EyeWorld Asia-Pacific September 2011 Issue

29 EW REFRACTIVE September 2011 Myoung Joon KIM, MD Associate professor, Asan Medical Center 88 Olympic-ro 43-gil, Songpa-gu, Seoul, Republic of Korea Tel. no. +82-2-3010-3975 Fax no. +82-2-470-6440 mjmjkim@gmail.com T he onset of keratoconus is typically during puberty. Its progression in 20s and 30s causes continuing visual impairment. Traditionally, eye glasses and rigid gas-permeable lenses were the only options before corneal transplantation. One of the most important problems with corneal transplantation is graft failure associated with allograft rejection. Vision-threatening complications such as glaucoma can also be problems. A high residual astigmatism offers only limited visual recovery. And although the graft survival rate is excellent in keratoconus, the endothelium in the graft is unstable even in clear grafts. Endothelial cell density is significantly lower and cell loss is more rapid than in normal eyes. Considering ages, keratoconus patients usually undergo keratoplasty while still in their 20s and 30s and have an integrity issue in the graft endothelium; keratoconus patients may have to undergo several regraftings during their lifetime. Meanwhile, it has been reported that deep anterior lamellar keratoplasty (DALK) has a better graft survival rate. And although the longer surgery time is a dis advantage of this procedure, there is no concern regarding endothelial rejection as the host endothelium is preserved. However, residual astigmatism and scattering due to interface haze can limit the patient’s vision recovery. In my personal experience, vision recovery has not been very satisfactory after DALK in a keratoconus patient because of the folds in the Descemet’s membrane caused by the difference in arc length between the host’s Descemet’s membrane and the posterior stroma of the graft. For the reasons mentioned above, I believe that keratoplasty should be delayed for as long as possible in keratoconus patients. How this is to be done has been my question for many years. And now I have the answer. Crosslinking or an intracorneal ring can be good options for keratoconus treatment before proceeding to corneal transplantation. With the newer technologies and their combinations, I as a corneal surgeon hope that corneal transplantation for keratoconus patients will soon become a thing of the past, as a study by the Cornea Clinical Committee of the American Society of Cataract & Refractive Surgery has suggested. Editors’ note: Prof. Kim has no financial interest related to his comments. Views from Asia-Pacific WANG Zheng, MD Professor, Zhongshan Ophthalmic Center, Sun Yat-sen University 54 Xianlie South Road, Guangzhou 510060 Tel. no. +86-1390-300-2594 gzstwang@gmail.com U ntil recently, the treatment for keratoconus and other corneal ectasia available to ophthalmologists in their practice had been limited to RGP lenses, intracorneal rings, and corneal transplantation. Now the paradigm is beginning to change. Unlike previous therapies, corneal collagen cross linking (CXL) directly addresses the potential cause of ectasia—corneal weakening. Although the mechanism is still unclear, CXL has been successful clinically. Currently, most experience with CXL is from Europe, where this treatment has been around for more than a decade. Numerous studies have shown that CXL can arrest keratoconus. Regarding the UCVA, however, about 70% of the patients won’t get improvement, or even get worse. So, setting realistic expectations is important for both the doctor and the patient. The goal of CXL is to stop the progression of keratoconus, avoid corneal transplant, and provide better BCVA. As a relatively new therapy, there are many questions that remain to be answered, such as: • What is the real reason for increasing corneal stiffness after crosslinking? • Biochemically, what happens after crosslinking? • How do we quantitatively measure the effect of corneal crosslinking? • How long will the effect of CXL last? • Can the cornea be re-treated? If yes, when and how? • What is the best combination of riboflavin concentration and UV-A dosage? • How much crosslinking do we need? • What is the harm of over-crosslinking? • Should the whole or only part of the cornea be treated? • Which technique is better, epithelium-on or epithelium-off? • Does UV-A light cause damage to the limbal stem cells and the conjunctiva? • What are the best objective parameters to measure the effect, and define the success or failure of crosslinking? • When combined with excimer laser treatment, should they be done sequentially or simultaneously? The bottom line is that this ground-breaking treatment can make ectatic corneas stronger and prevent the patients from ending up with keratoplasty. We need more research to make this procedure work even better and safer. Editors’ note: Prof. Wang has no financial interests related to his comments.