The macula lutea, a yellowish area in the central region of the retina, contains a concentration of cones, especially in the fovea centralis. Vision is most acute and colors are detected in the macula lutea. Macular degeneration in the elderly (or agerelated macular degeneration) is now the most frequent cause of legal blindness in the United States. Individuals with this condition have a distorted visual field: Blurriness or a blind spot is present, straight lines may look wavy, objects may appear to be larger or smaller than they are, and colors may look faded.
There are two main forms of age-related macular degeneration. "Wet" macular degeneration means that abnormal growth of new blood vessels is evident in the region of the macula. The blood vessels leak serum and blood, and the retina becomes distorted, leading to severe scarring that completely destroys the macula. "Dry" macular degeneration is not accompanied by the growth of blood vessels, and visual loss is less dramatic.
Heredity plays a role in the development of age-related macular degeneration: 15% of people with a family history of the condition develop the disease after age 60. Also, light-eyed people tend to be afflicted more frequently than dark-eyed people. Smoking, hypertension, and excessive sun exposure are possible contributing factors.
A yearly eye examination assists in the early detection of many eye diseases, including macular degeneration, cataracts, and glaucoma. When an ophthalmologist presents an Amsler grid (a crosshatched pattern of straight lines) to someone with macular degeneration, the grid looks blurred, distorted, or discolored. Signs of the "wet" form can be detected by an examination of the retina and confirmed by a fluorescein angiogram. In this test, a number of pictures are taken of the macula lutea after an orange dye has been injected into a vein in the patient's arm.
Currently, the only treatment for the "dry" form of macular degeneration is the use of vitamin and mineral supplements, which may help stem the disease. For example, research indicates that consumption of zinc may prevent further loss of vision. On the other hand, when the "wet" form of the d~ase is diagnosed early, laser treatment can sometimes stop: the growth of blood vessels.
Although people with age-related macular degeneration are classified as blind, they still have normal peripheral vision (outside the macula), which they can learn to use effectively. Because the periphery of the retina contains a high concentration of rods, vision here is less acute, and colors are not detected. But high-powered eyeglasses, magnifying devices, closed-circuit television, and special lamps can help patients see details more clearly.
Accumulating evidence suggests that both macular degeneration and cataracts, which tend to occur in the elderly, are caused by long-term exposure to the ultraviolet rays of the sun. Therefore, everyone-especially those who live in sunny climates or work outdoors-should wear sunglasses that absorb ultraviolet light. Large lenses worn close to the eyes offer further protection. The Sunglass Association of America has devised the system that follows for categorizing sunglasses . (Note: UV-B rays are the cancer-causing ultraviolet rays. UV-A rays are believed to increase the effect of UV-B rays.)
- Cosmetic lenses absorb at least 70% of UV-B rays, 20% of UV-A rays, and 60% of visible light. Such lenses are worn for comfort rather than protection.
- General-purpose lenses absorb at least 95% of UV-B rays, 60% ofUV-A rays, and 60-92% of visible light. They are good for outdoor activities in temperate regions.
- Special-purpose lenses block at least 99% of UV-B rays, 60% of UV-A rays, and 20-97% of visible light. They are good for bright sun combined with sand, snow, or water .
