of vision and fewer gla re p roblems with Zyoptix treatment. A more tem poral appraisal of the procedure h as to be carried out with comparison to standard LASIK. Short-term results suggest wavefront and topography guided LASIK may be a safe and effective procedure which improves the visual performance. CONCLUSION

Wavefront and topog raphy gu ided LASTK p rocedure Jeads to better visual performance by decreasing higher order aberration . Scotopic visual complaints may be reduced with this m ethod.

234

Topographic alld Aberrometer Guided Laser

Fig. 10: Third order coma

235

25 Refractive Change after RK Frank Jozef Goes (Belgium)

SIGNS AND SYMPTOMS

This 45-year-old man consulted because of visual deterioration in the Right Eye. In the clinical history we find R.K surgery in 1989 both eyes because of - 4.5 D myopia and Lasik Right eye in 2000 because of consequent hyperopic shift. 2005 Lasik Left Eye because of +3.25. Redo Lasik Left Eye 2006 because of residual myopia and astigmatism. Since several months progressive deterioration of visual acuity in Right Eye:UCVA Right Eye 0.3 best corrected Reye sf.+2, -1.25 axis 67', 0.8. Near vision: Right Eye uncorrected )lO. His major complaint is now fluctuating visual acuity Right Eye near and distance and headache and eyestrain therefore. General Condition; A kind of skin disease allergic type rosacealike-no other diseases, no medication. Examinations of fundus and ocular pressure were normal. The visual field showed no defects. Specular microscopy was normal each eye. Slitlamp examination demonstrated a dry eye syndrome and some squamous blepharitis. Pachymetry Right Eye 560 Micron .

236

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Instant Clinical Diagnosis in OphthalmologlJ (Refractive Surgery) FURTHER INVESTIGATIONS Differential Diagnosis Discussion

This patient w as relatively good corrected until the last two years .He w as 16 years spectacle free after radial keratotomy ,and again helped with Lasik in both eyes. N ow we had to decide on the treatment choice ~a La sik enhancement- spectacles-contact lenses or a refractive lensectomy.spectacles can be excluded since unacceptable-contact lens option is lU1fealistic because

of the d ry eyes and blepharitis.Remains refractive lensectomy;this option is rejected because of the patient's age45 yea rs. H e h as still some accommodation and a lens exchange could be an option in 10 years. At that time Accomodative or Multifocal IOL's will have improved and then his acconunodation would be wa y down from now.

So we decided on Lasik enhancement. First we had to make sure that medically speaking this was sa fe; the p ach ymetry was still 560 micron and specular microscopy was perfect;2200 cell/mm2 Then we had to decide on the program: we know that sometimes after RK due to corneal edema v isual acuity fluctuations may occur. That's why we performed three subjecti ve refraction measurements on different tjmes of the day and periods; no important

differences in topography and refrac tion occurred. The oblate cornea was demonstrated on atlas measurement. Wavefront measurement demonstrated an important coma such as after RK. We programmed a 6.5 treatment zone since the scotopic pupil was 6.0 mm .

238

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Inst ant C/illica [ Diagllosis in Ophtl1a [m o[ogtJ (R efractiv e SlIrgenJ)

TREATMENT Lasik enh ancement in an eye alter prev ious Radial Keratotomy Opening of the Lasik flap was very di fficult; the adhesions were very strong and using the Storz instrument manipulator elevator we had to cut the fla p loose in the different segments; then afte r ca relulliftin g we could open the flap completely, perform the laser treatme nt, reposition the flap after readjusting the different corneal segments as a pizza pie and put a bandage contact lens. Next day the CI was removed and the Ucva was already 0.6 \vith a clear cornea.

One week after surgery the topography was much more regular. Prognosis

We have experience of Lasik after Radial Keratotomy in more than 52 eyes; all d id well although sometimes, like it was the case here, some incisions opened. The treatment - primary Lasik or enhancement has to be done delicately and carefully and is still possible to perform an enhancement as we d id here. A contact lens is a mllst for at least one day. We are aware of the fact that the condition may be come unstable aga in after some years but in the meantime patient is helped a lot.

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Fig. 4: Topography

241

26 LASIK Complications and Management Yan Wang, Wenxiu Lu, Kanxing Zhao, Jinling Yu, Jianmin Gao (China)

Although the incidence of laser in situ keratomileusis (LASIK) complications has been decreasing with improvements in microkeratome technology and more sophisticated, some complications can stil1 occur and may result in permanent sequelae and visual impairments. Kn ow]edge and experience may minimize the incidence and reduce the risk of many potential complications. This chapter will focus on common complications and their Risk factors, prevention and management. MICROKERATOME-RELATED AND FLAP-RELATED Irregular Cap IFlap

Risk factors: • Physical obstruction passage of the micro keratome (Lid speculum, lashes drapes or debris conju nctiva, etc.). • Loss or poor suction. • Poor blade quality. Prevention • Good maintenance for microkeraton1e, meticulous attention to microkeratome assembly. • Signs for sufficient pressure and good suction. Measure intraocular pressure \,v ith a tomometer. The patient's vision dimn1ed and pupil dilated slightly . Palpate the cornea for firmness. The ring of suction grasps eye globe firmly. • Check the blade carefully.

Management: Depend on the extent of the uncut flap• If the flap's size is not large enough and irregular, stop the procedure, reposition the flap and reschedule the surgery 3 to 6 months later. • After the flap is replaced, flatten and dried it carefully. Tr y to rep lace any piece to the original position and place a bandage soft contact lens. 242

Button hole: Ring-shaped flaps with a central hole or thin area.

LASIK Complicatiolls nl1d Mmrngemell t

LAS IK complications

. Keratomerelated Inability to seat suction ring Inadequate

suctionl Loss of suction

Incomplete keratome pass Chemosis subconjunctival hemorrhage

+

i

+

Flap-related

Excimer laserrelated

Healing/infection! inflammation

Irregular capfflap incomplete flap

Decentered ablation

Epithelial defect f Corneal erosions

Thin flapl Epithelial tearl Button hole

Free cap Full thicknessl AC penetration Trauma tiC flap tears

Perioration - Flap striae of anterior chamber (AC)

Improper focus or improperly registered ablation

Misinformation ablation Ablation of nasal edge flap Astigmatism regularl irregular Undercorrectlonl Overcorrection Central island

Epithelial ingrowth

+

Others Dry eyes Glaucoma Ectasia Optic neuropathy

Reaction inflammation

~

~~'~c NSDIK Interface inflammation

Depos its metallicl lint I lipoid , etc Infections keratitis Neurotrophic epitheliopathy

Fig. 1: Complications classification

Fig. 2: Irregular flap with scar formation

243

Instan t Cli nical Diagnosis in OpllthalmologtJ (R efractive SlIrgenJ) Risk factors: o Lost suction d uring the proced u re. o Blade imperfections. o Steep corneal curvature (460 ). • Previous ocular surgery. Preve ntion: • Scrutinize extremely steep corneas or keratoconus \,vith topography. • Use a small suction ring o n a steeper cornea with K46D . o Use femtosecond laser for the patien ts with steep cornea.

M anagem en t: o In the cases with full thickness hole or a thin and irregular cap, laser ablation should be aborted. Replace the flap and recut 6 months later. o In the case of a thin flap wi tho ut b u tto n hole, abort the ablation or proceed with ablation if the rid ges are outside the 5 nun to 6 mm zon e. • Place a bandage contact lens. Free cap: Free corneal flap withou t a hinge. Risk factors: o Very flat (410) corneal curvature. • Suction is insufficient. • Suction ring is sma ll for the cornea. • A narrow hinge. o

Incorrect adjustment of the stopper device of the microkeratome.

Preventi on: • Proper microkeratome assembly. • Using a large suction ring on the fl at cornea to have a larger area of cornea been exposed to th e microke ratom e blade. o Replace the flap carefully if the wid th of the ring is narrow.

M anageme n t: • Find the cap on the surface of the cornea or microkeratome. o The cap is rep laced with the stromal surface down after ablation. o Cap must be in aligning the preplaced corneal mark and a few minutes should be taken to ensu re ad hesion wi th stromal bed. DISLODGED FLAP

Ri sk factors: • Poor flap adherence in the stroma. o Mech anical disrup tion (blinking, eye rubbing) in the first 24 hours afte r the surgery. • Patient squeezes the eye lids w hile the d rops and speculum is removed. • Trauma. 244

LASIK Complications alld Management

Fig . 3: Thin flap with corneal scar

Fig. 4 : 4DLK with central inflammation and striae post-LASIK

245

Installt Clinical Diagnosis in Ophthalmology (Refractive SlIrgenJ) Prevention: • Care should be taken while r en1QVe drops and eye lid speculum away from the eye. • Protection with glasses at firs t few hours or days. • Prolonged drying time. • Avoid eye rubbing and tra uma.

Management: • Treat as emergency . • The flap should be repositioned as soon as p ossible to prevent formation of fixed folds and epithelial ingrowth. • Place a bandage contact lens. Flap s triae : Wrjnkles, whicll are cl ass ifjed into two types : Faint striae (microstriae) and macrostriae.

FAINT STRIAE (MICROSTRIAE)

Risk • • • •

fa ctors: Thin flap, irregular flap . Epithelial defects or ingrowth. H igh myopia with deep ablations . Cut flap to retract towards the hin ge

Preven tion: • Flap is well seated especially for h igh myopia. • Gentle flap manipulation. • Prevent epithelial defect and ingrowth. Management: • If vision is affected, flap should be lifted , refloated and repositioned • If vision is not affected, none requjred .

MACROSTRIAE

Risk • • • •

246

factors: Misalignment of corneal flap. Flap desiccation and contraction. While removing the drapes, eye speculunl, etc. Patient rubs the eye.

Preven tion: • Proper positioning of the flap. • Prevent the location of the flap while removing the eyelid speculum and drops. • Use eye protection.

LASIK Complications and Management

Fig. 5 : Epithelia! ingrowth at interlace post-LASIK

Fig . 6: Epithelial ingrowth at interface post-LASIK

247

Ill st allt Clinical Diagll osis ill Opl.thalll1ology (Refractive SlI rgery) • Avoid eye rubbing and trauma. • The flap should be realigned ca refully at the marks. Managem ent:

• Gentle refloati ng of the flap followed by sweeps of a mois t sponge. • Use a parallel direction or a cen tral-to-peripheral radial technique. • Secondly epithelial wrinkles may not smooth out immediately, they will fade away after a few hours. • More than 3-5 minutes air drying ti me to have good adhesion. • Epithelial debridement over the w rinkled area may be helpful for the longer-standing folds . EXCIMER LASER-RELATED Decentered ablation

Risk • • •

facto rs: Eye drift during ablation. High amount of correction attemp ted. Patient's head or fixa tion is not at right position or have a high amount of kappa angle. • Ablation without eye tracker.

Preventi on

• Patient's head at right position. • Ask patient contin ue to fi xate on p roper visual target. Ablation should be centered on the line of sight. • Ensure the automated eye tracker engaged properly and remain aligned. • With iris registration. • Stop ablation immediately if the patient can not have good fixation. Management:

• Masking techniques to expand the ablation zone. • Retreatment with a small diame ter ablation zone at the edge of the original optical zone in the opposite direction. • Topography linked or wavefront-guided laser ablation is better options. UNDERCORRECTION, REGRESSION

Risk • • • • • 248

fac tors: Refractive stability is not good. High m yopia correction. Flatter preoperative keratometry « 43.5D). Smaller ablation zone. Less transition zone with small optical zone. Higher h umidity in the laser room and greater humidity of the stromal bed.

LASlK Complicatiolls and Managem ent

Fig. 7: Contact lens wearing for 6 months post-LASIK

Fig. 8: Corneal viral infiltration post-LASIK

249

Instant Clinical Diagnosis in Ophthalmology (R efracti ve Surgery) • The masking and va ulting effect of the fl ap . • Stronger wound healing (stromal synthesis and epithelial hyperplasia). • Ia trogenic keratecsia. Prevention:

• A stable refraction before the LASIK p roced ure. • Use newer laser system and nomogram. • Have good protocol fo r abla tion. • Keep proper hu mid ity in the room and avoid more tearing and

hydration of the stromal bed. • Topical steroids may be useful. Management:

• Flap lifting and reabla tion teclmique are advisable. • Ensure regression has stabilized and js not due to progressive ectasia . • Ensure the flap and abla tion depth n ot exceed 50% of the initia l preoperative thickness or the residual stroma l at least 250 m . • Choose surface ablation in son1e cases.

CENTRAL ISLAND

Risk • • • • •

factors: Old software in broad beam laser sys tem. Irregular profile of th e delivery beam. Uneven stromal hyd ration. Large ablation diam eters and high myopic correction. Temporal degrada tion of the laser optic.

Prevention: • Choose better laser abla tion pattern. • Modulate laser softvvare. • Avoid uneven stromal hydrabon during ablatjon . • Check the laser system carefull y before the surgery. Treatment:

• Give small optical ablation after lifting original flap according to the corneal topography. • Topography linked laser treatment or wavefron t guided ablation treatn1ent.

HEALING/INFECTION/INFLAMMATION Epithelial Ingrowth

250

Risk factors: • Flap misalignments and poor flap edge apposition. • Ep ith elial abrasions and defect at the flap edge.

LASIK Complicatiol1s and Management

Fig . 9: Metal remnants from the blade in the interface

Fig. 10: Interface remnants with LASIK procedure

251

Instant Clinical Diagnosis in Ophthalmology (Refractive SlIrgenJ) o

o o o o

Spillover of laser ablation at the bed margins and epithelial tags at the bed margins on retreatment. DLK. Loca l corneal edema. H yperopic LASIK when the ablation strikes the edge of the fla p . Postoperati ve flap slippage.

Prevention: o Meticulous attention to proper realignment of the fla p edges. o Limiting tissue manipulation, avoiding touching the lamellar bed with cornea l epithelial. o Avoid epithelial defect. o Irrigating stromal interface. Any epithelial includ ing tags and debris should be cleaned away from the interface. o Use 0.12 mm toothed forceps no t a spa tula when lifting a fl ap in enhancement LASIK. o Epi thelial defects with bandage contact lens. o Consider surface ablation (Prk-LASE K and EpiLASIK) rather tha n LASTK in patients w ith a history of poorly ad herent epithelium.

Management: o A small nest, no progressive of epithelium in the periphery can be monitored. o

o

o

o

If the epithelial ingrowth exceeds 2 mm an d progresses, removed immedia tely to prevent extension of cell and stromal melting. Lifting the fla p and scrape both the bed and cap wi th a dry surgical spur o r a blunt PRK spatula and clean the epi thelial remnants at the ed ges of the flap . A bandage contact lens should be required. If epithelial ingrowth reoccurs, short pulses of laser (5-10 pulses) PTK on the bed and cap may clean the remaining epithelial cell. In case of recurrent epithelial ingrowth, absolute alco hol swabbed sponge can be stroked on the bed and cap, 1-2 mm beyond the ingrowth area for 20-30 seconds, following by irrigating with BSS.

DIFFUSE LAMELLAR KERATITIS (DLK)

Risk factors: • Meibomian glands secretions. • Bacteri al endotoxin . o Toxin originating from the biofilm in the sterili zer. o Powder from gloves. o Metal particles or wax from the blade. o Ep ithelial defect. o Excessive femtosecond laser energy . 252

LASIK COII/plications alld Mallagell/ ellt

Fig . 11 : Neurotrophic epitheliopathy

253

Instant Clhlical Diagnosis in OphthalmologtJ (Refracti ve SlIrgenJ) Prevention: o Eyelids shou ld be draped to cover meibo mian glands orifices and eyelashes. o Cleaning off the deposition fro m microkeratome blade with distilled water or moist sponge. o Motor tip should be checked for oil. Conta mination. o Using powder-free surgical gloves. o The fl ap edge should be dried before lifting. o Properl y adjust the energy level of fe mtosecond laser or moist sponge.

Management: DLK has been staged for the purpose of trea tments. Error! Bookmark not defined. Stage 1: White granular cell s in the periphery of the lamellar flap,ou tside the visual axis.

Stage 2: White granular cells involving the visua l axis. Stage 3: Dense, white, clu mped cells in the visual ax is with relative clea ring of the periphery. Stage 4: Severe lamellar keratitis. Stromal meltin g and permanent sca rring is the likely resul t. o

o

o

o

o

In stage 1 and 2, intensive corticosteroid therapy should be given w ith prednisolone acetate 1% every hour for first few days. In the stage 3, the flap is lifted and washing the interface with BSS.

Topica l corticosteroids need to be continued. In the stage 4, care must be taken, since lifting the flap may be useless and loss the corneal tissue. Potent drops of dexamethasone and prednisolone are recommended no t fl uorometholone. An tibiotic prophylaxis is necessary.

INFECTIONS KERATITIS

Risk factors: o Blepharitis or dacryocystitis o Dry eyes, extended wear soft contac t lens. o HIV infection. • Entropion and trichiasis. o Use contaminated drops. 254 0 Epithelial defects.

LASIK Comp lications and Management Prevention:

• Treatment of underlying blepharitis and d acryocystitis. • Preoperative and postoperative treatment of dry eye and any infection in the eye. • Use topical antibiotics pre and postoperation. • Povidone iodine preoperation. Management: • Sta rt with frequent broad -spectrum topica l an tibiotics. • If it infiltrates in the flap interface, lift the flap and irrigate stromal bed wi th antibiotic solution, make microbiologic evaluation with scraping of the infiltrate. • If antibiotics treatment fa ils to halt the progression or if the flap becomes necrotic, the flap can be removed away. INTERFACE DEBRIS AND REMNANTS

Risk • • • • • • • •

factors: Foreign body from air or makeup. Meibomian secretions. Cotton fibers from the manipulation. Powder from the gloves or debris from the swabs used to clean the interface. Metal fragments from the rnicrokeratome blade. Mucus from the ocular surface. Blood from cut pannus. Excessive irrigation.

Prevention • Avoid face or eye make up on the day of surgery. • Trea t meibomian gland dysfunction preoperati vely . • Irrigate the flap interface w ith balanced sa lt solution properly. • Use the suction lid spectrum. • Use the Meracel sponge before lifting the flap.

Management: • Significant debris should be removed and irrigated and surface should be wiped ca refully with a moist sponge. • Avoid prolonged or repeated irrigation of the flap. • Check the patients wlde r the slit-lamp. 255

Instant Clinical Diagnosis in OphthallllololP} (Refractive SlIrgery) OTHERS Dry Eye/Neurotrophic Epitheliopathy

Risk factors: • Blepharitics and meibemianitis. • Abnormal schimer's test or break-up time result and tear-film dysfunction. • Low h umidity environment. • Aged people or with extended contact wea ring. Prevention:

• Careful screening of patients wi th dry eye. • Use non-preserved tea r substitutes in the pa tients who have slight symptoms or sign of d ry eye pre or postoperative period. • Avoid LASIK in the patient with severe symptoms of dry eye. • Perform a nasal hinge fla p or use surface ablation. • Avoid LASTK p roced ure with cornea and ocular surface problem. Ma nagement: • Determine exactly contributing factor to the d ry eye and resolve it and trea t it properly. • Use non-preserved artificial tears drops during the day and lubricating gels a t nigh t. • Av oid low humidity place and fin d th e way to hu m id ify the environmen t. ECTASIA

Risk • • •

factors: Thin cen tral cornea on preoperative pachymetry. Keratoconus, subcl in ica l keratoconus, o r fo rme fruse kera toconu s. A residual postoperati ve stromal bed less than 250 m or 50% of the original thickness. • High myopia correction.

Prevention: • Avoiding preexisting ke ratoconus or ke ratoconus suspects. • Measure the corneal thickness preoperatively and intraoperative ly using

pachym etry. • The min imal thickness of residua l stroma should more than 250 m or 50% of the original thickness. A range of 280-300 m is recommended.

256

LASIK Complicatiolls alld Mallagement

• For low or moderate myopia, the surface ablation procedure can be chosen if there is high risk of ectasia. • For extrem ely high myo pia, phakic IOL, refractive lens w ith TOL or combination of LASIK with other correc tion can be used. Management: • Use rigid gas permeable (RGP) contact lenses. • Intrastromal corneal rings may be successful in improving vision. • Penetrating keratoplasty can be used if all above fail. ACKNOWLEDGEMENT

The authors wish to recogn ize the contribu tion of Dr Zhen Xu ,Tianjin Eye Hospital, Tianjin Medical University ,for her assistance in prepa ring the photographs.

257

27 Cross-linking Plus Topography-guided PRK for Post-LASIK Ectasia Management A John Kanel/opoulos (Greece)

LASIK SURGERY has become a medical phenomenon throughout the world over the last 20 years. It all started in the laboratories of the University of !Crete in Greece and under the direction of loannis Pallikaris, MD in 1988. It was the natural evolution of the boom in automated lamellar surgery that was popularized in South America that same decade and the introduction of cornea shaping by the excimer laser. It has become one of the most common procedures humans undergo worldw ide, and for sure, the most common elective procedure that medicine offers today. Throughout the yea rs there have been several lessons in LASIK that have been learned by refractive surgeons. One of those has been the limitation to the amount of laser ablation that the human cornea can withhold, before changing its biomechanica l properties. Post-LASlK ectasia has been recognized as a serious complication from th e early years of LASIK development. Throughout this time several safety "parad igms" have been arbitrarily communi cated through meetings and publications establi shing the safety margin for residual stroma bed. Even today procedures performed yea rs ago may complicate and develop ectasia. In most cases a very small residual stromal bed is usually the isolated contributing factor along with irregular cornea topography preoperatively suggesting forme fruste keratoconus. It remains though quite a cha llenge to explai n wh y some "uneventful"procedures that had perfect preoperative topography and well documented "enough" residual stromal bed thickness may develop keratectasia. As a cornea surgeon Thave had the opportun ity to treat severa l patients with this dreaded complication in the past. The in itial treatment in the 90's was penetrating keratoplasty w hen the ectasia could not be rehabilitated with RGP contact lenses. In the early 2000's INTACS became a potential option. I have personally have not had a good clinical res ults with INTACS in regard to their stability in ecstatic corneas. In 2002 I became involved with collagen cross-linking with the use of UVA irradiation and topical riboflavin after I became familiar with the wo rk of Seiler Wollensak and Spoel in Dresden and Zurich with this applica tion. This is the case report of the first patient T 258 encountered:

Cross -linking Plus Topography-guided PRK for Post-LASIK

~'_IOI

w..

k 0(j)(j)@ or 0(j)(j)@

Fig. 1: This display 01 topographies depicts the following: 1. The cornea topography of this case when first seen by the authors with central cornea ectasia and mid-periphery flattening as an effect of the INTACS thaI were present. At this point BSCVA was 20/200 2. The cornea topography here is 2 months following the removal of INTACS and 1 month following UVA collagen cross-linking .. The central steepening is still present and the effect of the INTACS removal is appreciated compared to the previous image mostly at the mid periphery, that appears steeper now. At this point BSCVA was 20/200 3 . The lower row image in the center is an estimated cornea topographic ablation pattern as a laser treatment plan of the topog rap hy-guided procedu re that took place in the case. It is notable that this ablation pattern is highly irregular with "deeper" ablation plan just inferiorly and right to the center, that matches though the central cornea irregularity in the previous topographies. 4. The cornea topography here is 6 months following topography-gu ided PRK . The central cornea appears more regular and much flatter. At this point BSCVA and UCVA is 20/20-. 5. The lower row image on the left is a compa rison map. Thi s map depicts the difference of subtracting the cornea topography 4 (final result) from the cornea topography 1 (o riginal state of this complication when encountered by us). The difference resembles impressively the topography-gu ided ablation pattern (next image to the right) demonstrating effectively the specificity of this treatment in reducing the pathogenic cornea irregularity, which we theorize that contributed in the drastic improvement of BSCVA

259

Illstallt Clillical Diagllosis ill OphtlzalmologtJ (Refractive SlIrgenJ)

A 29-year-old patient tha t had underwent uniocular LASIK for the correction of m yopic astigmatism 3 years ago. His initial UCVA was 20 /80 and his BSCV A was 20/20 w ith a refraction of - 2.00 -175 x 85. Three months post-LASIK he began experiencing regression with myopia and astigmatism to the point of UCVA 20 / 200 and BSCVA 20/80 with - 3.50 - 2.00 x 120. Based on irregular topograph y and the loss in BSCV A, the treating physician soon recognized that a mechanism of ectasia had begun. Because tltis was not functionally correctable w ith spectacles or contact lenses, the decision was made to implant intracorneal ring segments for the management of this complica tion. Unfortunately, the patient's UCV A remained 20/200 and BSCVA 20 / 100. The treating surgeon recommended cornea transplantation as the next step. My initial evaluation of the pa tient was made 11 months post-LASIK and 3 months after intracornea l ring implantation. Corneal thickness-by Orbscan (Bausch & Lomb, Rochester, NY) and ultrasound pachymetry- was 410 ~m at the thinnest point, and the endothelial cell count was 2,750 cells per mm' (Noncon Robo; Konan Medical, H yogo, Japan). OPTIONS FOR TREATMENT

We have had poor long-term outcomes with intracorneal ring segments in post-LASIK ectasia, a fact which we discussed with the patient. We discussed the benefits and risks of corneal transplant, as well as combined ultraviolet radiation and riboflavin treatment in order to achieve collagen cross-linking and biomechanical stabilization of the corneal ectasia. We then obtained patient consent to remove the failed intracorneal ring segments. I trea ted his cornea with a single app lication of UV-A radia tion at 3 mW /c m' for 30 minutes (KeraCure; Priavision, Menlo Pari, Cal combined with 0.1% ribollavin ophthalmic solution. This treatment was performed after removing the corneal epithelium with 20% ETOH placed on the surface for 30 seconds. The ribofla vin solution was applied for about 2 minutes in order to soak the stromal bed and protect the iri s, crystalli ne lens and retina from UV irrad iation. One drop every 2 minutes was ap plied during the 30 minutes of irradiation. A bandage contact lens was placed on the cornea fo r 5 days, and the patients was treated with topical olloxacin 1% (Oculi ox; Allergan, Irvine, Cal and prednisolone acetate 1% (Predforte, Allergan) four times a day for 10 days. The bandage con tact lens was removed at day 4, following complete re-epithelialization. IMPROVEMENT IN VISUAL ACUITY

At 3 months, the patient's UCVA improved fro m 20 / 400 to 20 / 70 and his BSCVA improved from 20 / 200 to 20/40. The refrac tion changed fro m - 4.50 - 4.50 x 120 to - 4.50 - 4.00 x 115, and cornea l topography changed as seen. 260 The stability of these para meters and the corneal topography between months

Cross-iiI/king Plus Topography-guided PRK for Post-LASIK

Fig.2A

Fig. 26

OABSCAN

.-, .,

I.A/oF'R()P()lAOS. a.~

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_~.~. 2;t1l; ' 2 PM

0<

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261

Instant Clinical Diagnosis in Ophtlzalmologtj (Refracti ve Slirgenj)

1 and 3 of this treatment, encouraged us to proceed with topography-guided PRJ<. We sought to reduce the irregular astigmatism and attempt to provide the patient with visual acuity no t requiring spectacle or soft contact lens correction. Because the patient's corneal thickness was 410 ~m, we were able to trea t his full spectacle correction using the Allegretto Wave excimer laser (Wavelight, Edangen Germany) topography-guided customized ablation treatment (T-CAT) software. After placing 20% d ilution of EtOH on the corneal surface for 30 seconds and subsequent epithelium re mova l, T performed laser treatment. A bandage contact lens was placed for 5 days and the patient was trea ted again with ofloxacin and prednisolone fo ur times a day fo r 10 da ys. The bandage contact lens was removed at day 4, fo llowing complete re-epithelialization. One month after topography-guided treatment, the patient's UCVA was 20/20- and BSCVA was 20/20 with a refraction of + 0.50 - 5.0 x 160. The corneal endothelium count has remained stable at 2,700 cells per rnrn 2 11" patient complained of night vision symptoms of halos and ghosting. The patient is now at 34 months postoperative and enjoys UCVA of 20 /20 with some m ild n igh t vision problems and corneal topograph y as shown in Figure 1. One can also appreciate the d ifference map between pre and post topography-guided trea tment, as welJ as the actual ablation profile that was used for the treatment. TREATMENT OF IATROGENIC KERATECTASIA

Different techniques have been suggested for the trea tment of iatrogenic keratectasia w ithout satisfactory outcomes either biomechanically or visually, w ith the patien t's journey most frequently end ing with pentrating com eal graft. Reports of the use of riboflavin/UV A corneal cross-linking have been shown to slow down keratoconus and progressive iatrogenic ectasia. During the past 3years r we have h ad extensive experien ce with customized

topograph y-guided excimer ablations which we have presented and reported. This customized approach can, in our opinion, address the extreme cornea

irregularity that these cases may have and enhance visual rehabilita ti on . This was the first report of post-LASTK ectasia treatment using a combination of UV A collagen cross-linking to stabilize the corneal biomechanics, followed by surface excimer laser ablation for visual rehabilitation. Remarkable corneal stabilization, together with full visual rehabil itation, leads us to believe that this approach may have a wider application in the near future. Considering the tremendous burden on the patient in everyday life, as well as the medicallegal iss ues involved in such a complica tion of electi ve excimer laser refractive

surgery as iatrogeniC kera tectasia, we fee l that the combined procedure discussed here is now a va luable alter native to therapeutic cornea transplantation and should be considered in any case that enabl es the application of this treatment. 262

Cross-linking Plus Topography-guided PRJ( for Post-LASIK

.0ORBSCAN 01_.... _ MOo,,,"

Floot

LAMPROPOUlOS . ~

'02'" 00 - 9I5J!t5 , 10:11 :19At.1 ~~~~~-.... ~ -~

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F...:!.:! .......

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......

..

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Fig . 2E Fi gs 2A to E : A 28-year-old male physic ian underwent LASIK in November 2002. for

- 5.50 - 1.50 x 015 (20/20) 00 and - 4.25 - 1.25 x 0168 (20/20) OS. Four months following surgery, the uncorrected vision was 20/25 in both eyes. The manifest refraction was +0.25

-1.25 X090 (20/20) 00 and was + 0.25 - 0.25 x 110 (20/15) OS but the topography suggested the early development of ectasia. At this time , the keratometry readings were 38.75/39.25 x

22 (00) and 38.50/39.00 x 162 (OS) and the pachymetry readings were 375 microns (00) and 407 microns (OS) . The patient returned on February 21, 2005, with an uncorrected vision of 20/40 in the right eye and 20/20 in the left eye . A manifest refraction in the affected right eye of - 0.75 - 3 .50 x 09 1

(20/30), and + 0.75 - 0.50 x 0128 (20/20) OS. The topography at this point suggested the presence of ectasia only in the right eye (A) and Orbscan (C). Two years following UVA collagen cross-linking with refractive error of - 2.00 - 3.00 X 0170 (20/30). The uncorrected vision in the affected right eye was 20130, with a manifest refraction

of - 1.50 - 1.75 x 073 (20/20) . The Orbscan at this point is (0) and the comparison (8) and (E) of pre and post UVACCL appearance of the posterior cornea elevation is self explanatory

263

Instant Clinica l Diagnosis ill Ophtlznlmologzj (R efractive Surgery) It is though in my opinion necessary for the clinician to take special consideration in treating these cases. By no mea ns can the excimer laser be considered an instrument for enlIDetropia in these p atients in a fas hion similar to routine LASIK and / or PRK refractive cases. The treatment shou ld be directed towards " normalizing" the cornea s urface and allowing for improvement of BSCV A. There is an obvious danger in thinning these corneas to much by giving in to the "temptation" to correct the refractive e rror. This was the in itial desire of these patients anyway. Having no previous work to relay on, I arbitrarily took a con servative approach to the matter and limited the refractive laser treatment to the nlinimulll and never to allow re moval of over 50 microns th e thinnest cornea. Severa l cases followed this success story over the last 5 years. We have presented a case series at the AAO annual meetings in 2005 and 2006.

A Similar Example Follows

A 28-yea r-old male physician underwent LASIK in Novembe r 2002. for - 5.50 - l.50 x 015 (20 / 20) 00 and - 4.25 - l.25 x 0168 (20 / 20) OS. Four months following surgery, the uncorrected vision was 20/ 25 in both eyes. The manifest refraction was + 0.25 - l.25 x 090 (20 / 20) 00 and was + 0.25 - 0.25 x 110 (20 / 15) OS but the topography suggested the early development of ectasia. At this time, the kera tometry readings were 38.75/ 39.25 x 22 (00 ) and 38.50/39.00 x 162 (OS) and the pachymetry readings were 375 microns (00) and 407 microns (OS). The patient returned on February 21, 2005, w ith an uncorrected vision of 20/40 in the right eye and 20/20 in the left eye. A manifest refraction in the affected right eye of - 0.75 - 3.50 x 091 (20/30), and + 0.75 - 0.50 x 0128 (20/20) OS. The topography at this point suggested the presence of ectasia only in the right eye 2A and Orbscan 2C. MINIMAL CORNEAL THICKNESS

264

Specia l emphasis must be taken to ensure minim al cornea l th ickn ess preoperatively because of potential cytotoxic effects of VV A on corneal endothelial cells. Previous experimental studies in rabbit corneas have investigated dose-dependent cytotoxicity to the corneal endothelium. surface irrad iance according to the protocol described herein, may not be used in corneas thinner than 350 ~m. This mimimal thickness should also be respected in human corneas. The laser treatment must be applied with caution because more rigid corneas m ay h ave a different ablation depth-per-pulse than th e untreated on e. Indeed, it appears to resu lt in over-corrections when these corneas are treated with excimer laser vers us a normal PRK or LASIK procedure. For this reason, O Uf recommendation is to use 75 to 80% of the measured sphere and cylinder as a correction parameter when p lmming the abla tion w ith T-CAT software. Larger comparati ve studies and longer foli ow-

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Instant Clinica l Diagnosis in Ophtha lm ologtJ (Refractive Surgery) up is necessary in order to validate the long-term efficacy of this combined treatment with UV / riboflavin followed by topography-guided excimer laser treatment. The refractive and topographic stabi]jty of more than 3 years, however, appears to validate this minimally invasive treatment of iatrogenic keratectasia an d leads us to believe that it may have an even wider application in the nea r futu re. We have utilized this mod ality in idiopathic kera toconus cases as well with similar results. As a cornea surgeon I do feel that UV A eeL maybe the single most important introduction in cornea surgery and keratoconus and cornea ectasias in general over the last 25 yea rs. If our initial cli nical experience holds true I the future fo llow up it ma ybe be able to Significantly minimize the necessity for cornea transplanta tion in ectatic cornea disorders. ean LAS IK " regressions" be a form of ectasia? I wo uld like to present another case to you: Six yea rs ago, a 34-year-old female underwent LASIK for - 11.00 0 of myopia . Ouri ng the procedure a Moria M2 (Mor ia; An to ny, France) microkeratome was used to crea te a 125 !lm flap (calculated with subtraction pach ymetry) and an Allegretto 200 Hz laser (Wavelight; Erlangen, Germany), with a p lanned 6 mm optical zone, was used to conserve tissue. Total treatment centrally was planned to 130 !lm. The resid ual cornea bed measured 320 !lm. For 5 years after the surgery, the patien t was satisfied, and plano, w ith 20/20 visual acui-ty_ The patient now presents 20/40 UeVA and 20/20 BSeV A, with eyes measuring - 1.50 0 and - 0.75 O. No ectasia is evident on the topograph y and Oculus Penta cam (Oculus Opti kgerate GmbH, Wetzlar, Germany) . The patient's preoperative measurements: Central cornea thickness is approximately 460 !lm. I have relati vely extensive experience in cases like this, as I have seen many patients trea ted for high m yopia in the pas t. None of my cases have developed an y corneal I have seen this type of LASIK regression many times in the past and have add ressed the problem several d ifferent ways. In some cases, I have re-Iifted the flap to do an additional enhancement, after measuring the fl ap thickness intraoperatively in order to avoid Significantly reducing the postenhancemen t resid ual stromal bed_(Since 2000, I have tried to adhere to the guideline of 270 !lffi for residual stroma fo llowing LASIK.) Another potential method of treatment for this patient wo uld be to perform a cus tomi zed retrea tment with aspherici ty adjus tme nt as an ad ditive (Wave]jght400 Hz Allegretto Wave Eye-Q laser; Wave light Laser Technologie AG, Erlangen, Germany). I wo uld include a treatmentgoal of - 0.50 0 for the Q value (asphericity), in ordertoreduce spherical aberrations that are typically induced d urin g the correction of high m yopes. The hope is that the postenhancement Q value would be less positive. Through past experience, we have learned that correction of - 10.00 0 shifts the 30° asphericity of the 266 cornea from an average - 0.30 0 to ± 2, therefore ind ucing significant spherical

Cross-linking Plus Topography-guided PRJ( for Post-LASIK

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267

Instant Clinical Diagnosis in Oplttltallllologtj (Refractive SlIrgenj) aberrations. In the case of this patient, I chose not to use either of the previously mentioned options. Considering that the cornea was stable, I pulled from my experience with UV A collagen cross-linking as a means to rehabilitate ecta tic corneas after LASIK. I proposed that the patient was experiencing a late biomechanical shift of the thinned cornea. The patient and I discussed the option of cross-linking the cornea and then enhancement, if necessary. I determined that performing an enhancement first may not be successful if the refrac tion continued to regress in the future. We therefore decided to proceed with collagen cross-linking with the PriaVision device (PriaVision, Menlo Park, California) for 30 minutes in conjunction with 1% riboflavin solution applied every 2 minutes to the surface of the de-epithelialized cornea. Initially the patient was unsa tisfied and experienced pain and discomfort for the first 10 days while the epithelium healed. That changed at 1 month follow-up, however, when we d iscovered her UCVA was back to 20/20 and her refractive error was - 0.25 D. In the end, our patient achieved a VA of 20/ 15. I w ould therefore use this case to confirm previous reports on the biomechan ical changes of the cornea following LASIK, and establi sh a significant biomechanical effect of the UV A cornea cross-linking to the operated cornea-with a change in the posterior cornea contour centrally and paracentrally. Figure 3C show a comparison map of the posterior cornea surface by the Wavelight Oculyzer (Pentacam). The first map on the left is the pre-UV A CCL posterior cornea surface devoid of any signs of ectasia. The middle map is the same posterior surface one month following UVA CCL. It is evident that there has been been a fla ttening change, more evident in the difference map on the right, The mid-pe riphery of the posterior cornea shows a "flattening" effect confirming the biomechanical change in this cornea following the collagen cross-linking. This effect appears to have corrected the late regression of - 1 Diopter. I believe this case shows that any surprise regressions noted-even yearsafter LASIK could be biomechanical changes of the cornea, and could be treated by this minimally invasive alternative. Figures 4A and B decribe a similar case: These are Pentacam comparison maps of a 27 y / 0 female that underwent LASIK for - 10 au 5 years ago. She had an enllancement fro - 1.00 au 3 years ago and deteriorated again to 1.50. Instead of enhancement she underwent UVA CCL and the refraction regression reversed to plano. The pentacam comparison of pre and post UV A CCl for the sagittal curvature front and posterior cornea elevation shows the biomechanical change of cross-linking that produced the regression reversal.

268

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269

28 PRK for low to Moderate Myopia Michael O'Keefe, Caitriona Kirwan (Ireland)

INTRODUCTION

In 1983 Trokel demonstrated that the 193 NM wavelength could precisely remove corneal tissue. Initially two laser systems existed, Visx (Santa Clara, California ) and Summit Technology (Waltha m Massac h use t ts). The technology has evolved through animal and human studies to current cli nical practice. Much of the original data came from Europe. However there was resistance and scepticism particularly in academic circles as it was fea red that removing Bowman's laye r would result in loss of corneal transparency. At the time the proced ure was considered to be mainly cosmetic and therefore the original surgeons were pioneers in this area of ophthalmology. Pho to refra cti ve Keratectom y (PRK) involves the use of high energy photons produced by an excimer laser to remove corneal tiss ue and alter cornea l shape. Following the application of excimer laser to the cornea, a number of changes take place. Loss of Bowman's layer and the removal of stromal tissue results in a stromal wound healing response. Immediately follow ing ablation a pseudo membrane covers the ablated area . There is an immedia te epithelia l resp onse with ep ithelialization of the ablated area occurring in about 3 to 5 days and initially comprising 3-5 layers. The new collagen and p roteoglycan forms a pseudomembrane which soon disappears. There is an invasion of inflammatory cells from the tear film. They activa te kera tocytes which form new collagen and a proteoglycan matrix. Fibrocytes also repopulate the stroma. This proteoglycan which gives rise to haze ap pears at one month and is maximal at th ree months. It usually disappears during the first postoperative year. Sometimes it takes m uch longer and may remain indefinitely. Changes in treatmen t profiles, ablati on zones used and the delivery systems have improved both the technique and the results of PRK. Treatment zones have increased from the 4 mm optical zone to 6 mm or greater and many of these treatments include tra nsition zones. The laser beam has changed from the original broad beam to the scanning or spot size beam resulting in smoother ablation zones an d eliminati on of central islands. The initial problems encoun te red included overco rrection or hyperopic shift w hich in some cases times las ted u p to six mo nths pos to pera ti vely. Fortunately, th is was followed by regression and resulted in longer term 270 stable outcomes. Many people experienced night visual problems beca use of

PRK for Low to Moderate Myopia

Fig. 1: Grade 4 haze following LASEK

Fig. 2: Significant reduction in corneal haze in eye shown in Figure 1 following treatment

with mitomycin C

271

Illstallt Clillical Diagllosis ill Ophthalmoloi5'J (Refractive Surgery) the small optical zones and this manifested in glare and poor vision in dim light. There were cornea l changes due to haze which caused permanent scarring in a minority o f patients. Over time, posit.ive changes have occurred resulting in significant improvement in outcome. Unwanted hyperopic shift which was so worrisome to both surgeons and patients is no longer a problem. Haze and myopic regression which were troublesome have been reduced particularly in the treatment of low to moderate myopia. Pain after surgery which for many patients is severe has been modified but has not been elimina ted. Barraquer first described Cryolathe keratomileusis to correct myopia. In the late 1990's a procedure known as laser in situ keratomile usis (LASIK) grew in popularity. Patients who underwent this treatment had a rapid visual rehabilitation and minimal postoperative discomfort. This new form of treatment had greater efficacy in the treatment of higher degrees of myopia. Therefore, PRK was only used for certain specific indications such as thin cornea, narrow aperture, patients with surface corneal problems and patients who requested it (Table 1). Table 1: Indications for LASEK Corneal thickness < 500 11m

Surtace corneal erosions Anterior basement membrane dystrophies Post LA8lK flap complications Re-treatment after LASIK

Younger patients Contact sports

Economics

272

LASIK popularized and established the longer term future of refractive surgery to the point where it has become the most popular surgery in the world to day. Drawbac ks of many refractive surgical procedures over the last 30 years ha ve included their transient popularity, short-term problems and the lack of long-term follow-up. H owever, excimer laser has been the most enduring and most popular of all the refractive procedures that have been performed. We have seen a unique departure in refractive practice with the emergence of conunercial clinics and clinicians are no longer the masters but the employees. The push for high volume has been responsible for the lack of good long-term follow-up data. There a re no long-term prospective randomized studies published in the literature. The retrospective 12 year study by Rajah et al using 4 mm optica l zones and correcting up to 7 dioptres of myopia has shown stability over time. Corneal haze declined and there was no late haze. Night vision disturbance, haloes and glare was a major issue but it was not an unexpected with the s maller

PRJ( for

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optical zones treated. There was no ectasia or other long- term visual threatening complications. The other longer term retrospective study by O'Connor et al reported nigh t visual problems in 35% of their patients and reported as severe in about 2%. 5 mm optical zones were used in these patients. All patients who suffered these symptoms stated that they would undergo the su rgery again. In this study, good refractive stability was reported from 8 to 12 years with an excellent level of patient satisfaction. There have been a number of other studies with shorter term follow-up and all of these studies confirm the safety of PRK. Whilst there are no surgical risks, postsurgical complications such as infection, decentred ablations, haze, halos and glare, dry eyes, ectasia and ptosis are also less frequent than with LASIK (Table 2). Table 2: Complications of LASEK Infection Severe haze

Regression

Ectasia Haloes I Glare

Dry eyes Decentred ablation

Wrong correction Ptosis

Laser subepithelial keratomileusis (LASEK) is a modification of PRK and in contrast to the PRK the epithelial layer is replaced after the laser ablation is performed. Camellin et al first described their tecJu1ique involving the use of an 8 mm laser corneal trephine to create epithelial separation for removal in the treatment of myopia. The trephine is placed on the cornea and rotated through approximately 10 degrees. A special alcohol holding well is then placed on the cornea encircling the epithelial incision. This is filled with a 20% alcohol solution and left in place for 30 seconds. The alcohol is then absorbed with a wet sponge and the corneal surface is irrigated with saline solution. The epithelium is peeled back to 12 o'clock and following completion of the laser ablation the epithelial layer is repositioned on the cornea. In a technique described by Azar's, the 7rnm, semi sharp epithelial marker serves as a trephine. This is attached to a hollow metal handle and serves as a reservoir for a 18% alcohol solution. A button is pressed on the handle which releases the alcohol into the well of the marker. After 25 seconds the alcohol is absorbed with a dry cellular sponge. Loosened epithelium is peeled as a Singular sheet using a dry cellular sponge leaving a flap of epitheliu m still attached to the superior part of the cornea. Following laser ablation, the 273 epithelia l layer is repositioned on the corneal surface.

Instant Clinical Diagnosis in Ophthalmologt) (Refractive Surgen) Shah et al and Azar et al have shown that the plane of cleavage lies within the epithelial basement membrane, between the lamina densa and the lamina lucida. Therefore, there is sufficient basement membrane present to aid in epithelial flap reattachmen t w hich reduces apoptosis and keratocyte activation. Bowman's layer is not disturbed in the initial process of epithelial loosening. However, many epithelial cells are destroyed by the alcohol, even at concentra tion of 20% and thus they do not provide a mechanical barrier. During procedures where the epithelial flap is lost resulting in PRJ( there is less haze and rapid visual recovery compared with the older technique of performing this procedure and the results are compa rable to LASEK. A further modification of LASEK known as Epilasik has been described, whereby an epi-kertome separates the epithelium from the underlying stroma without the use of alcohol. The epithelium is repositioned on the stroma after the ablation is complete, although some surgeons chose not to and discard it. A number of d ifferent mechanical instruments are now available. O'Doherty et al showed comparable visual and refractive outcomes to the alcohol technique with lower post operative pain in the first two hours using the epi-keratome. However, there was a high degree of failure in flap creation with a 30% conversion rate to PRJ(. LASIK has been a magic operation. It is characterised by rapid visual recovery, minimum discomfort and absence of postoperative pain or haze. PRJ( on the other hand results in pain and slower visual recovery and for a long time has been relegated as the procedure for patients who where unsuitable for LASIK. These were patients with large pupils, thin corneas, those who played contact sports and those with small palpebral apertures. Over time, as the number of procedures performed has increased, problems ha ve emerged with LASIK such as button hole formation, free caps, incomplete caps, diffuse lamellar keratitis and the increased potential for keratectesia. LASEK, a modified version of PRJ( has to some extent redressed the imbalance as there induces less discomfort, less haze and has fewer associated severe operative complications. It offers a safer and improved chance of performing repeat surgery into the future. In one of the only studies published, visual improvement after LASEK was significantly slower than LASIK. However visual outcomes at three months postoperatively was similar in both techniques. A number of agents to modulate healing have become popular such as Mitomycin C and steroids. The objective of their use in LASEK and PRK is to minimize regression and corn ea l haze. Ep ithelial removal ac ti vates keratocytes on the corneal stoma and this triggers the production of different collagen which is much less organised than the normal stromal collagen and this may be in turn be a fac tor in the creation of haze. Topical steroids sometimes work to completely or partially removing haze. In some eyes the 274

PRJ( for

Low to Moderate Myopia

reversal in only temporary and in others there is no effect. Why this treatment works in some and not in other patients is not entirely known. It may relate to the type of collagen or indeed the intercellular matrix that is produced. Topical steroids have been used by most refractive surgeons but given that about 20% of patients are steroid responders and may develop glaucoma, ongoing intraocular pressure monitoring is required. Mitomycin C is an alkylating agent which inhibits DNA synthesis. Whilst it has other ocular indications, it has also established itself in refractive surgery where it is used intra-operatively during LASEK and PRJ( treatments of high myopia as a prophylactic measure to prevent the development of postoperative haze. It is also used to treat severe pre existing haze. Concentrations such as 0.03% and 0.02% applied for 20 seconds following ablation are used and there has been no report of short term corneal complications. Other medications such as ascorbic acid have been used both in vitro and in vivo. They have an antioxidative effect and inhibit corneal hydrogenase. Patients require large oral doses and there are no proper studies to show that they are of definite benefit. CONCLUSION

PRJ( was the first universally popular refractive procedure for the treatment of low to moderate myopia. Improved surgical technology resulted in the development of LASIK. The introduction of LASEK, a modification of PRJ( once again has popularized treatment on the surface of the cornea. Long term outcome is one of the frequently asked questions by patients contemplating laser surgery. The 12 years studies show stability, safety and a high degree of patient satisfaction in patients treated for low to moderate myopia by PRK. There are no comparable long-term studies published regarding LASIK. Therefore, LASEK has now established itself as an excellent alternative to LASIK in low to moderate myopia and indeed may soon challenge as an alternative in the treatment of higher degrees of myopia. Some of the older problems such as severe haze and permanent corneal scarring are no longer an issue. We are becoming more knowledgeable and experienced in the modula tion of corneal healing. Refinements such as the use of larger optical zones and wavefront technology are now being applied to PRJ( and LASEK. The fear of long-term complications and the emergence of ectasia, the lack of versatility and the lack of long-term data on LASIK have rekindled our interest in PRJ( and LASEK. However, the reality is that both procedures have a future.

275

29 LASEK Procedure with the Use of Mitomycin C Iwona Liberek, Justyna Izdebska (Poland)

276

Antimetabolites are chemical compounds which, due to the large similarity to body components participating in metabolic processes, replace them in biochemical reactions. They act on the basis of competitive inhibition. They join specified reaction, causing disorder of cell functionin g, including at times its death. During the last 15 years use of antimetabolites in wound healing became gradually more popular. These compounds, besides their primordial use in treatment of neoplastic lesions, were implemented also in ophthalmology. 5-fluorouracil was used as the first one in treating vitreoretinopathy. Mitomycin C joined subsequently proliferate changes treatment. Comparing these two substances, mitomycin C on account of the greater efficacy after an intraoperative application, seems to replace 5-fluorouracil. 5-fluorouracil is a pyrimidine analogue: • suppress cell proliferation th rough selective activity for the S phase (synthesis) of the cell cycle • is used in treatment of colorectal and breast carcinomas In antiglaucoma procedures mitomycin C is administered: in the form of postoperative subconjunctival injections (0.5 ml of solu tion 10 mg / ml); occasionally as well intraoperatively in the form of spongostan impregnated with 5-FU at a concentration of 50 mg / ml inserted for 5 min under sclera and conjunctiva flaps. Mitomycin C is widely used in glaucoma filtration surgery, in pterygium surgery, in treating superficial neoplastic lesions in eye bulb, in mucosal pemphigoid, in vernal keratoconjunctivitis, in strabismus surgery and, from the last few years, in refractive corneal surgery. Use of excimer laser in correction of refractive error by means of superficial methods leads to keratocytes activation and proliferation. Collagen produced by keratocytes is abnormal, much less organized with matrix-free areas and fibers with an irregular stereospatial relationship. Subepithelial fibrosis is pathologic corneal tissue response, described by Waring and Rodriques, developed after refractive surgery conducts to haze creation inducing postoperative astigmatism and causing weakness of vision. Before era of mitomycin C, the use of nothing but the steroid drops had been applied in order to prevent subepithelial scarification.

LASEK Procedure with the Use ofMitomycill C

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277

Instant ClinicaL Diagnosis in OphthaLmoLo",} (Refractive SJ/rgen}) However, their long-lasting administration causes rise in intraocular pressure and cataract initiation. MMC is an antibiotic deri ved from Streptomyces caespitosus. Its alkylating properties enable it to cross-link DNA between adenine and guanine, thereby inhibiting DNA synthesis through building crossed bonds within DNA double helix. Mitomycin C inhibits DNA, RNA and protein syntheses. It is an anti-cancer agent disturbing replication, transcription and translation processes, it has an anti-proWeration property. Fast-dividing cells are especially sensitive. Besides MMC is a radiomimetic agent with long-term effects on tissues. After MMC application variable types of complications were noted. Allergic diffuse papillomatous conjunctivitis in pterygium surgery, corneal epithelium defect in case of local administration (be prudent while using it because occasionally it may result from insufficiency of corneallimbal (stem) cells due to toxic action of mitomycin C). Delayed wound healing may occur, as well as closure of lacrimal points and lacrimal canaliculi (conjunctival neoplastic lesions treatment), iritis and uveitis, scleritis, maculopathy caused by hypotension in filtration surgery, and finally endophthalinitis. In the Microsurgery Eye Center LASER 0.02% solution (0.5-1 min) of Mitomycin C was used in 968 patients at one eye with the corrected error of -6.0 to -9.5 spherical dioptres and spherical equivalent amounting to -7.65 +/ -1).46 on average. The second eye or the eye with less refractive error was operated without MMC. The cornea thickness in these patients did not allow performing the LASIK procedure. After ablation cornea was cooled with 4'C BSS for 2 min. Procedures were conducted by means of excimer laser MEL 70 G-scan. Moist application of mitomycine C (0.2 mg/mI) applied from 30 seconds to 1 min. Contact lens remained on the eye during 6 days. Identical postoperative treatment plan was implemented (antibiotics with steroids, artificial tears, topically and oral NSAID). The follow-up period was between 13 to 28 months (24 month in 558 patients) The corneas were examined under a confocal microscope Confoscan 3 (Nidek Laboratory) at the following intervalls: before the surgery, 6, 12 and 24 months after surgery. In order to assess epithelial layer status and any changes in the corneal endothelium Over first days after the application of MMC the patients felt a greater discomfort than after the LASEK procedure alone. At 28 months' follow-up, late haze had appeared in 61 patients in the eyes not treated with MMC, reaching a maximum value of 1 degree in 23 patients, she said, noting no patients required re-operation. All the patients achieved 278 full re-epithelialization.

