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
Neurotrophic keratitis involves which nerve: September 2008 
Select and explain. 
A. Trochlear, B. Trigeminal, C. Abducens, D. Facial
B: Trigeminal
Answer: B: Trigeminal 
Explanation: Ans. B: Trigeminal Neurotrophic keratopathy occurs in cases in which trigeminal nerve is paralyzed, typically as a result of radical treatment for trigeminal neuralgia. It does not occur in all cases of peripheral lesions of the trigeminal nerve; thus, if the gasserian ganaglion is removed or the trigeminal nerve with alcohol for trigeminal neuralgia with proper precautions, only a few cases develop neurotrophic keratitis. Neuroparalytic keratopathy is seen in facial nerve palsy as occurs in Bell's palsy, leprosy or neurological disorders leading to ectropion, lagophthalmos and exposure keratopathy.