Light pollution exposure during pregnancy and risk of childhood strabismus

Purpose To explore the association between cumulative exposure to outdoor artificial light at night (O-ALAN) during pregnancy and risk of childhood strabismus. Methods In this nationwide population-based case-control study, an entire-South-Korean-population mother-child-pair cohort representing births for the years 2008 to 2011 and residing in urban areas was identified based on the National Health Insurance Service (NHIS) database. Average levels of O-ALAN at the residential addresses of mothers during pregnancy were estimated using time-varying satellite data, providing a composite view of persistent nighttime illumination at approximately a ∼1 km 2 scale. The odds ratios (ORs) and 95% confidence intervals (CIs) for the association between O-ALAN and strabismus risk were calculated using maximum likelihood estimation, adjusting for socio-demographic and area-based risk factors (e.g., nighttime traffic noise, particulate matter ≤10 μm). Results The study included 755,796 mother-child pairs (mean [SD] maternal age, 32.4 [3.9] years; 51.9% boys). An interquartile range (IQR) increase in O-ALAN (21.7 nW/cm 2 /sr) was associated with an OR of 1.159 (95% CI: 1.145, 1.172) for childhood strabismus. The exposure-response curve showed a non-linear pattern, with stronger associations at higher exposure levels (approximately 40 nW/cm2/sr). Sub-analysis revealed a significant association for exotropia (OR: 1.179 [95% CI: 1.158, 1.200]), but not for esotropia (OR: 1.011 [95% CI: 0.977, 1.045]) or vertical strabismus (OR: 1.107 [95% CI: 0.982, 1.250]). Conclusion Higher levels of residential O-ALAN during pregnancy were associated with increased risk of childhood strabismus in this cohort. Further research with more detailed information on exposure and potential mediators is warranted.