Dry Eye Syndrome

What is the tear film?

A film of tears, spread over the eye by a blink, makes the surface of the eye smooth and optically clear. Without our tear film, good vision would not be possible.

The tear film consists of three layers: an oily layer, a watery layer, and a mucin layer. Small glands at the edge of the eyelid, called meibomian glands, produce the outer, oily layer of the tear film. The main purpose of this oily layer is to smooth the tear surface and reduce evaporation of tears. The middle, watery layer is the largest of the three layers, and it makes up most of what we ordinarily think of as tears. This watery layer is produced by small glands scattered through the conjunctiva, the delicate membrane lining the inside of eyelid and covering the eyeball, and by the major tear gland, the large lacrimal gland. The innermost layer consists of mucus produced by goblet cells in the conjunctiva. This layer allows the watery layer to spread evenly over the surface of the eye and helps the eye to remain wet. Without mucus, tears would not adhere to the eye.