The Localization of Lesions Affecting the Ocular Motor System

Abnormalities of ocular motility serve as valuable signposts for the localization of lesions of the cerebral hemispheres, brainstem, cranial nerves, and even striated muscle. Ocular symptoms and signs are particularly helpful when examining the patient in coma (see Chapter 22). In this chapter, the term ocular motor refers to cranial nerves III (oculomotor), IV (trochlear), and VI (abducens), collectively, whereas the word oculomotor designates specifically cranial nerve III. This follows the convention adopted by Leigh and Zee [565] in their excellent review of ocular motility. We first review the anatomy and localization of lesions of the ocular motor nuclei and nerves and then the control systems that the brain uses to produce precise, smooth, quick, stable, and binocular eye movements. Disturbances of these “supranuclear” mechanisms, nystagmus, and eyelid disturbances are then discussed.