In April 2019 researchers from the USA published the results of their review of the medical scientific literature to assess whether increased outdoor activity reduced the risk of developing near/short sightedness among school-aged children. Five studies were included in the review. Results showed that that a greater number of hours of outdoor activities per week was associated with a reduced risk of developing near/short sightedness. In addition the overall rate of myopic shift rate was slower in those who spent a greater number of hours undertaking outdoor activities.
Deng L, Pang Y. Effect of Outdoor Activities in Myopia Control: Meta-analysis of Clinical Studies. Optom Vis Sci. 2019 Apr;96(4):276-282.