Keratoconus is an eye disorder that causes corneal tissue to become abnormally thin and the central area to protrude in a cone shape, distorting vision. The cornea is the clear tissue that covers the front of the eye and is crucial to focusing light on the back of the eye. In the US, keratoconus occurs in 50 to200 per 100,000 people; reported rates vary with the criteria used for diagnosis. Unofficial reports indicate this disorder may be more prevalent in the Indian subcontinent, Arabia, and New Zealand.
Although usually a progressive disease, recent data suggests that it stabilizes after time in most patients, and that treatment with rigid contact lenses is successful for many. Ten to 20 percent of keratoconus patients in the US eventually receive corneal transplants to restore their vision.
Co-investigators Mohan Rajan, MD, and Sujatha Mohan, MD, of the Rajan Eye Care Hospital, India, studied collagen crosslinking in 48 patients (60 eyes), aged 12 to 48 years, who had progressive keratoconus. The collagen crosslinking technique, developed in recent years, is under study for the treatment of several eye disorders. In keratoconus patients, drops containing riboflavin, a B-complex vitamin, are applied to the cornea which is then exposed to UVA light; this stimulates collagen fibers to connect to one another, or crosslink. Collagen is the primary protein constituent of the body's connective tissues. The procedure helps restore appropriate curvature and structure to the cornea, and makes it possible for most patients who need them to wear rigid contact lenses again. Collagen crosslinking may prove a viable alternative to cornea transplant, and three FDA-approved trials are now underway in the US.
The Rajan-Mohan study involved 40 eyes (group A) in which infected tissue and any foreign matter were removed from the top tissue layer, and 20 eyes (group B) in which the tissue layer was left intact prior to treatment. Patients received follow-up exams at one, three, six and twelve months. Vision corrected with eyeglasses or contact lenses improved in 45 percent of patients by six months, but no change was noted in any patients' vision when measured without eyeglasses or contact lenses. The corneal curve flattened appropriately in 51 of 60 eyes (85 percent), with more significant flattening in group A patients. Based on subjective reports, 46.6 percent of participants were better able to tolerate wearing contact lenses. No significant side effects were noted.
"In our study collagen crosslinking showed promising results," said Dr. Mohan. "The positive corneal changes observed in these patients, together with improved vision and contact lens tolerance, indicates that it was a safe and effective procedure for these keratoconus patients." Because it is less invasive than corneal transplant, the patient's surgery-related risks are reduced. As a less expensive, technically simpler procedure, collagen crosslinking could be particularly useful in developing countries where corneal transplant and other procedures may be difficult to access.
This research was presented at the 2008 Joint Meeting of the American Academy of Ophthalmology (Academy) and European Society of Ophthalmology (SOE ) that runs November 8 to 11 at the Georgia World Congress Center, Atlanta.
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