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.