Rahi, Jugnoo Sangeeta; (1998) The epidemiology of congenital and infantile cataract in the United Kingdom. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Congenital and infantile cataract is an important cause of visual impairment and blindness in childhood. Its prevention, through primary, secondary and tertiary strategies, remains an important international goal, requiring epidemiological data which are currently lacking. The work which forms the basis of this thesis was undertaken to determine the incidence, mode of detection, and underlying or associated causes of congenital and infantile cataract in the United Kingdom. A national cohort of incident cases of congenital and infantile cataract was identified through two national active surveillance schemes: a disorder-specific scheme in ophthalmology established specifically for this study, and an existing paediatric surveillance scheme for rare disorders. Capture-recapture analysis was used to assess level of ascertainment and derive ascertainment-adjusted incidence rates. In addition, completeness of notification of congenital cataract to the Congenital Anomaly System in England and Wales was assessed. During one year from October 1995, 248 children with newly diagnosed congenital or infantile cataract were identified, of whom 65% had bilateral disease. Overall ascertainment of infants through the surveillance schemes was estimated to be 92% complete. In contrast, 10%) of cases were notified to the national Congenital Anomaly System. The ascertainment-adjusted annual age specific incidence of cataract in infancy was 2.49 per 10,000 children, and is equivalent to cumulative incidence by one year of age. 47% of all cases had been detected through the national programme of routine examination of young infants, while 34% presented symptomatically. Only 57% of cases had been examined by an ophthalmologist by three months of age. Associated ocular disorders occurred in 47% of unilateral and 14% of bilateral cases (p<0.001) whereas 25% of bilateral and 6% of unilateral cases had associated systemic disorders (p<0.001). No cause for cataract was found in 92% of unilateral and 38% of bilateral cases. However possible contributing factors were noted in some of these idiopathic cases, including prematurity, low birthweight, and peri-natal hypoxia and hypoglycaemia. In contrast, hereditary disease accounted for 56% of bilateral cases. Prenatal infections and other systemic or environmental disorders were implicated in 5% of all cases. From this work, the observed incidence of congenital and infantile cataract is higher than previously reported, with evidence of under-ascertainment through existing routine sources. Nationally, the proportion of cases detected through screening is low, and could be improved. A higher than expected proportion of cases are idiopathic, suggesting a limited scope for primary prevention. Aetiological hypotheses, suggested by the findings of this research, warrant further exploration, as do factors associated with good visual outcome in later childhood. Active surveillance, combined with capture-recapture analysis, is an effective method for identifying children with congenital or infantile cataract and for determining its frequency, and thus merits application to the study of other rare ophthalmic disorders in the future.

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