What is the definition of low vision?
Low vision is the loss of sight that is not correctible with prescription eyeglasses, contact lenses or surgery. This type of vision loss does not include complete blindness, because there is still some sight and it can sometimes be improved with the use of visual aids.
Low vision includes different degrees of sight loss, from blind spots, poor night vision and problems with glare to an almost complete loss of sight. The American Optometric Association defines low vision as two categories:
- "Partially sighted": the person has visual acuity between 20/70 and 20/200 with conventional prescription lenses.
- "Legally blind": the person has visual acuity no better than 20/200 with conventional correction and/or a restricted field of vision less than 20 degrees wide.
The ratio measurement of vision describes visual acuity, or the sharpness of vision, at 20 feet from an object. For example, having 20/70 vision means that you must be at 20 feet to see what a person with normal vision can see at 70 feet.
Who is most at risk of having low vision?
Anyone can be affected by low vision because it results from a variety of conditions and injuries. Because of age-related disorders like macular degeneration and glaucoma, low vision is more common in adults over age 45 and even more common in adults over age 75. For example, one in six adults over age 45 has low vision; one in four adults over age 75 has low vision.
The most common types of low vision include:
- Loss of central vision: There is a blind spot in the center of one's vision.
- Loss of peripheral (side) vision: The inability to see anything to either side, above, or below eye level. Central vision, however, remains intact.
- Night blindness: The inability to see in poorly lit areas such as theaters, as well as outside at night.
- Blurred vision: Objects both near and far appear out of focus.
- Hazy vision: The entire field of vision appears to be covered with a film or glare.
Symptoms and Causes
What causes low vision?
There may be one or more causes of low vision. These are usually the result of disorders or injuries affecting the eye or a disorder such as diabetes that affects the entire body. Some of the most common causes of low vision include age-related macular degeneration, diabetes and glaucoma. Low vision may also result from cancer of the eye, albinism, brain injury or inherited disorders of the eye including retinitis pigmentosa. If you have these disorders or are at risk for them, you are also at greater risk for low vision.
Diagnosis and Tests
How is low vision diagnosed?
An eye exam by your eye care specialist can diagnose low vision. You should make an appointment with your eye doctor if your vision difficulties are preventing you from daily activities like travel, cooking, work and school. The tests the eye doctor will perform include the use of lighting, magnifiers and special charts to help test visual acuity, depth perception and visual field.
Management and Treatment
Can low vision be treated?
Some sight disorders, like diabetic retinopathy, can be treated to restore or maintain vision. When this is not possible, low vision is permanent. However, many people with low vision find visual aids helpful. Popular low vision aids include:
- Telescopic glasses.
- Lenses that filter light.
- Magnifying glasses.
- Hand magnifiers.
- Closed-circuit television.
- Reading prisms.
Some patients with retinitis pigmentosa who have no useful vision may be eligible for the Argus® II retinal prosthesis. This device partially restores vision to patients who have lost their sight. In some patients the restored vision allows for them to independently navigate through doorways, sidewalks, sort light and dark colored laundry, or even read large letters.
Non-optical aids designed for people with low vision are also very helpful. Some popular non-optical devices include:
- Text reading software.
- Check guides.
- High contrast clocks and watches.
- Talking watches and clocks.
- Large print publications.
- Clocks, phones and watches with enlarged numbers.
Visual aids improve both sight and the quality of life for many people. Talk to your doctor about where to purchase visual aids.
Can low vision be prevented?
Low vision may be preventable for patients with diabetes, and some patients with macular degeneration and glaucoma may be treated to prevent the further vision loss.