Association between diabetes and keratoconus—a systematic review and meta-analysis

Purpose To assess the association between diabetes mellitus and keratoconus. Methods PubMed, Google Scholar, Web of Science, and Scopus databases were searched for literature on the association between diabetes and keratoconus. The last literature search was conducted on April 4, 2021. A secondary form of the literature search was conducted by manually scanning the reference list of retrieved eligible articles. Included studies were cohort, case-control, or cross-sectional study design that used odds ratio or risk ratio to evaluate the relationship between keratoconus and diabetes. Egger's test was used to assess the presence of publication bias. The quality of eligible studies was assessed using the Newcastle-Ottawa Scale. Results Nine studies (six case-control and three cohort studies) published between 2000 and 2021 were included. The total number of keratoconus patients and controls were 27,311 and 53,732. respectively. Meta-analysis revealed no significant association between diabetes mellitus and keratoconus; the pooled odds ratio was 0.87 (95% confidence interval: 0.66–1.14; p = 0.314). There was significant heterogeneity ( Q (df = 7) = 33.36, p < 0.001; I 2 = 79.01, p < 0.001). Age of participants ( p < 0.0001), study design ( p < 0.001), and sample size ( p = 0.024) were significant sources of heterogeneity. There was no evidence of publication bias. Conclusion The current meta-analysis revealed no significant association between diabetes mellitus and keratoconus. Well-designed longitudinal prospective studies are, however, needed to investigate any association between diabetes mellitus and keratoconus.