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 ¼ 77) were recruited from a single clinical site and categorized into groups based upon tear osmolarity status (n ¼ 62 hyperosmolar, n ¼ 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-c, and TNF-a) 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-c levels (13.3 6 2.0 vs. 4.4 6 1.4 pg/mL, P ¼ 0.03). Cohen's effect size was large (0.8) for changes to tear IFN-c levels. Significant correlations were observed between IFN-c concentration and each of: tear osmolarity (r ¼ 0.34; P ¼ 0.007), total ocular surface staining (r ¼ 0.56, P < 0.0001), and Schirmer test score (r ¼ À0.33, P ¼ 0.003).CONCLUSIONS. Tear hyperosmolarity is specifically associated with higher levels of the proinflammatory cytokine IFN-c, 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.Keywords: dry eye, diagnosis, cytokine, inflammation, osmolarity, tear, interferon-gamma T ear hyperosmolarity is a consequence of reduced lacrimal secretion and/or excessive tear evaporation, and is recognized to be a key pathogenic mechanism in dry eye disease (DED). [1][2][3][4] While historically the clinical assessment of tear osmolarity has been hindered by difficulties associated with tear collection methods and access to laboratory facilities, technological advancements have enabled tear osmolar determinations to become clinically viable. Measurement of tear osmolarity has been suggested to be the single best objective indicator of DED severity.5 A diagnostic cut-off value of 316 mOsmol/L has been described to be highly specific for diagnosing clinically significant DED, yielding a sensitivity of 73% and a specificity of 90%. 6 In DED, abnormal elevation of the osmolarity of the tear fluid is proposed to induce epithelial injury through the activation of inflammatory events at the ocular surface, resulting in the liberation of inflammatory mediators that can induce epithelial cell apoptosis. 1,7 Short-term exposure of cultured human corneal epithelial cells to an hyperosmolar medium can induce IL-6 expression.8 In an animal model of ocular surface disease, tear hyperosmolarity resulted in conjunctival goblet cell death and tear film instability. 9 Fur...