Saccadic intrusions in internuclear ophthalmoplegia.

Saccadic intrusions disrupted forward fixation in four patients with bilateral internuclear ophthalmoplegia (INO). Three had multiple sclerosis and one had brainstem infarction. Sporadic bursts of monocular abducting saccades were recorded in either eye. Each saccade was followed by a slower return to midposition. The presence of the INO prevented conjugate saccades of the fellow eye. The adducting phases were faster than convergence eye movements or the glissadic smooth eye movements that sometimes follow saccades. Dynamic overshoot of the abducting saccadic phase may contribute to the relatively rapid adducting phase. The saccadic intrusions of INO are recognized clinically as monocular horizontal oscillation; low-amplitude intrusions are evident only during funduscopy. This distinctive dyskinesia is considered a sign of involvement extrinsic to the medial longitudinal fasciculi in patients with INO.