Nuclear and Infranuclear Ocular Motor Disorders

Binocular diplopia is usually caused by strabismus, whereas monocular diplopia is usually caused by ocular diseases. Incomitant diplopia is usually caused by an acquired strabismus resulting from abnormal innervation or mechanical restriction. The oculomotor (third) nerve: ■ Innervates the medial rectus, superior rectus, inferior rectus, inferior oblique, and levator palpebrae muscles ■ Carries parasympathetic fibers to the iris sphincter and the ciliary body. ■ Common causes of third nerve palsy: Adults: aneurysms, vascular disease (including ischemia, diabetes, hypertension, and inflammatory arteritis), trauma, migraine Children: birth trauma, accidental trauma, neonatal hypoxia, migraine The third nerve originates from the oculomotor nucleus complex, which lies at the ventral border of the periaqueductal gray matter in the midbrain. The nerve fascicle passes ventrally through the medial longitudinal fasciculus, the tegmentum, the red nucleus, and the substantia nigra, and finally emerges from the cerebral peduncle to form the oculomotor nerve trunk, which lies between the superior cerebellar and posterior cerebral arteries. The nerve then passes through the subarachnoid space, running beneath the free edge of the tentorium. It continues lateral to the posterior communicating artery and below the temporal lobe uncus, where it runs over the petroclinoid ligament. It pierces the dura mater at the top of the clivus to enter the cavernous sinus. Within the cavernous sinus, the nerve runs along the lateral wall of the sinus together with the trochlear nerve and the ophthalmic (V1) and maxillary (V2) divisions of the trigeminal nerve. As it leaves the cavernous sinus, it divides into the superior and inferior divisions, which pass through the superior orbital fissure, and enters the orbit within the annulus of Zinn. Within the orbit, the smaller superior division runs lateral to the optic nerve and ophthalmic artery and supplies the superior rectus and levator palpebrae muscles. The larger inferior division supplies the medial rectus, inferior rectus, and inferior oblique muscles, as well as the iris sphincter and ciliary body.