Third nerve palsy


Figure showing the mode of innervation of the recti lateralis from CNII.
Right eye
Eye movements by extra-ocular muscles and cranial nerve innervation
  • Third (oculomotor) nerve, innervates eyelid muscles and external ocular muscles (except lateral rectus and superior oblique) [1]
  • Nerve also carries parasympathetic fibers on external surface allowing for pupillary constriction
  • Palsy causes diplopia except in lateral gaze (lateral rectus innervated by CN VI)
  • Ptosis, headache


Clinical Features

Complete (isolated) third nerve palsy showing (a) left-sided ptosis, (b) restricted adduction movement of left eyeball, and (c) normal abduction movement of left eyeball.
  • Eye deviates laterally and down
  • Pupil exam:
    • If dilated/nonreactive likely secondary to space occupying lesion
    • If pupil is spared likely ischemic etiology
  • Loss of accommodation

Differential Diagnosis

Monocular Diplopia

Binocular Diplopia


  • If complete CNIII involvement with ptosis, mydriasis, and ophtalmoplegia:
    • Assume a compressive etiology from an intracranial aneurysm (PCOM aneurysm for example)
    • Proceed to a CTA brain
  • If complete oculomotor nerve palsy without pupil involvement then strongly favor an ischemic process
    • Consider a CTA brain
    • Coronal reconstruction on CT will allow visualization of orbits to rule out compressive process
  • If associated with other neurologic deficits:
    • CTA brain followed by MRI/MRA brain


  • If ischemic cause
    • Medical management, plus or minus ASA, with most self resolving in 6-8 weeks
    • Ophthalmology follow up
  • If aneurysm/mass
    • Neurosurgery consult
  • If diplopia
    • No driving or operating heavy machinery

See Also


  1. Capo, H., M.D., Warren, F., M.D., Kupersmith, M. , M.D. Evolution of Oculomotor Nerve Palsies. J Clin Neuroophthalmol. 1992 Mar;12(1):21-5. (12)1:21-25, 1992.
  2. Appenzeller S, Veilleux, M. Clarke, A. Lupus. Third cranial nerve palsy or pseudo 3rd nerve palsy of myasthenia gravis? A challenging diagnosis in systemic lupus erythematosus. 2009 Lupus. Aug;18(9):836-40.
  3. Chaudhary,N. et al Imaging of Intracranial Aneurysms Causing Isolated Third Nerve Palsy. J. Neuro-Ophthalmol 2009;29:238-244
  4. Kusner LL, Puwanant A, Kaminski HJ: Ocular myasthenia: Diagnosis, treatment, and pathogenesis. Neurologist 2006; 12:231-239
  5. Bushra JS: Miller Fisher syndrome: An uncommon acute neuropathy. J Emerg Med 2000; 18:427-430