Some instructive cases concerning the circuitry of ocular smooth pursuit in the brainstem

Abstract

Three cases with vascular brainstem lesions, clearly visible on magnetic resonance imaging (MRI) or CT scan, are reported. Dissociated paralyses of eye movements with preservation of smooth pursuit, documented with electro-oculographic recordings, existed in the three cases. In the first, there was a paralysis of all leftward saccades and of the left sixth nerve. This syndrome and the CT scan suggested damage to the caudal part of the left paramedian pontine reticular formation (PPRF). The preservation of leftward smooth pursuit confirms that the caudal PPRF is not crucial for this movement. In the second case, all downward saccades were absent. This syndrome and MRI suggested bilateral damage to the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). The preservation of downward smooth pursuit confirms that the riMLF is not crucial for this movement. Lastly, in the third case, all lateral eye movements were absent. Vertical saccades, upward oculocephalic movement and downward foveal smooth pursuit persisted, but downward oculocephalic movement was absent and upward smooth pursuit impaired. MRI showed a large bilateral pontine hematoma in the tegmentum, probably damaging the medial longitudinal fasciculi (MLF) but not the brachium conjunctivum (BC). It is suggested that downward foveal smooth pursuit is mediated by the BC rather than by the MLF.

Key Words:

• foveal smooth pursuit
• saccades
• downgaze paralysis
• lateral gaze paralysis
• reticular formations