Physiological tear film

The **physiological tear film** is a thin fluid layer that coats the ocular surface, primarily the cornea and conjunctiva. It consists of three main layers: - **Lipid layer**: Outermost layer produced by meibomian glands; reduces evaporation. - **Aqueous layer**: Middle layer secreted by lacrimal glands; contains water, electrolytes (Na+, K+, Cl-, Ca2+, Mg2+), proteins (albumin, lysozyme, lactoferrin), growth factors, immunoglobulins (mainly secretory IgA), vitamins, antimicrobials, hormones.[1][2] - **Mucin layer**: Innermost layer produced mainly by conjunctival goblet cells; provides wettability and stability to the ocular surface.[2] The tear film serves several essential functions including lubrication of the eyelids over the globe during blinking,[1] protection against pathogens through antimicrobial proteins like lysozyme and lactoferrin,[2] supply of nutrients such as glucose and electrolytes to avascular corneal tissue,[1] removal of metabolic waste products,[1] scavenging free radicals via antioxidants like vitamin C,[1] immune defense via immunoglobulins such as sIgA,[2] promotion of wound healing through growth factors like epidermal growth factor,[1] and maintenance of optical clarity. Disruption in any component can lead to dry eye disease or other ocular surface pathologies. The physiological tear film itself is *not* considered a therapeutic target in the sense used for receptors or enzymes—it is an anatomical/functional structure rather than a discrete molecular entity suitable for targeted pharmacologic intervention.[3] Therefore, — The entry "Physiological tear film" does *not* correspond to a canonical drug target molecule/receptor. — It should be flagged as incorrect if included in lists intended only for molecular targets.

Other names

Tear filmPrecorneal tear film