Blindness: Difference between revisions

Revision as of 15:28, 5 July 2005

Revision as of 21:41, 14 July 2005

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'''Blindness''' can be defined [[physiological]]ly as the condition of lacking [[visual perception]]. The definition as it applies to people thus legally classified is, however, more complex.

The term "blindness" also applies to partial visual impairment: In [[North America]] and most of [[Europe]], legal blindness is defined as vision of 20/200 (6/60) or less in the better eye with correction. 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 field of 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 actuallyfully 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 WHO International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less then 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.

By the 10th Revision of the [[World Health Organization|WHO]] International Statistical Classification of Diseases, Injuries and Causes of Death, ''low vision'' is defined as visual acuity of less then 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.

Approximately ten percent of those deemed legally blind, by any measure, are actually 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]].

==Causes of blindness==

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===Diseases===

Most visual impairment is caused by [[disease]] and [[malnutrition:]]. TheAccording to WHO estimates in 2002, the most common causes of blindness around the world are :
*[[cataract]]s (47.8% in 2002, according to WHO),
*[[Glaucomaglaucoma]] (12.3%), Age
*age-related [[Macularmacular degeneration]] (AMD) (8.7%),
*[[Trachomatrachoma]] (3.6%), Corneal
*[[cornea]]l Opacityopacity (5.1%), and
*[[Diabeticdiabetic 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 [[poverty]] and 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 [[Macularmacular degeneration]] and [[Diabeticdiabetic 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 [[Opticoptic nerve hypoplasia]] affect the nerve bundle that sends signals from the eye to the back of the brain, andwhich can lead to decreased visual acuity.

People with injuries to the [[occipital lobe]] of the [[brain]] can, despite having perfectly normal eyes and [[optic nerve]]s, still be legally or totally blind.

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===Genetic defects===

People with [[Albinismalbinism]] often suffer from visually impairment to the extent that many are legally blind, though few of them are actually sightless.

==Alternative techniques==

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===Mobility===

People with serious visual impairments can travel independently using a [[white cane]], the [[international symbols|international symbol]] of blindness.

A long cane is used to extend the user's range of touch sensation, beingswung 'swept'in backa andlow forthsweeping motion across the intended path of travel to detect obstacles. SomeHowever, some visually impaired peoplepersons do not carry these kinds of canes, however; 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-way]] be given to users of white canes or [[guide dogs]].

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===Reading and magnification===

Most blind and visually impaired people read print, either of a regular size or enlarged through the use of magnification devices. TheA restvariety readof [[Braille]] and [[Moonmagnifying typeglass]]es, orsome relyof onwhich talkingare bookshandheld andwhile readers.others rest Theyon usedesktops, computerscan withmake specialreading hardware such as scanners and refreshable [[Braille]] displays as well as software written specificallyeasier for thethose blindwith likedecreased optical character recognition applications and screen readingvisual softwareacuity.

The rest read [[Braille]] and [[Moon type]] or rely on talking books and readers. They use computers with special hardware such as scanners and refreshable Braille displays as 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 Handicapped in the United States, the [[National Library for the Blind]] or the [[Royal National Institute for the Blind|RNIB]] in the United Kingdom.

Some people access these materials through agencies for the blind, such as the [[National Library Service for the Blind and Physically Handicapped]] in the United States, the [[National Library for the Blind]] or the [[Royal National Institute for the Blind|RNIB]] in the United Kingdom.

A variety of [[magnifying glass]]es, some of which are hand-held while others rest on desktops, can make reading easier for those with decreased visual acuity.

[[Closed-Circuit Television]]s - pieces of, equipment that enlarge and contrast textual items -, are a more [[high-tech]] alternative to traditional magnification devices. So too are modern [[web browser]]s, which can increase the size of text on some web pages through browser controls or through user-controlled [[style sheet]]s.

===Computers===

Access technology such as Freedom Scientific's JAWS for Windows screen reading software enable 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 [[internet]] access. This bleak outlook is changing, thankshowever, to theas 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 accessibility]] is 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 [[seeingwithsound|seeing with sound]]

project are beginning to provide access to arbitrary live views from a [[camera]].

===Other aids===

People may use [[talking [[thermometer]]s, enlarged or marked oven dials, talking watches, talking clocks, talking [[weighing scale|scales]], talking calculators[[calculator]]s, talking compasses[[compass]]es and 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 extra-sensoryextrasensory abilities. Stories such as ''The Cricket on the Hearth'' (by [[Charles Dickens)]] provided 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 education]] for 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.