A 40-year-old man is found to have small, irregular, unequal pupils that react briskly to accommodation but not to light, and they dilate poorly in darkness. The most likely underlying condition is:
- A Diabetes mellitus
- B Neurosyphilis ✓
- C Chronic alcoholism
- D Multiple sclerosis
Correct answer: B. Neurosyphilis
Explanation
The Argyll Robertson pupil shows light-near dissociation with miosis, irregularity, and poor dilatation, classically caused by neurosyphilis affecting fibres in the dorsal midbrain near the aqueduct. The lesion destroys the light reflex arc while sparing the more ventrally placed near-response fibres. Diabetic pupils are typically small but react to light, and Adie tonic pupil is large, unilateral, and reacts slowly to near, which distinguishes it clearly here.
Reference: Parsons' Diseases of the Eye, 22nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.