What is the probable diagnosis in a patient with a dilated pupil not responsive to 1% pilocarpine?
A. Diabetic 3rd nerve palsy
B. Adie’s tonic pupil
C. Uncal herniation
D. Pharmacological block
Correct answer : D. Pharmacological block
All except D affect the 3rd nerve. But when pilocarpine is instilled, it acts directly on the muscarinic receptor (M3) found on the iris sphincter muscle, causing the muscle to contract and engage in miosis. If miosis does not occur with pilocarpine, it indicates that the muscarinic receptor on the the iris sphincter muscle is blocked – hence pharmacologic blockade is the answer.
Ref: Handbook of Neurosurgery By Mark S. Greenberg (via google books)