Increased time outdoors decreased incidence of myopia in childrenThe impetus for this study was the high incidence of myopia in young adults in some urban areas of East and Southeast Asia, where 80% to 90% of high school graduates have myopia. This study was based on previous research suggesting that time spent outdoors may prevent the development of myopia. This previous research, however, did not establish causality and did not provide sufficient, high quality evidence to inform public policy. To address these concerns, the current study used school-based cluster random assignment and a longitudinal approach to assess the efficacy of increasing time outdoors in preventing the onset of myopia in Chinese children.
Schools participating in this study were randomly assigned to an intervention or control group, with over 950 first grade children in each group. The two groups were matched closely in terms of longitudinal loss of visual acuity, which is associated with the development of myopia in children. Other characteristics of the students in the intervention and control groups at baseline were also similar.
Baseline data regarding visual acuity were gathered on children in first grade (ages 6-7 years) with annual follow-up to grade 4. Intervention consisted of an additional 40-minute class of outdoor activities each school day and the recommendation that parents engage their children in outdoor activities after school hours and during weekends and holidays. Children and parents in the control group continued their usual pattern of activity. The primary outcome measure was the 3-year cumulative incidence rate of myopia among the students who did not have myopia at the beginning of the study.
The cumulative incidence rate of myopia was 30.4% in the intervention group and 39.5% in the control group. This 9.1% difference showing more myopia in the control group indicates that the addition of 40 minutes of outdoor activity at school resulted in a reduced incidence rate of myopia over a 3-year period.
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