The Effect of Diabetes Mellitus on Central Corneal Thickness Values: A Systematic Review and Meta-Analysis

Diabetes mellitus (DM) is a chronic metabolic disorder that can induce systemic and ocular complications. Among the latter, an increase in central corneal thickness (CCT) has been reported, potentially affecting endothelial function and increasing the risk of ocular disease. This study aimed to determine the impact of DM on CCT and to assess its correlation with diabetes duration and glycosylated hemoglobin (HbA1c) levels. A systematic literature search was conducted in Web of Science (1980-2025) following a PICO-based strategy. Observational studies evaluating CCT in diabetic patients were included. Data were analyzed using a random-effects model. Statistical heterogeneity was assessed with χ² test, p values, and I² index. Publication bias was evaluated using Begg's funnel plot and Egger's regression test. Twenty-nine studies were included in the meta-analysis. Diabetic patients showed significantly higher CCT values compared to controls, particularly in those with long-standing DM (p < 0.001) and poor glycemic control (HbA1c, p < 0.001). Egger's regression suggested an association between increasing CCT, disease duration, and HbA1c levels, while funnel plot asymmetry indicated potential publication bias. CCT appears to increase in patients with long-term DM and inadequate glycemic control. These findings highlight the relevance of CCT assessment as a potential indicator of corneal changes in diabetic patients.