What condition presents with a light-near dissociation where the pupil constricts with near effort but not to light?

What condition presents with a light-near dissociation where the pupil constricts with near effort but not to light?

• A. Adie's pupil
• B. Argyll Robertson pupil
• C. Marcus Gunn pupil
• D. Horner syndrome

Answer: (B)

Light-near dissociation means the pupil can respond to accommodation (near effort) but not to bright light, showing that the near reflex pathway is intact while the light reflex pathway is disrupted. The classic instance of this is Argyll Robertson pupil, where both pupils are small and irregular, and they constrict when focusing on a near object but fail to constrict in response to light. This pattern arises because the neural circuits controlling the light reflex (pretectal area and edinger–westphal pathway) are affected, while the near reflex pathway, which involves cortical input and convergence, remains functional. Argyll Robertson pupils are traditionally associated with neurosyphilis. Other conditions don’t fit this exact pattern as well. For example, a tonic/adies pupil has a poor light response but a variable, often slow or irregular accommodation response due to ciliary ganglion dysfunction, and Horner syndrome causes miosis with anisocoria more prominent in darkness, with near responses typically preserved. Marcus Gunn pupil describes an afferent pupillary defect rather than a light-near dissociation pattern.

Light-near dissociation means the pupil can respond to accommodation (near effort) but not to bright light, showing that the near reflex pathway is intact while the light reflex pathway is disrupted. The classic instance of this is Argyll Robertson pupil, where both pupils are small and irregular, and they constrict when focusing on a near object but fail to constrict in response to light. This pattern arises because the neural circuits controlling the light reflex (pretectal area and edinger–westphal pathway) are affected, while the near reflex pathway, which involves cortical input and convergence, remains functional. Argyll Robertson pupils are traditionally associated with neurosyphilis.

Other conditions don’t fit this exact pattern as well. For example, a tonic/adies pupil has a poor light response but a variable, often slow or irregular accommodation response due to ciliary ganglion dysfunction, and Horner syndrome causes miosis with anisocoria more prominent in darkness, with near responses typically preserved. Marcus Gunn pupil describes an afferent pupillary defect rather than a light-near dissociation pattern.