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It is a clear, colorless and gelatinous gel that fills the space between the lens of the eye and the retina that covers the back of the eye.
It is often called vitreous humor or simply “vitreous”. It is produced by certain cells of the retina.
Structure
It is surrounded by a layer of collagen called the vitreous membrane that separates it from the rest of the eye. represents four fifths of the volume of the eyeball. The vitreous humor is similar to a fluid near the center, and similar to the gel near the edges.
The vitreous humor is in contact with the retina. It does not adhere to the retina, except in the optic nerve disc and the ora serrata (where the retina ends anteriorly), in the Wieger band, the dorsal side of the lens. It is not connected to the macula, the area of the retina that provides finer details and central vision.
Anatomical characteristics
The vitreous has many anatomical landmarks, which include the hyaloid membrane, the Berger space, the Erggelet space, the Wieger ligament, the Cloquet channel and the Martegiani space.
Characteristics of the surface:
Patellar fossa: superficial concavity similar to a saucer, on which the lens rests, separated by Berger’s space.
Hialoideocapsulare ligament (Wieger’s ligament): circular thickening of the vitreous 8-9 mm in diameter, delineates the patellar fossa.
Anterior hyaloid: vitreous surface anterior to the ora serrata. Continues and invests in the zonular fibers, and extends forward between the ciliary processes.
Vitreous base: denser cortical area of vitreous. Firmly adhered to the posterior 2 mm of the flat part, and the anterior 2-4 mm of the retina.
Posterior hyaloid surface: Applied closely to the internal limiting membrane of the retina. Sites of firm attachment along the blood vessels and at sites of retinal degeneration.
Space of Martegioni: a funnel-shaped space that covers the optical disk with condensed edge.
Cloquet Channel: A channel 1-2 mm wide inside the vitreous, from the space of Martegioni to the space of Berger, along an S-shaped course, mainly below the horizontal.
Internal structures of the vitreous:
The vitreous body at birth is homogeneous with a finely striated pattern. With early aging, the vitreous humor develops narrow transvitreal “channels”. The bark is denser than the center with development.
From adolescence, the vitreous tracts are formed from anterior to posterior. These vitreous tracts are thin vitreous condensations in the form of a lamina.
Retrolental tract: extends backwards from the hyaloidecapsular ligament to the central vitreous.
Coronary tract: external to the retrolental tract, and is subsequently excluded from a circular area that covers the posterior third of the ciliary processes.
Middle tract: it extends backwards from a circular area external to the coronary tract, in the anterior margin of the vitreous base.
Preretinal tract: extends from the ora serrata and the vitreous base.
Biochemical properties
Its composition is similar to that of the cornea, but the vitreous contains very few cells. It consists mainly of phagocytes, which remove unwanted cell debris in the visual field, and hyalocytes, which change the hyaluronan.
The vitreous humor does not contain blood vessels, and 98-99% of its volume is water (compared to only 75% in the cornea).
In addition to water, the vitreous is composed of salts, sugars, vitrosin (a type of collagen ), a network of type II collagen fibrils with glycosaminoglycan, hyaluronan, opticin and a wide range of proteins.
Despite having little solid matter, the fluid is substantial enough to fill the eye and give it its spherical shape. The lens, on the other hand, is replete with cells.
The vitreous humor has a viscosity two to four times that of water, giving it a gelatinous consistency. It has a refractive index of 1.336. Surprisingly, with so little solid matter, he holds the eye firmly.
The vitreous fluid is not present at the time of birth, but it is found after 4 and 5 years, and then increases in size. Produced by cells in the non-pigmented portion of the ciliary body, the vitreous humor is derived from embryonic mesenchymal cells, which degenerate after birth.
The nature and composition of the vitreous humor changes throughout life. In adolescence, the vitreous cortex becomes denser and vitreous pathways develop; and in adulthood, treaties are better defined and sinuous. A central vitreous liquefaction occurs, fibrillar degeneration and the tracts are broken (syneresis).
Thick filaments develop with aging. The volume of gel decreases with age, and the volume of fluid increases. The cortex may disappear in the sites, which leads to the excretion of the liquid vitreous in the potential space between the vitreous cortex and the retina (vitreous detachment).
Clinical significance
Unlike the fluid in the frontal parts of the eye (aqueous humor) that is continuously replenished, the gel in the vitreous chamber is stagnant. Therefore, if blood, cells or other byproducts of inflammation enter the vitreous, they will remain there unless surgically removed.
These are known as floats. If the vitreous separates from the retina, it is known as vitreous detachment.
As the human body ages, the vitreous often liquefies and may collapse. This is more likely to occur, and occurs much earlier, in nearsighted eyes (myopia). It can also occur after eye injuries or inflammation in the eye ( uveitis ).
Vitreous collagen fibers are kept separated by electrical charges. With aging, these charges tend to be reduced, and the fibers can be grouped. Likewise, the gel can liquefy, a condition known as syneresis, which allows cells and other organic groups to float freely within the vitreous humor.
These allow floats that are perceived in the visual field as stains or fibrous strands.
The floaters are generally harmless, but the sudden appearance of recurrent floats can mean a posterior vitreous detachment or other eye diseases.
Posterior vitreous detachment: Once the liquid vitreous enters the subhialoid space between the vitreous cortex and the retina, it removes the vitreous cortex of the retina with each eye movement.
Postmortem and forensic: After death, the vitreous resists putrification more than other body fluids.
The vitreous potassium concentration increases predictably within hours, days and weeks after death, and vitreous potassium levels are frequently used to estimate the time elapsed since death (post mortem interval) of a corpse.
The metabolic exchange and balance between the systemic circulation and the vitreous is so slow that the vitreous is sometimes the fluid of choice for postmortem analysis of glucose levels or substances that would spread, degrade, excrete or metabolize more rapidly. the general circulation.
