EyeWorld India December 2013 Issue

36 EWAP rEfrActivE December 2013 Prema PADMANABHAN, MD Medical Director, Sankara Nethralaya Medical Research Foundation 18 College Road, Chennai, Tamil Nadu, India Tel. no. +91-44-28271616 Fax no. +91-44-28254180 drpp@snmail.org D r. Trattler neatly summarizes the article “Refractive Surgery for Keratoconus” with a statement that “patients with keratoconus have more options and avenues for improving vision than they ever had before.” While this statement is irrefutable and made possible because of technological advancements, we need to recognize that opportunities and challenges are opposite faces of the same coin. Intracorneal ring segments The advent of the femtosecond laser has improved surgical precision to unprecedented levels, minimizing complications related to the construction of the corneal tunnels for the intracorneal ring segments. However, certain surgical and clinical issues await answers—e.g., the number, size, symmetry and centration of the ring segments. Long-term results, with the construction of dependable nomograms, will make the surgeon more confident of the results that a patient can expect. It must also be remembered that intracorneal ring segments only produce a limited refractive adjustment, without addressing (perhaps actually jeopardizing) the biomechanics of an already weak cornea. Combining the surgery with a simultaneous collagen crosslinking (CXL) would seem a logical adjunct treatment. PRK for keratoconus The proven efficacy of UVA-Riboflavin CXL in increasing the biomechanical strength of the cornea has tempted a few refractive surgeons to combine CXL with excimer laser photorefractive keratectomy. The question of simultaneous versus sequential treatment was decisively answered by Kanellopoulos et al.,1 who argued that performing a photoablation after the crosslinking would be ablating some of the very tissue that was crosslinked and would be counterintuitive. Simultaneous treatment would also need to respect the amount of tissue ablated, although there are, at present, no clear guidelines for the same. It must also be remembered that the biomechanical response of a crosslinked cornea to excimer laser ablation is not known and could well be different from that of a normal cornea. This would make refractive outcomes unpredictable and inconsistent. Refractive lens exchange The challenges that haunt a refractive lens exchange in a keratoconic eye pertain predominantly to the method and accuracy of the IOL power calculation. With a cornea that is irregular in contour, uneven in curvature, and non-uniform in thickness, how, where, and with what instrument should K be measured? It is not only the likely errors in measurement, it is also the inconsistencies among instruments and discrepancies between objectively measured and subjectively accepted refractive values that add to a surgeon’s consternation. The effective lens position (ELP), an often ignored variable, can play havoc on equations based on standard eye models. Ray tracing, which makes true geometric measurements, could perhaps improve biometric accuracy. While toric IOLs have been a boon for patients with astigmatism undergoing cataract surgery, we must remember that the astigmatism in patients with keratoconus is irregular and the cornea asymmetric. Toric IOLs cannot correct corneal asymmetry and do not address the problems of higher order aberrations. Finally, specialized contact lenses may still be required to improve the quality of vision in these patients. Reference 1. Kanellopoulos AJ. Comparison of sequential vs same day simultaneous collagen cross linking and topography – guided PRK for treatment of keratoconus. J Refract Surg . 2009;25:S812-S818. Editors’ note: Dr. Padmanabhan has no financial interests related to her comments. Alvin YOUNG, MD Chief of Service & Cluster Coordinator, Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital Shatin, Hong Kong Tel. no. +852-26322878 Fax no. +852-26482943 youngla@ha.org.hk F ifteen years ago, the standard treatment protocol for keratoconus was limited and pretty much still based on either “conservative” with contact lenses & glasses or “surgical” with a conventional penetrating keratoplasty. Although the exact etiology and pathogenesis of the condition are still not fully understood, great strides have been made over the past decade. Significant progress has allowed us to detect and diagnose the disease earlier with better imaging modalities. Over the past decade or so, we have seen exciting new and promising developments to alter the natural history of keratoconus in a favorable way. Much credit should be given to visionary colleagues such as Dr. Theo Seiler and Dr. Joseph Colin (whom we sadly lost earlier this year). Nowadays, the treatment paradigm has shifted and many options in various refractive modalities are possible in between the above two ends of contact lens and penetrating keratoplasty. Approval for newer technology may be slightly easier in Asia; however, some of the issues in our region would be accessibility and affordability. For more rural communities, both physical access and cost would be relative hurdles our patients would have to overcome. The jury is still out as to the best treatment approach—such as the energy level use, the treatment zone, epithelium on or off, how best to combine with corneal segments and as to the assurance of keratoconus stability in considering toric IOL implantation. We need to be well conversed with the limitations of each of the treatment options either individually or in combination, and manage our patients in an individually tailored approach. Exciting times are ahead of us, as further research to look at the algorithms for the best treatment sequencing and combinations, and the titration of specifics for each individual treatment option will surely lead to even better visual outcomes for our patients. Editors’ note: Dr. Young has no financial interests related to his comments. Views from Asia-Pacific Topcon Singapore Medical Pte Ltd Page: 9 Phone: +65 6872 0606 www.topcon.com.sg World Ophthalmology Congress (WOC2014) Page: 14 www.woc2014.org ASCRS Page: 23 , 25 , 28 , 55 www.ascrs.org APACRS Page : 2, 5, 19, 32 , 56 www.apacrs.org Index to Advertisers