( Scientists at the Harvard Department of...)Scientists discover why cornea is transparent and free of blood vessels, allowing vision

Scientists at the Harvard Department of Ophthalmology's Schepens Eye Research Institute and Massachusetts Eye and Ear Infirmary (MEEI) are the first to learn why the cornea, the clear window of the eye, is free of blood vessels--a unique phenomenon that makes vision possible. The key, say the researchers, is the unexpected presence of large amounts of the protein VEGFR-3 (vascular endothelial growth factor receptor-3) on the top epithelial layer of normal healthy corneas. According to their findings, VEGFR-3 halts angiogenesis (blood vessel growth) by acting as a "sink" to bind or neutralize the growth factors sent by the body to stimulate the growth of blood vessels. The cornea has long been known to have the remarkable and unusual property of not having blood vessels, but the exact reasons for this had remained unknown.

These results, published in the July 25, 2006 issue of the Proceedings of the National Academy of Sciences and in the July 17 online edition, not only solve a profound scientific mystery, but also hold great promise for preventing and curing blinding eye disease and illnesses such as cancer, in which blood vessels grow abnormally and uncontrollably, since this phenomenon, present in the cornea normally, can be used therapeutically in other tissues.

"This is a very significant discovery," says Dr. Reza Dana, Senior Scientist at the Schepens Eye Research Institute, head of the Cornea Service at the Massachusetts Eye and Ear Infirmary, and an associate professor at Harvard Medical School, and the senior author and principal investigator of the study. "A clear cornea is essential for vision. Without the ability to maintain a blood-vessel-free cornea, our vision would be significantly impaired," he says, adding that clear, vessel-free corneas are vital to any animal that needs a high level of visual acuity to survive.

The cornea, one of only a few tissues in the body that actively keep themselves vessel-free (the other is carti
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Source:Schepens Eye Research Institute

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