Arteries and veins carry blood throughout your body, including your eyes. The retina has one main artery and one main vein. When the main retinal vein becomes blocked, it is called central retinal vein occlusion (CRVO). When any branches of the main retinal vein become blocked, it is called branch retinal vein occlusion (BRVO).

Patient with CRVO. Color fundus photo (A) shows venous dilatation and tortuosity, disc and retinal hemorrhages, and cotton wool spots. Fluorescein angiogram (B) shows marked delay in arteriovenous transit time and blocking by retinal hemorrhages.

When the central or a branch retinal vein is blocked, blood and fluid spill out into the retina causing macular edema (swelling of the macula). Fluid can also collect under the retina in more severe cases. Such will result in decreased central vision. Eventually, without blood circulation, nerve cells in the retina can die which results in vision loss.

OCT scan showing macular edema and subretinal fluid in a patient with CRVO.

What Are Symptoms of BRVO or CRVO?

The most common symptom of BRVO or CRVO is vision loss or blurry vision in part or all of the involved eye. It can happen suddenly or become worse over several hours or days. Sometimes, you can lose all vision suddenly.

You may notice floaters which may appear as dark spots, lines, or squiggles in your vision. These are shadows from tiny clumps of blood leaking into the vitreous from retinal vessels.

Oftentimes, CRVO is more symptomatic than BRVO. In some more severe cases of CRVO, you may feel pain and pressure in the affected eye.

What Causes BRVO or CRVO?

BRVO or CRVO happens when a blood clot blocks the flow of blood through a retinal branch venule or the main retinal vein, respectively. Disease can make the walls of your arteries more narrow and stiffen them, which in turn compress the vein and leads to the occlusion.

What are the Risk Factors for BRVO or CRVO?

BRVO or CRVO usually happens in people who are aged 50 and older. People who have the following health problems have a greater risk of BRVO or CRVO:

  • High blood pressure
  • Diabetes
  • Glaucoma
  • Arteriosclerosis (hardening of the arteries)

To lower your risk, you should:

  • Eat a low-fat diet
  • Get regular exercise
  • Maintain an ideal weight
  • Refrain from smoking

How Is BRVO or CRVO Diagnosed?

Ancillary testing including a scan of the retina called OCT will be performed to look for macular edema (swelling), which causes vision to decrease. Another diagnostic procedure called fluorescein angiography provides images of retinal perfusion and the degree of retinal ischemia (inadequate blood supply) that may be present. It also demonstrates degree of fluid leakage from damaged or abnormal retinal vessels and if any subsequent complications have developed, such as macular edema and retinal neovascularization (abnormal growth of new blood vessels). Such complications can lead to significant vision loss.

People under the age of 40 with BRVO or CRVO may be tested to look for a problem with their blood clotting or thickening.

A) Color fundus photo and B) fluorescein angiogram of a patient with superotemporal ischemic BRVO.

How Is BRVO or CRVO Treated?

Treatment for retinal vein occlusion begins with identifying the underlying risk factors and addressing them. To assess such risk factors, monitoring blood pressure, evaluating and treating elevated blood cholesterol levels, and when appropriate, blood tests to determine if there is an abnormal tendency to form blood clots are recommended.

Treatment in RVO’s is aimed at treating the complications that can develop, rather than trying to relieve the blockage itself. The main treatment addresses macular edema or swelling of the macula. It is often treated with intraocular injections of anti-VEGF drugs designed to decrease leakage and stop the growth of abnormal new blood vessels in the eye. The use of these drugs may require frequent retreatment, but injection schedules are determined on a case-by-case basis. At times, laser treatment may be used along with anti-VEGF therapy in hard-to-treat cases. Intraocular injections of steroids are another potential treatment to help treat macular edema after retinal vein occlusions. Intraocular steroids can have some side effects such as an increase in eye pressure and cataract progression, however, in most cases, these side effects can be controlled.

In cases of retinal vein occlusion with severe ischemia, new abnormal blood vessels may grow. In the front of the eye, these new abnormal vessels can block the outflow of normal eye fluids, causing the eye pressure to increase and lead to glaucoma.

In the back of the eye, new blood vessels may cause bleeding and scarring. Treatment with anti-VEGF injections leads to prompt, but often temporary, control of the new abnormal vessels. Laser treatment tends to offer a more permanent effect. In many cases, both treatments are used.

It usually takes a few months after monthly treatments are started before you notice your vision improving. While most people see some improvement in their vision, some people won’t have any improvement. The severity of the BRVO or CRVO will determine whether your vision will improve with treatment.

Source: American Academy of Ophthalmology