Ординатура / Офтальмология / Английские материалы / Mastering Corneal Collagen Cross Linking Techniques (C3-R, CCL, CxL)_Garg_2009

Foreword

This is one of the most exciting times for ophthalmology in general, and cornea and refractive surgery in particular. The breakthroughs over the last several years are changing the way we approach the cornea and offering our patients new and exciting opportunities for visual rehabilitation. At present, there is no technology with more promise than corneal collagen cross-linking. It combines two relatively mundane entities: riboflavin or vitamin B2, which is a naturally occurring photosensitizer found in all human cells, and ultraviolet light. A remarkable change occurs in the cornea stroma when riboflavin and ultraviolet light react together at the right concentrations and for the correct duration. The crosslinking of the corneal collagen fibrils strengthens the biomechanical properties of the cornea with a resultant increase in the tensile strength of the collagen fibrils. Although

there may also be a slight flattening of the cornea, the most important effect of the cross-linking is that it stabilizes the corneal curvature and prevents further steepening and bulging of the corneal stroma. There is no significant change in the refractive index or the clarity of the cornea. The clinical applications of collagen cross-linking offers for the first time, a treatment for one of the most common corneal disorders, keratoconus, as well as the most dreaded complication of corneal refractive surgery, ectasia.

Corneal ectasia is a rare but well-described complication of laser in-situ keratomileusis (LASIK) and an even more rare complication of photorefractive keratectomy (PRK). Over the last several years, risk factors for ectasia have been identified, which include high myopia, deep ablations, reduced residual corneal bed, young age, thin pachymetry, and most importantly, pre-operative corneal irregularity. However, ectasia may occur with no risk factors despite our best attempts to prevent it. Corneal ectasia is a condition in which the cornea is weakened by LASIK or PRK so that it protrudes irregularly and bows outward. This creates progressive steepening and thinning of the cornea, loss of uncorrected visual acuity, and loss of best spectacle-corrected visual acuity. The final results of ectasia may be as minimal as the need for the patient to return to the use of glasses. However, many patients may require a lifetime of rigid contact lenses, intracorneal ring segments, or penetrating keratoplasty for visual rehabilitation. Collagen cross-linking may arrest the progression of ectasia and when combined at the same time or subsequently with topographic or wavefront guided photoablation, may return uncorrected visual acuity. Patients at risk for ectasia may be prophylactically treated to prevent its occurrence. The elimination of corneal ectasia as a risk of LASIK and PRK has the potential to open an era of refractive surgery where the most dreaded complication has been eliminated.

Keratoconus is a naturally occurring ocular condition similar to ectasia and characterized by progressive thinning and steepening of the central cornea. Keratoconus frequently affects patients in their teens and early twenties, progresses over the course of a decade, and leaves patients visually handicapped, often with high myopia, irregular astigmatism, and significant loss of best corrected visual acuity. Rigid contact lenses can be used to improve visual acuity in many patients, but keratoconus frequently progresses to the point that corneal transplantation is required to restore useful vision. It may recur following corneal transplantation and require further transplant surgery. The incidence of keratoconus in the general population is estimated to be approximately one in 2000 and in the United States, keratoconus is the third most common indication for penetrating keratoplasty. Corneal transplantation has undergone remarkable improvements, but it still has inherent risks

Preface

Corneal Collagen Cross-linking with Riboflavin and UV-A (C3-R) treatment is certainly a new and promising development in refractive surgery in recent times. The weakened cornea in form of Keratoconus or Post-Lasik/ PRK Corneal Ectasia (Keratoectasia) is one of the most challenging task for Ophthalmologists. Reduced corneal mechanical stability in Keratoconus and Corneal Ectasia can be treated by Photo-oxidative cross-linking of the Corneal Collagen. To achieve high absorption of irradiation energy in the cornea, Riboflavin at a concentration of 0.1% and UV-A light at a wavelength of 370 nm corresponding to the relative maximum of absorption of Riboflavin (Vitamin B2) is used. Therapeutic C3-R cross-linking procedure causes decrease in corneal curvature of about 2D which leads not only to stabilization but also to an increase in visual acuity and more compact and stronger corneas.

This book has been written with the aim of providing complete insight into this new technique for the benefit of refractive surgeons worldwide. Its 23 chapters have been written by International Experts of this technique and they cover all aspects of C3-R technique in a comprehensive manner. It deals with all steps mainly indications, contraindications, various surgical procedures, complications and their management. Video DVD given with this book shows the surgical steps of C3-R treatment by International Masters beautifully.

Our sincere gratitude to publisher Shri Jitendar P Vij (CEO), M/s Jaypee Brothers Medical Publisher Pvt. Ltd. (India), Mr Tarun Duneja (Director– Publishing) and all staff members who took active interest and done hard work in timely preparation of this book, first of its kind in the world. C3-R treatment alone or combined with INTACS provide real hope for patients with progressive Keratoconus and Keratoectasia.

We expect this book shall provide the complete information on C3-R procedures to refractive surgeons who are interested to master this technique for the benefits of patients.

Editors

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