Blindness

This article is about the visual condition. For the novel, see Blindness (novel).

Blindness can be defined physiologicallyas the condition of lacking visual perception. The definition as it applies to people thus legally classified is, however, more complex. Image:Millais-Blind Girl.jpg

"Blindness" also applies to partial visual impairment: In North Americaand most of Europe, legal blindness is defined as visual acuity(vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet from an object to see it with the same degree of clarity as a normally sighted person could from 200 feet. In many areas, people with average acuity who nonetheless have a visual fieldof less than 20 degrees (the norm being 180 degrees) are also classified as being legally blind.

Approximately ten percent of those deemed legally blind, by any measure, are fully sightless. The rest have some vision, from light perception alone to relatively good acuity. Those who are not legally blind, but nonetheless have serious visual impairments, possess low vision.

By the 10th Revision of the WHOInternational Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 6/18, but equal to or better than 3/60, or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction. Blindness is defined as visual acuity of less than 3/60, or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction. Visual impairment includes low vision as well as blindness.

Causes of blindness

Serious visual impairment has a variety of causes:

Diseases

Most visual impairment is caused by diseaseand malnutrition. According to WHO estimates in 2002, the most common causes of blindness around the world are:

• cataracts(47.8%),
• glaucoma(12.3%),
• age-related macular degeneration(AMD) (8.7%),
• trachoma(3.6%),
• cornealopacity (5.1%), and
• diabetic retinopathy(4.8%), among other causes.

People in developing countries are significantly more likely to experience visual impairment as a consequence of treatable or preventable conditions than are their counterparts in the developed world. While vision impairment is most common in people over age 60 across all regions, children in poorer communities are more likely to be affected by blinding diseases than are their more affluent peers.

The link between povertyand treatable visual impairment is most obvious when conducting regional comparisons of cause. Most adult visual impairment in North America and Western Europe is related to age-related macular degeneration and diabetic retinopathy. While both of these conditions are subject to treatment, neither can be cured.

In developing countries, wherein people have shorter life expectancies, cataracts and water-borne parasites—both of which can be treated effectively—are most often the culprits. Of the estimated 40 million blind people located around the world, 70–80% can have some or all of their sight restored through treatment.

Abnormalities and injuries

Eye injuries, most often occurring in people under 30, are the leading cause of monocular blindness (vision loss in one eye) throughout the United States. Both of these conditions, injuries and cataracts, affect the eye itself. Abnormalities such as optic nerve hypoplasiaaffect the nerve bundle that sends signals from the eye to the back of the brain, which can lead to decreased visual acuity.

People with injuries to the occipital lobeof the braincan, despite having perfectly normal eyes and optic nerves, still be legally or totally blind.

Genetic defects

People with albinismoften suffer from visual impairment to the extent that many are legally blind, though few of them actually cannot see.

Adaptive techniques

Visually impaired and blind people have devised a number of techniques that allow them to complete daily activities using their remaining senses. These might include the following:

• Adaptations of banknotesso that the value can be determined by touch. For example:
  • In some currencies, such as the euroand pound sterling, the physical size of a note increases with value.
  • A lot of banknotesfrom around the world have a tactile feature to indicate denomination in the upper right corner. This tactile featureis a series of raised dots, but it is not standard Braille[1].
  • It is also possible to fold notes in different ways to assist recognition.
• Labeling and tagging clothing and other personal items
• Placing different types of food at different positions on a dinner plate
• Marking oven, dishwasher, and dryer dials for ease of use

Most people, once they have been visually impaired for long enough, devise their own adaptive strategies in all areas of personal and professional management.

Tools

Image:Watch for the blind2.jpg Designers, both visually impaired and sighted, have developed a number of tools for use by blind people.

Mobility

People with serious visual impairments can travel independently using a white cane, the international symbolof blindness.

A long cane is used to extend the user's range of touch sensation, swung in a low sweeping motion across the intended path of travel to detect obstacles. However, some visually impaired persons do not carry these kinds of canes, opting instead for the shorter, lighter identification (ID) cane. Still others require a support cane.

