Infranuclear disorders of ocular motility are marked by abnormal eye movements caused by lesions below the level of the cranial nerve nuclei. These lesions include damage to the cranial nerves, the extraocular muscles, or the connective tissue of the orbit. Their origins range from relatively harmless disorders to severe diseases that are life threatening. Infranuclear disorders produce paretic and/or mechanical strabismus with severe deficits of visual perception by means of diplopia (image duplication), visual confusion (image overlap), and acutely by oscillopsia (illusory movement of the environment). The principle responsibility of the ophthalmologist is to provide some symptomatic relief, determine the most likely source of the problem, and to arrange for appropriate consultation with other clinical disciplines. The search for these goals requires a thorough exploration of the history, precise measurements of ocular motility, and attention to potential accessory signs and symptoms. This diagnostic process and the specific signs and symptoms to be investigated are arranged in this chapter according to the various structural components of the neuromuscular control system governing eye movements. Infranuclear Disorders of Ocular Motility