Neuroanatomy of the ocular motor pathways

Oculomotor-related structures in the brain stem extend from the rostral mesencephalon to the hypoglossal nucleus in the caudal medulla. This chapter reviews their location in man, their connections and some basic features of their function; these are summarized in Table 1. In addition to the extraocular motor nuclei (the oculomotor, trochlear and abducens nuclei) the brain stem contains premotor areas responsible for all five different types of eye movements and for gaze-holding. These premotor structures include the riMLF and PPRF for the generation of vertical/torsional and horizontal saccades, respectively. The role of the vestibular nuclei in the VOR and optokinetic responses is well established, and they probably also mediate smooth pursuit eye movements along with the dorsolateral pontine nuclei and the floccular region. In contrast, there is only scanty evidence for the function of the accessory optic nuclei relaying optokinetic information in man. Little is known about the neuroanatomy of the premotor areas for convergence. There is accumulating evidence that the INC and the vestibular and perihypoglossal nuclei are essential for the maintenance of gaze.