Researchers at Sun Yat-sen University in Guangzhou tested a simpler variable. Over three years, six elementary schools added one extra 40-minute outdoor class to every school day for first graders, while six other schools changed nothing. Parents at the outdoor schools were urged to add weekend outdoor time.
By the end of three years, 30.4 percent of children in the outdoor-time schools had developed myopia, compared with 39.5 percent in the unchanged schools, a relative reduction of nearly a quarter. The extra time was spent on ordinary outdoor activity, not special eye exercises or any particular sport.
The trial could not fully separate how much of the effect came from more daylight exposure itself versus less near-focused screen or book time during that hour, since both changed together outdoors. Later research across several countries has pointed to bright outdoor light as the more likely driver, and some school systems in East Asia have since added required outdoor time.
Read the original study
Forty minutes outside, a quarter less myopia.
Source
- He, M., Xiang, F., Zeng, Y., Mai, J., Chen, Q., Zhang, J., Smith, W., Rose, K., & Morgan, I. G. (2015). Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China. JAMA, 314(11), 1142. https://doi.org/10.1001/jama.2015.10803