Dry eye disease may be linked to specific levels of pollutants in the atmosphere, reports a study published online in JAMA Ophthalmology.1 Though air contaminants have previously been associated with adverse health effects like pneumonia and heart disease, few studies to date have examined their effects on the ocular surface.2,3,4

Researchers in South Korea evaluated the ocular surface conditions of 16,824 participants in the fifth Korea National Health and Nutrition Examination Survey, asking if their eyes have ever felt dry or irritated and whether they had ever been clinically diagnosed with dry eye. An initial compilation indicated females between the ages of 60 and 69 who live in urban areas and who have university-level education or higher responded positively the most. 

In the second part of the study, the team collected measurements on relative humidity, ozone, nitrogen dioxide and sulfur dioxide levels, as well as the concentration of ambient particulate matter (PM) measuring less than 10μm in diameter from 283 monitoring stations nationwide. Resulting data suggested decreased humidity levels and increased ozone levels correlated with the presentation of dry eye disease (DED). Nitrogen oxide levels were also somewhat associated with the condition, though the concentration of ambient PM was not, possibly due to reflex tearing flushing debris from the surface of the eye.

“Low humidity is a well-known risk factor for dry eye disease,” the researchers wrote. “Our study expands the evidence of the association of low humidity with DED from indoor humidity to outdoor humidity. We suggest that outdoor humidity may also be important in DED.” 

Previous research has also indicated ozone exposure in mice increases the production of inflammatory cytokines in tears and damage to corneal integrity and conjunctival goblet cells, they add. “To our knowledge, our study is the first epidemiologic investigation to observe that increaed ozone levels are associated with DED,” the authors wrote.

The researchers conclude by cautioning that “these results are just associations and do not definitively indicate a cause-and-effect relationship between DED and outdoor air pollution.” Additional research is necessary to make that connection. 

1. Hwang SH, Choi YH, Paik HJ, et al. Potential importance of ozone in the association between outdoor air pollution and dry eye disease in South Korea. JAMA Ophthalmol. 2016 Mar. [Epub ahead of print.]
2. Medina-Ramon M, Zanobett A, Schwartz J. The effect of ozone and PM10 on hospital admissions for pneumonia and chronic obstructive pulmonary disease: a national multicity study. Am J Epidemiol. 2006;163(6):579-88.
3. Kunzli N, Medina S, Kaiser R, et al. Assessment of deaths attributable to air pollution. Am J Epidemiol. 2001; 153(11):1050-5.
4. Torricelli AA, Matsuda M, Novaes P, et al. Effects of ambient levels of traffic-derived air pollution on the ocular surface: analysis of symptoms, conjunctival goblet cell count and mucin GAC gene expression. Environ Res. 2014;131:59-63.