Objective To understand the distribution of outdoor time among children in Shanghai and explore the relationship between different time-period patterns of outdoor time and their effectiveness in preventing and controlling myopia. MethodsThis study is a secondary analysis based on the Shanghai Time Outside to Reduce Myopia study of primary school students aged 6-9 years with complete smartwatch-monitored quantitative data. Data included outdoor time, axial length, cycloplegic refraction, demographic characteristics, and factors related to myopia such as near work. The smartwatch was worn from March 1, to December 31, 2018. Outdoor times were compared and categorized into weekday-dominant and weekend-dominant patterns. Additionally, morning and afternoon outdoor times were analyzed and classified into morning-dominant and afternoon-dominant patterns. Generalized linear models were used to analyze the correlation between different time-period outdoor activity patterns and myopia onset and progression. ResultsDuring the study period, the daily outdoor activity time of children was 84.83 (67.66, 105.47) min/day. Specifically, outdoor activity time was [90.93 (71.66, 113.09) min/d] on weekdays and weekends was [68.14 (51.09, 88.60) min/d], with weekday time significantly higher than weekend time (Z=39.64, P＜0.001). Outdoor activity time in the morning was [46.60 (37.51, 57.88) min/d] and afternoon was [48.99 (38.46, 61.28) min/d], with afternoon time significantly longer than morning (Z=?8.36, P＜0.001). After adjusting for age, sex, residential area, parental myopia, near-work time, and other confounding factors, compared with children with a weekday-dominant outdoor activity pattern, those with a weekend-dominant outdoor activity pattern had a 23% lower risk of myopia onset within one year [odds ratio (OR)=0.769, 95% confidence interval (CI) 0.596-0.993, P=0.044]. Furthermore, compared with children with a morning-dominant outdoor activity pattern, those with an afternoon-dominant outdoor activity pattern was associated with less axial elongation (β=?0.012, 95%CI ?0.023-?0.002, P=0.019) and less myopic progression in refractive error (β=0.029, 95%CI 0.002-0.057, P=0.036). ConclusionWeekend-dominant and afternoon-dominant outdoor activity time patterns are more beneficial for preventing and controlling the onset and progression of myopia.
