Tracking a Vision Thief
Science still searches for the cause of sight-robbing AMD.
WebMD Feature At first, the only clue might be slightly distorted or blurry vision, or difficulty reading. When it gets worse, you decide to see your eye doctor.
In doing so, you might learn you have a condition called age-related macular degeneration, or AMD. In AMD, the macula -- the area of the retina that is responsible for your sharpest central vision -- deteriorates.
According to the National Eye Institute (NEI), one million people have AMD, the leading cause of blindness in people over the age of 60. Every year, 200,000 new cases are reported -- a number expected to increase as the baby boomer population ages.
In "dry" AMD, the tissues of the retina thin and the cells of the macula "drop out." If this progresses enough, the resulting washed-out appearance of objects can make fine details on items, such as the letters on street signs, difficult to make out. Distortions or warping of images can also occur.
About 10% of patients have the "wet" form of the disease, in which abnormal blood vessels develop in the layer of tissue under the retina and leak blood and fluid, usually causing scar tissue, which creates a central blind spot. This more aggressive version of AMD accounts for about 90% of severe vision loss from the disease, according to the NEI.
There is no proven treatment for dry AMD. Other than advising people to avoid cigarette smoking and bright sunlight -- both considered risk factors -- and to watch their overall health, there's not much doctors can suggest.
Laser surgery can sometimes help those with the wet form. However, whether treatment is successful depends for the most part on how close the abnormal blood vessels are to the center of vision. (That's because the laser is used to cauterize, but in the process it destroys the overlying retina.) Under study is a new approach that uses a low-energy laser and light-activated medication.
"The message is, you have to live with this until we figure out what to do," says Lylas Mogk, M.D., an ophthalmologist with the Henry Ford Health System in Grosse Point, Michigan, who has written a book on the topic.
Fortunately, Mogk says, those who are "hard of seeing" can be taught to rely on magnification and better use of their peripheral vision. "There's an enormous amount of vision remaining," she says.
Searching for a Cause and a Cure
Scientists are working to better understand the disease in the hope of discovering ways to prevent and better treat it.
Eating modified dietary fats, such as partially hydrogenated vegetable oil, along with exposure to environmental pollution such as cigarette smoke may play a role, Mogk believes. "We are seeing the first generation [of those] who have lived their whole lives since we've been pumping the environment full of chemicals," Mogk says.
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Studies in the October 9, 1996 issue of the Journal of the American Medical Association partially support her theory. Researchers found smokers are two to three times more likely to develop AMD.
According to Mogk, avoiding cigarettes, modified fats (because they can be deposited in the retina), and exposure to blue light (the wavelength just above ultraviolet) might help minimize the risk of getting AMD. (Orange, yellow, or amber-tinted lenses can block blue light.)
Several current studies, including one conducted by the NEI, are focusing on the possible preventive effects of antioxidants, such as vitamins A and E. Studies so far have yielded conflicting findings.
Other scientists are looking to foods that contain the same pigments found in the retina, says Jeff Blumberg, Ph.D., a researcher at Tufts University in Boston. "[These pigments] filter out wavelengths of light that can damage the retina," Blumberg says. He is studying the body's ability to use lutein and zeaxanthin, pigments that are found in eggs, corn, and spinach.
According to a study he conducted, published in the August 1999 issue of the American Journal of Clinical Nutrition, lutein and zeaxanthin are absorbed more efficiently from egg yolks than from the vegetable sources. "The important thing is that we've identified these nutrients in the diet," he says. "When levels in the blood go up, the density of the pigment in the retina goes up."
The next step, to prove that consuming certain foods can prevent macular degeneration, will require another 10 or 15 years, Blumberg says.
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