Association between long-term PM_2.5 and NO₂ exposure and risk of myopia in children: A nationwide longitudinal cohort study

Background: The prevalence of myopia has risen sharply among children in East Asia, emerging as a major public health concern. While genetic and behavioral factors are established contributors, accumulating evidence indicates that air pollution may also play a role in myopia development. Methods: This nationwide longitudinal cohort study utilized data from South Korea's National Health Insurance Service–National Sample Cohort (NHIS–NSC). A total of 94,830 children aged 6–12 years without major ocular disorders were followed from 2003 to 2019. Myopia onset was defined as the first hospital visit with a primary diagnosis code for myopia. Time-varying two-year moving averages of fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) concentrations were assigned as exposures and analyzed using a Cox regression model, adjusting for individual- and district-level covariates. Results: Over 784,349 person-years of follow-up, 35,918 children developed myopia. Each 5 µg/m³ increase in PM_2.5 and 5 ppb increase in NO₂ was associated with hazard ratios (HRs) of 1.030 (95 % CI: 1.003–1.058) and 1.031 (95 % CI: 1.010–1.052), respectively. Greater susceptibility to air pollution-related myopia was observed among boys, younger children, and urban residents compared with girls, older children, and rural residents, although the difference by sex was not statistically significant. These associations remained robust across multiple sensitivity analyses. Conclusions: Long-term exposure to PM_2.5 and NO₂ was significantly associated with an increased risk of myopia in children. By combining a nationwide longitudinal design with high-resolution machine learning–based exposure estimates, this study provides novel evidence linking chronic air pollution exposure to pediatric visual health.