OBJECTIVE This study describes hemodynamic characteristics of the ophthalmic, central retinal, and posterior ciliary arteries in 16 eyes of 11 patients with the ocular ischemic syndrome. Understanding the hemodynamic characteristics of the retrobulbar circulation may elucidate the natural history and pathophysiology of the ocular ischemic syndrome and perhaps form the basis for rational treatment of this condition. METHODS Color Doppler imaging, a procedure that permits rapid noninvasive imaging of the ophthalmic, central retinal, and posterior ciliary arteries, was used to quantitate peak systolic blood flow velocities and vascular resistance (pulsatility index) within these vessels in study group eyes and in an age-matched control population. RESULTS We demonstrated markedly reduced ocular ischemic syndrome central retinal and posterior ciliary artery peak systolic velocities compared with control group eyes. Central retinal and posterior ciliary artery vascular resistance (pulsatility index) was greater in ocular ischemic eyes versus control group eyes. Reversal of ophthalmic artery blood flow was detected in 12 of 16 ocular ischemic syndrome eyes. Study group eyes with poor vision had no detectable posterior ciliary arterial blood flow. CONCLUSIONS Color Doppler imaging quantitates hemodynamic characteristics of the retrobulbar circulation in the ocular ischemic syndrome. There is markedly reduced peak systolic velocity and increased vascular resistance in ocular end arteries such as the central retinal and posterior ciliary arteries. Ophthalmic artery reversal of flow seems to represent collateral blood flow to lower resistance vascular beds. Posterior ciliary artery hypoperfusion may correlate with poor vision in the ocular ischemic syndrome.