What is the Vitreous? | Review of the Vitreous
The vitreous body is that part of the human eye that fills the space in the center of the eye. It is the largest structure within the eye, yet our knowledge of its molecular composition, supramolecular organization, and physiology are perhaps least of any of the other parts of the eye.
When we are young, the vitreous is primarily a watery gel. As we get older, and in nearsighted eyes, the gel becomes more liquid. Recent research has suggested many similarities with the joints in our body (vitreous fluid is similar to synovial fluid), opening the door to increasing our understanding of this unique gel by learning more about the joints in our body.
What are Different Parts Vitreous?
In the human eye, the anterior (in the front just behind the lens) vitreous seems to support the lens and assist in its function focusing vision at near when we read. The fluid contains anti-oxidants that may help protect the lens from oxygen and mitigate against cataracts.
The back, or posterior, vitreous is adjacent to the retina and is attached to the retina at specific points. The retina is the light receiving tissue that lines the inside of the eye.
The vitreous and retina are most adherent at the “vitreous base.” The base is located in the most forward portion of the retina, that is, the area just behind the iris. In most cases the retina and vitreous do not separate even after a posterior vitreous detachment (PVD). It is here that retinal tears can occur, at times, resulting in retinal detachment and blindness.
Function of the Vitreous
The primary purpose of the vitreous body is to keep the center of the eye clear so that light can get to the retina and vision can begin. The gel and its fluid allow oxygen and nutrients to flow from the front of the eye to the back of the eye. In youth, the vitreous body is a shock absorber during eye movement, head movement, and physical exertions of the body. It is also rich in anti-oxidants that protect the various parts of the eye.
These days, the vitreous can also function as a reservoir for drugs, which we inject into the eye to treat various diseases of the macula and retina. For example, we often inject anti-VEGF and various steroids for treatment of macular degeneration or diabetic retinopathy among others.
What Diseases are Associated With the vitreous?
Vitreous plays a role in several diseases that afflict different parts of the human eye. If it were not for the vitreous causing retinal tears, retinal detachments would likely not occur. Most retinal detachments start with a retinal tear. Retinal tears are a direct result of the vitreous pulling forcefully enough to tear this light sensitive tissue.
In the advanced stages of diabetic retinopathy, blood can fill the vitreous causing profound loss of sight as light is physically blocked from reaching and stimulating the retina.
A more common complication of diabetic retinopathy, called macular edema, also implicates the vitreous. In a patient with diabetic retinopathy, the normal retinal vessels tend to leak with time. This leakage can accumulate in the macula causing mild to severe vision loss. The overlying vitreous worsens this type of leakage.
Macular holes and macular pucker are caused by vitreous and these conditions are cured by surgically removing the vitreous body (vitrectomy).
Recent studies have indicated that vitreous plays a role in wet macular degeneration in age-related macular degeneration (AMD).
Floaters, or vitreous opacities, often occur due to degeneration of the vitreous and are common after a posterior vitreous detachment (PVD) occurs.