Sunlight intensity matters in outdoor interventions to prevent myopia in children

New research suggests that the intensity of sunlight, not just the amount of time spent outdoors, is crucial for preventing myopia in children.

Researchers conducted a secondary analysis of the cluster-randomized trial Shanghai Time Outside to Reduce Myopia (STORM). A school-based intervention study involving 16 schools from eight districts across Shanghai in China, STORM included 2,976 students (mean age 7.2 years, 51.2 percent girls) without myopia at baseline who consistently wore a smartwatch for a minimum of 6 hours daily, sustained for at least 90 days.

Outdoor exposure pattern, defined as the episode of time outdoors and instant sunlight intensity over a continuous period, was evaluated.

The children spent a mean of 90 minutes outdoors daily, with a mean sunlight intensity exposure of 2,345 lux. The major outdoor exposure patterns were time outdoors with at least 15 minutes, which accounted for 74.9 percent of minutes (33,677,584 of 45,016,800 minutes).

Only outdoor exposure periods of at least 15 minutes, coinciding with a minimum light intensity of 2,000 lux, correlated with less myopic shift in refraction (patterns with ≥15 minutes and 2,000–3,999 lux: −0.007 dioptre [D]; for ≥15 minutes and ≥4,000 lux: −0.006).

In light of the findings, the researchers suggested that future outdoor interventions focus not only on the overall time outdoors but also on the effective outdoor exposure patterns as a means to effectively prevent myopia in children.