Color Doppler imaging was performed to evaluate the venous stasis in 39 orbits, including 9 optic neuropathy orbits, of 20 patients with dysthyroid ophthalmopathy and 22 orbits of 11 healthy subjects. The superior ophthalmic vein (SOV) was detected in 26 dysthyroid ophthalmopathy orbits and in 13 control orbits. The blood flow in the SOV was in the anteroposterior direction in 20 dysthyroid ophthalmopathy orbits and in 13 control orbits. Reversed flow, ie, the flow in the posteroanterior direction, was seen in 6 dysthyroid ophthalmopathy orbits and in none of the control orbits. In dysthyroid ophthalmopathy orbits, the blood flow in the SOV was reversed in 5 (36%) of the 14 orbits with apical orbital crowding observed on computed tomography, which means there was compression of the optic nerve by enlarged extraocular muscles, as compared to in 1 (4%) of the 25 orbits without apical orbital crowding (P < 0.05). The percentage of the orbits having reversed flow in SOV was 44% of dysthyroid ophthalmopathy orbits with optic neuropathy as opposed to 7% of those without optic neuropathy (P < 0.05). Reversed blood flow in the SOV strongly supported the existence of severe venous stasis in the orbits, which may be related to the development of dysthyroid optic neuropathy.