Refractive status, visual behaviour, and parental myopia in Portuguese schoolchildren and adolescents

To investigate the association between refractive status and clinical, biometric, behavioural, academic, and familial factors in Portuguese children and adolescents. A cross-sectional study was conducted in 347 participants aged 6–18 years. Refractive status was assessed using non-cycloplegic refraction and classified as myopia, emmetropia, or hyperopia based on spherical equivalent. Clinical and biometric parameters were assessed, and sociodemographic, academic, parental, and behavioural data (study time, mobile phone use, and outdoor activities across seasons) were collected. Group comparisons were performed using ANOVA or Kruskal–Wallis tests, and associations were analysed using chi-square tests and correlation coefficients. A multinomial logistic regression model was constructed with emmetropia as the reference category to identify independent predictors of refractive status. Significant differences between refractive groups were observed for age, spherical equivalent, cylinder, mean spherical component, J0 component, and axial length (all p ≤ 0.005), but not for pupil diameter (p = 0.932). Myopic participants were older and had longer axial lengths, while hyperopic participants were younger with shorter axial lengths. Refractive status was significantly associated with age group, school grade, academic performance, and parental refractive error (all p ≤ 0.017). In the regression model, students in lower school grades had lower odds of myopia compared with those in higher grades after adjustment for axial length (OR = 0.19, p < 0.001). Poor academic performance was also associated with lower odds of myopia (OR = 0.21, p = 0.034). No statistically significant associations were observed for parental myopia. Mobile phone use showed significant associations with refractive status in winter, spring, and autumn (all p ≤ 0.024), but not summer (p = 0.102). Study time showed no significant associations in any season, and outdoor activities showed significant association only in spring (p = 0.003). Refractive status in Portuguese schoolchildren is strongly associated with objective measures including age, educational level, parental refractive error, and axial length. The counterintuitive association between poor academic performance and lower myopia odds likely reflects residual confounding by socioeconomic factors rather than a protective effect. Mobile phone use showed exploratory season-specific associations during school terms, though these findings require confirmation with objective measurement and longitudinal designs. Study time and outdoor activities showed weaker associations, likely reflecting measurement error in parent-reported data. These findings should be interpreted cautiously given the non-cycloplegic refraction methodology, which may overestimate myopia prevalence, particularly in younger children.