Effect of Outdoor Activities in Myopia Control: Meta-analysis of Clinical Studies

SIGNIFICANCE: Our meta-analyses assess the benefit of outdoor activities on myopia onset and myopic shift among school-aged children reported in prospective intervention studies. PURPOSE The purpose of this study was to investigate the reduced risk of myopia development, myopic shift, and axial elongation with more outdoor activity time among school-aged children. METHODS A literature search was conducted using PubMed, MEDLINE, Scopus, EMBASE, VisionCite, and Cochrane Library. Five clinical trials met our selection criteria. Three outcome variables were used to assess the benefit of intervention: relative risk (RR), difference in myopic shift rate, and difference in axial elongation rate. Meta-analyses were applied to each outcome variable under the random-effects model. Children were grouped according to their initial refractive status: initial myopes, initial nonmyopes, or mixed. RESULTS The pooled RR indicates that there is a reduced risk of developing myopia with more hours of outdoor activities per week (RR, 0.66; 95% confidence interval [CI], 0.49 to 0.89). The overall rate of myopic shift rate was slower in the intervention group compared with the control group (0.13 diopter/y; 95% CI, 0.08 to 0.18). The axial elongation was also slower (-0.03 mm/y; 95% CI, -0.05 to -0.00). The benefit of slowing myopic shift was observed in all initially nonmyopic cohorts (three of three) and most of the initially myopic cohorts (two of three). CONCLUSIONS The meta-analysis results suggest that there is a slightly lower risk of myopia onset and myopic shift with more hours of outdoor activities. Future clinical trials are needed to assess its long-term effect and whether the effect varies by initial myopic status.