Central retinal vein occlusion (CRVO)

Central retinal vein occlusion, or CRVO for short, is a condition in the back of the eye where the central retinal vein is blocked. Since the central retinal vein is the only blood vessel draining the retina, blood is 'dammed up' and fluid leaks out of the vein into the surrounding tissue. This can damage the retina and lead to loss of vision. Sudden and painless loss of vision is typical, but there are cases where the condition develops slowly over days or weeks.

It is also possible that the retina suffers a decrease in blood supply at the same time. This is called "ischemic" (from the Greek 'bloodless') CRVO. In these cases, the retina becomes so "starved" for oxygen that new blood vessels grow in various locations in the eye to improve the insufficient blood supply. Unfortunately these new vessels are in dangerous locations and are fragile and not properly formed leading to a variety of problems including a very dangerous type of blinding glaucoma. Ischemic CRVO is therefore considered the more severe form of the disease.

The ultimate cause of CRVO is not well understood but ends up as a blockage in venous outflow from the eye. In the place where the central retinal artery enters the eye and the vein leaves it, the vessels run within the optic nerve that leads the vision signals into the brain. These three structures have to pass through a small exit leaving the eye. It is thought that this tight place, where there is no room for swelling, may predispose for clot formation.

Various causes may contribute to the risk of these clots in the vein: Increased pressure in the eye called glaucoma, a hardened, sclerotic central retinal artery squeezing the soft and pliable vein, swelling of the optic nerve through inflammation, changes in the vessel wall, or blood clotting disorders.

CRVO may occur at any age, but the huge majority of cases are seen in people over 50. Men seem to be affected slightly more often than women. More than 66,000 people in European countries and more than 100,000 people in the United States are estimated to suffer from CRVO.

There is no known way of prevention of CRVO except treating the conditions predisposing to blood clots, such as diabetes, high blood pressure, and clotting disorders. Increasing age – another important risk factor – is, unfortunately, untreatable.

In cases of sudden or gradual loss of vision, the retina must be examined via ophthalmoscopy. By shining a light into the eye the doctor looks through the pupil at the small vessels in the back of the eye. If the patients suffers from CRVO, the doctor will see dilated and winding veins bulging from blood backup, bleeding into the retina, or swelling from fluid leaks.

One treatment option is a laser treatment called panretinal photocoagulation or PRP. This treatment destroys the outward parts of the retina and is reserved for very severe cases of ischemic CRVO. While it is reasonably good at preventing the dreaded complication of neovascular glaucoma, it does nothing to help the patient’s vision. In the last few years, another treatment option has emerged: Injection of modern medications called Anti-VEGF therapies blocks the growth factor that stimulates the growth of new abnormal blood vessels. VEGF, the vascular endothelial growth factor, contributes to the leaking of fluid out of the vessels, and anti-VEGF counteracts this effect. One anti-VEGF drug has been approved by the US drug authority FDA for treatment of CRVO. Anti-VEGF therapy works without destroying parts of the retina and can actually reverse some vision loss in a majority of the affected patients.

Bayer is currently investigating a new drug of the Anti-VEGF type which must be injected directly into the eye. The drug has already been successfully tested in another type of retinal disease. A Phase III clinical trial has shown encouraging results.

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