Association of Metformin Treatment with Reduced Severity of Diabetic Retinopathy in Type 2 Diabetic Patients

PURPOSE: To evaluate effects of long-term metformin on the severity of diabetic retinopathy (DR) in high-risk type 2 diabetic (T2D) patients. METHODS: A retrospective chart review study was conducted involving 335 DR patients with T2D ≥ 15 years from 1990 to 2013. The severity of DR was determined by Early Treatment Diabetic Retinopathy Study scale. The associations between metformin and DR severity were evaluated. Comparison with stratification for the use of sulfonylurea and insulin was performed to identify possible confounding effects. RESULTS: Severe nonproliferative diabetic retinopathy or proliferative diabetic retinopathy (SNPDR/PDR) was more often diagnosed in nonmetformin users (67/142, 47%) versus metformin users (48/193, 25%) (p < 0.001), regardless of gender and race of the patients. The odds ratio of metformin associated with SNPDR/PDR was 0.37 in all cases (p < 0.001), 0.35 in sulfonylurea use cohort (p < 0.05), 0.45 in nonsulfonylurea use cohorts (p < 0.01), and 0.42 in insulin use cohort (p < 0.01). Insulin users had a higher rate of SNPDR/PDR. Metformin had no influence on the occurrence of clinical significant diabetic macular edema. CONCLUSIONS: Long-term use of metformin is independently associated with a significant lower rate of SNPDR/PDR in patients with type 2 diabetes ≥ 15 years.