For Kids, More Time Outdoors May Mean Better Vision

Myopia—nearsightedness, a difficulty clearly seeing distances—is the most common vision problem in the world, affecting 1.45 billion people, according to the Brien Holden Vision Institute. That number is expected to grow to 2.5 billion in 2020, about a third of the world's current population.

Myopia is also increasingly affecting young children, in many cases affecting their ability to reach developmental and educational milestones. This type of vision loss is especially common in children in cities scattered throughout East and Southeast Asia, where 80 to 90 percent of high school graduates are nearsighted and need glasses to see clearly. The condition is also increasing in countries in Europe and the Middle East. Approximately 10 to 20 percent of the Chinese population was nearsighted 60 years ago, according to Nature.

Some experts have linked declining vision early in life to limited time outdoors, and researchers at the University of Guangzhou in China tested the theory by implementing a program that required students to spend an additional 40 minutes of their school day outside. Their findings were published Tuesday in JAMA .

The researchers followed 1,903 primary-school-age children (the equivalent of grades one through 12 in the U.S.) for three years. Six of schools that participated in the study implemented a program that required spending extra time outdoors, while another six kept their regular schedule with less time outside. Parents with children in the intervention schools were also encouraged to take their kids for outdoor activities after school, on weekends and holidays.

After three years, the researchers found there were 10 percent fewer cases of myopia in schools with the program. Thirty percent of students at schools taking part in the intervention program were diagnosed with myopia after that time period (259 out 853 students), versus 39.5 percent of students at schools without the program (287 out of 726 students). The researchers say their findings are significant since myopia that occurs early will mean a life of progressive vision loss.

"Thus a delay in the onset of myopia in young children, who tend to have a higher rate of progression, could provide disproportionate long-term eye health benefits," the researchers write in their study.

It is unclear to the researchers why extra time outside spells the difference between being able to read the chalkboard in class or not. An accompanying editorial suggests that increased amounts of outdoor light exposure may alter retinal dopamine neurotransmitters that are important for controlling the growth and development of young eyes.

This has been shown to be the case in animal studies on white leghorn chicken chicks. In one study, researchers fitted the birds with tiny goggles that altered the resolution and contrast of incoming images, then raised them in a controlled-lighting environment, which induced myopia. In another study, the researchers were able to slow the development of myopia by 60 percent when the chicks were placed in an environment lit similar to the outdoors. The researchers say the light exposure stimulates the release of dopamine and blocks nearsightedness. The same team demonstrated that dopamine is involved in vision. They injected dopamine-inhibiting drugs into chicks without vision problems. This induced myopia even though they were exposed to bright light.

The nature of our digital world may also explain why vision is deteriorating much faster and earlier in life. According to the American Academy of Pediatrics, kids today spend an average of up to seven hours a day looking at screens—whether it's a computer, television, phone or tablet. Too much screen time is a common cause of vision loss. Sitting too close to a television or computer screen strains eyes, causing them to work harder and eventually leading to some distance-vision loss.