Unilateral internuclear ophthalmoplegia and ipsiversive torsional nystagmus.

We report four patients with internuclear ophthalmoplegia and torsional nystagmus, ipsiversive to the side of the medial longitudinal fasciculus (MLF) lesion. The MLF lesion could be responsible for an inactivation of the ipsilateral interstitial nucleus of Cajal inducing a contraversive slow phase. The presence of a corrective ipsiversive quick phase implicates an intact rostral interstitial nucleus of the MLF.