- 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
