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Cranial Nerves

Inspection of the Pupils

February 15th, 2021


  • Look For

  • The size of the pupils (dilated, normal, constricted) and equality of size bilaterally.
  • Normal Pupillary Size

  • In the dark: 4-8mm
  • Under bright light: 2-4mm


Miosis refers to pupillary constriction that is out of keeping with the level of light.
If not bilateral, miosis will present as anisocoria.
  • Causes of Bilateral Miosis

  • Drugs - opiates, antipsychotics, acetylcholine, clonidine
  • Intracranial haemorrhage
  • Bilateral Horner's syndrome - autonomic dysfunction, amyloidosis, diabetes


  • Look For

  • Mydriasis refers to pupillary enlargement that is out of keeping with the level of light.
If not bilateral, mydriasis will present as anisocoria.
  • Causes of Bilateral Mydriasis

  • Cerebral lesion - cerebral herniation, encephalitis, visual cortex infarct, tumour, trauma, multiple sclerosis
  • Drugs - anticholinergics, SSRIs, SNaRIs, stimulants, barbiturates, methanol
  • Brain stem death


  • Look For

  • Unequal pupils.
Ask about whether the patient has had unequal pupils in the past, or if they have an old ID photo to compare to.
  • Causes of Anisocoria

  • Physiological (20% of the population)
  • Migraine
  • Post-ictal
  • Horner's syndrome (unilateral)
  • Drugs applied to one eye - pilocarpine, tropicamide, cocaine
  • Intraocular conditions - glaucoma, retinal detachment
  • Oculomotor (III) nerve lesion - nerve trauma, nerve compression, optic neuritis, Guillain barré
  • Adie's tonic pupil
  • CNS lesion - head trauma, intracranial tumour, subarachnoid haemorrhage, ischaemic stroke, multiple sclerosis
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