The carotid artery carries blood from the heart to the head and brain. There are two carotid arteries, one on each side of the neck. Over time, carotid arteries can become clogged with plaque as a result of coronary artery disease. Blockage of the carotid causes a decrease in blood flow to the head and eyes, and can also lead to blockages in the veins and arteries in the eye if plaque or clots breaks off the artery wall. Plaque, clots and decreased blood flow can all cause problems with vision.
Ocular Ischemic Syndrome
Ocular Ischemic Syndrome results from decreased blood flow to the eye, the Handbook of Ocular Disease Management says, and affects mostly people 50 and older. In 80 percent of cases, only one eye is affected. Ninety percent of the time, vision is affected, and pain accompanies the disease 40 percent of the time. Eye pressure may be elevated, and swelling in the macula, the central part of vision in the retina, can cause blurred or distorted vision.
Retinal Vein Occlusion
Retinal vein occlusion is caused by a blockage in the vein from plaque or from decreased blood flow to the eye. Retinal vein occlusion can affect the central retinal vein or the branch veins. A blockage in the vein acts like a kink in a hose; the vein or artery swells and often leaks behind the blockage. If branch retinal veins occlusion-- also known as BRVO--occurs, peripheral vision is usually lost. Blind spots can also occur, along with blurred vision. Chris Knobbe, M.D., says on All About Vision that central retinal vein occlusion, also called CRVO, causes sudden vision loss that's usually painless and may be mild or severe. Retinal vein occlusions can be treated with laser to seal off a leak; intravitreal injections of steroids are used in some cases of CRVO.
Retinal Artery Occlusion
Retinal artery occlusions are more difficult to treat than vein occlusions. Symptoms of artery occlusions are sudden, profound, painless vision loss that occurs in peripheral vision if in a branch and centrally if the occlusion is in the central artery, according to Knobbe. A central retinal artery occlusion, also called a CRAO, is sometimes referred to as a stroke in the eye. If seen promptly, CRAO may be treated with medications to decrease eye pressure or with paracentesis, which removes a small amount of fluid from the eye in an effort to dislodge the clot. Vision loss may be permanent if not treated within 90 minutes, Knobbe says, and even then, some vision may be lost.