August 2009

 

OPHTHALMOLOGY NEWS

 

Light at the end of the tunnel for myopia risk?


by Maxine Lipner Senior EyeWorld Contributing Editor

   

Outdoor activity may keep some from becoming nearsighted

Child on beach Outdoor play may help keep myopia at bay

Spending just a few hours outside may help to forestall myopia in children, according to Donald O. Mutti, O.D., Ph.D., professor, Ohio State University College of Optometry, Columbus, Ohio. In a recent paper published in the January 2009 issue of Optometry and Vision Science, Dr. Mutti reported that engaging in enough outdoor activity can help to counteract the heightened hereditary risk of having two myopic parents. “Kids who do more outdoor activity are less likely to become nearsighted,” Dr. Mutti said. There are three main risk factors considered for developing myopia. “The factors that are on the list typically include having nearsighted parents, having Asian ancestry, and in terms of environmental variables, doing intensive close work,” Dr. Mutti said.

Close look at near work

It is this environmental factor involving close work, a theory that dates back for a century, that investigators set out initially to exam. “We wanted to evaluate the most important theory—that doing a lot of reading is more likely to make a kid become nearsighted,” Dr. Mutti said. “We threw in sports and outdoor activity as an afterthought.” In the long-term study, beginning in 1989 investigators followed school-age children from first through eighth grade. The children were tested annually in the schools, and their parents were asked to report on their activities. “We asked parents each year to tell us, ‘How many hours a week does your child spend in various activities such as reading, studying, using the computer, watching TV, and participating in sports?’” Dr. Mutti said.

Of these activities, it was the time spent outdoors that proved to make the difference. While typically 6 in 10 children whose parents are myopic develop the condition, when outdoor activity tops 14 hours a week, this risk drops down to just two in 10, Dr. Mutti found. Surprisingly, when near work was factored in as well, this was not found to be a trade off. “There’s no correlation between the amount of sports time and the amount of near work time that these kids are doing,” Dr. Mutti said. “They’re not doing one at the expense of the other.” Just because a child is involved in sports does not mean that he or she is not also spending time reading. If anything, it was the active kids who tended to spend more time reading. “Either the correlation is not there, or it is actually a positive relationship,” Dr. Mutti said. “It is the kids doing a lot of sports who are also doing a lot of reading.”

These findings are bolstered by work done by other groups including studies conducted in Sydney, California, and Singapore, according to Dr. Mutti. The Sydney myopia study showed that in those of European ancestry, the greater risk of near work can be overridden by more time spent outside. In the California-based Orinda longitudinal study investigators found that children with a hereditary tendency toward myopia who spent enough time outside were at only slightly greater risk than those whose parents were not myopic. Likewise, the Singapore study showed the same effects but for those of Chinese, Malay, and Indian origin. “Several studies around the world are reporting this, so it’s not just one group’s findings,” Dr. Mutti said.

Potential mechanisms

There are a couple of different theories on the outdoor effect. “One is that when you’re outdoors you’re looking far away,” Dr. Mutti said. “In animal work looking far away negates any myopic effects.” This may explain why near work was not a powerful factor here. “One of the reasons that reading may not be related to nearsightedness is that if you go outside enough it may negate whatever reading you are doing,” Dr. Mutti said. “Somehow being outdoors and looking far away may be a powerful stop signal that puts everyone on a normal developmental track.”

Another theory centers on the effects of light on the physiology of the retina. “Becoming nearsighted in animal experiments starts at the retina, which is somehow reading whatever signals there are to make the eye grow,” Dr. Mutti said. “Extra light levels from being outdoors may negate those retinal signals in some way—change the physiology of the eye to make it grow more normally.”

While there appears to be a real effect here clinically, the implications remain unclear. “We don’t know what the mechanism is, and we don’t know if we should be telling parents to send their child outside—that this is going to take care of the risk of nearsightedness,” Dr. Mutti said. Determining this would take a randomized clinical trial. There is also the downside of being outdoors to consider. “You don’t want to have kids spending time outside and getting the frontal effects of this,” Dr. Mutti said. “We don’t want to trade nearsightedness for skin cancer.”

Going forward, Dr. Mutti sees the study as a good jumping off point for further work. “It doesn’t prove that sending your child outdoors is going to be a good thing,” he said. “But at least it starts us looking in possibly productive places.” Now further work must be done to determine the mechanism and see whether it can be harnessed in some way to do good for children at risk of myopia, Dr. Mutti believes.

Editors’ note: Dr. Mutti has no financial interests related to his comments.

Contact information

Mutti: 614-247-7057, DMutti@optometry.osu.edu

Light at the end of the tunnel for myopia risk? Light at the end of the tunnel for myopia risk?
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