Age-dependent and reversible refractive changes in 0-6 years old children associated with reduced outdoor activity: a six-year community-based study.

Outdoor activity is known to protect against childhood myopia, particularly in school-aged children. However, limited evidence exists regarding how reduced outdoor exposure influences refractive development in younger children, especially those under 3 years old. We conducted a cross-sectional, population-based study of 70,490 children aged 0-6 years in Guangzhou, China, from 2018 to 2023. Annual refractive screenings were performed using a validated non-cycloplegic photoscreener (SW-800 refractive screener, Suoer Electronics, China). Children were stratified by age group and screening year. We analyzed trends in mean spherical equivalent (SE) and premyopia prevalence (SE between - 0.50 and + 0.75 diopters (D)), focusing on the effects of reduced outdoor activity in 2020 . Between 2018 and 2019, the equivalent spherical refractive error (SE) in children across all age groups remained stable, indicating a consistent hyperopic reserve. For the 1-year-old group, the SE was 0.66 ± 1.30 D in 2018 and 0.64 ± 1.19 D in 2019. For the 2-year-old group, the SE was 0.61 ± 1.06 D in 2018 and 0.63 ± 0.95 D in 2019. In the 3-6-year-old group, the mean SE ranged from 0.35 ± 0.83 D to 0.56 ± 0.88 D. During the same period, the prevalence of pre-myopia was between 50.96% and 77.99%. In 2020, during the home confinement period, all age groups showed a significant myopic shift, with the mean SE decreasing by 0.36-0.56 D compared to 2019. Specifically, for the 1-year-old group, the SE was 0.14 ± 0.75 D; for the 2-year-old group, it was 0.07 ± 0.42 D; for the 3-year-old group, it was 0.08 ± 0.50 D; for the 4-year-old group, it was 0.04 ± 0.56 D; for the 5-year-old group, it was 0.08 ± 0.53 D; and for the 6-year-old group, it was - 0.01 ± 0.46 D. The prevalence of pre-myopia reached its peak in all age groups in 2020 (80.26% in the 1-year-old group, and exceeding 94% in the 2-6-year-old groups), showing a significant increase compared to 2018-2019.The risk of pre-myopia in 2018 and 2019 was significantly lower than in 2020 (all OR < 0.30, P < 0.001). This study employed a cross-sectional design, with participants studied by year and age group independently. The trends observed reflect population-level refractive changes rather than individual longitudinal recovery trajectories. Reduced outdoor activity is associated with transient, age-dependent myopic shifts in children aged 0-6 years, particularly among those under 3 years. Findings support early integration of outdoor exposure in paediatric myopia prevention strategies.