The vitreous or vitreous humor is a clear fluid which fills the eye between the lens and the retina. This fluid helps the eye hold its shape, with light being transmitted through it to the retina. As people age, they sometimes develop problems in this area of the eye which lead to floaters and dark spots in the vision. These issues can be addressed with a procedure known as a vitrectomy, in which part of the vitreous humor is removed.
99 percent of the vitreous humor is water. The remainder is a mixture of collagen, proteins, salts, and sugars. Although it is mostly made of water, it has a firm, jellylike consistency, and this helps the eye hold its shape. The contents remain fairly static over time, and has no vascularization, so once something gets into this part of the eye, it will not drift out on its own.
If objects do get into the vitreous, they can be removed in a vitrectomy. In this procedure, surgical tools are inserted into the eye and used to carefully pull out impurities in the vitreous humor which are leading to vision problems. Not all spots and floaters are caused by objects in this part of the eye, but when they are, a vitrectomy can bring about a radical improvement in vision quality very quickly.
One problem with the vitreous humor which can develop is vitreous detachment, in which it pulls away from the retina. This tends to be more common with age, and can also be accompanied with shrinking of the vitreous, which can lead to vision problems. Most commonly, when this occurs, people experience floaters in their vision which can be irritating or distracting, potentially making it hard to see or focus. An ophthalmologist can examine the eye to diagnose detachment and to explore other potential causes for vision problems.
The composition of the vitreous humor remains fairly stable throughout life, and after death, researchers once thought that it broke down in a very orderly fashion. For a time, it was fashionable in forensics to take a sample of this fluid after death for the purpose of estimating time of death. However, research showed that the composition of vitreous humor actually did not break down regularly and predictable, and that samples from the same person could vary radically; one eye might say that the decedent had passed away at 3:00 in the afternoon, while the other suggested 9:00 at night. When time of death was known, it often failed to match the estimates provided by testing the vitreous, so this practice was abandoned.