Greater residential exposure to outdoor artificial light at night may be associated with a higher risk of developing myopia among children.
Investigators conducted cross-sectional and prospective analyses using data from the Hong Kong Children Eye Study, a population-based cohort of 19,114 children with a mean age of 7.4 years, with a prospective analysis including 2,558 children without myopia at baseline who completed 3 years of follow-up. Outdoor artificial light at night (ALAN) exposure was estimated from time-varying satellite data within 500 m of each participant’s residence.
Myopia was defined as cycloplegic spherical equivalent refraction of −0.50 diopters or less in either eye. The investigators assessed prevalent myopia at baseline and incident myopia during follow-up. Models accounted for factors including age, sex, body mass index, outdoor and near-work time, parental myopia, parental education, family income, sleep duration, room lighting during sleep, greenspace, and fine particulate matter exposure.
About 55% (n = 1,410) of the participants in the prospective cohort developed myopia during follow-up. Each 34 nW/cm²/sr increase in outdoor ALAN exposure was associated with a 26% higher risk of developing myopia over 3 years after full adjustment. Children in the highest exposure quartile had a 34% higher risk of incident myopia compared with those in the lowest quartile.
The relationship between outdoor ALAN and incident myopia was nonlinear. Risk remained relatively stable at low to moderate exposure levels, but the investigators identified an inflection point at 93.08 nW/cm²/sr, closely corresponding to the level at which the increased risk first became statistically significant.
Cross-sectional findings showed a smaller association with prevalent myopia. At baseline, 27% (n = 5,153) had myopia. Each approximately 34 nW/cm²/sr increase in outdoor ALAN exposure was associated with 8% higher odds of prevalent myopia after full adjustment, and children in the highest exposure quartile had 16% higher odds compared with those in the lowest quartile.
Age modified the prospective association. Among children aged 7.35 years or older, greater outdoor ALAN exposure was associated with a 27% higher risk of incident myopia, whereas the association was not statistically significant among younger children. Though other factors were not statistically significant, subgroup analyses showed increased risks among children with 2 parents with myopia and those from families with monthly incomes below HK$20,000. The primary associations remained consistent in sensitivity analyses using alternative residential buffers, lagged exposure estimates, and methods accounting for loss to follow-up.
The study had several limitations. Satellite-derived outdoor ALAN did not measure personal indoor light exposure from sources such as computers, mobile phones, and televisions or account for measures that could block outdoor light, including curtains and shutters. Although the investigators adjusted for self-reported room lighting during sleep, the data were subject to recall bias. Loss to follow-up occurred, and the prospective findings may be most applicable to populations with characteristics similar to the retained cohort. Residual confounding from unmeasured factors such as school environment and urban density could not be excluded. The population consisted predominantly of Hong Kong Chinese children, limiting generalizability to other populations and environments.
“These findings should be interpreted cautiously, especially regarding causal inference,” wrote lead study author Yingan Li, of the Department of Ophthalmology and Visual Sciences at The Chinese University of Hong Kong, and colleagues. Additional longitudinal studies will be needed to clarify the potential mechanisms behind the association.
The study authors reported no conflicts of interest.
Source: Environmental Research