third nerve palsy
Also called oculomotor nerve palsy, CN III palsy, CN 3 palsy, oculomotor palsy
Third nerve palsy is 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 and the pupil is dilated and fixed.1,3 The eye rests turned out and slightly down under the pull of the two muscles still working.1,3
A palsy that involves the pupil is treated as an aneurysm of the posterior communicating artery until imaging proves otherwise.2 A microvascular palsy in diabetes or hypertension is the commonest acquired cause in adults, and it usually spares the pupil and recovers over months.2
Myasthenia can imitate the ptosis and the motility loss, but it never involves the pupil.2
More detail
The lateral rectus and the superior oblique set the resting position of abduction, slight depression and intorsion.1,5 Adduction, elevation and depression are limited, while abduction is normal. The eye intorts further on attempted downgaze because the superior oblique is intact, and accommodation is paralyzed along with the pupil.1,5 The other nerves can be checked through the palsied eye, since abduction proves the sixth nerve and intorsion on attempted gaze down and in proves the fourth.3 The palsy is also described by which parts are affected, as 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