Arteries carry blood from the heart to other parts of the body, and veins carry the blood back to the heart. A blockage in an artery or vein is called an occlusion or stroke. 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 theeye. 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 get 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.

Why do people lose vision from retinal vein occlusions?

1. 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.
2. Neovascularization. RVO 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 eye.
3. Neovascular glaucoma. New blood vessels in certain parts of the eye can cause pain and a dangerous increase in pressure inside the eye.
4. Blindness. The complications of RVO, especially if they are not treated, can lead to irreversible loss of vision

How do you diagnose retinal vein occlusions?

1. Optical coherence tomography (OCT). This is a high definition image of the retina taken by a scanning ophthalmoscope with a resolution of 5 microns. These images can determine the presence of swelling and edema by measuring the thickness of your retina. The doctor will use OCT images to objectively document the progress of the disease throughout the course of your treatment.
2. Ophthalmoscopy. The changes caused by RVO may be seen by examination of the retina with an instrument called an ophthalmoscope.
3. Fluorescein angiography. This is a test procedure in which a dye that is injected into a vein in the arm travels to the retinal blood vessels. Special photographs allow the physician to see the vessels.

How is retinal vein occlusion treated?

Unfortunately, there is no way actually to unblock retinal veins. However, the doctor can treat any health problems that seem to be related to the retinal vein occlusion.

Vision may come back in some eyes that have had a retinal vein occlusion. About one-third have some improvement, about one-third stay the same and about one-third gradually improve, but it can take a year or more to learn the final outcome. In some cases, the blocked vessels will lead to fluid accumulation in the retina like sponges absorbing water. In others, the ischemia causes the formation of new blood vessels.

Some of the treatments for retinal vein occlusion include:

1. Intravitreal injection of anti-vascular endothelial growth factor (VEGF) drugs. These drugs target VEGF, which is an important growth factor that causes macular edema.
2. Intravitreal injection of corticosteroid drugs. These drugs combat the inflammatory components which lead to edema.
3. Focal laser therapy. This treatment provides lasers to areas of swelling to cause a reduction in edema.
4. Pan-retinal photocoagulation therapy. This treatment is used when patients have new blood vessel formation following the retinal vein occlusion.

What is my follow up care?

Return visits with us are recommended to monitor your disease progress. It is important to detect changes in your condition and formulate treatment plans as needed. It is also important to inform your primary care doctor of your retinal vein occlusion, so he or she can evaluate and treat any underlying systemic illnesses.

References:

1. American Academy of Ophthalmology. Branch Retinal Vein Occlusion (BRVO) Treatment Accessed 4/7/2015.
2. Fletcher EC, Chong N, Augsburger JJ, Corrêa ZM. Chapter 10. Retina. In: Riordan-Eva P, Cunningham ET, Jr. eds. Vaughan & Asbury's General Ophthalmology, 18e. New York, NY: McGraw-Hill; 2011. library.ccf.org Accessed 4/7/2015.
3. National Eye Institute. Standard Care vs. Corticosteroid for Retinal Vein Occlusion (SCORE) Study Results Accessed 4/7/2015.