Sunday, December 10, 2006

Why Is Cornea Free of Blood Vessels?

Scientists at Harvard University's Department of Ophthalmology's Schepens Eye Research Institute and Massachusetts Eye and Ear Infirmary, Boston, say they 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, indicate 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 the most recent 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 spread of blood vessels. The cornea long has 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 not only serve to solve a profound scientific mystery, but 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, normally present in the cornea, can be used therapeutically in other tissues.

"This is a very significant discovery," emphasizes Reza Dana, an associate professor at Harvard University 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 or nonexistant."

The cornea, one of only two tissues in the body that actively keep themselves vessel-free (the other is cartilage), is the thin transparent tissue that covers the front of the eye. It is the clarity of the cornea that allows light to pass onto the retina and from there to the brain for interpretation. When the cornea is clouded by injury, infection, or abnormal blood vessel growth, vision severely is impaired, if not destroyed.

Scientists have been wrestling with the "clarity" puzzle for many decades. While some previous studies have revealed small clues, none have pointed to one major mechanism, until now.

Source: USA Today Magazine


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