Retinal Vessel Blockages
Most people know high blood pressure and other vascular diseases pose risks to overall health, but many may not know that these problems can affect vision by damaging the blood vessels (arteries and veins) in the eye. Arteries are the pipes that carry the blood from the heart and lungs to all the other parts of the body including the retina the light sensing nerve layer lining the back of the eye.
Veins are the pipes that carry the blood back to the heart and lungs. The retina has both arteries and veins. Blockages can occur in both types of vessels in either the main vessels or branches. Diabetes, high cholesterol, smoking and obesity also increase the risks of such problems.
Branch Retinal Artery Occlusion (BRAO)
Branch retinal artery occlusion blocks the small branch arteries in the retina. The most common cause of BRAO is a thrombosis, the formation of a blood clot. Sometimes the blockage is caused by an embolus, a clot carried by the blood from another part of the body.
Central vision is lost suddenly if the blocked retinal artery is one that nourishes the macula, the part of the retina responsible for fine sharp vision. Following BRAO, vision can range from norm(20/20) to barely detecting hand movement.
Central Retinal Artery Occlusion (CRAO)
Central retinal artery occlusion is a blockage of the main artery in your retina. The first sign of CRAO is a sudden and painless loss of vision that leaves you barely able to count fingers or determine light from dark.
Loss of vision can be permanent. Irreversible retinal damage occurs after 90 minutes. The goal of treatment is to restore retinal blood flow. After treatment, you should have a thorough medical evaluation.
CRAO usually occurs in people between the ages of 50 and 70. The most common medical problem associated with CRAO is arteriosclerosis, hardening of the arteries. Carotid artery disease is found in almost half the people with CRAO.
The most common cause of CRAO is a thrombosis, an abnormal blood clot formation. Sometimes CRAO is caused by an embolus, a clot that breaks off from another area of the body and is carried to the retina by the bloodstream.
Branch Retinal Vein Occlusion (BRVO)
A blocked vein can cause leakage of blood into the retina and vision loss. This is known as a branch vein occlusion and may be treated with medication or a laser.
Branch retinal vein occlusion blocks small branch veins in the retina. If the blocked retinal veins are ones that nourish the macula, the part of the retina responsible for straight-ahead vision, some central vision is lost. During the course of vein occlusion, sixty percent or greater will have swelling of the central macular vision area. In about one third of people, this macular edema will remain for over one year.
BRVO causes a painless decrease in vision, resulting in misty or distorted vision. If the veins cover a large area, new abnormal vessels may grow on the retinal surface, which can bleed into the eye and cause blurred vision.
High blood pressure is the most common condition associated with BRVO. About 10 to 12 percent of the people who have BRVO also have glaucoma (high pressure in the eye).
There is no cure for BRVO. Finding out what caused the blockage is the first step in treatment. Your ophthalmologist may recommend a period of observation, since hemorrhages and excess fluid may subside on their own. Depending on how damaged the veins are, laser surgery may help reduce the swelling and improve vision. Laser surgery may also shrink the abnormal new blood vessels that are at risk of bleeding.
Central Retinal Vein Occlusion (CRVO)
Central retinal vein occlusion blocks the main vein in the retina. The blockage causes the walls of the vein to leak blood and excess fluid into the retina. When this fluid collects in the macula-the area of the retina responsible for central vision-vision becomes blurry.
Floaters in your vision are another symptom of CRVO. When retinal blood vessels are not working properly, the retina grows new fragile vessels that leak blood into the vitreous, the fluid that fills the center of the eye. Blood in the vitreous clumps and is seen as tiny dark spots, or floaters, in the field of vision.
In severe cases of CRVO, the blocked vein causes painful pressure in the eye. Retinal vein occlusions commonly occur with glaucoma, diabetes, age-related vascular disease, high blood pressure, and blood disorders.
The first step is finding what is causing the vein blockage. There is no cure for CRVO. Your ophthalmologist may recommend a period of observation, since hemorrhages and excess fluid often subside on their own. Laser surgery may be effective in preventing further bleeding into the vitreous, or for treating glaucoma, but it cannot remove the hemorrhage or cure glaucoma once it is present.