Oculomotor nerve palsy

Last revised by Craig Hacking on 28 Dec 2023

Oculomotor nerve palsies, or third nerve palsies, result in weakness of the muscles supplied by the oculomotor nerve, namely the superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris muscles.

If the pupil is normal-sized and reactive to light, it is called a pupil-sparing third nerve palsy; conversely if the pupil is enlarged and non-reactive, it is called a non-pupil sparing third nerve palsy.

Classically, patients present with diplopia and physical exam findings ipsilateral to the oculomotor nerve (CN III) lesion:

  • "down and out" ocular positioning

    • abduction, slight depression, and intorsion (due to paralysis of adduction, elevation, and depression)

  • complete ptosis

  • +/- enlarged unreactive pupil

    • if present, suggests compression of CN III, because the parasympathetic pupillary fibers are located peripherally in the nerve and are more likely affected by external compression

It has numerous possible etiologies which can be divided according to which portion of the nerve is affected:

In post-traumatic oculomotor nerve palsy, gaze movement training and steroid injections may be helpful 2.

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