A significant visual impairment that cannot be corrected fully with glasses, contact lenses, medication or eye surgery is termed as low vision. It is caused by severe eye disease, in which visual acuity in the better eye is 20/70 or less, or where there is a significant loss of visual field (constriction to 20 degrees or less, termed tunnel vision).
Visual acuity of that a person with 20/70 vision who is 20 feet from an eye chart sees what a person with unimpaired (or 20/20) vision can see from 70 feet away. Low vision can impact people of all ages, but it is associated primarily with adults over the age of 60.
Causes and typical patterns of low vision which cannot be corrected include:
- Blurred or partially obscured central vision: Macular degeneration (both, age-related, and hereditary)
- Blind spots, blurriness and visual distortions: Diabetic retinopathy
- Poor peripheral vision, or tunnel vision: Glaucoma
- Poor peripheral vision, and inability to see in the dark: Retinitis pigmentosa
- Eye injuries
- Poor central vision which may progress to no light perception: Optic neuropathies which may be inherited or acquired (toxic)
In real life situations, vision loss that cannot be corrected and that which interferes with your daily activities may be termed low vision. It is better defined regarding function, rather than test results.
More often than not, your vision can be corrected using eyeglasses, contact lens or even surgery, as in the case of cataracts. If not, your doctor will conduct special tests to determine the cause, type, and severity of vision loss. After the initial assessment, he or she will help you take the next steps toward coping with your life circumstances.
Once the visual loss has been ascertained, the low vision specialist can prescribe appropriate low vision aids, best suited for your condition, and teach you how to use them. There are several low vision aids and devices to help you cope with your day to day living. The most commonly prescribed ones include lighted handheld magnifiers, digital desktop magnifiers, and bioptic telescopes. Newer software that simplifies computer use with magnification and text-to-speech features are also available and can be customised to your specific needs.
Low vision specialists also recommend non-optical adaptive devices, such as large-font books and magazines, audio books, special light fixtures and signature guides for signing checks and documents.
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.