Control of Eye Movements—Pathology

In addition to the pathways described above, each ocular motor nucleus also receives input for saccadic and pursuit eye movements that do not involve the vestibular nuclei. These pathways ultimately converge on the final common pathways for horizontal and vertical ocular motor control also used in the vestibuloocular system, but initially via different anatomic pathways. For example, saccadic eye movements (fast conjugate eye movements to a fixed target, either voluntary or reflex in origin) are initiated in the frontal and parietal lobes. The horizontal saccade pathway is a crossed pathway. Pathways from the frontal and parietal eye fields descend via the superior colliculus into the brainstem and cross at the level of the midbrain–pontine junction to synapse on the contralateral paramedian pontine reticular formation. The paramedian pontine reticular formation projects to the ipsilateral abducens nucleus, from which abducens neurons project to the ipsilateral lateral rectus muscle, whereas abducens interneurons project cross the midline to ascend in the contralateral medial longitudinal fasciculus and synapse on the medial rectus subnucleus of the contralateral oculomotor nucleus. The pathways for vertical saccades involve the rostral interstitial nucleus of the medial longitudinal fasciculus, the interstitial nucleus of Cajal, the posterior commissure, and the nucleus of the posterior commissure.

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