Most of us experience tears as a wet, salty substance that helps to keep the eyes moist. Rather than being a homogenous solution, tears are actually more complex, consisting of multiple layers, each serving a specific purpose.
The tear film consists of three distinct layers:
Oily layer: The oily layer is produced by the meibomian glands and makes up the outermost layer of the tear film. It helps to make the tear surface smooth and keeps them from drying too fast.
Watery layer: The watery layer is in the middle of the tear film and is produced by the lacrimal glands, located in the eye lids. This layer functions to clean the eye, washing away foreign particles.
Mucus layer: The mucus layer is the innermost layer of the tear film and is made in the conjunctiva —the clear tissue covering the white part of the eye and inside of the eyelids. This layer functions to help spread the watery layer over the surface of the eye and keep the eyes moist. Without the mucus layer, tears would not stick to the surface of the eye.