Transient blindness

Definition

Transient blindness, also called transient monocular blindness or amaurosis fugax, is a brief loss of vision. Vision loss usually occurs in only one eye and can last anywhere from a few minutes to a few hours. Transient vision loss is often a warning sign that a stroke is imminent.

Description

Transient blindness can occur because a blood vessel to the eye is blocked, the eye is damaged, or nerves to the eye are diseased. People who experience transient blindness may feel like their vision is gradually blurring, fogging, or fading out, or they may feel as if a dark curtain has suddenly descended over their field of vision. Most often, transient blindness affects only one eye. The condition can last anywhere from a few seconds to hours. Although vision returns, anyone who experiences transient blindness should see a physician promptly because it can be a symptom of an impending medical emergency.

Demographics

Because transient blindness has many causes, it can happen to people of any age, although it is often linked to cardiovascular disease and is more likely to occur in older individuals. Transient blindness is most common in white men over age 50.

Causes and symptoms

Transient blindness occurs for three main reasons: blockage of a blood vessel going to the eye, damage to the eye, or damage to the nerves that serve eye. Of these, blockage of the blood vessels going to the eye is the most common.

Blood vessel blockage

Amaurosis fugax is the temporary loss of vision caused by debris in the circulatory system that blocks blood flow to the retina. Typically, only one eye is affected at a time. The blockage often occurs because a bit of plaque from atherosclerosis breaks off from the lining of a main artery and travels to a smaller artery that delivers blood to the retina. Atherosclerosis is a condition in which arteries narrow because of a build up of debris, called plaque, on the inside of the arterial walls. When loose bits of debris lodge in an artery, blood flow is severely restricted or stops, which causes the retina to be deprived of oxygen and nutrients. The retina then stops functioning and the person loses vision. If the blockage lasts only a short time, vision is lost only temporarily and returns when blood flow to the retina begins again. Plaque that obstructs arteries to the eye most often comes from the internal carotid artery (an artery in the neck),

QUESTIONS TO ASK YOUR DOCTOR

• What caused my vision loss?
• Are there underlying health problems that are likely to have caused this vision loss?
• Do I need to be referred to a specialist?
• Do I need immediate treatment such as surgery?
• What should I do if I experience transient vision loss again?

although it can come from anywhere in the cardiovascular system. Arteries to the retina can also be blocked by blood clots . Often these clots arise in the heart from conditions such as atrial fibrillation or heart valve defects.

Amaurosis fugax can also occur when the arteries that serve the retina develop such severe plaque build up that blood flow is substantially reduced. In this case, vision loss is often triggered by sudden exposure to sunlight, which causes the retina to need more nutrients than the reduced flow of blood can deliver. Transient vision loss caused by any kind of blockage is a warning sign that a transient ischemic attack (TIA) or a stroke is likely to occur in the near future.

Occasionally amaurosis fugax occurs in healthy individuals during exercise . Vision loss lasts less than five minutes and is thought to be caused by a temporary spasm (vasospasm) of a blood vessel serving the eye, triggered by the release of certain chemicals into the blood. This type of vision loss is not a warning sign of stroke.

Inflammation of the retinal artery (giant cell arteritis) can also cause amaurosis fugax. The inflammation causes the artery to become partially or completely blocked. This condition is usually associated with headache. Various studies found that giant cell arteritis was the cause of temporary vision loss in 2 to 19% of people with amaurosis fugax.

Transient vision loss due to insufficient blood flow has also been reported as an occasional side effect of such drugs as sidenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) taken for erectile dysfunction . Individuals experiencing this side effect should stop using the drug and be evaluated by their physician.

Sudden vision loss can also be caused by psychological trauma. This condition is sometimes called hysterical vision loss.

Damage to the eye

Infection and inflammation of various parts of the eye can also cause temporary vision loss, as can a transient increase in intraocular pressure (the pressure inside the eye). Disorders such as closed-angle glaucoma and the build up of drusen (pigment clumps) can also cause temporary or permanent vision loss. Temporary vision loss has also been reported in young children who have had mild head trauma with no loss of consciousness.

Nerve damage

The optic nerve carries information from the retina to the brain, where the information is processed to create an image. Any event that damages the optic nerve or interferes with nerve impulse transmission can cause transient or permanent blindness. These events include inflammation of the optic nerve, compression of the optic nerve, temporary reduction in blood flow to the optic nerve, multiple sclerosis (nerve impulses are disrupted due to degeneration of the myelin sheath surrounding the nerve), tumors that infringe on the optic nerve, psychoactive drug use, and migraine headaches .

Symptoms

About one-fourth of patients describe their transient vision loss as a dark curtain descending across their field of vision, while the majority describe it as a dimming, fogging, or blurring of vision.

The sensation of a dark curtain obscuring the field of vision also characterizes a retinal detachment. Loss of vision due to a retinal detachment is not temporary. Individuals with sudden vision loss should seek immediate medical care. A retinal detachment is a medical emergency that can result in permanent blindness if not treated promptly.

Diagnosis

Diagnosing the cause of transient vision loss is difficult because by the time the patient sees a physician vision has often returned. Diagnosis begins with a thorough eye examination . The eye will be dilated so that interior structures can be seen using an ophthalmoscope and a slit lamp. An ophthalmologist will look for any signs of infection, bleeding, eye disease, or other condition that could have caused the vision loss. A complete eye examination can determine if the cause of vision loss is physical or psychological by the way the eye responds to light and movement. In the case of hysterical vision loss, the patient will be referred to a psychiatrist.

