Time spent outdoors has a protective effect on the onset of myopiaThe rising prevalence of myopia worldwide makes finding ways to prevent it an important public health issue. Research has already identified some environmental factors that could be considered in efforts to prevent myopia. These factors include physical activity (PA), time spent outdoors (TSO), and near work (NW). How these factors are interrelated, however, is not well understood. The aim of this study was to gather evidence from existing systematic reviews and meta analyses on how TSO, PA, and NW influence the incidence, prevalence, and progression of myopia.
Four systematic reviews were identified, three including a meta-analysis of the data. The four systematic reviews included 62 unique studies, involving over one million children. Only articles published in English were included. Studies with inappropriate and/or insufficient quality were excluded.
Most of the study participants were children, aged 7–15. A few studies included students, aged 11–20 and adults. Studies included in the review represent multiple countries and various ethnicities. The incidence of myopia was found to be greater in eastern countries than western countries. The reason for this is unknown but may relate to differing lifestyles and priorities. Parents in eastern (Asian) countries seem to pay more attention to academic, NW, and TSO. Parents in western countries seem more focused on PA and TSO. While these differences may be associated with differences in myopia prevalence, the related factors aren’t necessarily the cause of myopia.
This research found evidence of TSO having the most significant protective effect on the onset of myopia. One hour a day of TSO reduced the incidence of myopia onset by 45%. TSO had no effect on the progression of myopia once it began. TSO was also found to be more effective on younger children (6 years) than older children (11–12 years) due to the increased sensitivity of eye growth patterns at younger ages. Some evidence also suggests that a decrease in NW may have a protective effect in reducing myopia among people without myopia. There was no evidence of PA having an effect on myopia.
The authors note, "the protective effect of TSO on myopia may be due to several mechanisms working individually or in conjunction, starting from release of retinal dopamine due to sunlight, ultraviolet radiation, increased depth of focus, decreased image blur, low accommodative demand, and also the resultant reduced NW (substitution effect).
While this research was able to identify and synthesize the evidence available so far about the effect of TSO, PA, and NW on the prevalence, incidence, and progression of myopia, more research is needed to address some of the limitations of this review. Recommendations for future studies include making a clear distinction between PA and outdoor activity.
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