Time outdoors and the prevention of myopia: School-based implementation works.

Increased time outdoors has been convincingly associated with less myopia in observational studies. School-based interventions using increased time outdoors have been shown to reduce myopia onset, even in large-scale implementation. While each of the studies on which these conclusions are based has limitations, the consistent evidence has established that increasing time outdoors provides a powerful approach to controlling the current epidemic of myopia. A causal pathway for protection has been confirmed in studies on experimental myopia in animals, involving increased release of retinal dopamine by brighter outdoor light during daylight hours. This does not preclude involvement of other mechanisms, and initial results suggest that interventions to increase lighting in classrooms, or to provide environments rich in higher spatial frequencies similar to natural environments outdoors, may provide synergistic benefits. Whether increased time outdoors slows myopia progression is more controversial. Observational epidemiology and intervention trials have given inconsistent evidence, but studies on seasonal variations suggest that progression may also be regulated by light exposures and near workloads. At present, the evidence is sufficient to consider increased time outdoors as an adjunct therapy for myopia control, but primary control should be based on well-validated interventions. As increased time outdoors is increasingly used, one research priority should be to establish optimal protocols for school-based interventions. Another should be to explore the impact of these interventions on learning outcomes, since modern educational theory suggests that more play-based learning in the early years may lead to better long-term educational outcomes. The broader impacts on student mental and physical health should also be investigated. Little attention has so far been paid to how to reduce myopiagenic pressures associated with schooling, without compromising educational outcomes. This is an important area for future research, which should involve collaboration between experts in vision and ophthalmology and experts in education.