Ambient PM2.5 and O3 and their combined effects on prevalence of presbyopia among the elderly: A cross-sectional study in six low- and middle-income countries

Background: Ambient air pollutant directly contacts with the eyes, however, the effect of ambient fine particulate matter (PM2.5) and ozone (O-3) on vision impairment, such as presbyopia, has been kept largely unknown. Methods: We surveyed a total of 36,620 participants aged 50 years and above in six low- and middle-income countries. Ambient annual concentrations of PM2.5 and O-3 for the residential community were estimated using satellite data and chemical transport model. A mixed effects model was utilized to assess the effects of ambient PM2.5 and O-3 on presbyopia, as well as their combined effects. Results: A total of 13,841 presbyopia cases were identified among the participants with a prevalence rate of 41.17%. For both PM2.5 and O-3, we found a J-shaped exposure-response relationship with the threshold being identified at 15 mu g/m(3) for PM2.5 and 55 mu g/m(3) for O-3. The odds ratio (OR) of presbyopia was 1.15 (95% CI: 1.09, 1.21) for each 10 mu g/m(3) increase in PM2.5 above 15 mu g/m(3) and 1.37 (95% CI: 1.23, 1.54) for O-3 above 55 mu g/m(3) after adjusting for various potential confounding factors. There appeared to be a synergistic interaction between ambient PM2.5 and O-3 on presbyopia in the additive model, the combined effect was significantly larger than the sum of their individual effects, with a synergistic index of 2.39. Conclusion: This study supports that exposures to ambient PM2.5 and O-3 might be important risk factors of presbyopia among old adults, and simultaneously exposure to high level of the two pollutants could intensify their individual effects. (C) 2018 Elsevier B.V. All rights reserved.