Identifying Individuals with visual impairment in danish healthcare registries

Purpose: The prevalence of severe binocular visual impairment or blindness (SVI/B) in Denmark has been estimated at approximately 0.2% (12,500 individuals), although the exact number remains uncertain. While international studies have linked blindness to health disparities and reduced quality of life, this has not been thoroughly examined in the Danish context. The aim of this study was to establish a pragmatic registry-based approach for identifying individuals with SVI/B in Danish health registries, thereby enabling future research on health disparities among this population. Design: Register-based cross-sectional study. Participants: Individuals with SVI/B identified through the Danish Association of the Blind (DAB) and patients with relevant ICD-codes in the National Patient Register (NPR). Methods: Data from NPR and DAB were linked using the unique civil registration number (CPR). Capture-recapture analysis was applied to estimate the total population with SVI/B in Denmark. Results: Among DAB members, 86.4% had eye-related diagnoses recorded in NPR, whereas only 8.6% had diagnostic codes specifically indicating SVI/B. Using NPR data alone, a higher prevalence of individuals with comparable diagnoses was identified. Capture-recapture analysis estimated that 0.32% of the Danish population lives with SVI/B. Conclusion: Neither DAB nor NPR alone captured the entire population of individuals with SVI/B in Denmark, suggesting potential undercounting. However, when combined, these data sources provided a more comprehensive cohort for registry-based research on health and social disparities among individuals living with SVI/B.