Purpose: To compare the prevalence and association of diabetes mellitus (DM) between keratoconus (KC) and non-KC populations and evaluate whether DM has the potential to protect the cornea against developing keratectasia.
Methods: A retrospective case-control study was conducted on 1383 KC patients and 1383 non-KC controls. The presence or absence of either type 1 or type 2 DM was investigated in both groups. Statistical significance and odds ratios were calculated.
Results: The prevalence of DM in KC patients and the control group was 0.8% and 2.2%, respectively. Statistical analysis revealed a strong protective effect of DM against KC (odds ratio = 0.350, P = 0.001). This effect was only seen in type 2 DM patients (odds ratio = 0.079, P < 0.001) and not in patients with type 1 DM (odds ratio = 3.013, P = 0.073).
Conclusions: The results of this study suggest that DM provides a statistically significant protective effect against the development of KC. This investigation showed that the biomechanical effects of cross-linking were also reflected in epidemiological results.