Playing outdoors, vitamin D & sports.
Studies identified that short-sighted (myopic) children spent more time indoors and less outdoors than non-myopic children, had lower vitamin D, were more likely to be overweight and participate less in sports. These lifestyle factors may be risk factors for short-sightedness in early childhood (less than 6 years of age). Too much close work, such as reading and using hand-held devices, may also be a risk.
J Willem L Tideman, Jan Roelof Polling, Albert Hofman, Vincent WV Jaddoe, Johan P Mackenbach, Caroline CW Klaver. Clinical science. Environmental factors explain socioeconomic prevalence differences in myopia in 6-year-old children. British Journal of Ophthalmology June 2017 http://bjo.bmj.com/content/early/2017/06/12/bjophthalmol-2017-310292