EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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The latest in crosslinking March 2012 by Enette Ngoei EyeWorld Contributing Editor EyeWorld looks at the hottest areas in corneal crosslinking for the treatment of keratoconus C onsidering that kerato- conus is the second most common reason why pa- tients undergo corneal transplantation in the U.S., Eric D. Donnenfeld, M.D., co-chair- man of Cornea, Nassau University Medical Center, East Meadow, N.Y., said it is unfortunate that U.S. pa- tients are the only ones in the world who cannot have corneal crosslink- ing treatment done in an FDA-ap- proved way. It's been well established through worldwide experience that corneal crosslinking is an essential step in preventing keratoconus pro- gression, said John Kanellopoulos, M.D., associate clinical professor of ophthalmology, New York Univer- sity, New York, and director of laser vision, GR Institute, Athens, Greece. So while the ophthalmology community in the U.S. continues to await FDA approval, surgeons else- where are advancing their research beyond the standard technique used to treat keratoconus patients. Beyond epi-off One area of interest in crosslinking is whether there can be deviation from the standard epithelial-off method to an epithelial-on method. The risks of the epithelium-off method are small, Dr. Donnenfeld said. It has the risk of epithelial de- fect, similar to PRK, which has been done for 20 years in the U.S., and many studies have shown that the risk of infection is about 1 in 500, and the risk of vision loss is about 1 in 5,000, he said. So why the need for deviation? "I think the major reason why physicians are doing epithelium-on is for comfort; it's certainly more comfortable and people can go back to work more quickly," he said. Epithelium-on crosslinking has gained some support in the U.S., al- though there's no scientific data to support epithelium-on crosslinking as being equal and certainly not su- perior to epithelium-off crosslinking, Dr. Donnenfeld said. "As a matter of fact, at the Euro- pean Crosslinking Congress, which [recently] took place, there was a lot of data presented that suggested that epithelium-on crosslinking is not as effective as epithelium-off," he said. Transepithelial crosslinking is an area that's been studied by many groups and shows some promise, Dr. Kanellopoulos said. "We're not cer- tain we'll get the same amount of crosslinking when we work transep- ithelialy because some of the UV light is blocked by the epithelium. We're not sure how much riboflavin is penetrating within the cornea." "I think it's a great idea to do epithelium-on crosslinking in the- ory, but I think it's irresponsible to do epithelium-on crosslinking rou- tinely on all patients until there's data that shows that it's as good as epithelium-off, especially in a num- ber of more aggressive crosslinking patients," Dr. Donnenfeld said. Some surgeons, including Dr. Donnenfeld, are doing partial ep- ithelium-off crosslinking where they make little holes in the epithelium using devices, which gets better lev- els of riboflavin into the stroma, he said. There are others who are mak- ing pockets in the corneal stroma with lamellar incisions and using these incisions to apply crosslinking at a deeper level in the cornea, which is in a very early stage and is a controversial area as well, he added. Other areas of interest Researchers are also exploring whether or not crosslinking can be done at the same time as excimer laser photoablation. In Europe, surgeons are rou- tinely doing topographic ablations on patients with keratoconus and crosslinking them at the same time, Dr. Donnenfeld said. Probably one of the most inter- esting areas in crosslinking today is the use of increased energy and re- ducing the time period of crosslink- ing, Dr. Donnenfeld said. "We introduced the concept of higher fluence crosslinking 5 years ago with the thought of delivering the same energy to the cornea and reducing the potential toxicity of longer duration of UV exposure to the cornea," Dr. Kanellopoulos said. Traditionally, crosslinking is done with 3 mW/cm2, and now there are crosslinking units that have up to 30 mW for the same area. It's suggested that the crosslinking time can be reduced to 3-5 minutes, so there can be a much shorter time period, Dr. Donnenfeld explained. "We have seen it clinically work identical to shorter fluence crosslinking, and now we're seeing a lot of groups [creating] commercial products that embrace this tech- nique," Dr. Kanellopoulos said. According to him, Avedro (Waltham, Mass.) has a device that goes up to 45 mW fluence. IROC continued on page 80 EW CORNEA 79