Capture-recapture analysis of ascertainment by active surveillance in the British Congenital Cataract Study.

PURPOSE Active surveillance has not been widely used in ophthalmologic research. The use of capture-recapture analysis to determine completeness of case ascertainment by active surveillance in a national study of congenital cataract is reported. METHODS In 1 year in the United Kingdom, all incident diagnoses of congenital and infantile cataract were notified through independent ophthalmic and pediatric active surveillance schemes. Two-source capture-recapture analysis was applied to assess the level of ascertainment of infants (age < or = 12 months) by these two schemes. RESULTS In a 12-month period, 161 infants with newly diagnosed congenital or infantile cataract were notified. Overall ascertainment was estimated to be 92% complete and was higher in the ophthalmic (85%) than in the pediatric (45%) scheme. Comparison with the number of cases expected, from disease frequency reported in existing national congenital anomaly notification systems, suggests previous underascertainment of congenital cataract in such passive reporting systems. CONCLUSIONS This study shows the effectiveness of two-source active surveillance in identifying a nationally representative cohort that will provide better information about this disorder than has been available from sources of routinely collected data.