Diagnosis of ischemic optic neuropathy caused by dissection of the internal carotid artery: A case report.

Rationale: Ischemic optic neuropathy (ION), due to diseases of the arteries supplying the optic nerve, is an ischemic damage of the optic nerve. This report highlights a case with monocular decreasing visual acuity caused by dissection of the internal carotid artery (ICA), which is a relatively rare cause for ION. Patient concerns: A 44-year-old woman presented with a decreasing visual acuity and defected visual field in the right eye for 1 week. The best corrected visual acuity (BCVA) was 20/400 in the right eye, and 20/20 in the left eye. In the right eye, the pupil showed little reaction to light with a relative afferent pupillary defect. The visual field test disclosed a defect in the inferior field connecting to the blind spot. Electroretinogram recording showed no obviously declined retinal function. No recognizable waveforms were presented in pattern visual-evoked potential (PVEP) examination, whereas the flash visual-evoked potential result revealed a delayed peak time and a reduced amplitude of P2-wave. Diagnosis: The patient was diagnosed as ION with the aid of computed tomographic angiography of the brain and neck, which revealed a stenosis in the right ICA and an occlusion in the right cerebral middle artery. The stenosis was verified as dissection of the ICA by digital subtraction angiography. Interventions: Based on the clinical findings, stent implantation inside the right ICA was performed. Outcomes: The ICA was recanalized soon and the BCVA of the right eye was improved to be 20/25 five months later. A second PVEP examination revealed a recognizable waveform in the right eye, although the peak time and amplitude of the P100-wave was a bit abnormal compared to that of the left eye. Lessons: ION with the sign of decreasing monocular visual acuity could occur due to dissection of the ICA, with no obvious neurologic symptom at the beginning. The present case emphasizes the importance of suspicion of ICA problems as the underlying cause for ION, which could help to take in-time measure to save the vision and avoid further complications.