Abstract
Air pollution has broad effects on human health involving many organ systems. The ocular surface is an excellent model with which to study the effects of air pollution on human health as it is in constant contact with the environment, and it is directly accessible, facilitating disease monitoring. Effects of air pollutants on the ocular surface typically manifest as dry eye (DE) symptoms and signs. In this review, we break down air pollution into particulate matter (organic and inorganic) and gaseous compounds and summarize the literature regarding effects of various exposures on DE. Additionally, we examine the effects of weather (relative humidity, temperature) on DE symptoms and signs. To do so, we conducted a PubMed search using key terms to summarize the existing literature on the effects of air pollution and weather on DE. While we tried to focus on the effect of specific exposures on specific aspects of DE, environmental conditions are often studied concomitantly, and thus, there are unavoidable interactions between our variables of interest. Overall, we found that air pollution and weather conditions have differential adverse effects on DE symptoms and signs. We discuss these findings and potential mitigation strategies, such as air purifiers, air humidifiers, and plants, that may be instituted as treatments at an individual level to address environmental contributors to DE.
Highlights
Air pollution is becoming an increasing global concern, especially outdoor pollution in low-income countries and indoor air pollution in high income countries [1]
In the New Delhi study [27], individuals who commuted had more rapid TBUT and less tear production than individuals who walked to work (TBUT: 12.97 ± 6.12 vs. 19.23 ± 5.70 s, p < 0.001; Schirmer’s test 13.42 ± 6.67 mm vs. 15.95 ± 6.14 mm, p < 0.001); values in both groups were in the normal range, and the clinical significance of these differences is not clear
Using a multivariate linear regression, elevated microbial counts were associated with meibomian gland drop out when adjusting for age, gender, log, smoke exposure, allergy status, and number of observations ((OR 67.42, 95% CI = 1.18 to 3864.59, p < 0.05)
Summary
Air pollution is becoming an increasing global concern, especially outdoor pollution in low-income countries and indoor air pollution in high income countries [1]. Gaseous air pollutants include reactive gases, legislated by the US Environmental Protection Agency (EPA), as carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and volatile organic compounds (VOCs). The ocular surface is an excellent model with which to study the effect of various air pollutants on human health as it is in constantly in direct contact with the environment and airborne matter and it can be non-invasively accessible, facilitating disease monitoring. Air pollutants and weather conditions can compromise tear film and ocular surface health and affect the eye’s ability to lubricate and protect itself. Symptoms of DE include pain characterized as dryness, discomfort, irritation, burning, itchiness, stinging, foreign body sensation, are hypothesized to play etiological roles [17]. Oftentimes, DE symptoms and signs do not correlate with each other, and this complicates diagnosis and management [14,15]
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