Ocular tear film lipid layer (TFLL)

The **ocular tear film lipid layer** is the thin, outermost layer of the tear film, composed of lipids—primarily wax esters, cholesterols, fatty acids, phospholipids, and polar lipids—secreted by the meibomian glands that line the eyelid margin[1][3][5][6]. Its principal biological function is to reduce tear evaporation, maintain a stable air/tear interface, support ocular surface integrity, and provide a smooth refractive surface for vision[1][3][4][5]. Malfunctions or deficiencies in the lipid layer, especially due to Meibomian gland dysfunction, are a major cause of dry eye syndrome, leading to tear instability, chronic discomfort, and visual disturbances[5][6]. The lipid layer is not a discrete molecular target such as a receptor or enzyme but a heterogeneous assembly of many lipid molecules, and is better classified as a tissue-level or physiological barrier rather than a classical therapeutic target[1][3][5]. Therapies for dry eye disease (DED) often aim to supplement, stabilize, or mimic the tear film lipid layer but do not directly target an individual molecular entity. The composition and function of the lipid layer can vary greatly, and full mechanistic understanding is the subject of ongoing research, especially with respect to optimizing therapeutic substitutes for ocular surface disorders[3][6].

Other names

Tear film lipid layerTFLLLipid layer of tear film