After passing through the cornea, aqueous humor and lens (anterior segment of the eye), light finally enters the vitreous (also called vitreous humor). is a transparent, jelly-like substance that fills the vitreous body. The vitreous body is the space created by the lens, retina and optic disc. This is also referred to as the posterior segment of the eye.
The main functions of the vitreous are to transmit light to the retina, and to exert enough pressure to keep the retinal layers tightly pressed together. This pressure helps maintain the round shape of the eye so the lens can focus sharp images on the retina.
The vitreous is very different from the aqueous humor. This clear gel is made up of small fibers and water and is permanently formed at birth. Although substances can diffuse slowly through the vitreous, there is very little fluid flow.
The vitreous does not undergo a regular formation and drainage process like the aqueous humor. Instead, it stays permanently in the vitreous body of the eye.
Because the vitreous does not undergo continuous replacement, its contribution to the total fluid pressure of the eye remains relatively constant. As a result, changes in the internal pressure of the eye are due almost entirely to changes in the rate of formation or drainage of aqueous humor.