Study examines correlation between humidity, temperature, and air pollutants on dry eye disease patients

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A recent study suggests that higher exposures to lower temperatures and certain air pollutants could result in worsened ocular symptoms and increased tear osmolarity in patients with dry eye disease (DED).

The study was a retrospective cohort study conducted on patients with DED at the Department of Ophthalmology, Gachon University Gil Medical Center, between February 2019 and August 2021.¹ Patients included were over the age of 19 and had been diagnosed with DED based on the criteria outlined by the Korean Corneal Disease Study Group. Requirements from this study include the presence of at least 1 of the following: a tear break-up time (TBUT) of ≤ 10 s or positive ocular surface staining of Oxford grade ≥ 1.2.

Overall, 53 patients (17 men and 36 women) at an average age of 55.1 (± 12.0) years were included in the study, with both eyes being studied.

Patients who wore contact lenses had received ocular surgery within 3 months before study enrollment, had a history of prior refractive surgery or other ocular surface disorders, had systemic rheumatic conditions that might impact the ocular surface, or had been prescribed glaucoma medications were excluded.

The study looked at 2 meteorological parameters in relative humidity and temperature, and 4 air pollutants; particles with a diameter ≤ 2.5 μm (PM_2.5), ozone (O₃), nitrogen dioxide (NO₂), and carbon monoxide (CO)

Patients were assessed using the Symptom Assessment Questionnaire in Dry Eyes (SANDE) score, while tear secretion was measured using the Schirmer’s test without anesthesia. TBUT was determined as the duration between the last eye blink and the moment of tear breakup after fluorescein instillation.

SANDE scores are evaluated with 2 questions: How often do your eyes feel dry and/or irritated, and how severe you feel your symptoms of dryness and/or irritation are? An X is placed on a 100mm line ranging from rarely/very mild to All the time/very severe. The mark is measured in mm from left to right with a larger score (0-100) meaning the respondent feels worse symptoms. Past studies³ have shown that SANDE scores have the potential to provide clinicians with a short, quick and reliable measure for DED symptoms.

On days with the highest humidity and temperature, SANDE scores were significantly lower than when compared to those visiting on days with the lowest humidity and temperature (57.4 vs 68.4 points for humidity; 60.2 vs 69.5 points for temperature). Furthermore, similar trends were observed in OSS (0.9 vs 1.1 points for humidity; 0.9 vs 1.1 points for temperature) and tear osmolarity (295.2 vs 302.6 mOsm/L for humidity; 294.3 vs 302.9 mOsm/L for temperature).

A 1% increase in relative humidity showed a significant association with a decrease in the SANDE score. While a 1 °C increase in temperature demonstrated a significant association with decreases in the SANDE score and tear osmolarity.

In terms of air pollutants, participants who visited on days with the highest levels of PM_2.5 and NO₂ showed higher SANDE scores compared to those visiting on days with the lowest levels (73.6 vs 63.4 points for PM_2.5; 69.7 vs 58.4 points for NO₂).

Moreover, for NO₂, the participant group visiting on days with the highest levels exhibited significantly lower TBUT (4.0 vs 4.6 s) and significantly higher OSS (1.1 vs 0.8 points) and tear osmolarity (302.5 vs 295.6 mOsm/L) compared to those visiting on days with the lowest levels.

A 1 μg/m3 increase in PM_2.5 and a 1 ppb increase in O₃ and NO₂ indicated a significant association with increases in SANDE score and tear osmolarity as well.

Overall, results showed that after adjusting for all covariates, lower temperatures and higher exposure to PM_2.5, O₃, and NO₂ were associated with worsened ocular symptoms and increased tear osmolarity. While significant interaction effects were observed between humidity, temperature, and air pollutants on the SANDE score, tear secretion, TBUT, OSS, and tear osmolarity. However, no significant associations with CO were observed.

References:

1. Choi, YH., Song, MS., Lee, Y. et al. Adverse effects of meteorological factors and air pollutants on dry eye disease: a hospital-based retrospective cohort study. Sci Rep 14, 17776 (2024). https://doi.org/10.1038/s41598-024-68070-x

2. Hyon, J. Y. et al. Korean guidelines for the diagnosis and management of dry eye: Development and validation of clinical efficacy. Korean J. Ophthalmol. 28, 197–206 (2014).

3. Amparo F, Schaumberg DA, Dana R. Comparison of Two Questionnaires for Dry Eye Symptom Assessment: The Ocular Surface Disease Index and the Symptom Assessment in Dry Eye. Ophthalmology. 2015 Jul;122(7):1498-503. doi: 10.1016/j.ophtha.2015.02.037. Epub 2015 Apr 8. PMID: 25863420; PMCID: PMC4485570.