Indoor Particulates, Humidity Associated With Dry Eye

By Lisa Rappaport

July 27, 2020

(Reuters Health) - High levels of indoor particulate matter and humidity are associated with worse dry eye metrics, a new study suggests.

Researchers examined data on dry eye metrics for 97 veterans who underwent ocular surface exams and completed two symptom questionnaires: the Dry Eye Questionnaire 5 (scores 0-22) and the Ocular Surface Disease Index (OSDI) (scores ranging from 0-100, with higher scores indicating worse symptom severity). They also performed home indoor air quality tests.

Overall, dry eye symptoms were moderate, with mean OSDI scores of 31.2 and mean Dry Eye Questionnaire 5 scores of 10.5.

Inside veterans' homes, mean temperature was 24.1 degrees Celsius and mean humidity was 52.4%.

Humidity was positively correlated with dry eye signs including inflammation (r=0.32), eyelid vascularity (r=0.27), and meibomian gland dropout (r=0.27), and negatively correlated with Schirmer scores (r=-0.25).

In adjusted analysis, OSDI scores were higher with greater indoor exposure to fine particulate matter inside veterans' homes. Each one-unit increase in PM2.5 levels was associated with a 1.59-point increase in OSDI scores, a 0.39 decrease in Schirmer score (measured as millimeters of wetting at 5 minutes), a 0.07 increase in meibomian gland dropout (graded to the Meiboscale), and a 0.06 increase in inflammation score (measured using InflammaDry, Quidel Corporation).

"This study, for the first time, directly measured indoor environment, including particulate matter and meteorological conditions, and identified that elevated concentration of particulate matter adjusted for humidity were associated with the selected dry eye measures," said senior study author Naresh Kumar, an associate professor of environmental health at the University of Miami Miller School of Medicine.

"We show that high humidity exacerbates the effects of indoor particulate matter," Kumar said by email.

This is likely because fine particles in the air can become larger under humid conditions, and because certain types of mold, fungi, and bacteria grow more extensively in humidity and can lead to a higher concentration of particles in the air, Kumar said.

"High humidity, per se, should not affect our eyes, but it increases the number of particles and keeps them airborne longer," Kumar said.

Because the study was done in a sub-tropical climate where humidity is high year-round, it's possible that results would differ in other climates, the study team notes in JAMA Ophthalmology. Low humidity can also impact dry eye symptoms, the study term notes.

"Another limitation is that the study does not report data for functional outcomes, such as reading speed, which has been shown to be impacted in patients with dry eye," said Ian Saldanha, an assistant professor at the Center for Evidence Synthesis in Health at Brown University School of Public Health in Providence, Rhode Island, and author of a commentary accompanying the study.

Even so, it is important for clinicians to identify the potential causes of the conditions that contribute to patients' dry eye signs and symptoms, particularly because some environmental risk factors like indoor air quality may be modifiable, Kumar said.

People who have high humidity indoors may use a dehumidifier, for example, while those living in places with dry air may use a humidifier, Kumar advised. People should also change filters on these machines regularly, use exhaust fans in the kitchen and shower, use air purifiers, and keep lots of leafy plants indoors to improve air quality and minimize dry eye symptoms.

SOURCE: and JAMA Ophthalmology, online July 2, 2020.