Diabetes Mellitus and Keratoconus: A Systematic Review and Meta-Analysis

Purpose: Although previous studies have assessed the relationship between diabetes and keratoconus, the findings were controversial and warranted further clarifications. The objective of this study was to investigate the association between diabetes and keratoconus by conducting a systematic review and meta-analysis. Methods: A comprehensive literature search was performed to identify eligible studies reporting the association of diabetes with keratoconus from their inception to April 2021 through PubMed, Embase, and Web of Science. The quality of included studies was assessed using the Newcastle-Ottawa scale. Combined odds ratios (ORs) and 95% confidence intervals were calculated using a random-effects model. Results: In all, 8 case-control studies and 3 cohort studies reporting the association between diabetes and keratoconus were included in the meta-analysis. Diabetes was not associated with keratoconus in the overall analysis (combined OR = 0.85, 95% confidence interval: 0.66-1.10). The associations were found to be nonsignificant in subgroup analysis when stratified by study quality, design, source, types, and population. No publication bias was detected from either the Egger test (P = 0.46) or Begg test (P = 0.16). Sensitivity analysis revealed that differences between groups were not statistically significant. Conclusions: This meta-analysis indicates that current literature does not support a significant association between diabetes and keratoconus. Further studies with more definite control for confounders and well-designed cohorts or interventions are warranted.