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Vision testing is usually done by a healthcare provider, who test the person's eyesight with a wall chart or small card held in the hand. Normal vision is described as 20/20, where the person who is seated or standing 20 feet away from the eye chart can read all the letters (or numbers) on the chart at the 20/20 line. This is called visual acuity. When someone's vision is 20/40, that means that when they are standing or sitting 20 feet away from the eye chart, they they can only see letters (or numbers) on the chart that are large enough for a person with normal vision to see 40 feet away (the 20/40 line). So, the higher the second number (such as 20/100, 20/200, 20/400), the worse is the person's eyesight. Visual impairment is when the person's vision in the eye with the best eyesight is worse than 20/40 but better than 20/200. Vision must be better than this to have a regular driver's license in most states. Blindness is vision of 20/200 or worse in the better eye (even with glasses). People with vision that is this poor may be able to get Social Security Disability Income (SSI). Low vision is a loss of eye function that interferes with daily activities. You may have good visual acuity but still have low vision. For example, problems like loss of peripheral (side) vision, problems with glare, and problems telling apart objects based on how they appear (contrast sensitivity) may cause low vision.

Visual impairment is very common, and increases with age. About 12% of people over the age of 40 have visual impairment. More than half of these cases are treatable.

The most common causes of visual impairment can often be treated easily with new glasses or cataract surgery. Macular degeneration, open angle glaucoma, and diabetic retinopathy (eye disease from diabetes) are all common causes. All three of these conditions are explained below.

Age, as with many things, is an important risk factor. Some causes of visual impairment run in the family. Habits such as too much sun exposure and smoking, also increase your chances of visual impairment. Diseases like diabetes and certain medications, such as steroids, can lead to problems with vision.

Some of the risk factors can be avoided and others cannot. Steps you can take to reduce your risk of vision loss include avoiding too much sun exposure, and when you are in the sun, wear sunglasses with protection from UV (ultraviolet) light. Don't smoke. If you have diabetes, make sure that your blood sugar is under control. Many of these problems can be treated if they are caught early. You should see an eye doctor at least once every two years, unless you have diabetes, in which case, you should see an eye doctor at least every year.

If you have an eye disease that causes visual impairment, it is important that you go to your eye doctor on a regular basis. Depending on the cause, there may be different options for treatment. These include surgery, laser treatment, medications and eye drops.

Macular degeneration is a disease of the center of the retina (the place at the back of the eye), called the macula. The macula is the part of the eye that is used for detailed work, like reading, watching television, or driving. Macular degeneration comes on slowly, and hurts the center of the vision,. Macular degeneration usually causes blurry vision.

Glaucoma is an eye disease that causes loss of peripheral (side) vision. People with glaucoma usually have increased pressure inside the eye. Early on with glaucoma, the disease does not cause symptoms. So finding early glaucoma depends on regular eye exams that include checking the eye pressure, looking into the back of the eye, and testing for loss of peripheral vision. There are different types of glaucoma. Primary open-angle glaucoma is the most common in adults. The cause is not known. Treatment includes eye drops and sometimes laser or other surgery. Secondary open-angle glaucoma is due to another underlying problem, such as cataracts. Angle-closure glaucoma is less common and may happen quickly. If this occurs, you may experience eye and face pain, nausea and vomiting, and loss of vision. Angle-closure glaucoma should be treated as an emergency.

If your vision loss is interfering with your day-to-day living, a low vision rehabilitation specialist may be able to help. The low vision rehabilitation specialist will test the extent of your vision loss and how much your vision loss is interfering in your activities. Aids to improve your low vision include simple things, like magnifying glasses and special lighting, as well as high-tech devices that read letters and papers to you or special radios that receive broadcasts of the newspaper. A home assessment by the low vision rehabilitation specialist may help make it easier to do your daily activities at home.

National Eye Institute	The Lighthouse
2020 Vision Place	111 W. 59th St.
Bethesda, MD 20892-3655	New York, NY 10022-1202
Telephone: (301) 496-5248	Telephone: (212) 821-9200, (800) 829-0500, TTY
Fax: (301) 402-1065	(212) 821-9713
Website: www.nei.nih.gov	Website: www.lighthouse.org