Observed versus indirect estimates of incidence of open-angle glaucoma

Incidence data on open-angle glaucoma (OAG) are limited and difficult to ob tain. To date, few studies have reported incidence directly measured from p opulation-based cohorts. Other reported estimates have been derived indirec tly from age-specific prevalence by using several assumptions, and their va lidity is unknown. To the authors' knowledge, this report presents the firs t comparison of observed versus indirect estimates of OAG incidence based o n data from the population-based Barbados Incidence Study of Eye Diseases ( 1992-1997) (n = 3,427; 85% participation). The observed 4-year incidence of OAG was 1.2% (95% confidence interval (CI): 0.6, 2.1%) at ages 40-49 years , 1.5% (95% CI: 0.8, 2.5%) at ages 50-59 years, 3.2% (95% CI: 2.0, 4.8%) at ages 60-69 years, and 4.2% (95% CI: 2.6, 6.3%) in persons at ages 70 or mo re years. When incidence was calculated from the prevalence data, power fun ction fitting achieved a closer approximation to observed incidence than di d logistic curve fitting. Calculated incidence rates for each group were si milar when assuming mortality that was equal (incidence rate = 0.7, 1.3, 2. 3, and 4.8%) or differential (incidence rate = 0.7, 1.2, 2.4, and 4.8%). Ot her nonlogistic approaches also increased the resemblance of observed and c alculated estimates. In the absence of longitudinal data, reasonably valid incidence estimates of OAG were obtained from available prevalence data. Th ese estimation techniques can be useful when OAG incidence estimates are re quired for research or public health purposes.