Integrated tear vitamin D–IL-6–NRF2 signature associated with keratoconus severity: An exploratory cross-sectional study

PURPOSE: Tear-based biomarkers with consistent, severity-graded associations remain lacking in keratoconus. We examined, in an exploratory cross-sectional design, the association between tear vitamin D deficiency and disease severity, and characterised coordinated alterations in NRF2-dependent antioxidant regulation and IL-6-related inflammation, in a keratoconus cohort enriched for atopy and chronic eye rubbing. METHODS: was quantified by electrochemiluminescence immunoassay; IL-1β, IL-6, TNF-α, and NRF2 transcripts by optimised RT-qPCR. Disease severity was graded by ABCD staging. Exploratory mediation and ROC analyses were performed. RESULTS: Tear vitamin D was 43% lower in keratoconus (18.5 ± 8.2 vs 32.4 ± 10.5 ng/mL; P < 0.001; Cohen's d = 1.46) and inversely correlated with Kmax (r = -0.72) and ABCD stage within keratoconus (r = -0.68; P < 0.001), with a 72% reduction by stage IV. Exploratory mediation partitioned the vitamin D-Kmax association into a direct component (52%) and an IL-6-associated indirect component (48%); temporal directionality cannot be inferred from this cross-sectional design. NRF2 detectability was reduced in keratoconus (35.7% vs 74.3%; P = 0.004), declining monotonically from 100% at stage 0 to 0% at stage IV. The Molecular Tear Score (MTS-KC) achieved AUC 0.94 (bootstrap-corrected 0.91; 95% CI 0.88-0.99) versus healthy controls. CONCLUSIONS: In this atopy- and eye rubbing-enriched keratoconus cohort, tear vitamin D deficiency, reduced NRF2 detectability, and IL-6-associated inflammation constitute an exploratory molecular tear profile. These findings are hypothesis-generating and require confirmation in larger, phenotypically stratified, longitudinal cohorts before keratoconus-specific mechanisms or clinical applications can be inferred.