Observed versus indirect estimates of incidence of open-angle Glaucoma

ABSTRACT

Incidence data on open-angle glaucoma (OAG) are limited and difficult to obtain. To date, few studies have reported incidence directly measured from population-based cohorts. Other reported estimates have been derived indirectly from age-specific prevalence by using several assumptions, and their validity is unknown. To the authors' knowledge, this report presents the first comparison of observed versus indirect estimates of OAG incidence based on data from the population-based Barbados Incidence Study of Eye Diseases (1992-1997) (n= 3,427; 85 percent participation). The observed 4-year incidence of OAG was 1.2 percent (95 percent confidence interval (CI)ages 60-69 years, and 4.2 percent (95 percent CI 2.6, 6.3 percent) in persons at ages 70 or more years. When incidence was calculated from the prevalence data, power function fitting achieved a closer approximation to observed incidence than did logistic curve fitting. Calculated incidence rate for each group were similar when assuming mortality that was equal (incidence rate= 0.7, 1.3, 2.3, and 4.8 percent) or differential (incidence rate= 0.7, 1.2, 2.4, and 4.8 percent). Other nonlogistic approaches also increased the resemblance of observed and calculated estimates. The absence of longitudinal data, reasonably valid incidence estimates of OAG were obtained from available prevalence data. These estimation techniques can be useful when OAG incidence estimates are required for research or public health purposes. (AU)