Low vision is loss of vision in both eyes that interferes with normal daily activities such as reading, cooking, or shopping. The vision loss is permanent and cannot be adequately corrected by glasses, contact lenses, surgery, or medication.
Low vision is a general term for the loss of visual acuity. Normal vision is called 20/20 vision. It represents the line of print on an eye chart that a non-visually impaired person can read at a distance of 20 feet. If a person's vision is 20/40, this means that at 20 feet, this person see what a non-impaired person sees at 40 feet. A person with vision of 20/200 (the person sees at 20 feet what a non-impaired person sees at 200 feet) or worse in both eyes is considered legally blind in the United States. No specific reading is used to designate low vision, although people with
|*Low vision is defined as the best-corrected visual acuity less than 6/12|
(<20/40) in the better-seeing eye.
|source: Adapted from Archives of Ophthalmology, Vol. 122,|
|(Illustration by GGS Information Services. Cengage Learning,|
uncorrectable 20/70 vision or worse generally are considered to have low vision.
About 135 million people worldwide have low vision. Most of these people are over age 65. In the United States, low vision is most common among African Americans and Hispanics. This is primarily because these groups are more likely to contract diseases such as diabetes and that lead to permanent vision loss. African Americans also are more likely to develop glaucoma, a condition that also can result in low vision.
Causes and symptoms
Low vision is most often caused by disease, although it occasionally can be caused by injury or a birth defect. Age-related macular degeneration (ARMD) is the leading cause of low vision in the United States, accounting for about 45% of cases. In 2004 about 8 million Americans had ARMD and 1.75 million were severely affected.ARMD is a disease of the elderly, and the number of people with low vision is expected to climb in the future because more people are living longer.
Other causes of low vision include:
- diabetic retinopathy
- retinitis pigmentosa
- inoperable cataract
- corneal generation
- eye injury
- head/brain injury
- brain tumor
QUESTIONS TO ASK YOUR DOCTOR
- Is my vision likely to get worse?
- What diet and lifestyle changes can I make to protect the vision I have left?
- Should I be referred to a low vision or other specialist
- Can you refer me to training and services that will help me adjust to my loss of vision?
Low vision is characterized by the loss of visual sharpness either when looking at things far away, close up, or both. The visual field may also be reduced. Individual diseases that cause low vision may have additional symptoms.
Vision loss can be gradual or, less often, sudden.
Often people with low vision complain that the normal lighting is not bright enough for them to do see enough to perform routine household tasks. Individuals with low vision have difficulty doing things such as:
- recognizing the faces of people they know well
- performing activities such as sewing, cooking, woodworking, or reading
- matching colors, for example, correctly pairing socks or picking out matching items of clothing
- reading street signs or house numbers.
Diagnosis begins with complete eye examination, which takes about one hour. It begins with an individual health history, family health history, and list of medications currently being taken. The exam tests visual acuity (how well a person sees) and also evaluates eye health. When vision is seriously impaired, a special eye chart (Feinbloom low vision chart) is used to assess visual acuity.
Routine eye examinations are performed by an ophthalmologist who is a medical doctor (M.D.) or a doctor of osteopathy (D.O.) or by optometrist (O. D.). He or she may be assisted by an ophthalmic nurse, ophthalmic assistant, or ophthalmic technician. For conditions such as glaucoma, age-related macular degeneration, or diabetic retinopathy, the patient may be referred to an ophthalmologist who has special training in treating these diseases and others that cause low vision. A patient with cataracts may be referred to a cataract surgeon for evaluation.
Age-related macular degeneration (ARMD) —A chronic, painless eye disease occurring in people over age 50 that damages the macula, or central part of the retina causing irreversible loss of central vision.
Diabetic retinopathy —A condition in people with diabetes in which the blood vessels of the retina leak and cause permanent loss of vision.
