Vitreous humor

The vitreous body is a transparent, colorless, gel-like substance that fills the cavity of the eyeball. In front of the vitreous body are: the lens, zonular ligament and ciliary processes, and behind and on the sides is the retina. The vitreous body is the most voluminous structure of the eye, which makes up 55% of the internal contents of the eye. In an adult, the vitreous body normally weighs 4 grams, the volume is 3.5-4 ml.

The vitreous body is spherical in shape, somewhat flattened in the sagittal direction. Its posterior surface is directly adjacent to the retina, to which the vitreous body is fixed only at the optic disc and in the dentate line area at the flat part of the ciliary body. This belt-shaped area, 2-2.4 mm wide, is called the base of the vitreous body.

The vitreous body has the following structures: the vitreous body itself, the border membrane, and the vitreous (Clocket's) canal, which is a tube 1-2 mm in diameter that runs from the optic disc to the back of the lens, without reaching the posterior cortex of the lens. In the embryonic period of a person, the vitreous artery passes through the Cloquet's canal, which disappears by the time of birth.

Thanks to the use of modern methods of intravital examination of the vitreous body, it was possible to establish that it has a fibrillar structure and that the interfibrillar spaces are filled with a liquid, viscous, amorphous substance. The fact that the exposed vitreous body does not spread and can retain its shape even when a load is placed on it indicates that it has its own outer membrane. A number of authors consider it to be a thin, transparent, independent membrane. However, a more popular point of view is that this is a denser layer of the vitreous body, formed as a result of thickening of the outer layers of the vitreous body and condensation of fibrils.

In terms of chemical structure, the vitreous body is a hydrophilic gel of organic nature, 98.8% of which is water and 1.12% is dry residue, which contains proteins, amino acids, glucose, urea, creatinine, potassium, magnesium, sodium, phosphates, chlorides, sulfates, cholesterol and other substances. Proteins, which make up 3.6% of the dry residue, are represented by vitrochin and mucin and provide the viscosity of the vitreous body, which is several dozen times greater than the viscosity of water.

Normally, the vitreous body does not have fibrinolytic activity. But it has been experimentally proven that in cases of hemorrhage into the vitreous body, its thromboplastic activity increases significantly, which is aimed at stopping the bleeding. Due to the presence of antifibrinolytic properties in the vitreous body, fibrin does not dissolve for a long time, and this contributes to cellular proliferation and the formation of connective tissue opacities.

The vitreous body has the properties of colloidal solutions and can be considered as a structural but poorly differentiated connective tissue. Vessels and nerves are absent in the vitreous substance. The vital activity and constancy of the vitreous body environment is ensured by osmosis and diffusion of organic substances from the intraocular fluid through the vitreous film, which has directional permeability.

Microscopically, the vitreous body consists of ribbons of various shapes, soft gray in color, interspersed with point and club-shaped formations of a whitish color. When the eye moves, these structural formations "sway". Between the ribbons and inclusions are colorless, transparent areas. Over time, floating opacities and vacuoles may appear in the vitreous body. The vitreous body cannot regenerate and, if partially lost, begins to be replaced by intraocular fluid.

The presence of a constant fluid flow in the vitreous body is confirmed by the results of radiographic studies: the movement of indifferent dyes or radionuclide isotopes introduced extraocularly in the vitreous masses has been established. The fluid produced by the ciliary body enters the base of the vitreous body, from where it moves along the outflow pathways forward - into the anterior chamber and backward - into the perivascular spaces of the optic nerve. In the first case, the fluid mixes with the chamber moisture and is removed together with it, in the second case, from the posterior sections of the vitreous body bordering the optical part of the retina, the fluid flows out along the perivascular spaces of the retinal vessels. Knowledge of the features of the circulation of intraocular fluid allows us to imagine the nature of the distribution of medicinal substances in the eye cavity.

The vitreous body has low bactericidal activity. Leukocytes are found in it some time after infection. According to some authors, the antigenic properties of the vitreous body do not differ from those of blood proteins.

The main functions of the vitreous body:

• maintaining the shape and tone of the eyeball;
• conducting light beams;
• participation in intraocular metabolism;
• ensuring contact between the retina and the choroid