Spending an additional 40 min outdoors each day reduces the incidence of myopia among primary school children in China

Setting: 30 primary schools in Guangzhou, China. Patients: Students underwent annual visual acuity tests. Schools were stratified to six strata based on the proportion of students with ‘normal’ vision (uncorrected visual acuity >20/25) in grades 1–6. Two schools were randomly selected from each strata and all grade 1 students (age 6 years) enrolled in the study; one school to intervention, the other to control. Exclusions: Any student with pre-existing myopia, systemic or ocular disease. Intervention: Compulsory additional 40 min exercise class after school; parental consent not required for participation. Students in control group continued their usual daily routine. Outcomes: Primary outcome was the incident rate of myopia, defined as refractive error of −0.5 D or worse … Correspondence to Dr Robert J Barry; r.j.barry{at}bham.ac.uk