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mucin glycocalyx, tears could run of the corneal surface like water of a Tefon frying pan. (See "Functions of the Tear Film Mucins," page 13.) At the same time, the mucins act as a disadhesive so the corneal epithelium doesn't stick to the tarsal conjunctiva. Other mucins foat freely in the aque- ous compartment, which functions to clean, protect and transport nutrients and oxygen to the cornea. 4 Much more than water, the aqueous contains large and small chemical entities — including the 491 identifed proteins — as well as environmental debris that will be dis- posed of through tear drainage. 3 Above the aqueous is the lipid layer. Once considered a simple barrier to prevent evaporation, it is at least a two- layer structure, with polar lipids at the aqueous/lipid interface and a thicker layer of nonpolar lipids situated above the polar lipids and facing the air. 5 Te lipid layer aids in lubrication, prevents loss of aqueous, and helps maintain a smooth optical surface. Without the amphiphilic polar phospholipid inter- face, though, nonpolar lipids would spread poorly over the aqueous, creat- ing a less stable lipid layer and leading to more rapid tear flm break-up. 5 IMPACT OF A CONTACT LENS In healthy eyes, tear flm components work in harmony. When the tear flm is compromised, this system can break down, leading to dryness and discom- fort, corneal staining and conjuncti- val redness and vision disturbances. THE HUMAN TEAR FILM IS OPTIMIZED TO ADDRESS A UNIQUE CHALLENGE: CREATE A SMOOTH, OPTICALLY TRANSPARENT, REFRACTIVE INTERFACE BETWEEN THE EYE AND THE AIR. FE ATURE INSPIRED BY THE SCIENCE OF TE ARS 14 S P E C I A L E D I T I O N 2 0 1 5 • O P T O M E T R I C M A N A G E M E N T . C O M