Retinal Vein Occlusions
What is a retinal vein occlusion?
The retina is where the eye focuses the images we see. When the flow of blood from the retina is blocked, it is often because a blot clot
is blocking the retinal vein. This usually happens because of a person's underlying health problems (high blood pressure, high cholesterol
levels, diabetes, other health problems).
The eye is often compared to a camera. The front of the eye contains a lens that focuses images on the inside of the back of the eye. This
area, called the retina is covered with special nerve cells which convert light into signals that are sent via the optic nerve to the
brain, where they are recognized as images. Conditions that affect the retina affect the ability to see.
When a retinal vein is blocked, it cannot drain blood from the retina. This leads to hemorrhages (bleeding) and leakage of fluid from the blocked
blood vessels. There are two types of retinal vein occlusion: Central retinal vein occlusion (CRVO) is the blockage of the main retinal vein.
Branch retinal vein occlusion (BRVO) is the blockage of one of the smaller branch veins.
Nerve cells need a constant supply of blood to deliver oxygen and nutrients and blood vessels provide this supply. Most people understand what
happens in a "stroke”: a small blood clot blocks the flow of blood through one of the arteries in the brain, and the area that is not getting
blood becomes damaged. This same type of damage can happen anywhere in the body, not just the brain.
Why do people lose vision from retinal vein occlusions?
- Macular Edema: The macula is the small, central area of the retina that allows sharp, detailed vision, such as that necessary for reading.
Blood and fluid leaking into the macula cause swelling, a condition called macular edema, which causes blurring and/or loss of vision.
- Neovascularization: Retinal vein occlusions can cause the retina to develop new, abnormal blood vessels, a condition called neovascularization.
These new vessels may leak blood or fluid into the vitreous, the jelly-like substance that fills the inside of the eye. Small spots or
clouds, called floaters, may appear in the field of vision. With severe neovascularization, the retina may detach from the back of the
- Neovascular glaucoma: New blood vessels in certain parts of the eye can cause pain and a dangerous increase in pressure inside the eye.
- Blindness: The complications of retinal vein occlusions, especially if they are not treated, can lead to irreversible loss of vision.
Why do people get a retinal vein occlusion?
Retinal vein occlusion happens when a blood clot blocks the vein. Sometimes it happens because the veins of the eye are too narrow. It is more
likely to occur in people with diabetes and possibly high blood pressure, high cholesterol levels, or other health problems that
affect blood flow.
How does the doctor know whether someone has a retinal vein occlusion?
The symptoms of retinal vein occlusion range from subtle to very obvious. There is painless blurring or loss of vision. It almost always happens
in just one eye. At first, the blurring or loss of vision might be slight, but it gets worse over the next few hours or days. Sometimes there
is a complete loss of vision almost immediately.
If these symptoms occur, it is important to schedule an appointment with your doctor as soon as possible. Retinal vein occlusion often causes permanent
damage to the retina and loss of vision. It can also lead to other eye problems.