tear film

pre·cor·ne·al film

a protective film, 7-9 nm thick, consisting of external oily, intermediate watery, and deep mucoprotein layers.
Synonym(s): tear film
Farlex Partner Medical Dictionary © Farlex 2012

tear film

A liquid consisting of lipids, water, and mucin that coats the outer surface of the eye, lubricating it.

Patient care

A reduction in the tear film causes a sensation of a dry or gritty eye, such as is seen in Sjögren's syndrome, keratoconjunctivitis, sicca, disorders of the lacrimal gland, and other conditions. Keeping eyelids clean, using artificial tears, and withholding medications that may reduce the tear film can prove helpful for some patients. Other treatments may include the wearing of moisture chambers around the eye, and eye lid surgery. Topical lubricants can be used for symptomatic relief.

Medical Dictionary, © 2009 Farlex and Partners

film, precorneal

The field covering the anterior surface of the cornea which consists of lacrimal fluid and of the secretion of the meibomian and conjunctival glands. Its total thickness was thought to be about 9 μm but recent investigations have questioned that value and point to a much larger figure. It is composed of three layers: (1) The deepest and densest is the mucin layer (or mucous layer) which derives from the conjunctival goblet cells, as well as some secretion from the lacrimal gland. (2) The watery lacrimal fluid is the middle layer, called the lacrimal (or aqueous layer). It is secreted by the lacrimal gland and the accessory glands of Krause and Wolfring. It forms the bulk of the film and contains most of the bactericidal lysosyme and other proteins, inorganic salts, sugars, amino acids, urea, etc. (3) The oily layer (or lipid layer) is the most superficial and is derived principally from the meibomian glands in the lids as well as some secretion from the glands of Zeis. It greatly slows the evaporation of the watery layer and may provide a lubrication effect between lid and cornea (Fig. F6). Note: Some authors have suggested that the precorneal film is made up of only two layers; an innermost aqueous and mucin gel layer and an outer lipid layer. Syn. lacrimal layer; preocular tear film; tear film; tear layer. See hyperlacrimation; mucin; tear secretion; Tearscope; break-up time test.
Fig. F6 Diagram of the three layers of the precorneal film attached to the squamous epithelial cellsenlarge picture
Fig. F6 Diagram of the three layers of the precorneal film attached to the squamous epithelial cells
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
Fed by a tear duct, dyed blue, the eyelid spreads artificial tear secretions over the eye to form what is called a tear film.
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