Objective: To investigate the correlation between metformin therapy and diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (T2DM). Methods: The clinical data of 1 891 patients with type 2 diabetes mellitus attending the ophthalmology department of China-Japan Friendship Hospital from September 2015 to August 2020 were reviewed. A retrospective study was performed on 324 cases of these T2DM patients with disease duration ≥10 years. Medical records of all patients including general information, history of medical disease, diabetes treatment, ophthalmologic examination and blood biochemical indices were collected. According to whether metformin treatment was received or not, the patients were divided into a metformin-treated and a non-metformin-treated groups. DR is classified into non-obvious DR, non-proliferative DR and proliferative DR according to the fundus examination and the clinical diagnostic criteria of DR. Logistic multiple regression analysis was used to determine the effects of age, sex, age of DM onset, duration of DM, duration of hypertension,

duration of hyperlipidemia, years of smoking, body mass index, insulin treatment and fasting glucose, glycated hemoglobin, total cholesterol, triglycerides, uric acid and blood creatinine levels on DR. Results: There was no statistically significant difference in the risk of developing DR between the metformin-treated and non-metformin-treated groups (P>0.05). Univariate and multifactorial analyses of variables related to the occurrence and different stages of DR in patients with T2DM showed that years of smoking, fasting glucose and creatinine were positively associated with DR (P<0.05), while age was negatively associated with DR (P<0.01), and age of DM onset was significantly negatively associated with DR (OR=0.95, 95%CI: 0.92 to 0.98, P=0.0003). In T2DM patients treated with metformin, neither the duration of metformin (OR=1.02, 95%CI: 0.96 to 1.08, P>0.05) nor the mean dose(OR=1.50, 95%CI: 0.79 to 2.84, P>0.05) was significantly associated with developing DR. The risk of developing DR was lower in women than in men (P<0.05); combined insulin therapy was significantly positively correlated with the risk of DR (OR=3.11, 95%CI: 1.59 to 6.07, P<0.01); long-term smoking, glycosylated hemoglobin and uric acid levels higher than normal were positively associated with DR (P<0.05). In metformin users, there was a significant difference in the risk of developing DR between the no-insulin treatment group and the combined insulin group (P<0.01); and among patients not using metformin, insulin therapy was positively associated with the occurrence of DR (OR=12.43, 95%CI: 3.75 to 41.19, P<0.0001). Conclusion: There was no significant association between metformin treatment and DR among patients with T2DM for >10 years.