Argyll Robertson pupil

Pathophysiology: The light reflex pathway (retina → optic nerve → pretectal nucleus → bilateral Edinger-Westphal nuclei → oculomotor nerve → pupillary constriction) is disrupted at the level of the pretectal nucleus in the dorsal midbrain, classically due to neurosyphilis (tabes dorsalis). The near reflex pathway, which involves cortical input to the Edinger-Westphal nucleus via a different route (not requiring the pretectal relay), remains intact, explaining why accommodation is preserved while the light reflex is lost. Pupils are typically small (miotic) and irregular, and they may show mild dilation lag; they are bilateral and rarely symmetric, and do not dilate well with mydriatics. Clinical significance: Highly associated with tertiary syphilis, especially neurosyphilis (tabes dorsalis or general paresis). Also historically associated with diabetic neuropathy (rare) and other midbrain lesions. Mnemonic: "Argyll Robertson pupil accommodates but does not react" (also remembered as a "prostitute's pupil"—accommodates but does not react!). Diagnostic workup: Confirm with syphilis serology (VDRL/RPR, FTA-ABS, or specific treponemal tests) and consider CSF analysis if neurosyphilis suspected. Differentiate from other pupillary syndromes: - Adie tonic pupil: unilateral, dilated pupil with sluggish reaction to light and slow accommodation, due to ciliary ganglion damage (often idiopathic or post-viral). - Horner syndrome: miosis with ptosis and anhidrosis due to sympathetic chain lesion. - Marcus Gunn pupil (relative afferent pupillary defect): affects the afferent pathway of the light reflex, seen in optic nerve lesions. Management: Treat underlying syphilis with penicillin G; the pupillary abnormality itself is a permanent sign of prior CNS damage and does not typically reverse with treatment.