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.
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, glaucoma, and cataracts, 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.
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 cataracts. Low vision may also result
from cancer of the eye, albinism, or a brain injury. If you have
these disorders or are at risk for them, you are also at greater
risk for low vision.