FAST EYE-MOVEMENT INITIATION OF OCULAR TORSION IN MESODIENCEPHALIC LESIONS

Three patients with episodic ocular torsion and skew deviation due to mesodiencephalic lesions were studied by using binocular three-dimensi onal scleral search coils. The conjugate ocular torsion (upper pole of each eye rotating toward the side of the brainstem lesion) was initia ted by a torsional fast eye movement. During prolonged episodes, torsi onal nystagmus was also present. Cessation of the ocular torsion and s kew deviation occurred by slow eye movements with exponentially decrea sing velocities in 2 patients, and by multiple fast torsional movement s in 1 patient. In 1 patient, the abnormal eye movements were temporal ly linked to dystonic movements in the limbs on the side opposite the brainstem lesion. The occurrence of skew deviation with conjugate ocul ar torsion in brainstem lesions has been attributed to functional asym metry in vestibular pathways responsible for the slow-phase compensato ry eye movement response to roll. In comparison, the findings in our p atients show that in mesodiencephalic lesions conjugate ocular torsion with skew deviation may be generated by torsional fast eye movements, indicating activation of the burst cells of the rostral interstitial nucleus of the medial longitudinal fasciculus.