Get a child at least 2 hours outdoors every day, the only way to prevent myopia that is currently supported by a randomized trial

Cost

Free. But time has to be set aside every day, and most of it will come out of homework and online-class time. The hard part is doing it every day, not just for a few times.

What you get

First graders in 12 primary schools in Guangzhou were randomized by school (952 children in the intervention schools and 951 in the control schools, average age 6.6 years). The intervention added 1 outdoor activity class of 40 minutes on every school day and encouraged parents to take their children out more outside school. Over 3 years, the share who newly became nearsighted was 30.4% in the intervention group, 259 of 853 eligible children, and 39.5% in the control group, 287 of 726. The difference between the two groups was -9.1 percentage points (95% CI -14.1 to -4.1, P<0.001), so the true gap is roughly between 4 and 14 percentage points lower. Over 3 years, the deepening of prescription (change in spherical equivalent) was -1.42 D versus -1.59 D, a difference of 0.17 D (P=0.04), so the intervention group's eyes deepened slightly less. D is the unit for measuring prescription strength. Growth in axial length (the front-to-back length of the eyeball) did not differ between the two groups (P=0.07). The Ten Core Messages on Preventing and Controlling Myopia in Children and Adolescents (《防控儿童青少年近视核心知识十条》) call for children and adolescents to spend at least 2 hours outdoors in the daytime every day, or 14 hours in total per week. It notes that outdoor activity protects even on cloudy days, and asks people to avoid the hot, strong sun of the afternoon.

Notes

This trial ran for only 3 years, and the children were all starting from age 6. A 9.1-percentage-point gap in the share who became nearsighted means some children avoided myopia, but it doesn't guarantee yours will. The same Ten Core Messages give a few more practices. When reading and writing, follow “one foot, one fist, one inch” (一尺一拳一寸). After 20 minutes of close-up use of the eyes, look far away for more than 20 seconds. For primary and secondary students, screen use that is not for study should be no more than 15 minutes at a time and no more than 1 hour a day in total. “Being outdoors” is not the same as “having PE class,” and standing outside during a school break counts.

Evidence grade

A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.

Sources

1. He M, et al. (2015). Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China: A Randomized Clinical Trial. JAMA. https://doi.org/10.1001/jama.2015.10803
2. 国家卫生健康委办公厅 (2023). 防控儿童青少年近视核心知识十条（国卫办妇幼函〔2023〕278 号）. https://www.gov.cn/zhengce/zhengceku/202307/content_6894284.htm

Translated from the Chinese original. Original book, section 30, tip 4. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer