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Visual impairment refers to sight that has less quality, strength, or value than normal. Sight has become weakened or damaged in some way.

What is going on in the body?

Some people are born with visual impairments. Vision changes can also occur in people of any age for a number of reasons, including conditions within the eyes, as well as conditions within the brain. The change in a person's sight may be minor or severe. Vision problems can range from an inability to see certain colors to blurred vision or complete loss of sight. The visual impairment may be acute, meaning occuring suddenly, or chronic, which means that the visual changes last for a long period of time.

What are the signs and symptoms of the condition?

• blurry vision
• double vision, or seeing two of everything. This occurs when the images that are coming from each eye do not line up properly.
• difficulty focusing on either near or far objects
• cloudy vision, often described as "looking through a dirty windshield"
• seeing so-called floaters or black specks across the field of vision
• inability to see certain colors
• inability to see peripheral objects, meaning those objects that are to the side, up or down
• loss of depth perception
• ability only to distinguish light from dark
• total loss or absence of all vision

What are the causes and risks of the condition?

• damage to the visual nerves, such as that caused by head injury,brain tumor, or infection
• diabetes
• glaucoma, or abnormally high pressure inside the eye
• injuries to the eye, such as corneal injuries
• brain damage, such as that from a stroke, or brain attack
• refractive errors, which means that objects appear blurry only when they are up close or when they are far away. This is commonly known as being nearsighted or farsighted.

• color blindness, an inherited condition that is much more likely in males
• macular degeneration, a common cause of poor sight in the elderly. This condition affects the retina, or back of the eye, and occurs for unknown reasons.
• cataracts, another common cause of poor vision in the elderly, although it can occur even in newborn babies Cataracts describe a clouding of the lens, or focusing, part of the eye.
• aging, which can cause people to need reading glasses or bifocals starting around the age of 40 or 50. This condition is called presbyopia and is considered normal.
• astigmatism, or blurred vision in only certain areas of sight, which is caused by abnormal bending of light through the eye
• medication side effects, such as those from the heart medication digoxin (i.e., Lanoxin) or the antibiotic ethambutol (i.e., Myambutol)

What can be done to prevent the condition?

Prevention of visual impairment, when possible, is related to the cause. Prevention includes the following:

• screening for vision problems, which is often part of a routine checkup by a healthcare professional. All infants and children should be screened. This can help detect a condition called strabismus, or so-called lazy eye, which needs early treatment to prevent blindness in one eye. Screening for glaucoma is very important for people who are older than 40, especially those who are black or have a family history of this condition.
• controlling conditions such as diabetes that can lead to vision impairment. Controlling blood sugar levels has been shown to prevent or delay vision problems from this condition. Controlling glaucoma can also help prevent vision loss from this condition.
• wearing safety glasses or goggles during hazardous activities. Individuals should take care to keep foreign objects and chemicals out of the eyes. Sunlight can also harm the eyes. People should never look directly at the sun and are advised to wear sunglasses outside.
• following directions for proper wearing, cleaning, and storing of the lenses, for those who wear contact lenses. People must also watch for problems that can be caused by the lenses. These may include corneal injuries or corneal infections.
• providing regular prenatal care for pregnant women to help prevent problems in the developing baby
• seeking early evaluation and treatment for eye infections

How is the condition diagnosed?

The role of the eye care professional is to help determine the cause of visual impairment. This may be possible after a complete history and physical exam. First, the professional needs to ask about the eyes, any vision problems, and general health. Next, he or she will test the eye muscles to see if eye movements are normal. Peripheral vision, or the ability to see out of the side of the eyes, can be tested as well.

Often, the eye care professional will put special eye drops into the eyes that cause the pupils to open wider, or dilate. When the pupils are wide open, the provider can get a better view of the inside of the eyes with a special instrument called an ophthalmoscope. The pressure inside the eyeball can be measured to test for glaucoma.

After the eyeballs have been examined, the person is then asked to read a standard eye chart to determine how well the person can see or to check the visual acuity. Other tests may also be needed in some cases.

What are the long-term effects of the condition?

Visual impairment can limit a person's ability to work, go to school, and drive. Severely affected people may need special devices to help them with everyday activities. Other long-term effects depend on the cause. For example, glaucoma may lead to permanent loss of vision. Cases of nearsightedness or farsightedness often improve with the use of glasses or contacts. A stroke may cause permanent vision problems and other limitations from brain damage.

What are the risks to others?

Visual impairment itself is not contagious and poses no risk to others.

What are the treatments for the condition?

If vision impairment occurs, there may be ways to improve sight. Glasses and contact lenses are the most common ways to improve vision. Children with a lazy eye may wear an eye patch on one eye or need surgery to help with weak eye muscles. Therapists who have been trained in vision problems can suggest exercises that may improve some vision problems.

Surgery and medication may also be appropriate, as in glaucoma. Those who have cataracts and some other conditions are "cured" or improved by surgery or medications. If vision cannot be improved, training and special devices may help the person adjust to the impairment. It is possible to live a nearly normal lifestyle with most visual impairments.

Many people use eyeglasses or magnifiers so they can still perform certain activities. To function safely, affected people may, however, need to rely on signals other than sight. For example, some lighted signals at a crosswalk also make beeping sounds to indicate when it is safe to cross the street.

People who have severe vision problems or are blind can benefit from special devices and training. A white cane and a guide dog are familiar aids for helping blind people function on their own. Computers are now able to recognize speech and can talk to the person. Keyboards with Braille symbols, Braille books, and books on audio tape are also available.

What are the side effects of the treatments?

Side effects depend on the treatments used. Medications for glaucoma may cause stinging, blurred vision, eye redness, changes in heart rate, and headaches. Surgery can be complicated by bleeding, infection, or reactions to anesthesia.

What happens after treatment for the condition?

• There should be enough light available to people with reduced sight.
• Objects in the person's environment should not be moved without letting the person know. He or she will often "memorize" the environment and need to have things kept in the same place. For example, doors should either be kept fully open or fully closed.
• If the person is in an unfamiliar place, the location of objects should be described to him or her. Also, the affected person should be told when someone leaves or enters the area.
• If the person asks for assistance in walking, he or she will usually hold another person's arm just above the elbow and will follow along. The sighted person should alert the person when they are coming near steps, curbs, or other obstacles.

How is the condition monitored?

Those who notice a change in their vision should be seen promptly by an eye care professional. This may help prevent permanent vision problems.