He
M
,
Xiang
F
,
Zeng
Y
, et al
.
Effect of time spent outdoors at school on the development of myopia among children in China: a randomized clinical trial
.
JAMA
.
2015
;
314
(
11
):
1142
1148
; doi:
https://doi.org/10.1001/jama.2015.10803

Investigators from China and Australia conducted a study to determine if increased time outdoors would prevent the development of myopia in school-aged children. Elementary schools in Guangzhou, China, were randomized to either the intervention or control group. First grade students in intervention schools received 1 additional 40-minute class of outdoor activities each school day, while those at control schools continued their usual pattern of activity. Parents of children in the intervention group were also encouraged to play outdoors with their children after school, particularly during weekends and holidays. Schools in the intervention and control groups were matched on the distribution of their students’ visual acuity, which is collected annually in Guangzhou elementary schools. Myopia was defined as a spherical equivalent refractive error of at least −0.50 D measured during annual study eye examinations.

Characteristics of study children, such as demographics, time spent outdoors, myopia, and parental myopia, were collected at baseline. The primary outcome was the cumulative incidence rate of myopia development among children without baseline myopia over the 3-year study period. Rates of myopia were compared among children from intervention and control schools. A secondary analysis was performed after adjusting for parental myopia.

Among 30 schools that agreed to participate, 12 were randomized to the intervention (n = 6) or usual activity (n = 6) groups. There were 952 first-graders at intervention schools and 951 at control schools, with 853 and 726, respectively, included in the analysis. Baseline characteristics of child participants in each group were similar, although the proportion of parents with myopia was significantly lower in the intervention group compared with the control group. Over the 3-year study period, 30.4% of the intervention group developed myopia compared to 39.5% of the usual activity group (P < .001). After adjusting for parental myopia, the odds that the intervention group developed myopia over the 3-year study period remained significantly lower than the usual activity group (OR = 0.73; 95% CI, 0.57–0.92).

The authors conclude that increased outdoor time reduced the incidence rate of myopia among children.

Myopia, or nearsightedness, is a common condition influenced by both genetic and environmental factors. Though rare in US school children, myopia increases with age and affects up to one third of the adult population. In parts of Asia, the prevalence of myopia approaches nearly 40% of school-aged children. Even with the ability to improve eyesight with corrective eyewear and refractive surgery, myopia is a public health concern because of its cost, impact on quality of life, and association with vision-threatening ocular pathology such as retinal detachment and myopic macular degeneration.

In this study, prescribed outdoor play was associated with a small, but statistically significant, decrease in the development of incident...

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