BLOG: Catching a thief before it steals vision
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More than 25 years of global experience with collagen cross-linking has taught us two lessons: that cross-linking consistently prevents the progression of this disease and that the earlier it is performed, the better the patient’s outcome.
In the cover story of this issue of Ocular Surgery News, we explore the evolving trends in cross-linking that will make it more consistent, more safe and more precise.
But how do we identify patients before the clinical manifestations of keratoconus rob them of at least some of their vision? The answer may lie in a new genetic test that is becoming available in the U.S. The AvaGen genetic test from Avellino Lab helps stratify risk for patients who are family members of people with diagnosed keratoconus. It can also identify a number of transforming growth factor beta-induced corneal dystrophies by their pathognomonic genetic markers; its risk assessment for keratoconus is based upon more than 2,300 variants of 75 evaluated genes.
Unfortunately, there is no “pregnancy test” for keratoconus — a test with near perfect predictive precision. So, where do we draw the line in deciding in whom to perform cross-linking? Do we treat every patient whose risk assessment is greater than mild? Clearly that would be overtreating, and even though cross-linking is a mostly benign process, it does have risks and involves both cost and some degree of discomfort, although the latter is becoming less consequential as we migrate toward epithelium-on procedures. A more rational approach might mean following at-risk patients every 6 months with serial topography exams to identify progression before it would otherwise be suspected. If I had a family member in such a risk pool who had even mild signs of astigmatic shift, I would favor early cross-linking vs. waiting for a loss of best corrected vision. From a public health perspective, early treatment could prevent the need for hundreds of thousands of scleral and gas permeable contact lens fittings and 40,000 corneal transplant procedures annually in the U.S. alone.
Genetic testing for keratoconus has other important implications for refractive candidates as well. Here, its ideal use has yet to be worked out, but patients with a family history of keratoconus and a genetic risk score could be more intelligently guided from LASIK to PRK or other options.
The age of genetic testing in eye care has arrived, and I am personally excited about the opportunity to have better information to guide us toward better treatments.
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