tranenfilm

The tear film, sometimes referred to as the tranenfilm in Dutch sources, is a thin, multi-layered fluid that covers the corneal and conjunctival surfaces of the eye. It lubricates the eye, creates a smooth optical surface, nourishes the avascular cornea, removes debris, and provides a first line of defense against microbes and irritants.

Traditionally the tear film is described as a three-layer system: an outer lipid layer produced mainly by the meibomian glands that reduces evaporation; a middle aqueous layer produced by the lacrimal glands and other accessory glands; and an inner mucin-containing layer produced by conjunctival goblet cells and corneal epithelial cells that helps the tear film adhere to the ocular surface. The tear film contains water, electrolytes, proteins such as lysozyme and lactoferrin, immunoglobulin A, lipids, and mucins.

Blinking distributes the tear film across the eye and promotes debris removal. Tear turnover is continuous, with drainage through the puncta into the nasolacrimal duct, balancing secretion and drainage to maintain surface moisture.

Disorders of the tear film are common and can cause discomfort, visual fluctuation, and ocular surface damage. Dry eye disease is a broad category encompassing reduced tear production (aqueous deficiency) and increased tear evaporation (often due to meibomian gland dysfunction and evaporative dry eye). Other conditions include blepharitis and contact lens intolerance.

Diagnosis relies on tests such as tear break-up time (TBUT), Schirmer tests, tear osmolarity, and ocular surface staining. Treatment aims to stabilize the tear film and relieve symptoms, using artificial tears, lipid-containing lubricants, anti-inflammatory medications (for example, cyclosporine or lifitegrast), punctal plugs, lid hygiene, warm compresses, and, in selected cases, surgical interventions.