Vitreous humour

The vitreous humour (British spelling) or vitreous humor (U.S. spelling) is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous body or simply "the vitreous".

Composition, properties and function

The vitreous is the transparent, colorless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye. It is produced by certain retinal cells. It contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs, which reprocess the hyaluronic acid), no blood vessels, and 99% of its volume is water with salts, sugars, vitrosin, and a network of collagen type II fibers with the mucopolysaccharide hyaluronic acid accounting for the rest. The water content of the vitreous (98%) is greater than that of the lens (75%). However, the vitreous has a viscosity two to four times that of pure water, giving it a gelatinous consistency. It also has a refractive index of 1.336 [ [http://retina.anatomy.upenn.edu/~lance/eye/humor_vitreous.html The Vitreous Humor ] ] .

Although the vitreous is in contact with the retina and helps to keep it in place by pressing it against the choroid, it does not adhere to the retina, except in three places: around the anterior border of the retina; in the macula, the tiny spot in the retina which gives us our "detail" and central vision; and at the optic nerve disc (where the retina sends about 1.2 million nerve fibers (axons) to the brain).

Unlike the fluid in the frontal parts of the eye (aqueous humor) which is continuously replenished, the gel in the vitreous chamber is stagnant. Therefore, if blood, cells or other byproducts of inflammation get into the vitreous, they will remain there unless removed surgically (see floaters). If the vitreous pulls away from the retina, it is known as a vitreous detachment. As we age, the vitreous often liquefies and may collapse. This is more likely to occur, and occurs much earlier, in eyes that are nearsighted (myopia). It can also occur after injuries to the eye or inflammation in the eye (uveitis).

Pathology

The collagen fibers of the vitreous are held apart by electrical charges. With aging, these charges tend to reduce, and the fibers may clump together. Similarly, the gel may liquefy, a condition known as syneresis, allowing cells and other organic clusters to float freely within the vitreous humor. These allow floaters which are perceived in the visual field as spots or fibrous strands. Floaters are generally harmless, but the sudden onset of recurring floaters may signify a posterior vitreous detachment (PVD) or other diseases of the eye.

Clinical significance

The metabolic exchange and equilibration between systemic circulation and vitreous humor is so slow that vitreous humour is sometimes the fluid of choice for postmortem analysis of glucose levels or substances which would be more rapidly diffused, degraded, excreted, or metabolized from the general circulation.

External links

* [http://thebrain.mcgill.ca/flash/i/i_02/i_02_cr/i_02_cr_vis/i_02_cr_vis.html The Eye - explanations and diagrams from a McGill University web site]

References


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Look at other dictionaries:

  • vitreous humour — ► NOUN ▪ the transparent jelly like tissue filling the eyeball behind the lens …   English terms dictionary

  • vitreous humour — noun the clear colorless transparent jelly that fills the posterior chamber of the eyeball • Syn: ↑vitreous humor, ↑vitreous body • Hypernyms: ↑liquid body substance, ↑bodily fluid, ↑body fluid, ↑humor, ↑humour …   Useful english dictionary

  • vitreous humour — vitreous body the transparent jelly like material that fills the chamber behind the lens of the eye …   The new mediacal dictionary

  • vitreous humour — noun The clear gel that fills the eyeball between the lens and the retina …   Wiktionary

  • vitreous humour — the transparent jelly like material that fills the chamber behind the lens of the eye …   Medical dictionary

  • vitreous humour — noun the transparent jelly like tissue filling the eyeball behind the lens …   English new terms dictionary

  • vitreous humour — UK / US noun [uncountable] medical the liquid that fills the large space inside your eye between its lens and its retina …   English dictionary

  • vitreous humour — /vɪtriəs ˈhjumə/ (say vitreeuhs hyoohmuh) noun the transparent gelatinous substance filling the eyeball behind the crystalline lens …   Australian English dictionary

  • Тело Стекловидное (Vitreous Humour, Vitreous Body) — прозрачная желеобразная масса, заполняющая пространство позади хрусталика глаза. Состоит на 98% из воды со следами гликопротеинов, а также рыхлой сети коллагеновых волокон; желеобразная консистенция связана с высоким содержанием гиалуроновой… …   Медицинские термины

  • vitreous body — vitreous humour …   The new mediacal dictionary

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