What is low vision?
Low vision is reduced vision and/or visual field loss that cannot be corrected by conventional eyeglasses, contact lenses, medical treatment or surgical procedures.
In terms of visual acuity, low vision usually means a person’s best attainable eyesight is 20/70 or worse. (The smallest letters they can read at a distance of 20 feet can be seen by a person with normal vision at a distance of 70 feet.)
In terms of visual field, low vision usually means a person’s total horizontal visual field (with both eyes open) is restricted to 40 degrees or less. (A normal visual field is 180 degrees or more.)
Many people with low vision are legally blind. For income tax purposes in the United States, “legal blindness” is defined as best-corrected visual acuity of 20/200 or worse or a total visual field of 20 degrees or less.

What causes low vision?
The most significant cause of low vision is age-related macular degeneration (AMD). Approximately 45 percent of low vision cases are caused by AMD. Other causes include cataracts, glaucoma, and diabetic retinopathy.
Though low vision is most frequently associated with degenerative conditions occurring later in life, it can also be caused by congenital eye diseases and diseases occurring early in life—such as congenital cataracts, optic nerve disease, and retinitis pigmentosa.

How common is low vision?
One out of every six adults over the age of 45 has low vision. For those age 75 and older, the number increases to one out of every four (25%).

How is low vision treated?
Special optical aids called low vision devices can help individuals with low vision use their remaining vision as efficiently as possible. A single low vision device can enhance distance vision or near vision, but not both. Therefore, most individuals with low vision need more than one type of low vision device for routine visual tasks.
Optical aids for low vision can be divided into four categories:
• Head-borne devices (for distance or near vision)
• Hand-held devices (for distance or near vision)
• Stand magnifiers (for near vision only)
• Computer/video magnification devices (usually for near vision only).

Optical low vision aids provide a high degree of magnification to help people with low vision see things in greater detail. Non-optical devices that can also be helpful include large-print books, audio books, and high intensity reading lights.