Influence of environmental, economic, dietary, and behavioural factors on high myopia onset in children: a 4-year large-scale cohort study

Background: High myopia (HM) has become a major global public health concern, leading to irreversible vision loss and a growing socioeconomic burden. Despite rapid urbanisation and education-driven lifestyle changes, few large-scale longitudinal studies have examined how social and environmental factors interact with children's daily behaviours to influence the progression from myopia to HM. Methods: This 4-year population-based cohort study (2021-2024) included 204,238 students (grades 1-9) with baseline myopia from the TCARE programme. Exposures included area-level socioeconomic status (SES), school-based greenness (1 km normalised difference vegetation index (NDVI)), and behavioural factors (daily outdoor activity > two vs.≤2 hours and three dietary patterns: energy-dense, plant-based, and traditional nutrient-rich). Results: Among 204,238 participants (mean age 10.8 ± 4.7 years), 26,879 (13.2%) developed HMs. Children living in low-SES areas had a 54% greater risk than those living in high-SES areas did (hazard ratio (HR) = 1.54; 95% confidence interval (CI) = 1.49-1.59). Protective factors included outdoor activity >2 hours/d (HR = 0.92; 95% CI = 0.90-0.95) and plant-based diets (HR = 0.97; 95% CI = 0.94-1.00). A higher NDVI was associated with a generally lower risk across outdoor activity levels (HR = 0.90 vs. 0.94 in low-NDVI areas, P = 0.01), whereas low SES was associated with a weaker protective association of outdoor activity (HR = 0.96 vs. 0.89 in high-SES areas, P = 0.03). The strongest protective association was observed among children aged 6-12 years (HR = 0.88; 95% CI = 0.82-0.95). Conclusions: High myopia progression among children is driven primarily by socioeconomic inequities, whereas environmental greenness and outdoor behaviour provide measurable protective effects. Integrating SES-targeted resource allocation, urban greening, and early-life behavioural interventions is crucial for mitigating the paediatric HM epidemic.