Fig. 3.

The tear film protects the ocular surface from desiccation as well as infection from microbes. Meibomian glands secrete the top, lipid portion of the tear film which mostly prevents against evaporation. The lacrimal glands secrete the middle aqueous layer which also lubricates the ocular surface and contains many antimicrobial factors such as immunoglobulins, lactoferrin, lysozymes, lipocalin, complement, secretory phospholipase A2 and beta-lysin. Goblet cells produce the bottom mucosal layer which contains mucin, immunoglobulins, and leukocytes as a last line defense against pathogens