Inflammation-related molecules in tears of patients with chronic ocular pain and dry eye disease

Abstract

The purpose of this study was to analyze inflammation- and pain-related molecules in tears of patients suffering from chronic ocular pain associated with dry eye (DE) and/or a previous corneal refractive surgery (RS). Based on history, symptomatology, and clinical signs, the subjects (n = 180, 51.0 ± 14.7 years, 118 females, 62 males) in this cross-sectional study were assigned to one of five groups: DE and chronic ocular pain after RS (P/DE-RS, n = 52); asymptomatic subjects, i.e., without DE and chronic ocular pain, after RS (A-RS, n = 30); DE and chronic ocular pain without previous RS (P/DE-nonRS, n = 31); DE, no pain, and no previous RS (DE-nonRS, n = 35); and asymptomatic subjects with no previous RS (controls, n = 32). The tear concentrations of 20 cytokines and substance P (SP) were analyzed by immunobead-based assay and enzyme-linked immunosorbent assay, respectively. We found that tear levels of interleukin (IL)-10 and SP were increased in the RS groups. There were significant differences in IL-8/CXCL8 among the five groups. Nerve growth factor (NGF) tear levels were significantly higher in P/DE-RS than in DE-nonRS and controls. IL-9 had the highest percentage of detection in the P/DE-RS and P/DE-nonRS groups, while macrophage inflammatory protein (MIP)-1α, IL-2, and interferon (IFN)-γ were higher in the P/DE-RS, A-RS, and P/DE-nonRS groups. IL-17A was detected only in the A-RS group. Moderate correlations were observed in the A-RS, P/DE-nonRS, DE-nonRS and controls groups. A positive correlation was obtained between growth related oncogene concentration and tear break-up time (rho = 0.550; p = 0.012), while negative correlation was found between monocyte chemoattractant protein-3/CCL7 and conjunctival staining (rho = -0.560; p = 0.001), both in the A-RS group. IL-10 correlated positively with ocular pain intensity (rho = 0.513; p = 0.003) in the P/DE-nonRS group. Regulated on Activation Normal T Cell Expressed and Secreted/CCL5 correlated negatively with conjunctival staining (rho = -0.545; p = 0.001) in the DE-nonRS group. SP correlated negatively with corneal staining (rho = -0.559; p = 0.001) in the controls. In conclusion, chronic ocular pain was associated with higher IL-9 tear levels. IL-10, SP, MIP-1α/CCL3, IL-2, and IFN-γ were associated with previous RS. Higher levels of IL-8/CXCL8, MIP-1α/CCL3, IL-2, and IFN-γ were associated with DE-related inflammation, while NGF levels were related to chronic ocular pain and DE in RS patients. These findings suggest that improved knowledge of tear cytokines and neuromodulators will lead to a more nuanced understanding of how these molecules can serve as biomarkers of chronic ocular pain, leading to better therapeutic and disease management decisions.

Keywords: Chronic ocular pain; Dry eye; Neuromodulators; Ocular surface; Refractive surgery; Substance P; Tear cytokines; Tear film.