Higher ozone, lower humidity levels associated with dry eye disease

Air pollution is an important public health concern. According to the World Health Organization, most significant constituents of air pollution include particulate matter (PM), ozone, nitrogen dioxide, and sulfur dioxide. Ambient levels of air pollution are known to be associated with a wide range of adverse health effects that particularly affect the respiratory and cardiovascular systems. Ocular surface abnormalities related to air pollution are thought to be a subtype of dry eye disease (DED); however, to date, there has been no large-scale study evaluating an association between air pollution and DED that includes multiple air pollutants.

This study included data on 16,824 participants in the fifth Korea National Health and Nutrition Examination Survey, conducted from January 2010 to December 2012. Dry eye disease was defined as previously diagnosed by an ophthalmologist or the presence of frequent ocular pain and discomfort, such as feeling dry or irritated. Outdoor air pollution measurements (average annual humidity, particulate matter with aerodynamic diameter <10 µm [PM10], ozone, and nitrogen dioxide levels) were collected from 283 national monitoring stations in South Korea.

The researchers found that decreased humidity levels and increased ozone levels were associated with DED, after controlling for known risk factors such as sex, dyslipidemia, thyroid disease, subjective health awareness, and previous ocular surgery. "These results, however, are just associations and do not definitively indicate a cause-and-effect relationship between DED and outdoor air pollution."

PM10, one of the leading public health issues, was not associated with DED. The authors speculate that possible explanations for this finding is that reflex tearing might help flush PM from the ocular surface, or that environmental PM10 levels currently in Korea are not high enough to induce adverse effects on the ocular surface.