C is the correct answer The patient's history is consistent with a lesion in the medial longitudinal fasciculus (MLF), The MLF connects the nuclei of CNIII (oculomotor) and CNVI (abducens) to facilitate coordination of saccadic eye movements. Lesions in the MLF prevent this coordination from occurring, causing the adducting eye to move only to the midline, while the abducting eye will have nystagmus towards the adducting eye (towards its own midline). Demyelinating lesions in the MLF are a common early manifestation of multiple sclerosis (especially in a young woman with no other disease processes). (Choice A) Amaurosis fugax is a transient monocular vision loss, generally caused by a thrombus or emboli. The patient has 20/20 acuity, which makes this unlikely. (Choice B) Cataract is a gradual opacification of the lens of the eye. It does not present acutely as in this patient, and acuity is affected. (Choice D) Optic neuritis is an inflammation of the optic nerve, which is the most common presentation of multiple sclerosis in young women. Presentation is acute, often painful loss, partial loss of visual acuity, and often color vision is affected. This patient should be evaluated for optic neuritis, but her presentation does not suggest it. (Choice E) Panophthalmitis is an acute, suppurative (neutrophil-dense) often overwhelming inflammation of the inner eye tissue and sclerae.