OUTER LIPID LAYER:

This is secreted by the meibomian glands.
(1) Functions:
To retard evaporation of the aqueous layer of the tear film.
To lower surface tension of the tear film. This, in turn, draws water into the tear film and thickens the aqueous layers.
To lubricate the eyelids as they pass over the surface of the globe.
(2) Dysfunction of this layer may result in an evaporative dry eye.