Retinal Artery Occlusion
Definition: Retinal artery occlusion is blockage of the blood supply in the arteries to the retina -- the light-sensitive tissue in the back of the eye.
Causes: Retinal arteries may become blocked by a blood clot or substances (such as fat or plaque) that get stuck in the arteries. These blockages may occur due to hardening of the arteries in the eye. Also, clots may travel from other parts of the body and block arteries in the retina. A common source of a clot would be from the carotid artery in the neck or from the heart lining.
Most clots are caused by conditions such as:
- Disease of the two large blood vessels in the neck (carotid artery disease)
- High blood fats (hyperlipidemia)
- Heart rhythm problem (atrial fibrillation)
- High blood pressure
If a branch of the retinal artery is blocked, part of the artery will not have enough blood and oxygen. If this happens, you may lose part of your vision.
Retinal artery blockage or occlusions may last from only a few seconds to a few minutes. They also may cause permanent vision loss. The amount of vision loss is partly related to the location of the blockage.
People with retinal arterial occlusion, whether temporary or permanent, are at risk of stroke because clots may also move to the brain.
Retinal Vein Occlusion, Central (CRVO) and Branch (BRVO)
Definition: Proper blood circulation is needed for the retina to function. Normally, blood flows into the retina through the central retinal artery and leaves through the central retinal vein. Both of these blood vessels enter the eye through the optic nerve. Central retinal vein occlusion (CRVO) is caused by a blood clot in the vein that drains the blood from the retina, allowing blood to enter the retina but not allowing it to leave, due to the vein blockage.
As a result, blood and fluid back up into the retina, which causes a loss in vision. With further damage, the blood vessels in the retina may close, leading to more visual loss and the possible development of new abnormal blood vessels.
Branch retinal vein occlusion (BRVO) is a localized blood clot that develops in a branch retinal vein due to hardening of arteries in an adjacent branch retinal artery.
Symptoms: Signs and symptoms of CRVO can be full or partial, with mild to severe sudden, painless vision loss. You have a higher risk of developing a CRVO if you have high blood pressure, diabetes, chronic open-angle glaucoma, or atherosclerosis (hardened arteries).
BRVO may cause decreased vision, peripheral vision loss, distortion of vision, or “blind spots”. The condition usually affects one eye and develops in patients with high blood pressure or diabetes.
Detection of CRVO and BRVO is done through a dilated eye exam with an ophthalmologist. They may find mild to severe hemorrhages and spots in the retina, which can indicate obstructed blood flow. After a diagnosis of CRVO or BRVO has been made, many patients are advised by their doctors that lost vision may return on its own if nothing is done to the eye. However, spontaneous recovery of vision is very uncommon and when it does occur, the amount of recovery is usually very small. Your ophthalmologist may request a fluorescein angiogram to track blood flow in the retina. Patients are typically re-evaluated every one to two months to monitor swelling and growth of abnormal blood vessels.
Treatment: Treatment of CRVO is often done with an in-office laser procedure called Pan-Retinal Photocoagulation (PRP). An operation can also be done in which Tissue Plasminogen Activator (t-PA), which is a well known "clot busting" medication successfully used for treating heart attack and stroke patients, is introduced into the eye. The t-PA helps the clot to dissolve, which helps blood flow through the central retinal vein. This procedure can be done in addition to a vitrectomy, which is a surgery that is used by retinal surgeons to treat eye diseases.
Patients with BRVO may be treated with focal laser or injections of medication into the eye, which have also been shown to improve vision. After several months, many patients have resolution of the retinal hemorrhages and macular swelling, retaining good vision.