Nepedia
Back to Discover
Advanced Reader
🧬

Vitreous body

life science Maturity 9-11 Next article →

The vitreous body is a clear, gelatinous mass located inside the eye. Its name comes from the Latin word for glass-like. This substance fills the vitreous chamber, which is the space between the lens and the retina. It is a vital part of the vertebrate eye because it helps maintain the eye's spherical shape. The vitreous body makes up about four-fifths of the total volume of the eyeball. While often called the vitreous humor, it is distinct from the aqueous humor found near the cornea.

The structure of the vitreous is not uniform throughout the eye. It is a transparent, colorless gel that is thicker near the edges and more liquid-like near the center. A layer of collagen called the vitreous membrane, or hyaloid membrane, surrounds the mass. This membrane separates the vitreous from the rest of the eye. The gel is anchored to several specific anatomical landmarks. Collagen fibrils attach the vitreous to the optic nerve disc and the ora serrata. It also attaches firmly to the lens capsule, retinal vessels, and the macula. The macula is the specific area of the retina responsible for central vision and fine detail.

There are many complex anatomical features within and around the vitreous. For example, Cloquet's canal is a 1–2 mm wide canal that runs in an S-shape through the vitreous. It connects the space of Martegiani to the space of Berger. Another feature is the Wieger-band, which is a circular thickening of the vitreous about 8–9 mm in diameter. This band helps delineate the patella fossa, a shallow area where the lens rests. Other landmarks include Berger's space and the space of Erggelet. These structures define the precise layout of the posterior segment of the eye.

The composition of the vitreous is mostly water, making up 98% to 99% of its volume. It contains a variety of salts, sugars, and proteins to maintain its properties. For instance, it contains sodium at a mean concentration of 146.7 mmol/L and potassium at 5.73 mmol/L. It also includes glucose, which averages 2.97 mmol/L. The structural integrity comes from a network of collagen type II fibrils and a substance called hyaluronan. Specialized cells called phagocytes remove cellular debris, while hyalocytes manage the turnover of hyaluronan. This chemical makeup gives the vitreous a viscosity two to four times that of water.

As humans grow, the vitreous undergoes significant developmental changes. At birth, the vitreous is a homogenous mass with a finely striated pattern. By adolescence, the vitreous cortex becomes denser and forms thin, sheet-like condensations called vitreous tracts. These include the retrolental tract, the coronary tract, the median tract, and the preretinal tract. As adults age, the center of the gel may undergo syneresis, which is a process of liquefaction. During this time, the gel volume decreases while the liquid volume increases. This can cause collagen fibers to clump together due to reduced electrical charges.

Changes in the vitreous can lead to specific visual experiences or medical conditions. When the gel liquefies, organic clusters can float freely, creating what are known as floaters. These appear as spots or strands in a person's visual field. If the vitreous pulls away from the retina, it is called a vitreous detachment. This is more common in people with myopia, or nearsightedness. In highly myopic eyes, the axial length is increased, which can lead to a vitreous volume exceeding 9–10 mL. This is much larger than the average adult volume of approximately 4 mL.

Beyond biology, the vitreous has important applications in forensic science. After death, the vitreous body resists putrefaction longer than most other body fluids. The concentration of potassium in the vitreous rises at a very predictable rate after death. Scientists use this steady increase to estimate the post-mortem interval, or the time since death. Because the exchange of substances between the blood and the vitreous is very slow, it is an excellent medium for analysis. Experts may test the vitreous for glucose levels or other substances that might degrade quickly in the general circulation.

688 words

Where will your curiosity go next?

Keep exploring at your chosen reading level.

More to explore

🔬 Go deeper

More advanced topics to explore

🪜 Step back

Simpler topics to build understanding

What is Nepedia?

A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.