Pupils for PACES

Quick recap of some basic anatomy and physiology:
  • the size of the pupil is dependent on both sympathetic and parasympathetic nerve activity
  • sympathetic activity is unaffected by external stimuli but is less in the very young and very old, so small pupils may be 'normal' at the extremes of age
  • parasympathetic activity is via the 3rd cranial nerve (occulomotor).  This is the efferent limb of the light reflex; the afferent limb is via the 2nd cranial nerve (optic)

"Examine the pupils"
  • Observe: are they the same size and shape?
  • Shine a light into each eye twice, checking for firstly a direct light reflex (ie pupil the light is shone into constricts) and then a consensual light reflex (ie contralateral pupil constricts when light is shone into other pupil)
  • Check for any afferent pupillary defect by performing the swinging light test
  • Check accommodation by asking patient to focus on your finger at a distance, and then close up (pupils should constrict as eyes converge)

Possible abnormal findings:

Small pupils (miosis):
  • reacting: 
  • non-reacting:
    • use of pilocarpine eye drops (eg for glaucoma treatment)
    • drugs such as opiates, antipsychotics, cholinergics, organophosphate poisoning
    • pontine haemorrhage
  • irregular:
    • Argyll Robinson pupil - small, irregular, accommodates but does not react to light
    • iritis - small, irregular, neither accommodates nor reacts

Large pupils (mydriasis):
  • unilateral
    • Holmes Adie pupil
    • Iridectomy
    • Surgical 3rd nerve palsy
    • mydriatics
      • atropine
      • tropicamide
  • bilateral
    • drugs - TCA, amphetamines, mydriatics
    • can be normal in anxious state

Abnormal swinging light test:
  • damage to optic nerve before the chiasm
  • asymmetrical glaucoma
  • optic neuritis
  • trauma
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