Color Doppler imaging was used to analyze the blood velocity in the ophthalmic artery (BVA) of 33 normal subjects and 36 diabetic patients. Maximum systolic BVA (Vmax), minimum end-diastolic BVA (Vmin) and Pourcelot index (RI: index of vascular resistance) were determined by analyzing the pulse wave of flow velocity in the ophthalmic artery. The coefficient of reproducibility of Vmax, Vmin and RI in normal subjects was 10%, 9% and 4%, respectively, when analyzed twice at one-hour intervals. There was no significant difference in the indices of the right eyes compared to those of the left eyes. The averages of Vmax, Vmin and RI were 25.4 +/- 7.6 cm/s, 6.3 +/- 2.3 cm/s and 0.75 +/- 0.052 (mean +/- SD), respectively. Vmax and Vmin decreased significantly with age (Vmax: r = -0.65, P < 0.001; Vmin: r = -0.61, P < 0.001). RI did not change with age. Vmax, Vmin and RI were compared between normal subjects and patients. RI was significantly higher in diabetics (0.775 +/- 0.047 in patients without retinopathy, 0.779 +/- 0.084 in patients with background retinopathy and 0.786 +/- 0.081 in patients with preproliferative or proliferative retinopathy) than in normal subjects (0.728 +/- 0.054). This suggests there is a pathological increase in choroidal vascular resistance and/or a decrease in the diameter of the ophthalmic artery in diabetics.