Supplementary Material for: Relationship between Diabetic Retinopathy and Primary Open-Angle Glaucoma: A Systematic Review and Meta-Analysis

Background: Pathophysiological overlaps exist between diabetes and primary open-angle glaucoma (POAG) and presence of diabetes increases risk of POAG. Considering that diabetic retinopathy (DR) is an ocular complication of diabetes, one could speculate that DR as a severity measure may associate with or even predict POAG. Given that POAG is asymptomatic in early stages, an association to DR may prove clinically important and facilitate an earlier diagnosis of POAG. Objectives: To investigate if DR is associated with and predictive of POAG. Method: We systematically searched 11 literature databases on May 12th, 2021. We screened a total of 1,535 records and found six studies eligible for qualitative and quantitative analysis. Two independent authors reviewed the studies, extracted data, and evaluated risk of bias within individual studies. Studies were reviewed qualitatively, and meta-analyses were made based on the odds ratios (ORs) with 95 % confidence intervals of the association between DR and POAG using the random-effects model. Subgroup analyses were made on the association between subtypes of DR and POAG. Results: Six studies (two longitudinal and four cross-sectional) were eligible for review with a total of 255,614 patients with diabetes, of which 20,483 patients had any degree of DR and 5,258 had POAG. All studies were based on patients with type 2 diabetes except one with both type 1 and type 2 patients. Any DR was not associated with POAG (OR 1.17; 95% confidence interval (CI95%): 0.58–2.35; P = 0.65). Further stratification revealed that neither cross-sectional (OR 1.00; CI 95%: 0.56 to 1.81, P = 0.99) nor longitudinal studies (OR 1.47; CI 95%: 0.57 to 3.78, P = 0.43) demonstrated an association between DR and POAG. Conclusions: We did not find convincing evidence of an associations between DR and prevalent or incident POAG.