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PM Hart, C Patterson, F Kee; Estimating the Prevalence of Blindness from Diabetic Retinopathy: an Application of Capture-recapture Methodology . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4383.
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Purpose: The epidemiological value of blind and partially sighted registration statistics in the UK has been questioned in several papers reporting under-registration of the magnitude of approximatly 50%. This study used capture recapture methods, to provide a)an estimate of the point prevalence of blindness as a result of diabetic retinopathy in our region b) an assessment of the completeness of the regional statutory blind registration figures. Methods: A three-sample capture-recapture analysis was used to estimate the point prevalence of blindness from diabetic retinopathy (logMAR ≷ 1.3, WHO definition ) at 01.01.2000. Sources used were 1) statutory data 2) all low vision clinic data in the region 3) hospital clinic data and specialist diabetes nurses. Log linear models were fitted to the data in a 3-dimensional contingency table. This provided predicted values for the unobserved cell, that is the number of people who would meet the inclusion criteria but whom we have failed to identify from any source. Thus a final estimate of the total population of interest could be made. Results: The 3 sources provided a total of 189 eligible individuals. The statutory data identified 172( 91%)of these. The model which provided the best fit suggested that 21 cases had not been ascertained by any source. The estimated total therefore is 210. Statutory data identified 82% of this total. The prevalence of blindness from diabetic retinopathy at 1/1/2000 was 12.4 per 100,000 of the population. The choice of log linear model influences the estimation of cases in the missing cell, however the maximum (27) is not very different from the estimate of 21 from the chosen model. Conclusion: Diabetic retinopathy continues to be the leading cause of blindness in people of working age in the developed world. Recognising the limitations of the methodology, this study suggests that under registration may be less marked in the diabetic population than in the total visually impaired population. This is consistent with other studies which showed that increasing age was a risk factor for under registration. Capture-recapture techniques suggested that, in the region studied, statutory sources ascertained 82% population of interest.
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