Abstract: Objective To explore the prevalence and associated factors of myopia among Grade-1 and Grade-4 primary students in urban and rural regions of Beijing. Design School-based, cross-sectional investigation. Participants Two schools were investigated. Three hundred eight-two Grade-1 and 299 Grade-4 primary students participated in the study. Methods Comprehensive eye examination including visual acuity, ocular motility evaluation, auto-refraction, slit lamp biomcroscopy, ocular biometry and non-mydriatic fundus photography were carried out on all paticipants. Parents and children were administered detailed questionnaires including general information, nearwork, social-economic parameters and outdoor activity. Main Outcome Measures Prevalence and associated factors of myopia. Results According to different definitions of myopia (Spherical Equivalent, SE≤-0.50 D，≤-1.00 D，≤-1.50 D，≤-2.00 D), the prevalence was 48.1%, 27.9%, 17.5% and 11.6%, respectively. In multivariate logistic regression analysis, the prevalence of myopia（SE≤-1.00 D）was associated with age (P=0.003, OR=1.45, 95% canfidence intervals, CI: 1.25，1.67), place (P=0.000, OR=0.20, 95%CI: 0.14，0.29), parental myopia(P=0.000, OR=2.99, 95%CI: 1.83，4.89), outdoor sports (P=0.013, OR=0.14, 95%CI: 0.03，0.65), outdoor leisure (P=0.001, OR=0.33, 95%CI: 0.22，0.49), outdoor activity(P=0.001, OR=0.35, 95%CI: 0.24，0.50), studying indoors (P=0.001, OR=1.37, 95%CI: 1.09，1.72), watching television indoors (P=0.008, OR=0.66, 95%CI: 0.52，0.84). Correspondingly, axial length was significantly associated with higher age (P=0.000; standardized coefficient beta: 0.28), taller body height (P=0.001; beta: 0.18), parental myopia (P=0.03; beta: 0.09) and urban region of habitation (P=0.000; beta: -0.21), less time spent outdoors (P=0.001; beta: -0.16), outdoor leisure（P=0.001；beta：-0.15）and more time spent indoors with studying (P=0.02; beta: 0.10). Children with higher age, urban region of habitation, less time spent outdoors, parental myopia, more time spent indoors with studying had higher prevalence of myopia and longer axial length. Conclusions The prevalence of myopia and axial length were associated with older age, urban region of habitation, parental mypia, more indoor studying and less outdoor activity. More outdoor activity may potentially be helpful to reduce the high prevalence of myopia in the young generation. (Ophthalmol CHN, 2012, 21: 127-131)

Key words: myopia, associated factors, outdoor activity