EyeWorld Asia-Pacific March 2018 Issue

Views from Asia-Paci c Michael LAWLESS, MD Clinical Associate Professor, University of Sydney, Vision Eye Institute 4/270 Victoria Ave, Chatswood NSW 267 Tel. no. +6194249999 michael.lawless@visioneyeinstitute.com.au T his article raises so many interesting points. Having visited Bogotá and worked with José Barraquer in the mid-1980s, I can provide witness to the truth of the statement: keratophakia procedures were brilliant in concept but lacked precision, both in terms of measuring corneal lenticules and precisely reshaping them. The other change since the 1980s is improved eye banking storage of material and the shift from penetrating corneal transplants to DSEK and DMEK procedures, which has liberated corneal stroma for other uses. One of the problems of currently available corneal inlays for presbyopia is not just the foreign body reaction. This is a real problem in a minority of patients, but also the essential fact that they are changing the shape of the cornea as part of their treatment paradigm. This is a secondary effect and has two problems: Since it is a secondary effect rather than a primary shape change, the results are not as predictable as patients would like. The changed shape of the cornea leads to an altered ocular surface and problems with surface wetting, slow recovery, and the need for intensive follow-up to get these patients through the healing period. That is why Dr. Muller’s idea not to mimic what had been done before with corneal donor lenticules but to place the lenticule on top of Bowman’s membrane and allow the corneal epithelium to cover it within a few hours is attractive. It is ideal in that it is easily removable if the patients are not happy with the result. This sets it apart from other corneal presbyopia refractive procedures. I certainly feel wasteful every time I throw away a corneal lenticule after a SMILE procedure, and would like to think this corneal tissue could be used to good effect. Of course, presbyopia solutions should be directed at the problem, which is the lens. Lens rejuvenation procedures for those patients who are emmetropic and presbyopic in their late 40s and early 50s, prior to a time when most surgeons would be comfortable performing lens replacement, is needed. If an allogenic procedure on the surface, which was easily removable, could provide them with even 5 years of modest improvement in near vision, and it would be modest, then this would be something to consider and would certainly set it apart from any other corneal presbyopia procedure currently available. It would fill in the missing grey area for refractive surgery for those emmetropic, presbyopic patients between 45 and 55 years of age. Editors’ note: Dr. Lawless declared no relevant nancial interests. Myoung Joon KIM, MD Professor, Department of Ophthalmology, Asan Medical Center 88 Olympic-ro 43-gil, Songpa-gu, Seoul, 138-736, Korea Tel. no. +82-2-3010-3975 Fax no. +82-2-470-6440 mjmjkim@gmail.com T here’s a quote that says, “Winners learn from the past and enjoy working in the present toward the future.” Use of allogenic tissue to reshape the corneal surface has a long history. The rst trial was epikeratophakia. From the history, we learned that success in refractive procedures requires high precision. Now, we have various tools to measure and fabricate corneal tissue precisely. The cornea with its covering precorneal tear film is a very important optical structure, where refractive index changes dramatically when light comes into the eye. Reshaping the cornea can be successful using precise laser technology. However, the cornea is not a piece of plastic. There might be tissue reactions after implantation of allogenic tissue, resulting in inflammatory reaction and corneal opacity. Also, there is the possibility of tissue rejection, even though chances are very low. For the purpose of presbyopia correction, central corneal steepening can be achieved by PrEsbyopic Allogenic Refractive Lenticule (PEARL) inlay procedure. However, that procedure is not for every presbyopia patient. The tear film can become more unstable on a steeper cornea. Neural adaptation can be another issue. Corneal allogenic intrastromal ring segments (CAIRS) are another example of allogenic implants. I have concerns regarding variable and unpredictable biomechanical properties in the allograft. The allograft may be engineered to equalize its biomechanical properties among grafts. Allogenic implants have advantages over synthetic implants. Synthetic material remains a foreign body forever. Low grade inflammatory reactions can be persistent over a long time. On the other hand, the patient’s own keratocytes grow into an allograft and the graft is maintained as if it were the patient’s own tissue. In addition, allografts allow better diffusion of nutrients and oxygen through the cornea. I think these allogenic implants are an enjoyable option for surgeons working in the present. Editors’ note: Dr. Kim declared no relevant nancial interests. “ ...the cornea is not a piece of plastic. There might be tissue reactions after implantation of allogenic tissue, resulting in inflammatory reaction and corneal opacity. ” - Myoung Joon Kim, MD EWAP REFRACTIVE 39 September 2017 March 8