Results of a study involving 2,000 first-grade students prompted the researchers to suggest mandatory targets for the amount of time children spend outside during school hours.
Ian G. Morgan, PhD, of the Research School of Biology, Australian National University, Canberra, and the Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China, reported results of the Guangzhou Outdoor Activity Longitudinal Study here at the Association for Research in Vision and Ophthalmology meeting.
“The prevalence of myopia in East Asia has increased dramatically in the last 50 years, and a slower increase has been seen in Europe and North America,” Morgan said in his presentation.
The prevalence of high myopia, considered to be at least -6 D, is 20% in East Asia, he said, and prevention becomes essential.
The researchers recruited more than 2,000 first-grade students in 12 primary schools in Guangzhou. The school had been involved in previous studies, so records on visual acuity assessment dating back 20 years were available for children from this school, Morgan said.
One 45-minute class of outdoor activity was added at the end of the day, and children in the control group went home at the normal time, he said. The two groups of children were matched for prevalence of myopia, mean spherical equivalent and axial length.
Over the 3-year period, cumulative incident myopia was 39.5% in the control group and 30.4% in the intervention arm, a reduction of 23%, according to the study abstract.
“Differences in axial length did not quite reach statistical significance,” Morgan said. “It seemed to indicate that by increasing the amount of time outdoors, we were able to lower the level of incident myopia and prevalence of myopia. This is apparently a dose-response relationship.”
“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,” the authors concluded in their abstract.
Morgan asked: “Is the mechanism brighter light and increased dopamine release outdoors, or is it increased UV exposure outdoors? Evidence from animal studies favor the light-dopamine hypothesis, but a clinical trial of vitamin D needs to be done.”