Epidemiology and the protective effects of time outdoors

There is a major epidemic of myopia in developed countries in East and Southeast Asia, where the prevalence of myopia is now 80–90% in those completing secondary school. More importantly, the prevalence of high myopia is now 15–20%, exposing the future adult population to a much increased risk of pathological myopia and vision loss. In Europe and North America, the prevalence of myopia is also increasing, and now appears to be of the order of 40–60%. Genetic change cannot provide an explanation of these increases, which must involve changes in environmental exposures. The two key factors appear to be increasingly intensive education, with study pressures extending to increased homework loads and extensive use of tutorial colleges after school hours. The other environmental factor at work is the amount of time that children spend outdoors, with increasing amounts of time outdoors protecting from the onset of myopia. The time spent outdoors by children is particularly low in East and Southeast Asia, and two clinical trials have now shown significant delays to the onset of myopia by increasing the amount of time that children spend outside at school. Similar interventions could help to control myopia in other parts of the world.