Nancy A. Melville

May 15, 2014

ORLANDO, Florida — Spending too little time outdoors has a negative effect on the risk for myopia in children, even before they learn to read, according to a study conducted in the Netherlands.

However, when children with indoor lifestyles are subjected to daily outdoor exposure, rates of myopia significantly decrease, according to a study conducted in China.

Even in young emmetropic children, the amount of time spent outdoors and on near work is associated with axial length, said Jan Roelof Polling, from the division of orthoptics and optometry at the University of Applied Sciences Utrecht, and PhD candidate at Erasmus Medical Center in Rotterdam, the Netherlands. He was lead investigator on the Dutch study.

Jan Roelof Polling

"We found that children who played outside less than 45 minutes a day and those spending more than 2 hours a day on near work and computer games had the longest eyes," he told Medscape Medical News.

Polling presented results from the Generation R study here at Association for Research in Vision and Ophthalmology 2014 Annual Meeting.

A population of 6690 multiethnic children were examined for visual acuity and axial length at 6 years of age.

The prevalence of myopia in the cohort was 1.9%, which ranged from 0.9% in Dutch children to 3.2% in non-Western immigrants. Median axial length was 22.35 mm (range, 19.27 to 25.05 mm).

Completed questionnaires provided information on time spent outdoors for 4059 children. Axial length was significantly longer in children who spent less than 1 hour per day outdoors than in those who spent more than 2 hours outdoors (22.41 vs 22.33 mm; P < .001).

In addition, children who played outside for less than 1 hour per day had a 34% greater risk of having an axial length above average than children who spent more than 2 hours outdoors (odds ratio, 1.34; 95% confidence interval, 1.14 - 1.58).

The association between axial length and the amount of time spent doing near work was not significant (P = .14). However, a multivariate analysis looking at quartiles of exposure and near work showed significant trends, Polling reported.

"Both factors had an independent effect on eye growth. Children with an increased risk of near-sightedness, such as those from a near-sighted family, should be prompted to spend at least 15 hours a week outside and should avoid spending long hours doing near work, even when they are very young," he explained.

The association between myopia and time spent outdoors was also seen in a 3-year longitudinal study, which was presented during the same session. It involved more than 2000 first-grade children at 12 primary schools in Guangzhou, China.

Rates of myopia are exceptionally high in East Asia; researchers attribute this to the intensely rigorous homework requirements placed on children, keeping them indoors and focused on near-work activities.

The students were randomly assigned to 45 minutes of outdoor activity daily or to usual behavior. At baseline, the prevalence of myopia and mean spherical equivalence were similar in the outdoor and control groups.

After 3 years, the incidence of myopia was significantly lower in the outdoor group than in the control group (30.4% vs 39.5%; P < .001).

"These results provide proof of principle that increasing the amount of time that children spend outdoors through the school system can decrease the number of children who become myopic," the researchers conclude.

The study was conducted as part of a public education campaign designed to reduce myopia, explained lead investigator Ian Morgan, PhD, from the Research School of Biology at the Australian National University in Canberra.

The public health intervention to increase time spent outdoors worked well, but in East Asia, "it will almost certainly need to be backed up by a reduction in homework demands, which is a major factor in students not having enough time outdoors," Dr. Morgan explained.

The mechanisms behind the relation between outdoor exposure and myopia are not clear, but Dr. Morgan offered 2 prime suspects — dopamine and exposure to ultraviolet (UV) light. "Evidence from animal studies favors the light/dopamine hypothesis, but we need a clinical trial to resolve the issue," he said.

However, "it will be hard to distinguish in epidemiologic studies between dopamine release and increased UV exposure, because when you go outside, you get more light, more UV, but you also get more dopamine release," he explained.

This study provides support for evidence on myopia in children, said session moderator Donald Mutti, OD, PhD, from the College of Optometry at Ohio State University in Columbus.

"The study is a nice, longitudinal replication showing a protective effect against the onset of myopia in a population that has a very high prevalence of myopia," he told Medscape Medical News.

"It is also very nice replication of our group's finding that time outdoors seems to have some protective effect against the onset of myopia, but has little effect on the rate of progression once a child becomes myopic," said Dr. Mutti (Invest Ophthalmol Vis Sci. 2012;53:7169-7175).

He added that the study by Polling's team contributes to his group's findings by showing effects on emmetropic children.

"That study extends the field by showing that time outdoors has an effect on length in young children," he said.

Myopia is associated with an increased risk for more serious eye diseases, including glaucoma, cataracts, and retinal detachment, but even on its own, the condition has important public health implications, Dr. Mutti said.

"Even if the eye remains healthy, there is a financial burden reaching billions of dollars each year on consumers and insurers to diagnose and manage refractive error," he said. "Uncorrected refractive error is a major source of correctable visual impairment in the United States and around the world. "

Mr. Polling and Dr. Morgan have disclosed no relevant financial relationships. Dr. Mutti reports being a consultant for Vistakon Johnson & Johnson on issues related to myopia.

Association for Research in Vision and Ophthalmology (ARVO) 2014 Annual Meeting: Abstracts 1271 and 1272. Presented May 5, 2014.

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