Glaucoma —An eye disorder caused by damage to the optic nerve resulting in vision loss. Glaucoma is usually accompanied by inflammation and increased pressure in the eye (intraocular pressure). There are several types that may develop suddenly or gradually.
Histoplasmosis —A fungal infection that can affect the skin, lungs, and eyes.
Retinitis pigmentosa —A group of inherited disorders that affect the rod cells of the retina. Retinitis pigmentosa begins with loss of night vision, followed by gradual loss of peripheral vision, the development of tunnel vision, and finally blindness.
Toxoplasmosis —A parasitic infection acquired from cat feces or undercooked meat that can affect the brain.
Specific diseases that cause low vision may be treated. In some cases deterioration of vision may be slowed or stopped, but low vision, by definition, is permanent and cannot be reversed.
Visual rehabilitation encompasses training by a vision rehabilitation specialist in how to use optical devices that maximize the vision that a person has left.
A mobility and orientation specialist also provides training in the use of devices that assist in mobility and improve the ability to perform activities of daily living. Near aids are devices that assist in seeing close up objects. These include magnifiers, closed-circuit television systems that can be used for reading and writing, and high-magnification computer screens. Devices can be supplemented with low-vision aids such as excellent direct lighting, large-print books, large-number telephones, color-coded pillboxes, and similar items.
An array of telescopic devices are available to help improve distance vision. In addition, special glasses and goggles are designed to address specific deficits such as tunnel vision, loss of peripheral vision, and loss of central vision. Several organizations listed below specialize in the development of low-vision aids.
Low vision cannot be cured. The degree to which it can be slowed depends on the cause. Assistive devices can improve the lives of many people with low vision. Those who are legally blind may qualify for free mobility and orientation training and a service (“seeing eye”) dog.
Prevention depends on the cause of low vision. Many causes of low vision, such as ARMD cannot be prevented.
People with low vision are at higher risk of falling, tripping, and walking into objects. They may need assistance with activities of daily living such as cooking and will be dependent on public transportation or transportation by the care giver. Since most people with low vision have eye disease, the care giver will be responsible for maintaining the correct medication schedule and monitoring any dietary or other restrictions outlined by the individual's physician.
“ABLEDATA: Assistive Technology Research.” National Institute on Disability and Rehabilitation Research, United States Department of Education. Undated [cited April 15, 2008]. http://www.abledata.com.
Haddrill, Marilyn. “TenWarning Signs of Age-Related Eye Problems.” All About Vision. [cited February 16, 2008]. http://www.allaboutvision.com/over60/warning-signs.htm.
Heiting, Gary. “How Your Vision Changes as You Age.” All About Vision. [cited February 16, 2008]. http://www.allaboutvision.com/over60/vision-changes.htm.
“Living with Low Vision.” National Eye Institute. October 2007 [cited April 15, 2008]. http://www.nei.nih.gov//lowvision/content/living.asp.
“Low Vision.” National Institute of Health Senior Health.
April 9, 2007 [cited April 15, 2008]. http://nihse-niorhealth.gov/lowvision/toc.html.
“The Low Vision Gateway” Internet Low Vision Society. Undated [cited April 15, 2008]. http://www.lowvision.org.
“Vision Impairment and Blindness.” MedlinePlus. April 15, 2008 [cited April 15, 2008]. http://www.nlm.nih.gov/medlineplus/visionimpairmentandblindness.html.
American Optometric Association, 243 N. Lindbergh Blvd., St. Louis, MO, 63141, (800) 365-2219, http://www.aao.org.
EyeCare America Foundation of the American Academy of Opthamology, P. O. Box 429098, San Francisco, CA, 94142-9098, (877) 887-6327, (800) 324-EYES (3937), (415) 561-8567, [email protected], http://www.eyecareamerica.org.
National Eye Institute, 2020 Vision Place, Bethesda, MD, 20892-3655, (301) 496-5248, http://www.nei.nih.gov.
Tish Davidson A. M.