Which Light Near Dissociation is caused by a tectotegmental tract lesion and is most commonly associated with neurosyphilis?

• A. Argyll Robertson Pupil
• B. Adie's Pupil
• C. Hutchinson's Pupil
• D. Tonic Pupil

Answer: (A)

Light-near dissociation means the pupil constricts with accommodation but not in bright light. This pattern points to disruption of the light reflex pathway in the dorsal midbrain, while the near reflex pathway remains intact. Argyll Robertson pupil is the classic example: small, often irregular pupils that accommodate but do not react to light, and it is strongly associated with neurosyphilis. The syphilitic involvement typically damages the tectotegmental/pretectal circuits in the dorsal midbrain, so the light response is lost but the near response persists, producing the characteristic scattered, constricted pupils with preserved accommodation.

Other pupil findings describe different processes. Adie's tonic pupil involves parasympathetic damage to the ciliary ganglion with a poor light response, but it’s not the neurosyphilis-associated pattern of light-near dissociation. Hutchinson’s term and related “tonic” pupil concepts refer to other etiologies and don’t capture the specific neurosyphilitic dorsal midbrain pattern.