COMMENTARY

Reaching a Milestone in the Treatment of Keratoconus

Roger F. Steinert, MD

Disclosures

April 21, 2016

This month—April 2016—is a very special month for corneal crosslinking. We finally have corneal crosslinking available in the United States with the recent approval by the US Food and Drug Administration (FDA).

Those of you who are not cornea specialists may not have been following this very closely. Corneal crosslinking has been available in Europe and throughout the world for a decade.

The original technique, generally known as the Dresden protocol, was developed by Dr Theo Seiler and his coworkers[1] and involves de-epithelializing the cornea and applying the vitamin riboflavin to the cornea over 30 minutes to enable the riboflavin to soak in. This in turn enhances the absorption of ultraviolet, to which the cornea is exposed. The ultraviolet triggers some form of chemical interaction with the collagen fibers, which results in stiffening. This stiffening can be demonstrated quite dramatically in the laboratory. Studies[2,3] have not found evidence of toxicity as long as the protocol is followed.

Results have been quite dramatic in terms of halting the progression of keratoconus and its kissing cousin, ectasia associated with refractive surgery. In some cases, there is actually a bit of reversal of corneal steepening, by several diopters.

The Avedro results in the United States have largely paralleled the European experience. Avedro is using a more intense ultraviolet light and a different formulation of riboflavin so that the dosing of the riboflavin is not as cumbersome and the time for exposure of the cornea is not as long, yet the total effect seems to be the same.

Approval of this technique marks a new era for patients with keratoconus in the United States because this treatment should halt most cases of keratoconus that progress and relegate corneal transplantation for keratoconus to an only rarely needed procedure.

What's Next in the Field?

This will not be the end of development in this area—quite far from it.

Several companies, including Avedro, are pursuing other technologies. One group is trying different formulations of riboflavin, which may enhance penetration through an intact epithelium. Others have tried partial disruption of the epithelium so that there is not a full defect but only partial disruption, resulting in less pain and more rapid healing. This most likely will also prevent the sporadic cases of mild corneal haze that have developed with treatment that uses full de-epithelialization.

Other interesting approaches are being pursued, including different formulations, different exposure times, combining prophylactic crosslinking with LASIK, and a localized treatment known as PiXL, which is designed to apply selected amounts of ultraviolet—different doses to different parts of the cornea—in order to influence the reshaping. All of this will require ongoing FDA trials for validation in the United States.

Much more is to come, but the critical first step is the FDA approval for the basic application of riboflavin and ultraviolet light to stiffen the cornea and prevent the progression of keratoconus and corneal ectasia. Stay tuned.

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