Abstract: Objective To assess the change and associated factors of ocular biometry parameters in schoolchildren of Beijing. Design School-based, longitudinal study. Participants 382 Grade-1 and 299 Grade-4 students from two schools participated in the study located in DongCheng District (urban) and HuaiRou District (rural). Methods Baseline study was conducted in 2011, and followed up in 2012 and 2013. Comprehensive eye examinations were same in three years, including visual acuity, ocular motility evaluation, auto-refraction, slit lamp, ocular biometry with Lenstar Biometer and non-mydriatic fundus. Participants were administered detailed questionnaires including nearwork, social-economic parameters and outdoor activity. Multivariate regression analysis was used to analyze the change of ocular biometry, axial length/corneal curvature, refraction and associated factors. Main Outcome Measures Parameters of ocular biometry and refraction degree. Results Mean spherical equivalent was  (-0.55±1.30) D at baseline. Mean axial length was (23.03±0.96) mm. Mean axial length/corneal curvature (AL/CC) was (2.94±0.11). In 2012 and 2013, progression of refraction was (-0.07±0.88) D and (-0.62±1.03) D. Elongation of axial length was (0.26±0.49) mm and (0.32±0.92) mm. An increase in myopic refractive error, after adjustment for age, was significantly associated with less time spent outdoors for leisure (P=0.006), less total time spent outdoors (P=0.04), or more time spent indoors with studying (P=0.005). Elongation of axial length was significantly associated with less total time spent outdoors (P=0.02) and more time spent indoors with studying (P=0.007) after adjustment for maternal myopia (P=0.02). An increase in AL/CC was significantly associated with less time spent outdoors (P=0.01) after adjustment for paternal myopia (P=0.003). Conclusions Progression of myopia, elongation of axial length and change of AL/CC in schoolchildren of Beijing were associated with older age, urban region of habitation, parental myopia, more indoor studying and less outdoor activity after two years follow up. The study provides more evidence in myopia risk factors research. (Ophthalmol CHN, 2015, 24: 19-24)

Key words: ocular biometry, myopia/epidemiology