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: 
• unilateral: Horner's syndrome
• bilateral: normal at extremes of age
• 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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