Myopia Risk Lowered When Children Play Outdoors

Linda Roach

May 07, 2013

Elementary-school-aged children who spend more time playing outdoors are less likely to develop myopia than their peers who sometimes prefer to stay indoors during school recesses, according to a report by Taiwanese researchers published in the May issue of the journal Ophthalmology.

In a separate article published in the same issue, researchers who studied myopic children in Denmark found that seasonal changes in the mean number of daylight hours correlated significantly with 3 indicators of myopia progression: eye elongation (P = .00), myopia progression (P = .01), and corneal power change (P = .00). The figures increased in winter, when daylight is present for about 7 hours in Denmark, the study reports. During the 17.5-hour days of summer, myopic progression still occurred, but the increases were not as large, the report said.

The 2 studies are part of a worldwide boom in myopia research that has occurred during the last decade. The research began with the aim of illuminating the causes of large increases in prevalence of this refractive disorder during the second half of the 20th century.

Myopia prevalence has increased in the United States from 25% in 1971-1972 to 41.6% in 1999-2004, according to a 2009 report from scientists at the National Eye Institute. However, the prevalence has increased even more dramatically in Asia.

"Myopia has become very high in the last 30 years in Taiwan. It is a very severe public health problem," explained lead author Pei-Chang Wu, MD, PhD, in an interview with Medscape Medical News. "Ninety percent of college students in Taiwan have myopia. But in previous generations, the prevalence was about 10%."

Dr. Wu is director of ophthalmology at the Department of Ophthalmology, Kaohsiung Chang Gung Memorial Hospital, and Chang Gung University College of Medicine, Kaohsiung, Taiwan.

In the comparative, 1-year study Dr. Wu and colleagues performed autorefractions and measured axial length in 571 students at 2 elementary schools in a suburban area and collected other data on the children and their families via a parent questionnaire. The myopia prevalence in the 7- to 11-year-old children was nearly 50% at both schools.

After baseline measurements, one school began a simple intervention with its students (n = 333): They turned off classroom lights and encouraged children go outdoors during their 80 minutes of recess from class each day (6.7 hours per week). In the control school, there were no special recess programs, and children were allowed to stay indoors during recess periods. Both groups had 2 hours of outdoor physical education per week.

At the end of a year, the researchers retested the children's eyes. The measurements showed significantly fewer new cases of myopia in the test group (8.41% vs 17.65%; P < .001). There also was less myopic shift in the intervention group (−0.25 D/year vs −0.38 D/year; P = .029).

Bright, Natural Light Needed

These outcomes demonstrate how small changes might be able to expose children to the bright, natural light that their eyes apparently need to grow normally, Dr. Wu told Medscape Medical News. "Kids spend a lot of time in school. Therefore, if the educational design could change a little bit, we might get a change in myopia prevalence," he concluded.

In the Danish study, investigators looked for correlations between a surrogate measure of daylight exposure (the total number of daylight hours during winter and summer periods of 6 months each) and myopic progression in 235 myopic children between 8 and 14 years of age.

The scientists confirmed that lower total hours of daylight correlated with higher numbers in the 3 parameters they tested, and vice versa. With an average of 1681 hours of daylight over the course of 6 months, axial eye growth was a mean 0.19 ± 0.10 mm, myopia progression was 0.32 ± 0.27 D, and the corneal power change was −0.04 ± 0.08 D. This compared with axial eye growth of 0.12 ± 0.09 mm, myopia progression of 0.26 ± 0.27 D, and corneal power change of 0.05 ± 0.10 D during summer with 2782 hours of daylight.

Dongmei Cui, MD, PhD, the study's first author and an associated professor of ophthalmology at State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, People’s Republic of China, says it still is not clear what the light is actually triggering in the eye to arrest growth.

However, it is not too early for parents of children with myopia to heed the common underlying message of the 2 studies. "I suggest the parents make sure their children spend an adequate amount of time in outdoor activities," she said.

Kate Johnson, BAppSc(Optom)Hons, GradCertOcTher, a Brisbane, Australia, optometrist who fits myopic children with orthokeratology contact lenses because of recent research indicating that they slow down progression, said she routinely asks parents about their children's myopia risk factors, including how much time they spend on outdoor activities.

"If they spend all their time on an iPad, if they spend spent less than 1.5 hours outside every day, they're at risk," she said.

The Taiwanese study was supported by the Chang Gung Medical Research Project Research Grants from Kaohsiung Chang Gung Memorial Hospital, Taiwan. The Danish study was supported by the National Natural Science Foundation of China and by the Fundamental Research Funds of State Key Laboratory of Ophthalmology, in Guangzhou, People's Republic of China. Dr. Wu, Dr. Ciu and Johnson have disclosed no relevant financial relationships.