From Outdoor Light Exposure to Physical Activity in Childhood Myopia Prevention: A Narrative Review of the Evidence and Multilevel Mechanisms

The global prevalence of childhood myopia poses a major public health challenge. Increasing time spent outdoors is an established preventive approach, particularly for reducing myopia onset, but the extent to which physical activity contributes beyond outdoor light exposure remains uncertain. This narrative review synthesizes epidemiological, mechanistic, and intervention evidence on physical activity and childhood myopia. Longer time spent outdoors is consistently associated with a lower incidence of myopia. Bright outdoor light may contribute through retinal dopamine signaling and regulation of axial growth. In a two-year prospective cohort study involving 4,306 children, one year of smartwatch monitoring showed that a higher composite activity-load measure was associated with less myopic shift and less axial elongation, with stronger associations outdoors than indoors. These observational findings do not establish an independent causal effect of physical activity. Intervention studies suggest that increasing outdoor time can reduce myopia onset and myopic shift, whereas evidence for slowing progression in children who are already myopic is less consistent. Proposed mechanisms include light-related neurobiological pathways, ocular hemodynamic and systemic metabolic processes, and behavioral pathways such as reduced near work. Wearable technologies may support objective monitoring of activity and light exposure. Prevention strategies should prioritize sufficient daily outdoor time (often around two hours in current guidance) while promoting age-appropriate moderate-to-vigorous physical activity as part of an integrated strategy. Future studies should distinguish the effects of light exposure and physical activity through well-designed longitudinal studies and randomized trials and account for genetic susceptibility and family, school, and community environments.