Ocular ischemic syndrome can be of either the acute type (amaurosis fugax, retinal artery occlusion and ischemic optic neuropathy) or the chronic type (venous stasis retinopathy and ischemic oculopathy). We carried out etiological studies on 35patients (19men, 16women, aged 62±16years) with retinal artery occlusion and 21patients (13men, 8women, aged 47±19 years) with amaurosis fugax. In all patients, carotid ultrasonography was performed to clarify the extent of carotid artery disease ipsilateral to the retinal artery occlusion and amaurosis fugax. All the patients underwent electrocardiography and transesophageal echocardiography. Arterial stenosis exceeding 50% of the diameter of the internal carotid artery ipsilateral to the symptomatic eye was more frequent in patients with retinal artery occlusion than in those with amaurosis fugax. Patent foramen ovale more frequent in the latter than in the former. Patients with venous stasis retinopathy and ischemic oculopathy (neovascular glaucoma) had occlusion of the ipsilateral carotid artery with reversed ophthalmic artery or severe stenosis of the ipilateral carotid artery with stenosis of the ipsilateral ophthalmic artery. Neurosonologic studies can provide valuable clinical data on ocular ischemic syndrome.