third nerve palsy
Also called oculomotor nerve palsy, CN III palsy, CN 3 palsy, oculomotor palsy
Weakness of the structures the oculomotor nerve supplies: four extraocular muscles (medial rectus, inferior rectus, superior rectus and inferior oblique), the levator of the upper lid, and the sphincter of the pupil. When the palsy is complete the lid droops, the eye rests turned out and slightly down under the pull of the two muscles still working, and the pupil is dilated and fixed1,3.
A palsy that involves the pupil is treated as an aneurysm of the posterior communicating artery until imaging proves otherwise2. A microvascular palsy in diabetes or hypertension, the commonest acquired cause in adults, usually spares the pupil and recovers over months, and myasthenia can imitate the ptosis and motility loss but never involves the pupil2.
More detail
The lateral rectus and the superior oblique set the resting position: abduction, slight depression and intorsion. Adduction, elevation and depression are limited, abduction is normal, and the eye intorts further on attempted downgaze because the superior oblique is intact. Accommodation is paralyzed along with the pupil1,5. The other nerves can be checked through the palsied eye: abduction proves the sixth nerve, and intorsion on attempted gaze down and in proves the fourth3. The palsy is also described by which parts are affected: the muscles only (external ophthalmoplegia), the pupil and ciliary muscle only (internal ophthalmoplegia), or both (total ophthalmoplegia)4.
Sources (5)
- Kanski, Clinical Ophthalmology (2024), ch. 19
- Liu, Volpe and Galetta, Neuro-Ophthalmology, ch. 15
- Yanoff and Duker, Ophthalmology (2023), ch. 9
- Pickwell's Binocular Vision Anomalies, ch. 17
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 20
Reviewed October 2026