EyeWorld India March 2017 Issue

46 EWAP refractive March 2017 UV reduction than thin corneas,” Dr. Kling said in her presentation during Refractive Surgery Subspecialty Day. “In this study, we adapted the crosslinking protocol to the corneal thickness, so that the same UV energy per corneal volume was administered,” Dr. Kling continued. “Therefore, we may conclude that crosslinking in thinner corneas is more effective due to faster oxygen diffusion into the stroma. … In this study we have quantified this relationship.” Dr. Kling noted that UV restriction decreased viscous components of the cornea while oxygen restriction did not. Because rigid materials have a small viscous component, which is typically related to the extracellular matrix and not collagen, Dr. Kling said this shows “oxygen is probably related to proteoglycan crosslinking.” Dr. Kling told EyeWorld the results explain why transepithelial crosslinking, which is comparable to the contact lens protocol in the study, is less effective in the clinic. “[Our results] suggest that using a longer irradiation time and hence allowing for longer oxygen diffusion could partially compensate for the reduced diffusion rate. Also, increasing oxygen pressure could increase the efficacy of transepithelial crosslinking,” she said. This latter point, Dr. Kling said, could be achieved by saturating the air with oxygen or increasing the ambient pressure by performing the treatment within a pressure chamber. According to the study, differences in crosslinking efficiency were seen among the protocols tested, but “we cannot draw a conclusion as to which is the minimal necessary increase of corneal stiffness to prevent keratoconus progression,” Kling et al. wrote. “Currently, we speak of generalized standard, accelerated, or transepithelial crosslinking protocols,” Dr. Kling said. “In the future, I think a patient- specific crosslinking treatment will become available using either corneal thickness or topography data to determine the treatment parameters. We have learned that crosslinking consists of three main components: UV energy, riboflavin, and oxygen. Algorithms will need to be developed in order to determine the best parameter set for a given patient.” “Some of these new concepts are fascinating, but my professional advice is we should take a little longer to validate them before we sell the machine to the patient,” Dr. Hafezi said. “We have to make sure we have something that is effective.” For now, Dr. Hafezi still prefers the Dresden protocol, although he does accelerate it to 10 minutes because there is a solid body of evidence supporting its efficacy. “I want to protect the technique because it works wonderfully,” Dr. Hafezi said, noting that currently there is “total confusion” among his colleagues when it comes to the other, less established protocols. surgery.” EWAP Reference 1. Kling S, et al. Increased biomechanical efficacy of corneal cross-linking in thin corneas due to higher oxygen availability. J Refract Surg . 2015;31:840–846. Editors’ note: Dr. Hafezi has financial interests with EMAGine (Zug, Switzerland) and is co-inventor of the PCT/CH2014/000075 application (UV light source). Dr. Kling has no financial interests related to her comments. Contact information Hafezi: farhad@hafezi.ch Kling: kling.sabine@gmail.com Research - from page 45 Watch for our weekly emails every Saturday, broadcasting recorded live cornea presentations Learn from the experts @http:// Video Ed .CorneaSociety.org Copyright ©2017 Cornea Society. All rights reserved. The Cornea Society portal features cornea presentations and expert interviews from educational events throughout the year Watch, Learn & Share! Available on all mobile devices, tablets, and desktops All content is archived for future reference Watch, Learn, and Share! Video Ed