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: Ophthalmology
[{'content': 'Which is the least commonly involved nerve in herpes zoster opthalmicus? \nSelect and explain. \nA. Facial nerve, B. Frontal nerve, C. Lacrimal nerve, D. Nasociliary nerve', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Herpes Zoster Ophthalmicus is defined as Herpes Zoster involvement of ophthalmic division of trigeminal nerve. Branches of ophthalmic divison are frontal, lacrimal and nasociliary . Of these frontal nerve is most commonly involved. Hence, the least commonly involved nerve is the facial nerve.', 'role': 'assistant'}]