[Case of ruptured carotid-ophthalmic aneurysm splitting the optic nerve].

A rare case of ruptured carotid-ophthalmic aneurysm splitting the optic nerve was reported. A 52-year-old man presented with a sudden severe headache and bilateral visual deterioration. His right visual acuity was hand motion and the left was 2.0. His left visual field revealed a partial defect of the temporal visual field. Three-dimensional CT angiography revealed an ophthalmic aneurysm of 9 mm projecting superior-medially, The operation was performed to preserve the visual function as much as possible. The C2 portion aneurysm splitting the right optic nerve was visible. Before aneurysm clipping, the right anterior clinoid process and optic canal were drilled out to reduce the tension of the optic nerve. Intraoperative monitoring of visual evoked potential (VEP) under propofol anesthesia was performed to prevent further visual disturbance. Electroretinogram (ERG) was introduced to ascertain the arrival of the light stimulus at the retina even when the VEP could not be recorded. The right ERG was recorded, but the right VEP was flat. Both ERG and VEP were reproducible on the left side. Six months after the operation, the right visual acuity had improved to 0.08 and the visual field revealed nasal hemianopsia. The left visual acuity was unchanged while the visual field had improved to upper temporal quadrant hemianopsia. Various attempts to preserve the visual function were discussed.