Epidemiology of refractive error and refractive changes in preschool children in Belgium

PURPOSE: To assess the proportions and progression of refractive errors (spherical equivalent, astigmatism and anisometropia) in preschool children, to examine associations with demographic and environmental factors and to describe emmetropisation by providing normative reference values for early refractive development. METHODS: This retrospective cohort study included children in Flanders, Belgium undergoing routine vision screening, with non-cycloplegic refractive measurements at 12, 24 and 30 months using the PlusoptiX photoscreener, linked to maternal and child epidemiological data. Refractive errors were classified using predefined thresholds. Linear models assessed associations between SE and demographic, perinatal and socio-economic variables. Emmetropisation was evaluated using paired measurements, with rates defined as monthly changes in SE or cylinder power. RESULTS: Mean SE remained mildly hyperopic across all ages, with clinically negligible sex differences. Higher maternal education and more privileged socio-economic status were associated with slightly lower SE, particularly at 30 months. We observed clear ethnic differences in both SE and astigmatism type, with African children showing the highest SE, followed by Asian children and European children the lowest, highlighting ethnicity as a possible confounding factor for epidemiological studies. We observed evidence of emmetropisation for both SE and astigmatism, with faster rates of change in eyes with higher initial refractive errors. CONCLUSION: This study provides normative data on refractive development and proportions of early refractive errors in a multi-ethnic cohort of preschool children. The inclusion of normative emmetropisation tables offers practical guidance for paediatric ophthalmologists in clinical assessment. Observed ethnic differences highlight the importance of considering ethnicity in both clinical practice and future epidemiological research.