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Study: Outdoor activity may help control myopic progression in children
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Increased outdoor activity during the summer months may contribute to slowed eye growth in both myopic and non-myopic children, according to results from a longitudinal study of refraction and visual function.
In addition, the study found that non-myopes participated in more hours of sports and outdoor activities during the school year, which may protect against myopia development. This finding agreed with previous studies.
Li Deng, PhD, and her associates at the New England College of Optometry (NECO) Department of Vision Science examined the results from a visual activity survey conducted by the Children’s Vision Laboratory at NECO in 1999. Parents of 147 children 6 to 18 years old completed the questionnaire.
The survey results showed that myopes, or subjects with a spherical equivalent worse than -0.5 D, were found to spend fewer weekly hours outdoors during the school year than non-myopes, or subjects with a spherical equivalent of -0.5 D or better. However, both refractive groups were found to spend more time on outdoor activities in June, July and August, with less myopic progression reported during these months.
Parents of the subjects listed the number of weekly hours outside school the children spent reading for pleasure, studying, watching TV, using the computer or playing video games and engaging in sports or outdoor activities. Dr. Deng noted, however, that the survey did not ask specifically about time spent indoors.
“While our data show that myopes spent less time on outdoor activity than non-myopes during the school year, we do not know if this activity pattern occurred before the onset of myopia, which is important for determining causation,” she told Primary Care Optometry News in an interview.
Cause, prevention of myopia disputed
Near work is most often cited as an environmental risk factor for myopia, but no direct evidence supports this claim, the authors said. In fact, the study found myopes and non-myopes spent a similar amount of time studying during the school year (10.8 ± 5.58 hours/week and 9.14 ± 7.29 hours/week), as well as reading for pleasure (5.60 ± 4.37 hours/week and 4.95 ± 3.63 hours/week).
Conversely, myopes were found to watch significantly more hours of TV during the school year (12.78 ± 9.28 hours/week) than non-myopes (8.91 ± 5.95 hours/week). According to the authors, however, more research is needed on TV watching-induced myopia to confirm this association.
Despite the conflicting opinions on the cause of myopia in children, most research agrees on the “protective role” of outdoor activity in myopia progression, the authors said. While myopes in this study spent fewer hours (8.25 ± 6.24 hours/week) than non-myopes (10.95 ± 5.95 hours/week) on outdoor activity during the school year, both groups reported a high number of sports and outdoor activity time during the summer (19.41 ± 14.57 hours/week and 22.44 ± 13.56 hours/week).
According to the authors, it is not clear which aspects of outdoor activity slow myopic progression. Theories include pupillary constriction, increased dopamine levels and distance viewing.
“Current research findings suggest outdoor activity is protective against myopia development,” Dr. Deng told PCON. “Limited evidence shows this positive effect is due to being outdoors and not physical activity. However, more studies with substantial evidence are needed to better understand the exact mechanism.”
Ongoing studies
The subjects in this study were a subset of participants from a longitudinal study of refractive error that started in 1974 at the Massachusetts Institute of Technology and continued at NECO until 2006, according to the report. Of the 147 subjects, 33 were myopic and 114 were non-myopic, which may have limited the study conclusions.
However, an ongoing study from another research group is investigating the association of outdoor activity hours and myopia with a larger sample size, a narrower age range and a more detailed activity time survey, Dr. Deng said.
“The definite roles of lifestyle on myopia development have not been proven yet. However, in general, we recommend that children spend moderate amounts of time on outdoor play throughout the year and take breaks between long hours of near work,” she said. — by Courtney Preston
Reference:
- Deng L, Gwiazda J, Thorn F. Children’s refractions and visual activities in the school year and summer. Optom Vis Sci. 2010;87(6):406-413.
- Li Deng, PhD, is an associate professor of biostatistics at the New England College of Optometry and can be reached at 424 Beacon St., Boston MA 02115; (617) 266-2030; DengL@neco.edu.
