To report a case of posterior ischemic optic neuropathy accompanied by carotid artery plaque in a patient with retrobulbar optic neuritis.

Case summary: A 48-year-old man visited our clinic complaining of headache, decreasing visual acuity and defect of inferior visual field in his left eye for 3 days. The best corrected visual acuity was 1.0 in the right eye and 0.1 in the left eye. The anterior segment state, intraocular pressure, fundus examination and optical coherence tomography were normal in both eyes. Relative afferent pupillary defect, color vision deficiency and total scotoma were observed in his left eye. The results of the laboratory test and brain magnetic resonance imaging were normal. He was discharged from the hospital after 3 days of systemic steroid treatment on the basis of retrobulbar optic neuritis. A week later, fluorescent angiography and carotid ultrasonography were performed because of his history memory loss and left upper limb weakness before admission. A focal filling defect of the peripapillary area was found on fluorescent angiography. A plaque with a thickness of 1.9 mm and a length of 1.4 cm was found on carotid ultrasonography. After 6 months, the best corrected visual acuity was 0.4 in the left eye and the visual field showed a partially improved defect.

Fluorescent angiography is recommended for potential posterior ischemic optic neuropathy in patients with retrobulbar optic neuritis, even though it is rare. Carotid ultrasonography is useful in finding atherosclerosis to prevent stroke or cardiovascular disease if ischemic cause is suspected on fluorescent angiography.