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The media have given glaucoma much publicity as a cause of blindness, with accompanying warnings of the importance of regular eye examinations. However, a disease called age-related macular degeneration now accounts for more cases of legal blindness in the United States than any other cause. Macular degeneration afflicts 20 percent of people over age 75, and about one person in 16 aged 60-75.

Located in the exact center of the retina, where light is focused by the eye's lens, the macula is the retina's most sensitive part. The fine detail it provides to our vision is essential for carrying out many tasks, including reading. (The rest of the retina, on the other hand, provides the more general detail of whatever we are looking at.) A damaged macula can make objects indistinct or distorted, and may lessen color perception. An actual blind spot may develop in the center of the visual field.

There are two forms of the disease. In the more serious form, blood vessels begin to grow indiscriminately in the retina, producing hemorrhage that leads to distortion of the retina and eventually scarring, which may destroy the macula. Hemorrhaging in only one eye will have only a limited effect on central vision; however, chances are good that the other eye will eventually become involved as well.

Early detection of this form of the disease is very important. If the aberrant blood vessels can be destroyed by laser surgery before they do significant damage to the macula, central vision can be preserved. If the ophthalmologist sees small yellow spots on the macula, he may then choose to inject an orange dye into the patient's arm. The dye, when it makes its way to the retinal vessels, provides an easy target for laser surgery. Yearly eye examinations for persons over 40 will not only reveal macular degeneration, but other potentially disabling conditions such as glaucoma and cataracts.

The other form of the disease is not so serious (fortunately, because its cause and treatment are unknown). Eighty percent of cases are of this atrophic type, in which the macula tends simply to dry up, with limited visual loss. There is some evidence that zinc supplements may have some effect on this form of the disease, but it is not conclusive, and excessive amounts of zinc can be harmful. Persons using such supplements should therefore limit their intake to well under 100 mg of zinc daily.

Although they may be legally blind, persons with severe macular degeneration can learn to use their peripheral vision quite effectively with the help of magnifying instruments, good reading lamps, and large-print editions of reading material.
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Title Annotation:age-related macular degeneration
Publication:Medical Update
Date:Mar 1, 1992
Words:438
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