Combined Eye Movements

COMBINED EYE MOVEMENTS, gaze with both eyes to the sides, upward, and downward, is accomplished by the coordinated work of corresponding muscles and regulated by certain centers. For gaze in a particular direction, the coordinated work of the nucleus of the abducens nerve (VI) on one side and the nucleus of the oculomotor nerve (III) on the other side is first necessary. This coordination is carried out by the function of the fasciculus longitudinalis posterioris, and possibly also the fasciculus praedorsalis and some other systems. The fasciculus longitudinalis posterior transmits impulses to the aforementioned nuclei, originating from higher coordinating centers located in the brainstem. Their exact location has not yet been determined. The brainstem coordinating centers are in turn influenced by the cerebrum, cerebellum, and vestibular apparatus. The cerebrum is connected with them contralaterally, i.e., the right hemisphere acts on the brainstem centers that control gaze deviation to the left, and vice versa. In the cerebral cortex, there are several centers for combined eye movements: first, a center in the frontal lobe, in the posterior part of the second frontal gyrus; second, in the parietal lobe, in the area of the gyrus angularis (Ferrier's experiments); third, in the occipital lobe, in the area of the calcarine fissure (experiments of Sherrington and Grünbaum on higher apes). The frontal center apparently has great importance for voluntary deviation of the eyes to the sides, while the occipital centers are for visual reflexes, i.e., for the reflexive turning of the eyes toward a light stimulus. See also Deviation conjuguee.