Impact of Air Pollution on the Ocular Surface and Tear Cytokine Levels: A Multicenter Prospective Cohort Study

To assess air pollution-induced changes on ocular surface and tear cytokine levels.

As a prospective multicenter cohort study, 387 dry eye disease (DED) participants were recruited from five provinces in China and underwent measurements of ocular surface disease index (OSDI), Schirmer's I test (ST), tear meniscus height (TMH), tear film break-up time (TBUT), corneal fluorescein staining (CFS), meibomian gland (MG) function, and tear cytokines. The associations between ocular surface parameters and exposure to particulate matter (PM), ozone (O₃), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂) for 1 day, 1 week, and 1 month before the examination were analyzed in single- and multi-pollutant models adjusted for confounding factors.

In the multi-pollutant model, the OSDI score was positively correlated with PM with diameter ≤2.5 μm (PM_2.5), O₃, and SO₂ exposure [PM_2.5: β (1 week/month) = 0.229 (95% confidence interval (CI): 0.035-0.424)/0.211 (95% CI: 0.160-0.583); O₃: β (1 day/week/month) = 0.403 (95% CI: 0.229-0.523)/0.471 (95% CI: 0.252-0.693)/0.468 (95% CI: 0.215-0.732); SO₂: β (1 day/week) = 0.437 (95% CI: 0.193-0.680)/0.470 (95% CI: 0.040-0.901)]. Tear secretion was negatively correlated with O₃ and NO₂ exposures but positively correlated with PM_2.5 levels. Air pollutants were negatively correlated with TBUT and positively related with CFS score. Besides SO₂, all other pollutants were associated with aggravated MG dysfunction (MG expression, secretion, and loss) and tear cytokines increasement, such as PM_2.5 and interleukin-8 (IL-8) [β (1 day) = 0.016 (95% CI: 0.003-0.029)], PM with diameter ≤10 μm (PM₁₀) and IL-6 [β (1 day) = 0.019 (95% CI: 0.006-0.033)], NO₂ and IL-6 [β (1 month) = 0.045 (95% CI: 0.018-0.072)], among others. The effects of air pollutants on DED symptoms/signs, MG functions and tear cytokines peaked within 1 week, 1 month, and 1 day, respectively.

Increased PM_2.5, O₃, and SO₂ exposures caused ocular discomfort and damage with tear film instability. PM₁₀ exposure led to tear film instability and ocular injury. PM, O₃, and NO₂ exposures aggravated MG dysfunction and upregulated tear cytokine levels. Therefore, each air pollutant may influence DED via different mechanisms within different time windows.