Abstract

Background:

Evidence concerning the effects of greenness on childhood visual impairment is scarce.

Objectives:

We aimed to assess whether greenness surrounding schools was associated with visual impairment prevalence and visual acuity levels in Chinese schoolchildren and whether the associations might be explained by reduced air pollution.

Methods:

In September 2013, we recruited 61,995 children and adolescents 6–18 years of age from 94 schools in seven provinces/municipalities in China. Greenness exposure was assessed using the normalized difference vegetation index (NDVI) and the soil-adjusted vegetation index (SAVI) from July to August 2013. Visual impairment was defined as at least one visual acuity level (dimensionless) lower than 4.9 (Snellen 5/6 equivalent). Three-year annual averages of particulate matter (PM) with an aerodynamic diameter of $\le 1\mathrm{\mu }\mathrm{m}$ (${\mathrm{PM}}_1$) and nitrogen dioxide (${\mathrm{NO}}_2$) at each school were assessed using machine learning methods. We used generalized linear mixed models to estimate the associations between greenness and prevalent visual impairment and visual acuity levels and used mediation analyses to explore the potential mediating role of air pollution.

Results:

In the adjusted model, an interquartile range increase in ${\text{NDVI}}_{500\mathrm{m}}$ was associated with lower odds of prevalent visual impairment [$\text{odds ratio\hspace{0.17em}}\left(\text{OR}\right)=0.95$; 95% confidence interval (CI): 0.93, 0.97]. The same increase in ${\text{NDVI}}_{500\mathrm{m}}$ was also associated with $0.012$ (95% CI: 0.008, 0.015) and $0.011$ (95% CI: 0.007, 0.015) increases in visual acuity levels for left- and right-eye, respectively. Our results also suggested that ${\mathrm{PM}}_1$ and ${\mathrm{NO}}_2$ significantly mediated the association between ${\text{NDVI}}_{500\mathrm{m}}$ and visual impairment. Similar effect estimates were observed for ${\text{SAVI}}_{500\mathrm{m}}$, and our estimates were generally robust in several sensitivity analyses.

Discussion:

These findings suggest higher greenness surrounding schools might reduce the risk of visual impairment, possibly owing in part to lower ${\mathrm{PM}}_1$ and ${\mathrm{NO}}_2$ in vegetated areas. Further longitudinal studies with more precise greenness assessment are warranted to confirm these findings. https://doi.org/10.1289/EHP8429