Corneal Endothelial Pathology and Thickening in Early Diabetes Mellitus.

PURPOSE: To compare endothelial cell properties and central corneal thickness (CCT) between nondiabetic individuals and patients with early type 2 diabetes mellitus (T2DM) with good glycemic control. METHODS: This retrospective case-control study included patients diagnosed with T2DM within the past 10 years and nondiabetic individuals. All participants underwent comprehensive ocular examination and specular microscopy to measure endothelial cell density (ECD), central corneal thickness (CCT), and coefficient of variation (CV). Intergroup differences were analyzed statistically. RESULTS: A total of 312 eyes from 180 patients were included: 118 eyes in the diabetic group and 194 in the nondiabetic group. There were no significant differences in age (p = 0.08) or sex distribution (p = 0.49) between groups. The diabetic group had a significantly lower mean ECD compared with controls (2467.8 ± 334.5 vs. 2553.5 ± 289.2; p = 0.028) and a significantly higher CCT (558.8 ± 48.8 vs. 547.1 ± 44.6; p = 0.034). No significant difference was observed in the coefficient of variation. DISCUSSION: These findings suggest that corneal endothelial alterations may occur early in the course of type 2 diabetes mellitus, even in patients with good glycemic control and short disease duration. The observed reduction in endothelial cell density alongside increased central corneal thickness may reflect subclinical endothelial dysfunction or early metabolic effects on corneal hydration regulation, preceding overt clinical corneal disease. CONCLUSIONS: Early T2DM is associated with reduced ECD and increased CCT compared with nondiabetic individuals, despite good glycemic control. These results indicate that diabetes may affect corneal endothelial structure and function at an early stage.