THE ROLE OF ORTHOKERATOLOGY IN REFRACTIVE CORRECTION AND AN ANALYSIS OF CHANGES IN CORNEAL TOPOGRAPHY FOLLOWING OVERNIGHT ORTHOKERATOLOGY Dissertation submitted to THE TAMIL NADU Dr. M.G.R. MEDICAL UNIVERSITY CHENNAI

with fulfillment of regulations for the award of the degree of

M.S. (OPHTHALMOLOGY) BRANCH III

MADRAS MEDICAL COLLEGE CHENNAI – 600003

MARCH 2009

ACKNOWLEDGEMENTS

I wish to express my sincere thanks to Prof. Dr. T P Kalanithi,

MD, Dean, Madras Medical College, Chennai, for permitting me to conduct this study at the Regional Institute of Ophthalmology and

Government Ophthalmic Hospital, Chennai.

With profound gratitude, I thank Prof. Dr. M. Radhakrishnan,

MS, DO, Director and Superintendent, Regional Institute of

Ophthalmology and Government Ophthalmic Hospital, Chennai, for his valuable guidance throughout my post graduate course in ophthalmology and for his constant encouragement to pursue knowledge and learn its application in practical life.

I am extremely grateful to my mentor, my Chief, Prof. Dr. K.

Vasantha, MS, FRCS (Edin), for giving me every possible opportunity to learn and grow. I sincerely thank my Chief for the pearls of wisdom imparted during everyday work, for inculcating in me a desire to achieve perfection and for her unwavering encouragement and guidance during the conduct of this study and throughout my post graduate training.

With utmost respect and gratitude, I would like to thank

Prof. Dr. V. Velayutham, MS, DO, former Director and Superintendent,

RIO-GOH, Chennai, for instilling a sense of passion for ophthalmology and for his encouragement and support to this relatively new endeavour. I convey my heartfelt thanks to the assistant professors in my unit.

To Dr. M Anand Babu, MS, DO, for being a source of constant help, guidance and support in all my endeavours.

To Dr. K Mohan, MS, DO, for always being there and for his help, encouragement and valuable suggestions that made this study possible.

To Dr. MR Chitra, MS, DO, for her support and guidance throughout my course.

To Dr. Rajini, MS, DO, who with her cheerful demeanour, has been a constant source of support and valuable guidance.

To Dr. Kalaiselvi, MS, for her encouragement and support during my tenure in the unit.

I wish to thank all my Professors, Assistant Professors and my colleagues for their timely help, advice and support in all my endeavours throughout my course in ophthalmology.

Finally, I am greatly indebted to all my patients for their sincere cooperation which made this study possible. CONTENTS

S.No. TITLE Page PART I No. 1. INTRODUCTION 1 2. REVIEW OF LITERATURE a. Orthokeratology – history 1 b. Anatomy of the 11 c. Corneal metabolism 15 d. 18 e. Orthokeratology lenses 20 f. Mechanism of action of ortho-k lenses 24 g. Fitting of ortho-k lenses 32 h. Ortho-k lens care and handling 36 i. Problems with fitting 40 j. The role of corneal topography in orthokeratology 45 PART II 1. AIMS OF THE STUDY 51 2. INCLUSION AND EXCLUSION CRITERIA 52 3. MATERIALS AND METHODS 53 4. OBSERVATION AND ANALYSIS 54 5. ORTHOKERATOLOGY FOR KERATOCONUS 66 PATIENTS 6. RESULTS 69 7. DISCUSSION 71 8. CONCLUSION 73 PART III 1. BIBLIOGRAPHY 2. PROFORMA 3. KEY TO MASTER CHART 4. MASTER CHART 5. LIST OF SURGERIES PERFORMED

INTRODUCTION

Orthokeratology

The word ‘orthokeratology’ is derived from Greek roots and comes from ‘ortho’ meaning correct or proper and ‘keratology’ meaning having to do with the cornea. It thus means forming the cornea to a correct shape.1 Orthokeratology may also be considered to literally mean “the study of straight ”.2

Orthokeratology is defined as the reduction, modification or elimination of refractive error by the programmed application of specially designed rigid gas permeabl