Measuring and interpreting the incidence of congenital ocular anomalies: lessons from a national study of congenital cataract in the UK.

PURPOSE: Prevention of visual impairment due to congenital cataract is an international priority. Estimates of incidence are required for implementation and assessment of preventive strategies, but are not widely available, despite routine monitoring of birth defects at a national level in many industrialized countries. The purpose of this study was to determine the incidence of new diagnosis of congenital and infantile cataract in the United Kingdom. METHODS: All children with newly diagnosed congenital and infantile cataract in the United Kingdom in 1 year from October 1995 through September 1996 were identified using independent ophthalmic and pediatric national active surveillance schemes. Capture-recapture analysis was used to estimate completeness of ascertainment. Annual age-specific and cumulative incidence were estimated and adjusted for ascertainment. RESULTS: Two hundred forty-eight children with newly diagnosed congenital or infantile cataract were identified-an estimated 92% of eligible cases. The adjusted annual age-specific incidence of new diagnosis of congenital and infantile cataract was highest in the first year of life, being 2.49 per 10,000 children (95% confidence interval [CI], 2.10-2.87). Adjusted cumulative incidence at 5 years was 3.18 per 10,000 (95% CI, 2.76-3.59), increasing to 3.46 per 10,000 by 15 years (95% CI, 3.02-3.90). Incidence of bilateral cataract was higher than that of unilateral, but incidence did not vary by sex or country of residence. CONCLUSIONS: These estimates of congenital and infantile cataract incidence were higher than reported previously from routine sources relying on passive notification around the time of birth. Studies of congenital ocular anomalies that are not always readily diagnosed at birth should consider the potential influence on disease frequency of diagnostic practices as well as of underlying disease risk.