A model of the prevalence and incidence of low vision and blindness among adults in the U.S.

Population-based vision screening studies of the prevalence rate of low vision and blindness in the U.S. are reviewed to evaluate the sources of disagreement among studies. The major reasons that studies disagree on prevalence rate estimates are differences in best-corrected visual acuity criteria for low vision and differences in the age range of the oldest age category. When corrections are made for these differences, the results of all prevalence rate studies, except the Mud Creek Valley Study, fit the same prevalence rate vs. age function. The greater prevalence rate of low vision and blindness for each age category that was observed in the Mud Creek Valley Study can be attributed to the higher prevalence rate of cataract associated with a paucity of health care services in the Mud Creek Valley population. The time-derivative of the prevalence rate vs. age function fit to the data provided an estimate of the annual incidence rate of low vision and blindness vs. age. The estimated annual incidence agreed with estimates from unpublished 8-year incidence data of the Baltimore Eye Survey. The incidence rate of low vision and blindness for Americans aged 40 to 60 years is higher among blacks than among whites. For Americans greater than age 60 years, the incidence rate for whites exceeds that for blacks. This observation probably reflects the different natural histories of glaucoma, a leading cause of low vision and blindness among black Americans, and age-related macular degeneration, a leading cause of low vision and blindness among white Americans. Using the age-dependent models of prevalence rate of low vision and blindness for white and black populations, an estimated 1.5 million Americans over age 45 years have a best-corrected visual acuity in the better eye that is < or = 20/70. Based on the incidence rate estimates, approximately 240,000 new cases of low vision and blindness occur each year. With the aging of the U.S. population, that number is expected to double over the next 25 years.