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. 2021 Sep 4;1(1):100005. doi: 10.1016/j.aopr.2021.100005

Table 1.

List of human studies evaluating the relationship between keratoconus and diabetes

(adapted and modified from 26).

Study Study size Design Population Characteristics Findings Association
13 KC patients (n=571)
Non-KC controls (n=571)		 Retrospective case-control study
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    German population

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    Hospital/clinic-based

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    Ethnicity unspecified

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    Age range: 20–40 yo; Mean age KC: 28.86 ​± ​5.79 years. Mean age control: 29.45 ​± ​5.75

 T2DM showed a protective effect against KC development (odds ratio ​= ​0.2195) Inverse association of KC development with DM
14 KC patients without DM (n=269)
KC patients with DM (n=26)		 Retrospective cross-sectional study
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    United States population

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    Wilmer Eye Institute; Hospital/clinic-based

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    Ethnicity: White, Black, Other

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    Age range: 14–80 yo; Mean age 42.7 ​± ​13.4

 T2DM showed a protective effect against more severe KC (odds ratio ​= ​0.2); No difference in DM prevalence in KC population Inverse association of DM with KC severity
17 KC patients (n=1383) non-KC controls (n=1383) Retrospective case-control study
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    Iranian population

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    Farabi Eye Hospital; Hospital/clinic-based

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    Ethnicity unspecified

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    Age range: 18–49 yo. Mean age KC: 28.8 ​± ​5.3 years. Mean age control: 29.1 ​± ​5.8 years.

 T2DM showed a protective effect against KC development (odds ratio ​= ​0.350)
 Inverse association of KC development with DM
18 KC patients (n=16,053) non-KC controls (n=16,053) Retrospective longitudinal cohort study
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    United States population

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    Population-based

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    Multiple ethnicity (White, Black, Latino, Asian, Other)

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    All ages included; Mean age 40.4 ​± ​13.0 years (KC and matched controls)

 20% lower odds of KC development with uncomplicated DM; 52% lower odds of KC development with DM-associated organ failure Inverse association of KC development with DM
19 KC patients (n=2679) non-KC controls (n=26,7900 Retrospective longitudinal cohort study
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    Danish population

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    Population-based

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    Ethnicity: European vs. Non-European

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    All ages included. Mean age: 38.2 ​± ​15.9 (KC and matched controls)

 No significant difference in DM prevalence in KC patients. Total DM odds ratio=1.03, T1DM odds ratio=0.87, T2DM odds ratio=1.07 No significant association between KC development and DM
298 KC patients (n=575) non-KC controls (n=2875) Retrospective longitudinal cohort study
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    Korean population

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    Population-based

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    Ethnicity unspecified

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    All ages included. Mean age: 31.1 ​± ​16.0 (KC and matched controls)

 No significant difference in DM prevalence in KC patients. Multivariate odds ratio=1.02 No significant association between KC development and DM
299 29 studies incorporating 50,358,341 subjects Systematic review and meta-analysis
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    Global population; 15 countries

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    Hospital/clinic/population based

 Odds of developing KC were 23% lower in T2DM, but relationship was not significant No significant association between KC development and DM
22 KC patients (n=2051) non-KC controls (n=12,306 Retrospective case-control study
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    Netherlands population

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    Population-based, comparable socioeconomic distribution

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    Relative age group 10–40 years. Mean age KC and control: 30 ​± ​6.5.

 No significant association in KC and DM, with odds ratio 1.60 (0.89–2.89) and p-value 0.149. No significant association between KC development and DM
20 KC patients (n=1377) non-KC controls (n=4131)
AND T2DM KC patients (n=75) non-DM KC controls (n=225)		 Retrospective case-control and Cross-sectional study
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    United States population

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    Wills Eye Hospital Cornea Service; Hospital/clinic-based

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    Ethnicity unspecified

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    All ages included; Mean age KC: 44.64 ​± ​15.76 years. Mean age control: 45.06 ​± ​16.00

 Higher prevalence of T2DM in KC population compared to controls (6.75% and 4.84%, respectively); Higher severity of KC in DM patients (odds ratio ​= ​2.691) Positive association of KC development with T2DM
21 KC patients (n=1552) non-KC controls (n=7.760) Retrospective cohort study
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    South Korean population

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    Population-based

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    Ethnicity unspecified

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    All ages included.

 Higher prevalence of T2DM in KC population compared to controls (19.2% and 14.5%, respectively); Positive association of KC with DM (odds ratio ​= ​1.35) Positive association of KC development with DM