A lesion in this area would involve efferent pupillary fibres on the dorsal aspect of the Edinger-Westphal nucleus (associated with the response to light) while sparing the fibres associated with the response to near, which lie slightly more ventrally. Research has implicated the rostral midbrain in the vicinity of the cerebral aqueduct of the third ventricle as the most likely region of damage. Studies have failed to demonstrate a focal localising lesion. The pathophysiologic mechanism which produces an Argyll Robertson pupil is unclear, but is believed to be the result of bilateral damage to the pretectal nuclei in the midbrain. Adie's pupil is caused by damage to peripheral pathways to the pupil (parasympathetic neurons in the ciliary ganglion that cause pupillary constriction to bright light and with near vision). The two different types of near response are caused by different underlying disease processes.
There is continued interest in the underlying pathophysiology, but the scarcity of cases makes ongoing research difficult.
ĪR pupils are extremely uncommon in the developed world.
In general, pupils that accommodate but do not react are said to show light-near dissociation (i.e., it is the absence of a miotic reaction to light, both direct and consensual, with the preservation of a miotic reaction to near stimulus (accommodation/convergence). They are a highly specific sign of neurosyphilis however, Argyll Robertson pupils may also be a sign of diabetic neuropathy. Pupillary light reflex and accommodation reflex testsĪrgyll Robertson pupils ( AR pupils) are bilateral small pupils that reduce in size on a near object (i.e., they accommodate), but do not constrict when exposed to bright light (i.e., they do not react).
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