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Prevalence and causes of vision impairment in Norwest Portugal: a capture and recapture study

Aim: The aim of this study was to estimate the prevalence and causes of vision impairment (VI) in the Norwest of Portugal. Methods: Information about people with VI was obtained from different sources in the Norwest of Portugal during a period spanning years 2014-2015. Log-linear models were applied to estimate the number of individuals missing from lists of cases obtained from Primary Care Centres, blind association (ACAPO) and from hospitals (the PCVIP-study). Log-linear models were used to estimate the crude prevalence and the category specific prevalence of VI. Causes of VI were obtained from the PCVIP-study. Results: Crude prevalence of VI was 1.97% (95%CI=1.56-2.54), and normalized prevalence was 1% (95%CI=0.78-1.27). The age-specific prevalence was 3.27% (95% CI,=2.36-4.90), older than 64 years, 0.64% (95%CI=0.49-0.88), aged 25-64 years, and 0.07% (95%CI=0.045-0.13), aged less than 25 years. Prevalence amongst females was 1.3x higher than amongst males. The five leading causes of VI were Diabetic Retinopathy, Cataract, Age-related Macular Degeneration, Glaucoma and Disorders of the Globe. Conclusion: The prevalence of VI in Portugal was within the expected range and in line with other European countries. A significant number of cases of VI might be due to preventable cases and, therefore, a reduction of the prevalence of VI in Portugal seems possible. Women and old people were more likely to have VI and, therefore, these groups require extra attention. Future studies are necessary to characterize temporal changes in prevalence of VI in Portugal.