LASEK Procedure witlt tlte Use of Mitomycin C

Fig . 4 : Subepithelial scar tissue two weeks after LASEK surgery

Fig. 5 : Subepithelial scar tissue two weeks after LAS EK with adjunctive mitomycin C surge ry

279

Instant Clinical Diagnosis in Oplttlwlmologlj (Refractive SlIrgenj) The late haze appeared only at eyes not treated with mitomycin C (in 61 patients, 6.3%) reaching maximum value of 1 degree in 23 opera ted patients (2.38%) N one of the pa tients required re-operation. Full re-epithelialization was achieved afte r remo val of th e lens in all cases. No statistical differences in vision acuity between the groups in the 1 month after the procedure were observed We achieved UCV A 24 months after the procedure in total 558 patients. Confocal microscopy examination wi th the use of microscope ConfoScan 3 (Nidek Technologies) was performed in both eyes before the procedure and in the period of2 weeks, 1, 3, 12 and 24 months after the procedure. In examination u nd er confocal m icroscope considerab ly redu ced signs of kera tocytes activati on, less n eedle-like formations in the subepithelial area a nd in the anterior part of proper substance in the cornea after LASEK with MMC were stated compared with the cornea that underwent only LASEK procedure. Important differences in the appearance of epithelium, middle anterior, m iddle, and posterior pa rts of proper substance and endothelium with in compa red eyes were not no ticed. Subepithelial scar tiss ue revealed postoperatively in certain cases, had a reduced hiper-reflecti vity and was less firm and thinner in eyes tha t h ad undergone LASEK procedure with the mi tomycin use. Figu res 4 to 7 sh ow photos of compared eyes of the same patient. In following examinations the scar tissue reflectivity was being decreased in a comparable way in both eyes. Research on the in1pac t ofMMC appUca tion on the endothelium of cornea was made as well. 11,e average density of end othelial cells before the procedure was comparable an d stated 2968 / mm' +/- 347. After the LASEK and the LASEK w ith MMC p rocedures it did not sho w sta tistically significan t differences (p > 0,05 T-Student test). On the grounds of the 2 years long observation we conclu ded as follows 1. Th e use of mitomycin C allows qualifying for the LASEK p rocedure patients with large errors for w h om it would be dangerous to undergo the LASIK p roced ure due to insufficient cornea thickness. 2. N o side-effects of mitomycin C on the eye structure was observed in the studied group. 3. Based on the two years observa tion, the use of mitomycin C seems to be a safe method to prevent such comp lications as haze (confirmed by the confocal microscope examination). We did also resea rch on the process of cornea healing after the use of LASEK with the intraoperative MMC application in the correction of remaining refracti ve errors persisting after the LASlK procedure. We accepted the following indications for the use of LASEK after LASlK method in the correction of residual

280

refractive errors:

LASEK Procedure with the Use of Mitomycin C

Fig. 6: Anterior stroma 1 month after LASEK surgery- remains of scar tissue is visible

Fig. 7: Anterior stroma 1 month after LAS EK with adjunctive mitomycin C- no scar tissue remaining

281

Instant Clinical Diagnosis in Ophthaltnologt) (Refractive Surgen)

1. Stable refractive error from -1.0 0 , to -4.0 0 , astigmatism from - 1.0 0 to 2.5 0 2. Lack of patient's acceptance of the offered optic methods 3. Symptoms of dry eye syndrome in the period of 3 months after the LASIK procedure (contraindicated classic reopera tion) 4. Massive OLK after the primary procedure 5. Conditions after remova l of epithelium in case of ingrowth's under the flap 6. Irregular circular scar in the fla p's cut place Disorders of corneal structure were not demonstrated in preoperative confocal microscopy examina tion excluding presence of depOSits of medium and high reflectivity on level of interface and reduction of keratocytes density in this place. In some of the cases anomalies in the course of nervous fibers were stated. Postoperative confocal microscopy examination showed the presence of scar tiss ue under the epithelium and in the anterior part of proper substance in operated patients. On examinations performed 3 months after the procedure almost no scar forma tion w ar observed. Presence of pathological changes such as augmented number of excited keratocytes, presence of need le-like formations or infiltrative cells were not noticed either in examination 3 months after the procedure. Appearance of the epithelium did not differ from the phYSiologica l one except from insignificant thinning in the superficial layers in par t of the cases. It indicates the proper course of healing process No corneal haze was noted in the slit-lamp examination after LASEK reoperation in the analysed group . LASEK with MMC in our opinion seems to be a safe method for correction of residual errors after previous LASIK. SUMMARY

"According to Dr. Liberek, they perform LASEK when the cornea is less than 500 fIm thick, and they apply MMC when the patient is abou t -5 0 and the ablation depth needs to be more than 60).UIl . "Without MMC, [LASEK] would not be possible because [the case] wo uld be high myopia, and with high myopia, we observed haze," If MMC is not availab le, and the patient has more than -10 0 of myopia, phakic IOL use is indicated "To choose the phakic IOL or LASEK with MMC, so it depends on the cornea and the pachymetry, and it depends on the high refractive error." 282

LASEK Procedllre with the Use of Mitomycill C

Fig. 8: Unchan-ged endothelium in patient 12 month after LAS EK with adjunctive mitomycin C surgery

Fig. 9: Before LASEK surgery-very hyper-reflective deposits at l ASIK interface depth, the

keratocytes density is locally decreased

283

Installt Clinical Diagnosis in Ophthalmology (Refractive SlirgenJ)

Fig. 10: Sub-epithelial opacities (scar tissue) is reflecting light under healthy basal epi - thelium~ 1 month after LASEK surgery

Fig. 11 : Anterior stroma 3 months after LASEK surgery, no scar tissue detectable

284

LASEK Procedure with the Use of Mitomycill C

90% 77.70%

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Fig . 12: Comparison between BCVA before procedu re and UCVA after procedure

285

30 Transepithelial Cross-linking for the Treatment of Keratoconus Roberto Pinelli, E Milani (Italy)

INTRODUCTION

Keratoconus is a non-inflanlmatory cone like ecstasia of the cornea, which is

usually bilateral and progress over time, with consequent central or paracentral thinning of the stroma and irregular astigmatism. The relevance of keratoco n us in the general population seems to be relatively high, with approximately 1 in 2000, even if the diffusion of new diagnostic means will permit to find prevalence rates certainly greater. In nearly all cases both eyes are affected, at least from a topographic point of view. The cause of keratoconus is unknown, but it seem s that enzymatic changes in corneal epithelium, such as a decrease of the levels of the inhibitors of proteolytic ezymes and an increase of the lysosomal enzymes can be involved in the cornea degradation. At the begirming, glasses are sufficient to correct myopia and astigmatism still regula r or slightly irregular; successively, in cases of high astigmatism, it becomes necessary to apply hard contact lenses. Epikeratoplasty is effica cious in patients which do not end ure contact lenses and which do not show a significant central corneal opacity, but, due to its v isual outcomes not perfect,

it was dropped. Intracorneal rings also can be an option, but all these described techniques unfornmately only correct refractive errors and do not treat tl,e cause underlying the corneal ecstasia and therefore they do not permit to stop the progression of keratoconus.

In 1996 some theo retical studies sta rted investigating more deepl y the underlying causes of keratoconus and the possible parasurgical techniques to stop its progression. In all patients affected by keratoconus a reduced degree of cross-links in the corneal collagen fibers has been observed; that is, the aim of those studies was firstly to determine how to increase those cross-links to obtain an improved mechanical stability of the cornea and increase the resistance against enzymatic degradation.

286

Trallsepitllelial Cross-linkingfor the Treatment ofKeratoconlts

Fig . 1: Keratoconus

Gly

-

Pro

Al a

Fig . 2 : Collagen triple helicoidal chain

287

Instant Clinical Diagnosis in Ophthalmologt) (Refractive SlIrgen)) CORNEAL COLLAGEN NETWORKS

Collagen is a structural protein organized in fibers. Those fibers are responsible of limiting the tissue deforma tions and preventing mechanical brakes. The collagen fibers are chemically stable and have high mechanical properties. Inside the connective tissue, fibroblasts synthetize tropocollagen molecules, the base blocks of collagen fibers. Those molecu les have a typical weight of 300 kDa, a length of 280 nm with an average diameter of 1.5 nm. The molecule is composed by 3 helicoidal chains (alpha-chains) interlaced each other like a rope. The fac tors of stabilization of those collagen molecules are related to the interactions between the 3 helics and are due to Hydrogen links, Ionic links and intra-chain reticulations (cross-links) The stroma, composed mainly by collagen lamellae, gives to cornea 90% of its thickness. Between the lamellae keratocites can proliferate, migrate and turn into their active state. Integri ty of corneal epitheli um for the switch of keratocites (resting cells) in fibroblasts (active cell) is very important. Cheratansulphate type I is the most important mucopolysaccharide present in corneal stroma: it plays an important role for the orientation of collagen mashes and lamellae (corneal clarity, tensile strenght) and for corneal hydration (corneal edema). PHOTOCHEMICAL CROSS-LINKING

There are many different possibilities of cross-linking: • Lysyl oxidase (LOX) cross-links collagen enzymatically • Transglutaminase (12 h, pH=3) • Sugar aldehydes (d iabetes - Advanced Glycation Endproducts AGEs) • Chemical cross-linking (glutaraldehyde, formaldehyde, DPPA) • Photochemical cross-linking (UV, ionizating radiation) The interaction between organic tissues and radiation depends on the type of radiation used. The ionizing radiation has enough energy to turn out electrons from the atomsofthe tissues. Other types of radiation, i.e. UV radiation, ha ve not enough energy to turn out electrons but to make them jump to higher energy levels (exciting radiation). In the human biologic tissues, water molecule is present at a rate of 70 to 90% so it is clearly the main target of radiation . During the water radiolysis process, the energy applied to water molecules ionizes them ad generate free radicals molecu les. Free radicals are continuously produced in tissues and quickly inactivated by chemical or enzymatic transformation. In the eye, ascorbic acid absorbs UV radiation (a t cornea, lens and vitreolls

288

body d istricts); it is a cofactor of several enzymes, the best known of which are

Trallsepitheliai Cross-linking/or the Treatment o/Keratoconus

Fig . 3: UVA sou rce (Courtesy of Peschke GmbH)

1·Combined application of UVA and riboflavin Riboflavi n (Vii. 8 2) Ultraviolet irradiation O-H /

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Fig . 4: Photochem ical induction of cross-links

289

Instant Clinica l Diagnosis in Oplrtlralmolofflj (Refractive Surgenj)

prlyne hyd roxylase and lysine hydroxylase, enymes involved in byosinthesis of collagen. In vitreous body, after cataract surgery (absence of glutathione), ascorbic acid (in ascorbate form) absorbs UV not stopped by lens, resulting in the formation of free radicals, d isaggregation of hyaluronic acid and increase in cross-linking of collagen fiber networks. RIBOFLAVIN-UVA TREATMENT

A photo sensitizer is a substance which is activated by the absorption of light ata given wavelength and which can induce free radical reactions in its activate form. This substance can amplify light radiation effects on biologic tissues. The basic mechanism of the photochemical treatment of ke ratoconus is to use riboflavin as a photo sensitizer and apply on it UV irrad iation at a determined wavelength to induce free radicals reactions and increase this way the cross-links in the collagen fibers. Riboflavin has a high UV absorption between 360 nm and 450 nm; due its additional shielding all structures behind the corneal stro ma, including corneal endothelium, anterior chamber, iris, lens and retina, are exposed to a residual UV radiant exposure less than 1)1 cm2 (in

accordance with safety guidelines). The UV source is typically a group of 3 to 5 Light Emitting Diodes producing a radiation of 370 lUll wavelength and 3rnW Icm 2 intensity. The cross-linking effect is obtained in 3 steps. CORNEAL EPITHELIUM

The w idespread technique of cross-linking is based on a central corneal abrasion (with a diameter of 8 mm). This abrasion is made because the epithelium is believed to be a barrier to the correct diffusion of riboflavin so a possible factor of decreased effectiveness of the treatment. What has been observed during the different studies is that free radicals mediated by the riboflavin irradiated with UV light can create cell damage. Keratocytes showed (in both laboratory and clinical studies in epitheliumremoved eyes) cells dea th upto a 350 J.lm depth. After 6 months the area is repopulated by keratocites which, differently from corneal endothelium, can reproduce. To preserve the endothelium a minimum corneal thickness of 400 nm should be assured. The news in this treatment is represented by the possibility of realizing cross-linking keeping the epithelium unaltered. This natural barrier protect the cornea but it is not an impermeable stratus: it is an osmotic membrane thru which the riboflavin can penetrate to the cornea. Of course the riboflavin itself can not penetrate eaSily so the question is, at this stage, abo ut the real effectiveness of the treatment, compared with the "official" one. If we combine 290 the riboflavin drops w ith a tense-active substance, we can have a more efficient

Transepith elial Cross-linking/or the Treatment o/Keratoconus

Fig. 5: Patient eye under C3·R treatment

penetration to the cornea. This substance act as a vector for riboflavin, w ith a

double effect: reaching the cornea and filling the epithelium, contributing so far to its strengthening. The advantages of this particular technique is tha t all the macroscopic side effects related to the epithelium-removal technique are not present: no pain, no stromal edema (due to the ab rasion) and, more important, the possibility to treat both eyes in the same session (85% of patients has bilateral keratoconus, so the treatment is in most cases necessary in both eyes). Even if we assume that the riboflavin can no t penetrate efficiently the epithelium, we think that as the photo sensitizer is distributed homogeneously on the trea ted eye, we can at least obtain an increased rigidity of the corneal epithelium, thus a decreased instability in visual acuity of the patient. The rea l question is abo ut the effectiveness of the treatment, as the safety issues are not a worry of this technique: keeping the epithelium unaltered means reducing most of the side effects of the trea tment (included the death rate of keratocites and the number of endothelial cells). We continue our studies in this way because we believe that the epithelium removal is something that could be avoided in the treatment and transepithelial tecnique will become the standard in Cross-linking treatments. 291

31 Sub Bowman's Keratomileusis: Combining the Best of PRK and LASIK for Optimal Outcomes Daniel S Durrie (USA)

Photorefractive keratectomy (PRK) and laser in sit" keratomileusis (LASIK) have drawbacks in terms of technique and outcomes that are well known to both consumers, as well as physicians. Which begs the question-what if we could create a procedure that combines the best of these two techniques while leaving behind the negatives? Could a procedure like this win over skeptics and help create renewed interest among consumers in corneal refracti ve surgery? Sub Bowman's Keratomileusis (SBK) is a hybrid of PRJ< and LASIK that is designed to provide a superior method for performing corneal refractive surgery. This technique involves the use of a customized corneal flap of between 90 and 110).lm with diameter that is closely matched to the ablation zone of the excimer laser being used, typically 8.5 mm or less. Although there are mechanical microkeratomes capable 01 the creation of the thin corneal flap, the critical component in SBK is the use of a femtosecond laser for flap creation. This is due to the ability to the femtosecond laser to create an almost planar corneal flap. This allows for better predictability, as well as flap creation having less of an impact on the excimer laser ablation, as has been shown in studies wi th mechanical nticrokeratornes. With mechanical microkeratomes, the cornea l flaps are more meniscus in shape and are thinner in the center and thicker in the periphery. This chapter will explore the evolution that has led to SBK, the biomechanics of the procedure and then review a clinical study com paring a myriad of outcomes of SBK vs. PRK. The Evolution The argu ments in favor of PRK and LASIK are well documented. Some of the pros for LASIK include the patient pleaSing benefits of quicker visual recovery and less postoperative pain. On the con side of LASIK are dry eye, 292 flap comp lications, as well as the risk of cornea ectasia - although this last

Sub Bowman's Keratomilellsis: Combining tile Best of PRJ( and LASIK

o 100

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Fig . 1: The Visante OCT was used to measure corneal thickness following flap creation with the femtosecond laser. The average flap thickness was 112 ±S ~m, with an individual flap standard deviation of 4 Ilm

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Fig . 2 : High and low contrast acuity results at 3 months

293

Instant Clinica l Diagnosis in Ophthalmology (Refractive SurgenJ) point remains up for debate. On the pro side for PRJ< are fewer complaints of dry eye, better correction of high-order aberrations (HaAs) and better quality of contrast sensitivity and night vision. On the can side are slower visual recovery, more pa in particularl y in the immediate postoperative period, as well as the risk of haze. Advocates of LASIK and PRK, as well as newer procedures such as epiLASIK and laser epithelia l keratomileusis (LASEK), claim superiority when it comes to visual results. However, the published literature indica tes that visual outcomes are relatively equal between surface ablation techniques and LASIK, and that LASIK patients demonstrate better visual results during the first 4 postoperative weeks. The most notable of these papers is a Cochrane Collaborntion Methodology meta-analysis/ systemic review conducted by Shortt and Allan. As part of this analYSiS, the authors reviewed all published prospective and randomized controlled studies, along with the database of the US. Food and Drug Admini stra ti on of all LASIK and PRK studies conducted for US approval. Shortt and Allan concl ude that LASIK is safer and more accurate than PRK, however, taking note tha t most published studies are pre-200l and do not involve current technology or algorithms. A number of studies published in the latter half of 2006 and 2007 do compare LASIK against LASEK, epi-LASIK and PRK . A control -match comparison of LASIK and LASEK done at the Massachusetts Eye and Ear Infirmary looked at outcomes in a matched group of LASIK and LASEK eyes and foun d that the results were relatively similar with a mean postoperati ve UCVA of 20/ 21 in the LASEK group and 20/ 23 in the LASIK group. Two studies explore postoperati ve pain in surface ablation procedures. The first, from Mexico, looked differences in early postoperative pain between epi-LASIK and PRJ< in a prospective, comparative, bilateral study. The results showed that patients had similar pain in their epi-LASIK and PRJ< eyes on Day 1, but that the epi-LASIK eye was more painful On Days 3 and 6. The second stud y, from lreland, compared pain response in epi-LASEK, LASEK or PRJ<. In this study, patients were randomized to receive epi-LASEK in one eye and LASEK in the fellow eye. In cases w here the epi-LASEK failed, then these eyes were converted to PRJ<. There were a total of9S eyes included in the stud y and followed for 3 mon ths. Here, the epi-LASIK patients were fou nd to have the least pain in the immediate hours after surgery, although all 3 groups had minimal or no pain by 24 hours. In terms of visual results, the epi-LASIK group did the best, although the researchers noted that there was a high failure rate of epi-LASlK flap creation, necessitating a conversion to PRJ<. 294

Su b Bowma,,'s Kera tomileusis: Com bining tile Best of PRJ( and LASIK

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Fig. 4: Study patients found their PRK eye to be significantly more painfu l, particularly in the first week following surgery , compared to pain encountered with the SBK eye

295

Illstallt Clinical Diagnosis ill Ophthaltnolog>J (Refractive Surgery)

The conclusion to be reached is that neither of these approaches can tick all the boxes when it comes to providing excellent visual results, quickly, without a great deal of postoperative pain and discomfort. Biomechanical Evidence

296

Despite the fact that laser corneal refractive surgery has been available fo r more than 15 years now, it has only been in the past several years that much work has been done to evaluate the effects of laser procedures on the cornea. The interest has developed as refractive surgeons have sought to understand why there is a growing rate of keratoectasia, particularly following LASIK. A secondary factor is the availability of more sophisticated diagnostic testing that enables us to more accurately analyze how the cornea respond s. A study publ ished in the journal, Cornea, in 2005 reviewed the wound healing response of various laser refractive procedures and the common complications that most impacted healing. It found that overcorrection, undercorrectiol1, regression, and corneal stroma opacification all stem fran1 a biological response to surgery. Some of the processes involved included keratocy te apoptosis, keratocyte necrosis, keratocyte proliferation, the migration of inflammatory cells, as well as microfibroblast generation. A review article by Dupps and Wilson on biomechanics of the cornea published in 2006 delves deeper into the biomechanical responses of the cornea to laser refractive surgery noting that: "the ability to anticipate confounding biological responses at the level of the individual remains limited." Of the five layers of the corneal, only Bowman's layer and the stroma contain collagen fibrils, giving these layers the majority of the tensile strength, w ith most of the conlea's mechanical response coming from the stroma. Marshall and colleagues have explored this concept by looking at how four methods of laser refractive surgery - PRJ<, epi-LASIK, femtosecondlaser-assisted LASIK and mechanical microkeratome-assisted LASIK - affect wound healing and corneal biomechanics. With the use of confocal specular microscopy, electron microscopy, Shearing interferometry and histology, they found that the cornea is the strongest within the first 150 microns of depth and then again out at the periphery were the lamellae are packed the tightest. This interweaving of the lamellae provides an important structural foundation for shear (sliding) resistance, according to Dupps and Wilson. TIley note that d uring LASIK, PRJ< or other procedures where central ablation takes place, when a circumferential cutti ng of the central lamellae takes place, it also causes a relaxation of the lamellae out in the periphery of the cornea, which leads to peripheral stroma l thickening.

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297

II/stant Clinical Diagnosis in Ophthalmology (Refractive SlIrgenj) The conclusion reached by Marsh all et al was tha t PRK, epi-LASIK and lemtosecond-Iaser created Ilaps of approximately ±lOO microns leave the cornea with the greatest amount of stab ility fo llowing trea hnent, as well as providing better corneal transparency. In addition, they found that flaps that are thicker create a greater disruption of the lamellae, potentially wea kening the cornea . Marshall et al the impact 01 flap depth on corneal biomech anics and wo und healing in laser refractive surgery, unpublished data. JMarshall et al the effects of varying for ms of corneal flap creation on wound healing and biomechanics, unpublished data). This conclusion was supported b y a clinical study compa ring femtosecond-laser-created flaps in LASIK with LASEK by the Vissum Instituto Oftalmologico in Alicante, Spain. This study concluded that the biomechanical effect on the cornea ollemtosecond-assisted LASIK is equivalent to surface ablation. OL Alio et al Aberrometric outcomes and very high-frequency digital ultrasound evaluation of the flap thickness profile in LASIK surgery using three d ifferent methods of lamellar keratotomy, unpublished data). Based on this biomechanical evidence, it becomes quite clear that staying thin will help to protect the integrity of the cornea . In addition, it also becomes apparent that the corneal flap diameter shou ld be smaller than the typical LASIK flaps diameters currentl y seen, in order to protect the la mellae in the periphery of the cornea. The evidence su ggests that a femtosecond laser is able to achieve these two criteria more easily than a mechanical microkeratome. An additional aspect 01 the biomech anics in play here is the fact that corneal flaps created by lemtosecond lasers appear to be stronger than corneal flaps created with a mech anical microkeratome. This was the conclusion reached by a Korean study based on the amount 01 force needed to relift lemtosecond-Iaser flaps three months following flap creation compared to the amount ollorce need ed to relift a mechan ical microkeratome flap. The reason for this difference may lie in the methods used to create these flaps, acco rding to Marsha ll (Marshall, unpublished data). With a mechanical rnicrokeratome, the metal blade that is used creates a smooth surface for the corneal flap and the stromal bed. When the flap is placed back down following excimer laser abla tion, this smoothness can cause the two surfaces to slip against each other. With a lemtosecond laser, the corneal tissue is sepa rated using a process called photodisruption. The resulting surface has more of a texture, which allows the flap and the stromal bed to adhere together following exci mer laser ablation (Marshall, CRSTE Ref). Lastly, the corneal flap created by the fem tosecond laser has a more 298 un iform thi ckness across the entire surface, making it quite planar. The

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299

Instant Clinical Diagnosis in Ophthalmology (Refractive SlIrgery) method used by mechanical m icrokeratomes to create corneal flaps results in a flap that is thitmer in the center and thicker in the periphery - a meniscus shape. This results in less predictable flap thickness. In addition, studies have shown that a corneal flap created by mechanical rnicro keratome can have an impact on the visual results of LASIK, particularly customized procedures. The result of this biomechanical research is the next evolution in corneal refractive surgery - Sub-Bowman's Keratornileusis (SBK). We call it SBK because we believe that it most accurately reflec ts what a hybrid of surface abla tion techniques and LASIK should achieve: a customized flap designed to match the patient's needs and a diameter that is based on the type of excimer laser ablation being performed, w ith an intended flap thickness of between 90 and 110 microns. In theory, SBK should d eliver the following benefits for refractive surgeons and their patients: • A predictable, thin flap; • Quicker v isual recovery, with minimal pain and discomfort; • Outstanding visua l results, particularly during the first 3 months following surgery; • Minimal biomechanica l changes with fewer higher order aberrations; • Reduced incidence of postoperative dry eye, and; • A decrease in loss of corneal sensitivi ty. The SBK

VS.

PRK Study

To evaluate SBK and determine if the results do support the theory behind the procedure, a clinical study was developed to compare SBK w ith PRK. The study, done in conjunction with Stephen G Slade, MD, Houston, Texas, was a prospective, contralateral, randomized study. Patient Demographics

The two-center study enrolled 50 patients (100 eyes), with patients undergOing PRK in one eye and SBK in the fellow eye. Each site (Kansas City and Houston) enrolled 25 patients. Randomization was performed based on a schedule developed to assure that each group had an equal number of dominant eyes. Informed consents were obtained from all patients. All patients underwent correction for myopia, w ith or without astigmatism, using the Alcon LADARVision 4000 Excimer Laser (Alcon Laboratories, Ft. Worth, TX) with a customized wavefront treatment following the manufacturer's operational instructions.

300

Sub Bowl11at"S Keratornileusis: Combillillg the Best of PRK alld LASIK

The mean age of the patients was 33.24 ± 6.97 (range of 22 to 48) with 42% (n ~ 21) males and 58% (n ~ 29) females enrolled. Inclusion criteria included: • Spherical m yopia of -2 to -6.00 0 , with up to -3.50 0 of refractive astigmatism; • A stable refraction for 1 year; • A best-spectacle corrected visual acuity (BSCVA) of at least 20/20 in each eye; • An average central corneal thickness of greater than or equal to 500 microns in each eye. Soft contact lens wearers were required to di scontinue lens lise for at least 3 days prior to surgery, while rigid contact lens wearers were required to discon tinue use at least 3 weeks prior to surgery. As this was a contralateral eye study, the preoperative visual results were statistically similar. The mea n manifest spherical refrac tion in the SBK group was - 3.64 0 (-2.00 to -5.75 0) (SO ~ 0.97) and the mean manifest cylindrical refraction was - 0.63 0 (O to - 3.00 0 ). In the PRK group, the mean manifest spherical refra ction was - 3.68 0 (- 2.00 to - 5.75 0 ) (SO ~ 1.06) and the mean manifest cylin drical refrac tion was - 0.64 0 (0 to - 2.75 0 ). Th e mean preoperative BSCVA was 20/17 in both groups with a range of 20 / 12 to 20/ 20 (SO ~ 2.47). Preoperative uncorrected visual ac uity (UCV A) in both groups ranged from 20 /80 to count fingers. SURGICAL TECHNIQUES FOR SBK AND PRK

In the SBK eyes, flaps were created using a 60 kHz IntraLase FS Laser (Ad vanced Medical Optics, Irvine, CAl with a planned flap diameter of 8.5 mm and an intended flap thickness of 100 microns. A raster pattern was used with the hinge located in the su perior position. The same raster energy (1.0 ).Ij / spot) and spot / line separa tion (9 x 9 )lffi) was used by both centers. The hinge angle was set at 50° and the side-cut angle was 75°. The e- "pocket" software was enabled to decrease the occurrence of dense bubbles in the interface. In the PRK eyes, an 8.5-mm trephine was placed on the eye followed by the applica tion of 20% ethanol for 25 seconds and then irrigation and chilling with balanced salt solution within the trephine. Mitomycin C was not used in this stud y. All eyes received proparacaine 0.5% and tetracaine 0.5% drops intra-operati vely. The goal of all surgeries was emmetropia. Immediately following completion of surgery, all patients received a topical an tibiotic drop, a steroid drop, as well as preservati ve-free tears. In

301

Installt Clillica l Diagnosis in Ophthalmologtj (Refractive Surgery)

the PRJ( eyes, a bandage contact lens was placed and left on until the cornea re-epitheliali zed. Patien ts were placed on a topical antibiotic and steroid four ti mes a da y for the first postoperative week along with preservati ve-free artificial tears. In the PRJ( eyes, the steroid was tapered to TID in the second week, BID in the 3rd week and then to once per day. These eyes also received Acular LS (ketorolac, Allergan, Irvine, CAl not to exceed 3 times per day for the first three days, as well as acetaminophen / h ydrocodone 1 to 2 tablets, 4 to 6 times per day fo r pain control. Topical anesthetic drops we re not used. MEASUREMENT OF RESULTS

All patients were seen at 1 and 3 days, 1 week, 1, 3, and 6 months and at 1 year follow ing surgery. All eyes were assessed according to the FDA standard criteria for satisfactory LASIK/ PRJ( outcomes for safety and effectiveness. In add ition, pre- and postoperative outcome measurements included: • Wavefront aberrometry (LADARWave; Alcon Laboratories, Ft. Worth, TX); • Res idual postoperative manifest refraction; contrast visual acuity (Vecto r Vision 4M ETDRS Charts, Vector Vision, Greenville, OH); • Corneal sensitivity (Cachet-Bonnet esthesiometer); • Visante OCT imaging (Carl Zeiss Meditec, Oberkochen, Germany); • Corneal hysteresis (Ocular Response Ana lyzer, Reichert, Depew, NY); • Cornea l response fac to r and, light scatter and optical visua l acui ty assessment (OQAS, Visometrics, Terrassa, Spain) and • Pasca l Dynamic Contour Tonometer (Ziemer Ophthalmic Systems Group, Port, Switzerland). Addi tiona l testing was d one at one site onl y (Kansas City): Confocal microscopy (Confoscan 4. Nidek, Gamagori. Japan) and Artemis Highfrequency Ultrasowld Imagin g (Ultralink LLC, St. Petersburg, FL). Patien ts were also required to complete a subjective questionnaire, developed by the study sponsor (AMO/ IntraLase) on comfort and vision at all postopera ti ve visits. As part of this comparative study, patients' response to pain fo ll owing surgery were recorded and compa red. Patients were asked to record which eye had more pain at 1 day, 3 days, 1 week and then at 1 and 3 months. Statistica l analysis was performed using the Student's paired t test. For the subject questionnaires, McNemar's chi-square test was used. A P value less than or equal to 0.05 was considered sta ti stically Significa nt fo r all 302 analyses.

SlIb Bowlllan's Keratomi/ellsis: Combining the Best of PRK and LASIK

Res ults were compared using both traditional metrics (visual acuity, contrast acu ity), as well as newer measurements that included wavefront aberrometry, OCT flap thickness, corneal hysteresis and optical visua l acuity assessment. These newer diagnostic measurements were used in order to obtai n a more detailed picture of the cornea's response to these two techniques. Following is a brief overview of these tests, as well as the benefits in cornea l analysis:

OCT anterior segment imaging: The Visante OCT (Optical Cohe rence Tomography) Imaging system enables a m uch more precise view of the an terior segment, as we ll as prov iding full-thi ckness pachymetry measurements. Because it is non-contact, it is able to provide an accurate measurement of corneal flap thickness, as well as the residual stromal bed. (ref - CZM Brochure).

Pascal dynamic contour tonometer: This device is designed to provide lOP and ocula r pulse amplitude (OPA) measurements without the corneal compression needed with conventional applanation tonometers. A tip that matches the corneal curvature is able to capture 100 readings per second. Artemis 2: This is another method for imaging the anterior segment, this time, using very high frequency ultrasound to provide three-dimensiona l corneal thickness measurements.

Owlar response a/lalyzer: This system approaches corneal biomechanics from a new direction, using cornea l hysteresis to analyze corneal tissue. Hysteresis means a temporary resistance to change from a cond iti on previously induced.

In short, ORA is measuring the cornea's ability to absorb energy or the "viscous damping" in cornea tissue. It works by using rapid air impulse to record two applanation pressure measurements - one is done while the cornea is moving in ward and the second is done as the cornea moves outward again. The difference between these two measurements is called corneal hysteresis. A low corneal hysteresis val ue suggests that the cornea has weakened and is less able to absorb energy. A case study report on the technology in the Journal of Refractive Surgery demonstrated that a corneal flap does cause a reduction in corneal hysteresis.

OQAS (Optical quality analysis system): OQAS was developed to estimate the retinal image quality and contrast sensitivity. The system uses a double-pass technology that shines a low-power beam of diode laser light (wavelength ~ 780 nm) into the eye, producing an image of a punctual ci rcular spot on the retina. During the second pass, the reflection of this spot on the retina is

303

Instant Clinical Diagnosis in OphthalmologtJ (Refractive SlIrgenJ) measured by a highly sensitive low light camera which directly measures the point spread function (PSF) of the optical system. The system uses Fourier analysis to translate the point spread function to a modulation transfer function (MTF) value. The MTF value correlates to the loss of contrast in the retinal image for each spatial frequency. The higher the MTF value, the higher the optica l quality of the eye. STUDY RESULTS Flap Thickness Results

Flap thickness measuremen ts using Visante OCT demonstrated that the SBK flaps had a mean thickness of 112 ± 5 flm (range 87 to 118 flm). OCT measurements performed at 16 spots across the entire surface of each flap determi ned that the flaps were planar with no statistical d iffe rence in thickness. The standard devia tion for each indiv idual flap was 4 fl m. Visual Results

One of the goals of this study was to establish that SBK offered quicker and better visua l results in the immed iate postoperative period (out to 3 months). The results confirmed this. We also expected that the results would equalize between the SBK groups and the PRJ( groups between 3 and 6 mo nths as this is typica ll y when PRK patients begin to ach ieve their best visual results. Again, the visual results also confirmed this hypothesis. Table 1 shows the mean refractive spherica l equiva lent (MRSE) and cylinder at preoperative and then at 1, 3 and 6 months postoperative. Table 1: Mean MRSE and cylinder at baseline and 1, 3 and 6 months postoperative

Preoperative

1 month

3 months

6 months

SBK

- 3.95

0.10

- 0.11

- 0. 17'(p < 0.05)

PRK

- 3.99

- 0.02

- O.OS

O.OS·(p < 0.05)

SBK

- 0.63

- 0.3S

- 0.24

- 0 .29

PRK

- 0.64

- 0.25

- 0.32

- 0 .26

MRSE

Cylinder

• Statistically significant

304

Sub Bowm an's Keratom ileusis: Co mbin ing the Best of P RJ( an d LASIK

The uncorrected visual ac uity (UeV A) at I -month showed a statistically significant difference between SBK group and the PRJ( group with 88% of the SBK eyes at 20/20 or better compared to 48% of the PRJ( eyes (p
20/ 12.5 or

20/16 or

20/20 or

20/25 or

20/40 or

better

better

better

better

better

S8K

18

46

88

90

100

PRK

2

16

48

48

98

(% of eyes)

At 3 months, the UeVA in the PRJ( group did improve (92% SBK vs. 90% PRJ( 20/ 20 or better) (p>O.5). 100 percent of PRK eyes were 20/32 or better compared to 98% of SBK eyes at 3 months. This was due to 1 SBK eye with an undercorrection of -0.75 D. Seventy percent of SBK eyes we re 20 / 16 or better compared to 64% of PRJ( eyes. By 6 months following surgery, there was a further equalization with, 94 percent of the PRJ( eyes and 92 percent of the SBK eyes achieving a UeVA of 20 /20 or better (p=0.63) (Table 3). Table 3: UCVA results at 6 months postoperative

20/ 12.5 or

20116 or

20120 or

20125 or

20140 or

better

better

better

better

better

S8K

24

72

92

98

100

PRK

26

70

94

98

100

% of eyes

The BSeV A showed a similar trend at 1, 3 and 6 months with 42% of the SBK group gaining 1 or more lines of vision compared to 16% in the PRJ( group at 1 month (p < 0.000l). Forty-two percent of the PRJ( group lost 1 or more line of vision, compared to 22% losing 1 line in the SBK group (p < 0.0001). No eyes in the SBK group lost 2 or more lines of BSeV A, while in the PRJ( group, 6% lost 2 or more lines. The d ifference in BSeVA between the two groups was sta tistica lly similar at the 3-month visit with 57% of the SBK eyes showing an improvement of 1 or more line of BSeV A compared to 53% in the PRJ( group (p =0.33). Ten percent of the PRK group lost 1 line of vision, while no eyes in either group lost 2 or more lines. In the SBK group, 4% lost 1 line, with no eyes losing 2 or more lines of BSeV A at 3 months (p = 0.33). 305

[nstaut Clinical Diagnosis in Opllthalmologtj (Refractive Surgery)

At 6 months, 62% of the SBK eyes had gain ed one or more line compared to 56% of the PRJ( group (p=0.56) . Retinal Image Quality

At the Kansas Ci ty site, the OQAS system was used to measure the MTF and contrast values for each group at preoperative, 1 month, 3 months and 6 mon th postoperative. The average MTF value at preoperative was 30.09 ± 8 for the SBK eyes and 29.39 ± 10 for the PRK eyes (Table 2). At 1 month, the average MTF value increased by 6% in the SBK eyes and decreased by 13% in the PRJ( eyes (p < 0.05). At 3 months, the average MTF value was 30.88 ± 8 for the SBK eyes and 29.49 ± 8 for the PRJ( eyes (p < 0.05). This represented a gain in quali ty of vision of 3% in the SBK eyes compared to no change in the PRJ( eyes. At 6 months, the average MTF value for the SBK eyes was 29.93 and 27.81 for the PRJ( eyes (p
Preoperative

SBK PRK

1 month "

3 months

6 months

+6%

+3%

- 1%

- 13%

0%

- 5%

1 month'

3 months

6 months

+8%

+2%

- 1%

-13%

-1%

-7%

Change in contrast val ue from preoperative Preoperative

SBK PRK ·p
Contrast Visual Acuity

At 1 month, the SBK eyes had statistically better high (90%) contrast acuity: UCYA = 0.01 SBK vs. 0.12 PRJ(, p
The 1 month results indicated that the SBK eyes had the same or lower higher 306 order aberrations compared to the PRJ( eyes at the baseline meas urement

Sub Bowman's Keratomileusis: Combining the Best of PRJ( and LASIK

(50% SBK vs. 2S% PRK; p < 0.05). The total change in HOA RMS from baseline to 1 month was 0.04 microns in the SBK group and 0.11 microns in the PRK group (p = 0.61). There was no statistical difference between groups for vertical and horizontal coma or spherical aberration. At the 3 month follow-up, 41% of the PRK eyes showed improved HOA RMS res ults with the same or lower HOA RMS compared to baseline HOA. Forty-nine percent of the SBK eyes had the same or lower HOA RMS at 3 months. The d ifference in the to tal HOA RMS from baseline was 0.05 microns in the SBK g roup and - 0.04 in the PRK group (p = 0.49). Once again, there was no stat istical d iffe rence between th e two grou ps for ve rti cal and horizontal coma or spherical aberration. At 6 months, there was a change in the total higher o rder aberrations present in the two groups (-O.I S flm SBK vs. -0.29 PRK flm, p=0.23). Once again, there was no statistical difference between the SBK eyes and the PRK eyes for ho ri zontal (p = 0.49) and vertical (p = 0.05) coma, or spherical aberration (p = 0.01). Biomechanical Results

Two tests to eval uate the biomechanical effects of SBK and PRK on the cornea were carried out at one site (Overland Park, KS) as part of this stud y. The fi rst was to evaluate the corneal hysteresis and cornea l response fac tor (CRF) using an Op ti cal Response Analyzer (ORA). The second, using the Pascal Dynamic Contour Tonometer, meas ures ocular pulse am plitude (OPA) . ORA RESULTS

With corneal hysteresis and the corneal response fa ctor, the lower the number obtained with ORA, the weaker the biomechanical properties of the cornea. The preoperative corneal h ysteresis measurements for the SBK eyes were 10.4 and 10.5 for the PRK eyes. The preoperative corneal response factor measurements were 1l.1 and 11. At 1 month postoperative, ORA testing showed a corneal hysteresis of S.13 for the SBK eyes and 6.91 for the PRK eyes (p=0.0002) and a CRF of 7.20 for SBK and 6.77 fo r PRK (p=O.OS). At 3 and 6 months, this trend continued . The cornea l hysteresis measurement at 3 months for the SBK eyes was S.50 an d 7.96 for PRK (p=O.03). The CRF at 3 months was 7.62 and 7.27, respectively (p-0.12). At 6 months, the CH was S.26 for SBK and 7.74 for PRK (p=0.004) and the CRF was 7.40 and 7.15 (p=0.12). Cornea l hysteresis decreased after both SBK and PRK, meani ng that there was no adva ntage with PRK in preserving biomechanical strength. The same 307

Instant Clinical Diagnosis in Ophthalmologt) (Refractive Surgen)

is true w ith the CRF results, with a biomechanica l weakening seen in both the SBK and PRK eyes. PASCAL TONOMETER

The preoperative OPA in both groups was 1.8. At the 1 month follow-up, this measurement was 1.71 for the SBK group a nd 2.00 for the PRK group (p=O.OOl). At 3 months, the OPA was 1.69 and 1.83 (p=0.05) and at 6-months it was 1.80 a nd 1.81 (p=0.89). There was not much of a change between the preoperat.ive and postoperative m easurements, but more data is need ed to fully wlderstand the significance of these results. Dry Eye and Corneal Sensitivity Results Dry Eye

Schirmer's [ and Lissamine green staining were performed to evaluate if there was any d ifference in dry eye symptoms between the two groups. Schirmer's I: At preoperative, the two groups were relatively equal (17 mm SBK vs. 16 mm PRK, p = 0.12). At 1 month, there was a slight reduction in wetting in both groups: 14 mm in the SBK eyes vs. 13 mm in the PRK eyes (p = 0.41). At 3 months, the groups were equal: 16 mm (p = 0.79) and at 6 months, there was a slightly better performance in the PRK eyes: 19 mm SBK vs 20 mm PRK (p = 0.09). Lissamine Green Test: At 1 m onth, 98% of the SBK eyes and 92% of the PRK eyes have no corneal staining, with 8% of the PRK eyes and 2% of the SBK eyes having Grad e 1 staining. At 3 months, 90% of the SBK eyes had no staining, w ith the remaining 10% having Grade 1 staining. Ninety-two percent of the PRK eyes had no staining, with the remaining 9% having Grade 1. By 6 months, the groups were equal, with 98% having no staining and 2% having Grade 1 staining. CORNEAL SENSITIVITY RESULTS

Cornea l se nsi ti vity testing was performed us in g a Coche t-Bonnet esthesiometer with a 6-cm monofilament. At 1 mon th, there was an average reduction in corneal sensitivity of 15% in the SBK eyes, compa red to preoperative measurements, while the PRK eyes had an average reduction in cornea l sensitivity of 5%. At the 3-month follow-up, the average reduction in cornea l sensi ti vity in the SBK eyes remained at 15%, but increased to 7% in the PRK eyes. At 6 months, the corneal sensitivity in the SBK eyes had inlproved , with an average reduction of 13%, while it remained unchanged 308 in the PRK eyes at 7%.

Sub Bowman's Keratomilellsis: Combining the Best of PRJ( and LASIK Subjective Results

Pain response results: Patients found their PRJ( eyes to be significantly more painful, particularly during re-epithelization in the first 3 days after surgery. At Day 3, 88% reported the PRJ( eye to be more painful, with 10% indicating that both eyes felt the same, and 2% finding their SBK eye to be more painful. By I-week, this difference had decreased with patients reporting that the PRJ( eye had more pain (49%) or that both eyes felt the same or tha t they were unsure (49%), (2% felt the SBK eye was more painful). At 1 month, 74% reported that both eyes felt the same, with 22% indicating the PRK eye and 4% finding the SBK eye more painful (p=O.Ol). At 3 months, 88% of patien ts (p>0.69) sa id that both eyes fel t the same, which improved to 94% at 6 months (p=1.00). Patients also reported that their PRK eyes were dryer throughout every postoperative visit out to 6 months, although th is symptom also equalized over time. At 1 day, 43% felt the PRJ( eyes was d ryer, with 47% saying both eyes felt the same and 11% reporting the SBK eye to be dryer (p
Satisfaction with vision: Subjective patient questio nnaires were completed at all postoperati ve visits. Atthe 1 and 3 d ay and I-week visits, patients showed preference fo r their SBK eye by a factor of 20:1 (p < 0.000l). At the I-month visit, the ra tio was 10:1 and almost 2:1 at 3 months postoperative (p < 0.15). The greatest d ifference between the two eyes was seen in the early recovery period (Day 1 and 3 and 1 week), with a trend of equalization seen at 1 and 3 months, although patients continued to prefer their SBK eyes. At 6 months, 65% said that both eyes had the same vision, with 15% indicating the SBK eye and 20% favoring the PRJ( eye (p = 0.63). In ranking their distance vision, under various lighting conditions, on a scale of 1 (poor vision) to 10 (excellent vision), pa tients favored the SBK eye at all postoperative visits through 3 months. At 1 week, under sunlit conditions, patients gave their SBK eye a rating of 8.37 compared to 6.14 for the PRJ( eye; at 3 months, this improved to 9.43 fo r the SBK eye and 9.37 for the PRJ( eye (p < 0.05) . In dim lighting condi tions, patients gave their SBK eye a ra ting of 8.37 vs. 6.24 for the PRJ( eye at 1 week. At 3 months, the SBK and PRJ( ra tings were equal at 9.06 (p < 0.05). Figure 6 shows the subjective distance vision results out through 6 months. 309

Instant Clinical Diagnosis ill Ophthalmology (R efractive SlIrgenJ)

For near vision, the results were similar, with patients preferring their SBK eye, particularly up to the first month. At 1 week, under normal lighting conditions, patients gave the SBK eye a ranking of 8.76 compared to 6.98 for the PRJ( eye (p<0.05). At 3 months, patients sti ll preferred the SBK eye to the PRJ( eye, (9.22 vs. 9.14) (p < 0.05). In dim lighting cond itions, the SBK eye was given a rating of 8.55 at 1 week vs. 6.57 for the PRK eye (p<0 .05). At 3 months, there was no difference between eyes with a ranking of 9.10 for the SBK eye and 9 for the PRJ( eye (p < 0.05). Figure 7 shows the subjective near vision results through 6 months. At n o time did any p atients report dissa tisfacti on with the SBK eye, whereas 1 patient reported being dissatisfied w ith the PRK eye throu gh 3 months.

Patient complnints: Through the first postoperative week, patients reported that the SBK eye was less painful than the PRJ( eye at a ratio of 25:1 (87% vs. 8%) (p < 0.0001). At 1 month, this ratio improved to 5:1 (p ; 0.01) and than 2:1 at 3 months postoperative there was no differe nce (p ; 0.65). Patients reported that the SBK eye had less sensitivity and visu al fluctuation through 1 month postoperative compared to the PRJ( eye (28% vs. 38%) (p ; 0.09). They also reported fewer difficulties with night driving (12% SBK eye vs. 18% PRJ( eye) (p ; 0.08). Through the 3-month assessment, patients reported less double/ghost vision (2% SBK vs. 6% PRJ() (p >0.1 ??) and glare/ ha los (8% SBK vs. 12% PRK) (p ; 0.08). At 6 mo nths the most frequent complaint was fluctuating vision with 20% of PRJ( eyes and 18% of the SBK eyes experiencing this. The second most frequent complaint was difficulty w ith night driving with 10% of PRJ( eyes and 8% of SBK eyes experiencing difficulties. SIGNIFICANCE OF RESULTS In almost every aspect of the results, the SBK eyes outperform the PRK eyes,

particularly in the immediate postoperative period when we look at the visual results and pati ents' subjec ti ve experiences. In other areas, such as biomechanica l response, there were no differences between the SBK and PRJ( eyes, which suggest that SBK has a similar effect on corneal biomechanics as PRK. There was a g reater loss of corneal sensitivity U, the SBK flaps compared to the PRK eyes through 6 months. However, this decrease was significantly less with both SBK and PRJ( when compared to thicker LASTK flaps created w ith a femtosecond laser or a mechanical microkeratome (Durrie, personal data). 310

Sub Bowman's Keratomileusis: Combining the Best of PRJ( and LASIK The conclusion to be reached from this first study to compare SBK with PRK is tha t this new procedure does offer refractive surgeons and patients the advantages of both LASIK and PRK - with the quicker visual recovery of LASIK and the biomechanical changes and tear function similar to PRK. Yes, there is an equalization of the results between the 3 and 6-month postoperative visits. However, this should not come as much of a surprise given the general acknowledgement that PRK patients begin to achjeve their best visua l resul ts starting around the third postoperative mon th. Proponents of surface procedures who argue that it is unfair to compare the results between a flap-based and surface ablation procedure before the 3-month visit are missing the point. Tod ay's refractive surgery patients are looking for the "Wow" fac tor. They've seen the television ads where happy patients testify to waking up the first morning after surgery and seeing the alarm clock for the first tim e in their lives without glasses or contac t lenses. They are looking for that sa me thrill. Offering them a procedure that leaves them with pain and blurry vision for days, weeks or even months, is doing a disservice. Ofcourse, they also want the "Wow" with a re-assurance of safety. We believe SBK meets and, potentially, exceeds these expectations. [s the world of refractive surgery ready for the next "K?" Time will tell if there is widespread endorsement and use of SBK. Although fur ther clinical studies on SBK are needed, as well as a better understanding of these new biomechanical tests, these initial SBK results have definitely changed the way we curren tly perform surgery. In addition, in the future, we can expect to have grea ter fl exibi lity in how we customize a femtosecond- laser flap with the ability to customize the flap edge based on epithelial thickness or the flap shape to factor in astigmatism.

311

32 cTfNTM (custom Transepithelial "No-touch, One-step, All-laser") Refractive and Therapeutic Ablations with the iVISTM Suite Carlo Francesco Lovisolo, Charles Wm Stewart (italy)

After mo re than a decade of attempts to identify the optimal strategy to perform customized excimer laser treatments on the basis of corneal anterior

surface elevation data with d ifferent technological means, a new generation of ophthalmic surgical products first became commercially ava il able in Europe in the spring of 2006: a single platform for both custom refractive and custom therapeutic surgery. The iVIS Suite is the first system designed, engineered and manufactu red for the rigorous demands of customized corneal refractive and therapeutic surgeries. The iVIS Suite includes three synergistic applications areas: Diagnostic - to collect high precision, highly repeatable biometric measuremen ts; Design - to develop surgical p rofiles to treat both stable and unstable corneas; and Delivery - to implement the desired corneal surgery with a high performa nce, high resolution laser delivery system. DIAGNOSTIC PRODUCTS

The iVIS Suite's diagnostic products provide the surgeon with acc ura te and highly repeatable data as a fundamental for design of the surgical profiles. Importantly, this data is used to regularize the cornea thusl y correcting high and low order corneal aberrations while respecting the unique characteristics and dimensions of the eye's diaphragm, the pupil. The ultimate design of the surgical profile is based upon a synthesis of corneal shape, pupil dimensions, and refractive data. PRECISIOTM: HIGH DEFINITION CORNEAL AND ANTERIOR CHAMBER TOMOGRAPHY

312

Real, repea table measurements of corneal shape based upon corneal elevation, is fundamental to the design of a new, postoperative ideal aconic surface. Based upon the Scheirnpflug principle, Precisio'" measures over 39,000 da ta points

cTEN™ (custom Trallsepithelial "No-toJlch, Oue-step, A ll-la ser")

Fig. 1: Precisio's horizontal scan of Dr Lovisolo's left eye

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Fig. 2: PrecisioTM high definition corneal and anterior chambe r surgica l tomographe r

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313

Instant Clinical Diagnosis in Oph thalmology (Refractive SlIrgery) for each s urface: anterior cornea, posterior cornea, and iris plane/anterior lens surface. A 3-D pachymetry map is derived from the differences in elevation from anterior to posterior corneal surfaces. Precisio's data acquisition is from a rap id series of SO high resolution Scheimpflug images recorded in only one secon d from a tandem cameral system. A specialized eye-tracking subsystem is used with in conjunction with a 4 axis automated positioning system. Add itionally, ocular features including li mbal vessels and iris features are recorded for use as the basis of data registration during surgery an d active ro tational tracking . In vivo, repea tab ility is the only, though in d irect way to assess acc uracy (correspondence to true dimensions) of measurements, and Precisio's anterior corneal surface meaSLUements are repeatable w ith precision exceeding 1.5 microns centra lly and the posterior surface (and 3-D pachymetry) exceeding 10 microns. To achieve th ese levels of surgical precision, the Precisio system has been engineered to be very stable and damp to motion an d vibra tion. Precisio allows th e opera tor to select one of two modes, Surgical and Diagnostic. Diagnostic mode u tilizes single examina tion view of th e described ante rior segment surfaces. The Surgical mode requires the operator to acq u ire at leas t two seq uen tia l examinations, with a subsequent auto m ated d ifferential analysis of the da ta sets validating tha t the data is repeatable. Precisio's proprietary da ta validation removes subjective bias out of a critical process that with other systems may require the surgeon to visually determina te whether or not the da ta is repeatable and acc urate enough to be used as th e basis of surgery. Importantly, the validation process does not use multiple averaged da ta sets assuming that the average would be accep table. Upon completion of the sta tistical analysis of two or more da ta sets with low variability, Precisio will prompt the operator that the data may be exported for surgical plamUng. The su rgical d ata is comprehensive and includes patient 10, multiple elevation data sets, pu pil dimension at examination an d with its rela ti ve location to the da ta sets for data registration during surgery, and addition al ocu lar features mapping that is used for intraopera ti ve eye registration, identifica tion, and acti ve rotational tracking. The Clinical Applications

314

Precisio provides surgical g rade da ta which must be highly acc urate and repeatable d ata. This data is design ed to be used as the basis of custom refractive su rgery and custo m therapeutic surgeries. Examples of th ese surgical applications are to correct prior refractive surgery failures from too sma ll optical zone, decen tered aalations, induced irregular astigma tism, or

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315

Instant Clinical Diagnosis in OphthalmologlJ (Refractive Surgery)

lamellar procedures such as laser deep lamellar keratoplasty or epikeratophakia. The Precisio tomographer also provides useful data for phakic and aphakic IOL implantations such the 3-D anterior chamber dimensions. pMetrics™; Dynamic Pupil Assessment and Ideal Pupil Determination

It is essential that any surgical plan developed for refractive, therapeutic, or

cataract surgery must fully consider the patient's pupil sizes with respect to the balance of the overall visual system. In the past, surgeries were designed with a standard size optica l zone that mayor may not have any size relationship to the dynamic diaphragm limiting the patient's refractive system. To provide a surgical plan that is truly customized to the patient demands that the optical zone dimension adequately covers the pupil, but does not needlessly remove tissue because a standard size optical zone was used by default w ithout thought as to if was really "right sized". pMetrics™ provides critical pupil dimension data from analyzing d ynamically the pupil sizes from scotopic to photopic in controlled and calibrated lighting scenes (a true pupillography). This important data not only describes pupil dimensions in commonly encountered lighting conditions, but also provides new insight into to qualitatively understand the pupil's relative reactivity. pMetrics utilizes binocular eye-tracking with elliptical fitting, tele-centric optics with constant magnification within the depth of focus of the system, 30 micron preCision of pupil dimensions, and internal testing scenes that can be either standardized with calibrated illuminations, or custom defined environments by the operator. The Ideal Pupil

The examination data is collected binocularly and includes pupil dimensions (minimum, maximum, and mean) for each lighting scene. Uniquely, the data is statistically analyzed with a lifestyle weighting to determine an Ideal Pupil dimension that will cover two standard deviations of all of the visual conditions that the patient could be expected to encounter based upon a clinical assessment of typical visual environments. The 95%criterion is deemed to be a safe value. The Ideal Pupil dimension may be used by the surgeon as a basis for determination of the ablative optical zone and may also have useful indications for selection of IOL dimensions including the appropriateness of a particular multi-focal lens design. SURGICAL DESIGN PRODUCTS

The iVIS Suite incorporates new intelligent design tools that extend the 316 surgeon's capabilities to design physiologically sound, customized surgical

cTEN""M (custom Tratlsepitlrelial "NO-tOllch, Olle-step, All-laser")

Ideal pupil projection

Fig. 6: The ideal pupil

Ideal aconic surface

Volume of the ablation

Fig. 7: Since 1997, the original CI PTA (Corneal Interactive Programmed Topographic Ablation) considers the volume of the ablation as described by the intersection of the anterior surface of the cornea and the ideal aeonic corneal surface. Ablation takes into account the patient's real anterior corneal surface , not derived from mathematical calculation based upon lens application

317

Instant Clinical Diagnosis in Ophtl!alm ologtj (Refractive 5l1rgenj) plans. These surgical plans cover a m uch broader range than any o ther refractive platform, for example primary fu lly customized refractive surgery, complex corneas that are resultant from prior refracti ve surgery failures, and unstable corneas that prior wo uld have been relegated to a more serious, full cornea transplantation. CIPTATM - Corneal Interactive Programmed Topographic Ablation

CIPTA " , is a fundamental departure from refractive only treatments that have been marketed either as standard refractive treatments, wavefront adjusted or wavefront guided refractive treatments. As a synthesis of high definition elevation data, dynamic pupil dimensions, and refractive da ta, CIPTA incl udes corneal lower and higher order aberrations. This data synthesis is used to create a proprietary ideal aconic slirface that uniquely covers the projection of the Idea PlIpil dimension onto the surface of the postoperative cornea. The volume of this abla tion is defined by the intersection of the real corneal surface (measured by elevation topography) and the ideal acollic s/lliace that is lim ited to the ideal pllpil dime nsion. As an important poin t of differentiation, this is not derived from a single lens formula or matrix of lens formulas (spatially resolved ) as with wavefron t. This method also does not suffer fro m the spatial lirnitations of refractive only based ablations that only have information within the pupil at whatever illumination happened to be presen t when the refrac tive d ata was acquired, nor is it applied without specific know led ge or without regard to the underl ying corneal shape. Morphologic Axis vs. Optic Axis

Refractive based treatments are by definition acquired and calculated only along the op tical axis. Un iquely, CIPTA utilizes a p roprietary method to decouple the Morphologic Axis from the optic axis. The Morphologic Axis can dramatically minimize the total amount of tissue that is surgically removed, but generally incrementally spares more tissue with the higher the degree of irregularities present in the preoperative condition. cJENfM - custom transep ithelial "no-touch, on e-step, all-laser" treatJnent strategy. CIPTA provides multiple surgical planning strategies, inclusive of cTEN, a Single step, transepithelial ap proach which eliminates mechanical touching of the cornea. There is a resurgence in interes t with many well known surgeons claiming a steady increase in the percen tage of surface ablations performed due to safety, better results, and improved medical regin1Cns. With 318 CIPTA, the surgeon has a choice in selecting LASTK, LASEK, PRK, or the

cTENTM (custom Tran sepithelial "No- touc/r, Oue-step, A ll-la ser")

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319

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Su rgery)

new cTEN procedure. cTEN eliminates any mechanical or laser keratome induced aberrations that are unmeasured and unaccounted for with LASIK, in addition to any safety concerns with the use of microkeratomes. Variable Width Constant Slope Transition Zone

The CIPTA custom treatment includes a transition zone strategy w ith patented charac teristics that are novel to the industry. Treatment plans commonly are performed by adding a fixed width to the optical zone regardless of the slope from treated to untreated tissue. The ClPTA transition zone is developed as an additional customized element of the treatment. The accelera tion of the slope from the optical zone to the untreated cornea is controlled as a constant slope in each radial direction. This produces a va riable width to accommodate chan ges is power from astigmatism or local irregularities. The constant slope, variable w idth transition minimizes risk of regression by producing a phYSiologically smooth and constant shape as opposed to a sharply accelerated "blend zone" w idely used with legacy laser systems. This is especially dramatic with high amounts of astigmatism and hyperopic refractive corrections. CLApM - CORNEAL LAMELLAR ABLATION FOR TRANSPLANTATION

Keratoconus patients have h istorically required co rneal transplantations when no standard optical treatment w ill allow fun ctio nal vision and the patient has become contact lens intolerant with concomitant resultant corneal scarring. A penetrating keratoplasty ("PK") was the last resort and left the patient with an additional set of significant risks, complications, va riable clinical results and patient satisfaction issues. With CLAP" the surgeon may choose to utili ze a fully au tomated, custom lamellar transplantation of the cornea. As opposed to lamellar keratoplasties that are being attempted with mechanica l or laser keratomes, CLAT creates a uniform thickness receiving bed in which the new normal thickness transplant is placed. This eliminates most serious residual irregularities of the keratome prepared bed and thusly improves the resultant corneal optics. The Host

The receiving bed is created by calculating the intersection of the pachymetry map and the ideal cornea l bed for the pa tient. Thi s irregular volume is removed wi th the iRES laser

320

cTENTM (custom Transepithelial "No-touch, Olle-step, All-laser")

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321

Illstant Clinical Diagnosis ill Ophthalmologt) (Refractive Surgery) The new uniform thickness receiving bed now takes on membrane properties ... w ith no cross sectional rigidity. The Donor

The surgeon resizes the donor cornea thickness with the iRES laser from the endothelial surface by the a mount of the residual cornea receiving bed thickness ... A trephine will cut the cornea of the donor to an equal (or sligh tl y larger) diamete r than the diameter of the receiving bed. The donor is position ed . ... on th e receiving bed, on w hich a peripheral pocket may be created, an d then secured with conventional sutu res or tissue glue. IRESTM - HIGH RESOLUTION, ULTRA-FAST CUSTOM REFRACTIVE AND CUSTOM THERAPEUTIC LASER

iRES'" is the first refractive laser system spec ifica lly d eveloped to perform custom ized refractive and therapeutic corneal surgeries. Surgical computeraided design and planning usin g the principles of CIPTA n, an d CLAp M, integrates the real corneal shape, d ynamic pupil assessment, and refractive aberrations to define the abla tion profile. The iRES laser features a 1,000 H z deli vered frequency utili zing a proprieta ry dual beam syste m, each operating at 500 H z. The m icrometric 0.65 mrn spots each have a highl y symme tric, Ga ussian shape. The treatment position is con tinuously mon itored and corrected using a high-speed eye-tracker indudin g active rotational tracking. The system unit includes dual m onitors with, the surgeon centric monitor displaying eye tracking and surgical informa tion, and the ma in system monitor d isplaying overall system and abla tion details. CONSTANT FREQUENCY PER AREATM

Unique to the iRES laser is a p atented beam delivery method, Constant Frequency per Area'" (UCF / AU). CF/ A tunes the 1 KHz delivery frequency so that regardless of the abla tion layer area treated , the delivered freq uency remains constan t per area. With lasers that only randomize the laser spots, as the ablation layer becomes smaller in size, the affect of the plume becom es substantially higher, absorbing an u ndetermined am oun t of the laser energy. Legacy laser systems typically p rov ide a compensation or a lgo rith m to minimize the reductions in energy delivered as ex tra shots deli vered 322 compensate for energy absorbed by plume. Additional physician main tained

cTEN"M (custom Tran sepithelial "No- toll ch, One-step, A ll-laser")

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abla tion rate.

