The vitreous humor is a gel-like liquid located between the back of the lens and the front of the retina in the human eye. The fluid is stagnant, or immobile, and is mostly made of water, salt, sugar and small amounts of collagen.
Because proper sight demands that light pass through the lens to the retina, the substance of the vitreous humor is necessarily clear. In addition to being immobile, the vitreous humor does not interact with active blood cells, and it is neither regenerated nor replenished. In this sense, the vitreous humor differs from the aqueous humor, which is located in front of the lens.
The vitreous humor is the site of a number of complications that impair vision, either temporarily or permanently. For example, when foreign materials such as stray cells get caught in the vitreous humor, they become suspended and must be removed surgically. Aging can also cause the vitreous humor to thin, a condition that may lead to detachment of the vitreous humor from the retina. The most serious condition involving the vitreous humor is likely the detachment of the retina from the back of the eye, a complication that often requires surgery and may even lead to blindness in the affected eye.