Diagnostic utility of inflammation-associated clinical signs in detecting MMP-9 expression in dry eye disease: A cross-sectional conjunctival impression cytology and droplet digital PCR study

PURPOSE: Clinical test utility for detecting inflammation in dry eye disease (DED) remains largely uninvestigated. This cross-sectional study explored relationships between clinical tests and molecular biomarkers of ocular surface inflammation to determine their diagnostic utility. METHODS: Inflammation indicators including bulbar conjunctival hyperaemia (subjective and objective grading), InflammaDry® MMP-9 test, Ocular Surface Inflammation Evaluation® score (Tearcheck®) and ocular surface staining were assessed in individuals with and without DED. Conjunctival impression cytology samples underwent droplet digital PCR to quantify MMP-9, IL-8 and IL-1β gene expression. Receiver operating characteristic curves established clinical test utility for detecting elevated biomarker levels and optimal cut-off values. RESULTS: Of 47 participants (55 ± 18 years; 21% male), 79% met the TFOS DEWS II diagnostic criteria for DED, with 84% classified as lipid-deficient. Biological MMP-9 presence was associated with NIBUT <5.8 s, hyperaemia score (JENVIS >1.0 or Efron grading >1.5), positive InflammaDry results, positive symptom scores (DEQ-5 >9 or OSDI >33.3), and thinner tear film lipid layer grade (LLG ≤ 2; all p < 0.05). No significant clinical associations with IL-8 or IL-1β levels were found. Two or more positive assessments from hyperaemia (JENVIS), NIBUT and LLG offered within-sample diagnostic accuracy of 78.6% sensitivity and 78.8% specificity. CONCLUSIONS: A test battery comprising bulbar conjunctival redness (JENVIS >1.0), tear film instability (NIBUT <5.8 s) and lipid insufficiency (LLG ≤2) optimally identified individuals with detectable MMP-9 expression. Two or more clinical signs identified high-risk individuals and, while further validation is warranted, it suggests inflammatory marker detection is limited to those with higher DED symptom and clinical sign scores.