As the myopia epidemic gathers pace, with 5 billion people expected to be myopic and 1 billion predicted to have sight-threatening high myopia by 2050, there is an urgent need to identify targets for early intervention to mitigate the onset and progression of myopia among children.¹ Research has suggested that insufficient time spent outdoors in childhood is one of myopia’s major modifiable risk factors,² and public health interventions that increase time spent outdoors may therefore be the most scalable and efficacious preventative strategies. However, much of the time children spend outdoors consists of moderate-to-vigorous physical activity, and studies on the effect of time spent outdoors have typically not accounted for potentially confounding protective effects of physical activity against myopia.³ There is a noteworthy lack of research on and understanding of the independent association between myopia and physical activity, which might be measured independently of time spent outdoors by objectively studying physical activity in exclusively indoor environments or including ambient light sensors in studies on physical activity. This knowledge gap may impede the optimisation of behavioural interventions for myopia prevention.

Physical activity exerts myriad positive effects on paediatric health and may protect against other eye diseases including glaucoma,⁴ and there are compelling reasons to expect that it may also attenuate axial elongation independently of time spent outdoors, perhaps through promotion of choroidal perfusion and thickening,⁵ although this has been disputed.⁶ A 2017 systematic review by Suhr Thykjær and colleagues attempted to clarify the relationship between physical activity and myopia, but the authors were unable to draw strong conclusions owing …