The retina is a thin sheet of nerve tissue in the back of the eye where light rays are focused and transmitted to the brain via the optic nerve. Tiny blood vessels supply the retina with oxygen and other nutrients. Arteries deliver the blood, and veins carry it out. Sometimes one of these arteries hardens or swells and presses on a nearby vein. The vein can then become blocked, or occluded, making it difficult for blood to leave the eye. This is called a retinal vein occlusion. The restricted circulation leads to high pressure in the eye, which can in turn cause swelling, bleeding, growth of abnormal blood vessels, and partial or total vision loss.
Retinal vein occlusions are the second most common cause of blood vessel-related vision loss (the first is diabetic retinopathy). The condition occurs most often in men and women over the age of 50, particularly those in their 60s and 70s. Risk factors include atherosclerosis (hardening of the arteries), high blood pressure, high cholesterol, diabetes, smoking, glaucoma, and, rarely, blood clotting and inflammatory conditions.
Treatment and prognosis depend on the severity of the blockage and the location of the occluded vein. If the largest vein leaving the eye is affected, the condition is known as a central retinal vein occlusion, or CRVO; otherwise, it is called a branch retinal vein occlusion, or BRVO. Retinal vein occlusions do not cause a change in physical appearance, and BRVOs often occur with no pain or noticeable loss of vision. For these reasons, it is important to have routine eye exams and also to check one’s own vision by closing one eye at a time.
Retinal vein occlusions are detected during a retinal exam. A fluorescein angiogram may be performed to confirm the diagnosis and/or aid in treatment planning. Indications that an occlusion is present include hemorrhage (bleeding in the eye), macular edema (swelling of the macula, the part of the retina responsible for central vision), macular ischemia (irreversible closing-off of capillaries and consequent loss of blood supply) and neovascularization (compensatory growth of new blood vessels that can cause further damage such as bleeding, glaucoma and retinal detachment). These conditions occur with varying severity depending on the extent of the blockage. The initial bleeding often obscures other symptoms for three to six months or longer. The patient is monitored during this time until the hemorrhage clears.
There is no cure for retinal vein occlusions, so emphasis is placed on risk management, treatment of symptoms and prevention of further vision loss. It is critical to control high blood pressure, high cholesterol, diabetes and other health conditions that increase the risk of vascular hardening, narrowing and blood clotting.
Branch Retinal Vein Occlusions (BRVO)
Vision obscured by macular edema may be treated with lasers or, less commonly, steroids. Surgical removal may be necessary for any scar tissue that forms on the retina. Neovascularization typically appears six months to a year after the occlusion; because it can cause bleeding, retinal detachment and reduced vision in its advanced stages, laser photocoagulation treatment is recommended to slow or stop vessel growth. If bleeding continues, then a vitrectomy may be performed to remove the blood, abnormal vessels and some of the vitreous gel. Vitrectomy can also relieve tension from a retinal detachment. Patients with advanced cases may undergo a vitrectomy followed by an arteriovenous sheathotomy, a new procedure in which the blocked vein is surgically separated from the artery compressing it.
Central Retinal Vein Occlusions (CRVO)
Only laser treatment has proven effective for prevention of complications caused by CRVO. These include neovascularization and neovascular glaucoma, severe and painful high pressure in the eye that can cause substantial vision loss and blindness. Vision lost to CRVO or neovascular glaucoma cannot be recovered. Other treatments such as surgery and steroids are being tested.