Effects of Aspirin and Clopidogrel on Retinal Hemodynamics in Type 1 Diabetes

Abstract

Purpose:: Abnormal retinal blood flow has been reported in patients with type 1 diabetes with no or minimal retinopathy. Among the mechanisms suggested to explain this finding is the presence of platelet-fibrin microthrombi in retinal capillaries. We sought to measure the effects of two anti-thrombotic agents, aspirin and clopidogrel on retinal hemodynamics in such patients.

Methods:: Thirty-three patients with type 1 diabetes [age 29.2±6.9 years (mean±SD), duration of diabetes 8.8±4.5 years, 48% female, HbA1c levels 7.4±1.1%] with no or minimal retinopathy, and on no medications except insulin were included. Also included were 31 age and gender-matched healthy non-diabetic control subjects. Patients received either aspirin (81mg/day), clopidogrel (75 mg/day) or a placebo for two months. Control subjects received either aspirin or placebo. The Canon retinal laser Doppler instrument was used to measure arterial blood column diameter, centerline blood speed, and blood flow rate in a superior temporal (ST) retinal artery in one eye in each subject at baseline, on the last day of treatment, and two months thereafter. Results from the major ST artery were used for baseline comparisons via unpaired t-tests. Aspirin and clopidogrel effects were determined via repeated measures ANOVA.

Results:: At baseline, arterial diameter was 116±12 µm in the patients and 112±10 µm in the controls (p=0.18); blood speed was 32.9 mm/s in the patients and 34.8 mm/s in the controls (p=0.34); blood flow was 10.4±2.4 µl/min in the patients and 10.4±3.2 µl/min in the controls (p=0.99). Compared to baseline, arterial diameter was significantly larger (p=0.026) with aspirin vs placebo in the diabetic patients but not in the controls on the last day of treatment and two months later. There were no significant changes in blood speed or blood flow with aspirin in the patients or controls. There were no significant effects of clopidogrel on any of the hemodynamic parameters in the diabetic patients.

Conclusions:: Retinal hemodynamic parameters are not abnormal in type 1 diabetic patients with good glycemic control and no or minimal retinopathy. Anti-thrombotic agents do not affect the retinal blood flow in these patients. Low dose aspirin, however, appears to have a vasodilatory effect, the mechanism for which remains to be elucidated.

Keywords: diabetes • blood supply • retina