Argyll Robertson pupils

Argyll Robertson pupils demonstrate light-near dissociation: the pupillary light reflex is impaired or absent, while the near reflex (accommodation-convergence) remains intact. The pupils are typically small (miotic) and may be irregular in shape, often bilateral. The classic mnemonic is 'Prostitute's pupil'—it accommodates but does not react.

Pathophysiology: The lesion is thought to occur in the pretectal area of the midbrain, specifically affecting the fibers that mediate the light reflex (which synapse in the pretectal nucleus) while sparing the near reflex pathway (which has a different, more ventral route through the midbrain). The exact mechanism in syphilis involves damage to this midbrain region, possibly from chronic inflammation and gliosis associated with tertiary neurosyphilis.

Clinical significance: Argyll Robertson pupils are most classically associated with tertiary syphilis (neurosyphilis), particularly in the context of tabes dorsalis. They can also be seen rarely in diabetic autonomic neuropathy, though less classically described. This finding should prompt screening for syphilis with treponemal tests (FTA-ABS) and consideration of CSF analysis if neurosyphilis is suspected, along with VDRL/RPR testing.

Differential diagnosis includes: Adie's tonic pupil (which is typically unilateral, larger, and shows slow, tonic reaction to light with better response to accommodation, often associated with absent deep tendon reflexes in Adie syndrome), and other causes of light-near dissociation such as dorsal midbrain (Parinaud) syndrome from pineal tumors.

High-yield test association: On USMLE, this is frequently tested in the context of tertiary syphilis along with other manifestations like tabes dorsalis (sensory ataxia, loss of proprioception/vibration sense, Charcot joints), general paresis, and gummas.