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treatment layer for a Co nstant Freque ncyl mm2 (C FIA™). CFIA dramatically roduces the energy that Is variably absorbed by localized plume concentrations, thereby

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n. .,. '" Fig. 13: Example of successful repair of a decentration and induced irregular astigmatism following LAS IK for a -7. 00 D. After 2 years, the patient presented to us complaining of severe night vision disturbances. On examination, the UCVA in the right eye was 20/40 improving to 20/25 with + 1.50 - 1.00 x 10°. The contrast sensitivity was below the normal range for 3, 6, and 12 cpd. Topography showed a significant decent ration (lower left, 13a) and the wavefront ana lysis showed that the eye had significantly ra ised spherical aberrations with increased coma and higher order aberrations. The patient was treated utilizing a transepithelial surtace ablat ion strategy with the iRES laser implementing a topographically guided treatment designed using CIPTA software. The intended postoperative refraction was plano. Four months postoperatively (top left, 13a), the UCVA was 20/20 +, with a gain of 3 lines of BSCVA. The patient reported that the haloes and the starburst had disappea red . The postoperative topog raphy was well-centred with a large optical zone . The topography difference map (right, 13a) clearly shows the areas of temporal flattening and central and nasal steepening that were achieved corresponding to the ablation profile generated by the CIPTA algorithm (13b)

323

Instant Clinical Diagnosis in Ophthalmologt) (Refractive SlIrgen)) nomograms may be further applied to lessen variabili ty of clinical results. By mainta in ing the same frequency per area both throughout the entire ablation profile and from patient to patient, the laser benefits from improved predictab ility, improved ablation smoothness, and without extra shots delivered to the cornea. An additional benefit for custom and highly irregular ablation sha pes is highlighted by lasers without CF / A: the unpredictability of the plume effect becomes more unwieldy with no well defined algorithm for asymmetric and irregular shapes. Clinical Applications

With the iVIS Suite, complications such as decentrations, optical zones smaller than the entrance pupil d iameter, and irregular astigmatism secondary to infective or immunological stromal keratitis like DLK may now be more easily managed. Uniquely, regular or irregular ammetropias that may be residual after lamellar or penetrating keratoplasties, thermokeratoplasty, radial or arcuate ke ratotomy, cicatricial sequelae of contact lens-induced bacterial keratitis can be surgically corrected w ith optimized predictability, efficacy and safety ratios. For conven tional cases, the CIPTA customization allows the surgeon an unprecedented capability to con trol the width of the optical zone, the preservation of its aspherical profile and the volume of ablated tissue. This translates in extraordinary outcomes, as can be seen in the contrast sensitivity charts at six months postoperatively, for the high myopia group in particular.

324

cTEN'fM (cllstom TransepitiJelial "NO-tOIlC/!, One-step, A ll - la ser " ) Ablation map

,ea

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Fig. 14: Example of a laser enhanceme nt of small optical zone typical of olde r generation excimer laser ablations. The original treatment was performed to correct - 5.00 0 of myopia. The 31-year-old patient complained of severe halos during night driving. The anterior surface of the cornea was highly oblate (quotient of asphericity Q = + 1 in the pupillary area). On examination with the pMetrics pupillometer, the patient's mesopic pupil size was 8.8 mm! The UCVA was 20/20 improving to 20/ 15 with + 1.50. Cycloplegic refraction was + 3.00 and the contrast sensitivity below the normal range. The eye was treated as transepithelial surface ablation with the iRES excimer laser using a topographically guided treatment designed using CIPTA software (ablation profile: 14a). The intended postoperative refraction was + 0.75. Four months postope ratively, the UCVA was 20/20, cyclople gic refraction + 0.25 + 0.25 x 10°. Complaints of serious night time visual problems had disappeared. The topography di fference map (right, 14a) shows the enlargem ent of the optical zone with a restoration of a more physiological profile (Q = - 0.03)

325

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery)

Fig . 15: A 39-year-old male patient underwent three consecutive laser procedures (PTK), after a viral keratitis complicated the original AK procedure for a + 0 .25 - 4.00 x 90° mixed astigmatism

in the right eye. On an examination performed 15 years after the first procedure , the UCVA was 20/400, imp roving to 20/80 with - 2.75 - 2.00 x 110 0 and to 20/25 with pinhole. Haze 2 + and slight basement membrane dystrophy was found as partially responsible of the irregularities of the anterior corneal surface. esa corneal topography (bottom left, 1Sa) and corneal wavefront analysis (1Sb) showed that the eye had significantly raised higher order aberrations. The eye was treated with transepithelial surlace ablation procedure, using a topo-graphically guided treatment designed with the CIPTA software (15c, postoperative ideal shape and ablation profile) and the iRES laser system. 0.02% Mitomycin C was applied for 15 seconds at the end of the procedu re. The intended postoperative refraction was plano. One month postoperatively, the UGVA was 20/20 , improving to 20/ 15 with + 0.75 - 1.00 x 102! All haloes and starbursts disappeared with an impressing subjective and objective improvement. The postoperative topography was well-centered with a large optical zone

326

Fig. 16: Corneal topography (GSO) shows irregular astigmatism in the left eye of a 37-year-old male patient, 6 years after 7-mm penetrating keratoplasty for keratoconus (bottom left). BSCVA was 20/40 with - 2.25 - 4.25 x 80°, 20/25 with pinhole. Wavefront analysis showed that the eye had significantly raised higher order aberrations. The eye was treated with transepithelial surface ablation procedure , using a topographically guided treatment designed with CIPTA software. 0.02% Mitomycin C was applied for 120 seconds at the end of the procedure . The intended postoperative refraction was plano . Six months postoperatively, the UGVA was 20/ 30, improving to 20/20- with - 1.00 x 100°. The postoperative topography (top left) was regular, with a large optical zone and a physiologically normal asphericity

cTEN™ (cllstom Transepitilelial "No-tollcll, One-step, All-laser") Ablation map

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Fig. 17: Corneal topography (GSO) showing irregular astigmatism in the right eye of a 19-year-old male patient, 40 months after 7.5 mm penetrating keratoplasty for keratoconus (bottom left, 17a). BSCVA was 20/30 with + 3.50 x 165"' , 20/20 with pin hole. The eye was treated with transepithe lial surface ablation procedure, using a topographically guided treatment designed with CIPTA software (ablation profile , 17b). 0.02% Mitomyc in C was applied for 120 seconds at the end of the procedure . The intended postoperative refraction was + 1.00. Six months postoperatively, the UCVA was 20/25 , improving to 20/20- with + 1.25 x 165°, The postoperative topography (top lett, 17a) was regular, with a large optical zone and a physiologically normal asphericity

Fig. 18: 10 years after 6 corneal procedures (one exagonal keratotomy, three holmium laser thermo keratoplasty and two conventional PRK) for hyperopic astigmatism, the right eye of a 44-year-old male patient showed a BSCVA of 20/50 with + 0.50 + 4.50 x 85°. The eye was treated with transepithe lial surface ablation procedure, using a topograph ically guided treatment designed with CIPTA software . 0.02% Mitomycin C was applied for 120 seconds at the end of the procedure. The intended postoperative refraction was plano. Four months postoperatively, the UCVA was 20/30, improving to 20/30 + with + 0.75 x 85°. Preoperative (bottom left), postoperative (top left) and differential (right) topography maps are shown

327

Instant Clinical Diagnosis in Ophthalmology (Refractive SurgenJ) Ablation map

Fig . 19: 14 years after a combined RK-AK procedure complicated with an ectasia of the inferior astigmatic cut, the right amblyopic eye of a 36-year-old man showed a BSCVA of 20170 with + 0.50 + 7.00 x 50, not improvi ng with pinhole. Disabling visual symptoms, mainly glare and monocular diplopia, were described unde r mesopic light conditions. Corneal topography (bottom left, 19a) showed the ectatic changes of the inferior incisions. The eye was treated with transepithelial surface ablation procedure , using a topographically gu ided treatment designed with CIPTA software (ablation profile, 19b). 0 .02% Mitomycin C was appli ed for 120 seconds at the end of the procedure . T he intended postoperative refraction was plano . Six months postoperatively, the UCVA was 20/30 , improvi ng to 20/30'" with + 1.00 - 2 .00 x 170°. T he postoperative topography (top left, 19a) shows a part ial restoration of the corneal physiology

Fig . 20 : 23 years after a pseudomonas eruginosa corneal infection in a contact lens wearer, the topography of the left eye (bottom left, 20a) of a 47-year-old lady showed the irregularity caused by a deep stromal scar in the supratemporal quadrant. BSCVA was 20/50 with - 4.50 -6.00 x 165 0 • Disabling visual symptoms were described under mesopic light conditions . The eye was treated with transepithelial su rtace ablation procedure , using a topographically guided treatment designed with CIPTA software (ablation profile, 20b). 0.02% Mitomycin C was applied for 120 seconds at the end of the procedure. The intended post-operative refraction was 0 .50. Six months postoperatively, the UCVA was 20/25 , improving to 20/20 with - 0.25 - 0 .50 x 138°. The postoperative topography (top left, 20a) shows an almost complete restoration of the anterior surface corneal profile

328

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329

33 Astigmatism Frank Jozef Goes (Belgium)

SIGNS AND SYMPTOMS

This 22-year-old Malaysian man consulted because of progressive visual deterioration in the Right eye; according to his story because of progressive m yopia. The condition of the eyesight went down specifically the last 1.5 years. He obtained from an optician 3 different pairs of glasses during the last two years and was diagnosed with important astigmatism. General Condition; No diseases The visual acuity was uncorrected Right eye 0.1: With correction -2 -4 .73 axis 143 maximally 0.3. FURTHER INVESTIGATIONS Differential Diagnosis Discussion

Wavefront very abnormal Topography atlas; corneal distortion right eye. K values were normal each eye: values normal Kl 41.5 and K2 43 axis 2°. Since we could not find any reason for the low visual acuity in this right eye and since .he did not mention any amblyopia, further investigations were necessary. Fundus examination demonstrated to our astonishment a huge black greyish mass nasal superiorly obscuring the superior nasal quadrant; the optic disc and the macular area were normal. B scan Ultrasound demonstrated clearly the solid structure of the lesion. Slitlamp examination under dilatation demonstrated an asymmetrical deformation of the lens. The visual field showed an important defect inferiorly. Specular microscopy was normal each eye. Discussion

This young guy who came in for Refractive surgery; his myopia seemed to progress and the refraction changed in the direction of important astigmatism(too fasted) had indeed a voluminous tumor ca using deformation of the lens 330 and so doing creating an important astigmatism.

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331

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The tumor basal dimensions were 18 x 18 mm with a total thickness of 14.8 mm; causing infiltration of the ciliary body between 11 to 3 0' clock meridian. This case demonstrates the need for a complete clinical examination in all cases. Treatment

The diagnosis of melanoma-melanocytoma was made and lamellar sclerochoroido-cilio iridectomy tumor resection was performed by Prof Patrick De potter Clinigues Universitaires 5t Luc Belgium Brussels. At the end of surgery 20 mm iodine 125 plague radiotherapy was applied on the resection site. Histopathology confirmed the diagnosis of Melanocytoma. One week after surgery, the uncorrected visual acuity was 0.3. Prognosis

Seems to be fair although we don' t have the follow-up.

332

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333

34 Customized LASI K for Presbyopia: PML™ (Presbyopic Multifocal LASIK) Technique Roberto Pinelli (Italy)

Why "c /lstomization" in the LASIK treatment for presbyopia? The purpose of this chapter is to describe first of all the PMU" technique (Presbyopic Multifocal LASIK, the patented technique that we studied and developed at the Istitu to Laser Microchirurgia Oculare, Brescia, Italy), and then to show the customization of this treatment through cl inical cases. N o wa da ys, w e 've been perfor ming PMLTM a t the Is ti tuto Lase r Microchirurgia Oculare in Brescia since almost 6 yea rs with excellent results. Patients are very satisfied w ith their visual situation for far and for near. It's important to underline the fact that presbyopia should be trea ted in a slightly different way from the other "classical" visual defects for what the patient care and the management of the expectations are concerned. In particular, I'm using the questiOlmaire for patients' satisfaction evaluation that SICR (the Italian Refractive Surgery Society) prepared and validated (results of the validation process presented by Elena Scafficli, psychologist, psychotherapist at the ASCRS congress in San Francisco, March 17 - 22, 2006, and to be presented at the ASCRS congress in San Diego, 28/4 - 2/5 2007), in order to monito r the rate of satisfaction that the patients treated with PML'" reach in time. What my R and D team and I are considering at the moment is that one of the most Significant aspects of this trea tment is the custorniza tion. In this chapter the reader will find some clinical cases to better understand the customized approach for the treatment of presbyopia with PMU" (one myopic-presbyope, one hyperopic-presbyope, one emmetropic-presbyope and one mixed astigmatic-presbyope). Because of the customization of the procedure for each patient, the clinical histories reported ahead in the dlapter will show the VA pre- and postoperative for far and for near, and the aberrometrica l maps (WaveScan, VisX, Santa Clara, USA). The statisti ca l analysis that the reader will observe underlines the red istribution of the aberra tions which occurs through the PMUMtreatment, w hich also explains the brillia nt results obtained w ith this technique in terms 334 of visual acuity and quality of vision.

Customized LASIK for Presbyopia: PMLT"

Fig. 1

Fig. 2 Figs 1 and 2: Roberto Pinelli , MO , performing PM LTM su rgery at the Istituto Laser Microchirurgia Oculare , Brescia, Italy

335

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) THE CORRECTION OF PRESBYOPIA In all refrac tive surgery, our goal h as been to surgically correct the visual

defects, i.e. m yopia, hyperopia, astigm atism, and presbyopia. Correction of these defects is possible through corneal surgical procedures or lenticular surgery. Of all the visual defects, presbyopia h as been the most challenging to correct, partly because the mechanisms of accommodation and the causes of p resbyopia are complex an d n ot fully understood. Thus far, it has largely been managed through th e use of progressively stronger spectacles, which gradually take over the near focus work of the crystalline lens. Presbyopia is also unique in that it is the only refractive error that is consid ered to be progressive in nature.

Although our m anagement and most of our experience seem s to point to the progressive nature of presbyopia, in tru th, we don't know for sure that it truly progresses. It may be that in our "prosthetic culture" we have merely become unnecessarily dependent on our glasses and contacts. In an y case, a surgical alternative to the correction of presbyopia is appealing because of th e en ormous pool of presbyopic patients with a desire for good lIDcorrected vision. Mild hyperopes and emmetropes who have never worn glasses are particularly uncomfortable with presbyopia and its associated inconveniences. APPROACHES TO THE SURGICAL CORRECTION OF PRESBYOPIA

The mission of p resbyopic surgery-as with all other refrac tive surgeriesshould be to eliminate the symptom s of the refractive error, rather than to correct the anatomical defect itself. For this reason, I think an approach that provides pseudoaccomn10dation is n atural and appropriate. Ifwe can provide patients w ith good functional vision at multiple distances, it is not necessary

to restore true accommod ative function in the form of a dynamically adjusting optical power of the eye. 111ere are se veral potential sites for correction of presbyopia. The cornea is probably the m ost common target, as it is the area refractive surgeons are most

comfortable operating on. Theoretically, the anterior chamber provides another site for the correction of presbyopia, but this is as yet theoretical and would likely prove extremely difficult in reality. The human crystalline lens can be replaced w ith a multifocal or accommodative intraocular lens, of which n1any different styles are now under development and coming to market. Finally, a number of scleral implant or ciliary muscle surgical procedures have been developed. This approach, however, is complicated, largely untested, and seems 336 "n1ore surgical" than is necessary.

Customized LASIK for Presbyopia: PMI'M

Fig . 3: The operating theater at ILMO , Brescia, Italy

Fig. 4: Roberto Pinelli and his team performing PMLTM surgery

337

In stant Clillical Diagnosis ill Ophthalmologt) (Refractive Surgery) As a familiar corneal procedure, LASIK h as been the mos t popular and easiest surgical approach . In ad d ition to the surgeon comfo rt level with the procedure, patien ts in the presbyopic baby boomer generation are also familiar with an d accepting of the p rocedure. In addi tion, LASIK can be performed bilaterally on the same day, is relatively qu ick a nd painless, and has proven to be quite safe. Even with LASlK, we h ave several options fo r add ressing presbyopia. Most convention ally, we have taken a monofoca l app roach with surgically-induced monovision, but bifocal and multifocal approaches are increasin g. LASIK is ideal for presbyopia because of the absence of haze and its associated refractive complications, the absence of regression, and th e presen ce of a reg ular and, hopefully, thin flap that can protect the multifocality created in the stroma. In designing a multifocal LASIK p rocedure, we must ta ke ad vantage of some of the lessons learned from current and past procedures. Some m yopes treated with radial kera totomy have re tained good nea r and d istance vision well into the presbyopic age range. Why is that? Similarly, some hyperopic LASlK patien ts also have retained thei r pseudoaccommodative fun ction well into their old er yea rs . Again, why wou ld tha t be? The secret lies in the asphericity of the cornea. A prolate cornea seem s to have the capability to focus both fa r an d nea r better than an ob la te cornea. We have seen that again recently with conductive keratop lasty, which I perform and have been involved in studying u1 ltaly. CK is an excellent technique for correcting h ype ropia an d restoring near vision. It appears to provide some degree of m ultifocality because eyes corrected for near visual acuity with CK typically have much better distance visual acuity than would be expected. This may be due to the prolaten ess of the post-CK cornea. In any case, tl1e "b len ded vision" of CK permits the presbyopic patient to read by treating just the non-dom inant eye. [n the past six years, my p urpose has been to create a truly multi focal corneal procedure that can be performed bilaterally if necessary, and that w ill work for any eye, regardless of preoperati ve refractive error. Intuitively, we know that man y zones should do a better job of mimicking na tu ral vision than just two zones, but obtaining a gradual but effective multifocality is nonetheless challenging. The ultimate presbyopic LASIK procedure must also be easy to perform, with standardized nomograms that any surgeon can use as a basis for successful su rgery. THE PMLTM PROCEDURE

338

With the above goals in mind, I developed and have been investigating at ILMO a patented p rocedu re which we call PMUM (Presbyop ic Multifocal

Customized LASIK for Presbyopia: PMLTM

Fig , 5: A moment during PMLTM surgery at lLMO, Brescia, Italy

Fig. 6: Roberto Pinelli, MD, and his team after PMLTM surgery

339

Instant Clinical Diagnosis in OphthalmoloSlJ (Refractive SlIrgery)

LASIK). This procedure can be performed on presbyopic myopes, hyperopes, astigmats, mixed astigmats and emmetropes. Multifocality on the cornea is created using a multi-step treatment in which several independently calculated ablations are performed at various optical zones. Depending on the patient's refractive error, there may be anywhere from three to eight different concentric zones. In all cases, the goal is to treat the centra l cornea for d istance vision,

with a multifoca l peri pheral cornea that is able to provide functional nea r vision. Some other multifocal LASIK procedures take the opposite ap proach, w ith the near correc ti on in the center. How ever, the central cornea provides an excellen t site fo r dis tance vision because it is relatively aberration-free, while

peripheral abe rrations may actually be useful for near focusing. In this mu lti-step process, we first treat astigmatism in the classic manner, as if we were d oing a purely astigmatic laser correction. Next we treat the distance defect in a zone on the central cornea. Then, we treat the near defect in a larger optical zone. Finally, other zones may be created to ensure that the overall power of the cornea is emmetropic, even though there are varying powers in the different optical zones. It is a proced ure that is highly customizable for each patient's optical needs. J began d oing this proced ure in 2002, starti ng cautiously by treating 10 patients in only their non-dom inant eyes. One year postopera ti vely, five of these patien ts we re happy with their outcomes; the other fi ve required retreabnent. These unilateral patien ts experienced some of the benefits and problems of monovision . I became convinced that a bil ate ral approach would be more effecti ve, and began to adjust and refine the no mograms towards this end. CLINICAL CASES: EXAMPLES OF CUSTOMIZED PRESBYOPIC TREATMENT WITH PMLTM Case Example I: Emmetropic-presbyope

Clinical History

340

• Ma le, 56 yea rs old • PRE-OP uev A : - For far: RE 20/20, LE 20/ 20 - For nea r: J7 • PRE-OP BeV A fo r near: Jl add. +1 D • POST-OP UeVA (18 months) : - For fa r: RE 20/15, LE 20/15 - For nea r: )l natural

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Instant Clill ical Diagnosis ill Opltthalmolog<j (Refractive SlIrgenj) Case Example II: Hyperopic-presbyope

• Ma Ie, 55 years old • PRE-Or ueVA: - For far: RE 20 / 33, LE 20/ 50 - For near: )8 • PRE-OP BeV A - RE 20/ 20 sph. +1.25 D - LE 20/20 sph. +1.25 D - For nea r:)l add. +1.5 D • POST-Or uev A (18 months): - For fa r: RE 20 / 20, LE 20/15 - For near: J2 nat. Case Example III : Myopic-presbyope

• Female, 62 years old • PRE-Or uev A: - For far: RE 20/ 40, LE 20/ 40 - For near:)5 • PRE-OrBeVA - RE 20 / 25 sph. -0.5 D cy!. -1 D ax 180 0 - LE 20/25 sph. -0.5 D cy!. -0.5 ax 1600 - For nea r: )1 add. +2.5 D • POST-OP UeVA (18 months): - For far : RE 20/ 20, LE 20/ 20 - For near: Jl nat. Case Example IV: Mixed Astigmatic-presbyope

• Female, 53 years old • PRE-Or uev A: - For far: RE 20/ 40, LE 20/ 40 - For nea r:)5 • PRE-OP BeV A - RE 20/20 sph. -0.5 D cyl +1.5 D ax 90 0 - LE 20 / 20 sph. -0.5 D cyl +1.25 ax 80 0 - For nea r:)1 add. +1 D • POST-Or u ev A (18 months): - For far: RE 20/20, LE 20/ 20 - For near:)1 nat. 342

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Short comments of the author to the four cases As you can see there is a redistribution of the aberrations; as far as the SBF, (Spread Point FW1Ction) is concerned there is a significant reduction of the spread point and an increase of the Depth of Focus effect in all the eyes. The visual acuity and the quality of vision of all patients are excellent probably due to this reason, and no patient showed an y complain as far as halos and night vision performances.

Final Considerations

No doub t that the future development of the PMLT" technique will be always more the customization through the wavefront technology and aberrometries. The distribution and the quality of the postoperative abe rrations will be the key to find a "custom-curve" able to originate a perfect pseudo-accommodation for each single eye (visual acuity for far and for near and quality of vision). Despite these fundamental considerations, we will now describe the pearls and the lessons lea rnt in the past six years. We have found that it is better to overcorrect hyperopia and to undercorrect myopia, and that astigmatism must be fully corrected for a satisfactory outcome. In some cases (hyperopes and emmetropes), the cornea becomes more prolate; in other cases (primarily myopes) it actually becomes mo re oblate. Pupil size is not an important fa ctor in determining outcomes from this procedure. We ha ve no t had to manage patients with especially large pupils any d ifferently than we would with a monofocal LASIK proced ure. The PMLTM technique uses the same or less tissue as other laser vision correction procedures, so although pachymetry is important, it is no more a factor than in mono focal LASIK. Keratometry is very important, as it is essential to keep the pre- and postoperative K values constant. Patients must be willing to participate in training their eyes to learn how to see at near w ith the multifocal correction. OUf patients are instructed not to use

reading glasses after the procedure at all and to do visual exercises (for which we provide instruction) in order to maintain the eye's focusing power w ith age. In our experience so far, is a very successful procedure that has been wellaccepted by patients and is in high demand at our center. Currently, about 50% of our patients are PMLT" cand idates. The procedu re and the excellent results experienced by patients have enhanced the reputation of our center and generated many referrals. OngOing resea rch is req uired to determine whether and when regression might occur. 344

Customized LASIK for Presbyopia: PML'"

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Brief note to the vid eo: the PML'" represented in the video rega rds a hyperopic eye. Yo u can note a preplanned d ecentration of the position of the ring on the eye. The temporal decentration of the suction ring allows to create a perfect corneal flap and a proper small hinge, crucial in the h yperopic PMLTM treatment. We all know that often the white to white measuremen t is small in hyperopiC eyes and the asymmetrical position of the suction ring is fundamental to perform customized cut in them. In this case the white to white was 11.3 mm.

346

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347

35 Amblyopia Frank Jozef Goes (Belgium)

SIGNS AND SYMPTOMS

This 56-years-old lady WA consulted because of visual deterioration in the RIGHT eye. In the clinical history she mentioned an amblyopic RIGHT eye; corrective lenses were never prescribed and she was told that the condition was not suitable for any treatment. Since she had heard about our new VisuMax femtolaser, she ca me in with the request for Femtolasik treatment. General Condi tion was excellent; no diseases, no medication. The visual acuity was uncorrected Right eye 0.2 ... and left eye 0.9 ... With correction the visual acuity was Right eye 0.6 and left eyel.O. Correction R eye +2 cyl.-1.5 axis 5°L eye +0.75 Op tr. Kera tometry d ata were as follows; R K1 42 .75 and K2 47.35 d ptr; L 42.5 and 44.0. Examinations of fundus and ocular pressure were normal. The visual field showed a depression centrally in the righ t eye. Specular microscopy was normal each eye; 1946 cells mm 2 R eye and 2125 Leye. Slitlamp examination demonstrated already an irregularity of the cornea and forward bulging in the right eye. FURTHER INVESTIGATIONS

Since no optical correction was possible Wavefront measurement and Tomey topograph y we re done. These examinations clearly demonstrated the KERATOCONUS condition with high probability (see Klice Maeda index) and important wavefront anomalies (high coma) typical for keratoconus condition.

348

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349

Instant Clinical Diagnosis in OphthalmologtJ (Refractive SurgenJ) Differential Diagnosis- Discussion

In this case the condition was neve r correctly diagnoses since no topography measurement was ever done -.beside that never a good clinical examination

of the corneal curvature was made. Trus patient with an earlier diagnosis of amblyopia has indeed an evolutive keratoconus. This is rather exceptional at this age since usually the condition becomes manifest at a much earlier stage. Treatment

We know that treatment options for keratoconus are-Spectacles-Contact lensesIntacs-Surface ablation-Crosslinking-Corneal graft. Since spectacle or lens correction wo uld be impossible for such a cornea, our preferential approach would be CROSSLINKING .We hope to be able to inlprove the steepness and the irregularity of the cornea. After 6 months-according to the improvementsurface ablation or Contact lens prescription will be performed. Prognosis

Is moderately good. Using our approach we try to avoid-or at least- postpone corneal graft since the outcomes of this surgery are improving with the introduction of the Femtosecond laser.

350

Amblyopia

Fig. 28 Figs 2A and B: Topography

351

36 laser Scleral Ablation for True Accommodation for Presbyopia J T Lin (Taiwan)

INTRODUCTION

Accomm odation is the ability to focus on near objects through controlled changes in the shape and thickness of the crystalline lens and mediated by ciliary muscle contraction. To correct presbyopia, it is a ftmdamental necessity to understand how accommodation occurs and how it changes the optical and tissue parameters of an aged-eye. The effectiveness of ciliary body contraction for lens relaxation (or accommodation) may be influenced by the combined aging factors, including lens property changes (index, size, thickness and curvature), tissue elastic changes (in sclera and ciliary) and the zonular tension change. We note that methods using mechanica l sclera expansion techniques such as the scleral band expansion (SEB) su ffer from major regression due to tissue healing, whereas the laser method to be p resented in this Chapter showed a minimum regression. There is a fundamental difference between the mechanism behind laser and non-laser methods. The Lin-Kadambi hypothesis proposes the increasing of elasticity resulting from scars consisting mainly of sub-conjunctival tissue which fill s-in the gap of laser-ablated sclera area. This fillin g process also prevents the sclera tissue healing which closes the gap and thus minimizes regressio n. This Chapter shall review the mechanisms and techniques for the treahnent of presbyop ia with an emphas is on laser scleral ablati on. A 4-components theory which attribute to the lens accommoda tion (curvature changes) and to the anterior movemen t of the lens will be presen ted. Finally, T present the most recen t techilique usin g the collagen biomatrix which blocks the scarring and prevents the postoperative regression. THE AGEING EFFECTS OF HUMAN EYES

Many theories have been proposed for the age-related loss o f acco mmoda tion including: (a) lens-based theories; (b) geometric theories; (c) lenticular theories; and (d) multi -fac tor theory. The factors, which may contribute to changes in overall refractive power, include the cornea l shape and thickness, lens shape and thickness, anterior and vitreous cham ber depth and globe axial length. A 352 change in the refracti ve index gradient of the lens cortex has been suggested

Laser Scleral Ablation for Tnte Accommodation for Presbyopia

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353

Installt Clillical Diagllosis in OphthallllologtJ (Refra ctive SlIrgenJ)

(Koretz and Handelman, 1988: Pierscionek, 1993) to be a substantial factor contributing to the progression of presbyop ia. Pierscionek and Weale (1995) proposed that because of the increased thickness of the lens and the an terior shi ft of the zonula r attaclullents, presbyopia is a failure of the lens to be maintained in a fla ttened state. Cross-sectional studies of age-related changes in resting refraction show a drift towards hyperopia from abo ut age 30 to 65 yea rs and then a drift towards myopia after age 65 years (Slataper, 1950; Saunders, 1981) attributed to growth and the for wa rd movement of the lens. It should be noted that the "lens paradox" showing " myopic-shift' with ageing (d ue to lens curvature changes) may be counter-balanced by all those factors which may cause a hyper-shift including the decreases of lens equivalent index and globe axial length with age. We shall also note that the increase of lens power due to radii decrease is a weaker age-dependence that of the equivalent refrac tive index change, therefore, the "net effects" ca use a "hypershift" by ageing. PRESBYOPIA TREATMENT TECHNIQUES

Various technologies have been developed for the correction of hurnan visjons

including: (a) reshaping the cornea (therma lly or ablatively), (b) replacemen t of the intraoc ular lens, an d (c) changing the sclera and / or Ciliary body. In the following discussion, we shall foc us on the treatment of presbyopia. The effecti veness of Ciliary bod y con traction for lens relaxation (or acconunod ation) may be reduced by the combined aging fac to rs, including lens property changes (index, size, thickness and curvature), tissue elastic changes (in sclera and Ciliary) and the zonular tension change. Therefore, the treatment of presbyopia shall involve methods which may change one or more of these fac tors. Progressive addition spectacle lenses, monovision, bifocal or multifocal contact lenses, monovision, bifocal or multifocal cornea l refractive surgery, multi focal a n d di ffr active intraocula r lenses (l OLs) and accommodative intraocular lenses (AIOL) have been used for the correction of presbyopia. Thornton, attempted to cause scleral expansion through the p roced ure of anterior ciliary sclerotomy (ACS) which was shown to have major regression due to the tissue healing postoperatively. Schachar has proposed a scleral expansion band (SEB) procedure w ith the help of scleral inlplan ts. Fukasaku, wldertook anterior ciliary sclerotomy in combination with silicone implantation (SEP) wedged into the incision in the hope of achieving grea ter effect and greater stability. Fu kasaku and Schacha r believe that presbyopia is the result of crowding in the posterior chamber due to continuous growth of the lens throughout life. The SEP teclmique im proved the 24-m om th postoperative regression from about 94% (in a sinlple ACS) to about 39% (in SEP) according

354

Laser Scleral Ablation for Twe Accommodation for Presbyopia

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Fig . 5: The proposed filling effect of collagen biometrix after the laser scleral ablation

355

["st a" t Clinical Diagnosis ill OphtlwllllologlJ (Refractive Surgery) to Fukasaku's report in the ESCRS meeting in 200l. Baikoff, used a technique to posi tion the segme nts in fr o nt of t he ci liary bo d y in order to release the tension on the zonule and modify the shape of the crystaLline lens. The most recent method laser presbyopia treatment (LPT), proposed and patented by J.T. Lin in 2000, was to use an infrared or UV laser to ablate the sclera and increase its elastic prop e rti es exerting a positi ve effect on accommodation. Other methods which treat presbyopia using a monovision correction include Ho:LTK (using a Ho:YAG laser at 2.1 um), DTK (using a diode laser at about 1.88 um) and CK (conductive keratoplasty using ratio frequency). LASIK p rocedure also p rovid es bifocal or mul tifoca l cornea reshaping (using an excimer ArF laser). Other proposed technologies for presbyopia treatment include: Lens refilling phaco-Ersatz in tracaps ular-balloons); p h ocamodui ation, using Q-switch Nd:YAG laser to photodisrupt the crystalline lens to reduce lens volume or softened the lens nucleus. THE MECHANISMS

Presbyop ia, as trad iti onally accep ted H elmhol tz, is due to p rogressive weakening or atrop hy of the ciliary m uscles. However, Schachar believes tha t the ciliary m uscle d oes not really become weak but rather "fun ctionally, less efficient" . This inefficiency, he proposes, can be attribu ted to a p rogressive increase in the d iameter of the lens d u ring middle-age w hich causes a "crowding effect". Consequently, the Ciliary muscle is left with no space to contract. Th us, w ith a view to give the muscle "more room" for contract ion. Helmholtz hypothesis and Schachar h ypothesis expla in how accommodation occurs in a no rmal person. Helmholtz says that the ciliary muscles contract wh ich relaxes the zonules causing the lens capsule to become lax.ll1e jelly like lens material hence bulges in the center. There is a decrease U1 the equatorial d iameter in the process. Schacha r, on the other hand, postulates that when the ciliary muscles con tract the "equatorial" zonules tighten while the non-equatorial zonules relax. lhis has the effect similar to hold ing a balloon filled with wa ter at its two poles and p ulling it outwa rds. The net resul t is a bulging in the center, i.e. an increase in the anterior-posterior diameter. The degenerative changes, which have been observed in the ciliary muscle of presbyopic eyes, he postulates, may be related to disuse atrophy and no t suggestive of age-related atrophy. Comm ents on Schachar's theory, the concept of scleraJexpansion is under hot debate. Many stud ies have ac tually discounted Schachar hypothesis. A Glasser, MD and S Mathews, MD d emonstrated a decrease in the equatorial diameter of the crystalline lens as an effect of scleral expansion. They also found no evid ence of a dynamic change in power of 356 presbyopic patien ts provide by SchochaI.

Laser Scleral Ablation for Tnte A ccommodation f or Presbyopia In addition to th e classical theories of accOlmnodation and presbyopia that conflict w ith Schachar's ideas, there are additional reason s suggesting that further verification of the efficacy of scleral expansion surgery would be prudent. The repor ted e vidence sh owin g improvemen t in the human accommod ative amplitude is based solely on subjective push-up measures (YangGS, Yee RW, Cross WD, et aI1997) . Mathews had suggested in EyeWorld (2001) that some of the improved reading ability demonstrated with subjective push-up testing might be a result of inadequate testing procedures. It may be due to some kind of induced multifocality of the eye, either in the cornea or in the crystalline lens, as a consequence of these surgical procedures. Patients may be left w ith some kind of aberration, either astigmatism or higher-order aberrations of the eye, which allows them to have fi.mctional nea r and distance vision simultaneously. Mathews stated that itis difficult to find a physiological explanation fo r how a surgical procedure done on one eye should restore accommodation in the contralateral eye. THE L1N-KADAMBI HYPOTHESIS

Lin-Kadambi (2003) hypothesis attemp ts to explain the mechanism by which the procedure of LPT ca uses a positive effect on the range of accommodation. The immediate effect due to the scleral thinning is an increase in the elasticity of the scleral "ring" as a whole. The Ciliary muscle that takes its attachment on the inner side of this more elastic scleral ring is now able to work n10re efficiently as it now works against less resistance. Myo pic or h yperopic shift that has not been reported after LPT. Some studies seem to indicate a paradoxical increase in the scleral diameter. We are not convinced that there is any change in the scleral d iameter as there has been no reported change in the distance refractive status after LPT. However, we do not rule out the possibility of this occurring in some cases. Perhaps incisions and excisions that go full thickness may tend to produce this effect. Lin and Kadambi did not totally discount the existence of the phenomenon of "posterior chamber crowding". We believe that this phenomenon may exist in many cases but m ay not be d irectly related to the physiology of accommodation in all cases. After the LPT procedure the ablated scleral groove gets filled w ith sub-conjunctiva tissue. Alth ough this tissu e forms a good barrier to infection and adds some amount oflateral strength to the wound, it is our contention that the tissue is s till "softer" and more elastic. We also believe that the increased radial elasticity of the scleral ring is p reserved as a whole and hence the positive effect on accommodation retained. Under this scenario, it wj}1 not all be surprising if some regression of effect is observed. Clinically the regression has been reported as minimal over two years and more. We also believe that the "filing-in effect" of the scleral grooves b y the subconjunctival tissue plays a role in preventing regression. In acceptance of 357 the Lin-Kada mbi hypothesis.

Instant Clinical Diagnosis in OphthalmologtJ (R efractive SlIrgenJ) THE 4-COMPONENT THEORY

The von Helmholtz theory states accommodation is achieved by ciliary muscle contraction that causes zonules and lens relaxation. Lin (2004) proposed the two-component theory to analyze a true accommodation which excludes the myopic-shiltca used by axial length elongation or corneal curvature change. A new model co ns isting of 4 co mpon ents is shown in Table 1 and Figures 2 and 3. A ~ A1 + A2 +A3 + A4 Table 1: The Lin's 4-component theory for true accommodation (A) A=A1 + A2+A3+A4 A1 = CF x dR

A2 = mdS. m =(0.9-1 .6) D/mm A3 = MdL. M=(2.4-2.8) D/mm

A1: accommodation due to len s CUlvatu re change A2: accommodation due to len s anterior shift (dS) A3: accommodation due to axial length increase (d L)

A4 : accommodation due to corneal asphericity change

The CF is the conversion factor which translates the change of the lens power to the whole eye power. Typical value of CF~(0. 7 -0.8). One may also calculate the reported pseudo-accommodation (Singh, 2000) caused by a m yopic shift -2.6 diopter for an axial length increase 0.89 mm (with axial length of L ~ 22.94 mm). However, Uozato (Uozato, ARVO Meeting, 2003, Abstract) measured a very small axial length elongation (mean of 0.06 mm) in true accommodation. Therefore, our theory proposes lens relaxation (A1) and anterior shift (A2) to be the two major components in compa ring to A3 and A4. CLINICAL RESULTS

McDonald et al reported an eye at age 53 administered by pilocarpine induced an accommodation of 4.25 diopter after scleral buckling. Lens thickness increase (dt) 0.18 mm and anterior shift (dS) 0.57 mm were measured associated with the total accommodation A ~ A1 +A2, calculated by our theory to be A2 ~ 0.53D and A1 ~ 3.780, where a net an teri or shift dS ~ -0.57 + 0.18 ~ - 0.39 mm and change rate m ~ 1.36 (D/mm) are used. Lin and Mall o (2003) reported laser sclera ablation (LASA) procedures for presbyop ia patients (age 42-60, mean 53.2) where the laser ablated a portion of the scleral tissue o utside the limbus to cause a n1ean true accommodation of 358

Laser Scleral Ablation for Tnte A ccommodation fo r Presbyopia

1.96 diopter, without myopic-shift induced pseudo-accommodation. This was justified by no change of the far vision or corneal topograph y in treated eyes or comparing the p reopera ti ve and postopera tive kerometer (K) readings. The recen t study using collagen biomatrix to block the wound healing may offer a potential technique to red uce the postoperati ve regression (EyeWorid AsiaPacific, Ju ne, 2008). CONCLUSION

To conclude, the accommodation caused by a laser or non-laser techniques ihas very complicated mechanism and can only be unders tood quantitatively by treating the eye as a "whole". To increase the accommod ation amplitude (A) from the cur rent mean value of about 1.8 0 to >2.5 o would be the important subject for fu ture studies. In addition, regression is still a major issues for almost all the surgical methods and remains to be improved . Finally, nonsurgical methods with minimum invasive is under development by Lin which has the potential of enh ance the Ciliary-body (CB) contraction (accommod ation) by a directthermal stimulation olthe C B w ithout ablation of the scleral tissue.

359

37 Solid State Lasers for Refractive Surgery Emanuel Rosen (UK), Tarak Pujara (Australia)

INTRODUCTION BASIC LASER BACKGROUND Light Amplification by Stimulated Emission of Radiation

What is Light? Sometimes light behaves as if it is composed of waves and at other times as if it is composed of particles. For this reason, the na ture of light is often difficu lt concept to grasp . Light is a transverse electromagnetic wave, the energy 'waves' as it oscillates between an electric field and magnetic field. For light to also have the p roperties of a particle, it is useful to consider these waves to come in packets of a limited size (p hotons) When the electrons spinning aro und an atom are energized to a higher energy orbit and then decay back to lower energy orbit, they can give off a photon of a light. The wavelength of this light is inversely p roportional to the energy lost b y the electron, w hich in turn d ependent up on the type of atom . This process of light generation is ca lled spontaneous emission. Stim ulated emission occurs when this event is triggered by another photon that has an identical wavelength to that which the atom will produce. The amplification process is thus one p hoton triggering the release of a second, nea rl y identical photon. In a laser, each photon may then go on and trigger two more p hotons and so on. LASER PUMPS

Lasers need to consist of a 'pump' (a source energy to energize the atoms) a ' medium' that contains the atoms that do the lasing, and a cavity consisting of mirrors to d irect that ligh t backwa rds and forwards thro ugh the energized media to allow the amplification process to grow to a useful level. There are man y different methods for p umping lasers ranging from chemical reactions to electron beams. Probably two of the most common form s of p umping involve either electrical discharge or current, and light energy produced by either flash lamps, diodes or another laser. 360

Solid State Lasers for Refractive SlirgenJ

Fig. 1: PULZAR Zl (Solid state refractive laser)

213 nm wavelength

Fig. 2: Creation of 213 nm wavelength

361

Instant Clinical Diagnosis in OplrtJ/almology (Refractive SlIrgenJ) LASER MEDIA

The laser med i urn also comes in a large number of varia tions covering all the states of matter. Lasers with a gas medium include CO2 lasers, excimer lasers

and argon lasers; dye lasers have a liquid medium, while neodymium:YAG (Nd:YAG) and diode lasers are examples of solid medium lasers. Nd:YAG lasers are solid med ium lasers that are often pumped with flash lamps. In the laser, the medium is neod ymium atoms. The YAG crysta l holds the neodymium atoms in place and help to transfer the flash lamp pump energy to the neodymium atoms. It is vital that the pumped medium be in a state of population inversion for lasing to occur. Population inversion is when more than half of the atoms in the medium are energized to an excited state. An atom that is capable of being excited and then stimulated to emit a photon of light will also resonantly absorb a photon of the same wavelength when not excited. Hence, it is easy to perceive that unless there are more atoms in an excited state than in a nonexcited state, then the absorption process will exceed the stimulated emission process and amplification will not occur. COMMON PROPERTIES OF LASERS

Light from a laser has a number of prope rties that make it diffe rent from other light sources. Firstly, the divergence of a laser beam is much, m uch lower than that of other light sources. This allows the laser beam to be confined to very narrow beams and to be focused to very small spot sizes. Secondly, laser light is usually monochromatic, that is, the light is of a single very p ure color (single wavelength). Thirdly, laser beam light is usually coherent, that is, all the waves of the photons are oscillating in phase with each other. EXCIMER LASER Basic Concepts

'Excimer' is a contraction of the term 'excited dimer'. Dimers are usually considered to be molecules made up of two identical atoms. However, the term 'excimer' has subsequently been extend ed to include other excited molecules (though usua lly diatomic). If two systems (atoms or molecules) do not form a strong chemical bond when one of them is in an excited state, then the bound excited s tate is called an excimer. Currently ArP gas is used to generate 193 nrn wavelength forcomeal ablation in Laser Vis ion Correction.

Excimer lase rs usuall y consist of a large, elongated aluminum box. This box is filled with the appropriate gas mixture. Running the full length of this box is two metal electrodes spaced about 2-3 em apart. At one end of the box, 362 aligned w ith the gap between the electrodes, a minor is mounted and at the

Solid State Lasers f or Refractive SlI rgenJ

(Jain et aI., 2004; unpubl ished data) 100 90 80 .2 70 E 60 c 50 ~ 40 I30 20 10 0

0.9% NaGI transmission 213 nm transmits 1620 times more than 193 nm in 0.9% NaCI

~ ~

~

193 nm

'"

UV wavelengths (220-190 nm) Fig . 3: Transmissions through 0.9% of NaCL

BSS transmission ('!o ) 100 ~~----------------------------,

250

500 Depth

750

( ~m )

Fig. 4: Transmissions through BSS

363

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery)

other end a window. The window is usually an uncoated optic. The small amount of reflection that normally occurs from each surface is enough to provide laser action. Outside the box there is usually a large bank of capacitors and these are charged using a high voltage power sup ply to several tens of kilovolts. A special switch (thyra ton) is used to dump the energy stored in these capacitors across the electrodes inside the box. The electrical discharge through the gas between the electrodes ionizes the gas and allows the excimer molecules to form. Lasing ac tion usually occurs within nanoseconds. DISADVANTAGES OF EXClMER LASER High Voltage Requirement

The amount of energy involved and the rate with which it needs to he delivered across the electrodes to make excimer laser work is very high. With voltages around 30,000 volts and currents of approximately 10,000 amps reached within Sans, the electrical characteristics are like a bolt of lightning. Early Replacement of Special Switch

A thyra ton is usually used as a special switch to quickly initiate the discharge and carry the high currents. Thyraton failures were quite common and thereby expensive. However, modem excimer lasers, with linproved discharge circuit

designs and using techniques such as electrical pulse compression and insaturable inductors, have significantly reduced the load on those switches and thyra ton failures are now relatively uncommon. Corrosiveness and Toxicity of Fluorine Gas

To maintain the quality of the gas within the cavity is another major p roblem. Excimer lasers are usually specified to run at purities of 99.99995%. The fluorine in the gas usually makes upto 0.1 to 0.2% of the gas volume. However, fluorine is an extremely reactive gas and can react with most materials that make up the components inside the excimer laser cavity and will also react w ith most impurities that have either entered with the gas or are out-gasses from the material inside the laser cavity. These reactions not only use up some of the fluorine gas, so that the lasing action becomes very inefficient, but also create products that can absorb the laser radiation, interfere with the energy transfer process to the argon fluoride excimers and form deposits on the laser cavity optics. These processes can also significantly interfere with the lasing action. To make matters worse, the intense UV and hot plasma which is formed by the electrical discharge between the electrodes helps to initiate many of the reactions that occur.

364

Solid State Lasers fo r R efractive 5l1rgenJ

Fig . 5: T UNEL staining of rabbit cornea following PRK

Apoptosis-3 day

60

50 40

0213

30

Ii!I 193

20

Total cell days-3 day

160 140 120

100

80 60

rf

rt

iii 193

rf-

(f,

tIl

~

0213

rf

rfrt1

rt

rT

40 20

o

m

'0 ~ CE

2

III 3

5

3 4

Y 5

6

Figs 6A and B: Total live cells and apoptotic

' -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _--' cells in crater on day 3

365

Insta nt Clinical Diagnosis in OphtlralmologtJ (Refractive SlIrgery)

Gas leakage (Fluorine) is also a m ajor problem. It may cause serious health problem. Gas discharge into the atmosphere m ay be evid en t by a sharp, penetrating odor and by eye, nose, and throat irritation. Recurrent Expenses of Excimer Gases

Argon and Fluorine ha ve a shelf li fe. Su rgeries need to be completed within a certain pe riod of time after the gas charge is dispensed to the laser head. This results in restrictions on using the laser to maximize the usage of the gas charge. Consequently treatments are usually grouped together in a " List" and performed on only one or two d ays a week. This resu lts in a lack of fl exibility for patient trea tmen t an inability to efficiently perform treatments 'as required'. As the laser operates, fluorine is lost from the mixture and thus the fluorine must be replenished. A common p ractice called "boosting", is a process, in which a small amount of the dilu te fluorine/buffer gas mix ture is added to the laser to make up for the deple tion of fluorine that occurs du ring normal operation. This method can only be used for a given number of cycles after which the gas composition has been so altered the laser will not operate satisfactoril y. The gas charge must then be vented and the laser recharged with a new gas mixture. If not followed properly it will resul t in unwanted down time and u1Creased gas expend itu res. High Cost for Proper Storage of Toxic Gases and Training of a Technician

High-pressure excimer gas cylinders are contained in a protected compartment in any excimer system. Storage of add itional cylinders and the replacement of used cylinders must be done in accordance with "Gas Safety' and "Gas Maintenance" rules applicable to each country. The premix (argon / fluorine) gas mixture used in this laser system is highly toxic. It is always recommended that anyone working with the gas cylinders: 1) be trained in the proper handling of toxic and compressed gases, 2) know the location of the emergency exhaust fan / room purifier switch, 3) have easy access to all required protective equipment, and 4) be familiar with safety procedu res . Hydration Dependence of 193 nm

366

Fluid on the cornea can result in a reduction of the ablation ra te during refractive surgery procedures with 193 nm laser pulses. This red uction in ablation rate is evidenced by the high degree of absorption of 193 nm light in balanced salt solution (BSS). Underlyu1g tissue, is therefore effectively m asked from the incident radiation. An unknown reduction of abla tion rate can result in

Solid State Lasers for Refractive SurgenJ Histology 193 nm

213 nm

Fig . 7: Histological similarities of 193 nm and 213 nm

limbus

Conventional technology

-

1 f

Fig . 8 : ZTRAK technology

367

InstantClillical Diagnosis in Ophthalmology (Refractive SlI rgery) undercorrection or refractive errors or irregular ablations, such as the formation of corneal islands. Other Disadvantages of Excimer Laser

• Large foot print an d and bulk of excimer lasers requires a large surgical room and therefore higher overhead costs for the facility. • Excimer lasers are relatively noisy d uring operation. • High power consumption to charge gases increases usage costs.

• A small flying laser energy beam is very difficult to obtain but are required for custom ablations. • Longer warm up time

• Mature technology -little chances for further development. SOUD STATE LASERS IN REFRACTIVE SURGERY

Over the years, there have been several attempts to develop and market solid state lasers for use in refrac tive surgery. Currently only one company manufactures a solid state refractive lase r an d that is Custom Vis, based in Perth, Australia. Pulza r Z1 is a trade name for their commercial solid state laser. It is now clinically proven that it is at least equivalent to ava ilable excimer refractive lasers but superior in terms of simplicity, usage. Data produced so far suggests equivalent safety, predictability and reliability. The current excimer technology is approaching the end of its product development cycle and may welJ be replaced by Solid State Laser technology by resolving the disadvantages of excimer lasers and ye t performing at least equivalently. SOUD STATE LASER History

Attemp ts had been made in the late 1980s included nanosecond an d picosecond YAGs or YLFs that operated in the near infrared (IR) or at green wave lengths. Phoenix Laser Systems, headed by Alfred Sklar, attempted to take ad vantage of photodisruption with a doubled YAG. Intelligent Surgica l Lasers, under Josef Bille, used fast-pulsed near IR to vaporize tissue. Both lasers attempted to perform intrastromal ablation within the cornea without affectin g a corneal surface. The results were not very good and not reproducible. In the earl y 1990s, other companies tried to develop solid state lasers. Two of these were the Lase r Harmonic quintu pled YAG from J T Lin at Laser Sight and the LightBlade from Shui Lai at Novatec. Neither system made it to the market. The LaserSight system never got beyond the experimental stage. The ovatec system after some h uman clinica l trials simply ra n out of money. 368 Another company, Q-Vis, had developed the Quantum 213 solid state laser,

Solid State Lasers fo r R efra ctive Surgery

Determine the rest position of the eye using video image prior to surgery

Determine the current position of the eye during the treatment

Compare the current position of the eye to rest position and record difference in microns

Send offset position to the computer which offsets the laser scanner during treatment

Fig . 9 : ZT RAKTM

eye tracker flow-chart

·h. . .

,

~

Acceptable range

.......-tl--...... I

I

.

\

-

v--I\

'1"\

·.

-

Outside of acceptable range

I" I'

f /'

· ·

,.... .........

Back within acceptable range

Fig. 10: GAZETRAK technology

369

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery)

and also started FDA trials. After Dr. Paul van Saarioos, co-founder of Q-Vis and developer of solid state laser left the company; they were unable to progress much further and stopped production and dissolved. Present Situation

Currently the only company in the Solid State Laser in the Refractive market is the Pulzar Z1 manufactured by Custom Vis based in Perth, Western Australia. CustomVis, founded in Mardl, 2001, is aiming to be a major force in the refractive surgery industry over the coming decade. It has installations in 9 countries including Europe, South America and Asia pacific. Custom Vis has a very skilled Research and Development team. The company spent around 20 million US$ on research and development, and Dr Paul van Saarioos, Chief Scientist and Research and Development Manager has developed a vast experience in the refractive industry since eariy 1986. The PULZAR Z1 (Solid State Refracti ve Laser), is designed specifically for custom surgery, permitting an accurate approach to correcting both standard and non-standard vision disorders. The PULZAR Z1's small 0.6 mm Quasi Gaussian spot size, stable homogeneous beam energy, fast closed loop eye tracking, ad van ced solid sta te scanning technol ogy and sophisticated proprietary surgical planning software, all contribute to the system 's ability to overcome the traditional linlitations of excinler lasers in performing custom surgery. The Solid State Laser differs from all other commercially available excimer lasers. It uses a 213 nm waveleng th as opposed to the common 193 run wavelength used for excimer lasers, and it does not require gas as excimer lasers do. The 213 nm wavelength delivers a number of potential benefits over the 193 nm wavelength of tradi tional excinler lasers, including reduced dependence on tissue hydration, less thermal effect and more efficient tissue ablation. Future of Solid State Laser

Today's ophthalmologists use three different lasers for different surgical procedures, i.e. UV laser to correct refractive disorders, Nd:YAG for capsule operations and a green laser to coagulate blood vessels in the retina. It is possible to develop a laser using one solid state sources to produce a combined laser which w ill offer all three types of beam. 11lis w ill red uce cost and space requirements whilst inlproving clinical efficiency. The solid state diode pumped Nd:YAG (1064 nm) laser is frequency doubled in to green (532 nm) and passes through further frequency conversions to produce the 213 nm wavelength for refractive surgery. The multi-purpose laser w ill be able to take advantage of these wavelengths used for other ophthalmic 370 surgeries, in particular, YAG lasers which are currently used in post-cataract

Solid State Lasers for Refractive SlIrgenJ

Fig. 1 1: Limbus vs pupil eye tracker, limbus easily visible pupil not at all visible

Upright

Supine

Fig. 12: Cyclorotation

371

Instant Clinical Diagnosis in Ophtllalmologtj (Refractive Surgery)

surgery to remove the posterior opacity of capsule. Whilst, green lasers are used for treatment of va rious retina l conditions, such as, retinal photo coagulation, age related macular degeneration and ocular vein occlusion. Green lasers are also used to treat open angle glaucoma . TECHNICAL ADVANTAGES OF SOLID STATE LASER Solid State Technology

The laser system is based on a Quintupled Q-Switched Nd:YAG laser. The 1064 nrn Nd:YAG laser is flash lamp or diode pumped and frequency converted via a series of three non-linear optical (NLO) crystals, which are used to fa cilitate harmonic generation processes to produce the surgical beam with a wavelength of 213 nrn. The firs t NLO crystal doubles the fundamental 1064 nrn Nd:YAG infrared beam to green ligh t at 532nrn. The second crystal doubles the green light to ul traviolet light at 266 nm. The final crystal mixes the 266 nrn ultraviolet beam with residual Nd:YAG infrared light to produce far ultraviolet light at 213 nm. This wavelength, close on the spectral scale to the clinically well accepted 193nm ArF excirner laser beam, is used to perform the surgica l treatment. Advantages of Solid State Laser

• Stable homogenous beam energy • Longer laser source lifetime

• • • • • • • • • •

Improved reliability and efficiency Low power consumption Improved beam quality Greater pulse to pulse stability Extremely fa st 'Turn on', to 'Read y' period Fewer consumables, (i.e. Gas, and Fluence plates, not required ) No purchase or handling of toxic gas required Long Optic life - fewer optic changes required over life of laser Extremely fa st and accurate eye tracking (1000 hz closed loop) Faster patient turn arolmd due to automated routine set up and calibration needs.

