Walsh & Hoyt: Ocular Motor Syndromes Caused by Lesions of the Thalamus

Thalamic lesions are characterized by disturbances of both horizontal and vertical gaze. Conjugate deviation of the eyes contralateral to the side of the lesion (also called wrong-way deviation) may occur with hemorrhage affecting the medial thalamus. The reason for this contraversive deviation is unclear. The descending pathways from the frontal eye fields to the pons have not yet crossed at this level, although the notion of a precise ocular motor decussation is less certain now than in the past. Damage to the descending pathway for smooth pursuit might lead to a paretic, contraversive deviation of the eyes. Nevertheless, a patient with a defect of smooth pursuit directed toward the side of a small hemorrhage in the posterior thalamus and adjacent internal capsule still showed an ipsiversive gaze preference. Another possibility is that wrong-way deviation may be an irritative phenomenon, because neurophysiologic studies show that saccade-related neurons in the intralaminar thalamic nuclei mainly discharge for contralateral saccades.