A case of posterior ischemic optic neuropathy (PION) in a 41-year-woman with 19 years remission of multiple sclerosisis presented.She had complaints of acute unilateral loss of vision and underwent complex clinical and instrumental examination including B-scan of orbit, color duplex sonography (CDS) of orbital vessels and brachiocephalic arteries, magnetic resonance imaging (MRI). The significant stenosis of internal carotid artery due to its dissection was detected on the affected eye side. The results of ultrasound examinations and MRI excluded demyelinative retrobulbar neuritis (RBN) and determined the signs of blood flow impairment in vessels of orbital part of the optic nerve. Differential diagnostics of PION and RBN required the investigations of blood flow in orbital vessels and brachiocephalic arteries. Key words: posterior ischemic optic neuropathy, multiple sclerosis, retrobulbar neuritis, color duplex sonography, internal carotid artery.
