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
Mucin layer tear flilm deficiency occurs in: 
Select and explain. 
A. Keratoconjunctivitis sicca, B. Lacrimal gland removal, C. Canalicular block, D. Herpetic keratitis
A: Keratoconjunctivitis sicca
Answer: A: Keratoconjunctivitis sicca 
Explanation: A i.e Keratoconjunctivitis sicca