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    Collagen corneal cross-linking for keratoconus

    Corneal collagen cross-linking is a treatment for keratoconus that was approved in the United States in April 2016. The procedure has long been available in Europe, and Avedro’s approval of Photrexa brings it to many more patients in need.

    Let’s first understand the condition of keratoconus.

    Understanding keratoconus

    Keratoconus is a progressive, degeneration of the cornea which often begins in teenagers and slowly progresses at a variable rate for the rest of the patient’s life. It is estimated that the incidence of keratoconus in the United States is about one in 2000 patients, but that number may be much higher when using modern screening strategies. In some countries, keratoconus is much more common, affecting as many as one patient in 500.

    Because the cornea is the primary focusing lens of the eye, even mild cases of keratoconus have an effect on the quality of the patient’s vision. The most common early symptom of keratoconus is blurred vision caused by astigmatism Keratoconus is almost always bilateral, but it can be more advanced in one eye than the other.


    At first, glasses can adequately correct the vision; however, the amount and axis of the astigmatism in keratoconus changes frequently and in many patients glasses no longer provide clear vision and contact lenses are often required. Because the astigmatism is asymmetrical, rigid gas permeable contact lenses usually provide the best vision.

    Most patients can function for years with contact lenses, and in fewer than 10 percent of patients the degeneration becomes severe requiring corneal transplantation. Figure 1 shows a side view of a cornea with a cone-shaped protrusion indicating advanced keratoconus.

    James J. Salz, MD
    Clinical professor of ophthalmology, University of Southern California, Los Angeles


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    Optometry Times A/V