The Tear Film Structure

Traditionally, the tear film has been viewed as having three distinct layers:

• an outermost lipid (oily) layer
• an aqueous layer that makes up 90% of the tear film volume; and
• a mucin layer that coats the corneal surface.

However, it is now recognized that rather than being three distinct layers, the tear film is actually a lipid layer and phases of aqueous with differing concentrations of mucins throughout.

In addition, mucins in the tear film play a much more active role in maintaining tear film stability than was once thought.