Ocular surface oxidative stress, MMP-9, and corneal neuroimmune alterations in allergic conjunctivitis with dry eye: a cross-sectional study.

PURPOSE: To investigate the associations among ocular surface oxidative stress, MMP-9-associated barrier dysfunction, and corneal nerve alterations in patients with allergic conjunctivitis-associated dry eye. METHODS: In this cross-sectional study, participants were classified into healthy controls (HC), patients with allergic conjunctivitis (AC), and patients with AC-associated dry eye (AC + DE). Ocular surface symptoms and signs, tear film function, corneal fluorescein staining, and in vivo confocal microscopy (IVCM) parameters were evaluated. Tear malondialdehyde (MDA), superoxide dismutase (SOD) activity, and matrix metalloproteinase-9 (MMP-9) concentrations were measured. Spearman correlation analyses were performed in patients with AC and AC + DE, and receiver operating characteristic (ROC) curve analyses were used to evaluate the ability of tear biomarkers to distinguish AC + DE from AC alone. RESULTS: Compared with patients with AC alone, those with AC + DE exhibited higher Ocular Surface Disease Index scores, shorter tear film break-up time, lower Schirmer I test values, and more severe corneal fluorescein staining (all P < 0.001). IVCM further demonstrated reduced corneal nerve parameters and increased dendritic cell density in the AC + DE group. Tear MDA and MMP-9 concentrations were significantly higher, whereas SOD activity was lower, in patients with AC + DE. Exploratory correlation analyses identified associations among oxidative stress markers, MMP-9, and selected ocular surface parameters. The areas under the ROC curves for MDA, SOD, and MMP-9 were 0.822, 0.730, and 0.789, respectively. CONCLUSIONS: Patients with AC + DE exhibited greater oxidative stress imbalance, higher MMP-9 levels, impaired tear film function, and more pronounced corneal neuroimmune alterations than patients with AC alone. The observed relationships among oxidative stress markers, MMP-9, and tear film parameters suggest that these abnormalities may be interconnected within the AC + DE phenotype. Tear oxidative stress-related biomarkers may also help distinguish AC + DE from AC alone and warrant further evaluation in longitudinal studies.