October 25, 2011 (Orlando, Florida) — The results of a systematic review of the literature and a metaanalysis of data involving more than 10,000 subjects has revealed a link between being outdoors and the reduction in myopia, with more time outside related to decreased nearsightedness.
"Increasing children's outdoor time could be a simple and cost-effective measure with important benefits for their vision and general health. If we want to make clear recommendations, however, we'll need more precise data," said Anthony Khawaja, MBBS, from the University of Cambridge, United Kingdom, who presented the study results here at the American Academy of Ophthalmology 2011 Annual Meeting.
The findings are based on analyses of 8 previously published studies involving outdoor living and myopia in children and adolescents selected after careful screening with a battery of criteria. The total number of subjects was 10,399.
Statistical analyses of the data led to the following revelations. Each additional hour spent outdoors during the week decreased the risk of developing myopia by 2%. Children who were nearsighted stayed indoors nearly 4 hours more per week than their counterparts who had normal vision or hyperopia. No specific effect of outdoor activity could be linked to reduced nearsightedness. Simply being outdoors appeared to be sufficient for vision improvement.
The basis of the restorative effect of the outdoors is still very much an open question, Dr. Khawaja noted. Outdoor activity could put more demand on the eye for longer-distance vision. In a similar vein, being outdoors could naturally reduce near work. Two of the 8 studies that were analyzed addressed whether increased outdoor time in children was linked to less time engaged in near work, such as reading, studying, or playing video games. However, no definitive conclusions can yet be drawn.
Dr. Khawaja did note that the timing of the increase in myopia coincides with the exploding prevalence in computer use, but a definitive association requires more studies. Of note, Dr. Khawaja mentioned a recent study from China (not 1 of the 8 studies analyzed), which randomly mandated children to spend more time outdoors each week. The findings showed a lower incidence of myopia in these children than in those who spent less time outdoors.
"Future prospective studies will help us understand which factors, such as the increased use of distance vision, reduced use of near vision, natural ultraviolet light exposure, and physical activity, are most important," said Dr. Khawaja.
"I love this kind of study. It's really well done. A metaanalysis is a good way to uncover data. There are the usual difficulties with a cross-sectional study — you are assessing an anomaly at the same time as you are getting data on the child, when the actual cause could have happened months or years before," said Graham Quinn, MD, professor of ophthalmology at the Children's Hospital of Philadelphia, Pennsylvania.
"Designing a longitudinal study that could be funded and that has adequate follow-up will be problematic. Nonetheless, this work provides another example of the gene–environment interaction. My bet is that it could involve circadian rhythms and the effect on vision development," Dr. Quinn observed.
The findings come at an opportune time. Myopia has become markedly more prevalent in the United States and other countries in the past 3 to 4 decades. In some Asian countries, the prevalence of myopia in the population exceeds 80%.
Dr. Khawaja and Dr. Quinn have disclosed no relevant financial relationships.
American Academy of Ophthalmology (AAO) 2011 Annual Meeting: Abstract PA070. Presented October 24, 2011.
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Cite this: More Time Outdoors Reduces Nearsightedness - Medscape - Oct 25, 2011.