The study enrolled 4757 participants from 11 clinical centers between 1992 and 1998. Eligible participants had best-corrected visual acuity of 20/32 or better in at least 1 eye and media sufficiently clear to obtain adequate-quality stereoscopic fundus photographs. Participants were stratified by AMD severity at study entry. The clinical trial investigated the ability of high-dose antioxidant vitamins to slow the development or progression of cataract and of high-dose antioxidant vitamins and zinc to slow the development of advanced AMD. Advanced AMD was defined as (1) photocoagulation or other treatment for choroidal neovascularization (based on clinical center reports) or (2) photographic documentation, as graded by a centralized fundus photograph reading center, of geographic atrophy involving the center of the macula, nondrusenoid retinal pigment epithelial detachment, serous or hemorrhagic retinal detachment, hemorrhage under the retina or the retinal pigment epithelium, or subretinal fibrosis. In the AREDS Manual of Operations, written prior to study initiation, it was estimated that persons in category 1 (few or no drusen) or 2 (small or a few intermediate-sized drusen) would be at low risk of progression to advanced AMD during the trial. For category 1, the risk was anticipated to be so low that exposing these participants to risks of high-dose zinc would be inappropriate. Participants in this category were not included in the AMD trial.