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Yuanbo Liang, Zhong Lin, Balamurali Vasudevan, Vishal Jhanji, Tieying Gao, Ningli Wang, Kenneth Ciuffreda, Beijing Myopia Progression Study Group; Outdoor activity exhibit protective effect for myopia in children having a moderate near workload. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5698.
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To assess the relationship between near work, outdoor activity, their interaction and refractive error in school children in urban Beijing, China.
In this cross-sectional study, students recruited through the Beijing Myopia Progression Study (BMPS) were asked to complete a detailed questionnaire on both their near work and outdoor activities. In addition, cycloplegic and non-cycloplegic refraction were performed in the children and their parents, respectively.
A total of 370 students (172 boys and 198 girls) were enrolled. The total time of near work (e.g., reading) and outdoor activity (e.g., sport and leisure activities) was 4.04 ± 1.72 and 1.88 ± 1.25 hour per day, respectively. Activity levels were divided into low, moderate and high using population tertiles of the average daily hours spent in these different activities. The more time students spent on near work activity, the more myopic they became in all three outdoor activity tertile groups (p= 0.02, p< 0.001, and p= 0.01, respectively) after adjusting for children’s age, gender and average parental refractive error. However, significant protective associations with increased outdoor activity were only found in the moderate near work tertile group (near work activity ranged from 3.1 to 4.6 hours per day; the multiple-adjusted mean spherical equivalent was -2.19, -1.52 and -1.50D, p=0.03). No such protective effect was found in low (near work activity less than 3.1 hours per day; the multiple-adjusted mean spherical equivalent was -1.21, -0.89 and -1.18D, p=0.88) or high near work tertile group (near work activity more than 4.6 hours per day; the multiple-adjusted mean spherical equivalent was -2.02, -2.26 and -1.98D, p=0.81). No interaction was found between near work and outdoor activity tertile groups (p=0.92).
Higher levels of near work activity were associated with more myopic refraction in school age children in urban China. The protective effect of outdoor activity may exhibit its effect in children having a moderate near workload only.
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