Palsy, or paralysis, of the third cranial nerve (oculomotor nerve) usually presents with weakness or paralysis of the extraocular muscles and ptosis in 1 eye. The patient may experience this as diplopia, or double vision. There may be associated headache or ocular pain.

The annual incidence of third nerve palsy is estimated at approximately 4 per 100 000. It is most common in people over age 60. Infarction of the third cranial nerve is the most common cause and often occurs in patients with diabetes, hypertension, or atherosclerosis.

Palsy from infarction presents more acutely. Patients with ischemic third nerve palsies usually do not have pupillary dysfunction. In 20% of patients, the third nerve palsy is due to compression of the oculomotor nerve by tumors (eg, meningioma), herniation, or a brain aneurysm. If nerve dysfunction is caused by external compression (eg, from a tumor), pupil dilation may also occur due to the peripheral location of these nerve fibers. If the third nerve palsy is caused by compression from a tumor, symptoms are usually subacute in onset and gradually progressive. Other common causes include trauma and neurosurgical procedures.

Treatment is primarily aimed at the underlying cause. Most patients with a third nerve palsy require emergent evaluation and neuroimaging to evaluate for compressive lesions, including aneurysms.