Just 40 minutes of outdoor play a day could be a way to curb growing rates of short-sightedness.
This is the views of Chinese researchers testing six schools over a three year period.
It's believed that children need to balance "close up" work, such as reading and writing, with activities that relate to distance.
The findings in Jama lead experts to say although short-sightedness is now very common, the cause is still very much unknown.
Short-sightedness or myopia is believed to affect one in three people in the UK.
Myopia, limits the eyes focus making distant objects appear blurred.
People say this is something that 'runs in families', however, environmental factors like spending too much time on computers are also linked to the condition, leading to researchers carrying out their theory of changing a person's early environment to see if it would reduce risk of myopia.
"This is clinically important because small children who develop myopia early are most likely to progress to high myopia, which increases the risk of pathological myopia. Thus a delay in the onset of myopia in young children, who tend to have a higher rate of progression, could provide disproportionate long-term eye health benefits," the researchers say in Jama.
Dr Mingguang He, leading the research, recruited 12 primary schools in China to take part in the three-year-long study.
Six schools stuck to their usual timetable, whilst the other schools were asked to timetable a compulsory 40-minute session of outdoor play.
The children and their parents were also asked to keep a diary of how much outdoor play time they clocked up on weekends which surprisingly never varied between the two groups.
At enrolment, fewer than 2% of children in each group had myopia.
Over the course of the study, 259 children out of 853 (30%) in the intervention group and 287 out of 726 (40%) in the control group were judged to have myopia - a refractive error of at least minus 0.5 Diopter on an eye exam.
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