Indoor Environment Linked to Enhanced Dry Eye Metrics

Amy Huang

The indoor environment might be linked to a higher prevalence of dry eye symptoms.

A team, led by Amy Huang, University of Central Florida College of Medicine, examined whether there are links between the indoor environment, especially temperature, humidity, and air pollutants, and the symptoms and signs of dry eye.

In the prospective cross-sectional study, the investigators examined a sample of 97 veterans with a wide range of dry eye metrics that were recruited from the Miami Veterans Affairs Healthcare eye clinic between October 2017 and August 2018. The participants included South Florida residents with healthy eyelid and corneal anatomy.

The majority of the patients—81 of 97—were male, with a mean age of 58.2 years old.

At baseline, dry eye symptoms were in the moderate range with a mean Ocular Surface Disease Index score of 31.2.

At the beginning of the trial, dry eye metrics were evaluated in the clinic, followed by indoor home environmental metrics within 1 week using a handheld particle counter.

The investigators assessed the symptoms of dry eye using a standardized questionnaire and the signs of dry eye using a standard examination. The indoor environmental metrics included temperature, humidity, and particulate matter mass and count.

The indoor device was deployed for 90 minutes within 4 feet of the home’s air conditioning closet or air handling unit or within 8 feet of an air vent while the air conditioner was running.

For the first 45 minutes, the particle counter was set to mass mode to estimate particular matter mass by 4 sizes: 1.0, 2.5, 7.0, and 10.0 μm (PM₁, PM_2.5, PM₇, and PM₁₀, respectively). For the remaining 45 minutes, the particle counter was set to count mode to count the number of airborne particles measuring at least 0.5 μm and at least 5.0 μm/ft³ of air.

Humidity was linked to worse symptoms and signs, including OSDI score (r = 0.30; 95% CI, 0.07-0.49; P = 0.01), inflammation (r = 0.32; 95% CI, 0.10-0.51; P = 0.01), Schirmer score (r = −0.25; 95% CI, −0.45 to 0.02; P = 0.03), eyelid vascularity (r = 0.27; 95% CI, 0.05-0.47; P = 0.02), and meibomian gland dropout (r = 0.27; 95% CI,  0.05-0.47; P = 0.02).

In the multivariate analyses, particulate matter of 2.5 μm or less (PM_2.5) was linked with dry eye metrics when adjusted for demographic characteristics, comorbidities, medications, and interaction variables.

The investigators found a one-unit increase in instrumented PM_2.5 level was associated with a 1.59 increase in the OSDI score (95% CI, 0.58-2.59; P = 0.002), a 0.39 reduction in Schirmer score (95% CI, −0.75 to −0.03; P =0 .04), a 0.07 increase in meibomian gland dropout (95% CI, 0.01-0.13; P = 0.02), and a 0.06 increase in inflammation (95% CI, 0.02-0.11; P = 0.009).

“When adjusting for humidity, this study found that increased particulate matter exposure was associated with worse dry eye metrics,” the authors wrote. “Humidity was positively associated with dry eye metrics, potentially because higher humidity increases microbial growth and particulate matter size and mass.”

The worldwide prevalence of dry eye ranges from 5-50% and varies owing to population characteristics, disease definition, and other risk factors. In the US, there are approximately 16.4 million adults diagnosed with dry eye.

The study, “Association of the Indoor Environment With Dry Eye Metrics,” was published online in JAMA Ophthalmology.