213 nm Wavelength

The 213 nrn wavelength of the PULZAR Zl is generated by tran smitting the 1064 nrn Nd:YAG laser beam through th ree non-linear crystals. Be nefits of the 213 nm wavelength include: • Less dependence on tissue hydration • Production of clean and smooth ablated surface 372 • Reduced thermal effect and colla teral damage

Solid State Lasers for Refractive Surgen)

0.6 mrn Flying !Gaussian Beam Profile

Solid State

I Scanning technology Fig. 13: 0.6 mm Flying Gaussian Beam Spot and Crystalscan

Fig . 14A : Dry Bed - Before laser firing

373

Instant Clinical Diagnosis in Ophthalmologtj (Refractive Surgenj)

• More efficient tissue ablation • Less d amage to optics due to humidi ty issues. Tissue Hydration Study

Absorption coefficients were obtained for sod ium chloride solu tion (saline) and balanced salt solution at 193 nm and 213 11m laser wavelengths. This was achieved by measuring laser pulse transmission tl1Iough both solutions. Results were used to obtain an overall absorption coefficient and penetration d epth for balanced salt solu tion and 0.9% sodium chloride. Absorption coefficients in balanced sa lt solution fo r the 193 nm and 213 nm wavelengtlhs were fo und to be 140 and 6.9 cm-l , respecti vely. In 0.9% sodium chloride solution, the absorption coeffi cient was 81 cm-l at 193 nm and 0.05 cm -l at 213 run. Penetra tion d ep th of 193 nm in BSS is 72 ~m and in 0.9% sod ium chlorid e is 123 ~m, while penetra tion dep th of 213 run in BSS is 1450 ~m (almost 20 times higher than 193 mn) and in 0.9% sodium chloride is 2 x 10; I'm (over 1000 times higher tha n 193 run ). Absorption coeffi cients and penetration depths of variou s fluid s

193 nm Solution

BSS 0.9% Sodium

213nm

Absorption

Penetration

Absorpt ion

Penetration

Coefficient

Depth

Coefficient

Depth

72 123

6.9

1450

0.05

2.0 x 10 5

140 81

Ch loride

During refra cti ve surgery, fluid placed on tlhe surface of the cornea has p roved to be a barrier to ablation for the 193 nm wavelengtlh. The in creased penetration depth through sodium chloride and balanced salt solution for the longer 213 run laser wavelength is advantageous for laser vision correction as it has a very little effect from hydration. Clinical Advantage

This fea ture of 213 om has an important cl inical ad vantage. Fluctuations in corneal hyd ra tion or environmental humid ity are wilikely to have a Significant effect upon the performance of the solid state laser. The subtle effects of these conditions upon excimer laser perfonnance are the prima ry reason most refractive surgeons have personalized nomogram s. TI1€Se allows compensation for hydration issues related to surgeon technique (e.g. wet vs d ry technique, dura tion of bed exposure) and localized climatic cond itions. By taking theses 374 variables, the outcome of solid state proced ures are mo re prac tical.

Solid State Lasers for Refractive SlIrgenJ

Fig . 148: Wet Cornea-After laser fired

Fig. 14C : Wet Cornea - After laser fired

375

Instant Clinical Diagllosis in OpltthalmologtJ (Refractive SlIrgenJ) HISTOPATHOLOGICAL COMPARISON OF PHOTO REFRACTIVE KERATECTOMY (PRK) IN RABBITS WITH 193 NM AND 213 NM

Introduction

The cornea is commonly re-shaped by photorefractive keratectomy (PRK) which ablates the cornea by removing micron-thick layers of tissue from Bowman's layer and the anterior stroma. PRK is typically performed using a 193nm Excimer laser. However, there are concerns about the practicality and safety of the excimer (193 nm) laser for corneal surgery. To address these concerns, a solid state 213 nm (5th Harmonic) Nd:VAG laser has been developed. Programmed cell death, or apoptosis is particularly important to measure as it is a precursor for post operative corneal opacification, or haze. Other important contributors to haze a re cell proliferation, migration and morphological changes. A study was performed to examine the short term time course of live cells (keratocytes) and apoptosis in the cornea of adult rabbits following PRK treatment using a 193 nm or 213 nm laser. Methods

New Zealand White rabbits underwent PRK (-5 diopters, 6.5 mm optical zone, 7 mm transition zone) laser surgery with the 213 solid sta te laser or the 193 excimer laser. Corneas were evaluated after 3 days. Analysis

Photographs of the sections were taken with a fluorescence microscope. Six photographs of each section were taken, two inside the crater, two at the edges of the crater within the transition zone and two from the non lasered portions of the cornea outside of the ablation zone. Discussion

There was no difference in the amount of apop tosis induced by both lasers. The increased number of live cells (keratocytes) in the cra ter of the 193 nm lasered corneas suggests cell proliferation and / or migration. It also suggests that 193 nm lasered cornea has more inflammation than 213 nm lasered cornea. In conclusion these results demonstrate that the 213 nm solid state laser has similar cell dea th indUCing properties, but causes less cell proliferation / migration (inflammation), to the currently used 193 nm excimer laser, therefore making it a potentially superior tool for refracti ve surgery. 376

