Midbrain-diencephalic horizontal gaze paresis.

Four patients with predominantly right-sided infarcts at the midbrain-diencephalic junction had an ipsilateral oculomotor palsy and contralateral gaze palsy. The gaze palsy to the left was supranuclear in nature, because the restriction of abduction was overcome by the oculocephalic reflex. However, it was masked on the right eye by the third nerve palsy. In all cases upgaze was impaired bilaterally, and infraduction was absent on the right. The restriction of abducting saccades remained for months, considerably longer than with supranuclear cortical lesions, suggesting that the damage extended beyond involvement of the frontopontine pathways. These cases represent clinical instances of a recently described experimental syndrome of impaired horizontal saccadic eye movements with lesions at the paramedian midbrain-diencephalic junction.