Spending More Time Outside May Slow Kids’ Myopia Progression

Diana Phillips

September 15, 2015

Increasing the amount of time spent outdoors at school significantly reduced the progression of myopia in Chinese children over the course of 3 years, researchers show.

In a randomized controlled trial reported by Mingguang He, MD, PhD, from the Zhongshan Ophthalmic Center in Guangzhou, China, and colleagues published in the September 15 issue of JAMA, the addition of 40 minutes of outdoor activity at school compared with usual activity resulted in a reduced incidence rate of myopia and myopic shift in refraction over the course of 3 years.

The study enrolled 1903 students from 12 schools with similar distributions of uncorrected visual acuity in their students. The schools were randomly assigned to either the intervention group or the control group. Students in the intervention schools participated in a mandatory 40-minute outdoor class at the end of each school day, and parents were advised to encourage outdoor activity outside of school hours, whereas the control schools did not alter their activity schedules, the authors explain.

Of the 1903 children enrolled, 1579 (83%) completed the 3-year outcome assessment. At enrollment, fewer than 2% of children in each group had myopia. At the conclusion of the 3-year study, the prevalence of myopia was statistically significantly lower in the intervention group, at 30.4%, compared with in the control group, at 39.5%, the authors report. There was also a significant difference in the 3-year change in spherical equivalent refraction for the intervention group (−1.42 D) compared with the control group (−1.59 D). Further, in a post hoc analysis adjusting for parental myopia, an important risk factor for myopia, the risk for progression to myopia continued to be significantly lower in the intervention group.

"Our study achieved an absolute difference of 9.1% in the incidence rate of myopia, representing a 23% relative reduction in incident myopia after 3 years," the authors write. Although the reduction is less than the 50% reduction researchers had anticipated, it is still clinically important, they note, explaining that "small children who develop myopia early are most likely to progress to high myopia (≤−6 D), which increases the risk of pathological myopia."

Any delay in the onset of myopia in young children, who tend to have a higher rate of progression, "could provide disproportionate long-term eye health benefits" and reduce the personal and societal burden of myopia, the authors write.

The education program aimed at parents of children in the intervention schools did not have an effect on the amount of time the children spent outdoors outside of school hours, the authors observe.

Mechanism Unknown

"If maintained into adulthood, this observed reduction in the prevalence of myopia associated with increased time spent in outdoor activity would be a clinically important effect," Michael X. Repka, MD, MBA, from Johns Hopkins University School of Medicine, Baltimore, Maryland, writes in an accompanying editorial, noting, however, that longer-term follow-up of the children is required to assess the importance of the findings. "In some studies evaluating myopia treatment, there has been catch-up in the progression of myopia in the treatment group after the intervention was discontinued," he explains.

Also, the results may not be generalizable beyond children of Asian ethnicity, Dr Repka said in an interview with Medscape Medical News. "Whether or not the findings can be applied to children in the [United States] who do not spend as much time studying as Chinese children is totally unknown," he said. "The reduction could be less because the progression of myopia in US children seems less than that of Chinese children."

There is also no way to ascertain from the current findings whether the type of outdoor activity influences the progression to myopia, "because the mechanism by which increased outdoor activity may slow myopia development is not established," Dr Repka said.

For this reason, he writes, "Future studies should include information about the content of the additional outdoor activity, if the activity could be standardized, and how it differs from other studies. This information could guide further study and implementation of outdoor activities in the school setting."

Regarding the contribution of indoor activities to myopia development and progression, "it's totally unknown, but of much public interest, whether the nature of inside activities, including time spent playing video games or on computers or smart phones, influences the rate of myopia or its progression," Dr Repka said.

Funding for this trial was provided by the Fundamental Research Funds of the State Key Laboratory in Ophthalmology and by the National Natural Science Foundation of China. Dr He receives support from the University of Melbourne Research at Melbourne Accelerator Program Professorship. The Centre for Eye Research Australia receives operational infrastructural support from the Victorian government. The study authors have disclosed no other relevant financial relationships. Dr Repka reported that he receives salary support from the National Eye Institute (within the National Institutes of Health) and the American Academy of Ophthalmology.

JAMA. 2015;314:1137-1139, 1142-1148. Article abstract, Editorial extract

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