Outdoor Activity Less Protective for Premyopic Children, Study Says

In a trial involving more than 3,000 Chinese schoolchildren, researchers found that greater time outdoors protected hyperopic—but not premyopic—eyes from myopic progression. Smartwatch data revealed only modest benefit for premyopic children, even at high exposure levels, underscoring the need for earlier preventive measures and adjunctive strategies such as low-dose atropine or red-light therapy. Photo: Getty Images. Click image to enlarge. The role of outdoor activities in the prevention of myopia has become a significant area of research, with increasing evidence supporting its effectiveness. Gaps do exist, however, as most of the existing studies do not distinguish between non-myopic children who are at high risk (premyopes) and those who are low risk (hyperopes). Premyopia, recognized in 2019 as a precursor stage to myopia, is a crucial window for intervention, according to researchers who found that, in China, 62% of six- to eight-year-olds with premyopia progress to myopia within two years. The International Myopia Institute defines premyopia as refractive error of +0.75D to -0.50D in a developing child. Does increased time outdoors have an equal effect on children who are already in this stage? That question may be answered by a new study published in British Journal of Ophthalmology. Data was drawn from the Shanghai Time Outside to Reduce Myopia trial (STORM), a prospective, school-based cluster randomised trial from October 2016 to December 2018 in which participants wore smartwatches to measure their time outdoors. This was classified into four groups: ≤60 min/day, 61 to 90 min/day, 91 to 120 min/day and >120 min/day. Included in the present analysis were 3,194 participants, of whom 42.9% were premyopic and 57.1% hyperopic (mean age 8.2 years; 49.5% boys). According to the results, hyperopes showed reduced myopic shift with increasing outdoor time (plateau at about 120 min/day), but premyopes exhibited a J-shaped relationship between time outdoors and myopic shift. In comparison to the subgroup with daily time outdoors of less than one hour per day, the difference in SE change in the other subgroups was not statistically significant (61 to 90 min/d: -0.03; 91 to 120 min/d: -0.03). The reduced myopic shift was only observed with time outdoors >120 min/d, although it was still not statistically significant (>120 min/d: 0.04). Within one year, 31% of those with baseline premyopia became myopic, while only 0.3% of hyperopes became myopic, and 33.6% moved into the premyopic range.“This paper showed that contrary to the protective effect observed among hyperopic children, time outdoors offered limited benefit for premyopic children, with evidence of a protective effect only in the highest exposure group,” the authors wrote in their BJO article. They offered severed potential mechanisms for these differences, namely that other studies have indicated that the premyopic retina may not fully trigger the inhibitory arm of the emmetropization feedback loop and have the limited ability to inhibit eye growth at the myopic retina. “In our findings, the protective effect in premyopic children was modest and reached statistical significance only at the highest exposure levels. This highlights the need for both substantially greater outdoor exposure for premyopia and earlier interventions for hyperopia. Initiating increased time outdoors regimens at younger ages, prior to premyopia, could potentially offer more significant benefits,” they wrote.A significant limitation of this study was the inclusion of children at different stages of refractive development within the premyopia category, such as those with residual hyperopic reserve and those already showing rapid axial elongation and myopic refractive shifts. “This heterogeneity could dilute observed effects and reduce the sensitivity to detect associations. Whether decreased sensitivity to time outdoors occurs in parallel with the development of higher rates of myopic shift in refraction is not clear,” wrote the authors. “Second, while the objective measurement of exposures to light is a considerable strength, the light intensity captured by the smartwatch may differ from the light intensity received by the human eye, which could underestimate the light intensity.” The authors also could not adjust for residual confounding variables, including socioeconomic status, dietary patterns and genetic risks beyond parental myopia. They suggest future studies consider these variables and follow participants over a longer period of time.Despite the limited protective effect of outdoor time on children with premyopia, the study authors concluded that, “Nevertheless, in school-based interventions, given the other benefits of time outdoors, increased time outdoors should be provided for all children.” They added that additional interventions, such as atropine or optical corrections to slow myopia development, may also be useful.Click here for the journal source. Chen J, Qi Z, Morgan I, et al. Time outdoors prevents myopia in hyperopic children, but protection is weaker in premyopic children: A post-hoc analysis of a cluster-randomised trial. Br J Ophthalmol. October 8, 2025. [Epub ahead of print.] This article was developed by the editorial staff in conjunction with experts in the field. In the process, AI may have been among the editorial tools used to meet the goals of human editors, who approved all content.