Indoor Humidity, Particulate Matter Associated With Worse Dry Eye Symptoms

Increased particulate matter exposure is associated with worse dry eye metrics, after adjusting for humidity, according to a study published in JAMA Ophthalmology.¹ The study also found that humidity is positively associated with dry eye metrics, potentially due to the fact that higher humidity increases microbial growth and subsequent particulate matter size and mass.

Prevalence of dry eye ranges from 5% to 50% globally and varies depending on population characteristics, disease definition, and other risk factors. Symptoms of the condition can include dryness, burning, irritation, and poor or fluctuating vision. Approximately 16.4 million adults (6.8%) in the United States have dry eye.

“The ocular surface is continuously exposed to the environment,” the authors wrote. “Although studies have focused on associations between outdoor environmental conditions and dry eye, information on associations between the indoor environment and dry eye is lacking.”

To determine whether associations exist between the indoor environment (temperature, humidity, air pollutants) and symptoms of dry eye, researchers conducted a prospective cross-sectional study of 97 US veterans recruited from the Miami Veterans Affairs Healthcare eye clinic. Mean (SD) patient age was 58.2 (11.9) years, and 84% were male.

Participants with healthy eyelid and corneal anatomy were recruited between October 2017 and August 2018. Questionnaires were distributed to each participant to collect data on age, sex, ethnicity, ocular and medical history, and medication. Dry eye incidence was determined via the Dry Eye Questionnaire 5 and the Ocular Surface Disease Index (OSDI) (scores ranging from 0 to 22 and from 0 to 100, respectively). Each patient also underwent an ocular surface examination, which included a Schirmer test.

Patients’ home environmental conditions were assessed within 7 days of their initial eye clinic visit. Temperature, humidity, and particulate matter (2.5 μm or less [PM_2.5] and 10.0 μm or less [PM₁₀]) were all recorded.

The cohort’s dry eye symptoms were in the moderate range, with an average OSDI score of 31.2 (23.6). However, the study found that humidity was associated with worse dry eye symptoms and signs:

• OSDI score (r = 0.30 [95% CI, 0.07-0.49]; P = .01)
• Inflammation (r = 0.32 [95% CI, 0.10-0.51]; P = .01)
• Schirmer score (r = −0.25 [95% CI, −0.45 to 0.02]; P = .03)
• Eyelid vascularity (r = 0.27 [95% CI, 0.05-0.47]; P = .02)
• Meibomian gland dropout (r = 0.27 [95% CI, 0.05-0.47]; P = .02)

Multivariate analyses found that PM_2.5 was also associated with dry eye metrics when adjusted for comorbidities, medications, and other variables. In particular, researchers found that “a 1-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 = .002), a 0.39 reduction in Schirmer score (95% CI, −0.75 to −0.03; P = .04), a 0.07 increase in meibomian gland dropout (95% CI, 0.01-0.13; P = .02), and a 0.06 increase in inflammation (95% CI, 0.02-0.11; P = .009).”

Depression and arthritis were also associated with OSDI score, whereas age and body weight were associated with inflammation. Authors cautioned that the associations discovered do not amount to a cause and effect relationship.

High humidity may have been positively correlated with dry eye symptoms because of the interaction between humidity and particulate matter, as opposed to a direct effect of humidity on the eye, researchers hypothesize.

“Unlike with outdoor air pollution, individuals can improve their indoor environment by regulating humidity, temperature, and airborne particulate matter,” authors conclude. “These results suggest that future studies might investigate the efficacy of interventions on the indoor environment as they relate to improvements in dry eye signs and symptoms.”

In an accompanying editorial,² Ian Saldanha, PhD, noted that the study comes at an optimal time as large portions of the population are staying indoors due to the coronavirus disease 2019 (COVID-19) pandemic. “As a consequence, most patients with dry eye are now exposed to the indoor environment to a greater extent than ever before,” Saldanha wrote.

To confirm the findings related to humidity and particulate matter and to explore other components of indoor air, such as bioaerosols, larger studies with broader populations ought to be carried out.

“Because of social distancing, the current COVID-19 pandemic is greatly increasing patient exposure to the indoor environment and to longer screen time,” Saldanha said. Both of these factors have the potential to worsen dry eye outcomes.

“The time is ripe for identifying specific indoor environmental risk factors, which I hope can drive the development, evaluation, and refinement of more targeted and effective interventions,” he said.

Reference:

1. Huang A, Janecki J, Galor A, et al. Association of the indoor environment with dry eye metrics. JAMA Ophthalmol. Published online July 2, 2020. doi:10.1001/jamaophthalmol.2020.2237
2. Saldanha IJ. Learning about and addressing the indoor environment and dry eye. JAMA Ophthalmol. Published online July 2, 2020. doi:10.1001/jamaophthalmol.2020.2236