PLOS ONE · 14 authors, 8 centres
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This systematic review and meta-analysis of 19 cohort studies found that female sex, parental myopia, longer axial length, lower spherical equivalent, and less outdoor activity time are significant risk factors for myopia onset in children. The burden of myopia is higher in underprivileged countries compared to developed countries. These findings highlight the need for targeted prevention strategies focusing on modifiable environmental and behavioral factors.
**Background:** Myopia is a leading cause of visual impairment worldwide, with rapidly increasing prevalence in children. Both genetic and environmental factors contribute to myopia onset, but the relative importance of specific risk factors remains debated. This systematic review and meta-analysis aimed to comprehensively assess risk factors for myopia onset in children to inform prevention strategies.
**Methods:** The authors searched eight databases (CNKI, VIP, WanFang, PubMed, Embase, Cochrane, and two clinical trial registries) in June 2022 for cohort studies examining associations between potential risk factors and myopia onset in children aged 6-18 years. No language restrictions were applied. Risk of bias was assessed using the Newcastle-Ottawa Scale (NOS), and certainty of evidence was evaluated using GRADE. Meta-analyses were performed using fixed- or random-effects models based on heterogeneity (I²). The summary measure was risk ratio (RR) with 95% confidence intervals (CI).
**Key Results:** Nineteen cohort studies involving 3,578 children were included. Most studies were conducted in East Asia and were of high quality (NOS score 6-9). Key findings include: - **Gender:** Girls had a 28% higher risk of myopia onset compared to boys (RR: 1.28; 95% CI: 1.22–1.35; I²=57.0%; n=32,680; moderate certainty). - **Parental myopia:** Children with one myopic parent had increased risk (RR: 1.16; 95% CI: 1.05–1.27; I²=63.3%; n=24,460; moderate certainty). With two myopic parents, risk was higher (RR: 1.42; 95% CI: 1.26–1.57; I²=63.6%; n=24,460). - **Outdoor activity:** Longer outdoor time reduced risk (RR: 0.97; 95% CI: 0.95–0.98; I²=76.9%; n=16,455; low certainty). - **Near work:** More near-work time increased risk (RR: 1.05; 95% CI: 1.02–1.07; I²=22.2%; n=4,689; moderate certainty). - **Ocular parameters:** Longer axial length (RR: 1.38; 95% CI: 1.23–1.53; I²=90.0%; n=10,408; very low certainty) and lower spherical equivalent (RR: 2.01; 95% CI: 0.02–0.04; I²=93.1%; n=7,706; very low certainty) were associated with myopia onset. - **Geographic/ethnic factors:** East Asian children had higher risk than European Caucasians (RR: 5.28; 95% CI: 2.06–13.48; I²=87.5%; low certainty). - **Other factors:** Higher IQ (RR: 1.50; 95% CI: 1.19–1.89 for highest vs. lowest score), reading >6 hours/day (RR: 1.65; 95% CI: 1.05–2.57), and attending popular schools (RR: 2.04; 95% CI: 1.41–2.95) were associated with increased risk. Living in suburbs was protective (RR: 0.91; 95% CI: 0.83–1.00). - **Negative findings:** Age, household income, sleep duration, body mass index, and accommodative lag showed no significant association.
**Clinical Implications:** These findings support multifactorial etiology of myopia, with modifiable factors (outdoor time, near work) offering targets for prevention. Girls and children with myopic parents should be prioritized for early screening and intervention. Ocular biometric parameters (AL, SE) can help identify high-risk children. The higher burden in underprivileged countries underscores the need for public health interventions. However, the low to very low certainty of evidence for many factors highlights the need for further high-quality research.