Posterior vitreous separation is a common disorder occurring in about 80% of people in the United States. It frequently causes symptoms of floaters and flashing lights, but infrequently causes a loss of vision. It should not be confused with a retinal detachment and is therefore called a posterior vitreous separation.
What is the Vitreous?
The vitreous is a watery gel that fills the eye from the lens back to the retina. It is 99% fluid but contains tiny fibers that are attached to the retina and optic nerve. These fibers can usually only be seen with a microscope. The normal vitreous is totally clear and allows the light from the front of the eye to reach the retina undisturbed.
As the vitreous gel ages, it shrinks and pulls away or separates from the retina. It can also separate from the retina due to changes in the eye from diabetes, blocked blood vessels, inflammation or due to a sudden blow to the eye.
Flashes and Floaters
When the vitreous separates from the retina, it can pull or tug lightly on the surface of the retina. The retina responds to this pulling by sending the sensation of a flash of light to the brain. These flashes of light are usually the most noticeable symptom of a posterior vitreous separation and may last only a moment or may last intermittently for several months. Each time a flash of light occurs it is an indication that the retina has been tugged upon. In a small number of people, the vitreous can pull hard enough on the surface of the retina that a retinal tear forms.
Another common symptom of posterior vitreous separation is the sensation of floaters within a person’s vision. These floaters can consist of cobwebs, rings, dots, streaks or a combination of any of these. Floaters are usually caused by the clumping of the fibers that are normally present within the vitreous or due to the presence of normal cells on the back surface of the gel, called glial cells. Sometimes when the separation occurs a blood vessel may be torn and bleeding can occur into the vitreous gel. If a retinal tear develops, then pigmented cells from beneath the retina may enter the vitreous gel. These strands and cells block the passage of light to the retina resulting in small shadows and the sensation of black floaters.
Since both normal and abnormal conditions of the eye can cause the symptoms of flashes and floaters, it is necessary that a complete examination is performed at the initial onset of the flashers and floaters. Subsequent examinations should also be performed if the flashers or floaters should change or become worse.
Vision Loss and Vitreous Separation
As mentioned earlier, posterior vitreous separations are common but vision loss due to the posterior vitreous separation is infrequent. The most common cause of decreased vision is the persistence of the floaters. With time most floaters will become less noticeable, however, they rarely disappear entirely. Most people are able to adapt to the presence of floaters in their vision. A vitreous separation may also cause bleeding to occur into the vitreous gel. Usually this only causes a sensation of floaters but occasionally the bleeding is severe enough to cause a marked decrease in vision. The blood is slowly absorbed by the eye and eventually the vision clears. However, in a small number of people, the blood fails to clear and an operation called a vitrectomy is needed. In this operation, surgical instruments are inserted into the eye and the blood is removed.
The final cause of decreased vision following a posterior vitreous separation is the development of a retinal detachment. A posterior vitreous separation can cause the formation of retinal tears. These tears allow fluid to enter beneath the retina resulting in a retinal detachment. Your eye exam will include a detailed examination of the area of the retina where most tears develop. If a retinal tear is discovered it can usually be sealed with either the laser or the use of a freezing probe, preventing the formation of a retinal detachment. If a retinal detachment forms, a surgical procedure is needed to prevent vision loss.