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Today, kids are more likely to have a hard time seeing distant objects clearly than they would have even a few decades ago. That has been a consistent finding in studies from around the world. New Canadian research sheds more light on why this nearsightedness is increasing. Its conclusion: Kids today spend too little time playing outdoors.
The idea is not new. In parts of the world where people spend most of their time indoors, rates of nearsightedness — or myopia — have been skyrocketing. By adulthood, one in three people in the United States has myopia. In parts of Asia, the rates are far higher. In some nations there, more than 95 percent of children and teens may wear glasses to correct for myopia.
Previous research suggested this might stem from children spending too much time focusing on close-up objects. Those might include books, smartphones and video screens. Other research has linked rising rates of myopia to a drop in the time kids spend outdoors.
The new Canadian study goes further. It shows that for one additional hour of outdoor time per week, the risk a child will develop myopia drops by about 14 percent.
Mike Yang led the study at Canada’s Centre for Contact Lens Research in Waterloo, Ontario. As an optometrist, he examines eyes for defects and prescribes treatment, including glasses and contact lenses. Yang worked with researchers at the Canadian National Institute for the Blind in Toronto, Ontario. Their findings have just been issued in a new 29-page report.
The team examined the eyes of 166 students in Waterloo during the 2014 to 2015 school year. All were in first to eighth grade. Among these kids, the share with myopia rose dramatically by middle school. On average, just 6 percent of first graders were myopic. By age 13, nearly 29 percent were.
The researchers then surveyed the parents about their kids’ activities and how much time they spend on each. Those questions included ones on the time each child typically spends outside. And this outdoor time proved a big predictor of whether kids had become nearsighted.
Why might that be? "It probably has something to do with the lighting being much brighter than indoors," concludes Yang. Also, when outside, your eyes have more opportunity to focus on things in the distance, he notes. For now, he says, "No one is sure why these things make a difference."
Jeremy Guggenheim agrees. He is an optometrist who has studied myopia in Great Britain and Hong Kong. "While the exact cause remains unknown, the bright light levels outdoors are thought by scientists to be key," he says.
Guggenheim says the link between outdoor time and myopia rates could have an added explanation: Children who wear glasses may avoid outdoor sports for fear of damaging or losing their glasses. So children who wear glasses for myopia might just spend less time outside.
The Canadian study also found that almost one in every three children with myopia had not been diagnosed. So they were never prescribed glasses to correct for the condition.
"If they've never experienced perfect vision before, they may think everybody sees the same way," explains Yang. It’s therefore up to parents, he says, to see that their child’s vision is checked regularly.
Without glasses, he notes, myopic children probably can't see the blackboard. This can slow learning and hurt how well they perform in school. Even more worrying, Yang says, is that children are becoming nearsighted at younger and younger ages.
"Historically, myopia started at age 12 or 13,” he notes. “Now it is showing up more often in kids six or seven years old." Yang could not compare the number of young children with myopia in his study to those from earlier generations in Canada. His is the first to measure these rates among children there.
But research in other countries, such as the United States and China, show that myopia is becoming common in ever younger kids. That worries Yang. When young children become myopic, he says, they risk an even greater decline in their eyesight over time when compared to their parents’ and grandparents’ generations.
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