Outdoor time >120 min/day shows limited myopia protection in premyopic children

This post-hoc analysis, nested within the Shanghai Time Outside to Reduce Myopia (STORM) cluster-randomized trial, investigated the effect of objectively monitored daily time outdoors on myopic shift in premyopic children. The study included 3194 participants aged 6-9 years without myopia who wore smartwatches to monitor time outdoors from 2017 to 2018. All participants underwent cycloplegic refraction. Premyopia was defined as a cycloplegic spherical equivalent (SE) from -0.50 to +0.75 diopters (D). The primary outcome was myopic shift, defined as SE change from baseline to 1-year follow-up. The cohort included 1369 premyopic children, with a mean age of 8.2 ± 0.6 years and 49.5% boys. There was no statistical difference in time outdoors between premyopic and hyperopic children (p=0.303). Results showed hyperopic children had reduced myopic shift with increasing outdoor time, plateauing at approximately 120 minutes per day. In premyopic children, a J-shaped relationship was observed between time outdoors and myopic shift. Compared to the subgroup with daily time outdoors <60 minutes, the difference in SE change was not statistically significant for the 61-90 min/day subgroup (-0.03 D, 95% CI -0.10 to 0.05) or the 91-120 min/day subgroup (-0.03 D, 95% CI -0.11 to 0.05). A reduced myopic shift was only observed with time outdoors >120 minutes per day, but this was also not statistically significant (0.04 D, 95% CI -0.05 to 0.14). The authors conclude that among premyopic children, increased time outdoors has a limited protective effect on myopic shift.

We often hear that getting kids to play outside can help protect their eyesight and prevent nearsightedness. But a new look at the data suggests the story is more complicated, especially for kids who are already at high risk. The study followed over 3,000 children in Shanghai, using smartwatches to track exactly how much time they spent outdoors. It focused on two groups: kids who were slightly farsighted (hyperopic) and kids who were on the very edge of becoming nearsighted (premyopic). For the farsighted kids, the message was clear: more time outside meant less shift toward nearsightedness over a year, with benefits leveling off after about two hours a day. But for the kids already at the brink of nearsightedness, the results were different. They showed a 'J-shaped' relationship with outdoor time. Compared to kids who spent less than an hour outside, those who spent between one and two hours outdoors saw no significant difference in their eye prescription change. Only when kids spent more than two hours outside was there any hint of a protective effect, and even that result was not strong enough to be statistically certain. The study concludes that for children already at high risk for nearsightedness, simply increasing outdoor time may have a limited effect, and we might need to look at longer durations or additional strategies to help them.