This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of orbit, Lids and lacrimal apparatus, Subject name: Ophthalmology
Meibomian glands secrete which components of tears? 
Select and explain. 
A. Water (aqueous), B. Mucin, C. Protein, D. Lipid
D: Lipid
Answer: D: Lipid 
Explanation: (Refer: AK Khurana Comprehensive Ophthalmology, 6th edition, pg no.366) The major function of lacrimal apparatus is to secrete and drain the tear. Tear film consists of 3 layers:- Mucous or mucin layer (innermost):- Secreted by conjunctival goblet cells, crypts of Henle, glands of Manz, lacrimal glands The meibomian glands of the lid produce a lipid material whose synthesis is dependent on neuronal, hormonal, and vascular factors. This lipid material is fluid, spreads easily, is a surfactant as well as an aqueous barrier and must remain functional after a blink. Lipid layer (outermost):- Secreted by the Meibomian, Zeis, and Moll glands