Solid State Lasers for Refractive Surge"}

Fig. 140: Wet Cornea - Increases

~~~

______~UL__~~~~~'

Emergency stop

Fig. 15: Laser enable button and emergency stop button

377

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) SCIENTIFIC BENEFITS

The UV wavelengths within 190-220 nm represents the acceptable 'win dow of abla tion' within which p hoto-abla tion of corneal tissue can occur with a high degree of precision and minimal collateral/thermal damage to adjacent areas. It is also the range where cells exposed to these wavelen gths are less susceptible to cellular inactivation and mutation, this is due to a screening or

protecting intervening layer of cytoplasm before DNA located in the core produces a similar clinical and histopathology course to the excimer 193 nm laser in a vivo rabbit study and produces a clean, smooth ab1ation surface on in vitro porcine tissue.

The Pulzar Zl's 213 nm wavelength is close to the absorption peak of collagen and has low absorption in fluid . These contribute to its high corneal ablation efficiency. It proves that the Solid State 213 nm laser produces a similar clinical and histological course to the excimer 193 nm laser. SPECIAL FEATURES AVAILABLE TO THE PULZAR Z1 Eye Tracking

The PULZAR Zl features three eye-tracking technologies: ZTRAK includes, • Video eye-tracker, • Fast analogue eye-tracker (1 kHz closed-loop response) G aze tracking • Video gaze-tracker. ZTRAK

The video eye-tracker tracks the position of the limbus in a video image and adjusts the position of the treahnent every frame. It also tracks iris p attern and limbal blood vessels continuously. The fast analogue eye tracker monitors and adjusts the position of a pair of LEDs (Light Emitting Diodes) that track the limbus through a 1kHz analogue feedback circuit. 111e combined position of the LEOs is then used in combination w ith the most recent video eye-tracking data to determine the current position of the eye for every pulse. Gaze Tracking

Gaze tracking is a unique technology developed by the Custom Vis research team to ensure the accuracy of laser treatment. The v ideo gaze-tracker monitors

reflections off the iris through a second video camera to determine the direction of the patient's gaze: • Monitors the angle of the patient's gaze and the changes in the fixation of 378 the eye intraoperatively;

Solid State Lasers for Refractive SurgenJ

Fig . 16: Treatment generation screen in ZeAD

Fig. 17: Simulated postoperative topography - Fitted optical view

379

InstalltClinical Diagnosis in Ophthall1lology (Refractive Surgen}) o

o

Deactivates the laser automatically as the patient's gaze angle shifts by more than a set maximum threshold, until gaze d irections restores; Ensures accurate laser spot placement on the eye delivering the correct laser pulse to the exact corneal location.

Unique Advantages of Limbus Eye Tracking (PULZAR ZI Tracking System)

Limbal tracking is not affected by cornea l dryness or wetness, laser plumes or flashes as it is tracking the limbus which is unaffected by any laser treatments. It proves that, o Limbal Based Eye Tracking has the potential to be significantl y more accura te (about twice as accurate) than Pupil Based Eye Tracking during LASIK; o Limba l Based Eye Tracking allows more accurate registration of custom Treatments. Pupil Tracking Problems in any conventional excimer laser o Looking through LASIK bed (Eye Tracker can not see pupil well, o Excimer laser dries corneal surface making it even less optical o Ablation plume and laser flashes also affects accuracy o Pupil centre moves upto 0.7 mm as it changes size Video 3 Centration Video - Pupil Center changes up 0.7 mm with size changes.

Cyclorotatlon Intelligent 'Pattern ReCOgnition Technique' (Iris Pattern Recognition Technique (IPRT) and Limbus Registration) is used to determine the patient's cyclorotation angle between the preoperative upright position and supine position. Iris pattern and blood vessels on the sclera are used as a 'guide' to determine the angular rotation between the patient's supine and upright position. The treatment is appropriately rotated to compensate for any cyclorotation between the two states relative to the patient's eye for accurate ablation of the corneal surface. It provides a more precise positioning of the ablation profile as it detects and compensates for cyclorotation and pupil centroid shift. This minimizes chances of human error and gives great results for astigmatism .

0.6 mm Flying Gaussian Beam Spot

380

A beam size of less than 1 mm is essential for the creation of a superior customized profile. The current Solid State Laser available in market (PULZAR Zl, Custom Vis, Australia) has a 0.6 mm Gaussian shaped flying spot, which is one of the smallest spot sizes on the market in the refractive industry. 0.6 mm is also considered as an ideal spot size for customised surgery.

Solid State Lasers for R efractive SlIrgenJ

Fig . 18: Auto selection of pupil and limbus

Fig. 19: iTrace visual function analyser

381

Instant Clillical Diagnosis in Oplttltalmologtj (Refractive SlIrgenj)

The Gaussian beam profile w ith smaller spot size permits fine sculpting of corneal tissue producing smooth ablation surfaces. The flying spot ablates the cornea in a non-sequential pattern to avoid the effects of laser plume and enables tissue thermal relaxation. These improvements create:

• Improved pulse to pulse energy stability. • Minimal thermal heating of the cornea. • Precise customised ablation profile.

CRYSTALSCAN The currently available Solid State Laser (PULZAR Zl) is equipped w ith CRYSTALSCAN high performance ul tra fast solid state scanning technology. This advance soli d state scanning teclmology is significan tl y fas ter than galvanometer based systems used in conventional laser systems, which is very importan t for achieving a 1kHz closed looped response. CRYSTALSCAN has following advantages. • Allows m uch faster response time to eye movements

• High relia bility, efficiency and accuracy • Allows true fl ying spot scan patterns and complex custo m surgery wi thout increasing treatment time • Co-ax ial scan path eliminates ablation errors d ue to e levation misalignment of the eye • Greatly red uced 'overshoot' and settling times of scanners = fewer positioning errors.

Smoother Surfaces -predictive of greater precision issues in custom surgery and believed, but not yet proven, to resul t in better healing and out comes. Capability for correcting hig h er o rd er ab errations - w ith a fas t scan mechanism, each pulse etches away a very thin layer of the tiss ue (submicrometer) w ithin a small area, delivering ( Uston1 con touring of a surface to

any desired shape, allowing corrections of all optical aberra tions, not just myopia or hyperopia and astigmatism. Non-sequential pulse placement - where no one laser spot is placed directly next to the previous spot. This semi-randomised placemen t of the pulses is essential to avoid thermal build up and imp roper plume evacuation during treatment.

382

Solid State Lasers for Refractive 511rgenj (SE ~ -150) .'

16.00 12.00 "0 Q)

> Q) :E

8.00

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0.00

2.00

4.00

6.00

8.00

10.00 12.00 14,00 16.00

Attempted Note : The graph has come overlapping points

Fig. 20: Myopia and myopic astigmatism, 3 month follow-up (n=436)

Myopia

(~

-14.5 0) and Myopic astigmatism ( ~ - 5.5 0) attempted vs. achieved correction 3 months follow-up (n =436)

III FDA

iii Pulzar Z1 100%

80% V>

~ 60% ~

*'0

40% 20% 0% .j..
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617. 5

UCVA

Fig. 21: Myopia and Myopic Astigmatism , 3 month follow-up (n=436)

383

Ills tallt Clillical Diagn osis ill Oplltl1flll1lo1ogtJ (Refractive Surgery) HINGE PROTECTION

This is a special feature available with the PULZAR Zl, which au tomatically protects the hinge in LASIK or Epi-LASIK trea tments. After selection of the position of the limbus the surgeon can enter the distance of the flap hinge from the limbus then the software will not fire a single pulse from the limbus to the hinge. Advantages of Hinge Protection

• No need to constantly monitor flap. • No laser pulses w ill be fired on the hinge, decreasing the chance of astigmatism or over-correction being induced by laser ablation over the hinge. • More predictab le and accurate results can be achieved. AUTO-CENTRATION

The PULZAR Zl software provides an automated beam-centration procedure that allows the user to align the laser beam if it is observed to be decentered during the da ily system checks. It takes empirical measurements through the eye-tracking system to ensure that the beam is correctly positioned at the treatment plane. AUTO-CALIBRATION

The system ca libration is an automa ted procedure in the PULZAR Zl. This ensures accuracy of the system's laser output and automatically adjusts the internal operating parameters accordingly if required. Advantages of Auto-calibration

• Being an automated proced ure it avoids chances of human error. • No need to have expensive fluence plates as required by excimer lasers • Set up time is fast as calibration time is about one minute - no need to

manually adjust fluence of laser FREEDOM TO SELECT TREATMENT CENTER

The PULZAR Zl allows the surgeon to select the treatment center for standard treatments accord ing to their preference. An image is captured while the patient is on the bed and the surgeon is free to select the pupil-center, corneal vertex (center of the ring light) or any other location they deem appropriate.

384

Solid State Lasers for Refractive SlIrgenJ Hyperopia and mixed astigmatism Postoperative UCVA Al lalest foltow ·up of 3 months (n; 195)

100%

:,'

80%

60% 40% 20%

UCVA

Within ±O.SD

Within ±1 D

Attempted vs achieved

Fig. 22: Hyperopia and hyperopic astigmatism - 3 months follow up--UCVA and FDA vs Pulzar

,

385

II/stant Clil/ical Diagnosis in Ophtha/mol0I5'J (Refractive Surgery) CORNEAL HYDRATION DURING ABLATION

213 run has a special characteristic. As 213 nm lase red pulse is deli vered on to the corneal bed it will produce a fluid over the corneal surface. 193 run laser (Excimer Laser) behaves in the exact opposite way by drying ou t the cornea. As 213 run is less affected by the hyd ration or fluid on the cornea, there is no need to contin uously wipe acc umu lated fluid. Fl uid over cornea will allow patient to have a more clear view of the fixation target than 193 run lasered dry cornea. It allows patients to fix their eye very well during whole treatment reducing chances of decentered treatmen t and increases comfort for patient and surgeon. Figures 14A to D clearl y show the production of fluid over corneal bed as 213 nm laser fires. NOMOGRAM ADJUSTMENT

The 213 nm laser wavelength has increased penetra tion depth through sodilun chloride and balanced salt solution. It proves to be very good fo r laser vision correction as it has very little effect from hydra tion. These allow us to compensate as best we can for hydration issues related to surgeon techniques. While 193run excinler laser resu lts depend on the corneal hyd ration or environmental humidity requiring personalized nomograms for every surgeon. ANYTIME SURGERY - FREEDOM TO DO SURGERIES AT YOUR CONVENIENCE

Anytime Surgery is pOSSible onl y with the Solid State Laser as there is no need to charge or refill gases. You can just switch on the laser and start doing surgeries w ithin 5 minutes (Dramatically reduced warm lip time). There is a no need to keep special surgery days, as there is no extra cost involved in doing surgery at any time and any number of eyes, may be even a Single eye. LESS MAINTAINANCE AND COST

Electricity - 10 Amp supply with a maxim um of 2400 watts is the requ irement to run Solid State Laser. This is much less than excimer lasers enabling a reduction in energy bill. Gas - N o need to use any toxic and expensive gases any time for refractive

surgery. No more worries for transport and storage of ArF gases. It will save a huge amoun t of money over a period of time. Replacement of optics - Absorption peak of optics is near 185 nm. 193 nm is close to 185nl11 causing damage to optics more frequently than 213 nm which is little longer wavelength and away from 185 nm. It will allow us to replace optics less frequently than with excimer lasers. Less downtime - The long term stability of the Solid State Laser indicates a 386

minimum down time over the year.

Solid State Lasers for Refractive 5l1rgenJ SAFETY FEATURES Foot Switch

A footswitch is built into the system . The surgeon enables treatment by depressing the footswitch after the software has been told to start the treatment until the treatment is completed. As such, the treatment can be paused and resumed at any time by removing their foot from the footswitch. The computer automatically d isables the footswitch at the end of the operation to p revent accidental firing of the laser. Laser Enable Button

The laser enable button is included as a safety precaution intended to preven t the laser from firing following an interrup tion of normal operating conditions. The button must be pressed after switching the system on, after the interruption of the system mains supply or after the emergency stop button has been activated to allow the laser to fire. Emergency Stop Button

The emergency stop button, when pressed d isables the laser, bed and control panel but does not d isable the system computer or touchscreen moni tor. The button is intended to be used only in case of emergency to stop the laser firing or to prevent movement of the bed which could potentially result in danger to the patient. TREATMENT PLANNING In the PULZAR Zl system standard treatmen ts can be planned directly on the

device and custom treatments, both topography and wavefront based, can be planned on a separate PC using the CustomVis ZCADTM custom treatment planning software and transferred to the laser via CD-ROM.

STANDARD TREATMENTS Treatments are designed to alter the curvature of the cornea by a given astigmatic ma nifest refraction, within the entirety of the optical zone. The size of the optical zone is entered as a diameter in millimeters. A spectacle distance must also be provided to correctly interpret the refraction. Standard treatments also require an average preoperative keratometry input in diopters to accurately ap ply the refracti ve correction to corneas of all sizes.

387

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) STANDARD TREATMENT FEATURES IN PULZAR Z1 Maintenance of Preoperative Corneal Asphericity

Standard treatment performed w ith the PULZAR ZI, maintain preoperative asphericity of the cornea. This helps to prevent the introd uction of high-order aberrations. This feature increases patient comfort and postoperative visual quality. Saving Entered Treatments

Patient trea tmen ts can be saved and stored for later use. This gives the surgeon the ability to enter all p atient data prior to surgeries allowing surgeons to save time on the day of operation. The trea tment to be performed can be selected from a lis t of treatments not yet perform ed. In addition, past trea tments can be reviewed. Resuming an Aborted Ablation Process

If, for an y reason , the surgeon needs to ab ort a treatmen t then the aborted treatment can be eaSily recommenced by selecting from a list of incomplete treatments. The treatmen t will then be res umed from the exact pulse that it was aborted on , e .g. if a treatmen t was aborted after the 1000th pulse then the treatment w ould be recommenced starting from the 1001st pulse. This fea tures reduces the severity of issues such as power failure that fil ay require a treatment to be aborted by allowing the original treatmen t to be completed a t a later time from where it left off. CUSTOMISED TREATMENTS

The Custom Vis™ Puizar'" Zl laser system is specifically designed to facilitate custom refractive surgery. Rather than sim ply modifying existing technology that was intended to perform standard procedures, Custom Vis combines a number of proprietary technologies designed from the ground up to satisfy the requirem ents of custom surgery. One such technology is ZCADTM, an intelligent surgical planning system that is used to create a unique treatmen t plan for each eye, ens u ring tha t each patient is treated in dividually. ZCADTM integrates information from various diagnostic sources including topog raphy, wavefront analysis, pupil size, pach ymetry and refractive data, and allows the surgeon to alter the treatment zone, optical zone an d refraction param eters to determine the optimal treatment plan. ZCADTM also simulates the post-op erative corneal top ography, ensuring that surgeon s are satisfied with the projected treatment outcom e. The treatment p lan is then tran sferred to the PULZAR ZI system via a CD.

388

Solid State Lasers for Refractive Su rgery Special Features of ZeAD

Freedom of Choice of Optical Zone and Treatment Zone • Ideal to maximize resu I ts for higher corrections

• Optical zones from 2-9 mm for sphere and cylinder available for all treahnent types • Great way to optimize tissue abla tion. Refraction Adjustments - Surgeon's Choice

• Flexibility for fine adjuShnents in refraction in 0.01 0 steps • Wavefront and topography data ca n be used together • Allows surgeons to plan more individualised treahnents. Automatic Cylinder Notation Conversion

• Surgeons can program treahnents in any cylinder notation - our software automatically converts it into the most tissue-saving ablation pattern • More safety for surgeon and the patient by the saving of tissue and allowing a higher refracti ve correction. Corneal Asphericity Customization

• PULZAR standard treatments allow the surgeon to maintain the preoperative asphericity of the cornea • ZCADTM provides the flexibi lity to select the postoperative corneal asphe ricity • Surgeons can choose postoperative eccentricity appropriate to the pre-

operative asphericity of the cornea. 6 d ifferent options are ava ilable for postoperati ve eccentricity. Depth Offset • This feature allows the surgeon to save tissue or ablate additional tissue

if the need arises, e.g. in PTK trea tments. • The depth-offset allows PTK treatments to be performed either at the same time as a refractive procedure, or independently by entering zero subjective correction.

• The depth-offset also allows the maximum depth of the plan to be reduced by entering a negative offset, provid u1g a means of saving tissue that is particularly useful in highly irregular cornea requ iring custom treatment. • The dep th offset feature is also available for standard surgeries U1 Pulzar.

389

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) CT Sca le

• Custom treatments take a CT Scaie (Corneal topography scale) parameter that weights the influence of the topography on the trea tment plan from zero (topography is ignored) to 1 (full topography-based p lan). This allows for finer control over topography-based treatmen ts and provides a means of planning a s€ln i-custom treatment with a more tailored plan than a s tand ard trea tmen t bu t w ith less tissue loss th an a full custom treatment. ZCADTM can generate custom trea tment plans based on topography data alone, or a combination of wavefront and topography data. ZCADTM currently suppor ts the Tracey'" VFA wavefront an alyser and associated EyeSys® top ographer as well as the Orbscan'" top ographer. Cu stom treatments support all the parameters accepted for standard treatments w ith the exception of the APK (Average Preoperative Keratometry) setting which is in s tead calc ula ted m ore accurately fr om the corneal topograph y, allowing p lans to be created more appropriately for aspherical con1eas. Custo m treatments incorporating wavefron t data calculate an auto-

refraction based on a combination of the wavefront and topography data and compare this to th e entered manifes t refraction. If a significant difference is observed then the user is given the op tion of using the manifes t refraction, the auto-refraction calculated from the w av efront exam or to use the auto-refracted

astigmatism but with the manifest spherical equ ivalence. ZCADTM also provides a simula ted postoperative top ography p rovid ing a means of verifying the treatment p lan 's suitability to the patient. Finally, the pupil and limbu s n eed to be selected on an image of the subject taken at th e time of the preoperative exam s fo r registratio n purposes. Both ZCADTM and the Pulzar'" software provide an auto-detection fa Cili ty to detect the pupil and limbus, requirin g only minimal adjustment in most cases. Once treatment generation is complete, the treatrnentdata needs to be written to a C D. This CD then contains all the d ata required for PULZ AR to p erform the customised surgery exactly as p lanned. TRACEY WAVEFRONT ANALYSER

The TraceyTM visual function analyser utili zes fundamental thin beam principle of optical ray tracing, an d combines it w ith th e EyeSys® corneal topography . The iTrace, a unique wavefront device, intended to solve the 'science of refraction' u sing a delivery method adaptable to eye care, w hich is quick and easy to use. The instrument, capable of measuring both lower and higher order aberrations of the eye, while separating lens and corneal aberrations, is unique in ll1any ways w hen compared to s impler wavefront devices that are available

390

Solid State Lasers fo r Refractive Slirgery

today. By an alysing the refracti ve power of the eye consistent with the optical path in natural vision, that is rneasurin gfonvard aberrations as thin beams of light pass through the cornea, pupil and lens to focus on the retina, the iTrace can:

• Rapidly measure one point at a time, separately, to avoid overlapping or d ata confusion. • Projects 256 points in to a pupil as small as 2 mID or as large as 8 mm • Obtain a high d ynamic range, from -150 to +150 • Measure light rays going in to the eye, instead of coming out of the eye • Detect the retinal location of each thin beam going in the eye to generate a true retinal spot pattern • Avoid becoming compromised by opacities or other opaque or irregular areas • Separate out corneal aberrations from lens aberrations using the ability to register with corneal topography. Data Displays

The iTrace d isplays the data it processes in various ways using combinations of both lower and higher order aberrations (total aberra tions), and higher order aberrations a lone. The data can be viewed as simulations of what the patient actually sees, colour coded maps in- diopters or microns of wa vefront error, and as bar graphs or charts of Zemike terms. There are 6 types of d isplays, 1. Wavefront total and Wavefront HOA 2. Refrac tive total and Refractive HOA 3. PSF total and PSF HOA 4. Snellen letter total and HOA 5. Zernike chart 6. Lens aberration analysis. Other Advantages of Tracey

1. Detects night m yopia

2. Uncover latent hyperopia 3. Measure acconunodative volmne 4. Reduce need for cycloplegic refraction by performing a true distan t exam binocularly. Tracy and Custom Vis Pulzar Z I

Custom Vis and Tracey technologies have formed an ag reement for the supply of iTrace Visual Function Analysers that have been specifically configured to export topography and wavefront aberrometry data to the ZCADTM planning software.

391

Instant Clil/ical Diagl/osis in Ophthalmologlj (Refractive SII I'genj) CLINICAL OUTCOMES

The PULZAR Zl has been used for the treatment of virgin eyes, the re-treatment of patients who have had sub-op timal outcomes from previous refracti ve surgery as well as irregular astigmatism. LASIK, LASEK and PRK have been performed. Latest Clinical Results

The PULZAR Zl has been used to trea t a wide range of myopia, myopic astigmatism, hyperopia, hyperopic astigmatism and presbyopia (presbyopia is un der clinical trials). More than 12,000 eyes with highly satisfactory results were treated at more than 9 international sites; the PULZAR has been used effectively and regularly to treat standard and custom surgery. Myopia - Moderate to High (Up to -14.50 Sphere and up to -5.50 of Astigmatism)

Four hundred and thirty six eyes were followed for a minimum of three months (Upto -14.5 D sphere and up to -5.5 D of astigmatism). Out of436 eyes, 367 eyes (84%) were within half a diopter of intended refractive correction and 428 eyes (98%) were w ithin one diopter of intended refraction. A total of 27 eyes gained one line in their Best Spectacle Corrected Visual Acuity (BSeVA) and noeye lost more than 1 line of BSCVA. 74 % of eyes had 6/ 6 or better uncorrected visual acui ty (UeV A) and 88% had 6/ 7.5 or better UCVA. Attempted Vs Achieved graph

195 hyperopic eyes were followed for 3 months. Preoperative SE was upto + 6 o and mixed astigmatism were up to -6.5 D. 68 % were within + / - 0.5 0 of intended refractive correction and 88% were w ithin + / - lO af intended refractive correction 86% of eyes had 6/6 or better u e v A. Cu rrentl y presbyopia softwa re is under clinical trial s at var iou s international clinica l sites. More than 100 eyes have been treated with new multi-zone presbyopic software. Cen tral and peripheral zones were used for distance vision and a middle zone was used for near vision . All patients had very good near and far vision though near vision was better than far vision. the presbyopic software will be available commercially as further trials confirm the early results. The presented clinical da ta supports the safety, predictab ility and effectiveness of the PULZAR Zl Solid State Refractive Laser (213 nm) for the correction of a whole range of refraction including high myopia, hyperopia, mixed astigmatism and presbyopia. 392

Solid State Lasers for Refractive Surgery THE BOTTOM LINE

Solid State technology promises to meaningfully advance the state of the art in refractive laser surgery by streamlining design, increasing predictability of results, improving results and eliminating the need for high voltage power sources.

The clinical ad vances that stand to be gained are related to precision and predictability. Predictability will be enhanced, in the larger part because the laser energy at 213 nm can pass through the NaCL 0.9 % and BSS (Balanced Salt Solution) with very little energy loss. As a resu lt, a 213nm laser's performance is less susceptible to variations in humidity or corneal hydration. The precision of the solid state laser system, now clinically proven, is a result of enhanced tracking and ultra fa st scanning, which also supports a faster pulse rate. Clinical results from all international sites are promising, exceeding the expectations of patients and surgeons. Solid State Laser is a good alternati ve to the current excimer laser. It also looks to be the future of Refractive Laser Surgery.

393

38 Dry Eye after Refractive Surgery Belquiz A Nassaralla, Joao J Nassaralla Jr (Brazil)

INTRODUCTION

The past two decades have seen changing trends in refractive surgery, with the evolution of several different procedures. Reshaping the anterior corneal surface by excimer laser photorefractive keratectomy (PRK), laser in situ keratomileusis (LASLK) or laser subepithelial keratomileusis (LASEK) has shown considerable promise for the surgical correction of refracti ve errors. Ln PRI<, the refractive surgical ablation is performed on the corneal surface after epithelial debridement. During LASIK, a hinged lamellar corneal flap is raised with a mikrokeratome followed by ablation in the stromal bed and repositioning of the flap. A LASEK procedure involves preserving the extremely thin epithelial layer by lifting it from the eye's surface before laser energy is applied for reshaping. After LASEK, the epithelium is replaced on the eye's surface. Injuries to the ocular surface, occur with all three procedures.

394

Dry Eye after Refractive Surgery

Fig. 1: Photorelract;ve keralectomy lor myopia (PAK)

Fig. 2: Flap creation during LASIK. The $uperlicial corneal liap Is

attached to the underlying cornea by hinge

395

Instant Clinical Diagn osis in OphthalmologtJ (Refractiv e Surgery) INVESTIGATIONS

Corneal sensitivity is mediated by stromal nerves originating from the long ciliary nerves that penetrate the cornea in the middle and an terior stromal layers and run forward in a radial fashion toward the center of the cornea. These nerves fo rm a network called the subepithelial plexus, beneath Bowman's layer, with free nerve endings in the corneal epithelium. Ordinarily, the production of tears is monitored by the long ciliary nerves, which create a feedback loop that links the lacrimal glands to sensory receptors on the ocular surface. During flap creation and laser ablation, corneal nerves are transected, resulting in decreased cornea l sensitivity and a transien t ne urotrophic cornea. As a result, i t derails the reflex arc of

lubrication. Clinical and experimenta l evidence shows that decreased afferent input from the corneal surface results in decreased tear secretion, decreased m ucin production, decreased blink rate, and loss of trophic effects on surface celis, leading to dry eyes. Dry eyes are a common complaint after refractive su rgery, with an incidence ranging from 3 to 60%. Over the course of weeks to months to years, the nerves regenerate, and tear dynamics can return to normal.

396

Instant Clinical Diagnosis in Ophthalmolo:?,} (Refractive Surgery) INVESTIGATIONS

Corneal sensitivity is mediated by stromal nerves originating from the long ciliary nerves that penetrate the cornea in the middle and anterior stromal layers and run forward in a radial fa shion toward the center of the cornea. These nerves form a network called the subepithelial plexus, beneath Bowman's layer, with free nerve endings in the corneal epithelium. Ordinarily, the production of tears is monitored by the long ciliary nerves, which create a feedback loop that links the lacrimal glands to sensory receptors on the ocular surface. During flap creation and laser ablation, corneal nerves are transected, resulting in decreased corneal sensitivity and a tran sient neurotrophic cornea. As a result, it derails the reflex arc of lubrication. Clinical and experimental evidence shows that decreased afferent input from the corneal surface results in decreased tear secretion, decreased mucin production, decreased blink rate, and loss of trophic effects on surface cells, leading to dry eyes. Dry eyes are a common complaint after refractive surgery, with an incidence ranging from 3 to 60%. Over the course of weeks to months to years, the nerves regenerate, and tear dynamics can return to normaL

396

On) Eye after Refractive SlIrgen)

12

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Fig . 4: Subepithelial plexus. beneath Bowman's layer, with free nerve endings in the corneal epithelium (MOiler et al )

397

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) CLINICAL SIGNS AND SYMPTOMS

Dry eye signs and symptoms after refracti ve surgery are usu ally transient but can cause significant discomfort for many patients; in rare cases, they persist for m ore than a year postoperatively. Several mechanisms for dry eye symptom s after refrac tive surgery h ave been proposed ; these include damage to the goblet cells by suction-ring-induced pressure in LASIK, decreased corneal sensation and blink reflex, altered tear-film stability caused by changes in corneal curvature, inflammation caused by surgical trauma and med ica tion-induced effects. Patients should be prepared for some postrefractive surgery dry eye symptoms, including pain, itchiness, redness, and bouts of blurred vision. Som e pa tients with dry eye after refractive surgery w ill suffer more severe symptoms than others. CHRONIC DRY EYE AFTER LASIK

If postrefractive surgery dry eye symptom s persist, they can d evelop into chronic dry eye syn drome. In a certain percentage of patients, dry eye after refractive surgery ma y last for a prolonged period of time and can even become permanen t. It is crucial that patients consider the potential for chronic dry eye after LASIK among the risks associated with refrac tive surgery.

398

Dnj Eye after Refractive SlIrgenj

Fig . 5: Slight superficial punctate keratopathy 18 months

after PRK for high myopia (- 7.5 D)

399

Instnnt Clinical Diagnosis in Ophthalmology (Refractive Surgery) RISK FACTORS FOR DRY EYE AFTER REFRACTIVE SURGERY

The risk factors for developing dry eye after refractive surgery include the preopera tive level of myopia, the ablation dep th, and the LASIK flap thickness. The increased risk of dry eye accompanying these factors may be explained by their effects on the corneal sensory nerves. The greater the amount of m yopia that is trea ted, the greater the ablation depth that is required, and the greater the distance the surgically ampu tated nerve trunks will have to regenerate to reinervate the corneal epithelium following surgery. Some patients with pre-existing dry eyes are at risk for prolonged dry eyes that can cause significant symptoms and persist for many years following surgery. For this reason, it is important to screen for dry eye prior to refractive surgery and decide whether patients sho uld be treated for dry eyes in advance. TREATMENT

The selection of treatment modalities for patients with dry eye after refra ctive surgery depends largely on the severity of their disease. Mild cases may require no more than the use of artificial tear solutions. If the cond ition is not su ffi Ciently managed with artificial tears, the use of sustained-release ocular lubricants may be considered. It ma y also be appropriate to modify the patient's environment in an effort to reduce evaporation of the tear film. Severe dry eye after refractive surgery is rare; however, in this case, therapy includes all of the above measures as well as punctal occlusion. The mainstay of treatment for dry eye is the use of topica l tear substitutes (eye drops, gels, and ointments) . Preservative-free tear substitutes are recommended to avoid toxicity in patients who use these agents frequently. Topical cyclosporine has been proposed as a treatment for the inflammatory component of dry eye after refractive surgery. Although there are several dry eye treahnent options available for postrefractive surgery dry eye, prevention should always be a top priority.

400

Dry Eye after Refractive Surgery

Fig. 6: Normal tear film. Notice an adequate tear lake between the lower lid and the cornea. The cornea is clear and there are no staining irregularities of the corneal epithelium

Fig. 7: Dry eye syndrome. Dry eyes can occur as both quantitative and qualitative disorder of tear production. In this example , there is a moderate superficial punctate keratopathy. This is a common finding in patients with dry eye syndrome

401

39 Corneal Biomechanical Properties Jorge L Alia, Mohamed H Shabayek (Spain)

INTRODUCTION

Corneal refrac ti ve surgery advanced rapidly d uring the past two decades, due to the encouraging, pred ictable and stable results of corneal remodeling by photoab lation using excimer lasers. A result of such advancement a new frontier of d iagnostic equipments and tools became accessible to ophthalmic surgeon such as; corneal topographer, wavefront sensors, very high frequency optical coherence tomography (VHF OCT), and confocal microscopy. This technology aided in analysing not only the optical but also the structural properties of the cornea. Recently the biomechanical properties of the cornea have been introduced as a new parameter in corneal refra cti ve surgery, parameter that evaluates corneal characteristics form the biomechanical perspective; such as the corneal resistance factor, and corneal hysteresis. These parameters can be helpful for diagnosi ng certain corneal pathologies especially cornea l ectatic d iseases, were the biomechan ical corneal characteristics are different form normal corneas. TERMINOLOGY Corneal Hysteresis

The term "H ysteresis" is derived from an an cient Greek word wh ich means

"corning behind". It was first introduced into scientific vocab ulary in 1890 by the Scottish physicist, Sir James Alfred Ewing. Hys teresis is a property of physical systems that do not instantly follow the forces ap plied to them, but react slowly, or d o not return completely and instantaneously to their original state. Corneal Resistance Factor

The static resis tance component of the cornea which indicates the overall cornea l resistance or simply the p ressures "force" needed to applanate "deform" the cornea, this deformation is proportiona l to applied force and is expressed in mmHg. H owever, measuring the biornecha nica l properties in vivo is a challenging task, and has been approached by several methods, whether invasive as 402 anterior Chamber saline injection and measuring ocular rigidity or non

Conleal Biomechanical Properties

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Fig . 2: Ocu lar response analyzer (ORA)

403

Instnnt Clin ical Diagnosis in Opltthnlmo logtJ (Refractive SlIrgenJ) invasive as dynamic con1eai imaging w ith central indentatio n and dynamic

bidirectional air applanation. Pallikaris et al measured the ocular rigidity in living human eyes increasing the intraocular pressure by injecting a saline solution into the an terior chamber; while, Grabner et al used the dynamic corneal imaging method by central indentation to assess the in dividual elastic properties of eyes. Where as, Luce determined the biomechanical properties of the cornea using the Reichert ocular response analyzer (ORA), based on a dynamic bidirectional applanation process. OCULAR RESPONSE ANALYZER (ORA)

The Ocular Response Analyzer, (ORA) Reichert Ophthalmic Instruments, Depew NY measu res the cornea l biomecha nical properties by using a dynamic bidirectional air applana tion p rocess (nonin vasive method). It is composed of an air pump which ap p lies a fo rce on the an terior corneal surface (specific point) through a pressure transducer while an infra red light emitter is focused on the same poin t and the reflection of this infra red beam is moni tored by a light intensity detector. This system records two applanation pressure measurements; one while the cornea is moving inward, and the other as the cornea returns. Due to its biomechanical propert.ies, the cornea

resists the d ynami c air pu ff cau sing del ays in the inw ard and ou tward applanation even ts, resulting in two different pressure values. CORNEAL BIOMECHANICAL PROPERTIES IN NORMAL, KERATOCONIC EYES AND POSTLASIK EYES

In prospective, conventional, comparative, interventional study, that reported the corneal biomechanical properties in normal non-complaining individ ual and kera toconic eyes using the Ocular Response Analyzer (ORA). The study i.ncl uded a total of 250 eyes divided into three grou ps: 164 normal eyes, 21 keratoconic eyes and 65 eyes that had undergone a corneal refracti ve sm gery procedure to evaluate the effect of LASIK on the corneal biomechanical properties. The author's incl usion criteria were: for normal and postrefractive surgery

groups, patients with any irregular patterns of corneal topography or history of ocular disease were not included; and for keratoconus group, only eyes with keratoconus with at least one clinical sign that was confirmed by corneal topography. Results of this study, demonstrated that in the normal group, a decrease in the corneal biomechanical properties was observed in elder patients. This implies a loss of the elastic properties of the cornea with age, which coincides with the increase of ocular rigidity found by Pallikaris et al. As fo r the post LASIK surgery g roup, or the effect of excimer laser photoablation on the corneal biomechanical properties, a significant decrease in the bio mechanical properties was fou nd alter the surgery. This result 404 coincides w ith other studies and implies that the creation of the fl ap and the

Corn ea l Biomechan-ical Properties

Applanated Cornea

Fig. 3: The infrared light intensity is maximally detected when the anterior corneal surface is applanated

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corneal thinn ing by ablation weaken the cornea and decreases its elastic properties. This could lead later to corneal ectasia after refrac tive surgery. This can be an indicator for the imp ortance of eva luating corneal biomechanical properties precisely the corneal hysteresis and resistance factor in screening refracti ve surgery candidates. In keratoconic eyes, the corneal hysteresis (CH) and the cornea l resistance factor (CRF) were sign ificantly lower than in normal eyes and post-LASIK surgery corneas. Low values of CH imply that the cornea is less capable of absorbing the energy of the air pulse, where as, low values of CRF, indicates the cornea rig idity is lower than normal. 405

40 Future of lASIK Surgery Arun C Gu/ani, Tracy Schroeder Swartz (USA)

INTRODUCTION

Refrac tive surgery encompasses the entire spectrum of eye surgeries which aim to help patients see without an y aid s like glasses and contact lenses. The pursuit of this noteworthy ambition has been a challenge for every generation for centuries.

LASIK has by far enjoyed the most success, notoriety and med ia attention than any surgery before its time. Technological advances however over the recent decade have raised the bar not only in the diagnostic arena but also increased our abil ity to treat the entire range of ammetropia and resulted in raised expectations like "Supervision". ADVANCED TECHNOLOGIES Wavefront m easurement continues to evolve with the incorporation of fourier

transform-based algoritlun which greatly increases the mathematical power of the system to describe the wavefront. While it may be academic when appl ied to the h uman cornea, where human healing limits the effect of wavefront application, measurement using Fourier rather than Zernicke polynomial may be beneficial. Hartman -Shack lenslet arrays lose data during processing using Zernicke polynomials. Interpolation of areas of missing data is required, effectively smoothing the wavefront. This is especially true for diseased eyes and those with history of keratorefractive procedures. Smolek and Klyce studied Zernicke fitting methods for corneal elevation and reported 4th order Zernicke polynomials ma y not be adequate in their description of corneal aberrations in significantly aberrant eyes. More data points are used

in the fourier algorithm producing a more detailed map, especially for highly aberrant eyes. Use of advanced wavefront technology for ablation has resulted in a resurgence of surface abla tion. LASIK with conventiona l microkeratomes

covers the detailed ablation patterns w ith a relatively thick fl ap, essentially el iminating the benefi t of wavefront ablation. This may theoretically be lessened using a thin, sub-Bowman/s flap created w ith newer microkeratomes.

Topography has also become more robust to asses more aberrant eyes and aid refractive surgeons as well. Originally used to demonstrate corneal 406 curvature, new technologies address both curvature and shape as well as

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optical pach ymetry. Many systems employ neural netwo rks to aid clinicians with indices ind icating the likelihood of diseases such as ke ratoconus and pell ucid marginal degeneration, or if the patient has unde rgone refractive surgery. Examples of such programs are the Zeis-Humphrey Atlas' Pathfinder program and Nidek's Magellan detailed statistic analysis. Other systems combine wavefront aberrometry and corneal topography to produce corneal wavefronts which allow aberrations from the lens to be differentiated from those of the an terior cornea. Clinicians are often more comfortable with wavefron t then elevation represe n tation of corneal abnormalities. An example is shown in Figure 3. Such technology is used to differentiate the cause of vision loss when more than one pathology is present. Topographers have moved past the an terior surface to view the posterior surface and allow pachymetry withou t touching the cornea. The Orbscan (Bausch and Lomb, Rochester NY) slit scanning device was the first to visualize the posterior surface and perform optical pachymetry. However, the orbscan fails to correctly identify the posterior surface in patients SI P LASIK and pachymetry measurements showed increased va riability. Scheimpflug photography gave birth to the Pentacam (Oculus), a three dimensional anterior segn1ent imaging system which also allows measurement of the posterior surface of the cornea and optical pachymetry (Gulani AC. Pentacam Basic and Advanced course: KMSG Conference- Madrid, Spain, July 2006). These systems may be better at identifying risk factors for ectasia following refractive surgery, as well as to evaluate patients followulg surgical complications, such as flap tea rs, scarring and straie (Gulani AC. Pentacam in Full Spectrum Refractive Surgery: Ad vanced Corneal Topography CourseAAO, Las Vegas. Nov 2006). Highl y detailed pachymetry maps such as that in Figure 4 may indicate early keratocon us in patients seeking LASIK. The Pentacam measured central corneal thickness values closer to ultrasound pachymetry and with less variability then Orbscan. It was also found to have the highest rep roducibility compared to Orbscan and ultrasound. Also new to the refractive scene is ocular coherence tomography (OCT), a noninvasive optical imaging techniq ue that was previously used to inlage the posterior segment. OCT instruments use optical interferometry to generate a log reflectivity profile describing the different layers of the cornea and allow the separation of reflective structures to be measured. OCT also yields optical pachymetry values across the cornea. Surgeons prefer optica l pachymetry. Several systems now measure pach ymetry optically, and yield pachymetry values across the cornea, allowing identification of thin spots much like topography yields steep areas of curvature. This is especially important to refractive surgeons evaluating patients for elective keratorefractive surgery_

Ultrasound remains the standard for pachymetry, but it does have its drawbacks. There is a high degree of reproducibility but the probe does 408 require anesthesia and direct contac t with epithelium. It is a single-spot

Future of LASIK Surgery

Fig. 3: Tracey corneal wavefront example

Fig. 4: Pentacam pachymetry map In a patient with early keratoconus

409

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) measurement with limited precision. Slit-scanning yields pachymetric maps but is less accurate. Pentacam appears to be more accurate but is not able to differentiate the layers of the cornea. Ultrasound imaging can map these layers but requires a cumbersome waterbath technique. OCT has been shown to yield values similar to ultrasound in virgin as well as cornea SIP LASIK. OCT yields detailed pachymetric analysis and visualizes the layers of the cornea. This is beneficial in patients SI P LASIK seeking enhancements or those needing progression analysis of keratoconus. Such an example is shown in Figure 5. This technology is invaluable for surgeons attempting to correct complications from previous surgery such as flap trauma and repeated enhancements. SURFACE TREATMENT VS LASIK

These advancements in technology have increased our understanding of the posterior surface and corneal biomechanics SIP keratorefractive surgery. PRK was initially used with excimer lasers, and the associated pain and risk of corneal hazing are well known. The haze results from damage to the epithelium and stroma simultaneously during the procedure, resulting in cross talk between the stromal keratocytes and epithelial cells. LASIK was preferred due to the quick visual recovery, significantly less pain and convenience for patients. Increased understanding of the biomechanics of flap creation and ectasia following LASIK, in addition to the dry eye and complications from manual microkeratomes led to increased use of femtosecond lasers for flap creation and a resurgence of surface ablation. Complications from LASIK, although rare, include dry eye, corneal weakness and ectasia, and questionable corneal flap adhesion. Dry eye continues to be the most cornmon complication from LASIK. Up to 37% of patients without pre-existing dry eye will be symptomatic six months after LASIK. Flap creation causes damage to corneal nerves, which may not regenerate to their preoperative level. Total disappearance of the subepthelial nerve layer at one month SIP LASIK has been reported. Prolonged recovery of corneal sub-basal nerve density after LASIK compared to PRK has also been reported. Three years after LASIK, a 34% reduction was found compared with a nearly unchanged subbasal nerve density following PRK. The reduction of corneal nerve regeneration and actual number of fibers noted in post-LASIK patients was not found in patients post-LASEK. Thus, many surgeons are increasing the amount of surface ablations to alleviate dry eye complaints postoperatively. In addition to the dry eye complications, LASIK has been found to be less stable long-term due to the severance of collagen fibers. This is illustrated by the dislocation of flaps years after surgery. The National Institute for Clinical Excellence reported the main problem with LASIK was long-term risk of 410 corneal ectasia.

Future of LASIK Surgery

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411

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) To avoid these complications, many surgeons have turned to laser-created flaps for LASIK. Femtosecond laser planar flaps are clearly advantageous over meniscus flaps created by conventional microkeratornes. The creation of thin flaps less then 100 microns may produce less biomechanical changes and dry eye. The reliability of flap thickness makes them safer for those with thin corneas and prevention of ectasia. Wavefront ablations were found to lead to faster recovery, better uncorrected vision, and better corneal sensitivity compared to treatments using conventional microkeratomes. Unfortunately, the femtosecond lasers are expensive, enticing other surgeons to turn to surface ablations: PRK, LASEK, and Epi-LASTK. The application of wavefront to refractive surgery in conjlU1ction with improved pain management alternatives has also increased surgeons willingness to return to surface ablations. Epi-LASIK, which uses an epi-keratome to remove the epithelium along Bowman's membrane, has the advantages of LASIK and PRK without the disadvantages of either. Without a stromal flap, less higher order aberrations are induced. Patients who underwent LASEK or other surface ablations report less night vision problems including smaller starbursts, and have better contrast sensitivity then those SIP LASIK. Mild corneal opacities are easily treated using surface ablations as well. In summary, I personally do feel that surface ablations will lead the way as I do with my concept of CorneoplastiqueT M which increases the scope of refractive surgery to help refractively address even pathological corneas. Lenticular Refractive Surgery

Elective cataract surgeries with multifocal IOLs have become a great option for the baby boomers (Gulani AC: Full Spectrum refractive Surgery: FSO meeting, Naples, Florida - Aug 2006). Having personally participated in one of the First US clinical trials of Phakic implants (Gulani AC, Neumann AC. Phakic Implants 6 year follow up- ARVO, 1996) using three lens models, i.e. Anterior Baikof£, Mid-Anterior Momose and Posterior-Fyodorov lenses of four different materials in three different locations in the eye, we confirmed a predictable future for this technology. Now, with the approval of the Verisyse and Visian IOLs in the US and soon to be approved foldable phakic implants (personal communication: Gulani AC, Potgeiter F: SASCRS, Durban, South Africa- Aug 2005) we have choices for higher ammetropias and combinations like Bioptics therein. Surgeries using the entire anterior segment comprising of corneal and intraocular combinations and various permutations throughout the lifetime of a refractive candidate will finally lead the future. 412

Fuhlre of LASIK Surgery

Fig. 6: Combination surgery. Intraocular multifocal lens for previous RK-AK with high Hyperopia and Astigmatism , followed by laser surface ablation

LASIK is a surgery tha t has been around fo r nearly half a cen tury as for its concep t and technique. Wha t has changed is the technology to achieve those same goals albeit with heightened awa reness, raised expectations and of course the pursuit of Super-Vision .

413

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41 Refractive Management of Hyperopia Ahmad K Khalil (Egypt)

INTRODUCTION

Refractive correction o f hy peropia is often needed. Deci sion making is not a

straight forward one, because of several variables and difficulties to be tackled and several treatmen t options w ith their abilities and inabilities. CLINICAL SIGNS AND SYMPTOMS

l ow to moderate degrees of h yperopia would probably pose no serious ann oyance to the pa ti ent till his early fourties when his distance erro r becomes manifest and mo re d isabling. On the other hand, higher hyperopia errors, though not very com.m on, would usually be a nuisance at a much earlier age. Glasses correction is usually in to lerable because of the narrower field, and

increased aberratio ns associated with a powerful plus lens at glasses vertex d istance added to an already aberrated eye. INVESTIGATIONS

Biometry of the eye can be va riabl e especially in higher erro rs. Odd K-readings from mid 30s u p to early 50s ca n be seen in high hyperopes, naturally associa ted w ith various sorts o f aberratio ns . Similarly va riations in

axial length, AC depth, lens thickness can be seen. All these parameters should be known using relevant equipment as wavefront analysis and ultrasound biometry prior to planning any refractive in terference. MANAGEMENT

Several options are available for the refractive management of hyperopia; Corneal approach (Laser vision correction, thermokeratoplasty, corneal inlays), phakic 10L imp lantation (PIOl), and re fractive len s exchange (RL E) . Thermokeratoplasty including conducti ve Kera toplasty do not provide a permanent solution, and corneal inla ys are still in the experimenta l and clinical trials s tage. 416

Refractive Management of Hyperopia

Figs 1 A and B: (A) A diagram representing a cornea with a flatter central surface (oblate) , (8 ) Hyperopic laser treatment increases central cornea steepening (prolateness)

417

It/stant Clinical Diagnosis in Ophtllalmol0I5'J (Refractive SlIrgenJ)

Decision making depends on degree of hyperopia, age of the pa tient and biometry of the eye. Lower degrees of hypero pia up to + 6 wo uld usually benefit from laser vision correction. Various recent studies have s hown the

long-term stability of lase r treatment for hyperopia up to + 6 D. Lens and cornea ha ve a role to play in decision making of this group. Lenticular opacities and / or significant aberrations would direct trea tment modality away from the cornea. A steep corneal curvature (K-readings over 48.0) would similarly exclude laser v is ion correction from treatment options, as hypero pic treatment in vo lves increasing corneal prolatiol1, hence markedly further s teepening the already s teep cornea, and increasing its aberrations . VVhen lens and cornea

condition does not precl ude laser treatment, then it is probably well justified even in older populations. The increased prolation gives an added advantage

of pseudo-accommodation, which partially eliminates the dependence on near correction. When there is a cornea or lens con traind ication for laser correction,

P IOL and RLE as described below, are resorted to. Because of a hi gher incidence of regression, hyperopia over + 6D would ta ke us away from laser vision correction to lens options. PIOL (ICL or iris clip) can be warranted in yo unger populations where there is a good amount of accommodation to be preserved, otherwise RLE would be the proced ure of choice. EspeCially so, as this patient population commonly has shallower AC rendering PIOL surgery more difficult and risky. RLE becomes th e procedure of choi ce in high hyperopia w ith lost accommo dation , mod-low hyperopia; h avi ng corneal or le nticular contraindications for laser correction and / or narrow anterior chambers with

risk of closure. IOL power calculation can become very tricky with standard formulas in short globes. In eyes shorter than 20 mm, Holladay 2 or Hoffer Q give more predictable results. IOL power measurements can sometimes reach

over + 40.0D, and piggy-backing can be a necessity for emmetropia in these cases. This might be associated with an increased incidence of inte r-lenticular

opacification (ILO). The combination of 2 silicone lenses one in the bag and the o ther in the sulcus seems to be the best combination to reduce the incid ence of

lLO. Elevating the irrigation bottle height during phacoemulsification can overcome difficulties associated with a sha llow AC. PROGNOSIS

With proper choice of the modality of trea tment, refractive management of hyperopia is usuall y rewarding for both patient and surgeon.

418

Instant Clinical Diagnosis in Oplltl,almologlj (Refractive SlIrgeYlj) Decision making depends on d egree of hyp eropia, age of the patient and biometry of the eye. Lower degrees of hyperopia up to + 6 wou ld usually benefit from laser vis ion correction . Various recent studies have shown the long-term stability of laser treatmen t for hyperopia up to + 6 D. Lens and cornea have a role to p lay in decision m akin g of this group. Lenticular opacities and /o r signHicant aberra tions w ould direct treatmen t mod ali ty away fro m the cornea. A s teep cornea l curva ture (K-readin gs over 48.0) would similarly exclude Jaser v ision correction from treatment options, as hyperopic treatment involves increasing corneal prolation, hence marked ly further steepening the already steep cornea, and increasing its aberrations. When lens an d cornea condition does not precl ude laser treatment, then it is probably well jus tified even in older populatio ns. The increased prola tion gives an add ed advantage of pseudo-accommod ation, which pa rtially eliminates the depen dence on n ear correction. When there is a cornea or lens contraind ication for laser correction, PIOL an d RLE as d escri bed below, are resorted to. Beca use of a higher u1Cidence of regression, hyperopia over + 60 would take us away from laser vision correction to lens options. PIOL (IeL or iris clip) can be warranted in yo un ger populations wh ere there is a good amount of accommod ation to be preserved, otherw ise RLE would be the procedure of ch oice. Especially so, as this pa tient pop ula tion commonly has shallower AC rendering PIOL surge ry more d ifficul t a nd risky. RLE becom es the procedure of choice in h ig h hy p ero p ia w ith lost a ccomm od a tion, m od- low h yp e rop ia; ha v ing co rneal or le n t icul a r contra ind ications fo r laser correction and/ or narrow anterior chambers w ith risk of closure. IOL power calcula tion can become very tricky w ith standard formu las in short globes. In eyes shorter than 20 m m, Hollad ay 2 or Hoffer Q g ive more predictable results. lOL power m easurements can sometimes reach over + 40.00, and piggy-backing can be a necessity fo r emm etropia in these cases. This might be associated w ith an increased incidence of inte r-lenticular opacification (ILO). The combination of 2 silicone lenses one in the bag and the other in the sulcus seems to be the best combination to reduce the incidence of ILO. Elevating the irriga tion bottle heigh t durin g p hacoemulsification can overcom e d ifficulties associated with a sha llow AC. PROGNOSIS

With proper choice of the modality o f trea tment, refrac ti ve manage ment of hyperopia is us ually rewa rd ing for both patie nt and s urgeon.

418

Refractive Management of Hyperopia

Fig . 2 : Implanting a second (piggy-backing) lens in a case of high hyperopia

419

42 Restoration of Accommodation Capsular Bag Refilling

by

Okihiro Nishi, Kayo Nishi, Yutaro Nishi, Shiao Chang (Japan)

INTRODUCTION Refilling the lens capsule with an injectable material, while preserving capsular integrity including zonules and ciliary muscles, offer a potential to restore ocula r accommoda tion. The greatest technical challenge in this procedure was prima rily preventing the leakage of injectable IOLs. To prevent lea kage, we developed a silicone plug to seal the capsular opening . We could confirm someacconunodation in the young macaca monkies. Figure 3 shows the Scheimpflug pho tographies of the eye of a monkey before and after surgery, show ing evidence of some accommodation being obtained. After applica tion of 4% pilocarpine, there is thickening of the le ns with steepening of the anterio r capsule a nd shallowing of the anterior chamber, both before and after surgery, altho ugh the findin gs were much less marked after surgery. From these experiments, we ha ve concluded that refilling the lens ca psule is technically qu ite fa sible. It is suggested that the procesure may restore ocular accommodation in humans. However, there are some essential problems to overcome: Refining and sim pEfying the techn ique; Prevention of anterior caps ul e opacifica tion (ACO) and posterior ca psule opacificatio n (PCO ); Reducing surg ica Uy-induced astigmatism because the unilateral CCC, though tin y, ca used a great astigmatism (unpublished data). He re, Twill d emonstrate a comple tely new concept and novel lens refilling proced me that may solve these proble ms. We had tlus concept alread y in 1989 and resumed the technjque, because endocapsular balloon technjque and the capsular plug technique will not be supposed to be applied clinically, a nd the technjque will solve the problems mentioned above.

420

Restoratioll of Accommodatioll by Capsular Bag Refilling

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421

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) REFILLING THE LENS CAPSULE WITH CAPSULOTOMY-CAPTURING INTRAOCULAR LENS IOL

The rOL shape is similar to that of a conventional rOL, but the optic has small narrow grooves over its entire circumference. The CCC edge is put in this groove, which chokes the rOL, preventing leakage of the injected material. Figure 5 illustrates the procedure and Figure 6 shows the most recent foldable version of the IOL. Surgical Procedure As in conventional cataract surgerYr CCC, around 4 mm in diameter, is created

in the middle of the anterior capsule. After phacoemulsification aspiration, viscoelastics are injected into the capsular bag in the usual manner. The folded IOL is introduced entirely into the capsular bag. A Sinskey hook is introduced underneath the IOL, and the IOL is lifted by the hook, so that the optic edge groove of the lower half of the rOL is captured by the lower half of the CCc. The lower half of the groove is captured almost automatically while lifting the lower half of the rOL, because the 10L is firmly fixed in the middle by both haptics remaining in the capsular bag. Then, the viscoelastics are completely removed by aspiration, during which an 1/ A cannula is introduced underneath the upper half of the rOL, which is now outside of the capsular bag. Viscoelastics are injected into the anterior chamber onto the IOL. The upper half of the IOL is then captured by the CCC by pushing the IOL downward and posteriorly at the middle part of the IOL optic edge with a push-pull hook until the upper IOL clears the upper CCC edge to be captured. A small portion ofthe CCC edge at the optic groove is now hooked with the Sinskey hook and pulled slightly to introduce the injection cannula . The injectable material, actually a mix of two liquid silicones is then injected into the capsu lar bag. It polymerizes in 2 h in vitro.

RESULTS AND DISCUSSION

We have refilled many pig cadaver eyes and rabbit eyes using this technique. After the TOL was correctly captured by the CCC, there was no leakage of the injected silicone. Thus, the apropriate size for the CCC, not too small to capture but not too large to capture firmly the 10L, is crucial for surgical success. If the CCC is appropriately sized, the procedure is highly reproducible. We marked a 5 mm circle on the cornea using a Hoffer optic zone marker for 5 rrun, according to the technique described by Wallace, and used this mark as a guide for an appropriate CCC diameter around 4 mm.

422

Restoration of A ccommodatioll by Capsular Bag Refilling

Fig . 3: Sche impfl ug photog raphs of a mon key eye before and after refi ll ing the lens capsule. Note that there was thickening of the lens with steepening of the anterior capsule and shallowing of the ante rior chamber. After su rgery (right), there were simitar findings, though less remarkable. Note also that there were discontinuous zones in the lens before su rgery, while the refilled lens was optically empty due to the silicone compound

Anterior capsule-supported IOL for sealing /

eee

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Nishi 0, Nishi K, Graefe's archives of clin. Exp Ophthalmology 1990

Fig . 4: Anterior capsule-supported IOL for sealing eee. The arrows show the small narrow, grooves at the optic (Reprinted by permission of Graefe's Archives of Clinical and Experimental Ophthalmology)

423

Instunt C/inicnl Diagnosis in Oplltl1almologlJ (Refractive SlIrgety) Expected Mechanism of Accommodation

The expected mechanism of accorrunodation in vo lves forward-movement of the TOL and thickening of the lens. These expected mechanisms are based on two recent stud ies. Nawa and his coworkers d emonstrated the accommodation-a mplitude obtain ed per 1 mm forward movement o f the IOL. For this purpose, a ray-focusin g equation for pseudophakic eyes was established using the ra y- traci ng method w ith dedicated compu te r softwa re. It was found that the amplitude depends on axial length and cornea l power (Table 1). [n eyes with an ax ial length of 21 mm and an IOL w ith 30 d iopte rs, 1 mm fo rwa rd moveme nt yields 2.3 0 of accommodation. Accordingly, in an eye with a length of 23 mm and 24 diopters, 1.6 0 of accommodation will be obtained, while only 0.8 0 w ill be ob tained w ith va lues of 27 mm and 11 d iopters. These fi n dings ind ica te tha t improvements may be obtained with the recen tly developed accommod ating IOL such as the Crysta lens or 1CU, specifica lly in hyperopic eyes with a short axial length. Table 1: The relationship between AL and dioptric power of an MA30BA IOL and amount of accommodation per 1.0 mm forward movement Axial Length (mm)

Paramete r

21 .0

22 .0

23.0

24. 0

25.0

26.0

27.0

IOL power (IOL)

30.0

27.0

24 .0

20.0

17.0

14.0

11.0

2.3

1.9

1.6

1.3

1.1

0 .9

0.8

Accommodati on pe r 1.0 mm forward IOL move ment (D)

(Preprinted by permission of J Cataract Refract Surg)

Van der Heijde and co-workers measu red microfluctuations of steady-state accommodation using ultrasonography, and d em onstrated that fluc tua tions in accommodation are mainly caused by fluctuations of lens th ickness. They fo und that on average, the lens increases by about 56 11m in thickness per diopter during flu ctuation. That m eans that 3 diopters could be obtained by about 0.17 mm change in thickness. Enhancement of Accommodation-Amplitude and peO-Prevention by Dual-Optic

To prevent PCO and possibly to augument accommod ation-am plitude being attained, we have drafted a dual-optic concept, as Fig. 11 shows. First, a conventional fold ab le IOL w ith sharp edges and the en hanced haptic angulation is implan ted in to the cap su lar bag. It has a concave optic with a minus diop tric power, which m ay imperatively give a greater power to the

424

Restoration of Accommodation by CapslI lar Bag Refilling

Fig . 5: Surgical lens refilling procedure using anterior capsu l e~supported IOl (Reprinted by permission of Graefe's Archives of Clinical and Experimental Ophthalmology)

Fig. 6: Anterior capsu le-su pported foldable IO l and Its dimensions

425

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) anterior optic, achieving emmetropia. During accommodation, the anterior capsule moves forward, while the posterior capsule stays relatively unmoved, so that an anterior optic with a greater power may enhance the acc-ommodationamplitude attained. A large angulation of the haptic will press the sharp optic edge against the posterior capsule to create a strong compression on it for the prevention of PCO. The injected silicone mix will additionally press the 10L on to the posterior capsule. As an alternative technique, the same CCC-capturing 10L can be implanted after a posterior CCC is performed. Then, a CCC-capturing 10L is introduced into the capsular bag which contains the 10L being implanted previously and captured by the anterior CCC, as already described. To refill the bag, silicon e mix is injected between two 10Ls that are captured by the anterior and posterior CCCs. SUMMARY

To summarize, the novel anterior capsule-supported 10L is technically quite feasible. Some accommodation might be obtained by forward-movement and thickening of the lens. We will test this procedure in primate eyes. Anterior and posterior capsule opacification at least in the optical axis can be avoided. Postoperative emmetropia is supposed to be achieved more eaSily due to the predetermined optic. One of the advantages is tha t postoperative in viva power change may be possible using an adjustable 10L. In conclusion, restoration of accommodation by refilling the lens capsule is a goal of refractive cataract surgery. Technical feasibility has been repeatedly demonstrated by obtaining some useful accommodation in primates and will be further facilitated by modern technology. Capsular opacification is one of the essential problems to be overcome. The technique shown here may provide a breakthrough for pOSSible clinical application to refilling of the lens capsule.

426

Restoratiotl of Accommodatiotl by Capsular Bag Refillitlg

Fig. 7: A well·refilled pig cadaver capsule. The anterior capsule-supported tOL was firmly fixed , and there was no leakage of the material injected

Fig. 8: A refi ll ed rabbit crystalline lens. Three weeks after su rgery. Note that the IOL was firm ly and sec urely fixed . There was no leakage of the injected silicone compound . Poste rior synechia

427

Instant Clitlica l Diagtlosis itl OphthalmologtJ (Refractive Surgery)

Fig. 9 : An enucleated rabbit lens refilled

Fig . 10: Histopathological findings of an enucleated rabbit lens refilled . T hree weeks after surgery

428

Restoratiol1 of Accomll1odatioll by Capsular Bag Refillillg

Fig. 11: Dual optic refilling concept I. The concave poste rior IOL with a minus power and sharp edges is pressed on the posterior capsu le, so that LEG migration might be prevented

Fig. 12 : Dual optic refilling concept II. The concave posterior IOL optic is captured by the posterior eee. The poste rior visual axis is expected to rema in peO-free

429

43 Custom ICLs Carlo Francesco Lovisolo (Italy)

INTRODUCTION

430

Since the celestial engineer provided the eye with two lenses, the surgical solutions to correct refractive errors may exploit tvvo anatomical objectives (by modifying the optical behavior of the cornea or the crystalline lens) or a prosthetic one (by inserting a supplementary lens inside the eye). The lifelong stable, elliptical architecture of the cornea has been designed to deliver very high vergence (more than 70% of the total focusing power of the eye), while minimizing optical aberrations. Even with highly sophisticated optimized and / or customized laser treatments, corneal procedures are subject to physical limitations and challenging complications, mostly related to the issues of wound healing and biomechanics. The optical quality of the outcomes may therefore be less than ideal when treating high ammetropias (myopia higher than 6-7 diopters, hyperopia higher than 3 diopters) and patients with large mesopic pupil sizes. Newcomer keratoplasty techniques, using tissue engineered or synthetic lenticules as refractive onlay or intrastromal inlay have, so far, only shown the potential to overcome these drawbacks. The crystalline lens gives one fourth of the power and is responsible of the autofocus mechanism of the eyes optical system. It grows and becomes sclerotic throughout life, causing changes of refraction and progressive loss of the accommodating power. The benefits of its irreversible extraction (CLE) and substitution with an artificial toric, aspheric, multifocal or accommodating implant is still controversial among eye-care providers. Accommodating IOLs ha v e so far clinically failed to solve the main complication of lens removal, presbyopia. Multifocal optics inherently decrease contrast sensitivity and require neuroadaption. Beyond the unpleasant loss of accommodation in young people, long-term safety is_a major concern for CLE, risk of influencing retinal detachment and macular pathology in eyes naturally prone to posterior segment pathology (i.e. high myopia). Instead, a supplementary intraocular lens (phakic lOLl implanted between the cornea and the lens has several theoretical advantages. It allows the crystalline lens to retain its function without risking vitreo-retinal side effects;

Custom lCLs

Figs 1 A to C: (A) Oversized ICLs may lead to ang le closure glaucoma. (6) Artist's view of the bulging of the iris diaphragm induced by the lens implant; (C) VH F echography image of an ICL-induced papillary block). Urgent lens explantation or multiple iridotomies are requ ired

431

Itrstnnt Clinical Dingnosis in OplrtlralmologrJ (Refractive SlIrgenJ)

since the quality of the implant surfaces is above the optical limits of the eye, its nod al points are nearer the pupil and the optic can be convenientl y wid e, may improve the natural properties of the eyes optical system to enhance the quality of the retinal image, allowing excellent vision even in all light conditions. It is removable and exchangea ble, permitting potential reversibility to the preoperative condition. The result is highly predictable, easily adjustable with complementary fine-tuning corneal surgeries and immediately stable, because the refractive outcome depends less on hea ling processes. The major dra wbacks of aphakic IOL surgery are essentially related to the intra-operative and early postoperative risks of a n open-eye procedure and to the long-term tolerability of the lens implant. The re is enough evidence that the dangers of an intraocular proced ure ma y be properly managed and minimized with proper care and proctoring of an accomplished surgical tea m and en VllOl1ll1ent. THE CONCEPT OF CUSTOM PHAKlC IOL

There is no doubt that the same concepts behind the universa l trend towards clistomization of cornea l refractive surgery must be immed iately applied to phakic IOL procedures. Considering the wide va riabil ity o f biological presentations, the va riety of anatomica l shapes, sizes and range of optical e rrors, the need for a custom-made lens implant w ould ap pear even more obvious than personalized corneal laser treatment. Custom-designed lenses that perfectly lit the individual anatomy o f each single eye a re obviously sa fer than conventionall y-sized ones, as late postoperatj ve complica tions relate mainly to unstable implants and less than ideal dista nces from the internal structures. Once inside the eye and over time, w ithout a perfect fit, each site of haptic fi xation has its own area of unique concern and accurate preoperative assessment of the lens im plant-to-tissue clearances becomes vital to avoid safety concerns. Angle-fixated and iri s-supported 10Ls may induce acute and recurrent subchronic iritis, ischemic subatrophy of the iris, pupil distortion, progressive endothelial cell loss, secondary glaucoma, and breakage of the blood / aqueous barrier with persiste nt aqueous flare and cystoid nlacular edema. When too long, posterior chamber phakic, like the Visian ICU " (Staa r, Monrovia, CA, USA), excessively vau lted between the iris posterior pigmented laye rs and the anterior crysta lline lens, may cause the iris diaphragm to bulge forwa rd, w ith narrowing of the irido-corneal ang le, chafing of the poste rior iris surface, pig ment dispe rsion and subsequent risk of angle closure and pigmentary g laucoma, ocular pain or tenderness due to nerve irritat ion by excessive 432 pressure in the Ciliary sulcus, cyclitis and macular edema. On the other hand,

Custom lCLs

Figs 2A to C: (A) Artists view; (B) Scheimpflug camera and (C) Slit lamp images of typical iatrogenic anterior subcapsular opacities of the crystalline lens caused by the lack of vaulting of an undersized ICL

433

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) lack of vaulting because of short has caused iatrogenic anterior subcapsular cataract by preventing the nutritional turnover on the lens surface and implant decentration. We should be aware that the vast majority of these iatrogenic damages to the delicate inner structures depend on human errors: the wrong selection of an unwelcome intraocular enVir0111nent or the wrong choice of the overall length of the implant. Custom sizing the Overall Length

C .. the choice of the implant overall length appears particularly critical .... Unfortunately, proper measurements of the inner diameters are not achievable by any means .. " at

Since the prophetic words of Benedetto Strampelli of the early 1950s

