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.