AMD and cataract are the leading causes of visual impairment and blindness in the United States. Based on many clinical studies, it is apparent that the frequency of both diseases increases dramatically after age 60. Although excellent treatments for cataract are available, there are no equivalent treatments for AMD. As the average lifespan of our population increases, the number of people who develop AMD will increase dramatically in the years ahead. Unless successful means of prevention or treatment are developed, blindness from AMD -- and its importance as a public health problem -- will increase.

Neither the etiology nor the natural history of AMD or cataract is known. Epidemiologic studies suggest that a number of risk factors may be associated with AMD and cataract, but the strength of the evidence in support of these hypotheses varies. Possibly associated with AMD are personal characteristics, such as age, race, height, family history, and strength of hand grip; ocular characteristics, such as hyperopia and color of iris; and cardiovascular diseases, smoking, lung infections, and chemical exposures. Clinical and laboratory studies suggest the following factors may be associated with progression of AMD: drusen type, choroidal vascular diseases, and photic injury.

Epidemiologic studies of cataract suggest that associated risk factors may include personal characteristics, such as age, sex, race, occupation, and educational status; ocular characteristics, such as iris color; and diabetes mellitus, hypertension, drug exposure, smoking, and sunlight exposure. Animal studies and observational epidemiologic studies suggest that deficiencies in vitamins C and E, carotenoids, and the trace elements zinc and selenium also may be associated with the development of the two diseases, especially cataract. Although surgical treatment to remove cataract is very effective, cataract surgery carries risks, as does any other surgery. Therefore, many research efforts focus on preventing or slowing cataract development, as well as on determining the causes of cataract formation.

The Age-Related Eye Disease Study (AREDS) is a major research program to improve our understanding of the predisposing factors, clinical course, and prognostic factors of AMD and cataract. Eligible patients are randomized to treatment with placebo, antioxidants, zinc, or antioxidants plus zinc, and are followed for a minimum of 5 years.