Sunlight Does Explain the Protective Effect of Outdoor Activity Against Myopia

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“Keep myopia away! Go outdoors and play!" This is the slogan for the 21st century children as there is a mounding burden of myopia globally. Both genetics and environment play a role in myopia. Time spent outdoors has recently emerged as a protective factor against myopia and this relationship has been studied extensively for more than a decade (refer reviews by French et al. Ngo et al. Sherwin et al. through cross-sectional and cohort studies as well as the randomized controlled trials. Results from these studies, particularly, the cohort studies and randomized controlled trials have addressed the question of the protective role of increased outdoor time on myopia prevention.

Time spent outdoors and myopia – facts from cross sectional studies

In the SMS, Rose et al. reported that an increase in the time spent outdoors was significantly associated with a more hyperopic refractive error and lower myopia prevalence in 12-year-old Australian children. They also reported a significant interaction between near work and the time spent outdoors. With increasing levels of outdoor activity, the refractive error was more hyperopic in children with low and moderate levels of near work. Children with high levels of near work and low levels of outdoor activity were 2.6 times more likely to have myopia when compared to children with low near work and high outdoor activity. Dirani et al. showed lower myopic refraction and smaller axial length in Singaporean teenagers aged 11-20 years with an increase in the outdoor time. Furthermore, children with increased hours of outdoor activity were less likely to be myopic, thus showing a protective effect of outdoor activity on myopia. In a recent crosssectional study among 681 Chinese children in Beijing, time spent outdoors was significantly associated with myopia (adjusted OR=0.32, 95% CI: 0.21, 0.48, P<0.001) [8]. Chinese children (n=370) with low level of outdoor activity had significantly more myopic refractive error> <.001). Chinese children (n=370) with low level of outdoor activity had significantly more myopic refractive error (-1.34 ± 2.45D) compared to those with moderate (-0.29 ± 2.11D) & higher levels of outdoor activity (-0.25 ± -2.06D; Ptrend=0.003).

Time spent outdoors and myopia – facts from cohort studies and randomized intervention trials

In a population-based cohort study of 7 to 15-year-old British children, increased time spent outdoors was associated with a lower risk of developing myopia compared to less time outdoors (HR=0.75, 95% CI: 0.60, 0.96, P=0.023). In yet another population based cohort study [12] among 6 & 12 year old children in Australia, low and moderate levels of outdoor activity were linked with higher odds of developing myopia compared to increased outdoor activity in both younger (adjusted ORs=2.84, 95% CI: 1.56, 5.17 & 1.14, 95% CI: 0.59, 2.21, respectively for low & moderate groups, Ptrend<0.0001) and older cohorts (adjusted ORs=2.15, 95% CI: 1.35, 3.42 & 2.00, 95% CI: 1.28, 3.14 respectively for low & moderate groups, Ptrend><0.001). The Guangzhou Outdoor Activity Longitudinal study (GOAL), a randomized controlled intervention trial of schoolchildren in China, showed that 40 min/day outdoor activity decreased myopia onset by 9% a…er 3 years [13]. Another intervention study in Taiwan showed that 80 min/day of intermittent outdoor time during recess could decrease myopia onset up to 9% in only 1 year [14]. A recent metaanalysis showed that with every additional one hour of outdoor time per week, the risk of myopia onset reduced by 2% in children and adolescents [3].>.

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