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

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.

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
References in periodicals archive ?
In patients with DES and Sjogren's, the absence of adequate tear production disrupts the normal function of the tear film in protecting the surface of the eye, resulting in increased friction that damages the integrity of the corneal and conjunctival surface.
These bacteria can block glands in the eyelids that produce an oil that keeps our tear film from evaporating, Dr Sheppard explains.
No7 is promoting its Medmont topographer, a tear film surface quality video module.
The most widely used diagnostic tests for tear film examination are tear break-up time (TBUT) test, corneal and conjunctival staining with fluorescein, rose bengal and lissamine green dye, Schirmer test, tear film osmolarity test and impression cytology.
This mechanism utilizes the electrostatic attraction to stabilize the tear film and protect against moisture loss and provide long-lasti ng comfort.
According to the company, Mega-3 is formulated with flaxseed and castor oil, two natural, plant-based oils that protect tears from evaporating while nourishing the lipid layer damaged by dry eye and providing hydration to all three layers of the tear film.
People with dry eyes generally don't produce enough tears, their tears evaporate too quickly, or, most critically, they have a low quality of tear film.
Intraocular pressure, Schirmer's test, tear film break-up time and central corneal thickness were evaluated in all subjects.
In pugs, a key suspect is dry eye, when the tear film is insufficient either due to a lack of tear production or as a result of the eye shape.
The International Dry Eye Workshop (2007) defined dry eye as a “multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface.
Dry eye is produced due to tear film abnormality, stemming from aqueous deficiencies, or evaporation of tear film, (1) although it may also arise from lid closure abnormality or environmental condition.
When blinking slows, the tear film evaporates, drying out the eyeball and damaging the cornea (the outer layer), which becomes red and sore.