The liquid that covers the eye during the normal course of a day isn't just a simple layer of basal tears, however. The human eye's "tear film" is actually comprised of three different layers, each of which is produced by a unique gland in the eye area. The mucous layer sits directly on the surface of the eyeball and is made up of a gel-like proteins called mucins, which are secreted by little glands on the inside of the eyelids. Because it is hydrophillic (water-attracting) it helps promote even dispersal of the tear liquid across the eye.

The aqueous layer sits on top of the mucous layer , in the middle of the tear film, and is comprised of the basal tears discussed earlier. On the outer-most surface of the tear film is the lipid layer, which is made up of oils secreted by glands on the rim of the eyelids. The hydro-phobic secretions of the lipid layer, called meibum, coat the aqueous layer and keeps it from evaporating or spilling out before it reaches the drainage channels in the inner corner of the eye.