Oculomotor nerve

From Ganfyd

The third of the cranial nerves. Leaves skull via Superior orbital fissure

Supplies

• all muscles of eye except
  • lateral rectus
  • superior oblique

Lesion

• loss of motor to most of eye movements and parasympathetic supply to pupil
• All muscles paralysed except lateral rectus and superior oblique
• Eye points down and out
• Pupillary fibres run on outside of 3rd nerve
  • Pupillary-sparing lesion is likely to be ischaemic
  • Pupillary-involving is likely to be compressive → More dangerous

Examination

• General
  • Ptosis
• Acuity
  • normal
• Fields
  • normal (limited by ptosis)
• Pupil
  • dilated
  • no reaction if complete lesion
• Movements
  • Abducent nerve intact
    • eye moves laterally
  • Trochlear nerve intact
    • eyes intorts on trying to look down and in
• Fundi
  • normal
  • Papilloedema if space occupying lesion

Causes

• Solitary (i.e. with dilatation of pupil)
  • idiopathic
  • raised ICP → uncal herniation through tentorium
  • aneurysm of ipsilateral posterior communicating artery (PCA)
  • Tumour
• without dilated pupil
  • Diabetes mellitus
  • nerve trunk infarct
  • midbrain lesion
  • vascular
  • demyelination
  • giant cell arteritis
  • syphilis
• Smallprint
  • encephalitis
  • meningiomas
    • parasellar
    • sphenoidal wing
• With IV and VI
  • stroke
  • tumours
  • Wernicke's encephalopathy
  • aneurysms
  • multiple sclerosis
  • myasthenia gravis
  • muscular dystrophy
  • myotonic dystrophy
  • cavernous sinus thrombosis

Investigations

• blood glucose
• CT / MRI
• carotid arteriography