Retinal Vein Occlusion

What is Retinal Vein Occlusion?

At the front of the eye sits a lens that focuses images onto the inside of the back of the eye. This area is the retina — the surface on which the eye focuses the images we see. It is lined with special nerve cells that convert light into signals, which travel along the optic nerve to the brain, where they are recognised as images. Conditions affecting the retina therefore affect the ability to see.

Arteries carry blood from the heart to the rest of the body, and veins carry it back to the heart. A blockage in an artery or vein is called an occlusion, or a stroke. When blood flow from the retina is blocked, it is often because a clot has blocked a retinal vein. This condition is called retinal vein occlusion.

Nerve cells need a constant supply of blood to provide oxygen and nutrients, and blood vessels deliver this supply. In a stroke, a small blood clot blocks the flow of blood through one of the arteries of the brain, and the area deprived of blood is damaged.

The same type of damage can occur anywhere in the body. When a retinal vein is blocked, it can no longer drain blood from the retina. This leads to haemorrhages and to fluid leaking from the blocked blood vessels.

There are two types of retinal vein occlusion:

• Central retinal vein occlusion (CRVO) is a blockage of the main retinal vein.
• Branch retinal vein occlusion (BRVO) is a blockage of one of the smaller branch veins

Before retinal vein occlusion treatment:

After retinal vein occlusion treatment

How does retinal vein occlusion (RVO) cause vision loss?

• Macular oedema: The macula is the small, central area of the retina that provides the sharp, detailed vision needed for activities such as reading.
• Neovascularisation: Retinal vein occlusion can cause the retina to develop new, abnormal blood vessels — a condition called neovascularisation. These new vessels can leak blood or fluid into the vitreous, and small spots or clouds, called floaters, may appear in the field of vision. With severe neovascularisation, the retina can detach from the back of the eye.
• Neovascular glaucoma: New blood vessels in some parts of the eye can cause pain and a dangerous rise in the pressure inside the eye.
• Blindness: The complications of retinal vein occlusion, especially if left untreated, can lead to irreversible loss of vision.

Why do people get retinal vein occlusion?

A retinal vein occlusion occurs when a blood clot blocks the vein. Sometimes this happens because the veins of the eye are too narrow. It is more likely to occur in people with diabetes, and possibly in those with high blood pressure, high cholesterol or other health problems that affect blood flow.

How does the doctor know if 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, almost always in one eye only. At first the blurring or loss of vision may be slight, but it worsens over the following hours or days. Occasionally, vision is lost almost completely and almost immediately.

If these symptoms occur, it is important to arrange an appointment with your doctor as soon as possible, because retinal vein occlusion often causes permanent damage to the retina and loss of vision.

How is a blockage of the retinal veins diagnosed?

• Optical Coherence Tomography (OCT): This produces a high-resolution image of the retina, captured by a scanning device with a resolution of 5 microns. The images can confirm the presence of oedema by measuring the thickness of your retina, and your doctor will use them to objectively document the course of the disease throughout your treatment.
• Ophthalmoscopy: The changes caused by retinal vein occlusion can be seen by examining the retina with an instrument called an ophthalmoscope.
• Fluorescein angiography: In this test, a dye injected into a vein in the arm travels to the blood vessels of the retina. Special photographs allow the doctor to see the vessels.

How is retinal vein occlusion treated?

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

Vision may return in some eyes that have had a retinal vein occlusion. About one third show some improvement, about one third remain the same, and about one third get worse gradually — but it may take a year or more to learn the final outcome. In some cases, the blocked vessels lead to a build-up of fluid in the retina. In others, they can trigger the formation of new blood vessels.

Some of the treatments for retinal vein occlusion include:

• Intravitreal injection of anti-vascular endothelial growth factor (VEGF) drugs: These drugs target VEGF, an important growth factor that causes macular oedema.
• Intravitreal injection of corticosteroid drugs: These drugs combat the inflammatory processes that lead to oedema.
• Focal laser treatment: This treatment applies laser to areas of oedema in order to reduce it.
• Pan-retinal photocoagulation treatment: This treatment is used when patients develop new blood vessels after a retinal vein occlusion.

What is the follow-up care?

Return visits are recommended so that the course of your condition can be monitored, any changes detected, and your treatment plan adjusted as needed. It is also important to tell your primary care doctor about your retinal vein occlusion, so that any underlying systemic diseases can be assessed and treated.