What is third cranial nerve palsy (oculomotor cranial nerve palsy)?

Updated: Oct 08, 2018
  • Author: James Goodwin, MD; Chief Editor: Andrew G Lee, MD  more...
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Answer

The third, fourth, and sixth cranial nerves innervate the extraocular muscles that position the globes in the orbits. Extraocular muscle paralysis resulting from lesions in one or all of these cranial nerves results in failure of one or both eyes to rotate in concert with the other eye.

The primary symptom is diplopia caused by misalignment of the visual axes, and the pattern of image separation is the key to diagnosing which particular ocular motor cranial nerve (and extraocular muscle) is involved. With unilateral third cranial nerve palsy (ie, oculomotor nerve palsy), the involved eye usually is deviated "down and out" (ie, infraducted and abducted), and there may be partial or complete ptosis. In addition, pupillary dilatation can cause anisocoria (greater in the light), symptomatic glare in bright light, and accommodation deficit that may cause blurred vision for near objects.

A painful pupil-involved oculomotor nerve palsy may result from a life-threatening intracranial aneurysm. Therefore, recognition of oculomotor nerve palsy is critical to ensure prompt and appropriate evaluation and treatment.

See the image below.

Patient with left posterior communicating artery a Patient with left posterior communicating artery aneurysm and third cranial nerve palsy. Courtesy of James Goodwin, MD.

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