- Macular degeneration
- A disease that progressively destroys the macula, the central portion of the retina, impairing central vision. Macular degeneration rarely causes blindness because only the center of vision is affected. However, injury to the macula in the center of the retina can impair the ability to see straight ahead clearly and sometimes make it difficult to read, drive, or perform other daily activities that require fine central vision. The macula is in the center of the retina at the back of the eye. As we read, light is focused onto the macula where millions of cells change the light into nerve signals that travel to the brain and tell it what we are seeing. This is our central vision. With normal central vision, we are able to read, drive, and perform other activities that require fine, sharp, straight-ahead vision. There are a number of forms of macular degeneration that affect young people. However, the disease occurs most commonly in people over 60 years of age. This disorder is termed age-related macular degeneration (AMD). There are two types of AMD — the dry type and the far more frequent wet type. Neither type causes pain. An early symptom of wet AMD is that straight lines appear wavy. This happens because the newly formed blood vessels leak fluid under the macula. The fluid raises the macula from its normal place at the back of the eye and distorts vision. Another sign that a person may have wet AMD is rapid loss of central vision. This is different from dry AMD in which loss of central vision occurs slowly. In both dry and wet AMD, the person may also notice a blind spot. If any of these changes in vision is noticed, an ophthalmologist should be consulted without delay. Supplements of zinc and the antioxidants vitamin C, vitamin E and beta-carotene reportedly slow the progression of wet AMD. In people with intermediate-stage disease, zinc reduced the risk of the disease progressing to the advanced stage by 11%, and the antioxidants reduced the risk by 10%. When the two were combined, the risk was reduced by 19%. The daily doses of the antioxidants used in the study were 500 milligrams of vitamin C, 400 milligrams of vitamin E and 15 milligrams of beta-carotene (a molecule the body converts to vitamin A). The daily dose of zinc was 80 milligrams with 2 milligrams of copper. These amounts are well above the usual levels recommended by the Food and Drug Administration (FDA): 3 times as much vitamin A, 8 times as much vitamin C, 13 times as much vitamin E and 5 times as much zinc.
* * *macular degeneration n progressive deterioration of the macula lutea resulting in a gradual loss of the central part of the field of vision esp age-related macular degeneration
* * *a group of conditions affecting the macula lutea of the eye, resulting in a reduction or loss of central vision. Age-related macular degeneration (AMD, ARMD) is the most common cause of blindness in the elderly. Two types are commonly recognized. Atrophic (or dry) AMD results from chronic choroidal ischaemia: small blood vessels of the choroid, which lies beneath the retina, become constricted, reducing the blood supply to the macula. This gives rise to degenerative changes in the retinal pigment epithelium (RPE; see retina), clinically recognized by macular pigmentation and the deposition of drusen. Wet AMD is associated with the growth of abnormal new blood vessels under the retina, derived from the choroid (see neovascularization). These can leak fluid and blood into the RPE, which further reduces macular function. Laser surgery (see photocoagulation) can halt the degenerative process.
* * *degenerative changes in the macula lutea. Age-related macular degeneration (q.v.) is the most common cause of blindness in persons over age 65. Less common types that are congenital are Best disease and Stargardt disease (see under disease).
Medical dictionary. 2011.