Background: Diabetes mellitus is a chronic metabolic disorder that can lead to various ocular complications, including corneal changes. This study aimed to investigate the correlation between HbA1c levels, central corneal thickness (CCT), and corneal endothelial parameters in patients with type 2 diabetes mellitus using non-contact specular microscopy.Methods: This observational study included 181 patients with type 2 diabetes mellitus who underwent a comprehensive ophthalmic examination, including non-contact specular microscopy. The correlation between HbA1c levels, CCT, endothelial cell density (ECD), coefficient of variation (CV), and hexagonality (HEX) was analyzed. The association between the severity of diabetic retinopathy and corneal parameters was also evaluated.Results: A significant positive correlation was found between HbA1c levels and CCT (p6.5% had a mean CCT of 579.24±19.47 µm, compared to 537.73±16.92 µm in those with HbA1c levels between 4-5.6% (p<0.001). The duration of diabetes was also significantly associated with increased CCT (p<0.001). Patients with PDR had the lowest mean ECD (2091.88±121.34 cells/mm²), highest mean CV (51.01±4.78%), and lowest mean HEX (30.10±3.92%) compared to those with no diabetic retinopathy (p<0.001 for all).Conclusion: HbA1c levels and duration of diabetes significantly correlate with CCT and corneal endothelial changes in patients with type 2 diabetes mellitus. Non-contact specular microscopy is a valuable tool for detecting early corneal changes in diabetic patients, enabling timely intervention and prevention of visual impairment.