KEY TERMS

Artery —A vessel that carries oxygen-rich blood to the body.

Atherosclerosis —A chronic condition characterized by thickening and hardening of the arteries and the build up of plaque on the arterial walls. Atherosclerosis can slow or impair blood circulation, and be the source of debris that travels to and blocks other arteries.

Balloon angioplasty —A surgical procedure performed to reopen a partially blocked artery so that blood can flow through it again at a normal rate. A tiny tube (catheter) is threaded through blood vessels to the point of the blockage. The catheter contains a balloon that is then expanded to stretch and open the artery.

Drusen —Clumps of pigment that accumulate under the retinawhenwastes build up faster than they can be removed. Drusen are a sign of dry age-relatedmacular degeneration.

Echocardiogram —A non-invasive imaging procedure used to create a picture of the heart's movement, valves, and chambers.

Electrocardiogram (ECG) —A test that measures electrical impulses in the heart.

Embolism —A blood clot, air bubble, or clot of foreign material that travels in and blocks the flow of blood in an artery. When blood supply to a tissue or organ is blocked by an embolism, infarction (death of the tissue the artery feeds) may occur. Without immediate and appropriate treatment, an embolism in a critical blood vessel can even be fatal.

Glaucoma —An eye disorder in which increased pressure in the eye (intraocular pressure) causes damage to the optic nerve, resulting in vision loss. There are several types of glaucoma, and glaucoma may develop suddenly or gradually.

Plaque —Fatty material that is deposited on the inside of an arterial wall.

Retina —Light-sensitive tissue on the back of the eye that receives images and converts them into nerve impulses to be sent to the brain by way of the optic nerve.

Retinal detachment —Separation of the retina of the eye from its underlying layer of tissue. This separation results in loss of vision. A retinal detachment is a medical emergency.

Stenosis (plural, stenoses) —The narrowing or constriction of an opening or passageway in the body.

Because transient vision loss may indicate a serious cardiovascular condition, the patient usually needs evaluation by an internal medicine specialist or cardiologist. Screening can include an electrocardiogram (ECG), 24-hour Holter monitoring (in which the patient wears a portable monitor that records heart contractions for 24 hours), echocardiogram , and an ultrasound or other scan of the head and neck to assess the degree of arterial blockage.

Treatment

Treatment depends on the cause of vision loss. If an artery in the neck is more than 70% blocked, the patient may benefit from surgical unblockage, often by balloon angioplasty . If the condition of the patient makes surgery undesirable or the blockage is less than 70%, the patient may be given blood-thinning drugs such as warfarin (Coumadin) and drugs to lower cholesterol to prevent additional plaque build up.

When damage to the eye has occurred or an underlying disease is present, these conditions are treated.

Nutrition/Dietetic concerns

Since transient vision loss is often caused by plaque in the arteries, dietary changes are directed at preventing plaque build up. A low-cholesterol, heart-healthy diet low in fats, especially saturated (animal) fats and high in fresh fruits, vegetables, and whole grains is recommended by the American Heart Association. Calorie and portion control is also important in maintaining or reaching a healthy weight.

Prognosis

Although people with transient vision loss regain their vision without any permanent disability, short-term loss of vision is often a forewarning of stroke or other serious medical problem and should not be ignored.

Prevention

Prevention involves preventing the underlying problem that causes the transient loss of vision. If the cause of vision loss is due to narrowed or blocked blood vessels, then following a heart-healthy diet, maintaining a healthy weight, and exercising regularly, controlling blood sugar levels and blood pressure , and not smoking are all helpful. Some causes of transient vision loss cannot be prevented.

Caregiver concerns

Caregivers should arrange for the person in their care who experiences transient vision loss to see a doctor promptly, even if vision loss is only momentary and vision then returns to normal. Transient vision loss is a warning sign that a more serious health problem is likely to occur in the near future.

Resources

OTHER

“Amaurosis Fugax.” Medline Plus. September 10, 2006 [cited February 24, 2008]. http://www.nlm.nih.gov/medlineplus/ency/article/000784.htm.

Farina, Gino A., and Nicholas Lorenzo. “Sudden Vision Loss.” eMedcinie.com. November 8, 2005 [cited February 24, 2008]. http://www.emedicine.com/neuro/topic480.htm

Sowka, Joseph W., and Alan G. Kabat. “Sudden Vision Loss: Now They See It, Now They Don't.” Review of Optometry Online. March 15, 2000 [cited February 24, 2008]. http://www.revoptom.com/archive/FEATURES/ro0300f7.htm.

ORGANIZATIONS

American Heart Association, 7272 Greenville Ave., Dallas, TX, 75231, (800) 242-8721, http://www.americanheart.org.

American Optometric Association, 243 N. Lindbergh Blvd., St. Louis, MO, 63141, (800) 365-2219, http://www.aao.org.

EyeCare America Foundation of the American Academy of Ophthalmology, PO Box 429098, San Francisco, CA, 94142-9098, (877) 887-6327, (800) 324-3937, (415) 561-8567, [email protected], http://www.eyecareamerica.org.

National Eye Institute, 2020 Vision Place, Bethesda, MD, 20992-3655, (301) 496-5248, [email protected], http://www.nei.nih.gov.

National Heart, Lung, and Blood Institute Information Center, PO Box 30105, Bethesda, MD, 20824-0105, 301) 592-8573, http://www.nhlbi.nih.gov.

Tish Davidson A. M.