PURPOSE: To describe the change in visual acuity in a 15-year period. DESIGN: Population-based study. METHODS: setting: Beaver Dam, Wisconsin. participants: 4068 persons 43 to 86 years of age at the time of a baseline examination in 1988 to 1990, and with follow-up examinations every five years thereafter. observation procedures: Best-corrected visual acuity after refraction, assessed by a modification of the ETDRS protocol. main outcome measure: Doubling of the visual angle; incidence of visual impairment. RESULTS: Eight percent of the population developed impaired vision (20/40 or worse), 0.8% developed severe visual impairment (20/200 or worse), 7% had doubling of the visual angle, and 2% had improved vision. People 75 years of age or older at baseline were more likely to develop impaired vision (odds ratio [OR] 12.8, 95% confidence interval [CI] 9.6 to 17.1, P < .001), doubling of the visual angle (OR 7.8, 95% CI 5.6 to 10.7, P < .001), and severe visual impairment (OR 20.6, 95% CI 9.5 to 44.8, P<0.001) compared with people younger than 75 years of age. CONCLUSIONS: These data provide population-based estimates of the cumulative 15-year incidence of loss of vision over a wide spectrum of ages. In people 75 years of age or older the cumulative incidence of visual impairment accounting for the competing risk of death is 25%, of which 4% is severe, indicating a public health problem of considerable proportions as the US population in this age is expected to increase by 55% from 18 million in the year 2005 to 28 million by the year 2025.