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Chapter 029. Disorders of the Eye (Part 20)

Oculomotor Nerve The third cranial nerve innervates the medial, inferior, and superior recti; inferior oblique; levator palpebrae superioris; and the iris sphincter. Total palsy of the oculomotor nerve causes ptosis, a dilated pupil, and leaves the eye "down and out" because of the unopposed action of the lateral rectus and superior oblique. This combination of findings is obvious. More challenging is the diagnosis of early or partial oculomotor nerve palsy. In this setting, any combination of ptosis, pupil dilation, and weakness of the eye muscles supplied by the oculomotor nerve may be encountered. Frequent serial examinations during the evolving. | Chapter 029. Disorders of the Eye Part 20 Oculomotor Nerve The third cranial nerve innervates the medial inferior and superior recti inferior oblique levator palpebrae superioris and the iris sphincter. Total palsy of the oculomotor nerve causes ptosis a dilated pupil and leaves the eye down and out because of the unopposed action of the lateral rectus and superior oblique. This combination of findings is obvious. More challenging is the diagnosis of early or partial oculomotor nerve palsy. In this setting any combination of ptosis pupil dilation and weakness of the eye muscles supplied by the oculomotor nerve may be encountered. Frequent serial examinations during the evolving phase of the palsy help ensure that the diagnosis is not missed. The advent of an oculomotor nerve palsy with a pupil involvement especially when accompanied by pain suggests a compressive lesion such as a tumor or circle of Willis aneurysm. Neuroimaging should be obtained along with a CT or MR angiogram. Occasionally a catheter arteriogram must be done to exclude an aneurysm. A lesion of the oculomotor nucleus in the rostral midbrain produces signs that differ from those caused by a lesion of the nerve itself. There is bilateral ptosis because the levator muscle is innervated by a single central subnucleus. There is also weakness of the contralateral superior rectus because it is supplied by the oculomotor nucleus on the other side. Occasionally both superior recti are weak. Isolated nuclear oculomotor palsy is rare. Usually neurologic examination reveals additional signs to suggest brainstem damage from infarction hemorrhage tumor or infection. Injury to structures surrounding fascicles of the oculomotor nerve descending through the midbrain has given rise to a number of classic eponymic designations. In Nothnagel s syndrome injury to the superior cerebellar peduncle causes ipsilateral oculomotor palsy and contralateral cerebellar ataxia. In Benedikt s syndrome injury to the red nucleus .