Vitreous

The vitreous fills about 80% of the eye's volume. It is a transparent substance composed of collagen, hyaluronic acid and water. The body of the vitreous is made up of two main parts: a) the central part – the nucleus; b) the cortex – the outer part.

The most anterior part of the vitreous is the anterior hyaloid membrane. This is an area of dense proteins that takes on the shape of the posterior part of the lens that enters it. The recess formed as a result of the lens is called the patellar fossa.

There is a region of the vitreous called the vitreous base, in which the collagen fibers are especially dense. This region extends 2 mm anteriorly and 3 mm posteriorly to the ora serrata. These are fibers that are very hard to detach during surgery. There are especially dense collagen fibers that run mainly in the cortical part of the vitreous, and between the fibers there are hyaluronate molecules that bind to water and fill the remaining space. The vitreous is most tightly attached at the vitreous base, but also in the following areas:

a. Retinal blood vessels

b. The optic nerve

c. The macula – in this area the attachment occurs at three different surrounding zones, with the fovea forming the center of all of them,
which greatly affects the morphology of macular disorders that arise from traction.

The liquefaction process of the vitreous begins as early as age 2 in the area in front of the posterior pole and produces a cavity called the premacular bursa. There are apparently additional bursae within the vitreous that are connected to one another. Over time, more and more pockets/bursae of liquefaction appear. A combination of enzymatic processes, cross-linking of collagen fibers, oxidative damage, and a decrease in the density of collagen fibers leads to instability of the vitreous, which begins to contract and create traction on the retina. Focal traction can lead to tears or holes in the retina, or more diffusely cause traction and elevation of the retina, as in vitreomacular traction syndrome. Patients with vitreomacular traction syndrome will complain of blurred vision and distortion of the central axis. Focal traction in the area of the fovea can lead to foveal cavitation or a macular hole. When the vitreous cavity detaches from extensive areas of the posterior pole, this is a posterior vitreous detachment.

Posterior vitreous detachment happens to everyone in the end. Broadly, it follows the age rule: at age 60, 60% of people will already have it; at age 70, 70% will already have it, and so on…