Scientists say the "outdoor effect" on nearsighted children is real: natural light is good for the eyes. (Photo by Bill O'Leary/The Washington Post)

It's long been thought kids are more at risk of nearsightedness, or myopia, if they spend hours and hours in front of computer screens or fiddling with tiny hand-held electronic devices.

Not true, say scientists. But now there is research that suggests that children who are genetically predisposed to the visual deficit can improve their chances of avoiding eyeglasses just by stepping outside.

Yep, sunshine is all they need -- more specifically, the natural light of outdoors -- and 14 hours a week of outdoor light should do it.

Why this is the case is not exactly clear.

"We don't really know what makes outdoor time so special," said Donald Mutti, the lead researcher of the study from Ohio State University College of Optometry, in a press release. "If we knew, we could change how we approach myopia."

What is known is that UVB light, (invisible ultraviolet  B rays), plays a role in the cellular production of vitamin D, which is believed to help the eyes focus light on the retina. However, the Ohio State researchers think there is another possibility.

"Between the ages of five and nine, a child's eye is still growing," said  Mutti. "Sometimes this growth causes the distance between the lens and the retina to lengthen, leading to nearsightedness. We think these different types of outdoor light may help preserve the proper shape and length of the eye during that growth period."

The scientists are also studying whether visible light outdoors, not just UVB, might contribute to healthy eyesight. Even on an overcast day, outdoor light is at least 10 times brighter than indoor light, they said.  When a person is outdoors, certain specialized cells in the retina control pupil dilation, letting in more of less light.

"Our initial research suggests that the pupil responds more if these cells have been exposed to a lot of sunlight in the previous few days."

Ultimately, there are more questions to be answered, says Mutti, but he believes his team's findings are already contributing to finding those answers.

"I think the research we are doing now will help us finally solve the mystery of the outdoor effect, and maybe help some people avoid a lifetime of wearing glasses," he said. "In the meantime, I tell parents don't worry about reading, get their kids outside, but don't forget ... sunscreen."