Layer and zone-specific study of corneal optical density in dry eye disease: links to tear film metrics.

AIM: To assess the differences in corneal optical density (COD) between young patients with dry eye and healthy controls, as well as to evaluate the correlations with tear film parameters. METHODS: This cross-sectional study involved 30 patients with dry eye and 60 age-matched controls (aged 18-35y). All participants underwent a thorough ophthalmic evaluation, including visual acuity testing, refraction, the Ocular Surface Disease Index (OSDI) questionnaire, tear break-up time (TBUT), the Schirmer's test, corneal staining, and Pentacam densitometry. RESULTS: The groups were matched for age (21.93±2.88y vs 20.80±2.27y) and sex (females: 60.0% vs 63.3%; P>0.05). No statistically significant differences were found in refraction parameters, best-corrected visual acuity, or mean keratometry when comparing the two groups (all P>0.05). Patients with dry eye exhibited significantly poorer tear parameters including OSDI (25.5±10.6 vs 8.3±6.6, P<0.001), TBUT (6.2±2.2s vs 12.9±6.4s, P<0.001), and Schirmer score (20.9±11.2 vs 26.0±11.4 mm, P=0.02). Dry eye patients displayed a significantly higher average COD in the midperipheral zone (6-10 mm) for both the anterior (18.81±2.15 vs 17.25±1.66, P<0.001) and central layers (11.56±1.35 vs 10.78±0.90, P=0.002) compared to the controls. The anterior COD in the 6-10 mm zone (β=0.329, P<0.001) and the middle COD in the 6-10 mm zone (β=0.267, P=0.006) showed a statistically significant direct relationship with OSDI. CONCLUSION: Young patients with dry eye exhibit increased COD, especially in the anterior and middle corneal layers, which correlates with symptom severity. These results imply that corneal densitometry could act as an objective measure of dry eye severity, supplementing traditional clinical evaluations.