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Tear film structure. Evidence suggests the tear film consists of membrane associated mucins (MAM) such as MUC16 that form the glycocalyx on the apical epithelium, a secretory mucus layer containing soluble MUC5AC mucin secreted by the conjunctival goblet cells, aqueous fluid and electrolytes, and proteins secreted by the lacrimal glands. The surface of the tears is covered with a lipid layer with polar lipids adjacent to the aqueous layer and nonpolar lipids interfacing with the air.
