A 40-year-old man with tabes dorsalis has small, irregular, unequal pupils that do not react to light but constrict briskly on accommodation. The lesion responsible lies in the:
- A Edinger-Westphal nucleus bilaterally
- B Pretectal region of the dorsal midbrain ✓
- C Ciliary ganglion
- D Intermediolateral column of the spinal cord
Correct answer: B. Pretectal region of the dorsal midbrain
Explanation
Argyll Robertson pupils show light-near dissociation with miosis, irregularity and poor dilation in darkness, classically due to neurosyphilis. The lesion sits in the dorsal midbrain near the pretectal nuclei, interrupting the afferent limb of the light reflex while sparing the more ventrally placed fibres mediating the near response. Edinger-Westphal destruction would abolish both reactions, and a ciliary ganglion lesion produces a large tonic pupil, not a small irregular one.
Reference: Khurana's Comprehensive Ophthalmology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.