the Societ" Oftalmologica Lombarda, December 1953) proper sizing h as been considered for decades the 'mission impossible to optimize safety of phakic IOL surgery. Anachronistically, after more than half a centu ry and despite the lack of scientific proof behind it, the vast majority of surgeons worldwide sti ll behave like him, selecting the overall diameter of the lCL according to the 'golden rule of thumb, by empirically adding 0.5-1.0 mm to the horizontal corneal diameter (white-to-white di stance, W-to-W) obtained externally. Wh ether measured at the slit lamp by comparison with a ruler or gauge, or under the operating microscope using the surgical caliper, white-to-white is an unreliable landmark, as the points where white begins and gray starts at the limbus are open to each surgeons personal interpretation. More standardized strategies, based on the analysis of digital photographs from video-keratography or laser partial coherence interferometry images-have sli ghtly improved the precision achieving acceptable reprodu c ibility tolerances. Nevertheless, numerous findings from in vivo ultrasound and MRl studies, anatomic observations on cadaver eyes have definitely showed that, regardless of the accuracy of the Ineasure ment of W-to-W, there is no proportional anatomical correspondence between external measurements and internal dimensions of the anterior segment compartment. Internal anatomy cannot be predicted by external measurements. As a consequence, W-to- W distance alone is totally adequate for sizing lCL. Instead, the exact internal linear sulcu s-to-sulcu s (5-to-5) distance, the iris-to-crystalline lens relationship (distance between the iris and the ciliary processes, w idth of the irido-corneal angle and of the iris-crystalline angle) - m easured point-by-point at different levels, should be used. Accurate imaging of these hidden anatomical sites can be obtained with high-resolution ultrasound devices that use very high frequency (VHF) waves in the 35-to-50 MHz range, like the Artemis 2 (Ultralink;-St. Petersburg, FL, USA) and the Vu-Max (Sonomed, New York, NY, USA). Optical devices like slit scanning systems with or without rotating Scheimpflug camera (like the Precisio, Ligi, Taranto, italy, the Pentacam,

434

Custom ICLs

Figs 3A to C: (A) In a series of 200 patients where the W·to-W distance was accurate ly measu red with the Orbscan and the 'golden rule' (W-to-W + 0.5 mm = overall length) meticu lously applied, we achieved the desi red outcome (vault height between 200 and 700 microns) in 59% of cases (8 ); in 24% of cases we got sign ificant Qvervault, superior than 700 micron s; and (C)

and in 17% an insufficient vault, inferior than 100 micron

435

Illstallt Clillical Diagnosis ill OplrthallllologtJ (Refractive Su rgery)

Oculus, Germany and the Galilei, Ziemer, Germany), or infrared ligh t optical coherence tomography sys tems (OCT Visante®, Ze iss-M editec, Jena, Germany) permit high-resolution cross-sectional anterior segment imaging w ith excellent reproducibility of mea surements by using the interference profile of the reflections from the cornea, the iris and the crystalline lens. These methods are not interesting for sizing the ICL, since the retro-irideal space cannot be perfectly visualized by optical devices and the sta tistical correlation between angle and sulcus diameters is as poor as between external w hite-to-white and internal d imensions. On the basis of our experience, started more than 13 years ago (September 1993), the ideal central vault height for a n lCL is conside red to be around 350 J.lm in m yopic and 250 J.lm in hyperopic implants, to provide safe separa tion from the anterior surface of the crystalline lens and minimize untoward effects on aq ueous hydrodynamics. H yperopic can have a lower va ult than their myopic cou nterparts beca use the peripheral geometry of positi ve lenses leaves more space in the pe riphery to the ci rculation of nutrients and hype ropic eyes tend to have shallower chambers with narrower angles. For myopic implants, a minimum mid-peripheral clearance of 150 pm is require d. When we observ e lower or mechani ca l contact, leL explantation and / or exchange with a larger overall size should be considered for the hjgh risk of iatrogenic cataract. Since 1997, we have been using a modified trigonome tric formula to predict vault height precisely. The va riables entered into the formu la included the sulcus-to-sulcus distance, as measured with the lABDTM(Innova tive Inc, Canada), and the radius of curvature of the anterior surface of the crystalline lens (obtained with the EAS 100QTMScheim pflug camera, NlDEK, Tokyo, Japan). The constants in the formula included the elasticity (elongation factor) of the colla mer and the base-curve of the ICL. Since then, we have improved the formula and now are using a proprietary software to simulate the expected clearances between corneal endothelium, iris and crystalline lens. The last LOVISOLO ICL S/ZER® software takes into consideration: • The three-dimensiona l map of the biome tric data of the patients anterior segment as obtained from VHF ultrasonography (Artemis 2 or VuMax scans);

436

• The specific features of the chosen lens implant (overall length, vault, central and peripheral optic thickness, flexibility); a corrective factor, considering the va riation of ICL dimension from the labelled size (as measured in vitro at 20°C) when going into the aqueous envi ronment. Intraocularly, for instance, a 125V4 ICL enlarges from 12.5 to 13.2 mm; • Its behavior und er compression, as predicted by finite element analysis; • The age and the life expectancy of the patient. As the human lens grad uall y grows, doublulg its thickness and displacing anteriorly by 0.4 rnm during the lifetime of a 90-year-old, due to the li fe-long mitotic activity of the sub-

ClIstOIll I CLs

Precisio -~-

..........

T

N

S

Dr i..• .

Close

--

Figs 4A and B: Bidimensional maps (A) and cross-sectional scan (8) of the anterior chamber provided by the precisio rotating Scheimpflug camera (UGI, Taranto , Italy); authors left eye OCT Visante image

437

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) capsular epithelial cells at the lens equator, the anterior chamber depth drops by 0.75 mm over a 50-year span. An average red ucbon olthe anterior chamber depth of 0.015 mm per year is calculated to predict the anatomic relationships even after 50 years; • New anatomical safety parameters are introduced (Table 1); a warning signal if more than one parameter shows a difference higher than 20% from normal value. In our most recent personal series on 394 eyes implanted with the TCL V4, after a maximum follow-up of almost 9 years (since April 1998) and a mean follow-up of 39 months, we have not yet observed any cases of iatrogenic cataract, pigmentary dispersion or angle closure glaucoma. The mean central vault height was 386 flm, with a standard deviation of ± 113 )lm. The minimum vault obtained was 189 flm. In the 95% confidence interval, an expected vs. achieved vault height in the ± 150 )lm range was obtained in the 95% confidence interval. In comparison with the group control of 237 eyes, where the ICL was implanted on the basis of the W-to-W, the mean central vault height was 406 mm (not statistically significant), but the standard deviation was highly significant (± 667 )lm). The minimum vault achieved was 0 mm and the incidence of size-related compli cations (angle closure glaucoma, cataract and clinically significant pigmentary dispersion) was around 8%. The reference point of the 95% confidence interval as referred to the expected vs. achieved vault height was reached for the range of ± 730 )lm. For further comparison, the reader should know that similar values could be easily obtained from multivariate regression analysis by sizing the ICL on the basis of anterior chamber depth, corneal pachymetry, opening of the iridocorneal angle, angle-to-angle distance, axial length, but also shoe, hat, or glove size! While recognizing that researchers are still far from fully understand the de tailed mechanisms of ICL-induced cataract formation, we attribute these results to the meticulous selection of the anatomic features of each single eye and to the precise sizing of the implanted lenses, allowing an ideal prediction of lens vaulting. With the extraordinary confidence the system provides to our practice, we now consider as relative contraindications and evaluate on a case-by-case analysis many of the conditions that have been considered exclusion criteria

Crystalline lens rise over the iris plan (cycloplegia): 0.4 mm Iris configuration (sclera-iris angle): 28.1 " Ciliary body position (sclero-ciliary angle) : 53.1 " Irido-Corneal Angle: 31.3" Crystalline lens anterior curvature: = 12.08 mm (cycloplegia)

- R

438

R

= 10.3

mm (non-accommodating miosis)

Custom lCLs

Figs 5A and B: The first generation of the Lovisoto te l Sizer® software. As the ultrasound cone width was lim ited to 8 mm, two scan images were pasted together to measu re the sulcus diameter (from left and right ciliary recesses to the geometrical center of the crystalli ne lens) and the anterior curvatu re of the crystalline lens was measured (A and B) then the trigonometric Fumagalli sag formu la was applied

Figs 6A and B: Snapshots of the second (A) and last (8 ) generation of the Lovisolo tel Sizer®. In B a predicted versus obtained vault is shown

439

Instant Clinical Diagnosis in Ophthalmology (Refractive SlIrgenj)

(Table 2). Pediatric age, for instance, is not an absolute preclusion to surgery any more. An original excess of caution made it wise to avoid implanting phakic in children, but special cases of unilateral ammetropia or hi gh anisometropia with contact lens intolerance and functional strabismus are worth reassessing, to prevent amblyopia. Old absolute contraindications ha ve now proved too conservative, like in the case of stable ectatic corneal disorders (keratoconus, pellucid marginal degeneration, iatrogenic ectasia) and sequelae from trauma, infection or unsatisfactory previous corneal surgeries (like PKP, LKP, RK, ALK, epikeratoplasty, LTK, PRK, LASIK) that may be dealt with successful outcomes. Eyes with anterior chamber depth (ACO, endothelium to anterior crystalline central distance) less than 2.8 mm can also be implanted with an excellent safety ratio. Although still a preclusive medico-legal reference point, a single measurement of the central ACD, usually obtained by conventional A-scan ultrasound biometry, cannot help in preventing angle closure glaucoma after ICL surgery if no information is provided on the opening of the irido-corneal angle, the shape of the anterior segment, the crystalline lens rise over the pupil plane. No complication was encountered in a series 61 eyes, where the ACO was lower than 2.8 mm, but the other parameters were considered safe. Eyes w ith endothelial cell count lower than 2000 cell s/mm (postkeratoplasty ammetropias for instance are excellent candidates) may safely undergo ICL surgery as the iris_-barrier between the ICL and the cornea protects against corneal decompensation. Our long-term (based on more than 10 years of maximum follow-up) cell losses are completely similar to physiological decay (0.6% per year). Moreover, in the retrospective analysis of our last 6 years series, we observed that no intraoperative endothelial cell sacrifice is required any more. The mean postoperative ceUloss was 0.4%, with as much as 46% of eyes whose count and morphometric indices improved . Apart from some unavoidable endotelioscopy bias, these apparently paradoxical findings are probably due to the postoperative tiiifYf';:;~ Table 2: Generally accepted inclusion criteria (Safety guidelines) :"" ",",;//"

for phakic IOL surgery Age> 21 years Stable ammetropia, not amenable to excimer laser surgery Intolerance of contact lenses or spectacles Centra! ACD ';:;>: 2.8 mm Irido-corneal angle aperture,;:;>: 300 Endothelial cell count> 2,000 cells/m m2 Overall length based on external White-to-White distance No previous ocu lar surgery No ocular pathology (glaucoma, uveitis, cataract, etc.)

440

No systemic diseases (diabetes, autoimmune disorders, etc.)

:5>

":'r

~;"" ,~

Custom ICLs

-_ _.) ...-------------------....., .

Figs

7A

and

B:

AnsysTM finite element

analysis

(A)

and

mechan ic al compression data (8 ) were compared to get the intraocular behavior

of every lens

441

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery)

centrifugal migration of peripheral endothelial cells and to the cell enhanced metabolism after stopping contact lens wear. Using VHF echotomography (Artemis 2) and scann ing s lit optical tomography (Orbscan II) we realize that there is no precise correlation between central and peripheral depths of the anterior chamber (Sizing Phakic, presented by Lovisolo CF at the ASCRS meeting, San Francisco, April 2003). A certain number of eyes show a progressive narrowing fro m center to periphery, with the nasal regions about 20% shallower than the temporal counterparts. However, some are strangely shallower in the center and each single eye seems to have its own anterior chamber shape and volume, w ith no general rule. In a sample of288 eyes scanned with VHF Echography, the largest

cross-sectional internal sulcus diameters was found horizontally in 27%, obliquely in 15%, vertically in 58% of cases. The largest external diameter (white-to-white) was found to be horizontal in 100% of cases. W-to-W was found larger than S-to-S in 59%, the opposite was found in 41% of eyes examirted.

As regarding efficacy and functional performance, the same concerns abou t the quality of vision in kerato-refractive surgery apply equally to phakic. To prevent the symptoms of the 'GASH-tetrad syndrome (glare, arcs, starbursts, halos), the customized optic would ha ve: J. The necessary sphero -cylinder power. Like in second a ry IOL implantation in aphakic eyes, or piggy-back pseudophakic implantation, the power of an [CL positioned intraocularly is equivalent to the power of the lens measured at a given distance from the corneal vertex. It is not

necessary to determine the axial length, the crys talline lens thickness and the vitreous chan1ber length, as they remain completely unchanged. This calculation depends very much on precise refractive measurements,

442

but also on the ability to predict the intraocular position of the nodal points of the lens (ELP or Effective Lens Position, the distance between the secondary principal plane of the cornea and the principal plane of the lOLl to avoid over or undercorrection. Currently ava ilable refined tori c lens implantation requires an astigmatically neutral surgical incision and robust fixation site to provide rotational stability over time. For that reason the 6-to-7 mm opening of the eye needed for in1planting the Artisan PMMA lens seems too challenging for the average surgeon, while the rninin1al size (2.5 rnm) achievable with the ICL seems ideal. The rotational stability of the toric ICL is even more important, as the cylinder correction decreases with increasing deviation of the lens implant from the target axis by following a non-linear relationship. As shown in a stud y where the positions of a g roup of s ized w ith VHF echography we re docum ented by superimposable slit-lamp photographs (Carlo Lovisolo, unpublished da ta), the mean lens deviation from the original meridian over time

Custom lCLs

Fig. 8: A toric tel was implanted three months after a couple of intrastromal corneal ring segments ( INTACS) we re inserted in an advanced stage case of pe llucid marg ina l degenerat i on . Preoperative ly, the BSCVA was 20/80 with -13 .00 -12.00 x 1 t5°; after INTACS implan· tation BSCVA was 20/30 with -11 .25 -6.75 x 98°; 6 months after teL

surgery UCVA was 20/ 20!

Figs 9A and B: As can be seen from the two Orbscan maps (A and 8 ), similar peripheral

narrowing of the anterior chamber (depths equal to about 1.9 mm at 3 mm of eccentricity) corresponds to completely different shapes and volumes of the ante rior segment [(central depth 01 3.8 mm in (A) 2.6 mm in (B)I

443

Instant Clinical Diagnosis in Ophtl/almologtj (R efractive 5l1rgenj)

444

(three years) is less than 5°, i.e. compati ble with a maximu m of 10% loss of as tigmatic correction. Once aga in, as small implants may rotate, accurate sizing is mandatory. II An effective d iameter at least as large as the mesopic entrance pu pil diameter. Infrared pupillometry has shown that scotopic pupil d iameter in young m yopic patients - the average candidates to ICL surgery - is signilicantly larger than in the emmetropic group. Our observations on more than 3,000 Caucasians m yopic eyes, ranging from 21 to 39 years of age, showed a mean scotopic pupil diameter of 6.87 ±0.72 mm, the range of minimum-maximum value going fro m 5.6 to 8.9 mm. For that reason, d ue to the limited diameter of the optica l zone, all currently available phakic have been reported to induce diiferent degrees of night time visual disturbances (mainly halos and g lare when dri ving ve hicles). The successful trend of combining different surgical approaches (Bioptics and / or Adjustable Refracti ve Surgery) has highlighted not orily the concept of fine-turting residual refracti ve errors after implantation but also the need for a wide functional optical zone. For a -1 7.00 correction in a patient with a 6.0-mm meso pic pu pillary diameter, for ins tance, postoperative quality of vision is unquestionably better if we select a Wide-optic implant (a -12.00 lCL has a 5.5-mm diameter and corrects approxima tely -10.00), and combine it with a -7.00, 6.0-mm optical zone excimer laser ablation, instead of implanting a -20.00, 4.65-mm optic ICL, fully correcting the -17.00 dt ammetropia. As a trend, taking advantage of new designs and higher index materials, it is easy to foresee that the average effective optical zone of futu re lenses will soon be made larger; III. A proper geometric shape factor (asphericity) to respect physiology. Conventional high-power (more than - 12.0 and + 7.0 0 of correction) spherical phakic with an average optic size of about 5.0 mm inevitably induce moderate amounts of spherical aberration and coma, thus red ucing contrast sensitivity and increasing glare and halos for the ave rage mesopic p upil. An aspheric phakic lens can be designed on the basis of theoretical assumptions (to li mit spherical abe rration without reducing the depth of focus), or wavefront analysis from aberrometers (to correct not only on-axis aberrati ons like spherical aberration, but also higher-order aberrations like trefoil and coma). The weak point of aspheric lenses is the need for perfect aligrunent with the cornea and crystalline lens (centration and tilt). When measured as a mod ulation transfer function, the optical performance of an aspheric IOL is not degraded if the IOL is decentered less than 0.4 mm and tilted less than 7°. Larger discrepancies between lens optical center and visual pathway could cause Significant symptoms. Our observa tions with infrared photography and VHF echography on a group of patients implanted with d ifferent phakic

Custom ICLs

Figs 10A to C: Artemis 2 (Ultralink) images of external, white-la-white (W-to- W) and internal measurements, angle 10-angle (A-IO -A) and sulcus -ta-sulcus ( S-foS) distances, relevant for sizing ICLs. Without a statistical correlation or a rule , some eyes show almost identical Ata -A and S-to-S distances (A); in the majority of cases A-toA is larger than S-Io-S (6), in the minority the opposite is true (C)

Figs 11A to C: VuMax (Sonomed) VHF echography images of a perfectly sized teric Visian lCL with a central vaulting of 355 microns (A) and retroirideal details of haptic positioning in the ciliary sulcus (8 and C)

445

In stant Clinical Diagnosis in Ophthalmologtj (Refractive SlIrgenj)

showed that pupil decentration is 0.32 nun and tUtisSo on average (Carlo Lovisolo, unpublished data). H owever, in patients with largely positive angle kappa , even an accurate sizing co uld cause a s ign ificant misalignment with the line of sight. Once this becomes more accurate and standardized, we can foresee a demand even for haptic customization, wit h asy mm etri cal loops and wings to match individual pupil decentration. Otherwise iris-fixated lenses that can be nicely centered over the pupil will be preferred to sulcus-supported lenses. N. quality of the surfaces higher than the eyes optical limi ts, possibly designed on the basis of wavefront detection. Custom ICL could be therefore indicated in piggybacking pseudophakic eyes w ith Significant residual ammetropia, as well as in pediatric patients with aniridia, albinism, anisometropic amblyopia or in eyes with naturally occurring or iatrogenic, stable corneal disorders (keratoconus, marginal pellucid degenera tion, post-RK h ype ropic shift, pos t-LASIK iatrogenic keratec tasia, post-trauma or post-keratoplasty astigmatism ... ), which cause significant higher-order aberrations and may theoretically be tackled by making the compensa ting corrections intraocularly instead of on the corneal surface. CONCLUSIONS

We can roughly estimate that around 100,000 phakic have been implanted to date throughout the world. Many surgeons worldwide actually share my opinion that, so far, the Visian-ICL is the winner of every competitive analysis of the products available on the market. Its collamer material offers the best biocompatibility; the surgeon's learning curve and experience in sorting out intraoperative difficulties is not as steep as for other models; its fo ldability aLlows minimally invasive, smooth insertions as well as safe removals under topical anesthesia and through anastigmatic small incision, with absolu te patient comfort and the fas test rehab ilitation amo ng anterior segment procedures; it prod uces excellent results in terms of precision, pred ictability (the percentage of eyes obtaining ± 1.00 0 from the desired refraction is 100%), and stability of the refractive outcome; a toric optic may correct high degree of astigmatism with unbelievable outcomes in 'desperate cases; the iris-barrier protects against the most feared complication of phakic IOLs, progressive endothelial cell loss; the incidence of catastrophic events like endophthalmitis and retinal detachment (only anecd otal reports) is accep tably low; provided that a perfect lens sizing guarantees a smooth, wuform distribution of mit1imal pressures at the fixating points without lOSing intraocular stability, the long term risk/ benefit ratio is more than acceptable, as late comp li ca tions, iatrogenic cataract in particular, are mainly due to hwnan errors in sizing, so 446 they can be expected to become less frequent as surgeons gain experience.

ClIstom lCLs The absence of synechiae and chronic inflammatory p henomena encapsulating the haptics will facilitate future implant exchange or the 'bilensectomy, procedure w hen the time comes for cataract surgery in these subjects. The reported nighttime visual symptoms (halos, arcs and gla re) are d isabw1g only in a minority of cases and are destined to become minor issues with the latest and fu ture generations of wide-optic customized lenses. SU1Ce the im plant is generally inserted into pristine, young patients eyes, the ethical endeavor to ensure a li fe lon g enduring ha rmonious relationship w ith the internal structures is mandatory. Only a Cus tom ICL, perfectly designed on the u1dividual ana tomic and optical features of each single eye may accomplish all these goals. At last, after almost a decade of sterile d ebate, I sincerely hope that times are mature to:

• Abandon empirical technique, like the 'junk White-to-White based state of the art sizing method; • Perform the most crucial choice (size the overall length of the [CL) on the ba sis of anatomically corre lated measurements, obtained with the newest high resolution biome try devices (VHF Echography) and calculated by an accomplished soft ware; • ask the firm marketing the ICL to provid e at least the intermediate sizes (0.25 mm s teps) and a wid er range (from 11 to 14 mrn) of lens diameters; • Closely monitor the [CL implant-to-tissue clearances yearly, w ith the same High-Res instruments and decide fo r prompt removal! exchange if vault height values are outsid e the safety limits.

447

44 Mini Incision lOt ImplantationCurrent Scenario Roberto Bellucci, Simonetta Morselli (Italy)

Mini incision 10L implantation has many features different from standard 3.2 mm incision 10L implantation. The main differences are in the 10L design and material, in the cartridge and plunger design and material, and in the injection teclmique. As a rule, current three-piece hydrophobic 10 Ls are not suitable for sub 2.5 mm implantation, because of the possible damage of the loops or of the loop attachments when forced through the 1.6-1.8 mm intemal lumen of a mini incision cartridge. Among the single-piece 10L we should consider: • 10Ls that have been developed to be implanted th rough mini incision • 10Ls already developed for 3.2 mm incisions, that can be implanted through mini incision. MINI-INCISION 10LS

Mini-incision [OLs are d efined as the TOLs that have been conceived and designed to be implanted through 1.6-1.8 mm internal d iameter cartrid ges. Therefore, they need to have reduced volume and diameter when folded. To do so, they could be thinner than regular 10Ls, smaller in optic diameter, and with some optical features allowing add itional thickness reduction. ote that the leng th of the 10L is no t an issue w hen conSid ering mini incision implantation. As for the material, the properties required for mini incision 10Ls are favo u ring hydrophilic acrylic materials with high water content. Most of currently used polymers seem suitable to construct mini incision 10Ls, and several Single-piece hydrophilic acrylic 10Ls are appea ring. There a re several elements that favour mini incision 10L design. Among them the d esigners and the prod ucers select the combination that seem s the best option to obtain an ]OL with the same optical and mechanical properties as the 3.2 mm incision ]OLs. So far, the results ha ve been encouraging, but we are only close to the solution of this problem. Mini Incision 10L Design Thickness

The basic thickness of the 10L can be red uced simply by designing a thinner optic border. However, several problems cOl~ d arise when doing so. The thinner 448 border cou ld prevent posterior capsule opacification by Elschni g pearls

Mini Incision IOL Impiatltation-Current Scenario

Fig . 1: A three-piece IOL of the currently available designs cannot be delivered through a mini incision cartridge of reduced size

Figs 2A and B: T hin IOLs are commonly produced in a 4-haptic design to ensure stability inside the capsular bag

449

Instant Clinical Diagnosis in OphthalmologJ) (Refra ctive SlI rgert)) formation at a lower extent than a thicker border, an issue d irectly related with the edge curvatu re radius. In addition, the position and the stability of the IOL inside the eye could be affected by the position and movement of the vitreous body, thus g iving rise to pseud ophakic refractive inaccuracies and / or to refractive variations. The possibility is to increase pseudoaccommodation, the risk is to randomLy reduce distance vision. Moreover, any uneven pressure on the posterior optic surface or any loop compression at bag equator could produce optic tilt or loca lized displacement, increasing the resulting optical aberrations. For these reasons new thin IOLs show newly designed four loop haptic, that favo ur IOL stability inside the eye with good res ulting optical quality. Optic Diameter

The reduction of the optic d iameter from 6 to 5.5 mrn or even to 5 rnm can be a further way to IOL volume reduction, either maintaining an overall optic diameter of 6 mm or reducing it to 5.5 or to 5 rnm. PMMA IOLs of 5.5 rnm optic diameter have been extensively used in the past, with no complication about postoperative vision. With these IOLs, the problems could be related with the capsulorhexis d iameter, that could be difficult to center over the IOL optic border, and with the loop length and stability. IOL displacement due to capsular shrinkage, unwa nted refraction inaccuracies and pseudo accommodation could be an issue with these thin and small optic IOLs. Op tic Properties

450

There are ad d itional methods to reduce the optic thickness. The use of Fresnel optics has been implemented in intraocular lenses, with the app roach to use an entirely Fresnel lens, or to combine a center refractive and a peripheral Fresnel optic. This second ap proach has been used in clinka l prac tice, leading to a big reduc tion in lens thickness and allowing a 6 rnm optic implantation through a 1.5 mm incision. However an d despite the good visual acuity, the optical quality as measured by aberrometers and the quality of vision as judged by patients have not been completely satisfying, so tha t this approach has been almost aba ndoned. A second method to red uce center thickness while mainta ining the same border thickness is to implement an aspheriC design on one or on both optic surfaces. EspeCially with high positive lenses, the aspheric design is much fla tter than the spherical design, and this fl attening can give ri se to a thicker border, or it ca n be used to reduce the IOL center thickness. A third way towa rd s thinner IOLs while maintaini.ng thick borders is the use of high refractive index (RI) materials. Current hydrophilic and hydrophobiC acrylic materia ls have RI between 1.43-1.46, and only one well proven material has a RI of 1.55. [n the past, hydrophobiChigh RI IOLs have been observed to give rise to mo re dysphotopsias than other IOLs, and some imp rovement in

Mini Incision IOL Implantation-Current Scen ario Paraluex anterior and-+ poslerior surface Third posterior optical surface _ Second posterior surface ____ So micron night ....... Apex Central surface _ /

Central axis Lach posterior has of save focal point

Fresnel lens 1a

Ught rays

Refractive lens 1b

Figs 3A to C: The combination of a center refractive and of a peripheral Fresnel optic allows great thickness reduction as compared with conventional design (dotted line)

451

Instant Clinical Diagnosis in Oplttll alm ologtJ (Refractive Sllrgery) IOL design was necessary to solve this problem. Therefore, any design considering high RI should take into account the necessity of steep anterior curvatures, that could reduce the advantages of this material for small incision IOLs. IOLs that can Fit Mini Incision Some of the properties of IOLs designed for mini incision can be found in IOLs designed for 3.2 mm incision. For example, the combination of aspheric design to reduce central thickness, high refractive index and 5.5 mm optic diameter allow the single piece Acrysof IQ to pass through a reduced size cartridge. A few currently available 6 mm optic IOLs can be implanted through incisions that are 2 to 2.5 mm wide, provided they are properly loaded and provided they have some additional properties favourin g the passage through the cartridge and the unfolding inside the eye. As the cartridge is hydrophobic, the contact with an hydrophobic IOL could generate mo re friction than with an h ydrophilic IOL. Therefore, h ydrophilic IOLscould be preferred in this respect. Among hydrophilic IOLs, specific surface characters can be of help during injection. For example, the limited duration of the polishing p rocess is of great importance in obtaining square edges and smooth surfaces. An additional reason to prefer hydrophilic IOLs is their ability to express some water when compressed, thus showing some adaptation to small cartridges. When the ca rtridge is very small, the plunger calUlot reach the cartridge tip without breaking it. Therefore, the plunger can only initiate the lens delivery, that should continue and be completed automatically once sta rted. The elastic force of the lOL, aiming at restoring its original form once folded, is of outmost importance in this respect. If the lens has great elastic force, like with silicone or some hydrophilic acrylic materials, this force will extract the lens from the cartridge tip without need of pushing force from the plunger. If this elastic force is low, like with some hydrophobic acryliC materials, then it is necessary for the plunger to complete its action by reaching the cartridge mouth. Mini Incision Cartridges

452

Although the perfect solution for small incision cartridges is still lacking, there are some features for the cartridges to allow injections through sub 2.5 mm incisions. The main character is the width of the internal lumen, that should be 1.6-1.8 mm in diameter to allow 1.8-2.2 mm of external diameter. The inner diameter is in relation with the ability of the IOL to be compressed to the required dimensions. The outer diameter is in relation with the incision width. The thickness of the cartridge wall is in relation with the abil ity of the cartridge not to enlarge itself while IOL d elivering, that could impair the actual size, stretch the incision and even cause cartridge rupture. For this reason, there is the need for thinner but stiffer walls.

Mini l ucision IOL Implantation-Curren t Scenario

Fig. 4A : The 6 mm optic IOL must be loaded with the haptic outside the optic to fit a mini incision cartridge

Fig. 48: The elastic force of the IOL favours unfolding and can extract the IOL out of the mini cartridge even if the plunger will not reach the mini cartridge opening to avoid cartridge rupture

453

Instant Clinica l Diagnosis in Opll tlwlll1ologtj (Refractiv e SlIrgenj)

The cartridge tip design should favour the entrance through small incisions. Short cuts on both sides of the cartridge tip can allow the tip itself to close to smaller dimensions and to enter more easil y through a mini incision. However,

with this design the tip itself m ust enter the incision to prevent the lens fro m opening outside the eye. Uncut tips can be only applied to the incision without entering it. It is the lens that opens the incision lips and enters the anterior chamber, that saves the space occupied by the cartridge wall. With this injection method, however, some counter pressure must be exerted to prevent the lens from opening outside the eye. This counter pressure is obtained by pulling the eye towards the cartridge by means of an inst rument inserted through the side port incision. A drawbac k of this method is the frequent Joss of viscoeJastic material from the anterior chamber, with poor visibility, more difficuJty of the maneu ve r and increased risk of damage. With small incision cartridges, the plunger can be a problem. A stiff plunger may not adapt to the wide Jumen at Jens folding and to the narrow lumen at lens delivery. If too thick, it will not adap t to the cartridge tip, w ith risk of ca rtridge rup ture. If too thin, it w ill en trap a lens haptic with possible hap tic damage or rup ture. The solution found in practice is a grooved p lunger, that can be compressed through a very small tip, or a very soft one, that can adap t to various diameters. Even a viscoelastic plunger has been found effective and entered some clinical practice.

454

Mini Incision IOL Implantation-Current Scenario

Fig. SA: The compressed IOL can enlarge the mini cartridge during implantation, with possible cartridge rupture or IOL damage

Fig . 58: The mini cartridge tip can only be applied to the mini incision without penetrating, and only the IOL enters the eye

455

45 Monofocal HOA Free IOL to Correct Secondary Presby-LASIK Frederic Hehn (France)

INTRODUCTION

Presby-LASIK in phakic eyes has got now a world wide acceptance among ophthalmologist's community. In my experience it's possible to compensate presbyopia, in monofocal pseudophakic eye. CLE (clear lens extraction) and RLE (refractive lens extraction) become more and more popular with the newest relracti ve-diffractive Mu lti foca l IOL. But there are some medical risks with CLE, and the results 01 MF IOL are not always as good as it would have been expected. Then some surgeons propose a wavelront lasik enhancement, after MF IOL. Because there is some residual ametropia~ astigmatism or halos. We don't think that a bioptic could be better than a primary presby-LASIK. It w ill be always better to modified only one lens of the eye (cornea) rather than two (cornea and crystalline lenses). With the both phakic or pseudophakic eye we preler a presby-LASIK technique. Presby-LASIK in pseudophakic eye make sense to proof the truthfu~,ess of the optical basement 01 this technique; and consequently the durability of the results in phakic patients. In this article we analyze the relationship between Q value asphericity and the amount of spherical aberrations. We observe what's happen during accommodation; propose 3 shapes 01 corneal presbyopia compensation, and finall y give some exa mples with topolink treatments. PRESBY-LASIK IN MONOFOCAL PSEUDOPHAKIC EYE

Presby-LASIK could logically compen sate presbyopia in emmetropic pseudoph akic eyes w ith monofocal IOL (intraocular len s), as the M F (multilocal) TOL does. The centered presby-lasik technique with distant vision in the center can give a very good distant vision and a useful optional near and intermediate vision. Natural eye is a bi-optic optical system with a variable axial myopic additional power due to the crystalline lens. Because evidently along visual axis (object to macula) the vision will be the more discriminate with the best contrast sensitivity and MTF (modulation of transfer function) for the both near and far vision. This bioptic system produces the best near and distant 456 visual acuityr in using crystalline lens accommodation which can be achieve.

Monofoeal HOA Free IOL to Correct Secondary Presby-LASlK

Visual axis

~ ~

Retina Cornea Fig. 1: Coma

Ps eudophakic monofocal = DV

Pupil

Fig . 2

Increasing MF cornea jv-+nv

Fig. 3

Figs 2 and 3: Corneal multifocality can give inte rmediate and near vision in pseudophakic

eyes

457

Illstallt Clill ical Diagnosis in Opilti1almologtJ (Refractive Surgery)

Because Presby-LASIK can not restore accommodation, it just can be a good compromise between near and distan t vision. Natu ral eye present some coma HOA due to the difference between visual axis (object to macula) and optical axis (a pex of cornea to the center of crystalline lens). Tha t's the reason why we are thinking that presby LASIK teclm ique does not increase the natural existent coma. Then to avoid to increase conla presby-LASIK must be centered. Insp ired of multifocal or bifocal soft lens for presbyopia, tha t's give good resul ts in many cases, the therapeutic choice will be to place distant vision in center or not. Some authors have got good results with a small optica l zone for near vision in the the very center cornea. INTEREST OF USING AN IOL HOA FREE TO CORRECT PRESBYOPIA IN PSEUDOPHAKIC EYE

If we are using the BandL akreos adapt IOL, Q value of this IOL is -0.55 then it creates no SA. Therefore the crystalline implantation does not modify the corneal rebuilt shaping for presbyopia compensation. A pseudophakic eye with this kind of IOL, give us a pure human corneal model, to well understand what exactly presby-LASIK does. Secondly Presby-LASIK in pseudophakic eye make sense to proof the truthfulness of the optical basement of this techni gue; and consequently the d urability of the results in phakic patients. And we are thinking that: when our patients would have been cataract surgery, they would keep the results of their previous presby-LASIK. Monofocal IOL give a good distant vision (OV). But the patient, d ue to the natural multifocality of the cornea, can ha ve also an intermediate vision (iv): that's called the depth of focus. By a modifica tion of the SA of the cornea it w ill be possible to increase the dep th of focus until patient will be able to read without glasses. RELATIONSHIP BETWEEN Q VALUE ASPHERICITY AND AMOUNT OF SPHERICAL ABERRATIONS

The d ifficulty is to understand that, the Q value asphericity and the spherical aberrations (SA) make change together, but they haven't got the same 0 reference. Q value is due to the d ifference of kera tometry between the center cornea and the medium cornea (6.5 mm OZ). Ifkeratometry increase from the central to the peripheral cornea Q value is positive, and the cornea profile is ca lled oblate. At the contrary Q value is negative an d the cornea profile is called hyper-prolate. In normal cornea mean Q < 0 (- 0.25) and SA > 0 (0.25)1). If the keratometry is constant the cornea profile is spherical Q = 0, and SA » 0 (1)1 or more). If Q value = - 0.55 then SA = O. These basements are checked up just below. Q value is measured by the topograph, for instance the TOPOLYZER of Wavelight, it can give also the amount of SA due to the cornea. At the contrary the aberrometer like ANALYZER of wavelight, measure the total SA of the both 458 corneal and crystalline lens. Generally negati ve SA occurred in the crystalline,

Mon%cal HOA Free IOL to Correct SccondanJ Presby-LASlK

SA> 0

I»

Fig. 4: Q value and SA relationship

I SA is proportional to accommodation "f'l'

Cheol/It IIQ II JK II I'Opul,>,,,,,, ~h"ly nn ~1>~n'lM I" W 'v" 'h." ,'hon~ .. n H<>"~t<,,, TX 1721W 2020 USA J VI .. 20(}4 Apr 1(; 414) 712 80

0.35

E

•

0.3

•

•

2

Accommodation change (0)'--_ __ --'

·0.0435 ~I m I Diopter r = 0.85

Fig. 5

459

Instant Clinical Diagnosis in Ophtl/almology (Refractive Surgery) and positive SA in the cornea, therefore the total amount of SA in young people is often null. WHAT HAPPENS WITH Q VALUE AND SA DURING ACCOMMODATION

The augmentation of anterior curvature of the crystalline lens give a myopic shift with an in creasing of Z2,0 zernike polynoma : without myopia no near vision possible. But in concern of HOA only spherical aberration C12 or Z4,0 have significant modification according to a study. These authors demonstrate that during accommodation the variation of spherical aberration are always negative, and most interesting point is that variation is precisely and linearly correlated to the amount of accommodation in using a Hartmann-shak aberrometer system. Variation of SA = - 0.0435 }.lm / diopter. Therefore 3 diopters of accommodation correspond to a variation of - 0.130 }.l m in SA. Presby-LASIK technique must simulate accommodation in creating a myopic zone and also negative spherical aberration. We have verified this fact in using our tcherning wavelight aberrometer system and obtain exactly the same results: we place our 16 years old son behind aberrometer and present to him myopic lens to turn he to hyperopia and force he to accommodate; we relate these results just below. Then presby-LASIK must mime natural accommodation with Q value negative, ideally Q = - 1.00 And increasing negative spherical aberration. The variation between preoperative and postoperative SA has to be: !1 SA = - 0.l30}.l for 3 Diopters of accommodation. Then we have to pass from a prolate cornea to a hyper-prolate cornea; hyper-prolate cornea = pseudoaccommoda tive cornea. PRESBY-LASIK HAS TO MINE CRYSTALLINE ACCOMMODATION ,

WITH Q VALUE < 0 TO INCREASE THE DEPTH OF FOCUS Three profiles of centred presby-LASIK which can give Q = -1.00 The choice of the better option depends on amount of ametropia and pupil size. Distant vision in Central Cornea

The centered presby-Iasik technique with distant vision in the center give a very good distant vision and a useful optional near and intermediate vision. The difficulties remain the necessity to get high luminance for reading a book. The goal of presby-Iasik is not to completely erase spectacles but to decrease the patient's glasses dependency. This way give excellent distant vision and an optional useful near and intermediate vision. We practice at first a hyperopic treatment of + 3.00 diopters on a large 6.5 or 7.0 mm OZ to get a good near vision. Secondly we performed 460 a myopic treatment of - 3.00 on a small OZ depending on pupil size to get a

Mon%cal HOA Free IOL to Correct Sccot/dan} Presby-LASlK ~

Stimulated accommodation -~<~;

~~'-~

Analyzer + Aberroscopic lens

3 Oiopters

= -0.130 pm SA

Fig. 6

FIgs 5 and 6: During crystalline accommodation SA decrease of -0.130

~

for 3 diopters

Fig. 7: Lens accommodation

461

Instant Clinical Diagnosis in Ophthalmol0:5'J (Refractive SurgenJ) very good vision in central cornea as naturally it is. We measure also our results in using the TOPOLYZER topograph of wavelight. We are using the very precise allegretto wavelight, argon fluor excimer laser, w ith a little flying spot of O.S mm diameter and a high speed delivery system of 400 Hz, and eye tracker so. This first presby-LASIK approach gives an annular ring in medium cornea for near vision. This profile is useful in case of small pupil, and for myopic eye. In myopic eye you have just to make a myopic treatment on a small OZ. It's very tissue saving, but the very oblate profile, can gives some halos. Near Vision in Central Cornea

We make exactly the contrary; like som e authors do; at first myopic treatment and secondly h yperopic treatment. That's the best of because, that's give large OZ. It' s a good compromise for emmetropic and hyperopic eyes. the resulting shape is a continuous hyper-prolate shape. Near vision will be excellent, but distant vision could be poorer. This technique is perfect for large pupil. Direct Q Value Adjustment with F-CAT In the F-CAT program allegretto we can choice a Q value target. If we choice the Q value = - 1.00 , the results are the sames that the second technique. But the

real useful OZ will be smaller, and we must be careful to compensate the hyperopic shift induce by this treatment. For a constan t OZ of 6.50 mm, each variation of - 0.1 of Q value induce approximately + 0.13 h yperopic shift. STRATEGY: ONLY TOPOLINK IS RECOMMENDED IN PSEUDOPHAKIC: T-CAT ISTHE CLUE

Topolink can compensate the angle kappa. Angle kappa is due to the difference between visual axis (object to macula) and the center of the pupil. This angle is calculated by the topograph. The topolyzer waveligh t gives the both angle kappa and the dynamic pupillometry which can help surgeon to adapt the OZ of the treatment with the pupil size in mesopic and photopic conditions, especially in case of presby-LASIK. The visual axis, crosses the cornea at a point which is approximately the point of fixation of the patient. In the case of a topographic measurement, we consider that the point of fixation, is the center of the very center ring of the machine. If Angle kappa it is more than 100 /J, the laser treatment, even in case of a spherical treatment can induce the both coma and astigmatism. Then we have to consider Angle kappa especially in hyperopic eye, with often nasal fixation, enhancement for decen tration, and dual treatment like presby-LASIK. Secondly presby-LASIK occurred generally in older patient than in LASIK; it will be not logical to treat crystalline aberrations; because after the crystalline 462 lens extraction, wavefront analyzer will revea1 some others new HOA. Then

MOIlOfocal HOA Free 10L to Correct Secondary Presby-LASlK

Ideal presby lasik profile

Distant

Q <0

VISion

A natural conce pt

Near vision

Fig. 8

Ideal presby-Iasik profile

Q <0

A natura l concept

Fig. 9 Figs 8 and 9: Distant vision in central cornea is a natural shape

463

Instant Clinical Diagnosis in Ophtlw lmology (Refractive SlI rgerl))

it's preferential to modify only the cornea and do not compensate the crystalline aberrations. Finally in case of pseudophakic eye, the wavefront data are often not ava ilable, because there is a capsular fibrosis, and a pupil d istorsion, and a lot of reflexion of the laser ray. Then often wavefront measurement are not valid in case of pseudophakic eye. Therefore we ha ve three reasons to use only T-CAT treatment for prebyLASIK in the both phakic and pseudophakic eyes. CLINICAL EXAMPLES

We show results in two examples of pseudophakic patients with monofocal IOL. Distant Vision in Central Cornea

The first patien t a 53 years old man has got hydrophilic STABIBAG IOLTECH laboratories in the both eyes. In this case we remark some irregularities in the topographic map due to the fact in this first case studying we have not ever practice a previous A-CAT (aberrometric customized ablation trea tment) treatment to make sure to get a free HOA eye before performing presby-LASIK. The second point is that this patient get in monocular vision ve ry good results on the defocus curve. That's a proof of very good depth of focus with this technique as so good than with MF IOL it is. Near Vision in Central Cornea

The both eyes have got a corneal excentricity = 1.00 that's mean that Q value = -1.00 This patient previously emmetropic, obtained an excellent results with 20/ 20 jl uncorrected binocular vision. CONCLUSION

Presby-LASIK could be logically compensate presbyopia in emmetropic pseudophakie eye with monofoeal IOL, like the MF IOLs do. The centered presby-LASIK technique with d istant vision in the center gives a very good distant vision and a useful optional near and intermediate vision. At the contrary near vision in the center give only a useful distant vision. That's the reason wh y, preferential multifocality could be a good compromise. T-CAT treatment is the clue for presby-LASIK in the both phakic and pseudophakic eyes. Presby-LASIK seems to get as good results as Multifocal IOL, especially in terms on intermediate vision, and defocus curve. IOL HOA free are very interesting to well understand, what the presby-LASIK exactly does. We are thinking that presby-LASIK is an excellent technique to compensate presbyopia in pseudophakic eye espeCially in eyes implanted with monofoca l HOA free 464 IOL. Is presby-LASIK will become a non penetrative alternative of the clear lens exchange?

Monof ocal HOA Free IOL to Correct Sccon danJ Presby- LASIK

Fig. 10

"="~

"

I + 3.00 " - 3.00

I~S

\ Fovea

\

~

I 20/20 I

~ I

I

J3

= Fig. 11

I

~ --

Figs 10 and 11 : Distant vision in central cornea is excellent , but near vision is only useful

465

Instant Clinical Diagnosis in Ophthalmologt) (Refractive Surgen)

Fig. 12

- 3.00 If + 3.00

Iris

16/20

J1

Fig. 13 Figs 12 and 13: Near vision in central cornea is excellent, but distant vision is only useful

466

MOll%eal HOA Free lOL to Correct Secondary Presby-LASIK

Fig. 14

Fig. 15 Figs 14 and 15: If Q value decrease , OZ decrease also

467

Instant Clinical Diagnosis in Ophthalmology (Refractive SurgenJ)

Fig. 16: Angle kappa

Fig. 17 : Bilateral distant vision in center

468

Monofocal HOA Free IOL to Correct Sccol/dary Presby-LASlK

M

53 years old

Pseudophakic

Defocalisation curve

Good distant vision

12

A

10 8 6 4

2

o

/

7

Good near vision

7\ v~ I'

Good depth of focus

"-

I-+- UCDVA I

better than any MF IOl

"

Fig. 18: Excellent defocus curve

NATIONS VISION

Fig. 19: Bilateral near vision in the very central cornea

469

46 Managing Intraoperative Floppy Iris Syndrome David F Chang (USA)

In 2005, John Campbell and I first described a new small pupil syndrome associated with systemic tamsulosin that we named intraoperative floppy iris syndrome (IFIS). In addition to a tendency for poor pupil dilation, we identified a triad of intraoperative signs th at characterize IFIS - iris billowing and floppiness, iris prolapse to the main and side incisions, and progressive intraoperative miosis. Particularly w hen such iris behavio r is unexpected, the rate of complications such as posterior capsule rupture, vitreous loss, and iris

tra urna is increased with IFIS. Tamsulosin (Flomax), a systemic alpha-1 antagonist, is the most widely prescribed treatment worldwide for benign prostatic hyperplasia (BPH), which is characterized by increased urinary frequen cy. Systemic alpha-1 antagonists improve the lower urinary tract symptoms of BPH by relaxing the smooth muscle in the prostate and lower bladder wall. By allowing m ore complete emptying of the bladder, these medications decrease nighttime urinary frequency. Alpha-1 receptors also mediate contraction of the iris dilator muscle, and we proposed that loss of dilator muscle tone and rigidity was the cause of the floppy iris. Furthermore, we postulated a semi-permanent effect because of several cases of IFIS in patients w ho h ad discontinued tamsulosin several years before surgery. Indeed, in a prospective trial, stopping tamsulosin preoperatively did not prevent or decrease the severity of IFIS. Since our initial report, it h as become clear that other systemic alpha-1 blockers such as d oxazosin (Ca rdura ), terazosin (H ytrin), and alfuzosin (Uroxatral) can also cause IFIS. However, the frequency and severity ofIFIS is much less with these non-specific alpha-1 antagonists, as compared with tamsulosin. This difference may relate to the much greater affinity and specificity of tamsulosin for the alpha-1A receptor sub-type that predominates in both the prostate and the iris dilator muscle. IFIS can be classified as being mild (good dilation; some iris billowing w ith out prolapse or constriction), m oderate (iris billowing with some constriction of a moderately dila ted pupil), or severe (classic triad and poor preoperative d ilation). In a prospective study of 167 eyes in patients taking tamsulosin, the distribu tion of IFIS severity using this scale was as follows: 470 10% no IFIS, 17% mild, 30% modera te, and 43% severe. There can be Significant

Managing Intraoperative Floppy Iris Syndrome

Fig . 1: Intraoperat ive floppy iris syndrome in a patient taking tamsulosin. In addition to iris prolapse to the phaco and side port

incision, the pup il s has constricted limit ing visibility

Figs 2A and B : Pup il d iameter in tamsulosin patien t before (A ) and after (8) injection 01 0.2 ml of intracamera l ep inephrine solution (bisulfite-free 1:1000 mixed 1:3

with BSS)

471

Illstallt Clinical Diagnosis ill OplltlzalmologJJ (Refractive SlIrgery)

variability in the severity ofIFIS between different patients, and even between two eyes of the same patient. This makes it difficult to determ ine whether one pupil management strategy is superior to another. In fact, the various IFIS techniques discussed in this chapter can be combined and it is therefore helpful to master several complimentary approaches. As general surgical principles for [FIS patients, one should make a well constructed shelved incision, perform hydrodissectionmore gently than usual, and reduce the irrigation and aspiration flow parameters if possible. Bimanual microincisiona l cataract surgery may be helpful, particu larly for mild to moderate IFIS. This technique utilizes water tight incisions and allows the surgeon to dissociate the irrigation and aspiration currents. Keeping the irrigation inflow anterior to the iris can lessen the iris billowing and prolapse. In our original report, we noted that mechanical pupil stretching, performed with or without partial sphincterotomies, did not prevent iris prolapse or pupil constriction with IFIS. Excessive iris manipulation may in fact worsen the iris prolapse in IFIS. Instead, we found that mechanical pupil expansion, such as with iris retractors, was far more effective. Subsequently, several other strategies for the surgical management of IFIS have been suggested, and are outlined below. Because IFIS results from alpha-I receptor blockade of the iris dilator muscle, a variety of pharmacologic strategies for managing IFIS have been proposed. As first suggested by Sam Masket, preoperative atropine drops (e.g. 1% !.i.d. for 1-2 days preoperatively) can provide sufficient cycloplegia to prevent intraoperative miosis. However, as a Single strategy atropine alone is often ineffective for more severe cases ofIFIS. Stopping tamsulosin preoperatively is of unpredictable and questionable value, and has the potential to cause acute urinary retention in patients with severe BPH. This is particularly true if preoperative atropine is used. Direct intracameral injection of alpha agonist drugs is an excellent pharmacologic strategy for preventing or mitigating IFIS. Richard Packard first reported using intra cameral phenylephrine and Joel Shugar subsequently suggested using epinephrine for this purpose. By presumably saturating the alpha I -A receptors, these agents can further expand the pupil. Alpha agonists may also prevent billowing and prolapse by increasing iris dilator smooth muscle tone and maximizing iris rigidity. Preserved solutions should be avoided and one should use a diluted mixture (e.g. 1:1000 bisulfite-free epinephrine (American Regent) mixed 1:3 with BSS or BSS+) in order to buffer the acidic pH of the commercial preparation. Finally, Sam Masket reported excellent results with the synergistic combination of preoperative topical atropine with intracameral epinephrine in a small series patients taking tarnsulosin. 472

As first described by Bob Osher and Doug Koch, Healon 5 (Advanced Medical Optics) is a maximally cohesive ophthalmic visco-surgical device

Managing Intraoperative Floppy Iris Syndrome

Fig. 3: Healon 5 viscomydrias is in a patient with IFIS following removal of the cortex

473

Managillg llltraoperative Floppy Iris SYlldrome

Fig . 3 : Healon 5 viscomydriasis in a patient with IF IS following removal of the cortex

473

Instant Clinical Diagn osis in Ophthalmology (Refractive Surgery)

that is particularly well suited for viscomydriasis and for blocking iris prolapse in !FIS. However, to avoid immediately aspirating Healon 5 the surgeon must employ low flow and vacuum parameters (e.g. < 175-200 mmHg; < 26 mil min). This strategy is therefore less suitable if a surgeon wishes to use high vacuum settings for denser nuclei. Wendell Scott has proposed injecting Healon 5 peripherally over the iris, and then filling the central chamber w ith a dispersive agent such as Viscoat (Alcon) to create a Healon 5 "d onut". The Viscoat will better resist aspira tion and delay the evacuation of Healon 5. For surgeons favoring high vacuum and flow settings, DisCoVise (Alcon) has been advocated by Satish Modi. A final set of strategies utilizes d evices to mechanically expand and maintain the pupil diameter during surgery. Both the Morcher 5S Pupil Ring and the Milvella Perfect Pupil are disposable PMMA pupil expansion rings whose grooved contours are threaded alongside the pupillary m argin using metal injectors. In contrast, a disposable plastic injector is used to insert Eagle Vision's Graether disposable silicone pupil expansion ring. All of these rings are more difficult to position if the pupil is less than 4 mm wide or if the anterior chamber is shallow. Iris retractors are a more popular mechanical stra tegy for pupil expansion

in IFIS. Placement of the hooks in a diamond configuration has several significant advantages. The subincisional hook retracts the iris downward,

and out of the path of the phaco tip. This maximizes exposure in front of the phaco tip while the nasal hook facilitates chopper placement. One millimeter limbal paracenteses are made in each quadrant, including a separate stab incision made just posterior to the temporal clear corneal incision. In this way, the subincisional hook and the phaco tip access separate entry tracks. If the pupil is fibrotic, overstretching it with iris retractors can cause bleeding, sphincter tears, and permanent mydriasis. This typically does not occur with the IFIS p upil, which is so elastic that it readily springs back to physiologic size despite being maximally stretched. Options include 6-0 n ylon d isposable retractors (Alcon) or reusable 4-0 polypropylene retractors (Katena, FCI). Being of the same size and rigidity as an IOL haptic, the latter are easier to manipulate and can be repeatedly autoclaved making them more cost effective to use. It is much easier and safer to insert iris retractors and pupil expansion rings prior to creation of the capsulorhexis. If the pupil dilates very poorly or billows during injection of intracamerallidocaine, one should suspect severe !FrS and consider using these mechanical d evices. Often, the pupil d ilates reasonably well preoperatively, and it is not until after hydrodissection or during phaco that the prolapse and miosis occur. Healon 5 and intracameral epinephrine are excellent "rescue" tedmiques in this situation where it is difficult to visualize the capsulorhexis edge. If one chooses to insert iris retractors at this point, one should retract the pupil margin with a second 474 instrument to avoid hooking the capsulorhexis margin with the retractors.

Managing Intraoperative Floppy Iris Syndrome

Figs 4A to C: Mana gement of IFIS using a

Marcher PMMA pup il expansion ring (A): Ring

i s inse rted with an injector (8 ): Ring is threaded along pup il margin to maintain a constan t diameter (C) : Following removal of the

ring , iris prolapse and pupil constriction occur during removal of the viscoelastic

475

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery)

Eliciting a history of current or prior alpha-blocker use should alert surgeons to anticipate IFIS and to employ these alternative strategies either alone or in combination. A prosp ective, multi-center prospective trial using these techniques in 167 consecutive eyes from patients on tamsulosin demonstrated excellent outcomes and only a 0.6% posterior capsular rupture rate. Because of the variability in IFIS severity associated with tamsulosin and other alpha-l blockers, surgeons may consider using a staged approach in dealing with this condition. Pharmacologic measures alone are often adequate for managing the pupil in mild to moderate IFIS cases. Even if they fail to expand the pupil, intracameral alpha agonists can reduce or prevent iris billowing and prolapse by increasing iris dilator muscle tone. If the pupil diameter is still inadequate, viscomydriasis with Healon 5 can further expand it for performing the capsulorhexis. Finally, mechanical expansion devices insure the most reliable and optimal surgical exposure for severe IFIS, and should be considered when other complicating risk factors (e.g. dense nuclei, narrow angles, posterior synechiae, weak zonules, pseudoexfoliation, etc.) are present.

476

Managing Intraoperative Floppy Iris Syndrome

Figs SA and B: Management of IFIS using 4-0 prolene iris retractors in a patient taking tamsulosin (A): Retractors placed in a "diamond" configuration , with the sub-incisional retractor placed directly behind the clear corneal phaco incision (8 ): Pupil constriction and iris prolapse occurring after removal of the iris retractors

477

47 Artisan, Toric Artisan and Artiflex Phakic Intraocular lenses Johan A de Lange (South Africa)

GENERAL DISCUSSION

What is aPhakic IOL? It is an IOl which is inserted into the eye without removing the normal crystalline lens of the eye. The main indication for use of aphakic IOl is the treatment of refrac tive abnormalities such as myopia and hyperopia, with or without astigmatism.

Different Types of Phakic IOl's [PIOl's] l. Anterior chamber PIOL's l.1 Angle Supported anterior chamber PIOl's l.2 Iris fixated PIOL's. 2. Posterior chamber PIOL's. 1. Anterior Chamber PIOL's 1.1 Angle supported PIOL's are placed in the Anterior Chamber and have 3 or 4 haptics resting anterior of the iris in the anterior chambe r angle. The optic of this TOl is also in the anterior chamber. Typical examples are the Vivarte and BaikofPTOl's. 1.2 Iris Fixated PIOL's are placed in the anterior chamber but they are attached to the iris and do not reach the angle of the anterior chamber. They have their haptics as well as the optic in the anterior chamber. The Artisan PIOl is an excellent example of this PIOL. In the USA and elsewhere the Artisan PIOL is also marketed under license by AMO as the Verisyze PIOL. 2. Posterior Chamber PIOL's are inserted into the posterior chamber. It means that their hap tics as well as optics are behind the iris in the area between the iris and the normal crystalline lens of the eye. The ST AAR ICl is the best known example. This chapter will concern itself with the Artisan group of Iris fixated PIOL's.

478

Artisan, Toric A rtisan and Artiflex Phakic Intraocular Letlses

Fig. 1 : Schematic drawing of artisan PIOl attached to iris in a phakic eye

Fig. 2: Artisan spheric phakic intraocular lens

Fig. 3: Superior scleral tunnel incision

479

["stant Clinica l Diagnosis in Ophthalmologo) (Refractive Surgert) History

In February 1986 a group of Dutch ophthalmologists, gathering in a French ski

resort discussed the possibilities of designing ap hakic IOL. It seemed appropriate as most of them had a problem with radial keratotomy, which was at that moment the treatment for the correction of myopic refractive errors. The concept of the iris claw lens seemed a good basis for such a design. They formu lated the main conditions for the design as fo llows: • Smooth claws to avoid damage to the delicate iris. • Ample space for natural aqueous humor flow. • Sufficient space between PIOL and cornea. • Sufficient space between PIOL and natural lens. • OveraLl diameter limited to 8.5 mm. 3 Types of Artisan Iris fixated PIOL's are available 1. Artisan Spheric. 2. Artisan Toric. 3. Artif!ex Foldable. Originally only the spheric Artisan PIOL's were designed. Myopic as well as hyperopic lenses were developed. These PIOL's had a number of excellent qualities: • Between the enclavation site and the peripheral cornea an iris bridge is formed. • This iris bridge protects the endothelium from touching the PMMA, because the lens does not reach the periphery where the AC is shallow. • It has safe clearance from the crystalline lens. • Unrestricted pupil dila tation and constriction is possible. • Unique possibility to position the lens in the optical center of the eye. • Excellent Centration. Once fixated the lens will not decenter. • Lens axis direction can be varied, allowing for astigmatism correction. • Maximal surgical visibility, accessability and controlability. • Optimal postoperative visibility of lens and lens fixa tion. • The Artisan PIOL is cosmetically in visible. • It is easy to reposition, reversible and exchangeable. • There is no interference with the vascular iris physiology [no leakage of iris vessels was demonstrated on fluorescein an giography]. • High predictability of postoperative results. • One size fits all. We wi ll d iscuss these Iris fixated PIOL's of the Artisan gro up in sequence.

480

Artisan, Toric Artisan and Artiflex Phakic Intraocular Lenses

Fig. 4: Introduction of P IOl into AC

Fig. 5: PIOl rotated to a ho rizontal position

Fig. 6: Artisan PIOl

481

Insta nt Clin ical Diagnosis in Opllthalmology (Refractive SurgenJ) Qualities of the Artisan Spheric PIOl

The Artisan spheric PIaL is a PMMA [perspex CQ-UV] PIaL. Myopic as well as hyperopic Artisan IOL's are available. The myopic Artisan is available in O.5D increments from - 23.5 to -1.00. The optic diameter is 5 mm or 6 mm; the overall diameter 8.5 mm; the height is 0.96 mm

The h yperopic Artisan is available from +1.0 to +12 Oioptres in 0.5 0 increments. Optic diameter isS mm, overall diameter 8.5 mm, total height is 1.0 mrn. The thickness of the lens can vary depending on the diop tr ic power of the lens.

Indications for the Artisan spheric PIOL 1. Myopic or H yperopic refractive errors. Patients with stabilized axial myopia or hyperopia who will not achieve sa tisfactory visual correction w ith glasses, contact lenses or refracti ve Excimer laser.

Requirements for the Artisan spheric PIOL 1. 2. 3. 4.

ACO more than 3.2 mm Normal corneal endothelium and corneal clarity Corneal astigmatism of -1.750 or less Flat normal iris.

Can tra-indications 1. 2. 3. 4. 5.

Corneal endothelia l dystrophy Endothelial cell count < 2000 per square mm. ACO less than 3.2 mm Bulging iris Small ACO, i.e. deep enough centra lly but white to white less than 10.5 mm

6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

482

Cataract Recurrent or chronic uveitis Angle closure gla ucoma Wide angle gla ucoma Small refractive errors. In this case Lasik may be better Astigmatism of more than -1.750 [better to use toric Artisan PIaL] Insufficien t iris to support PIaL, abnormal iris or pupil Spherical equivalent outside the available d ioptres of the Artisan PIaL's Previous retinal d etachment Patien t younger than 18.

Artisan, Tonc Artisan and Artiflex Phakic Intraocular Lenses

Malerial: Optic diameter: Overall diameter: Total Height:

Weight (-10 0 ): Sterilization :

Perspex

ca·uv

5mm B.Smm 0.96 mm ± 9 mgr EO

OJ

·EI Plio! • 0°

Ptiol ·90°

A

B

•

~si are L:J ~.,t u, Vh'.~

~ .

Figs 7 A and B : Artisan toric PIOL features

r

. . !U/mif!.!3.°_

Fig. SA: Arti!lex PIOl

Fig . 8B : Technical specification of PIOl

483

Ins tallt Clillicai Diagllosis in OplzthalmoloS'J (Refractive Surgery) Surgery for the Artisan PIOl Anesthesia

This surgery can be performed under topical, peribulbar or general anesthesia. It is the surgeon's choice but w ill naturally be influenced by patien t expectations and preferences. In the USA and Europe topical anesthesia is popular. However, pa tien ts receiving Artisan PIOL's are often yo ung people who may not tolera te topical anesthesia very well. For them general anesthesia may be a very good aJternative.

Incision

More than one incision type is possible My prefer red incision is a superior scleral tunnel unde r a limbal based conjunctiva l flap. The incision width is 0.5 mm larger than the d iameter of the lens optic, e.g. 5.5 or6.0mm Two limbal clear corneal parasyntheses are made at the 3 and 6 0' clock positions. These are used to introduce the enclavation forceps to enclavate the iris.

Some surgeons prefer to make verticallimbal parasyntheses at the 2 and 10'0 clock positions. Through these they introduce a special enclavation need le to do the enclavation. After making the incisions, acethylcholine is injected into the anterior chamber to crea te instant miosis.

This is fo llowed by an OVD [Ophthalmic viscosurgica l dev ice previously known as a visco-elastic] into the anterior chamber to fill the AC. 1t should be a cohesive OVD to prevent adhesion to the intraocular structures. It is mandatory that this OVD should be easily removable after the P[OL has been inserted. Then the PIOL is removed from its container and introduced in to the AC. In the an terior chamber it should be rotated to a horizontal position and must be well centered over the pupil. At this stage the PIOL is held with a special holding force ps an d the first pair of haptic claws are attached to the iris by enclavating iris between the two curved haptic claw tips. This proced ure is repeated for the second pair of haptic claws. Now the PIOL is securely attached to the iris and the peripheral iridotomy can be done at the 12 0' clock position. Then it is time to rem ove the OVD which should be done very thoroughly. This is fo llowed by wou nd closure, with sutures if necessa ry, as well as closure of the conjunctiva.

484

Artisan, ToricArtisan and Artiflex Pllakic Intraocular Lenses

Fig. 9: Well centered PIOL

Fig. 10: Implantation techn ique of PIOL

485

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgen)) Follow-up This is done after 1day, 1 week, one month, 3, 6, 12 months. Complications

Preoperative • Anesthetic complications Some patients cannot tolerate topical anesthesia and must receive peribulbar or general anesthesia. For young patients the peribulbar injections may also be a problem and they may prefer general anesthetic. • Calculating the power of the PIOL. This is done by the manufacturer Ophthec.1t is based on refractive information provided by the surgeon.

Intra-op complications: Wound complications • The incision should be the correct size [0.5 mrn larger than the lens optic] and as small as possible to avoid mmecessary postoperative astigmatism. • Leaking of the wound can occur and will require a suture.

avo complications During enclavation the OVD may escape from the AC and should be kept at adequate volmne to facilitate surgery. Inadequate volume of OVD in the AC will not protect the endothelium and may lead to endothelial damage. Enough OVO is n ecessary to elevate the PIOL to make it possible for the surgeon to grasp it. If an adhesive OVO is used, it will be very difficult to remove it from the anterior chamber.

Insufficient removal of the OVO ma y cause postoperative wide angle secondary glaucoma.

Complications of position of the PIOL • In some cases it may be difficult to place the PIOL directly over the center of the pupil. Any decentration should be avoided but if it does happen it is better to err towards the nasal side because most eyes have a slight nasal displacement of the visual axis. • Sometimes the first attempt to endavate th e PIOL results in a wrong position of the PIOL. If this happens it should be rectified immediately. It is very easy to disendavate the PIOL by just pushing the iris bach through the claws of the PIOL. 486

Artisan, Torie Artisan and Artiflex Pltakie Intraoctllar Lenses

"

PHTEC

~lrtlf\tz.toIOI

Fig. 11 A: Artiflex implantation kit

Fig. 11B: Artiflex implantation technique

Figs 12 A and B: Special holding forceps for artiflex PIOl

487

Instant Clinical Diagnosis in Ophtlwlmologt) (Refractive Surgert) Complications of the peripheral iridotomyliridectOlny It may happen that the iridotomy I iridectomy is not patent and this may lead

to postoperative acute pupillary block glaucoma. If a peripheral iridectomy is performed it may be too large and give rise to various postoperative symptoms like awareness of the PI, glare, etc. Postoperative Complications

• Postoperative mild uveitis will ocasionally be present. • In case of a non-patent peripheral iridotomy, acute pupillary block glauco ma may develop within hours after the surgery. • Cornea l edema is rare but in case of excessive manipulation it is possible.

• Traumatic cataract may be caused by lens touch d uring careless surgery. • Hemorrhage [hyphema] is very rare but not impossible. • Infection, e.g. endophthalrnitis is also rare but the usual precautions must be taken. • Decentration of the PIOL will impact negatively on visual acuity and will also lead to various optica l disturbances such as halo, glare, monocular diplopia, etc. • A frequently encountered complication is the presence of unwanted postoperative astigmatism. This is usually the result of too tight sutures in the superior scleral tunnel. This creates with-the-rule astigmatism. As time goes by this astigmatism reduces to acceptable levels but most patients find it very disturbing. That is one of the very good reasons why the Artiflex foldable PIOL has been developed . Results of the Spheric Artisan PIOl

Predictability excellent: If the preoperative refractive measurements are correct, the predictabili ty is excellent and > 95% of eyes are wi thin 1 0 of emmetropia. Efficacy excellent: uev A as well as BSeVA are Significantly better than preoperative. 1rnprovement in BSeVA is very common and also occurs in eyes that were previously regarded as amblyopic. This happens more often in the myopia group and the improvement in best corrected vision is probably caused by the magnification effect of the PIOL. Safety. In most reports no eyes lost any line of BSeV A. Serious complications are rare . Please refer to complications. Qualities of the Artisan Toric PIOl

488

This is also a PMMA PIOL. The optic diameter is 5.0 mm.

Artisan, ToricA rtisan and Artiflex Phakic Intraocular Lenses

1-

"~

Study results

1o0 Preop BSCVA J

Efficacy

Postop UCVA

100%

"-

90%

-

80% 70%

,., ~ ~

w

60%

---

I-

50%

"- - -

I-

40%

-

-

30%

II-

--

1-

-

20% 10%

I.

-

0%

=fll20/>20

20/20

-

-

-"

- "

--

f-

-

-

1-

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-

-

-

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-

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-

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-

-

=i

-

-

-

-

20/25 20/40 20/32 Snellen visual acuity

20/50

20/63

Efficacy index (UCVA postop/BSCVA preop) 1 "01 at 1 year postop

:. ~

Fig . 13: Efficacy index at 1 year postoperative

PIOl Predictability

e:

0

c

-3

.."

N = 305

!!J

"~

~

0"

"

-6

·12

-9

·3

o

Intended spherical equivalents (0 ) 90% deviated < 0.5 0 from emmetropia 98% deviated < 1.0 0 from emmetropia

Fig . 14 : PIOl predictability index

489

Instant Clinical Diagnosis in Ophthalmologt) (Refractive Surgen)

The length of the IOL including the haptics is 8.5 nun. The thickness of the lens varies between 0.96 and l.2 nun depending on the dioptric power of the lens. It is available in 0.5 dioptre spheric increments from -2.5 to -21.0 d ioptres as well as from +2.00 to + 7.50 combined with the required cylinder. The cylinder is available from -2.0 Oioptre to -7.50 at whatever axis necessary. The toric Artisan is custom made and delivery is 8-10 weeks after order approval. A unique feature of this PIOL is the variation of the cylinder position relative to the shape of the PIOL. The cylinder can be ordered in such a way that the surgeon can onl y implant the PIOL in a horizontal position to ensure the correct cylinder axis. But this may vary and the surgeon should be aware of the possible va riation in cylinder position. The lens is also fixated to the iris in two spots using an iris enclavating technique. Indications for the Artisan Toric PIOL

1. Myopic or h yperopic astigmatism with sphere of -20.0 to -2.0 as well as +2.00 to +6.00 combined with: 2. Astigmatism of -2.0 to -7.50 diopters 3. Phakic eyes 4. ACO more than 3.2 nun. 5. Normal corneal endothelium. 6. Normal iris. 7. Stable keratoconus with good BSCVA 8. Correction after Lasik overcorrection 9. Correction after PKP.

Contra indications for Toric Artisan [same as for Artisan PIOL] 1. ACO less than 3.2 nun. 2. Bulging iris. 3. Small ACO, i.e. deep enough but because of short white to white and high K-readings the peripheral haptic of the PIOL w ill be too close to the endothelium. 4. Cataract.

5. Recurrent or chronic uveitis.

490

6. 7. 8. 9.

Angle closure glaucoma. Wide angle glaucoma. Small refractive errors. In this case Lasik may be better. Astigmatism of less than -l.7S 0 [Here we use Artiflex PIOL]

Artisan, Torie Artisan and Artiflex P//akie IntraoClllar Lenses

~

Study results Safety

60%

N=305

,40%

-

'">-

" w

20%

0%

n

n Lost 1

Unchanged

Gained 1

Gained 2

Gained 3

Change in BSCVA

IL

