A Unique Case of Compressive Optic Neuropathy From an Internal Carotid Artery Aneurysm.

Compressive optic neuropathy (CON) is a condition characterized by optic nerve damage caused by abnormal mechanical pressure. Here, we report a rare case of bilateral CON due to a large, right supraclinoid internal carotid artery (ICA) aneurysm. A 66-year-old female presented to the clinic with complaints of prior, intermittent headaches and decreased visual acuity. Notably, no relative afferent pupillary defect (RAPD) was present on exam. Visual field testing revealed an inferior altitudinal defect oculus dexter (OD) and a superotemporal defect oculus sinister (OS). This visual field pattern strongly suggested a central lesion in the form of a junctional scotoma despite the noted absence of a RAPD on exam. Subsequent magnetic resonance imaging (MRI) revealed a large, right supraclinoid aneurysm, and the patient was treated accordingly. Through this case, one can appreciate how the classically described RAPD may not be present in all cases of CON if both optic nerves are affected. A provider must subsequently use other findings to distinguish between a central and peripheral nerve etiology. The importance of formal visual field testing in all cases of vision loss is highlighted to assess its etiology and aid in making this distinction between a central and peripheral lesion.