Elementary tear fluid biomarkers in glaucoma subtypes

Background Glaucoma is a leading cause of irreversible blindness worldwide; however, molecular differences among glaucoma subtypes, particularly those reflected in tear fluid, remain insufficiently characterized. This pilot study investigated tear fluid biomarkers across different glaucoma subtypes and evaluated their potential utility in glaucoma assessment alongside established clinical parameters. Methods Tear fluid samples were collected from 32 patients representing different glaucoma subtypes, including suspected glaucoma, ocular hypertension, primary open-angle glaucoma, primary angle-closure glaucoma, secondary glaucoma, and pseudoexfoliation glaucoma, as well as from seven healthy controls. Matrix metalloproteinases (MMPs; MMP1, MMP3, and MMP9) were quantified using multiplex ELISA, whereas dopamine concentrations were measured using a standard ELISA assay. Both raw and protein-normalized biomarker data were analyzed using nonparametric statistical tests, PERMANOVA, and correlation analyses. Results Raw concentrations of MMP1, MMP3, and MMP9 were descriptively higher in patients with glaucoma than in healthy controls. Protein-normalized MMP1 demonstrated significant overall differences among diagnostic groups (p < 0.05), although no pairwise comparison remained significant after false discovery rate correction. No significant group differences were observed for MMP3, MMP9, or dopamine. Multivariate analyses using PERMANOVA revealed no significant separation among glaucoma subtypes. A significant correlation between intraocular pressure and normalized MMP1 (ρ = 0.53) was identified in the unadjusted analysis; however, this association weakened after adjustment for diagnostic group. Relative to normative values, patients across glaucoma subtypes exhibited characteristic clinical changes, including reduced retinal nerve fiber layer thickness, increased cup-to-disc ratio, and mild visual field impairment. Conclusions The findings suggest that tear fluid biomarkers may provide complementary molecular information relevant to glaucoma assessment, although clear differentiation among glaucoma subtypes was not achieved in this pilot cohort. Protein normalization reduced variability associated with tear production while preserving subtle group-level patterns, supporting the need for further investigation in larger, longitudinal studies.