UNIVERSITY OF LONDON THE DEVELOPMENT OF EXCIMER LASER CORNEAL SURGERY A thesis submitted for the degree of Doctor of Medicine David S Gartry MB,BS,FRCS(England),FRCOphth,BSc(Hons),DO(RCS),FBCO Formerly: Iris Fund Excimer Laser Research Fellow The United Medical and Dental Schools of Guy’s cmd St Thomas’ Hospitals and The Institute of Ophthalmology, London Currently: Comeal Fellow Moorfields Eye Hospital City Road, London June 1995 ProQuest Number: 10042908 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10042908 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. 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Box 1346 Ann Arbor, Ml 48106-1346 TABLE OF CONTENTS Title Page............................................................................................................................. 1 Table of contents ................................................................................................................. 3 List of figures...................................................................................................................... 11 List of tables........................................................................................................................ 17 Abstract of thesis..................................................................................................................21 Acknowledgements ............................................................................................................... 23 SECTION I INTRODUCTION...............................................................................................................25 CHAPTER 1: CONVENTIONAL CORNEAL SURGERY.................................................................... 27 1.1 The structure and function of the normal cornea ................................... 29 1.2 Essential prerequisites of comeal surgery.......................................... 31 1.3 Indications for comeal surgery .................................................... 32 1.4 Current comeal surgical procedures and their limitations ............................. 32 1.4.1 Epithelial debridement and anterior stromal puncture ................... 32 1.4.2 Superficial keratectomy for band keratopathy .................................. 32 1.4.3 Lamellar keratoplasty........................................................................ 33 1.4.4 Penetrating keratoplasty .................................................................... 33 1.5......................... Refractive comeal surgery........................................................ 34 1.5.1 Introduction ...................................................................................... 34 1.5.2 Radial keratotomy..............................................................................34 1.5.3 Arcuate keratotomy........................................................................... 36 1.5.4 Keratomileusis................................................................................. 37 1.5.5 Keratophalda ...................................................................................... 37 1.5.6 Epikeratophakia ..................................................................................37 1.6 General comments ............................................................................................38 CHAPTER 2: LASERS IN CORNEAL SURGERY.............................................................................. 39 2.1 The potential of lasers in comeal surgery......................................................41 2.2 The basic principles of lasers ....................................................................... 41 2.2.1 Monochromaticity ..............................................................................42 2.2.2 Directionality ................................................................................... 42 2.2.3 Intensity/brightness ............................................................................42 2.2.4 Coherence ........................................................................................ 42 2.2.5 Mode structure............................................................................... 42 2.3 The production and emission of laser light .................................................. 43 2.3.1 The active lasing medium............................................................... 43 2.3.2 The energy source........................................................................... 43 2.3.3 The optical resonator ....................................................................... 43 2.4 Interaction of laser light with the cornea .................................................... 44 2.5 Historical overview of laser comeal surgery............................................... 46 CHAPTER 3: THE DEVELOPMENT OF EXCIMER LASER CORNEAL SURGERY..................... 47 3.1 Background.......................................................................................................49 3.2 The lasing medium and beam-tissue interactions ........................................... 50 3.3 Hazards of excimer laser radiation and safety ............................................... 57 3.3.1 Penetration of excimer laser radiation at 193nm ........................... 58 3.3.2 Mutagenesis........................................................................................58 3.3.3 Secondary fluorescence and cataractogenesis ............................... 59 3.3.4 Acoustic shock waves..................................................................... 60 3.3.5 The generation of toxic free-radicals ............................................. 60 3.4 The first clinical applications of the excimer laser ...................................... 61 3.4.1 Treatment of comeal scars ............................................................. 61 3.4.2 E arly’incisional keratotomy* ......................................................... 62 3.5 Aims in the evaluation of excimer laser comeal surgery............................ 63 3.5.1 Efficacy and safety of phototherapeutic keratectomy ................... 63 3.5.2 Efficacy, safety and predictability of PRK ................................... 63 3.5.3 The role of topical corticosteroids following PRK ........................ 63 SECTION n INSTRUMENTATION.................................................................................................... 65 CHAPTER 4; TECHNICAL DESCRIPTION OF THE LASER USED IN THIS STUDY.................. 67 4.1 Production and emission of excimer laser radiation ................................... 69 4.2 The beam delivery system ............................................................................ 70 4.3 Photorefractive keratectomy algorithms....................................................... 72 SECTION HI THE DEVELOPMENT OF PHOTOTHERAPEUTIC KERATECTOMY.............. 79 CHAPTER 5: LABORATORY MODELS OF CORNEAL SMOOTHING............................................. 81 5.1 Introduction ......................................................................................................83 5.1.1 Preliminary laboratory evaluation/aims of the study ..................... 83 5.2 Materials and Methods ................................................................................. 84 5.2.1 Excimer laser pattern ablation in cadaver eyes ........................... 84 5.2.2 Excimer laser smoothing of lameUar keratectomy beds ............... 85 5.2.3 Histopathology................................................................................... 85 5.4 Results.............................................................................................................. 86 5.4.1 Excimer laser pattern ablation in cadaver eyes ............................. 86 5.4.2 Excimer laser smoothing of lamellar keratectomy beds ............... 90 5.5 Discussion........................................................................................................ 94 5.5.1 Conclusion .......................................................................................... 100 CHAPTER 6; PHOTOTHERAPEUTIC KERATECTOMY - ORIGINAL CLINICAL STUDIES 101 6.1 Introduction ........................................................................................................103 6.1.1 Aims of the study ............................................................................. 103 6.2 Methods and study design ............................................................................... 104 6.3 Results................................................................................................................106 6.4 Selected case studies ...................................................................................... 114 6.4.1 Group 1. Rough (uncomfortable/painfiil) band keratopathy 114 6.4.2 Group 2. Smooth (glare inducing) band keratopathy ................... 120 6.5 General comments .............................................................................................132 6.6 Discussion .......................................................................................................