More sun, less myopia: validating CUVAF as a biomarker for outdoor exposure in a cohort of Spanish schoolchildren

Introduction The increasing global prevalence of childhood myopia has become a significant public health concern. Among environmental risk factors, reduced outdoor activity (OA) has been consistently associated with a higher incidence of myopia. While questionnaires are traditionally used to estimate sunlight exposure, conjunctival ultraviolet autofluorescence (CUVAF) has emerged as an objective biomarker for cumulative ocular UV exposure. Methods A cross-sectional case–control study was conducted among 2,616 children aged 7–8 and 11–12 years from 39 schools in Madrid, Spain. After reviewing the exclusion criteria, 354 children were removed from the study, leaving 2,262 participants in the sample. Participants were classified based on refractive error and underwent ocular examination and lifestyle questionnaires. The CUVAF area was measured in 1,129 children for logistical reasons, and they were grouped according to weekly time spent in OA (