Association of long-term exposure to ambient air pollution with retinal neurodegeneration on optical coherence tomography: the prospective Alienor study

Background and aim Chronic exposure to air pollution may have adverse effects on the central nervous system (CNS). The retinal nerve fiber layer (RNFL) is a part of the CNS. RNFL thinning is a hallmark of glaucoma, the second leading cause of blindness worldwide and may constitute a biomarker of neurodegenerative processes. We investigated the relationship of air pollution exposure with longitudinal RNFL thickness changes. Methods The Alienor study is a cohort of residents of Bordeaux, France, aged 75 years or more. RNFL thickness was measured using optical coherence tomography imaging every 2 years from 2009 to 2017. Exposure to air pollutants during the 10 years preceding the first RNFL measurement (particulate matter with diameter ≤2.5 µm (PM2.5 (μg/m3), black carbon (BC (10-5/m)) and nitrogen dioxide NO2 (μg/m3)) were estimated at the participants’ geocoded residential address using Land-Use Regressions models. Longitudinal associations of air pollution exposure with RNFL thickness were assessed using linear mixed models adjusted for potential confounders. Results The study included 694 subjects, 62% were female and the mean age was 82 years. The median concentration (Interquartile Range (IQR)) were 22.03 (1.57) µg/m3 for PM2.5, 2.26 (0.30) 10-5/m for BC and 29.04 (6.32) µg/m3 for NO2. Exposure to higher levels of PM2.5 and BC in the previous 10 years was significantly associated with a faster RNFL thinning during the 8-year follow-up (-0.39 microns/year (95% confidence interval (CI) [-0.57;-0.20]) and -0.33 microns/year (95% CI [-0.50;-0.16]) per IQR increment; p<0.001 for both). The size of the effect was similar to one year of age (-0.36 microns/year). No statistically significant associations were found with NO2. Conclusions This study evidenced a strong association of chronic exposure to fine particulate matter with retinal neurodegeneration, at air pollution levels below the current recommended thresholds in Europe. Keywords air pollution, retina, neurodegeneration