Last year, during frequent travels to Singapore, I saw public health billboards proclaiming, “Keep myopia away, go outdoors and play!” I saw them so often my interest was piqued to discover how playing outdoors was beneficial for children’s eyesight. What I found in scientific and medical journals was both fascinating and compelling – and a definite call to action to get our whole family outdoors as much as possible.

Dr. Donald O. Mutti at the College of Optometry and the College of Public Health, Division of Epidemiology and Biometrics at Ohio State University, and his colleagues have done numerous studies on how parental history of myopia (or nearsightedness, caused by elongation of the eyeball) affects the prevalence of the condition in their children and how playing sports and doing other outdoor activities affect prevalence. They have also studied how, and if, indoor activities, like reading and screen usage contribute to onset of nearsightedness.

In a study Mutti and colleagues published in “Investigative Ophthalmology & Visual Science”, they write that an estimated 25 percent of adult Americans are nearsighted. Examination and treatment costs exceed $4.6 billion yearly, so “being able to slow or stop myopia progression and ultimately prevent the occurrence is important.”

Mutti and colleagues analyzed 514 children, looking at the prevalence of myopia in their parents, how many hours the children spent reading, and how many hours the children spent outdoors. Their results, “Lower amounts of sports and outdoor activity increased the odds of becoming myopic… “

In e-mail correspondence, Dr. Mutti explained, “The current theory is that the benefit of being outside comes from the brighter light outdoors compared to indoors. Even the cloudiest day is 10 times brighter than being indoors.” Dr. Mutti said that this light stimulates dopamine in the retina, which then slows the growth of the eye. The benefit could be caused by UVB creating more vitamin D, but that theory is not yet widely accepted. But the idea that sunlight leads to better eye health is.

Dr. Ian Morgan, who works at Australian National University and at Sun Yat-sen University in China, said, “Recent controlled trials have shown that introducing time outdoors into schools, with about two hours a day halving the rate of new cases of myopia.” In medical terms, those two to three hours translates to 10,000 Lux per day (the unit of light measurement or intensity), which is the amount needed for what Dr. Morgan calls “the protective effect.” (In contrast, bright office or school light has about 500 Lux.)

These results are similar to what Dr. Mike Yang found. Yang, from the Canada’s Centre for Contact Lens Research, worked with researchers from the Canadian National Institute for the Blind and studied students in grades one through eight during the 2014-2015 academic year. They found that “the risk a child will develop myopia decreases by approximately 14 percent with just one additional hour of outdoor time per week.”

With similar results around the globe, the importance of outdoor sunlight to eye health is obvious, but as Dr. Mutti conceded in his e-mail, “There are lots of good reasons to be outside, but more time outdoors does not help the child who is already myopic.” So far no study has shown that myopia progress rates are slowed by sunlight. But Dr. Mutti said he and his colleagues are working now to try and figure out why.

In the meantime, the kids and I will be outside for a few hours each day, clouds or shine, walking the dog, kicking a ball, gardening, or doing whatever we can to soak up the sun.