Vitreous body

At a glance

English

Vitreous body

Latin (TA2)

Corpus vitreum

System

Eye

Region

Head

Side

Paired, left and right

About the vitreous body

The vitreous body occupies the vitreous chamber, the space behind the lens and its zonular fibres, and makes up some eighty per cent of the globe's volume. It is transparent and colourless and rests against the inner surface of the retina all round, from the optic disc to the region of the ciliary body. In front it has a shallow depression, the hyaloid fossa, in which the back of the lens sits, separated from it by a narrow potential space. It should not be confused with the aqueous humour, the thin watery fluid in front of the lens.

Although it is about ninety-eight to ninety-nine per cent water, the vitreous keeps the form of a gel because a fine scaffold of type II collagen fibrils is held apart by hyaluronan and other large molecules. Its outer zone, the vitreous cortex or hyaloid membrane, is denser than the centre. It is anchored most firmly at the vitreous base, a band straddling the ora serrata covering the pars plana's hind part plus the forward edge of the retina, and less firmly at the optic disc, along retinal vessels, at the macula and to the back of the lens. A narrow hyaloid canal (Cloquet's canal) runs through it from the disc to the lens, marking the path of the hyaloid artery that supplied the lens before birth. Only a few cells, chiefly hyalocytes, live in it, and it has no blood vessels.

The gel lets light pass undisturbed to the retina, its refractive index being close to that of water. It also helps maintain the shape of the globe, cushions it, and holds the retina against the pigment epithelium.

With age the centre of the gel gradually liquefies and the collagen clumps, which people notice as floaters drifting across their vision. Eventually the cortex may separate from the retina, a posterior vitreous detachment, which happens earlier in short-sighted eyes and after injury or inflammation. Usually harmless, it can pull on the retina and tear it, so a sudden shower of floaters or flashes of light needs urgent examination. Bleeding into the vitreous, often from diabetic vessels, clouds vision. The gel can be removed and replaced by fluid or gas in a vitrectomy.

Function and supply

Function

Transmits light to the retina, maintains the shape and internal pressure of the globe and supports the retina against the back wall of the eye.

Blood supply

Avascular in the adult; the fetal hyaloid artery that crossed it regresses before birth, leaving the hyaloid canal.