Bilateral Internuclear Ophthalmoplegia (INO) in a patient with multiple sclerosis. This disorder is due to interruption of the ipsilateral median longitudinal fasciculus (MLF) after fibers have crossed from interneurons of the contralateral abducens nucleus projecting to the ipsilateral medial rectus nucleus. This results in paresis or paralysis of adduction of the ipsilateral eye on horizontal gaze to the contralateral side, and horizontal jerk nystagmus in the contralateral abducting eye. INO is most commonly due to multiple sclerosis in young adults and stroke in the elderly.