Is primary open-angle glaucoma a risk factor for diabetic retinopathy?

PURPOSE To compare the prevalences of diabetic retinopathy in diabetes mellitus patients, with and without primary open-angle glaucoma, with a view to determine if glaucoma is a risk factor for the development of diabetic retinopathy. METHODS Cross-sectional, comparative study consisting of 86 diabetic patients with glaucoma matched with 86 diabetic patients without glaucoma. The two groups were matched by age, sex and duration of diabetes mellitus. Demographic data were obtained via patient medical records and self-administered questionnaires. Participants underwent a standardized examination protocol including blood pressure measurement and ocular examination. Main outcome measure was the presence of diabetic retinopathy. RESULTS Two hundred and ninety-two eyes (144 glaucomatous eyes and 148 non-glaucomatous eyes) of 172 participants with diabetes mellitus were assessed. The prevalence of diabetic retinopathy among 86 participants with glaucoma comorbidity was 23.6%, while the prevalence among 86 non-glaucomatous participants was 33.8% (p = 0.06). After the regression analysis, controlling for systemic and ocular risk factors for diabetic retinopathy, the odds of developing diabetic retinopathy were significantly higher in the glaucomatous eyes compared with eyes without glaucoma (OR: 2.75; p = 0.03; 95% CI: 1.10-6.87). CONCLUSION This study demonstrated that glaucomatous diabetic eyes were almost three times more likely to develop diabetic retinopathy compared to non-glaucomatous diabetic eyes. Prospective studies may be required to establish a risk-cause relationship. Ocular perfusion pressure control should be considered in patients with diabetes mellitus and glaucoma.