This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
All of the following are differential diagnosis for constricted pupils except 
Select and explain. 
A. Horner's syndrome, B. Pontine myelinosis, C. Opioid withdrawl, D. Organophosphaste poisoning
C: Opioid withdrawl
Answer: C: Opioid withdrawl 
Explanation: Opioid poisoning: Pin point pupils.
Opioid withdrawl: dilated pupils.