Time outside may reduce myopia risk in children

This meta-analysis, which included a total of 23 studies on myopia in children and teens up to 20 years old, suggests that increasing time spent outdoors may reduce the risk of developing myopia and its progression in children and adolescents.

Using information from seven studies that included populationwide data on the risk of nearsightedness, they found a significant protective association between increasing time spent outdoors and prevalent myopia in nearly 10,000 children and adolescents. Each increase in hours per week of time spent outdoors was associated with a 2 percent reduced odds of myopia.

Another three studies that followed children over time showed that increasing the amount of time they spent outdoors slowed the progression of myopia.

The results also suggest that environmental factors, such as the amount of time spent in front of TVs or reading books, may help explain rising rates of myopia in certain groups.

"Even though a substantial proportion of myopia cases can be explained by inheritance, this does not exclude strong environmental influences being the driving force behind the rapid increases in the prevalence of myopia over time, especially in East Asia."

Investigators stress that these studies were observational and can only show an association between time spent outside and the risk of myopia, not cause and effect. Future randomly controlled studies are needed to confirm the role of outdoor time in myopia development.

The authors offer a variety of potential explanations for the protective effect of spending time outside. For example, spending time outdoors may help protect against myopia by increasing the release of dopamine in the eye in response to sunlight. Or it may reduce the amount of time spent on other work requiring near vision, like watching TV or reading.