In examining a 30-year-old male patient with multiple sclerosis, you notice that when you ask the patient to look to the left, the right eye fails to adduct and when the patient looks to the right, the left eye fails to adduct. However, both eyes in the patient can adduct during convergence. There is no noticeable strabismus when the eyes are focused on a far point. During abduction, both eyes display nystagmus. You record on the patient’s chart a diagnosis of bilateral internuclear opthalmoplegia. Which of the following neural structures is affected?
(A) fourth cranial (trochlear) nerve
(B) medial longitudinal fasciculus (MLF)
© second cranial (optic) nerve
(D) sixth cranial (abducens) nerve
(E) third cranial (oculomotor) nerve