Safety index (Postap BSCVAlPreop BSCVA) 1.10at1 yearpostop

Fig. 15: Safety index at 1 year postoperative

Study results Stability 4

e: LU

0

N = 30 5 -0,12

(f)

c --4 .2 1) ro

'""

'"

-8

-7,23

-12~--~-~~-~--~--_--~

Preop

1 day

1 week

3 months 6 months

Average SE at 1 day postop

1 year

= -0.04 D ± 0.4

SE remains stable until 1 year postop

Fig. 16: Stability index

491

Instmrt Clinical Diagnosis in OphthalmologtJ (Refractive Surgery)

10. Patient yo unger than 18. 11. Spherical or astigmatic error outside the available diopters of the Artisan PIOl's. 12. Endothelial cell count < 2000 per square rnrn. 13. Corneal endothelial dystrophy. 14. Insufficient iris to support PIOL. Surgery for Torie Artisan PlOL The surgery is essentially the same as for Spheric Artisan PIOl A few important adjustments must be made for the fac t tha t this is a toric PIOl Preoperative marking of the enclavation sites. The surgeon must be aware of the axis of the cylinder relative to the shape of the PIOL. This means that every PIOl may potentially be implanted in a different axis. A simple way of marking the enclavation sites of the PIOl is to make small YAG laser burns on the iris at the correct spots preoperative. An alternative for marking the correct cylinder axis is to use a surgical marker to mark the limbus. Anesthesia. As for spheric Artisan this surgery can be performed under topical, peribulbar or general anesthesia. Incision.

A superior 5.5 rnrn scleral tunnel under a limbal based conj unctival flap. The incision wid th is 0.5 mm larger than the diameter of the lens optic. Two limbal clear corneal parasyntheses are made at the correct positions, keeping in mind the marked enclavation sites and the surgeon's technique. After making the incisions, acethylcholine is injected into the anterior chamber to create instant miosis.

This is followed by an OVD into the anterior chamber to fill the AC. It should be a cohesive OVD to prevent adhesion to the intraocular structures. This OVD should be easily removable after the PIOl has been inserted. Then the PIOl is introduced into the AC. In the anterior chamber it should be rotated to the correct position and must be well centered over the pupil. At this stage the Toric Artisan is held with a special holding forceps and the first pair of haptic claws are attached to the iris at exactly the correct spot as marked preoperative with the YAG laser. This procedure is repeated for the second pair of haptiC claws, once again making sure that it is enclavated at exactly the correct position . Now the peripheral iridotomy can be done superiorly but not always precisely 492 at 12 o'clock.

Artisall, ToricArtisan and Artiflex Pllakic Intraocular Lenses

ARTISAN® Lens Manufacturing Information PMMA lenses are manufactured by using Compression molding technology. During the compression molding process the molecular structure of PMMA (fig . 1) is enhanced by redistributing the molecules into longer chains (fig .2). This results in a much stronger material. Compression molding technology gives a high tensile strength, combined with superb flexibility of the lens haptics. The risk of fracture is minimal. The tumbling process gives a special surface treatment to the PMMA lenses. Ultra smoothness of the haptics is the result.

Figs 17 A and B: Artisan PIOl specifications

0000 Model 206W ARTISAN ""

ARTISAN '"" hyperopia,

myopia lens

model 203W

ARTISAN "" myopia, model204W

ARTISAN"" aph akia model 205Y

1991

1992

1997

1998

Fig. 18: History of artisan lens

493

Instant Clinical Diagnosis in Oplt tltalmologz) (Refractive Surgen) Then the OVO is removed completely. The incision as well as conjunctiva is closed. Follow-up Visits are schedu led for 1day, 1 week, one month, 3, 6, 12 months. Complications Preoperative complications • Anaesth etic complica tions Some patients, particula rly young people, cannot tolerate topical anesthesia and must receive peribulbar or general anesthesia. Young patients may preler general anesthesia to peribulbar injections. Calculating the Power of the Toric PIOL

TIUs is done by the manufacturer Ophthec. It is based on relractive information provided by th e surgeon. Intraoperative complications: Wound complications. Some scleral tunnels may leak without the use 01 sutures. OVO complications. During enclavation the OVD may escape from the AC and should be kept at adequate volume to facili tate surgery. Inadequate volume of OVD in the AC will not protect the endothelium and may lead to en dothelial damage. Insufficient OVO is necessary to elevate the PIOL to make it possible for the surgeon to grasp it. Insufficient removal of the OVO may cause postoperative wide angle secondary glaucoma. Complications of Position of the Toric Artisan PIOL

• Any decentration should be avoided and more so because this is a toric lens • Misalignment of the cylinder axis: If the PIOL is not positioned in the correct axis, a postoperative refractive error will be the result. • Sometimes the first attempt to enclave the PIOL results in a wrong position 01 the PIOL. If this happens it should be rectified immediately. It is very easy to disenclavate the lens by just pushing the iris bach through the claws of the lens. Complications of the peripheral iridotomy /iridectomy • A peripheral iridotomy is better than an iridectom y. • However it may h appen that th e iridotomy is not pa tent and this may 494 lead to postoperative acute pupil block glaucoma.

A rtisan, Torie A rtisan and Artiflex Plrakie In traoelliar Lenses

History

-===--

~

~

ARTISAN"" lone lens 90°

ARTISAN"" phalic tOL

1999

1999

2005

ARTISAN""

tone lens O'

Fig. 19: History of artisan lens (contd)

Comparison chart Power range (S)

ARTISAN®

ARTIFLEX®

+ 12.00 up to - 23.5 0

- 2.0 0 upto-14 .S 0

Power range (5)

2.0Dupto7.5D

None

Body 0 Overall 0

5.0 mm IB.O mm

6.0mm

Optic material Refractive index Optic design Optic configu ration Anti glare edge design

Haptic shape Cross flow design Recommended incision width

Passport system

7.5 mm 18.5 mm

8.Smm

PMMA

Hydrophobic polysiloxane

1.49

1.43

Spherical

Polynomial

Convex-concave

Convex-concave

no

Yes

Claw®

Claw«l

4 Lateral side ports

4 Lateral side ports

5 .2 mm 16.2 mm

3.2mm

None

Insertion spatula flo!

Instruments

ARTISAN" kit

ARTIFLEX® kit

Viscoelastics

ArtiVisc N I ArtiVisc plus TM

ArtiVisc TN I ArtiVisc plus TM

Fig. 20: Comparison chart of specifications of PIOLs

495

Instant Clinical Diaguosis in OphthalmologtJ (Refra ctive Surgery)

• A peripheral iridectomy may be too large and give rise to various postoperative symptoms like awareness of the PI, glare, etc. PPP PI. Postoperative Complications

[These are very similar to those of the Artisan spheric PIaL] • Postoperative mild uveitis will ocasionally be present. • In case of a non-patent periphe ral iridotomy ac ute pupillary block glaucoma may develop within hours after the surgery. • Corneal ed ema should not occur but in case of excessive manipulation it is possible. If the crys talline lens is to uched during surgery it may cause early postoperative traumatic cataract.

• Hemorrhage [hyphema] is very ra re. • Infection, e.g. endophthalmitis is also rare. • Decentration of the PIaL will im pact negatively on visual acuity and w ill also lea d to va rious optical disturbances such as halo, glare, monocular diplopia, etc. • A frequently encountered com plication is the presence of unwanted postoperative astigmatism. This is usua lly the result of too tight sutures in the superior scleral tunnel which creates with-the-rule astigmatism. As time goes by this astigmatism reduces to acceptable levels but most patients find it very disturbing. That is one of the very good reasons why the Artiflex foldable PIa L was developed. Results of the Toric Artisan PlOl

Predictability excellent: If the preoperative refractive measurements are correct, the predictability is excellent and >90% of eyes are within 1 0 of emmetropia. Efficacy is excellent: UCV A as well as BSCV A are significantly better than preoperative. As with the other PIaL's some patients gain as many as 3 or more lines of best corrected vision. Safety: In most reports no eyes lost any line of BSCVA. Complications can happen as d iscussed. However, the complication rate is low and very few serious complications ocelli. ARTlFlEX FOLDABLE IRIS CLIP PIOl

Qualities of the Artiflex Spheric PIaL. • It is also an Iris fixated PIaL • It has a foldable optic made of polysiloxane

496

Artisan, Toric Artisan and Artiflex Phakic Intraocnlar Lenses

• The optic d iameter is 6 mm • The length of the IOL including the hap tics is 8.5 mm • The Artiflex PIOL has PMMA haptic claws into which iris must be endavated in a similar fashion as with the Artisan PIOL • A specia l spatula is provided with the Artiflex PIOL to fold the PIOL before introducing it into the AC. • The Artiflex IOL is only a Myopic Spheric PIOL and is available in 1 diopter increments from -14.5 to - 2.00 diopters. Indications for Use of the Artiflex PIOL

These indications are basically the same as for the Artisan spheric PIOL. The Artiflex PIOL will probably soon replace the Artisan PIOL for myopia. Indications 1. Refractive errors between - 2 to - 15.0 [Lens is - 2.0 to - 14.5] 2. Phakic eyes 3. Anterior chamber depth more than 3.2 mm. 4. Normal corneal endothelium and clarity.ECC >2000. 5. Cornea l astigmatism of -1.750 orIess. 6. Normal pupil and flat iris. Contra-indications

1. ACO less than 3.2 mm 2. Bulging iris 3. Small ACO, i.e. deep enough but white to white too short to provide ample space in the AC 4. Cataract 5. Recurrent or chronic uveitis 6. Angle closure glaucoma 7. Small refractive errors. In this case Lasik may be better 8. Astigmatism of more than - 1.75 D [Here we use toric Artisan PIOL] 9. Insufficient iris to support PIOL 10. Endothelial cell count < 2000 cells/ mm 3 Surgery

See Figure 10. Anesthesia

The main advan tage of the Artiflex IOLis that it can be inserted through a clear 497 corneal incision.

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery)

Therefore the operation can quite comfortably be done under topical anesthetic combined with intracameral lignocaine. 1his surgery can also be performed under peri bulbar or general an esthesia. As w ith the Artisan lens it is the surgeon's choice but will naturally be influenced by patient expectations and preferences. In the USA and Europe topical anesthesia is popular. Incision

More than one ulcision type is possible. An excellent option is a superio r clea r corneal incision. It can be made with

a diamond knife and the ainl is to make the incision 3.2 mm wide and 1.5 to 2 mm in length. This is followed by two limbal clear corneal parasyntheses at the 3 and 6 o'clock positions. These are used to introduce the enclava tion fo rceps to enclavate the iris.

Some surgeons prefer to make ve rticallinlbal pa rasyn theses at the 2 and 10'0 clock positions. Through these they introduce a special enclavation needle to do the enclava tion. After making the incisions acethylcholine [miochol or equivalent] is injected in to the anterio r chamber to create ins tant miosis.

1his is followed by an OVD into the anterior chamber to fill the AC It should be a cohesive OVD to prevent adhesion to the intraocular structures. It is mand atory that this OVD should be easily removable after the Artiflex lens has been inserted. Then the Artiflex PIOL is removed from its container and loaded onto the insertion spatula. This little procedure is very easy but needs to be executed correctly. The Artiflex PIOL is gently introduced into the AC with the help of the injector. When the optic of the Artiflex PIOL is well into the AC the injector can be retracted. 1his maneuvre will leave the Artiflex lens in the AC In some cases the follow ing haptics could still be outside the eye and can gently be moved forward into the AC It may well be asked: why would the following haptics not enter the AC with the PIOL? The problem is that the injector's tip may reach the inferior AC angle before the haptics are altogether in the AC superiorly. It is then safer to retract the injector ra ther than d amage the inferior AC angle. If the following haptics are still outside the AC it ca n be moved inwards without a problem. Once in the anterior chamber the Artiflex PIOL should be rotated to a horizontal position. Care should be taken to make sure it is well cen tered over 498 the pupil.

Artisan, ToricArtisan and Artiflex Plrakic Intraocular Lenses At this stage the PIOL is held with a special holding forceps. These holding forceps are different from those used for the Artisan PIOL. It is important to note that only the hap tics are held and the optic should never be touched with these forceps. As with the Artisan PIOL the first pair of haptic daws are attached to the iris by endavating iris between the two curved haptic daw tips. The enelavation can be done using special forceps or a special enelavation needle. This procedure is repeated for the second pair of haptic daws. Now the PIOL is securely attached to the iris and the peripheral iridotomy can be made at the 12 0' d ock position. Then the OVO is removed very thoroughly and the AC is filled with BSS. If required the incision edges may be hydrated. No suturing is necessary. Follow-up 1day, 1 week, 1 month, 3, 6, 12 months. Results

Fast visual recovery: Because the elear corneal incision ind uces very little astigmatism the visual recovery is very quick. Many patients w il have 1.0 unaided vision the day after surgery. Efficacy: Excellent visual acuity results. The efficacy index [UCV A postoperative/BCV A preoperative] was measured as 1.01 in one series. Due to the high quality of the Artiflex lens and the stability and predictability of the lens the visual acuity is excellent. Final UCV A after 3 months is often 20 /20 or better and BSCVA is often better than preoperative. As with other lenses of the Artisan group a high percentage of patients will experience up to 3 or more lines of improvement of BSCV A, probably due to magnification of retinal images. High predictability: The preoperative calculations are extremely accurate and it provides exceptionally good predictability. Safety: The surgery is fast, smooth and atraumatic. Very few significan t complications are reported. The safety index was 1.10 at 1 year postoperative. Stable results: The endavation technique is remarkably stab le and the lens position will not change during any no rmal physical activity [boxing is not advocated!] Therefore the result is maintained over many years. Complications

Preoperative • Anesthetic complications Some patients cannot tolerate topical anesthesia and mu st receive 499 peribulbar or general anesthesia

Instant Clinical Diagllosis in Ophthalmology (Refractive SlIrgery)

• For yo ung patients the peribulbar injections may also be a problem and they rna y be very comfortable with general anesthetic • Calculating the power of the PIOL. This is done by the manufacturer Oph thec. 1t is based on refractive information provided by the surgeon. INTRAOPERATIVE COMPLICATIONS Demanding Surgery

The surgery is actually quite easy, except for one maneuvre. The enclavation of the ha p tics can be very diffic ult, and fo r this proced ure good training is recommended. Wound Complications

The incision is remarkably free of complica tions but wo und leakage is an unlikely pOSSibility. A clear corneal incision of 3.2 mm should give rise to not more than approxinlately -0.25 to -0.50 diop ters of astigmatism. OVD Complications

During enclava lion the OVD may escape from the AC and should be kep t at adequate volume. Insufficient volume of OVD will lead to endothelial touch and damage. It will also make it very difficult to pick the PIOL u p with the hold ing forceps when mani pulating the lens. A cohesive OVD should be used to lacilitate removal 01 the OVD from the AC.

Remova l 01 the OVD at completion of the operation is very im portant to avoid postoperative acute secondary wide angle glaucoma. Complications of Position of the PIOl

It is extremely important to place the PIOL over the center of the pupil. Any

decentration should be avoided but if it d oes happen it is better to err towards the nasal side because most eyes have a slight nasal displacement of the visual axis. Sometimes the first attempt to enclava te the PIOL results in a wrong position of the PIOL. If this ha ppens it should be rectified in1mediately. It is very easy to disenclavate the PIOL by just pushing the iris bach through the claws of the PIOL.

500

Artisa", ToricArtisan andArtiflex Phakic [n traocular Lellses

Complications of the peripheral iridotomy/iridectomy A periphera l iridotomy is preferred to an iridectomy. However it may happen that the iridotomy is not patent and this may lead to postoperative acute pupillary block glaucoma. A peripheral iridectomy may be too large and give rise to various postoperative symptoms like awareness of the PI, glare, etc. Postoperative Complications

Postoperative mi!d uveitis will ocasionally be present. In case of a non-patent peripheral iridotomy acute pup illary block glaucoma may develop within hours after the surgery. Corneal edema might occur after excessive manipulation during surgery. Lens touch d uring surgery may cause a traumatic cataract. Hyphema is very rare. Infection, e.g. endophthalmitis is also rare. Decentration of the PIOL may cause reduction of visual acuity as well as various optical disturbances such as halo, glare, monocular diplopia, etc. Late Complications

At 1 year the following complications were reported Pigment deposits: 5.6% Haloes: 5.2% Glare: 3.6% Non pigment deposits: 3.6% Synechiae 0.3% Explantation 0.3% Lens exchange 0.3%. EFFECTS OF ARTISAN AND ART1FlEX PHAK1C IOl'S ON THE EYE Effects on the Endothelium

A main concern for any IOL in the anterior chamber would always be its effect on the end othelium. A number of good studies have been done to evaluate this. The concensus of opinion is that the initial surgery w i! cause a loss of endothelial cells of 0 to 4%. After this initial loss of endothelial cells the endothelial cell count will not show any Significant deterioration for as long as 10 yea rs postoperative. A recent multicenter stud y done on the Artiflex PIOL has shown 0% endothelial cell loss after the first yea r postoperative. 501

Instant Clinical Diagnosis in Ophthalmologt) (Refractive Surgen)

The present belief is that the PIOL may not anywhere be closer to the endothelium than l.0 mm. That is why an AC depth of 3.2 mm preoperative is so important. If the AC is shallower, the peripheral edges of the PIOL will be too close to the endothelium. Effects on the Iris

The claw-haptic of the PIOL does cause some iris depigmentation at the site of enclavation, but if enough iris is enclava ted, this will not lead to any problems. Iris necrosis and PIOL dislocation is extremely unlikely. If the initial enclavation is not well done and only a very thin piece of iris is enclavated, it ma y well lead to erosion of the iris by the claw-haptics, which in turn will cause disinsersion of one or both haptics and therefore dislocation of the PIOL into the AC. The peripheral iridotomy or iridectomy will cause some pigment dispersion into the AC and this pigment will be most visible on the PIOL as well as the crystalline lens and the endothelium. No reports of secondary pigmentary glaucoma due to the small amow1t of pigment dispersion have corne to our attention. Effects on the Crystalline Lens

The main concern for the patient's crys talline lens is of course the formation of cataract.

The most dangerous time is during surgery. If the crystalline lens is inadvertently touched it may lead to instantaneous traumatic segmentary cataract.

In case of good successful surgery the chances of development of cataract at a later stage is not more than that of the normal population. The fact that the PIOL is in the AC, has very little effect on the crystalline lens. Effects on the Intraocular Pressure

The main concern is postoperative pupillary block glaucoma in the presence of a non-patent peripheral iridotomy. Obviously prevention is better than cure. Make sure the PI is open during surgery! The Artisan and Artiflex PIOL's have no proven long-term direct effects on the lOP. These PIOL's should not be used in the presence of angle closure glaucoma. Effects on the Anterior Chamber Angle

These PIOL's do not touch the anterior chamber angle and will have no effect 502 on the angle.

Artisall, Toric Artisall mid Artiflex Phakic Illtraocular Lellses

A review of the benefits of the Artisan or Artiflex PIaL's compared to other PIaL's: • It has the longest clinical history of all the PIaL's. The first Artisan PIaL was implanted on November 2, 1986. • One size fits all: Other PIaL's need sizing for a proper fit. This applies to the anterior chamber as well as posterior chamber PIaL's. • Extremely versatile: The Artisan lenses are designed for aphakia, myopia, hyperopia as well as astigmatism. • Reversibility of fixa tion: Easy to reposition or exchange. • Safe distance from crystalline lens: Virtually no PIaL related lenticular opacifjcations occur. • Safe distance from endothelial cells: The initial cell loss is surgery related. • High predictability: 98% of patients obtain a refractive resu lt within 1 Diopter of emmetropia. • Excellent Centration: Once fixated the lens will not decenter. • Normal pupil. The lens does not affect dilatation or constriction of the pupil. SUMMARY

The Artisan group of iris fixated PIaL's is an excellent option when considering refractive surgery. It is very effective, safe, predictable and stable and can be often used when other modalities ma y be inadequate.

503

Orthokeratology

Fig. l A: Pre lit

Fig. 2A: 15t generation flat conventional lens

Fig. 18: Post ortho-K

Fig. 1C: 2 weeks after suspend ing

Fig. 28: 2nd generation

Fi g . 2C: 3rd generat ion

three -zone reversegeometry

four-zone reverse-geometry

Fig. 3: Typical fluore-scein pattern (ESA-ortho6)

505

Instant Clinical Diagnosis in OplJtllalmologtj (Refractive Surgenj) cases, the final result can be achieved with only one pair of lenses, in a period of time between one and two weeks. Treatment of astigmatism is controversial. Work is in progress to design toric reverse-geometry lenses for the specific treatment of astigmatism, and results are awaited with interest. Treatment of hypero pia and possibly presbyopia through corneal steepening is also under current investigation; preliminary studies suggest that corneal steepening with apical clearance lens designs may be possible, although the time scale and limits to this procedure require furthe r study. OVERNIGHT ORTHOKERATOLOGY

In the last years, orthokeratology procedures involve the overnight use of contact lenses: the cornea is reshaped during the sleeping time and lenses are taken off when the patient wakes-up. In most cases, the effect lasts until the evening. This proced ure has the advantage of eliminating some environmental factors (dust, wind, conditioned air, sports) that can give trouble during the day; in addition, the pressure of closed lids improves the rapidity of corneal molding. For overnight wear, high oxygen permeable materials are necessary to provide sufficient oxygenation to the cornea, even if lids are closed. When rigid gas permeable (RGP) lenses are worn during waking hours, oxygen can reach the cornea via two mechanisms: by circulation of oxygen-rich tears behind the lens, d ri ven by a lid-activated tear pump, and by diffusion through the lens material. An estimated 10-20% tear exchange occurs with each blink under a rigid lens. PoIse estimates a tear exchange per blink of only 1% under soft lenses, due to their greater diameter and flexibility. On the contrary, both lens types provide oxygen to the cornea during closed-eye wear by diffusion through the lens material. Thus, soft and RGP lenses of comparable Dk/ t will induce similar levels of overnight edema. On awaking, the lid-activated tear pump is much more efficient with RGP compared to soft lenses, so oxygen is supplied in more quantity, facilitating rapid corneal recovery from overnight hypoxic stress. And rasko and Holden, et alhave demonstra ted that the cornea deswells more rapid ly after overnight wear ofRGP lenses than with soft lenses, because of the greater tear pumping efficiency of rigid lenses. This recovery is even more rapid if we talk about overnight wear, with the lens taken off on wakening, rather than continuous wear. The removal of the lens allows both cleansing of the lens and the elimination of debris and waste products trapped behind the lens.

506

Orthokeratologtj

Fig . 4 : Decentration of the molded area due to

dislocation of the lens

Fig. 5 : Corneal war page due to lens binding

Fi g . 6 : Pre : RX 51. - 2.25 ; Posl: UC VA 12/10

507

Instant Clinical Diagnosis in Ophthalll101ogtJ (Refractive SIII'gery) REVERSE GEOMETRY CONTACT LENS DESIGN

Modern contact lenses for orthokeratology have a curvature profile that is "reversed" from traditional rigid lens design, so they are usually defined "reverse-geometry contact lenses". Traditional lens designs have secondary and peripheral curves flatter than the central curve of the lens. On the contrary, reverse-geometry lenses have one or more peripheral curves steeper than the curve of the optical zone. In modem reverse-geometry lenses for orthokeratology, we can identify four main functional zones: Optical Zone, Reverse Zone, Alignment Zone and Peripheral Zone. Usually reverse-geometry lenses for orthokeratology have a diameter larger than traditional RGP lenses. The back optical zone determines the shape that the cornea will assume after the corneal molding, and so it determines the amount of refractive error corrected by the orthokeratological treatment. Usually, it is a spherical curve. The radi us of curvature of this zone is calculated in order to get the desired orthokeratological effect. The lift of peripheral curves over the cornea around the Optical Zone creates a tear reservoir.

The Reverse Zone allows the joining of the Optical Zone with the Alignment Zone. In the reverse zone, there are one or more curves s teeper than the back optical zone. The Alignment Zone is the bearing zone of the lens; it gives stability to the lens and keeps it centered on the cornea. In some particular lens design, it also enhances the corneal molding, putting a pressure in the periphery of the cornea that aids the redistribution of corneal tissue towards the optica l zone. The curvature of the alignment zone is flatter than the reverse zone, but steeper than the optica 1zone. The Peripheral Zone allows the lens ed ge to lift from the cornea, to achieve an adequate tear turnover under the lens. This tear exchange is necessary for two reasons: to get in new tear liquid to oxygenate the cornea, an d to get out the debris and metabolic residuals formed under the lens. If the lens has a proper aligmnent and a right lift in the Peripheral Disengagement Zone, during the blinking we have an effective pumping action of tear fluid. Besides this primary function, the tea r meniscus under the peripheral curves allows a capillary attraction helping the lens to keep centered. The edge lift has other functions too: it controls the pressure of the edge of the lens minim izing the risks of corneal insult and helps the removal of the lens by mean of lid tension . The curvature of the Peripheral zone is fl atter than the Alignment zone. 508

OrtllOkerat%:5'J

Fig. 7: Pre: AX Sph. - 6.00; Post: Sph. - 0.75

Fig. 8: Pre: AX -7.50 -0.50 x 180 ; Post: UCVA 9/10

509

Instant Clinical Diagnosis in Ophthall1lol0I5'J (Refractive SltrgenJ) THE IDEAL FITTING

Reverse-geometry contact lenses are designed in order to produce a hydrodynamic force on the cornea, that aims at causing epithelial ceLis to migrate, so as to obtain a change in the first ceLlular layers. In order for this force to work efficaciously, the fitting should have definite characteristics as regards the position of the lens, its movement and the clearance between the cornea and the lens. Let us analyse them in detail: • Positioning: The centration of the lens is critical for the efficacy of orthokeratological effect. Decentred lenses cannot produce the desired myopia reduction; it may cause an increase in astigmatism and corneal

distortion. A poorly centred lens can induce poor visual acui ty after lens removal.

• Movement: The lens should have a 0.2-1.0 mm blink induced movement. Orthokeratology contact lenses should show less mo vement than conventional lenses. • Fluorescein pattern: The typica l fluorescein pattern of reverse-geometry lens fitting should show an image characterised by concentric rings: dark center (minimal apical clearance, without touch), green ring (tear reservoir, with variable thickness, depending on the corrective effect, usually between 30 and 50 microns), dark ring (mid-periphery touch, alignment zone), thin green ring (edge lift, 80-100 micron). The transition between the different zones should be blended. After first adapta tion, there should not be air bubbles. This would indicate an excessive lift in the tear reservoir zone.

SELECTION OF PATIENTS

Usually orthokeratology can be used in low and moderate myopia, up to 6.00 0 , even if associated with low astigmatism. In higher myopias, orthokeratology can reduce the refractive error, w ithout correcting it totally. This kind of correction can be useful as well, in people who wish either less dependence on optical aids, or who wish to wear more functional and well-designed spectacles. In most cases, this technique is contra-indicated in high astigmatism. Primarily, o rthokeratology is indicated when m yo pic patients are contraindicated to refractive surgery or they are unwilling to undergo any surgery. Not aLi myopic patients are willing to undergo an operation, however safe it is, and however low the risks of failure or complications may be. Besides not all myopic are suitable for surgery, for example due to their age or because they have a myopic progression: refractive surgery is not ad visable 510 until myopia is not stable definitely. Refractive surgery should not be performed

Orthokeratology .50,-_ _~R~'~frn~dj~·~"~O~"~too=m~'_ _- ,

Quality of vision scores

'E 0.00 ......... {

'*

-.50

"S-1 .00 Z -1 .50

"Morning "Evening

:§ -2.00 -2.50 g. -3.00 (f) -3.50

~

r-

_ Morning Afternoon

-4 .00.L,~---.-_---,-~_--,.-J

BL

10

2W

1M

[

r-1-1-

2w

1m

3m

Safety index

1.2,

~I

r'-

..

.8

Morning

.6

_ _~(~B~CV~.""f>O~'~U~BC~V ~A~P~f~'L ) _ _,

,r-~ r-1~r'-1r-1r'-~1

m

~.8

;;: .6

Memoon (;

&

~.4 ~

Iw

r-

r-

'-

3M

Efficacy index (UCVA posUBCVA pre)

1.2

~ ~

IW

r-

'--

1-

mA

.2

o

10

IW

2W

1M

3M

Fig. 9: Refractive outcome, quality of vision score , efficacy index, and safety index

Fig. 10A: Pretreatment corneal wave-front

511

Instant Clinical Diagnosis in Opiltilalmoiogtj (Refractive SlI rgenj) on young people or teen-agers. Also in cases of young adults we have to be sure that there are not fWlctional conditions promoting a future myopic progression. As w ell, some patients have a low refractive error and wish nlore independence from standard corrective aids, spectacles or contact lenses. Pilots,

athietes, police officers, fire fighters, etc. might need more independence from corrective aids, without undergoing surgery. LIMITS

Orthokeratology is not suitable to every patient, because it ha s some contra indications and Limits. Orthokeratology is contraindicated in all those ocular cond itions that do not allow the use of conventiona l contact lenses. These are: acute and subacute inflammations or infection of the anterior segment of the eye; any eye disease, injury, or abnormality that affects the cornea, conjunctiva or eyelids, which ma y be exacerbated by wearing contact lenses; any systemic disease, which may affect contact lens wear, as inunune system diseases, or metabolic dysfunctions; allergic reactions 01 ocular surfaces or adnexa which ma y be induced or exaggerated by wearing contact lenses or by the use of contact lens solutions; alterations of tears (d ry eyes). Lintits of orthokeratology treatment ha ve to be explained in detail to each candidate. At the beginning, it is necessa ry to adapt to rigid contact lenses, which in a few cases can be troublesome in the initial period, even if this trouble is reduced to the minimum in overnight wear. Then, results depend on pre-treatment ocular conditions: corneal shape, lid position and action, corneal tissue response, presence or absence of astigmatism, etc. and usually 20/ 20 can be achieved only for low or middle myopia. For some patients, the main limitation of orthokeratology is that results are temporary. Actually, changes achieved with orthokeratology do not last forever. To maintain the reduction of myopia, lens wear have to be continued on a prescribed wearing sched ule. At the begiruting of treatment, the clear vision period ma y last few hours, and then visua l ac uity begins to decrease progressively. With time, we have an increase of the clear vision period after lens removal. When vision is no longer acceptable, the patient needs to wear retainer lenses. For people who wish to get rid of any correction for good, the temporary results are definitely a limitation. However, in some cases, reversibility of treatnlent can be an advantage. 512

Orthokeratologtj

Fig . lOB : Postortho-k corneal wave-front

Fig . 11: Confocal microscopy

580 570 560 u 550 :.5 540 •c 530 u ~ 520 c 510 • () 500

[ ~ •c ~

BMorning OEvening

"

"

Fig. 12: Changes in

BL

1D

1W

2W

1M

3M

cen tral corneal thickness over time

513

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) RISK ANALYSIS

Even if the recent literature reports a series of cases of microbial keratitis, we do not expect that contact lenses fo r orthokeratology may provide a risk that is greater than other contact lenses. The incidence and prevalence of microbial keratitis related to corneal reshaping contact lens wear is not known. Any overnight wear of contact lenses increases the risk of infection, but it is not known whether the risks of microbial keratitis are greater fo r corneal reshaping overnight contact lens wearers than other form of overnight contact lens wear. However, besides the side effects that are common to all rigid contact lenses, there are some specific complications due to corneal distortion. Sometimes we observe some corneal irregularities that can be due to lens displacement. Usually they are slight and do not affect quality of vision. Sometimes we have a greater decentration of the molded area. This decentration may be due to dislocation or binding of the lens. In this case, strong irregularity of corneal profile may cause an inadequate refractive condition and high order aberration, troubling effects in twilight and night vision. Since orthokeratology does not produce permanent and irreversible corneal changes, when such a problem occurs, we can modify lens p arameters until we obta in a satisfactory result in terms of both positioning and correction. In most problematic cases, we have to stop lens wear. As rega rds corneal staining, w e can have this problem because of both a loose lens, w hich causes mechanical abrasion on corneal epithelium, and a tight lens, which adheres to the cornea. Moreover staining may be due to debris trapped behind the lens or to deposits on the lens. Finally, it is reconunended that ongoing education be provided to practitioners and staff regarding saiety, informed consent, and prevention of potential problems, with special emphasis on the critical need to properly and thoroughly disinfect lenses that will be worn overnight. SOME CASES

The following figures show some successful cases. Efficacy and Safety of Overnight Orthokeratology by Means of a Customized Hexa-curve Reverse Geometry Lens

A growing numbe r of clinical studies ha ve reported on the efficacy of modem orthokeratology using a range of different reverse-geometry lens d eSigns. One of u s (AC) patented a new design a nd calculation method to customize a multi-curve reverse geometry lens. A prospective, randomi zed study to 514

OrtilO k erat%gtj

evaluate the safety, efficacy, predictability, stability, quality of vision and adverse reactions of overnigh t orthokeratology by means of this customized hexa-curve reverse geometry lenses (ESA ortho-6) in hyper-Ok gas-permeable material (Boston XO, hexafocon-A) . Fifty eyes of 25 myopic patients aged from 11 to 44 years, without any tear, corneal, ocular and / or systemic disease at the baseline time and without any previous ocular surgery were treated. The baseline refractive error was from1.00 to -6.00 0 spherical equivalen t, WTR astigmatism up to 1.50 0 and ATR astigmatism up to 1.00 O. The results sh owed that the cornea responds rapidly wi th significan t (p < 0.05) central corneal flattening and improve ment in visual acuity after just 60 min of lens wear. The corneal shape changes from prolate to oblate asphericity after 1 night of wear; in the majority of cases im provement in unaided visual acuity up to 0.1 Log MAR can be obtained fo r a t least 12 h after lens removal in the first week of treatment. These changes were sustained at 1 and 3 months. In the first week, there was a significant improvemen t in subjective ra tings of quality of d ay and night vision (p < 0.05) but a Significant increase of corneal spherical aberration (p < 0.05) due to post-treabnent oblate sh ape of the cornea. The spherical aberration was correlated with the amount of trea ted myopia and with p upil diameter, while coma-like aberration was correlated with the displacement of the pupil as regard s the geometric center of the cornea. Subjective ratings continued to improve after objective measures stabilized at 1 week. Biomicroscopy showed no corneal infiltrates or ulcers; there were son1e observations of grade 1 fluorescein staining of the cornea, and imp rinting in the morning that disappeared in the evening; no other significant ocular adverse events were observed during th e trial. No Significant change was observed in the central thickness of the cornea (p > 0.28). No significant ch ange was found in the intraocular pressure (p > 0.08). Specular microscope showed n o measurable chan ges in the endothelium . Confocal microscopy: in several subjects, b asal layer of the epithelium showed larger an d less regular cells after the trea tm ent. We can explain this phenomenon with a mild cellular edema d ue to the hypoxia or the mech an ical effect of the treatment. A few subjects showed a slight increasing in reflectivity of Bowman's layer and of anterior s troma. The appearance and the activation rate of keratocytes were not modified. Therefore, the slight increase in reflectivity could be explained by a mild increasing of corneal glycosa minoglycans prod uction, that is a

reversible phenomenon due to an aspecific reaction of anterior stroma to different traumas. No other significant alterations were observed in the anterior epithelium, sub basal nerve plexus, mid an d deep stroma and end othelium.The 515

Instant Clillica l Diagnosis in Ophthalmologtj (Refractive Surgery) results of this study suggest that the corneal epithelium can be molded or redistribu ted very rapidly in response to the tear film forces generated behind this reverse-geometry lens design. Safety and efficacy of the procedure appear to be fa vorab le without significant adverse reactions. CORNEAL THICKNESS

516

One of the concerns of m yopia correction by corneal molding is the thllu1.ing of central epithelium of the cornea induced by a direct compression of the optical zone. As it happened in the radial kera totomy or intastromal corneal rings procedures, we think that it is possible to bring on a central flattening, working in the periphery of the cornea and we designed a lens geometry that would aid the displacement of peripheral epithe li um to wards the optical zone. Our biomechanical hypoth esis is th at the central flatten ing might be seconda ry to a mid-peripheral s teepening, induced by a displacement of the ep ithelium that results from a p roper compression in the alignment zone of this lens. TI,e hexacurve reverse geometry lens design (ESA ortho-6) we mention above attempts to mold the periphe ry of the cornea with a minimum compression in the center of the lens. A prospectjve, consecutive study was performed to evalua te the corneal response an d central corn ea l th ickness (CCT) changes after overn ight orthokeratology by means of this customized hexa-curve reverse geometry lens in hyper-Ok gas-permeable material (Boston-XO). Twenty-eigh t eyes of 14 myopic patients (ranging from - 1.00 to -4.25 0 sph, and astigm atism up to 1.000) were enrolled in the study. Assessment criteria included uncorrected visua l acuity, best-corrected visual acuity, manifes t refract ion, ultra soun d pach ymetry, corneal topog raphy, and biomicroscopic data. Th ese data were collected at baseline, and then after one night, one week, two weeks, one month, and three months of lens wear. All the examinations were performed in the mornin g immed iately after lens removal and repeated in the evening of the same da y. An ultrasound pachymete r (Allergan Humphrey model 850, Carl Zeiss Meditec, Dublin, CAl, using a velocity of 1640 m is, was used to measure central corneal thic kness. The results of this study showed th at th e cornea responded rapidly with significant (p < 0.05) central cornea l flattening and inlprovement in visual acuity after the first night o f contac t lens wear. By the end of one week, all cornea l and visual changes had reached a maximal level and remained stable during the day. These changes were sustained at the following visits. After the first molding, the fluorescein pattern showed a clearance under the center of the lens that demonstrated a minimal cen tral tOllch. Biomicroscopy showed

OrthokerntologlJ

no significant ocular adverse events. The average pretreatment CCTwas 533 ± 31 "m. During the period of the study, ultrasound pach ymetry did not show any significant change in the central thickness of the cornea (repeated measures ANOV A: p = 0.978), both in the morning and in the evening (Bonferroni/ Dunn post- hoc test: p > 0.414). Figure 1 show the details of the difference in CCT. The lack of chan ge found in the central pachymetry data suggests that the overnight contact lens can successfull y flatten the cornea without direct compression of the center of the cornea. The absence of change in CCT during the day may exclude a masking effect due to edema. Contrary to these finding, the majority of previous studies reported that orthokeratology and corneal refractive therapy ca uses central epithelial and total corneal thi.nning. This difference could be caused by the different geometry and behavior of the lenses. These results seem to confirm the biomechanical hypothesis that the central flattening of the cornea might be achieved as secondary to a mid-peripheral steepening, induced by a displacement of the epithelium that resu lts from a proper compression in the alignment zone of this lens.

517

49 Aspheric IOls (Wavefront Based IOls) Sanjay Chaudhary (India)

Convention al sph erical IOLs (Clariflex, Acrysof, Akreos, etc.) have a positive spherical aberration, which results in reduced contrast sensitivity under mesopic and scotopic conditions. Aspheric IOLs like the Tecnis (AMO), Acrysof IQ (Alcon) and Akreos AO (B and L) minimize the spherical aberra tion resulting in improved vision. A normal corneal spherical aberration is positive, i.e. + 0.27 microns (}l1Il) ± 0.02 }lm. Tecnis h as a n egative spherical aberration of - 0.27}l1Il, AcrysofIQ -0.20}lm and Akreos AO - O.O}lm (neutral). Following is a comparison of these three different lenses. (Key words: SA-Spherical Aberration, CS -Contrast Sensitivity) UNDERSTANDING SPHERICAL ABERRATION

A spherical aberration occurs when parallel rays of light do n ot focus on one point. The central bunclle of rays may focus in front of or behind the focus of the peripheral bundle of ra ys. The refractive power in the periphery of the lens may either be too weak or (usually) too strong. When the peripheral rays of light foc us in front of the central rays, it is called positive SA, and if they focus behind the central rays, it is called negative SA. The resultin g image despite a SA might be clear, but it has less contrast than an ideal optic. SPHERICAL ABERRATIONS IN A HUMAN EYE

The human cornea has a positive SA. This means that the light entering the eye from the peripheral parts of the cornea converge more to focus in front of the rays en tering the central portion of the cornea. The SA of the cornea hardly changes during lifetime. In a 4 mm pupil, rays from th e peripheral part of the cornea are obstructed and therefore the eye would manifest w ith very little SA. If the pupil dilates to 6 mm or more, the peripheral rays also reach a focus within the eye. Such an eye w ith a co-existing large quantum of SA would experience a loss of contrast. 518

Aspheric lOLs (Wavefront Based lOLs)

,

/' ,

V Negative spherical aberration

;

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.....

,-

;

,

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Positive spherical aberration

Fig. 1: Spherical abe rration (SA) in a lens system

--=== ---~ - - - -~ ~:::D ----::::-----~

Cornea -

L

.

SA showing spread of light on the retina

L Retina Fig. 2: Positive SA in a normal human cornea . Peripheral rays focus in front of retina

Fig . 3: 3-0 representation of SA

51 9

Instant Clinical Diagllosis it! Opiltilalmol0/5') (Refractive SlIIogen)) In a Young Eye

The cornea of a young eye has a positive spherical aberration, which gets compensated by the negative spherical aberration of the crystalline lens. TI1ere is a young ad ult, the rays of light come to a point focus on the retina, and the contrast sensitivity is good. In the Elderly Eye

TI1e lens is grow ing over a lifetime. In the process, it gets thicker. Its refractive index also increases. So from a negative SA, w ith age it develops a positive SA. In an elderly person, the cornea has a positive SA, and the crystalline lens also has a positive SA. The two lead to an even stronger effect, grea tl y increasing the overall SA and a marked decrease in contrast. CONVENTIONAL SPHERICAL IOLs

They also have an inherent positive SA and therefore they also amplify the SA of a cornea. THE TECNIS LENS (AMO)

This is a multi piece second-generation silicon lens. It has a negative prolate surface design ed on the an terior surface of the lens and has a SA of - 0.27 "m.It has a square edged optic design. It refractive index is 1.46 and an edge thickness is 0.50 mm. It can be injected through a 2.8 mm incision with the help of an injector system. Fitting Philosophy

The lens is designed to fully correct the +ve SA of the cornea thereby enhanCing the contrast sensitivity to the maxin1um. The lens is based on the Z-sharp optic teclu1010gy. The peripheral part of the anterior surface of th e lens gets a more concave desig n and therefore neutralizes the positive SA of the peripheral cornea. Various stud ies have shown that the asphericity of the cornea is + 0.27 >'ffi with a s tandard deviation of ± 0.02. This lens has a nega ti ve SA of - 0.27 "m and targets to full y correct the to tal corneal SA of the eye. THE ACRYSOF IQ (IMAGE QUALITY) (ALCON)

This lens is a single piece hydroph obic acrylic and is a blue light filtering lens (lens is in1p regnated with yellow ch romophore). The asphericity is designed on the posterior surface of the lens by thinning the lens in the center. The lens

520

Asp/wric TO Ls (Wav efrollt Ba sed IOLs)

Fig. 4: 2-D color coding of SA

Fig . 5: Point focus on the retina as negative SA of young lens neutralizes positive SA of co rn ea

521

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) has a -ve SA of - 0.20 )lm. It has a refractive index of 1.55, an ed ge thickness of 0.21. It can be injected through a 2.8 mm incision with the injector system. Fitting Philosophy

Studies reveal that a normal vision is best when there is a residual positive SA of +0.1 /Jm in the optical system of the eye. This lens has a - ve - 0.20 )lm SA and after neutralizing the +ve SA of the cornea (SA of + 0.27 )lm), there is still a residual +ve SA of +0.07 ± 0.02 iJffi Tanzer and Schallhorn reported that 338 Navy pilots had a mean positive spherical aberration of approximately 0.1 )lm (6.0 mm pupil) (ASCRS Symposium, May 1-5, 2004, San Diego, CAl • Levy et al (AjO, 2005) fo und that for 70 "supernormal" eyes with an UCVA 2. 20/15, the positive spherical aberration of the whole eye was 0.11 )lm ± 0.077 iJffi, with a 6.0 mm pupil. These clinical observations suggest that preserving a moderate amount of positive spherical aberration may enhance the quali ty of vision in normal pseudophakic eyes. AKREOS ADAPT AO (ADVANCED OPTIC) (BAUSCH AND LOMB)

This is a single piece hydrophilic acrylic with a square edge. Its refractive index is 1.458 (hydrated). It has an anterior and posterior aspheric surface. It neither has a positive or a negative SA, i.e. a SA of ± 0.00 )lm.1t therefore does not result in any aberration being introduced in the eye. It can be injected through a 3.0 m incision. The lens has a uniform power from the centre to the edge. This gives the lens independence from the eye's optical alignment. Therefore the image quality is not disturbed even if the lens is slightly decentered. Fitting Ph ilosophy

The aberrations present in a human eye differ from person to person. Therefore an aspheric lens, which is aberration neutral, offers control of SA, which is independent of the patient's profile. Th is implies tha t the other lens manufacturers assume that the corneal SA is + 0.27 ± 0.02 iJffi in all cases. Some studies show that the variation may be even more. Therefore, if the corneal +ve SA were less than the amount assumed, these lenses wo uld result in an overall-ve SA that is worse. The best situation would be not to have a +ve SA of a conventional lens, and at the same time avoid disturbing the SA of the cornea. This opinion is supported by the Bell curve which shows that only 68 522 % of the human cornea's fall in the bracket of a standard +ve SA.

Aspheric rOLs (Wavefrout Based lOLs) ...

~

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I I I I I

Fig. SA: A young lens with a negative SA

Retina

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Fig. 68: An age ing lens with a positive SA

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Fig. 7: The +ve SA of an ageing lens com pounds the +ve SA on the cornea

Young eye

Ageing eye

Fig. 8: Reduced contrast sensitivity during the day (Courtesy AMO)

523

Instant Clinical Diagnosis in OphtlwlmolopJ (Refractive SlIrgenJ) Comparison of Aspheric IOLs 6.0mm Pupil size

524

Lens

Sperica/ Aberration

Residual Spherical

Aberration

AcrySof IQ

- 0.20

~m

0.10

~m

Tecnis

- 0.27 11m

0.00

~m

Akreos AO

0.00

0.27

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~m

Aspheric 10Ls (Wavefront Based 10Ls)

Fig . 9: Glare and Halos at night (Courtesy AMO)

Fig . 10: The +ve SA of conventional IOL add to SA of corn ea

Fig. 11: The Tecn is lens

525

Instant Clill ical Diagnosis in Oplltllnlmol0:5'J (Refractive Surgery)

•r

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Fig . 12: The -ve SA on the anterior surface compen sates for the +ve SA of cornea

Fig. 13: The Aerysof 10

526

Aspheric l OLs (Wavefrollt Based lOLs)

Fig . 14: The Akreos Adapt AO (Bausch and Lomb)

21 dpt

21 dpt

= dp

21 dpt

Fig. 15: Uniform power of the Akreos AO from center to edge

68%

Bell curve

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z

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+/~

one standard deviation is only 68% of patients!

Fig. 16: Bell curve showing the variation in the corneal SA

527

50 Dual Optic Accommodative IOls GU Auffarth (Germany)

The last step in successful cataract or lens removal surgery is the restoration of accommodation. Several single-optic systems have been in troduced on the market. In Germany the ICU IOL man ufactured by Human optics AG (Erlangen, Germany) came on the market as single optic TOL based on Paten ts by Hanna. Several studies in Europe have shown certain limitations for th ese TOLs based on the anterior shift principle. Those lenses need movements of around 1.5 to 2.5 mm to achieve 3 diopters of accommodation. Even though the lens showed satisfactory clinical results, the amount of accommodation measured never exceeded 0.75 to 1 diopter, indicatin g a big range of pseudoaccommodative parameters (such as residual refraction , myopia, astigmatism, pinhole effect of pupil, corneal refractive changes, etc.). On the US-Market the Crystalens AT 45 was actually FDA approved and widely u sed. Apart from visual acuity results no objectiv e means for accommodative measurements were presented in the peer reviewed literature. Studies in Europe by Find\. and coworkers indicate a similar performance of this sinfle optic l OL like the l eU. A dual-optic design offers potential advantages over single-optic designs in that less lens movement is necessary with the dual optic to achieve a certain amount of accommodation. For example, in order to ach ieve 2.0 D of pseudoaccommodation, a 22 D single-op tic IOL w ould need to move forward 1.6 mm within the capsular bag. A dual-optic 10L with a +30 D front lens and a -8 D posterior lens (overall power = 22 D) would only require 0.8 nun of separation to achieve 2.0 0 of power change. Two dual optic IOLs are curren tly tested. The Sarfa razi Elliptical Accommodating IOL and the Visiogen Synchrony len s. Both utilize a pluspowered biconvex front lens connected to a negatively powered concave-convex lens. During the accommodative effort the two lens componen ts increase their distance fro m each other, resulting in increased effective power of the overall lens. The Sa rfa rzi TOL is now unde r evaluation by Bausch and Lomb. No clinical data h ave been presented so fa r. The Visiogen Synchrony accommodative IOL consists of a high power (30 D ptr.) anterior optic and a variable minus pow er posterior optic. It is made of Silicone material. Implantation of the first generation models were done with 528 folding forcep s. The latest generation h as now an injector for implantation.

50 Dual Optic Accommodative IOLs GU Auffarth (Germany)

The last step in successful cataract or lens remo val surgery is the restoration of accommodation. Several single-optic systems have been in troduced on the market. In Germany the lCU IOLmanufactured by Human optics AG (Erlangen, Germany) carne on the market as single optic IOL based on Patents by Hanna. Several studies in Europe have sh own certain limitations for these 10Ls based on the anterior shift principle. Those lenses need movements of around 1.5 to 2.5 mm to achieve 3 diopters of accommodation . Even though the lens showed satisfactory clinical results, the amount of accommodation measured never exceeded 0.75 to 1 diopter, indicating a big range of pseudoacconunodative parameters (such as residual refraction, myopia, astigmatism, pinhole effect of pupil, corneal refractive changes, etc.). O n the US-Market the Crys talens AT 45 was actually FDA approved and w idely used. Apart from visual acuity results no objective means for accommodative measurements were presen ted in the peer reviewed literatu re. Studies in Europe by Find!. and cowo rkers indicate a similar performance of this sinfle optic IOL like the lCU . A dual-optic design offers potential advantages over single-optic designs in that less lens movement is necessary w ith the dual optic to ach ieve a certain amoun t of accommodation. For exam pi er in order to ach ieve 2.0 0 of pseudoaccommodation, a 22 D single-optic IOL would need to move forward 1.6 mm within the capsular bag. A dual-optic IOL with a +30 0 front lens and a -8 D posterior lens (overall power = 22 0) would only require 0.8 mm of separation to achieve 2.0 D of power change. Two d ual optic 10Ls are currently tested. The Sarfarazi Elliptical Accommodating IOL and the Visiogen Synchrony lens. Both utilize a pluspowered biconvex front lens connected to a negatively powered concave-convex

lens. During the accommodative effort the two lens components increase their distance from each other, resulting in increased effective power of the overall lens. The Sarfarzi TOL is now under evaluation by Bausch and Lomb. No clinical da ta ha ve been presen ted so far. The Visiogen Synchrony accommodative TOL consists of a high power (30 D plr.) anterior optic and a variable minus power posterior optic. It is made of Siticone ma terial. Im plantation of the first generation models were done with 528 folding forceps. The latest generation has now an injector for implantation.

Dual Optic Accommodative rOLs Synchron y TM Accommodative tOL Synchrony vs single-optic accommodative tOL

~ 8 0 15. 7 .Q

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Synchrony-dual optic system

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'"

Fig . 1: Graphical illustration of the accommo-

dative effect in relation to amount of optic shift of single and dual optic systems

Fig. 2. Clinical retroillumination photograph and still picture of the Synchrony tOl

Fig. 3: Injektor system for Synchrony tOL 2 years follow-up: Synchrony TM Accommodative tOL

1 Month

12 Months

Fig. 4

24 Months

529

Instant Clinical Diagnosis in OplttltalmologtJ (Refra ctive Surgery)

The Synchrony IOL as been extensively studies in laboratory (rabbit) models as well as in mul ticenter clinical trials in Europe and Latin America. Clinical data are avai lable with a 3-4 years follow u p now. The lens is also now CEmarked in Europe and therefore available for clinical use. The first clinical generation of the Synchrony dual optic accommodative IOL showed over a 2-3 years follow up period good fu nctional results, stable refrac tion and low to mediocre PCO development. lnterlenticular opacification (ILO) was the main concern regarding these dual-optic IOLs. To date, however, this has not been reported as a complication of these [O Ls. Studies of the IOL in rabbits suggest that the design features of the Synchrony may help prevent posterior and anterior capsule fibrosis. In another stud y in rabbits the incidence of [LO was zero, also ind icating that the lens material (silicone) ma y prevent interlen ticular lens epithelial cell migration. Ossma and coworkers could demonstrate by ultrasoun d biomicroscopy movements between the two IOLs of upto 0.6 to 0.8 mm . The residual near addition to reach) l was around 0.78 diop ters and UDVA and UNV A was in all cases >20 / 40. Dick et al and Auffar th et al presented si milar results with the early Synchrony model. In contrast to single optic designs the d ua I optic designs offer theoretically and practically the chance of a real accommodative effect. Several questions still need to be scientifically evaluated. The IOL calculation or in other words the exact location of the IOL in side the capsular bag is difficult to pred ict o r to determine. The preven ti on of posterior capsule opacifica tion (PCO) is still a longterm concern. New instruments such as the "perfect capsule" system by Milvella Inc (Sydney, Australia) offer nowadays new means to target the elimination of lens epithelia l cells (LEC). In summa ry the dual optic TOLs seem to be the most effecti ve design or [OL type achieving a significant amoun t of accommod ation. Other (new) concepts in accommod ative IOLs includ e the Powervision Fluidvision IOL, which is capa ble of curvarture changes to achieve accommodative changes or the smart lens, a lens refilling device consisting of a thermoplas tic material. ew clinica l studies espeCially with the now clinically approved Visiogen Synchrony IOL will show how successfu l these dual optic designs on the marke t w ill be.

530

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery)

The Synchrony IOL as been extensively studies in laboratory (rabbit) models as well as in multicenter clinical trials in Europe and Latin America. Clinical data are ava ilable with a 3-4 years follow up now. The lens is also now CEmarked in Europe and therefore available for clinical use. The first clinical generation of the Synchrony dual optic accommodative IOL showed over a 2-3 years follow up period good functiona l resuits, stable refraction and low to mediocre PCO development. Interlenticular opacification (ILO) was the main concemregarding these dual-optic IOLs. To date, however, this has not been reported as a complication of these IOLs. Studies of the IOL in rabbits suggest that the design features of the Synchrony may help prevent posterior and anterior capsule fibrosis. In another stud y in rabbits the incidence of ILO was zero, also indicating that the lens material (si licone) ma y prevent interlenticular lens epithelial cell migration. Ossma and coworkers could demonstrate by ultrasound biomicroscopy movements between the two TOLs of upto 0.6 to 0.8 mm. The residual near add ition to reach)1 was around 0.78 diopters and UDVA and UNV A was in all cases >20/40. Dick et al and Auffarth et al presented similar results with the early Synchrony model. Tn contrast to single optic designs the dual optic designs offer theoretically and practically the chance of a real accommodative effect. Several questions still need to be scientifically evaluated. The IOL calculation or in other words the exact location of the IOL inside the capsular bag is difficult to predict or to determine. The prevention of posterior capsule opacifica tion (PCO) is still a longterm concern. New instruments such as the "perfect ca psu le" system by Milvella Inc (Sydney, Aust ralia) offer nowadays new means to target the elimination of lens epithelial cells (LEC). In su mmary the dual optic TOLs seem to be the most effective design or IOL type ach ieving a significant amount of accommodation. Other (new) concepts in accommodative IOLs include the Powervision Fluidvision IOL, which is ca pable of curvarture changes to achieve accommodative changes or the smart lens, a lens refilling device consisting of a thermoplastic material. New clinica l studies especially with the now clinically approved Visiogen Synchrony IOL will show how successful these dual optic designs on the market will be.

530

Dual Optic Accommodative lOLs 2 Years Follow up : Sync hrony TMAccommodative IOl

Fig. 5 Figs 4 and 5: Retroillumination photograph of Syn-chrony IOLs with a 24 months follow-up_ Only small amount of pee, no ILO

0 .59 mm

Fig. 6 UBM : Pat. LBB. 6 Mon. postop

0 .80 mm

Fig. 7 Figs 6 and 7: Ultrasound biomicroscopy of Synch rony IOL indicating movement between lenses of 0.59 (Fig. 6) and 0.80 mm (Fig. 7)

531

51 Anterior Chamber Phakic IOl with Angle Fixation Juan C Rocco (Argentina)

ADVANTAGES The va lidity of the concept of a myopic implant has been proven by 30 years of experience with the Kelman's multiflex implant. owadays we have near of 20 yea rs of use of the first Baikoff model and a lot of happy ex-high myopic patients. With these teclmiques we have a lot of advantages like: excellent visual results; fast visual recovery; preserva tion of accommodation; easy operation

teclmique to anterior chamber surgeon; reverSibility; the possibili ty to combine with excimer laser surgery in very high m yopic patients; the option to correct

astigmatism with the phakic IOL and the predictability of visual result. Since the stan dard deviation of the residual postoperative refracti on is in nea r one d iopter, in almost all the patients, which appears to be the best of all the refractive surgical techniques and also is a very reproducible surgery. In the past there was concern about the long-term potential damage to anterior chamber structures, meanly the endothelial loss, but with the new lens design are safer and this proble m is almost disappea r. In these last years we can see a lot of very good result and with a precise technique is a very useful

options for patients with high myopia.

HISTORY The use of anterior chamber lens to correct myopia was developed first time in 1950s by Strampelli et al and Barraquer and Choyce et aI, also Feclmer and colleagues with the "Worst-Fechner iris claw" and Praeger and Baikoff, all of them collaborated to develop this option fo r high myopic patients. After tha t joly in 1987 modified the Kelman Multiflex four-point fixations lens that was used to ca taract surge ry and now it is used in anterior chamber

to correct high myopia. The first generation of this kind of lens to correct myopia was designed by Dr George Baikoff and the Company Domilens in France, and was called Balkoff ZB Lens. This was a Z shaped haptic derived from the Kelman 's Multiflex type, 532 which a!Jows a certau) suppleness of the lens that can adap t to the different

Anterior Chamber PhakicIOL with Angle Fixation

Fig. 1: Kelman's multiflex implant

Fig. 2. Anterior chamber phakic IOL angle fixations

533

InstnlltClillicni Dingllosis ill Opl/tlwllllology (Refractive Surgenj ! dimensions o f the an terior chamber. The foolplates we re too large to avoid the iris wrapping. This model was designed with 25 degree vaulting to p roject in front and very near of pupil and have to maintain a distance abo ut 2 mm back from the central cornea and about 1 nun U1 front of the p upil. Its optic was 4.50 mm and the thickness of the ed ges is 0.7 mm. There was a lot of complications w ith this model, mainly a high ra te of endothelial loss because an excessive con tact between the optic ed ge and the peripheral endothelium . Baikoff realized of this problem and modificated the angle of the lens and was born the new model Z B5M, to reduce the contac t between the lens and the pe rip heral epithelium and ga ined 0.6 mm of space between the cornea and the lens, in comparation with the ZB lens. The first model has to be explan ted in several patients for high rate of endotheli al loss, but the last model was safer and pred icable because the loss of endothelial cells occurs only m ainly during the opera tion, but the first model the endothelial loss appeared during and after the surgery. TYPES OF PHAKlC LENS

Marcher GMBH 93 A

• Plano Concave

• • • • • • •

PMMA UV Ra ys Block Length: 12.50 to 13.00 mm Posterior Angle 19 0 Optic Size: 5.50 mm Diopters Range: - 6.00 to - 22.00 d iopters Compan y: Marcher Gm bH

Baikoff Model ZB5MF • Biconcave

• • • • • • •

PMMA UV Rays Block Length: 12.50 mm - 13.00 mm - 13.50 nun Posterior angle 200 Optic Size: 5 mm Diopte rs Ra nge: 7.00 d iopters to - 20.00 d iopters Company: Domilens

Phakic 6 Model 130 534

• Biconcave • PMMA

Allterior Chamber Phakic lOL with Angle Fixatioll

Fig. 3: Anterior chamber phakic IOL in high myopia case

Fig . 4: Worst Fechne r iris claw lens

535

Instant Clinical Diagnosis in Oplr tlwlmologtJ (Refractive SlIrgenJ)

• • • • • •

UVBlock Length: 12.00 rnm to 14.00 mm Posterior angle 14° Optic Size : 6 mm Diopters Range: - 2.00 diopters to - 25.00 diopters Company: Ophthalmic Innovations Internationa l Inc.

Nuvita Baikoff MA 20 • Biconcave

• • • • • •

PMMA UV Block Length: 12.50 rnm to l3.50 mm Optic Size : 4.50 diopter Diopter Range: From - 7.00 diopters to - 20.00 diop ters Company: Bausch and Lomb.

Kelmnan Duet

• • • • • • •

Two piece

H aptic PMMA Optic foldable Length: 12.00 rnm - 13.00 mm - 13.50 rnm Optic Size: 5.50 rnm Diopter Range from - 8.00 diopters to -20.00 diopters. Compan y: Tekia, Inc.

INCLUSION CRITERIA

The selection process must be very strict and the patients must have real expectative before surgery. The patient will be refraction stable at last 8 month; older than 21 years old, has a m yopia between - 4.00 diopters to - 22.00 diopters; has problem w ith using contact lens; can not wear spectacles (for a physic appearance 0 work restriction); endothelial cell density greater than 2.500 cell / m m; an terior chamber depther than 3.4 rnm; without any eye disease ~ke: glaucoma, uveitis, retinal detaclunent, conjW1ctivitis, autoimmune disease; any retinal problem must be treated before the surgery (retinal photocoagulation). Before surgery we need know exact manifest and cyclopegic refraction, visual acuity, slit lamp examination, d irect and indirect ophthalmoscopy, oecular pressure, pupil diameter. SURGICAL TECHNIQUE

The patient has to firm informed consent.

536

Anterior Chamber Phakic l OL with Angle Fixation

-r-----::._;=-- - - - -

g <0

'. ..!..--==-- _.-.-.Fig. 5: Morcher GMBH 93A Phakic IOL

Fig. 6: Baikoff phakic IOL

"

Fig . 7: Phakic 7 model IOL

537

Instant Clinical Diagnosis in OphthalmologtJ (Refractive SurgenJ)

The decision to use Phakic lens to correct myopia should be rigorously studied. The power of the implant can be determined using a mathematical calculation, using the formula of va n der Heijde and coauthors, that takes into account the keratome try, the depth of the anterior chamber and the amount of refraction. Same man ufacturer advice the use of theoretical tables to determine the exact diopters of each phakic lens. A much simpler and useful way to do it is take the refraction of the patient's eyeglasses in spherical equivalent ve ry precise, is reco mmend ed use autorefractometry and skiascopy using cycloplegic drops. If a patient has 10.00 diop ters of myopia, we have to use a -10.00 diopters phakic lens, for a 15.00 d iopters of myopia we have to use a phakic lens of - 14.00 and for a myopia of -22.00 diopters we use a -20.00 d iopters phkaic lens. In any case is preferable to leave the patient slightly under corrected by 1 or 2 d iopters that are better than over correction . Each phakic lens company use d ifferent approach to calculate the lens. To choose th e Phakic lens's length was selected by measuring the horizontal white-to-white distance and we add 1.00 mm to this distance, in general 60% of the lens is of 12.50 mm; 30 % of 13.00 mm and 10% of 12.00 mm. One day before surgery the patient received 500 mg of acetazolamida orally and Ciprofloxazine (d rops) four times a day. Who wear contact lenses, this will be remove ten days before surgery. Is recommended gave sed ation via oral for a quiet surgery. One hour before surgery, we constrict p upil with 2% Pilocarpine for a easy and non-complication introduction of lens. Clean the whole eye zone and lashes w ith beta dine 2%. Before the introduction xilocaine intracamerular , we use topic Proparacaine fi ve drops. Collocation speculum and drape de lid' s border. Paracenthesis in anterior chamber and introduction of 2 cc. Xilocaine 10% and filled with viscoelastic material. A 6 mm corneoscleral incision was made in the steeped meridian if the patient has astigmatism. Introduction a special silicone glide in the anterior chamber and re-fill with viscoelastic substance, then w ith a forceps the Phakic IOL is inserted in anterior chamber in front of the iris, with very carefully to touch any structure of anterior chamber like iris, lens, endothelium or angle iridocom eal. We use the silicone glide to push the lens very slowly into the eye until de upper portion of the lens and with the help of forceps, is introduced behind the limbus in contact with the angle iridous-comeal. After that introduce a air bubble in anterior chamber w ith the object to put back the Phakic lens and ensure a good position and it is rotate with Sinskey hook to get a good cent ration with the pupil. 538

Anterior Chamber PhakicIOL with Angle Fixation

Fig . 8: Nuvita 8aikoff IOL

Fig . 9: Kelman duet phakic IOL

539

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) A small peripheral iridotomy is performed with mini scissors (Vannas) to prevent any rise of intraocular pressure in the post-operative pe riod.

Is very important a carefully remove of all the viscoelastic material of the anterior chamber, because if remain same of this substance can produce endothelium edema increase intraocular pressure. A single nylon 10.0 was used to close the incision and the eyes were not occluded after surgery. We prescribe drops of ciprof]oxacine and prednisolone 1% four times a da y, during 15 days and are examine in 1-3-6 and 15 days. The suture is removed when the astigmatism is controlled. COMPLICATIONS

Pupil ovalization: It is discrete and non-progressive, occurred along the axis of the lens. In genera l havenot symptoms, only the appearance. Halos and glare: May appear in any time, this phenomenon is because the small diameter of the optic zone; more common in lights eye color and it is relation with pupil diameter in dim light. Giant papillary conjllnctivitis: It is related with nylon suture, but if you use only one suture and hide the knot, is very strange that appear. Postoperative uveitis: Only appear in 2% of the cases, one can See cells in anterior chamber, but disappear with use of corticosteroid eye drops. Elevated intraoclilar pressure: In 22% of the operated eyes; is transitory and is related w ith the use of corticosteroid eye drops and material viscoleastic that is not removed after the surgery. Lens rotation: It is rare (only 4%) if one made a good measurement of white to white to choose a good phakic lens, it appear when the lens is too small. If the rotation is evident and persist, the lens w ill be replace for a bigger one. Conclusion

The essential problem with this technique remains the long-term effect on the endothelium, although with the new models this damage is very low and is not a real problem now like in the past. The results in all authors is very satisfactory and was determined that endothelial damage mainly is produced during the surgery and improving the technique and using correct instruments and viscoelastic material, this is a effiCiency, precise, predictable, reproducible, stable and safety option to correct myopia.

540

Allterior Chamber Phakic lOL withAlIgle Fixatioll

Fig . 10: Small peripheral iridotomy periormed to prevent lOP rise in postoperative period

Fig . 11; Non -prog ressive pup il-ovalization

541

52 Advances in Microphakonit for Refractive lens Exchange (MIRlEX)A New Technique Arturo Perez-Arteaga (Mexico)

SUMMARY

Microphakonit is a technique described by Amar Agarwa l MD to perform a Bimanual Cataract Surgery trough 2 0.7 mm ports with 700 nticrons cannulas and Phaco tips. It is until now, the smallest instrumentation to perform a cataract surgery. What we are going to describe here is the use of these 700 microns instrumentation and technique to perform Refractive Lens Exchange (RLE). The advan tages of this technique over the traditional coaxial RLE and over the traditional 1.0 mm Phakonit are first to be mininlaUy invasive and second to have a complete control of the eye and over the anterior chamber stability during the entire procedure. HISTORY

Refractive Lens Exchange (RLE) started as a high controversy teclutique because the potentia l consequences of aphaquia. In the early days of intracapsular and extracapsular techniques it appeared to be crazy to introduce a patient to all the nightmare of ca taract surgery just for refractive purposes; the price at that tinle was very high. So other refractive procedures gain popularity like Incisional Surgery, Excimer Laser Ablations and Phaquiq intraocular lenses. I started my surgical practice in 1990; at that tinle I learned a bimanual technique to perform clear lens extraction for refractive purposes from Ignacio Barraquer MD from Colombia, trough Enrique Ariza MD and Guillermo Lieja MD from Mexico. The teclmique was perfoffiled trough two side port 1.0 mm incisions, with irrigation / aspiration w ith two "hand made" 21 gauge cannulas. At that time we used a very high bottle of intraocu lar solution and gravitatory force for irrigation and a peristaltic pump for aspiration. With the time we sta rted to use the Irrigation /Aspira tion (1/ A) system of the phacoemulsification equipments. The incisions were made only for 1/ A, so at the end a 3rd incision was done to introduce the intraocular lens (IOL). No ultrasonic power was needed, because no cataract was present; if some nucleus 542 was very hard to aspirate by it self, a mecl1anical phacofragmentation between

Adv ances in Microplzakonit for Refractive Lens Exchange (MlRLEX)

Fig. 1: Bimanual irrigation/aspiration through two 21 gauge cannulas

Fig. 2 : Internal forced infusion obtained with the Millenium System

543

Instant Clinical Diagnosis in OphthalmologtJ (Refractive Surgery) the two cannulas was very easy to perform in order to obtain small pieces of nucleus easy to aspirate. We described our rate of complications with this technique. This bimanual II A technique we u sed for many years even for cataract surgery; we did a traditional coaxial phacoemulsification, and after that the cortical material was aspirated w ith this technique. It was very safe, very stable and more efficient to obtain small pieces of cortical material in all positions of the eye, in comparison to traditional coaxial I I A, were the surgeon can experience troubles with the cortical material at 12 o' clock position. Then Prof. Amar Agarwal came with Phakonit. The entire concept for us changed, because it was not more needed to switch from a coaxial systen1 for nucleus extraction, to a bimanual mode for cortical II A. These concepts were fast adopted to RLE patients. We started to use new instrumentation like the Duet system, new techniques like forced infusion and new parameters and ultrasonic power modulations. So an exciting new era for RLE based in the Phakonit technique started. We published by first time the concept MIRLEX (Microincisional Regfractive Lens Exchange) to describe the extraction of the clear lens and the implantation of a microincision IOL with the ultrasmall incision teclu1iques (Phakonit) only for refractive purposes. As the refractive surgeons worldwide found limitations of laser procedures and phaquic IOL's implantations and at the same time a lot of new models of refractive IOL's has arrived to the refractive field, RLE has regained popularity; many bimanual Phaco surgeons have found safety in the Bimanual Lensectomy. In fact we do believe it s the time for a new born of this technique with a lot of improvements in the clear lens extraction and in the IOL technology. At this time there is not an IOL that can go inside the eye safe trough a Imm incision or less, even so this Bin1anual Technique for RLE is gaining p opularity because their advantages in stability even there is the need to open a third incision to implant any kind of IOL the surgeon wants. Last year Amar Agarwal MD described Microphakonit, the Bimanual phacoemulsification technique performed wi th two 0.7 lnm cannulas and phaco tip, breaking so the barrier of 1.0 mm incision for cataract surgery. So we started also to perform MIRLEX trough 0.7 mm finding safety and efficacy in this minimaly invasive procedure. This is the technique that the reader will find in this chapter. SURGICAL TECHNIQUE Instrumentation

