Vitreous body

The vitreous body (Latin: corpus vitreum) is the largest structure of the eyeball located posterior to the lens. The vitreous body does not contain blood vessels, and nerve ends. It consists of gel-like liquid - the vitreous humor - surrounded by a capsule. Even though the vitreous body contains vitreous humor, the vitreous body can also be referred to as the vitreous humor. The vitreous body protects the lens and gives the eyeball its specific shape.

Structure of the vitreous body

The vitreous body has a dense cortex but a liquid center. The center of the vitreous body is looser. The vitreous body attaches to the surrounding structures. In the pars plana region of the ciliary body and the nearby ora serrata is an attachment called the vitreous base. This is the strongest attachment place. Within the margin of the optic disc, the vitreous body attaches to the neural retina. The lens' attachment to the vitreous body happens along the periphery of the hyaloid fossa.

In front of the vitreous body is the hyaloid fossa (the anterior concavity), where the lens sits. The hyaloid canal, a remnant of the hyaloid arteria from the embryonic period, passes through the vitreous body. During the fetal period, the hyaloid artery supplies the lens. The hyaloid canal is narrow, usually curved, and approximately 1-2 mm wide. The canal starts from the optic disc and ends at the posterior pole of the lens. 

The vitreous body experiences changes during aging. At adolescence, it starts to have physical changes. The volume of the gel decreases while the liquid volume increases. The liquid increase starts in the center of the vitreous body and continues to progress with age. The changes could be caused by the alteration in the hyaluronic acid-collagen interaction.

The vitreous humor

The vitreous body or the vitreous humor has no colour, and it is almost filled with water. The vitreous humor appears only at the age of 4-5 years and increases in volume over decades until occupying half of the vitreous body around the seventh decade. The vitreous humor contains hyaluronic acids, amino acids, proteins, salts, ascorbic acid, and a network of fine collagen fibrils. Most of the collagen is type II. The cortex has more collagen than the periphery. Mononuclear phagocyte-type-like cells called hyalocytes are seen in the cortex.

Function of the vitreous body

The vitreous body contributes to the refraction of light, even though its dioptric index is much smaller than the cornea index and lens index. The vitreous body also supports the lens and helps to hold together the neural and the pigmented part of the retina.  It is thought that the vitreous body assists in retinal metabolism.