Purpose: To assess whether tear hyperosmolarity, being diagnostic of dry eye disease (DED), is associated with specific alterations to the cytokine content of human tears that may provide a biomarker for DED.

Methods: In this prospective, cross-sectional, clinical study, participants (n= 77) were recruited from a single clinical site and categorized into groups based upon tear osmolarity status (n= 62 hyperosmolar, n= 15 normo-osmolar). Comprehensive anterior eye clinical assessments were undertaken. Concentrations of seven cytokines (IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-γ, and TNF-α) in basal tears were assayed using multiplex cytometric bead array. The main outcome measure was difference in cytokine concentration between groups. Group comparisons were undertaken using 2-tailed t-tests. Cohen's effect size was calculated for each finding. Spearman correlations between cytokine concentrations, clinical symptoms, and clinical parameters of DED were calculated.

Results: Tear hyperosmolarity was specifically associated with increased tear IFN-γ levels (13.3±2.0 vs. 4.4±1.4 pg/mL, P= 0.03). Cohen's effect size was large (0.8) for changes to tear IFN-γ levels. Significant correlations were observed between IFN-γ concentration and each of: tear osmolarity (r= 0.34; P= 0.007), total ocular surface staining (r= 0.56, P< 0.0001), and Schirmer test score (r=− 0.33, P= 0.003).

Conclusions: Tear hyperosmolarity is specifically associated with higher levels of the proinflammatory cytokine IFN-γ, which correlate with key clinical parameters of DED. The calculated effect size (0.8) suggests that this assay has diagnostic power as a biomarker for evaporative DED.