Tear film (corneal surface)

The **tear film** is a thin, multi-layered fluid coating that overlays the corneal and conjunctival epithelia, forming a critical interface between the eye's external environment and its epithelial surfaces. It is essential for protecting the ocular surface from desiccation, mechanical damage, pathogens, and debris while also providing lubrication necessary for comfortable blinking. The tear film consists of several distinct layers: - An innermost glycocalyx formed by membrane-associated mucins (notably MUC1, MUC4, MUC16) tethered to epithelial cells. - A mucous layer primarily composed of secreted gel-forming mucin MUC5AC from conjunctival goblet cells. - An aqueous layer containing water-soluble proteins and electrolytes. - An outermost lipid layer that reduces evaporation. These layers work together to maintain optical clarity as the first refractive surface encountered by light entering the eye. Disruption in any component can lead to dry eye disease subtypes—aqueous-deficient dry eye (ADDE), decreased wettability dry eye (DWDE), or increased evaporation dry eye (IEDE)—each requiring targeted therapy based on which component is deficient. While drugs such as diquafosol sodium and rebamipide are used therapeutically to enhance specific aspects of tear production or stability, **the "tear film" itself is not a molecular target but rather a physiological structure** composed of multiple molecules with protective functions.[1][3][4] Because "corneal surface protection/lubrication via film formation" refers broadly to this physiological process—not a discrete molecule/receptor—it should not be considered a canonical therapeutic target like an enzyme or receptor. Instead, it describes an outcome achieved through modulation or supplementation of various molecular components within the tear film system.[1][3][5]

Other names

Pre-corneal tear filmOcular surface tear filmTear layer

Enhancement or supplementation of tear film components (e.g., stimulating secretion or mimicking mucins/lipids/aqueous layers)[4]