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Ian George Morgan, Fan Xiang, Yangfa Zeng, Jincheng Mai, Qianyun Chen, Jian Zhang, Kathryn Ailsa Rose, Mingguang He; INCREASED OUTDOOR TIME REDUCES INCIDENT MYOPIA - THE GUANGZHOU OUTDOOR ACTIVITY LONGITUDINAL STUDY. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1272.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether increased time outdoors reduces incident myopia in a school-based cluster-randomised three year trial.
Twelve primary schools were chosen from those monitored annually for uncorrected visual acuity by the Guangzhou Student Health Bureau. The schools were stratified by recent visual acuity data into 6 strata. One school from each stratum was randomly allocated to the control and intervention arms. All Year 1 classes in each school were enrolled in the study. Schools in the intervention arm had an additional 45 minute outdoor activity class at the end of each day. Control schools followed their normal activities. Parent information campaigns were conducted in the intervention schools. Cycloplegic refraction and axial length were measured at baseline and annually, for three years. Myopia was defined as spherical equivalent refraction of ≤ -0.5D. Results were adjusted for the cluster-sampling design using mixed models.
At baseline, the two arms were not significantly different in prevalence of myopia or mean spherical equivalent. Over three years, incident myopia, the primary outcome measure, was 39.5% in the control arm, compared to 30.4% in the intervention arm - a 23.0% reduction in cases of incident myopia (p<0.001). Small but statistically significant reductions were seen in myopic shift in mean spherical equivalent refraction. Less axial elongation was also seen in the intervention group, but this difference was not statistically significant. The intervention group reported an increased amount of time outdoors, outside of school hours (82.7 vs 61.0 minutes per day, p<0.0001), in addition to their additional outdoor time at school.
These results provide proof of principle that increasing the amount of time that children spend outdoors through the school system can decrease the number of children who become myopic. The estimated total difference in time outdoors between arms was 66.7 minutes per day (p<0.0001). The effect size is small, but epidemiological evidence suggests a dose-response relationship between protection and time outdoors. We therefore recommend that myopia control programs based on increased time outdoors be developed in primary schools, at least in countries with currently high prevalence rates for myopia, with evidence-based mandatory targets for the amount of time children spend outdoors.
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