Very few instrumentation is needed to perform this technique: 1. Phacoemulsification machine with internal or external forced infusion. 2. 0.7 mm infusion cannula: We believe that the double ended irrigating 544 cannu la provide the best irrigation and anterior chamber stability for

Advances in Microphakonit for Refractive Lens Exchange (MIRLEX)

Fig . 3: Forced infusion trough a double ended 0.7 mm irrigating cannula

Fig . 4: Aspirating and Irrigating 0.7 mm system of cannulas

545

Instant Clinical Diagnosis in Opirtilalmol0:5'J (R efractive SlIrgenJ)

this procedure. The one opened cannula can reject the nuclear and cortical pieces and this is why we do not use it. TI,ere is not need to have irrigating choppers because the nucleus is soft and there will be not need to chop. Even if the surgeon finds a hard nucleus there is not need to use irrigating chopers and a no-irrigating mopper technique can be used. 3. 0.7 nun aspirating cannula: we believe a one-superior opened aspirating cannula is the best for this technique because the hole is in the opposite side of the posterior capsule and is always in the field of view of the surgeon. 4. MicroPhakonit tip (0.7 mm Phaco tip) is not needed in most of the cases,

because the nucleus is soft, so on ly the vacuum is needed to aspirate it and no ultrasonic force is used. This is only an irrigating-aspirating technique with an air pump at one side (forced infusion) and aspiration (vacu um or perista ltic pump) in the another side. 5. 0.7 nun diamond or saphire blad es. It is important to be sure that the incision will be made with the exact size for this technique. It is almost a closed enviroment in the anterior chamber and will be possible only with the proper incisions. A large incision will lead to surge even if forced infusion is used, complicating so the procedure. 6. MicroPhakonit capsulorhexis forceps. You can use any model you want, just be sure that your 0.7 mm incision is enough to permit the entrance of the instrument to the anterior chamber. 7. Forceps, viscoelastics, anesthetic eyedrops, IOL implan tation devices, etc. Patient Preparation

Before start the surgeon must be sure to have the follow ing data: 1. Refraction: Because it is a refra ctive procedure the surgeon must be sure

of the exact refractive sta te of the patient. 2. Corneal tophography: We believe that the astigmatism can be reduced wi th the implantation incision placed at the steepest corneal meridian. 3. IOL power calculation. We believe for these refractive cases the best tool is the Interferometry Biometry (JOL Master Calculation) 4. Preoperative investigation of the h ealt of the patient (diabetes, hypertension, renal diseases, etc.) 5. Signed informed consent about a RLE proced ure and it's potential complications. Complete knowledge about the procedu re and abou t the JOL to be used (multifocal, mono focal, pseudoaccommodative, etc.). Also the signed possibility of a second procedure (posterior capsulotomy, astigmatic relaxing incisions, photo refractive procedures, JOL exmange). Finally a preoperative preparation as the surgeon use to perfo rm the cataract procedu res with top ical anesthesia in the operative room. We do believe that 546 topical anesthesia must be the rule in RLE and of course in 0.7 mm MIRLEX,

A dvances in Micraphakanit far Refractive Lens Exchange (MIRLEX)

Fig . 5 : Hydrodissection trough a 0 .7 mm sideport

Fig. 6: 0.7

mm irriga-tion/aspiration system ready to go afted hydrodissection has been completed

547

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery) because the advan tage for the patient that will be able to see just leaving the operating room, the early use of eyedrops to avoid inflamatory complications and th e painless of a minimally invasive procedure. Surgical Steps

548

1. Place sterile drapes over the eye as u sual. 2. Place some eyedrops of an esthetic and give the instruction to the patient to see the microscope light always w ith this eye. If you find a photophobic patient, decrease the light of th e microscope for yo ur firs t incision, place intra cam eral lidocaine and then you can increase the intensity of your light safety because of th e effect of the intracameral anesthesia. 3. Place your self at the meridian of the eye of your implantation incision. It means that if your patient h as an astigmatism with the rule (at 180 0 or n ear) you must perform the implantation incision a t 90', so this is the place where the surgeon must seat. The irrigation-aspiration incisions will be at 3 and 9 o'clock p osition an d will be astigm aticall y neu tral. 4. H old the eye very soft with a forceps with one hand and perfo rm w ith the 0.7 mm blade the first incision at 3 o' clock position w ith the an other hand . To be sure it w ill be a self sealed incision first go d irectl y perpendicular to the cornea and before entry th e anterior chamber change the direction parallel to the iris plane. Do it with a single movem en t, and be sure not to open more your incision when you retire your blade. S. If you w ant you can p lace intracam eral anesthetic and / or ad ren ergic drugs to obtain good mydriasis. After this, fill the ante rior ch amber with viscoelastic material. The main goal of th is techniqu e is to maintain the anterior chamber always open. 6. Use th e viscoelastic cannula to hold the eye with your left h and trough this first incision. The advantage of a bim anual technique is that you can control always the eye movements with two hands during the en tire procedure. Also it avoids the use of forceps over the conjuncti va to avoid surface damage or pain sensation. 7. Une th e righ t hand to perform a second side port incision at 9 o'clock position at the same plane h old ing the eye with the viscoelastic cannula insid e the first incision . Do it in the same plane th a t the first one. Both incision must be made aprox 1 mm inside the limbus, totally over the cornea. Some of these patients are soft contact lenses users and with a lot of limbal vascularization. 8. Keep h oldin g the eye w ith the viscoelastic cannula at your left hand an d in troduce the cysti tome trough the second incision to cut the anterior capsule. Perform capsulorrhexis with cystitome or forceps trough th e second incision w ith yur right hand while holding the eye with the viscoelastic cannula with the left. If you want during th e rhexis you can switch hands to h elp your procedure; you can re-fill th e ch amber w ith viscoelastic any time you need.

Advances in Micmphakonit for Refractive Lens Exchange (MTRLEX)

Fig. 7: Nuclear material 0.7 mm bimanual aspi-

ration

Fig . 8: Cortical material 0.7 mm bimanual aspi -

ration

Fig. 9: Incisional edema and viscoelastic ext · racti on

549

Instant Clillicn i Dingllosis in Oplttlta[mo[ogtj (Refrac tive Surgenj)

9. O nce the capsulorrhexis is done (the size will depend the IOL you will use), pe rform hydrodissection and hyd rodelamiJ1ation of the nucleus . Sta rt just below the anterior capsule to seperate first the cortex from the ca psule, d ecreasing so the asp iration time, and then follow wi th epinucle us and nucleus. 10. Once yo u a re sure all the lens material has been hydrodissected yo u p repare to insert the 0.7 mm irrig ation / asp iration cannulas. Be sure of

yo ur forced infusion; we use l30 to 160 cm of H 20 for possiti ve pressure w ith the 700 microns system. We suggest also, high va cuum levels (400 mmHg) with this system because the small diam eter of the aspirating cann ula. YOll mlist test these parameters before en ter the an terior chalnber otherwise this system will not work properly. 11. Introduce the irrigating 0.7 mm cann ula first wi th the irrigation on. You can introduce your irrigation d irectly to the nucleus to complete separate the layers of it. A small amount of viscoelastic mate rial can fluid trough the incisions. Then introduce the 0.7 mm aspiratin g cannula trough the second sid eport. 12. Con trol your aspirating force with the footpeda!. Go first for the nucleus, then the epinucleus and finally the cortical materia!' There is not need to move so much your hands; if you have your correct parame ters the hydrodynamic forced will do the surgery for yo u. Just be su re to aspirate nea r the iris plane to avoid the posterio r capsule. l3. With the same 0.7 mm cannula you can pulish the posterior and an terior I

ca ps ule after the cortical material has been rem oved.

14. Take out the aspirating cannula keeping the irriga ting one inside the eye and with continuous irrigation to keep the an terio r chamber w ide open.

Sw itch w ith your ri ght hand from the as pira tin g cannula to the viscoelastic material and introduce it trough the aspirating incision. Slowly fill the anterior chamber with viscoelastic and stop the irrigation. O nce your anterior chamber is totally fill wi th viscoelastic you a re able to take Ollt the irriga ting cmmula. This maneuver will help yo u to keep an anterior chamber formed all the time. 15. Now you ca n d o your implantation incision at the meridian you need. Do it clea r cornea, in two steps just like ti,e side ports, w ith an exact size of yo ur blade according your implant, and holding the eye w ith your left hand trollgh your irrigating side po rt w ith the viscoelastic cannula in orde r to avoid forceps. 16. Do your IOL implantation and remember that you have two side ports to help you to manipulate the IOL. 17. Perform hydratation of the cornea with pressu re enollgh to take out the v iscoelas ti c mate rial. Do not aspirate the viscoe las tic, you can hav e an

wlestab le anterior m amber after this; just with the pressure of a 10 cc syringe yo u can hydratate the peri-incisional strome and take out the 550

viscoelastic material at the same time.

Advances in Microphakollit for Refracti ve Lens Exchange (MIRLEX) 18. Place a soft bandage contact lens, some intracameral antibiotic and you

are ready to go. Avoiding Complications

Most of the complications become when the teclmique is done improperly. • Inap ropiate wOlmd construction will lead to lickeage and surge. In this case the best solution is to close this wound with stromal hydratation and perform another. • Bad programmation of parameters. For 700 microns teclmique Forced Infusion is mandatory; gravita tory force will be never enough to fill the anterior chamber and avoid surge. It is also mandatory because high vac uum levels are also mandatory to be able to aspirate trough 700 microns aspirating cannula. • Unexpected eye movements are easy to avoid uting the viscoelastic carmula as a stabilization instrument with the left hand while performing maneuvers with the right hand. Be sure to perfor "bimanually" almost all our maneuvers; it is one of the main advantages of the technique. • Inappropriate instrumentation; be sure to have 700 microns system. At the time of writing this chapter only the Duet system from Microsurgical Technology (MST) is avaliable. • Inappropriate hydrodissection; be sure to perform it many tin1es. The clear lens is soft so if you perform vigorous hydrodelamination, your aspirating time will be reduced and your movements inside the eye also will be less. Be sure to aspirate fa r away from the corneal endothelium, posterior capsule and iris in order to avoid damage to intraocular structures.

• Learn to use your both hands; it is a bimanual technique and also minimally invasive. You have the advan tages that the eye is always in your control, so there is not need to perform "one ha nd maneuvers"; also you have the advantage to have an "always formed " anterior chamber. Learn to switch your instruments between both hands in order to take the maximum advantage from a "no-collapse technique". • If posterior capsule is broken follow this steps: 1. Keep with the irrigating cannula inside the eye w ith the irrigation on, but decrease the irigation force to 100 cm H 20. 2. Take out the aspirating cannula with your right hand and switch it fast for your vitrectomy system . If it is not ready, fill the chamber with viscoelastic trough yo ur as pirating sideport before take out the irrigating cannula. 3. Yo u might need to enlarge to 1 mm the aspira ting incision because your vitrectomy system can be larger that 700 microns. 4. Perform bin1anual vitrectomy with 100 em H 20 of irrigation force, 800 cuts per minute and 200 to 250 mmHg of vacuum, keeping the system 551

Instant Clinical D iagnosis in Oplttlwl111ologtJ (R efractive SlI rgenJ)

closed. It is your main advan tage, a bimanual vitrectomy in a closed chamber. 5. Take out your vitrector while keeping the irrigation on and fill the anterior chamber with viscoelastic material trough your aspirating port. Do not stop and take out the irrigation cannula until you are sure your eye is filled with viscoelastic. 6. Avoid the vitreus from the incisions and place your IOL in the sulcus. Use miotic intracameral medication to be sure there is not vitreous trough the incisions. Postoperative Care The postoperative care of your patient will be easy if the technique was done properly. It will include anti-inflammatory, antibiotic and anti-hipertensive eyedrops since the first day. The bandage contact lens can be retire the day after the surgery. MOnitoring the intraocular pressure is key; you have access to the anterior chamber trough the side port incisions at the slit lamp any time during the inmediate postoperative period to decrease ultraocular pressure if needed; it is another advantage of a bimanual technique. The refraction w ill be very stable d uring the first 4 to 6 weeks; remember that your implantation incision was made only for this purpose, implantation; no other maneuver has been done trough this incision (like exposure to ultrasonic power, enlargament in two planes), so it will be very stable soon. The side port incisions are astigmatically neutral so you will be ready to obtain a final refraction very soon and decide if you need an aditional refractive proced ure. Your patient will feel like a LA5IK patient; a 10 minute procedure done under topical anesthesia and inmediate visual recovery. So you have to be in communicaton and make see him or she that it was an intraocular procedure and must be taking care in the postoperative period. Final Comments The main goal, and also the main advantage of this technique, is to keep an anterior chamber w ide open all the time, in a closed env ironment. The no surge

and no collapses technique has many advantages: • 0 endothelial cell damage. • Maneuvers far away from the posterior capsule. • No vitreous movement: this is of particular importance in the miopic patient where a collapse can be the key to a retinal detachment. • Always you have a positive pressure avoidulg choroidal effu sions • Wide open pupil because there are not changes in intraocular pressure that can produce miosis. 552 • a flat chamber even in case of vitreous loss.

A dv ances ill Microphakonit for Refractive Lens Exchallge (MIRLEX)

The forced infusion (positive pressure), also manda tory, has many ad vantages: • Wide anterior chamber; this is of particular importance in the hyperopic patient where the anterior chamber is too shallow . • Tense and "far away" posterior capsule. The reader, and new bimanual surgeon, can think that the forced infussion can lead to a lot of irrigation inside the eye, but you will experience that the entire surgery is done with less that 100 cc of intraocular solution with this 700 microns system. In fact with the time, when you currently perform this technique fo r all yo ur RLE patients, you will see that no more than 50 to 60 cc per case will be need. We do believe that this is a very safe technique for your RLE patient; it also is a ve ry safe technique fo r the surgeon, it is relatively easy and reproductible, so he or she can be su re that the patient is doing fine. The surgeon ca n sleep well.

553

53 Blue light Filtering Intraocular lenses Swati Phuljhele, Lalit Alok, Anand Agarwal, Tanuj Dada (India)

Ultraviolet (UV) radiation comprises invisible high energy rays (200-400 nrn) from the sun that lie just beyond the blue end of the visible spectrum. Violet (400-440 nm) and blue (440-500 nm) light comprise the shorter wavelength part of the visible spectrum. The UV radiation present in sunlight is not useful for vision. There are good scientific reasons to consider that UV absorption by the eye may contribute to age-related changes in the eye and a number of other serious eye diseases. UV-RELATED EYE DISEASES

Ultraviolet radiation has a contributory role to play in the development of various ocular disorders such as cataract, pterygium, cancer of the skin around

the eye, photokeratitis and corneal degenerative changes, solar retinopathy, and may contribute to age-related macular degenera tion. The bright illumination of ophthalmic instruments, such as the indirect ophth almic instruments may also cause retinal damage. There are several evidences to suggest that wavelengths between 350 nrn in the UV spectrum and 441nm in th e visible spectrum are potentially the most dangerous in causing retinal photo toxicity, which can lead to or accelerate age related macular degeneration. There is now considerable evidence that it is the loss of retinal pigment epithelial cells that leads to second ary photoreceptor cell degeneration in AMD. The most pronounced aging chan ge in the retinal pigment epithelium (RPE) is the acc umulation of a fluorescent material that constitutes the lipofuscin of the cell . This increased accumulation of the photosensitiser lipofuscin may impair free radical control mechanisms leading to apop tosis. A major fluorophore of RPE lipofuscin, the compound A2E, is maximally excited by blue light of the spectrum and has been shown to be capable of mediating b lue light damage.

554

Blue Light Filterillg Intraocular Lellses 13.0

6.0

1 Fig. 1: AcrySof SN60AT

Fig . 2: Hoya® AF-1 UY

555

Instant Clinical Diagnosis in OpJrtllalm ologtJ (R efractive SlIrgenJ) PROTECTIVE MECHANISMS IN THE HUMAN EYE

The human eye has its own naturally protecting mechanisms like pupil constriction, lid squinting, and eye mo vements. An essential component of an eye's light filtering system are the cornea and crystalline lens. The cornea protects from UV radiation shorter than 300 nm while the crys talline lens blocks most UV radiation between 300 nm and 400 nm. The age related nuclear sclerosis causes yellowing of lens thereby attenuating blue light. Removal of the cataractous lens in elderly patients followed by implan tation of an IOL that does not attenuate blue light may leave RPE cells v ulnerable at an age when their conten t of blue light sensitive lipofuscin is the highest. This has led to the development of an IOL that can block UV as well as short wavelength blue-violet light. The first PMMA intraocular lenses transmitted UV light Ul addition to visible light. The incorporation of UV blocking chromophores began in 1986. The introd uc tion of IOLs blocking visible light (blue-violet spectrum) is the latest developmen t Ul the field of cataract surgery. MECHANISM OF ACTION OF FILTERING IOLs

These IOLs consist of polymers (ch romophores) that are photochromic and are capable of filtering at least a portion of blue light incident thereon. The photochromic and light-filtering property of the polymers is activated by light havulg wavelengths in the blue range, i.e., from about 400 nm to abou t 500 nm. Upon being activated, the polymer also absorbs, thus filters out, a portion of incident light having different wavelengths Ul the blue range. In one aspect, the polymer is also capable of fil tering at least a portion of UV rad iation (i.e. radiation having wavelengths in the range from about 180 nm to about 400 nm) incident thereon. TYPES OF FILTERING IOLs

1. UV only blocking IOLs-block only the UV rays and transmit the blue

556

light which is potentially harmful to retina, e.g conventional lOLs. 2. UV + blue + violet blocking IOLs-these lenses block UV ra ys as well as shortwave lengths of visible spectrum. These lenses provide complete photoprotection but at the cost of scotopic vision; e.g Ac rySof® Natural IOL, AcrySof ® IQ IOL, Hoya® AF-l UY. 3. UV + violet blocking IOL-these lenses block the UV rays and violet rays. They p rovide less photoprotection than the above group but the scotopic vision is better, e.g AMO® Optiblue.

Blue Light Fiiteri"g r"traocular Lellses AcrySof Natural® lOL SN60AT®, Alcon laboratories, was the first one to be introduced in this category. The lens is made up of hydrop hobic acrylic with UV light and blue light chromophores. Rodriguez-Galietero A et al compared the AcrySof Natural IOL (SN60AT) w ith AcrySofSA60AT in diabetic patients and concluded that the AcrySofNatural IOL provides better contrast sensitivity than the AcrySof SA60AT. The blue-light filter of the AcrySof Natural IOL did not cause chromatic discrimination defects based on total error scores and improved color vision in the blue-yellow chromatic axis in diabetic patients. Cionni compared color vision in patients with bilateral AcrySof Natural IOL implants with bilateral AcrySof single-piece UV-blocking lenses using the Farnsworth IOO-hue magnetic color perception test and fowld no difference in color perception between these groups. There was also no inlpact on color perception if the patients Wlderwen t implantation with the AcrySof Natural IOL in 1 eye and the AcrySof single-piece lens in the other. This lens is now modified to accommodate a special featu re in the form of a posterior aspheric surface and is now available as AcrySof ®lQ lOL SNWF®. The multifocal version of the lens is available in form of AcrySof® ReSTOR® natura llOL. Hoya® AF-l UY is a high quality UV-absorbent single-piece acrylic foldable intraocular lens. This lens uses a safe and uniform soft acrylic resin for the optics; the PMMA haptics are specifically designed to be stable within the capsule. TI,e yellow-filter is incorporated into the acrylic material. Hoya AF-1 UY admits natural color tones sinlilar to the human crystalline lens. It protects the retina by absorbing UV-light and a part of visible short wavelength light. AMO® Optiblue is a violet blocking [OL that provides less photoprotection than the blue light blocking lens but a better photoreception. CLINICAL USE

Age-related macular degeneration and diseases affecting macula like diabetes are the major indications for the implantation of blue light filtering IOLs. A few recently published clinica l trials have evaluated the efficacy with regard to the blue filtering IOLs vis avis the standard hydrophobic acrylic lenses. Mayer S et al did an intraind ividual comparison in 14 patients of the contrast sensitivity Wlder mesopic conditions with one eye being implanted the AcrySof na tural IOL and the other eye the conventional AcrySofIOL. They reported no significant differences in contrast sensitivi ty under different lighting conditions using the FACT test (Functional Acuity Contrast Test). A projected cost benefit analysis in preventing the potential treatment of ARMD

557

Instant Clillical Diagnosis in Opll tllalmologt) (Refractive Surgen)

developing after cataract surgery was recently published by Redd y P et a1. Estimated savings with blue light filtering IOLs per 100 eyes were $4275, $29997, and $111 734 in the 55 to 64-year-old, 65 to 74-year-old, and >or= 75year-old cohorts, respectively. They d id acknowledge the current limitations with regard to the lack of proven evidence against AMD protection. Moreover the data used for the model were derived from the animal and lab studies that may not be d irectly extrapolated onto human beings. But these cost benefits analyses w ill no doubt be increasingly coming to clinical practice in the future especially in resource poor countries like India especially while formulating public health policies on the management and prevention of AMD as tl1e life expectancy of the people here also increase with improved health resources. LIMITATIONS

The most important draw back of blue light filtering IOLs is the red uced scotopic vision. The data regarding scotopic contrast sensitivity as of present is controversial with different authorities having different opinion on the issue. IOLs blocking UV and blue light reduce the phototoxicity but they also reduce the light reaching the photo receptors, especially the 5 cones, and rods which are best stimulated by short wavelength light. As a result the scotopic vision in these eyes is affected. Moreover these are the eyes that already have compromised rod function due to age-related photoreceptor degeneration. This may add to the disability of night vision in such patients. Mainster MA compared the various types of IOL in his study and he concluded that UV, violet and blue light are responsible for 67%, 18% a nd 14% of UV-blue photo toxicity, respectively, in the spectral region from 350-700 nm where optical radiation can potentially reach the retina of a pseudophakic eye. The violet light blocking IOL provides better aphakic scotopic photosensitivity. However, in a recent clinical study on scotopic contrast sensitivity with the use of blue filtering IOLs, Schwiegerling J et al reported a 52% in1provement in light entering the eyes in pseudophakic patients in scotopic cond itions. The apparen t discrepancies between the recent and the previous clinical studies comes from the da ta interpretation of the rod spectral sensitivity curves in phakes and aphakes/pseudophakes, there being no internationally accepted standards that are ava ilable for aphakes/ pseudophakes.

558

Bille Light Filtering Intraocular Lenses CONCLUSION

All the above lenses are still under trial, and while a few early reports regarding their performance are available, their long term follow up effects are yet to evaluated and reported. Their will be ongoing clinical evaluation with regard to the efficacy both in terms of reducing the incidence of AMD after cataract surgery with the use of new blue blockulg [OLs vis a vis the apparent reduction in mesopic contrast sensitivity. The present studies are limited with regard to the linUted follow up, small series of patients in which these IOLs have been inlplan ted, the confounding effect of p upil size on retinal illuminance, and optimal methods of data acquisition rega rding light transmittance by these IOLs. The future studies will also have to address the issues of posterior capsular opacification in degrading the optical qualities of these IOLs especially under low illuminance conditions. Further prospective studies are required before these IOLs become accepted as the standard method for optical rehabilitation after phacoemulsification.

559

54 Refractive lens Exchange: Current Perspectives* I Howard Fine, Richard, S Hoffman, Mark Packer (USA)

The treatment of presbyopia has many suboptimal modalities including progressive-lens spectacles, bifocal contact lenses, monovision IOLs, and conductive keratoplasty. There are also investigational modalities including scleral implants, multifocal excimer ablation and corneal inserts. In 2001, my partners and I published a paper documenting that we could, with power modulations, reduce the energy input into the eye to a tenth of one percent of previously used levels, remove all grades of nuclear density cataracts, and still have dramatic improvements U1 visual outcomes, as n oted by very high levels of totally clear corneas and uncorrected visual acuities of 20/40 or better in the immediate, two to 24 hour, postoperative period. Th is stud y also documented that uncorrected visual acuities were inversely proportional to the amount of energy introduced in the course of cataract surgery: the lowest levels of energy resulted in the best levels of uncorrected visual acuities, independent of patient age or cataract density. We subsequently surveyed all of the new phacoemulsification technologies and showed tha t once again, w ith utilization of these technologies, we had dramatic further improvements in outcomes. We have also refined our technique for refractive lens exchange in clear lenses and soft catarac ts. The procedure is performed under topical anesthesia after appropriate informed consent, preoperative measurements for IOL determina tion, and preoperative dilation and antibiotics. A Mastel Para trap d iamond keratome (Mastel Precision Surgica l Instruments, Rapid City, sD) is utilized to create two 1.2 mm clear corneal incisions 30-45° from the temporal limbus (60-90° from each other). One-half cc of non-preserved lidocaine 1% is instilled U1to the anterior chamber followed by comple te expansion of the an terior chamber wi th Viscoat®. A straight 25 gauge need le is then inserted through the

560

·This chapter is a combination two articles. The fi rst was originally published in 2004 in the Journal of Cata ract and Refracti ve Surgery (v . 30:550-554), and the other was submitted for publication in the Journal of Refracti ve Surgery in April of 2006 .

Refractive Lens Exchange: Curren t Perspectives

Fig. 1: Left-handed 1.2

mm

clear

corneal

mic roinc ision placed

45° from the temporal limbus utilizing a Mastel Paratrap diamond knife

Fig. 2: A straight 25

gaug e nee dle beg ins the capsu lorhexis by perforating the central

anterior lens capsu le wh ile simu ltaneously

lifting a flap edge

Fig . 3: Capsulorhexis

formation utiliz ing an AS ICO microinc ision

capsulorhexis forceps

561

Instant Clinical Diagnosis in Ophthalmologtj (Refractive Surgenj)

right-handed microincision to perforate the central anterior lens capsule while simultaneously lifting a flap edge to begin a capsulorhexis. Needles routinely bent at the tip for conventional capsulorhexis initiation have been found to lacerate the roof of the microincision during withdra wal of the needle. The straight unaltered 25 gauge needle is less likely to result in this complication. After removal of the needle, a capsulorhexis forceps, specially designed to fit and function through a 1mm incision is then inserted through the same incision and used to complete a 5-6 mm rhexis. Cortical cleaving hydrodissection with decompression is then performed in two separate dista I quadrants followed by a third row1d of hydrodissection to prolapse the entire lens or at least one-half of the lens out of the capsular bag. The microincision irrigating handpiece is placed in the left-hand incision and the unsleeved phaco needle is inserted through the right-hand incision. Lens extraction is then performed in most cases without phaco power, utilizing high levels of vacuum while carouselling the relatively soft lens in the plane of the iris until it is consumed. Small amounts of ultrasound energy can be utilized when needed. Care should be taken to avoid directing the infusion flow towards the phaco needle tip so as to prevent dislodging nuclear material from the tip. While maintaining infusion with the irrigating handpiece, the phaco needle is removed and the aspiration handpiece is inserted to remove residual cortex and polish the posterior capsule. If subincisional cortex is difficult to extract, the 1/ A hand pieces can be alternated between the two incisions in order to gain easier access to the subincisional capsular fornix. Once all cortex has been removed, the aspiration handpiece is removed and viscoelas tic is injected into the capsular bag and anterior chambe r while withdrawing the irrigating handpiece. Following this, the viscoelastic cannula is removed from the eye and a new 2.5 mm clear corneal incision is placed between the two rnicroincisions for IOL insertion. After IOL insertion, stromal hydration of the 2.5 mm incision is performed to assist in it's self-sealing. Bimanual 1/A is performed to remove all viscoelastic. The aspiration handpiece is then removed and irrigation of the anterior chamber maintained. Stromal hydra tion of the empty incision is performed to assist in closure of the microincision. The irrigation handpiece is then removed followed by stromal hydration of that incision. In this manner, the eye is fu lly formed and pressurized throughout the procedure avoiding h ypotony and shallowing of the anterior chamber. We investigated laser phacoernulsifica tion and although we achieved excellent results, we realized tha t we were limited to very soft nuclei. We used equivalent or greater levels of energy than ultrasound with modulations. We 562

Refractive Lens Exchange: Current Perspectives

Fig .

4:

The

duet

system (MST micro su rgical technology ) beveled irrigating handpiece within the left handed microincision

Fig. 5: The solt lens is carouselled in the iris plane and consumed utilizing high vacuum levels . Forward movement of the lens is prevented with the irrigating handpiece

Fi g. 6: Subincisiona l cortex is easily removed using the duet system (M ST) bimanua l irri gation and asp iration handpieces (Note the effective phaco time EPT = 0 and average percent phaco power AVG = 0 following lens

removal)

563

Instant Clinical Diagnosis in Ophtlwllllologt) (Refractive SIII'gen))

put three times as much fluid through the eye and the surgeries took two to three times as long as ultrasound phacoemulsification w ith power modulations. As a result, at this time, laser phacoemulsification is no competition for ultrasound. Based on these stud ies, we concluded that cataract / lens extrac tion is incredibly safe and efficacious. In 2002, we published a paper in which we described our participation in the FDA-monitored stud y of the [OL Master documenting that partial coherence interferometry was as accurate as immersion ultrasound axial length measurements, using the Quantel Axis-II system. The coefficient of correlation of these two modalities was .996. During that study, we documented fully that 48% of our patients outcomes achieved precisely the spherical equivalent for which were aiming, 92% were within a quarter of a diopter of the desired spherical equivalent, and the mean absolute error was 21 diopte rs. This leads us to conclude that preopera tive measurements and calculations today allow for excellent results and continue to improve. Improved cataract surgery outcomes as a result of lower energy, smaller incisions, and adjunctive astigmatic techniques with increased accuracy and safety, has lead to an evolution of lens surgery into refractive surgery. We also have to recognize that corneal refracti ve surgery has certain limitations. These include high hyperopes, higher myopes, patients with thin corneas and with cataracts, and also presbyopes. We also have to recognize that spherical aberration remains stable in the cornea but increases in the crystalline lens with increasing age. Anything that is done to the cornea as a refractive surgery modality will degrade over time as the spherical aberration in the human crystalline lens changes. When we look at the available IOLs for refractive lens exchange, we realize that options are becoming increasingly larger in number and better in what they offer. New lenses include the eyeonics crystalensT>' (Aliso Viejo, CAl which is the first accommodative IOL that has become available in the United States. With its improved 3600 square posterior ed ge and ability to be injected through a 2.5 mm incision, this is an extremely attracti ve option. One hundred percent of our patients in the FDA-monitored stud y who were binocularly implanted with the crystalens'" were at least 20/30 or better at all distance and 71 % were 20/20 or better at all distances. Figure 10 demonstrates the stability of these results over three years.

We have noted, however, that 15.7% of our patients, all of whom were hyperopes, were more than one diopter from the desired spherical equivalent. 564 We believe this is related to an inability to predict the final position of the optic

Refractive Lens Excha1Jge: Current Perspectives

FItiEBI MAHUAd

Fig. 7: Viscoelastic is injected into the capsular bag while maintaining infusion with the irrigating handpiece

Fig . 8: The eyeonics crystalensTM SE

565

Instant Clinical Diagnosis in Ophthalmology (Refractive Surgery)

within the eye. A small capsular bag w ill compress the haptics and result in a more posteriorly located optic, resulting in hyperopia, and a large bag will compress it less resulting in an anteriorly located optic, which will result in myopia. We enhanced all of these patients with excellent results by implanting a piggybac k IOL in the ciliary sulcus which is quite far in front of the crystalensT>l and does not appear to impede the mechanism of accommodation of the lens. We have completed quality of life surveys on our crystalens'" patients and ha ve found that spectacle independence is achieved in 73% of our patients and that is exactly the percentage of our patients that were at least 20 / 25 or better at all d istances. This mirrors the experience we have had earlier with the Array Multifocal IOL (Advanced Medical Optics, Santa Ana, CAl. In that group of patients, 44% were at least 20 / 25 or better at all distances and that is the exactly the same percentage of patients who were spectacle independent. This may be what Richard Lindstrom, MD, has previously indicated as 20/" happy", that visual ac uity that will allow for complete spectacle uldependence. Other lenses that move in the eye include the Kellen TretraFlex (Lenstec, St. Petersburg, FL) and the HumanOptics I CU (HumanOp tics AG, Erlangen Germany), both of which ha ve been tested in Europe, but we have had no experience within the United States. Other accommodative IOLs include dual-optic IOLs. The first that has come to clinical studies in the United States is the Visiogen Synchrony'" dual-optic IOL (Irvine, CAl. This is a lens with a minus-powered optic loca ted against the posterior capsu le attached by flexible haptics to a plus-powered optic located more anteriorl y within the capsular bag. The flexible haptics allow for greater separation between the two optics during accommodative effort on the part of the patient. This is essentially a Galilean telescope and theoretical evaluation of dual-optic lenses promises greater amplitude of accommodation than singleoptic lenses that move in the eye. The early data for the Synchrony'" [OL has been good. This lens is also injectible through a 3.5 mm incision by a new injection system. Perhaps the most promising technology for increased amplitudes of accommodation in accommodative [OLs is deformable optic [OLs. The Power Vision [OL (Power Vision, Santa Barbara, CAl has a reservoir that allows for fluid to be stored there during relaxation of accommodation. The fluid is pumped into the central portion of the lens during accommodation, resulting in a greater curva ture of the optic and a greater plus power. One of the most exciting technologies is the NuLens Accommodating 10L from Herzliya, [srael. The manufacturers of this lens beUeve that at least eight 566

Refractive Lens Exchange: Current Perspectives

Uncorrected distance, intermediate and near vision n = 24

100% 90% 80%

80%

70%

70.8%

60% 50% 40%

30% 20% 10% 0%

100%

~

r--r--r--r---

L-

r--r--r--r--r--r--r---

I-I-I-I------c

0151.20/20 or

0151.20/25 or

DISt.20/32 or

better better better In!. J1 or better Int. J2 or better In\. J3 or better Near J2 or Near J3 or Near J1 or

better

better

better

Fig. 9: Results for binocular implantations of the crystalens at Drs Fine, Hoffman and Packer as part of the FDA-monitored study

III] 100% 90%

Distance

0 Intermediate

80% 70%

et-t--

40% 30%

II-

20% 10% 0%

t-20/25 or better

I

1'-(1

~

60% 50%

o Near

20/32 or better

lt-t--

-

-

;i

l: :. l,'i

lll-

-

20/40 or better

Fig. 10: Three results of binocular implantations of the crystal ens

567

Instant Clinical Diagnosis in OplltilalmologlJ (Refractive Surge,y)

568

diopters of accommodation are required for comfortable, continuous activity: one diopter for adjustment of the far plane, three diopters for near and an accommodative amplitude of twice tha t, resulting in a need for eight diopters of accommodation in order to avoid accommodative fatigue. The lens is based on a naturally occurring system of deformable optics which is present in the Merganser. This is a bird that flies but also fishes for food and is able to see under wa ter by forcing the an terior surface of the lens thi'ough a stiff pupil, resulting in a marked increased curva ture of the lens. The N uLens is essentially built by putting a comp ress ible pol yme r between two firm p lates . Accommodation results in a p ressing of that polymer through the aperture in the anterior plate and an increased curvature, which theoretically can give up to 30 diopters of accommodation. The Flex Optic, by Quest Vision Technologies (Tiburon, CAl, is now licensed by AMO. It has a plus-powered optic that changes shape on accommodation in addition to moving forward. The hap tic is a balloon configuration and depending on the refractive index of the material, there is anywhere from 3.3 diopters of accommodation to 4.5 diop ters of accommodations. In addition, there are several injectible polym er TOLs on the horizon . The most promising is the Smart TOL (Medennium, Inc., Irvine, CAl, which is a hydrophobic acrylic that is designed to completely fill the capsular bag so there w ill be no decentration or edge effects. It is con ve rtible, at roo m temperature, to a stiff rod and when it is implanted through a small incision into the eye, the thermodynamically active material reconstitutes to its original, size, shape, and dioptric power. At body temperature, it is a very flexible polymer an d with a high refrac ti ve index, has a large amplitude o f accommoda tion. This lens also has the advantage of being a stable gel so that if a YAG laser caps ulotomy became necessary, it could be perfo rmed because the lens would not extrude into the vitreous cavity. A new and unu s ua l solution is th e LiquiLens (Vision Solution Technologies, Rockville, MD), which is a lens that has a fluid filled central aperture contain.in g two inuniscible liquids, one wi th a lower refractive index that fill s the p upillary space with the patient in an upright posi tion, and a higher refractive index fluid above that. When the patient tilts his head down, as for reading, there is a redistribution of the polymers so that some of the highrefractive index falls within the pupillary space and allows for a more pluspowered lens. Light adjustability, as in the Calhoun lens (Calhoun Vision, Pasadena, CAl, is a technology that may be applicable to all other IOLs, either in the form of thin lens that can be piggybacked on top of o ther IOLs, or with an incorpora tion of the photosensitive rnacromers into o ther lenses.

Refractive Leus Exchn nge: Curreut Perspectives

Intended v achieved correction Crystalens, n = 83

8 c 6 0

:u~

5v

">

4

~

~

:E

~

•

2

0

v ..: -2 -4

-6

-8

-10

-

-8

-6

-4

-2

o

2

4

6

8

10

Intended correcti on , 0

Fig . 11 : Scatterplot of intended versus achieved spherical equivalent for implantations of the crystalens™

Summary of Visiogen Synchrony ™ Dual -optic IOL Clinical Data

Feb 2005 - Synchrony (24 yea",) BCVA 20/40 or better

DCNVA 20/40 or better

6 Months 100%

(24 /24 ) 96%

(23/24 ) Defocus curve

3.22 D

Fig. 12 : Summary of six month data for the Visiogen SynchronyTM dual-optic IOL

569

Instant Clinical Diagnosis in Oplltl/almologt} (Refractive Surgery)

An interesting new technology from Medennium (Irvine, CAl is the Photochromatic Matrix IOL, which would be a blue-blocking IOL under high levels of UV light, but would rever t bac k to a clear lens under scotopic and mesopic conditions of illumination. Finally, the Vision Membrane (Vision Membrane Technologies, Carlsbad, CAl has multiorder diffractive optics and, like other anterior chamber multifocal IOLs, is capable of being implanted into the anterior chamber of people who are already monofocally implanted pseudophakes, seekin g relief from presbyopia. It is essential to emphasize that new phacoemulsifica ti on and IOL technologies are expandu1g at a rapid rate, and that an y alterations to the cornea for refraclive purposes will be compromised by changing spherical aberration of the crystalline lens as the patient ages. This leads us to conclude that refractive lens exchange will be the dominant refractive procedure of the ftl ture and addresses all components of the patients' refractive errors, including presbyopia. Today, children with refractive errors wear spectacles, teenagers and young adults wear contact lenses, older young adults get refractive surgery, middle aged adults wear bifocals, and senior citizens undergo cataract surgery. We believe that tomorrow, children will wear spectacles, and teenagers, contact lenses, but the groups that today undergo corneal refractive surgery, wear bifocals and undergo cataract surgery will all opt for refractive lens exchange. This represents a quadruple-win. Patients can enjoy a predictable refractive procedure with a rapid recove ry that addresses all types of refractive errors including presbyopia and never develop cataracts. That is a significant advantage because of the changing spherical aberration in so-called clinically inSignificant cataracts. The second w in is that surgeons ca n offer these procedures w ithout the intrusion of private or government insurance and establish a less disruptive relationship with their patients. The third w in is that ophthalmic ind ustry can anticipate profits fr om their research and regulatory expenses which can further expand the emerging IOL technology. FU1ally, the government can enjoy the decreased financial burden from their number one health care expense, cataract surgery, for the ever increasing ranks of baby boomers as more and more of these patients opt for lens exchange to address their refractive goals, ultimately reaching Medicare coverage as pseudophakes.

570

Refractive Lens Exchange: Current Perspectives

Sychrony TM Most Recent Patients (29 eyes at 3 months)

Distance VA Best corrected 20/40 or better

100% Fig. 13 : Best corrected near and distance visual acuities for

Near VA Distance corrected 20/40 or better 93%

the most recent implantations of the Visiogen SynchronyTM Dual-optic IOL

=~

Single Lens with Dynamic Optic

Power Vision IOL ••

[

,

!'

' Incorporates new "applied micro fluidic· technology in a single piece IOL ' Upon accommodative stimulation, micro fluidic pumps reversibly alter radius of curvature, affecting anincrease in IOl power for near vision purposes

Side view

Input reservoir

Actuator

J~ ,

Non- Accommodated <

CD

>

Accom modated

Fig . 14: Schematic of the power vision IOL

Fig . 15: Illustration of the physica l principle behind the NuLens accommodating IOL: The Merganser

571

II/stallt Clillical Diagnosis ill OphthalmologtJ (R efractive SlIrgenJ)

Fig. 16 : Schematic of the FlexOptic tOL

Rigid rod (at room temp)

Changing to lens (at body temp)

Soft gel lens (at body temp)

Fig . 17: Schematic drawing of the concept of the Smart IOl

572

Refractive Lens Exchange: Current Perspectives

Fig. 18: Demonstration of the physical principles underlying the UquiLens

Fig. 19: The vision membrane phakic IOL

573

55 Advances in Optic Designs to Reduce peo Wolf Buehl, Oliver Findl (Austria)

INTRODUCTION

Posterior capsule opacification (PCO, or after-cataract) re mains a common problem after cataract surgery with implantation of an intraocular lens (IOL). It resulted fro m the transition from intracapsular (ICCE) to extracapsular cataract extraction (ECCE), where the posterior lens capsule is left intact during surgery. Patien ts with PCO suffer from decreased visual acuity, impaired contrast sen sitivity and from glare d isability. Clinically, two different components ofPCO can be differentiated, namely a regenera tory and a fibrotic componen t. Regeneratory peo is much m ore common; it is caused by residual lens epithelium cells (LECs) from the lens equator region m igrating and proliferating in the space between the posterior capsule and the IOL, forming layers of lens m aterial and Elschnig pearls. Fibrotic PCO is caused by LECs from the an terior capsule that undergo transform ation to m yofibroblasts and gain access to the posterior capsule, ca using whitening and w rinkling of the capsule. This can lead to decen tra tion of the IOL and hind er visualization of the peripheral retina. Both components of PCO lead to a decrease in visual function when they affect the central region around the visual axis. PCO can easily be treated by Nd:YAG laser capsulotom y, however, this may lead to other complications, including an increase in intraocular presstue,

ocular inflammation, cystoid macular edema, and retinal detachinent. Besides, Nd:YAG laser capsulotomy does not improve visualization of the peripheral retina, increases the costs for cataract treatment, and is not available in large

parts of the developing world. Therefore, many efforts are mad e to prevent the formation of PCO. These efforts include mainly modifications in lens design and material as well as modifications in surgical technique, but also application of drugs, and others. While there is curren tly no commonly used surgical technique and / or d rug which would lead to a significan t reduction in PCO, the development of new IOL m odels in order to redu ce PCO has made significant progress. OPTIC EDGE DESIGN

574

During the past years it has become obvious that optic edge d esign plays an important role in the p revention of PCO. When the AcrySof MA60BM lens

Advances in Optic Designs to Reduce pea

Fig. 1A and B: Mechanism of the optic edge barrier effect. (A) An IOL with both anterior and posterior round optic edges allows lens ep ith elial cells to migrate and proliferate on the posterior capsule. (6) In an IOL with a sharp posterior optic edge, the capsular bend which is created at the sharp optic rim leads to contact inhibition and/or mechanical pressure between JOL and capsule

Fig . 2 : Intra -individual comparison of round and sharp optic edges in an acrylic IOL. Retroillumination image of a round edge (left) and sharp edge (right) acrylic. IOL 2 years after surgery. Right and left eye of the same patient; both IOLs differ only in optic edge design

575

Illstallt Clillical Diagllosis ill OphthalmoloSIj (R efra ctive Surgery)

(Alcon Labora tories, Inc., Fort Worth, TX) was introd uced in the early 1990s, several stud ies showed that peo development was Significantly less than with other IOLs. First, this was attribu ted to the acrylic material and to the surface properties of the IOL. Later it could be shown that the sharp edge design of the lens seemed to be the key factor for this effect. The sharp IOL edge was a result of the man ufacturing p rocess, and its effect on lens ep ithelial cell migration, therefore, rather coincidental. Further studies confirmed that the rectangular shape of the IOL rim w ith its sharp edges, in combination with the acrylic material, was in fact the main reason for the reduced formation of peo. Studies by Nishi revealed that the d iscontinuous capsular bend seems to be a key factor fo r the preventative effect of a sharp edge optic. There are two major theories to explain the barrier effect at a sharp posterior optic edge: The capsular bend at the posterior optic edge may cause mechanical pressure at the posterior capsule and /or it leads to contact inh ibition of LEe growth on the posterior capsule. The "fusion" process of the capsular bag at the IOL optic edge was also doc ume nted in studies by Sacu et al. lt is caused by contraction of the lens capsule in the first postoperative days and weeks, depending on the IOL type ("capsular sealing"). Anterior capsule fibrosis and a circumferential IOL / rhexis overlap have been shown to be important factors for this sealing process. As a result of these findings, several new IOLs w ith a sharp optic edge design were introduced in the past yea rs and compared in clinical trials . However, with some exceptions, most of these trials were not randomized or compared IOLs d iffering not only in edge design but also in IOL material. As the effect of the optic material on peo growth remains unclea r, the exact reason for lower /higher peo rates with certain IOL types could not be determined in many of these trials. 111erefore, a number of studies varying only one parameter (either optic edge design or optic material) were performed also by ow- group. In one of these studies we compared 2 acrylic IOL types differing only in the design of the posterior optic edge. An identical study was performed with 2 types of silicone IOLs and a very similar study with 2 types of PMMA lenses. In all 3 stud ies there was significantl y less peo in eyes with sharp edge IOLs than in those with round edge IOLs. Nd :YAG laser capsulotomy rates were up to 10 times higher in the round ed ge groups. This confirms that the sole modification of the posterior optic edge from a round edge to a sharp edge leads to a significant red uction of peo by inducing a discon tin uous bend at the posterior capsule. Unfortu na tely, sharp optic ed ges of intraocular lenses also have disadvantages. In some cases after im plantation of lenses with a rectangular edge shape (such as the AcrySof lens), an increased incidence of persistent edge glare phenomena was reported . Sharp-edged IOL designs cause the light rays that are refracted through the peri pheral IOL to be more intense on the peripheral retina. Round-edged IOL designs disperse the rays of light over a larger surface area of the retina, lead ing to less glare. However, the "halfrounded" ed ge profile of some newly developed IOLs with a round anterior 576 and sharp posterior optic edge seems to avoid this disturbing side effect.

Advances in Optic Designs to Reduce pea

Fig . 3: Intra-individual comparison of roun d and sharp optic edges in a silicone IO L. Retroiliumination image of a round edge (left) and sharp edge (right) acrylic tOl 2 years after surgery . Right and left eye of the same patient ; both IOLs differ only in optic edge design

Fig . 4: Intra -in dividual comparison of round and sharp optic edges in a PMMA IOl. RetroiUumination image of a round edge (left) and sharp edge (right) acrylic IOL 2 years after surgery. Right and left eye of the same patient; both IOLs differ only in optic edge design

577

Instant Clinical Diagnosis in Ophtllfllmologt) (Refractive Surgen) IOL OPTIC MATERIAL

While the PCO inhibiting effect of a sharp posterior optic edge has been clearly demonstrated in several trials, the role of different IOL optic materials (i.e. PMMA, h yd rophobic acrylic, h ydrophilic acrylic = hydrogel, silicone) in reducing PCO remains uncertain. Although many studies comparing different IOL materials have been performed, significantly higher PCO rates have only been shown for h ydrophilic acrylic (h ydrogel) and for PMMA IOLs in comparison to other materials (i.e. acrylic and silicone IOLs). YAG capsulotomy rates of 24% were found for sharp-edge PMMA lenses compared to 71 % for round-edge PMMA lenses between 3 and 5 years after surgery in a study by Findl et al. However, in a similar study, YAG capsulotomy rates of less than 1% (sharp) and 39% (round) for acrylicIOLs and ofless than 1% (sharp) and 15% (round) for silicone lenses were fowld 3 years after surgery. This shows that sharp edge PMMA IOLs lead to similar high or even higher capsulotomy rates than rOl/nd edge acrylic or silicone IOLs. A few studies comparing acrylic and silicone lenses did not find significant differences between these two materials. The results of several other studies which found differences between acrylic and silicone IOLs or other IOL materials are questionable, because the compared IOLs differed not only in IOL material but also in IOL optic design (especially optic edge design), as already pointed out previously. First, the low PCO rates observed with the AcrysofIOL (Alcon, Fort Worth, USA) were attributed to the hydrophobic acrylic optic material used. However, this study compared the sharp edge hydrophobic IOL to IOLs of silicone and PMMA material with round optic edges and edge design was thus not accounted for. Nishi and coauthors investigated the efficacy of the barrier created by a sharp edge optic in a rabbit model. They found a loss in barrier function in a round edge variant of the Acrysof IOL. Also, in the animal model, the sharp edge 3-piece silicone CeeOn® 911 IOL (Pharmacia, Groningen, The Netherlands) and the 3-piece acrylic Acrysof MA60 BM IOL (Alcon, Fort Worth, USA) were equally effective in p reventing PCO. Similar results were found in randomized clinical trials w ith intraindi vidual comparison of these IOLs by Prosdocimo et al and Find I et al.Therefore, there is evidence that silicone and hydrophobic acrylate are at least equally effective in preventing PCO in the presence of a sharp optic edge up to 3 years after surgery. There is even some evidence that silicone IOLs might produce less PCO than acrylic IOLs, however, there are too few randomized bilateral trials varying only the IOL optic mate rial. Looking at 2 (randomized, bilateral) studies comparing sharp and round optic edges in acrylic and in silicone IOLs, we also found lower PCO scores in the silicone IOL stud y, both in the sharp and in the round edge group. The IOL optic design was very similar in these 2 studies; however, the difference might also be a result of the different patient groups. Nevertheless several authors independently found very low PCO rates in sharp edge silicone IOLs, also in the long-term follow-up. 578

Advances in Optic Designs to Reduce pea

Fig. 5: 1·piece (left) and 3'piece (right) acrylic IOL 3 years after surgery. Pronounced pea (lens epithelial cell ingrowth) can be observed near the haptic-optic junction. However, there is no significant difference in overall peo intensity between the 2 IOL models (right and left eye of the same patient)

579

Instant Clillical Diagnosis in Oplrtlwlmologt) (Refractive SlIrgert)

The reasons for the material effect on PCO rates are still unclear. Studies have shown that the speed of forma tion of a capsular bend at the optic edge is significantly faster with silicone and acrylic rOLs. Linnola hypothesized that bioactive rOLs, such as acrylic rOLs, would prevent PCO better than PMMA or silicone JOLs, which have good biocompatibillty but are bioinert. In a bioactive IOL, a single lens epithelial cell would act as a tie between JOL and posterior capsule, producing a "sandwich pattern" of IOL, cell monolayer, and posterior lens capsule, thus preventing further PCO growth (sandwich theory). However, the theory is put into question by the low PCO ra tes in silicone IOLs. IOL HAPTIC DESIGN Haptic Angulation

The PCO preventati ve effect of sharp ed ge optics suggests that it might be useful to maximi ze the barrier effect at the posterior optic edge by pushing the IOL backwards against the posterior capsule. This ca n be achieved by angulated haptic designs. Con sequently, suc h pos terior vaulting characteristics can be found in many modern 3-piece IOLs. However, studies showed that these designs interestingly d o not lead to a smaller lens! capsule distance and do not seem to have a better PCO inhibiting effect than rOLs with little or no hap tic angulation. This might be explained by the fact that most angulated hap tics lose their memory and the backward force against the posterior capsule thus might be too low for a significant effect, or the reduced contact to the anterior capsule, leading to less anterior fibrosis, might antagonize the PCO-inhibiting effect. 1-piece/3-piece IOLs

New manufacturing methods led to the introduction of single-piece IOls some years ago. Unlike 3-piece IOLs, which usuaLly consist of 2 d ifferent materials (optic and hap tics), these IOLs are produced in a single step from one material. l-piece IOLs tend to be more stable and the production process is cheaper. However, most l-piece designs fea ture broad hap tic shoulders at the transition to the IOL optic. This raised the question whether these lenses might weaken the PCO-preventative effect because of the incomplete sharp posterior optic rim and because of the compromised capsular bend formation due to reduced capsular fusion at the (thicker and broader) haptic-optic junction. Nevertheless, several clinical trials (some of them still ongoing) did not show significant differences in PCO rates between l -piece and 3-piece optics. However, the interrupted sharp optic rim might lead to problems in new ultra-thin l-piece lOLs developed for (bimanual) micro-incision surgery. Additionally, some of these lens models also use plate haptics, which had almost disappea red before because of high PCO rates due to the missing barrier effect. Similar haptic designs have also been used for so-called "accommodating" IOls over the 580 past years. Most of these rOl models showed poor results concerning PCO

Advances in Optic Designs to Reduce pea

ra tes, also primarily because of too man y or too broad haptics and therefore reduced capsular bend fo rmation. SUMMARY

Looking at modifications in IOL design, the concept of a sha rp posterior optic edge has been proven to be the most effective method to reduce PCO up to now. As a result, round-ed ge TOLs practically have d isappeared from the market. However, although d rastically reduced, the problem of PCO has not entirely been eliminated. The role of 10L optic material remains unclear; while hydrogel and also PMMA lenses have been shown to have a high PCO incidence, there is still an ongoing debate whether acrylic or silicone IOLs should be preferred with respect to PCO development. Other concepts of modifying an [OL, such as extremely posteriorly vaulted IOLs, did not lead to a significant reduction of PCO. On the other hand, sin gle-piece IOLs with an incomplete sharp optic rim also do not -as antici pated - show significantl y higher PCO rates up to now . However, new ultra-thin 10Ls which are currently being developed for microincision surgery might be a new challenge in the battle against PCO, due to their thin optic rim a.nd therefore possibly weak barrier effect at the optic edge.

581

Index A Aberrometer 21 4 Aberropia: A new refractive entity 214 materials and methods 216

results 216 Absolute presbyopia 22 Accommodation and presbyopia 20 fail ure of accommodation 22 theo ries of accommodation 20 Advanced su rface ablation (ASA) with custom ablation 190

Advances in epiLASlK and LASEK 192 compa riso n of the different

technique 194 data analysis 196

methods 192 ep iLASIK surgery procedure

194 examination 192 patients 192

surgery procedure 194 su rgery procedure LASEK 194 results 196 efficiency 196 pred ictabili ty 196 safety 198 Advances in microphakonit for refracti ve lens exchange

(M IRLEX) 542 surgica l technique 544 avoid ing complications 551 fina l comments 552 instrumen tation 544 patient preparation 546 postoperative care 552

surgica l steps 548 Allegretto

eye~Q

excimer laser 157

Amblyopia 348 further investigations 348 differen tial d iagnosis 350

Anterior chamber phakic IOL wi th angle fixation 532 compI.ications 540 elevated intraocular pressure

540 giant papillary conjunctivitis

540 halos and glare 540 lens rotation 540 postoperative uveitis 540 pupilova li za tion 540 inclusion criteria 536 surgical technique 536

types of phakik lens 534 Baikoff model ZB5MF 534 Kelmnan duet 536 Morcher GMBH 93 A 534 Nuvita Ba ikoff MA 20 536 Phakic 6 model 130 534 Argon fluoride excimer laser 156

Artiflex foldable iris clip PIOL 496 complications 499 contraindications 497 indication 497 results 499

surgery 497 Artisan spheric phakic intraocular lens

479 Artisan toric PIOL 488 complications 494 postoperative complications

496 contraindications 490

indications 490 qualities 488 results 496 surgery 492 Aspheri c IOLs 518 acrysof lQ 520 fit ting philosophy 522 akreos adapt AO 522

prognosis 350

compar ison of aspheric IOLs

treatment 350

524 fi tting phi losophy 522

signs and symptoms 348 Angle kappa 109

conventional spheri ca l IOLs 520

583

Ins tant Clinical Diagnosis in Opll th alnwloS'J (Refractive SlI rgenJ) spherical aberrations in human eye 518 in a young eye 520 in the elderly eye 520 tecnis lens (AMO) 520 fi tting philosophy 520 Astigmatism 8, 208,330 further investigations 330 d iffe rential diagnosis discussion 330 prognosis 332 treatmen t 332 signs and symptolTIS 330 types 208 based on ax is of the principal meri d ia ns 208 based on focus of the principal merid ians 208 photorefrac ti ve excimcer laser astjgmatic co rrection 208 wavefron t-guided laser vision correction 210

B Balanced salt solu tion 128 Basic optics of re fractive surgery 10 aberra tion, wavefront aberratio n, chrom atic aberration 12 curvature, radius of curvature 14 emmetropia, myopia, hyperopia, p resbyopia 12 light, physical optics, geometrical op tics 10 MTF, PSF 16 optical axis, visual axis 14 Q-factor, prola te, oblate 14 reflec tion, refraction, diffraction, scattering of light 10

c

584

Common properties lasers 362 Corneal biomechani cal properties in normal, ke ratoconic eyes and postlasik eyes 404 Cornea! w ound healing 144 Cross-linking p lus topography-g uided PRK lor post-LASIK ec tasia management 258 improvemen t in visual acuity 260

minimal corneal thickness 264 options for treatment 260 treatment of iatrogenic keratectasia 262 Crystalline acco mmod ation 99 cTENTM refractive and the rapeutic ablations w ith the iVISTM sui te 312 CLATThl 320 donor 322 host 320 co nstant frequency per area TM 322 clinical applications 324 diagnostic prod ucts 31 2 iRESThl 322 precisio™ 312 clinical applica ti ons 314 su rgical design prod ucts 316 Custom phakic TOL 432 C ustomised trea tments 388 Cus tomized exci mer Lase r treatmen t 156 Cus tomized LASTK for presbyopia: PMLThl techni que 334 approaches to the s urgical correction of presbyopia 336 clini cal cases 340 correction of presbyopia 336 PM L™ procedure 338

D Decentration 144 Distance blur 22 Distant vision in central cornea 100,464 Distribution of Zernike terms 131 Dry eye after refractive surgery 394 chronic dry eye after lasi k 398 clinical signs a nd sym ptoms 398 investigations 396 risk factors 400 treatment 400 Dual optic accorrunodative IO Ls 528

E Effects of artisan and arti flex phakic IOLs on the eye 501 effect on the iris 502 effects on the an ter ior chamber angle 502

Index difference behveen wavefront guided and topography guided custom ablation 164 different maps 172 oculyzer map 176 topolyzer maps 172 indications for custom ablation 166 general indica tions 166 indica tions for A-CAT 170 indications for custom Q treatment 166 mdications for oculink ablation based on the oculyzer 170 T-CAT after previous RK 168 T-CAT following previous PKP 168 obtaining maps for custom ablation treatment 172 measuring technique 172 requirements for cus tom ablation 160 data 160 eyetracking 160 scarming spot 160 tracker 160 results 184 results of custom Q treatment 184 results of wavefront guided treatment 184 results of wavefront optimized treatment 184 T-CAT result 184 treatment principles 158 corneal asphericity 158 trea tment programs 176 custom Q program 178 oculink treatmen t program 182 standard treatment program 178 T-CAT after previous penetrating ke ratoplasty 180 T-Cat after previous RK 180 T-CAT for other indications 182 T-CAT treatment 180

effects on the crystalline lens 502 effects on the endothelium 501 effects on the intraocular pressure 502 EpiLASIK and LASEK 118 EpiLASIK with mitomycin C 110 histological findings 112 intraopera tive course 114 postoperative treatment 114 clinical deductions 116 principle of epiLASIK 112 proced ure 112 Epithelial fla p 128 Epithelium-rhexis 124 Etiology of presbyopia 23 Excimer laser 362 basic concepts 362 disadvantages 364 cor rosiveness and toxicity of fl uorine gas 364 early replacement of special switch 364 high cost for proper storage of toxic gases and trainmg of a tech nician 366 high voltage requirement 364 hydra tion dependence of 193 nm 366 recurrent expense of excimer gases 366

F Functional presbyopia 22 Future of LASIK surgery 406 advanced technologies 406 surface treatment vs lasik 410 lenticular refractive surgery 412

G Gaussian bea m profile 157 complications of customized ab lation 186 complications of A-CAT 188 complications of custom Q ablation 186 complications of standard (WFO) ablation 186 com plications ofT-CAT 188 general complications 186

H Histopathological comparison of photorefractive keratectomy (PRK) in rabbits with 193 nm and 213 nm 376 scientific benefits 378

585

Instant Clinical Diagnosis in Ophthalmologtj (Refractive SlI rgenj) Hypermetropia 6 clinical signs and symptoms 6 differential diagnosis 7 investigations 7

optical principles 6 prognosis 7 treatment 7

ICL-induced ca taract formation 438 Incipient presbyopia 22 Interest of using an IO L HOA free to correct presbyopia in pseudophakic eye 458 IOL haptic design 580 1-piece/3-piece IOLs 580 haptic ang ulation 580 TOL optic materia l 578

L LASEK procedure w ith the use of mitomycin C 276 Laser med ia 362 Laser pumps 360 Laser scleral ablation for true accommodation for presbyopia 352 ageing effects of human eyes 352 clinical resu lts 358 Lin-Kadambi hypothesis 357 mechanisms 356 presbyopia treatment techniques 354 LASlK complications and management 242 central isla nd 250 prevention 250 risk factors 250 trea tmen t 250 diffuse lamellar keratitis (DLK) 252 management 254 prevention 254 risk factors 252 ectasia 256 management 257 preventio n 256 risk facto rs 256 586

excimer laser-related 248 decentered ab lation 248 faint striae (microstriae) 246 management 246 prevention 246 risk factors 246 healing / infection/ inflammation 250 epithelial ingrowth 250 infections keratitis 254 management 254 prevention 254 ri sk facto rs 254 interface debris and remnants 255 management 255 prevention 255 risk factors 255 macrostriae 246 management 248 prevention 246 risk factors 246 microkeratome-rela ted and f1aprelated 242 dislodged flap 244 irregular cap/flap 242 wldercorrection, regression 248 management 250 prevention 250 risk fac tors 248 LASIK technique 124 Lens accommodatio n 101

M Managing intraoperative flopp y iris syndrome 470 Mechanism of accommodati on 424 Mechanism of action of filtering IOLs 556 Mini-incision IOLs 448 IOLs that can fit min i incision 452 mini incision cartridges 452 mini incision IOL design 448 optic diameter 450 optic properties 450 thickness 448 Myopia 2 clinical signs and sy mptoms 2 investiga tions 4 differential diagnosis 4 prognos is 6 treatment 6

Iudex Myopic photorefractive keratec tomy usin g solid state laser 50 achiev ing the fifth harmonic 52 confocal microscopy analys is 58 custo mvis Pulzar Zl solj d state laser 54 clinical results 56 experimental corneal histology 56 lasers pr inciples of func tion 50

N Near vision in central cornea 100, 464 Nidek advanced vision exci mer laser system (NA VEX) 148 ablation profiles 154 final fit 152 NAVEX 152 OPD scan 150 OPD software 150 octurnal presbyopia 22

o Oblate cornea 148 Ocular response analyzer (ORA) 404 One-shot ep ithelium-rhexis:persona l tech nique 118 Optic edge design 574 Optical zone 142 Orbscan 24, 214 analysis of the normal eye by the orbscan map 30 clinical appi.ications 32 elevati o n 26 im aging in the orbscan 30 map colo rs conventions 30 orbscan I an d II 26 p araxial op tics 24 ray trace or geometric optic 24 specular vs back-sca ttered reflection 28 Orthokeratology 504 cornea l thickness 516 ideal fitting 510 limits 512 overni ght o rthokeratology 506 reverse geom etry contact lens design 508 risks analysis 514 selection of patients 510

p Painless epiLASIK 80 eyedrops 84 postopera tive management 83 bandage contact lens 83 surgery proced ure 80 epiLASLK technique 82 epi-treph ine assisted LASEK technique 80 Phakic IOL 124, 478 types 478 an teri or chamber 478 posterior chamber 478 Photorefrac ti ve kera tectomy after penetra ting keratoplasty 42 investigations 42 preoperative considerations 45 Photo refracti ve kera tectomy fo r res idual myopia folJow ing rad ia l keratotom y 62 investiga ti ons 66 preopera tive considerations 64 Photorefractive keratectomy with mito mycin C for hig h myopia 36 investiga tions 38 Phototherapeutic keratectomy on recurrent corneal erosions 46 clinical sig ns and sympto ms 46 differentia l diagnosis 46 investigations 48 prognosis 49 treatment 48 Presby-epiLASIK in pseudophakic eyes w ith the wavelight Allegretto 92 Presby-LASIK 96 Presby-LASIK in monofocal pseudophakic eye 456 Presbyopia 9, 22 clinical signs and sympto ms 9 differential d jagnosis 9 in vestiga tions 9 optical princi ples 9 treatmen t 9 PRK for low to moderate myopia 270 Protective mechanisms in the human eye 556 Pseudophakic eyes 97

587

II/stal/t Clil/ ical Diagl/osis iI/ Opilti1allllol0S'J (R efractive SlIrgenJ) Q

Q va lue and SA rela tionship 93 Qua li ties of the arti sa n spheric PlOL 482 contraindications 482 indications 482 requirements 482

R

roo

Regular surface ablation 128 Relations hip between Q value asphericity and amount of spherical aberrations 458 Restoration of accommoda tio n by ca psular bag refillin g 420 Resu lts of the spheric artisa n PIO L 488

5

Solid state laser 368 Recent advances in photorefrac tive future of solid state laser 370 keratectorny 70 present situatio n 370 ascorbate prophylaxis after PRK 73 Special features availab le to the pulzar PRK in the treatment of presbyopia ZI 378 78 0.6 mm fl ying Gaussian beam spot PRJ( with MMC 70 380 haze after PRK 70 au to-cali bra tion 384 mitomycin C side effects 73 advantages 384 mitomycin C use as prophylaxis au to-cen tration 384 and trea tm ent fo r haze 72 cornea l hydration dur ing ab lation surgical technique of PRJ( with 386 MMC 73 crys talsca n 382 PRK with solid state lasers 79 cyclorotation 380 Q fac tor custom ized PRJ( 76 eye tracking 378 freedom to select treatment center topography-guid ed PRJ( 75 384 wavefront-guided PRK 74 comparison between stan dard gaze tracking 378 PRK and wavefron t-g uided hinge protection 384 PRK 74 advan tages 384 comparison of waevfrontless maintenance and cost 386 guided PRK wi th wavefrontnomogram adj ustmen t 386 guid ed LASIK 75 ZTRAK 378 Standa rd treatment fea tures in pul zar Refilling the lens capsula r wi th 21 388 capsulotom y-capturin g intraocular lens 422 maintenance of preoperative co rneal asphericity 388 surgical procedure 422 Refractive change after RK 236 resum ing an aborted ab lation process 388 d ifferential dia gnos is 238 investigations 238 saving entered treatments 388 prognosis 240 Sub-Bow man's keratomi leusis 292 signs an d symptoms 236 corneal sensitivity resu lts 308 treatment 240 subjective results 309 Refractive lens exchange: current measurement of results 302 perspectives 560 ORA results 307 Refrac tive management hyperopia 416 pascal tonometer 308 clinical signs and symp toms 416 sig nifi cance of results 310 investigations 416 study results 304 management 416 biomechanical resu lts 307 prognosis (i::'~1"'8":':-=--.-,-,-,- -,-.--,-,-.---,\ contrast visua l acuity 306

Illdex fla p thi ckness resul ts 304 retin al image qua lity 306 visua l results 304 wave front aberrom etry 306 surgical teclmiq ues for SBK and PRK 301 Su rface abla tion after laser in si tu ke ratomi leusis; retreatment on the flap 126 technique 128 Surface abla tion technique 124 Surgery for the artisan PIOl 484 anesthesia 484

complications 486 in tra-operati ve compl ications 486 p roperties complica tion 486

T Tear film 146 Technica l ad van tages of solid sta te laser 372 213 nm waveleng th 372 ad vantages 372 clin ica l ad van tage 374 solid sta te techno logy 372 tissue hyd ra tion study 374 Topographic and aherromete r guid ed laser 226 aberrati ons 226 aberrometer 228 orbscan 228 results 230 zylink 228 zyoptix laser 226 Topograph y data 164 Topolink in pseud ophakic 462 Tracey wavefront analyzer 390 cl inica l outcomes 392 attemp ted vs achieved graph 392 lates t clinica l results 392 m yopia-moderate to high 392 Transepi thelial cross-linking for the treatm ent of keratoconus 286 cornea l collagen networks 288 corneal epi thelium 290

photochemical cross-linking 288 riboflavin-UVA trea tment 290 Types of filtering TOl s 556

u UV-rela ted eye diseases 554

w Wavefront aberration 131 Wavefront analysis and its clinical sign ificance 130 concept of the wavefron t abe rration 130 interaction among wave aberra tions 132 clinical examples 132 methods of desc ribin g wavefront aberra tion 130 significance of Zern ike aberrations 132 Wavefron t data 164 Wavefr ont lasik 134 advantages 134 biomechanical issues 140 laser factors 138 limi tations 138 role of the pupil 140 Wavefront optimize and asti gmatism correction w ith the Allegretto exci mer laser 202 cli n ical impl ica tions 206 normal cornea l shape and Asphericity 202 spherical aberra ti on 204 wavefront op timi ze technology 204 Wavefront optimized profile 191 Wavefront-guided p hotorefractive keratectomy 86 cl inica l resul ts 88 custom wavefront PRl< 88 limitations 91 Wave light Allegretto eye-Q 156

z Zernike method 220 Zernike polynomial 130 Zyoptix p rocedure 216

589