Each of these is painted white for maximum visibility, and to denote visual impairment on the part of the user. In addition to making rules about who can and cannot use a cane, some governments mandate the right-of-waybe given to users of white canes or guide dogs.

A small number of people, about one percent, employ guide dogs. These companions are trained to lead blind individuals around obstacles on the ground and overhead. Though highly intelligent, guide dogs neither interpret street signs nor determine when the team ought to cross a street. Visually impaired people who employ these animals must already be competent travelers.

Reading and magnification

Most blind and visually impaired people read print, either of a regular size or enlarged through the use of magnification devices. A variety of magnifying glasses, some of which are handheld while others rest on desktops, can make reading easier for those with decreased visual acuity.

The rest read Brailleand Moon typeor rely on talking books and readers. They use computers with special hardware such as scanners and refreshable Braille displaysas well as software written specifically for the blind, like optical character recognition applications and screen reading software.

Some people access these materials through agencies for the blind, such as the National Library Service for the Blind and Physically Handicappedin the United States, the National Library for the Blindor the RNIBin the United Kingdom.

Closed-Circuit Televisions, equipment that enlarge and contrast textual items, are a more high-techalternative to traditional magnification devices. So too are modern web browsers, which can increase the size of text on some web pages through browser controls or through user-controlled style sheets.

Computers

Access technology such as Freedom Scientific's JAWS for Windowsscreen reading softwareenable the blind to use mainstream computer applications. Most legally blind people (70% of them across all ages, according to the Lighthouse for the Blind) do not use computers. Only a small fraction of this population, when compared to the sighted community, have Internetaccess. This bleak outlook is changing, however, as availability of assistive technology increases, accompanied by concerted efforts to insure the accessibility of information technology to all potential users, including the blind.

The movement towards greater web accessibilityis opening a far wider number of websites to adaptive technology, making the web a more inviting place for visually impaired surfers.

Experimental approaches such as the seeing with soundproject are beginning to provide access to arbitrary live views from a camera.

Other aids

People may use talking thermometers, enlarged or marked oven dials, talking watches, talking clocks, talking scales, talking calculators, talking compassesand other talking equipment.

Social attitudes towards blindness

Historically, blind and visually impaired people have either been treated as if their lack of sight were an outward manifestation of some internal lack of reason, or as if they possessed extrasensory abilities. Stories such as The Cricket on the Hearth by Charles Dickensprovided yet another view of blindness, wherein those affected by it were ignorant of their surroundings and easily deceived.

The authors of modern educational materials (see: blindness and educationfor further reading on that subject), as well as those treating blindness in literature, have worked to paint a truer picture of blind people as three-dimensional individuals with a range of abilities, talents, and even character flaws. Certain individuals are gifted, and others licentious, but nothing definitive can be said of the blind as a class but that they cannot see well.

See also

• Accessibility
• Amaurosis
• Blind musicians
• Braille
• Color blindness
• Cortical blindness
• International Agency for the Prevention of Blindness- Global Blindness Prevention
• List of blind people
• List of eye diseases
• Low vision
• Night blindness
• Scotoma
• Snow blindness
• Visual loss

External links

• Access Watch: Blind users review accessibility of mainstream software
• ?.Ca: A Comprehensive Directory of Blindness Information
• American Council of the Blind
• American Foundation for the Blind
• Blind Access Journal: Visual impairment in the real world
• VISION 2020: The Right to Sight
• International Agency for the Prevention of Blindness (IAPB)
• International Braille Research Center
• Literature Bibliography and Resources List
• National Braille Press
• National Federation of the Blind: Civil rights and consumer advocacy
• National Library for the Blind
• National Library Service for the Blind and Physically Handicapped
• Recording for the Blind and Dyslexic
• Royal National Institute for the Blind
• Scottish Sensory Centre
• WHO Fact Sheet on Visual Impairmentcs:Slepota

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This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Blindness Wikipedia article Blindness.