Effect of Metformin on the Development and Severity of Diabetic Retinopathy

Abstract

Purpose: To investigate whether metformin use is associated with decreased incidence of severe diabetic retinopathy requiring panretinal photocoagulation.

Methods: This is a retrospective study of patients with longstanding type 2 diabetes. Patient charts were reviewed from January 1990 to September 2013. Patients with type 2 diabetes for more than 15 years were included. Patients were included if they never used metformin or used metformin for at least 5 years prior to onset of diabetic retinopathy. Patients without ophthalmic or primary care records were excluded. The primary outcome was to compare the rates of severe diabetic retinopathy requiring panretinal photocoagulation in patients on metformin with those not on metformin. The secondary outcome was prevalence of diabetic macular edema requiring focal/grid photocoagulation.

Results: 333 patients with diabetic retinopathy are included in our current analysis, 191 patients on metformin and 142 patients not on metformin. In the metformin group, only 48 patients had severe diabetic retinopathy requiring PRP (25.1%), while in the non-metformin group, 67 patients required PRP (47.2%) (P<0.001). 73 patients in the metformin group (43.2%) required focal/grid laser for macular edema while 64 patients (48.9%) did in the non-metformin group (P=0.329).

Conclusions: Although other confounding factors may contribute to the severity of diabetic retinopathy, our study shows that metformin use may be associated with lower incidence of severe nonproliferative and proliferative diabetic retinopathy. No correlation was found with incidence of diabetic macular edema. A large scale prospective study is required to confirm our findings.

Keywords: 499 diabetic retinopathy