Glaucoma-Like Compressive Optic Neuropathy Associated With a Supraclinoid Internal Carotid Artery Aneurysm: A Case Report

Compressive optic neuropathy can mimic glaucoma, and the classic clues to compression may be absent or subtle.An 80-year-old woman reported that she had been undergoing fundus examinations for diabetes mellitus and follow-up of a right retinal nerve fiber layer (RNFL) defect at another clinic.Over several days, she noticed a vague difficulty seeing with the right eye, without headache, ocular pain, or diplopia, and was referred to our hospital by a different clinic.Decimal visual acuity was 0.7 in the right eye and 0.9 in the left eye, and intraocular pressure (IOP) was 18 mm Hg in both eyes.A mild right relative afferent pupillary defect (RAPD) was present.The right optic disc appeared essentially normal, with a cup-to-disc ratio of 0.3 and no rim thinning or pallor.Optical coherence tomography (OCT) showed a localized inferotemporal RNFL defect, but the average peripapillary RNFL thickness was within normal limits.In contrast, macular ganglion cellinner plexiform layer (GCIPL) thickness was reduced in both the superior and inferior hemispheres.Humphrey 30-2 perimetry showed glaucoma-like loss, predominantly nasal and involving the superior and inferior hemifields, with a mean deviation of -16.45 dB.This field loss was out of proportion to the disc appearance and the RNFL findings.The optic disc, OCT, and visual field findings in the left eye were normal.The new symptom and the RAPD at normal IOP prompted magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA).Imaging showed compression of the right optic nerve by an approximately 10-mm supraclinoid internal carotid artery aneurysm.The aneurysm was treated with a flow diverter at another hospital, and postoperative visual acuity and visual field data were not available.Comparison with six previously reported cases shows that aneurysmal compression can present with glaucoma-like findings at normal IOP and that visual outcomes after treatment are variable.In eyes with a glaucoma-like RNFL defect or visual field loss, three features should raise the possibility of a nonglaucomatous cause, including aneurysmal compression: unilateral damage at normal IOP, a recent change in vision, and field loss out of proportion to the disc and RNFL findings.These features lower the threshold for neuroimaging.