[Lesions of the vertical and horizontal systems in the optokinetic vestibular system]

Symptoms of vestibulo-ocular disturbances may be classified into two major groups; i.e., vertical plane and horizontal plane disturbances. Vertical plane symptoms arise from midline lesions of the cerebellum or the brainstem and also from diffuse or symmetrical lesions to either. Vertical plane symptoms also arise from lesions which simultaneously effect both peripheral vestibular systems. Horizontal plane symptoms originate from a unilateral disturbance in the vestibular system. Thus, vertical plane symptoms indicate bilateral disturbances and the symptoms appear symmetrically in the eyes, trunk or extremities. Vertical plane symptoms appear in the sagittal plane, or the plane of the vertical semicircular canals. On the other hand, horizontal plane symptoms appear in the horizontal plane, or the plane of the horizontal semicircular canals.