Objective: To provide 4-year cumulative incidence and progression rates of age-related lens opacities in a population > or =40 years of age, which is mainly of African origin.
Design: Cohort study that reexamined surviving members of the population-based Barbados Eye Study 4 years after baseline.
Participants: Three thousand four hundred twenty-seven members of the Barbados Eye Study cohort (85% of those eligible).
Main outcome measures: The Lens Opacities Classification System II (LOCS II) was used at the slit lamp. Cumulative incidence was defined as the development of any nuclear, cortical or posterior subcapsular (PSC) opacities (LOCS II scores > or =2) among persons without that opacity type at baseline. Cumulative progression was defined by at least two-step increases in scores among persons with preexisting lens opacities.
Results: The incidence of cortical opacities was about five times greater in black than white participants (age-gender adjusted relative risk = 4.7; 95% confidence interval: 1.9-11.4). In the black population, the 4-year incidence rates were 22.2% (20.4%-24.0%) for any cortical, 9.2% (8.2%-10.4%) for any nuclear, and 3.3% (2.7%-4.0%) for any PSC opacities; rates increased greatly with age. Four-year progression rates were 12.5% for cortical, 3.6% for nuclear, and 23.0% for PSC opacities, without consistent pattern by age. Women had a greater risk of cortical and nuclear opacities (P<0.05) than men and greater progression of nuclear opacities. The presence of PSC opacities at baseline seemed to at least double the incidence and progression rates of other opacities. In persons initially opacity free, single cortical opacities were the predominant type to develop at followup. Visual acuity loss frequently accompanied incident opacities.
Conclusions: This longitudinal study provides new population-based data on the natural history of lens opacities. Incidence and progression of opacities, especially of cortical opacities, were high. After 4 years of followup, 1 in 4 to 5 participants developed cortical opacities, 1 in 11 developed nuclear opacities, and 1 in 30 developed PSC opacities. The information obtained attests to the public health impact of age-related cataract, as well as its extent, in this and similar black populations.