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
Which is the least commonly involved nerve in herpes zoster opthalmicus? 
Select and explain. 
A. Facial nerve, B. Frontal nerve, C. Lacrimal nerve, D. Nasociliary nerve
A: Facial nerve
Answer: A: Facial nerve 
Explanation: 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.