Central retinal vein occlusion (CRVO)
Central retinal vein occlusion (CRVO) is a disorder characterized by blockage of venous blood flow from the retina. The retina is the nerve tissue in the back of the eye. Like the film in a camera, the retina is sensitive to light. It transforms light energy to nerve stimuli, and “sends a picture” through the optic nerve to the brain.
The retina consists of several layers and requires oxygenated blood for nourishment. The retina receives oxygenated blood through the central retinal artery, which enters through the optic nerve and branches out to supply blood to the entire retina. The deoxygenated blood leaves the eye through a network of veins that join at a central retinal vein and exit through the optic nerve. A central retinal vein occlusion is a blockage of this vein.
The occlusion (blockage) is caused by the formation of a thrombus (clot) in the central retinal vein. It is more common in patients with elevated intraocular pressure or glaucoma. Symptoms of central retinal vein occlusion in most patients are experienced as either a sudden or ongoing decrease in vision of the affected eye.
A CRVO causes decreased vision because the blockage of blood flow leaving the eye interferes with the overall circulation of the eye. This results in hemorrhages within the retina and swelling of the optic nerve and macula (the central part of the retina used for central vision).
During a retinal examination, there are several clinical signs a physician may observe that support the diagnosis of CRVO. These include bleeding, swelling, and the engorgement (or “flooding”) of veins.
Fluorescein angiography may be performed to confirm the diagnosis and to evaluate the extent of the effects of the blockage on the retina. Fluorescein angiography is a test in which a water-soluble dye is injected into a vein in the arm. The dye quickly passes through the circulation to the eye, and serial photographs are taken to examine retinal circulation.
The possibility for vision to improve depends on several factors, including:
- The severity of the blockage
- The amount of permanent damage to the retina
- The age of the patient—younger patients generally have more return of vision
- The body’s own ability to heal itself—this involves the natural formation of collateral vessels. Collateral vessels carry blood around the blockage
There are currently several treatments for CRVO. A surgical procedure called radial optic neuropathy (RON) involves a vitrectomy to remove the vitreous in the eye, during which an incision is made in the optic nerve next to the occluded central vein. Early results show that vision circulation can be improved with increased vision as a result.
For patients with persistent macular edema, injection of kenalog, a steroid solution, can eliminate the edema and improve vision. This injection can be repeated if the edema returns. Patients are monitored closely, and if iris neovascularization develops, laser treatment will be recommended to avoid a condition called neovascular glaucoma.
In most cases, it is impossible to determine what caused the blot clot to form, although CRVO has an increased incidence in certain systemic conditions, such as diabetes mellitus and hypertension. Sometimes, an evaluation may be recommended by your doctor for conditions that can lead to an excessive tendency for blood to clot.