1. This study found that adding 40 minutes of outdoor activity to the school day resulted in a reduction in the incidence of myopia over a 3-year period.
2. Cumulative myopic shift, a measure of myopia, was also significantly less with addition of outdoor activity after 3 years.
Evidence Rating Level: 2 (Good)
Study Rundown: Areas of East and Southeast Asia are experiencing alarming levels of myopia with 80-90% of high school graduates affected and 20% of this group having high myopia. There are currently limited interventions for preventing the onset of myopia. However, recent studies suggest that there may be a protective benefit of spending time outdoors in preventing its onset.
This study, the Guangzhou Outdoor Activity Longitudinal Trial, aimed to investigate the effect of time spent outdoors in preventing the onset of myopia in a population of children from China. It found a statistically significant reduction in the incidence of myopia over a three-year period when an additional 40 minutes of outdoor activity was added to the school day. Cumulative myopic shift, a measure of myopia, was also significantly less with addition of outdoor activity after 3 years. Limitations of the study included a less than anticipated reduction in incident myopia, refusal of cycloplegic refraction in the control group, and possible observational bias, as examiners were not masked. Despite this, the results provide valuable preliminary evidence that time outdoors may influence myopic onset. Further studies to test the generalizability of these results are needed.
Relevant Reading: Myopia
In-Depth [cluster randomized trial]: This cluster randomized, school-based trial in Guangzhou, China randomized students in 6 schools (n = 952) to an intervention of one additional 40-minute class of outdoor activity added to the school day. Parents of the intervention group were instructed to encourage outdoor activity after school, during the weekends, and over holidays. The control group consisted of students in 6 schools (n = 951) for which parents of the children were instructed to continue usual pattern of activity. The primary outcome was the 3-year cumulative incidence rate of myopia. There was a statistically significant reduction of 9.1% in cumulative incidence rate of myopia in the intervention group (30.4% in intervention group vs. 39.5% in control group, p < 0.001). Secondary outcomes were the changes in mean spherical equivalent (myopic shift) and axial length over the 3-year period. Cumulative change in spherical equivalent refraction was significantly reduced in the intervention group compared to the control group (mean -1.42D vs. -1.59D, respectively; p = 0.04). There was no significant difference in axial length between the two groups.
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