Tear film and ocular surface microenvironment (LFU)

The tear film and ocular surface microenvironment is a complex, integrated physiological system comprising the cornea, conjunctiva, lacrimal glands, meibomian glands, and the interconnecting sensory and motor nerves, collectively known as the lacrimal functional unit (LFU) (Willcox et al., 2017; PubMed: 28736335). Its primary biological role is to maintain a stable, smooth refractive surface for vision, provide lubrication to prevent mechanical damage during blinking, and serve as a protective barrier against microbial pathogens and environmental stressors (Craig et al., 2017; PubMed: 28736334). Homeostasis within this microenvironment is maintained by a delicate balance of tear production, evaporation, and drainage. When this balance is disrupted, it leads to conditions such as dry eye disease (DED), characterized by tear film instability, hyperosmolarity, and chronic inflammation of the ocular surface (Bron et al., 2017; PubMed: 28736336). Pharmacological treatments targeting this environment include immunomodulators like cyclosporine and lifitegrast, which reduce inflammation to restore natural tear production, and secretagogues like varenicline that stimulate the trigeminal parasympathetic pathway to increase tear volume (Jones et al., 2017; PubMed: 28736338). Additionally, newer agents like perfluorohexyloctane target the lipid layer to prevent excessive evaporation, highlighting the multifaceted approach required to manage this microenvironment.

Other names

Ocular surface ecosystemLacrimal functional unitPrecorneal tear filmTear film

Immunomodulation via calcineurin inhibition; antagonism of the LFA-1/ICAM-1 interaction to inhibit T-cell mediated inflammation; activation of nicotinic acetylcholine receptors to stimulate the trigeminal parasympathetic pathway; and physical stabilization of the tear film layers to reduce evaporation and friction.