Preocular tear film (PTF)

The preocular tear film is a complex, multi-layered fluid structure that covers the ocular surface, including the cornea and conjunctiva (StatPearls, 2023; NIH, 2018). Traditionally described as having three distinct layers—an outer lipid layer, a middle aqueous layer, and an inner mucin layer—modern models view it as a mucoaqueous gel covered by a thin lipid film (TFOS DEWS II, 2017). Its primary biological functions include providing a smooth refractive surface for clear vision, lubricating the eye to prevent friction during blinking, and protecting the ocular surface from pathogens and environmental damage (IntechOpen, 2020). Dysfunction or instability of the tear film leads to dry eye disease (DED), characterized by hyperosmolarity, inflammation, and ocular surface damage (Mayo Clinic, 2023). Therapeutic strategies target the tear film through various mechanisms, such as supplementing specific layers (e.g., lipid-based drops), stimulating natural production (e.g., secretagogues or neurostimulators), or reducing the underlying inflammation that disrupts tear film homeostasis (Frontiers in Medicine, 2022).

Other names

Lacrimal filmTear filmPrecorneal tear filmOcular surface fluid

Mechanisms include lubrication and hydration of the ocular surface, reduction of tear evaporation through lipid layer stabilization, inhibition of T-cell mediated inflammation, stimulation of aqueous and mucin secretion via P2Y2 receptor or nicotinic acetylcholine receptor agonism, and osmotic stabilization.