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Blindhet kan defineres fysiologisk som en tilstand uten evne til å fange synsintrykk. Den juridiske definisjon av tilstanden er dog mer kompleks. Det komplette fravær av evne til å oppfatte strukturer og lys blir klinisk beskrevet som ingen lyssans, men blindhet imbefatter også delvis visusreduksjon. I Nord-Amerika og det meste av Europa er blindhet i juridisk sans definert som synsstyrke 20/200 (6/60) eller mindre i det best fungerende øye med den best mulig korreksjon mulig. Dette innebærer at et en juridisk blind person 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 synsfelt of less than 20 grader (the norm being 180 grader) 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 redusert syns, possess low vision.

By the 10th Revision of the WHO Den internasjonale statistiske klassifikasjonen av sykdommer og beslektede helseproblemer, low vision is defined as synsstyrke of less than 6/18, but equal to or better than 3/60, or corresponding synsfelt loss to less than 20 grader, in the better eye with best possible correction. Blindhet is defined as synsstyrke of less than 3/60, or corresponding synsfelt loss to less than 10 grader, in the better eye with best possible correction. Redusert syn inkluderer low vision så vel som blindhet.

Årsaker til blindhet

Betydelig nedsatt synsstyrke har en rekke årsaker:

Sykdommer

De fleste tilfeller av redusert syn er forårsaket av sykdom og feilernæring. I følge en et anslag i en rapport fra WHO i 2002, så er det mest vanlige årsakene til blindhet globalt:

Mennesker i utviklingsland er signifikant mer more likely to experience redusert syn 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 redusert syn is most obvious when conducting regional comparisons of cause. Most adult redusert syn 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.

Misdannelser og skader

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

People with injuries to the bakhodelappen i hjernen can, despite having perfectly normal eyes and optic nerves, still be legally or totally blind.

Genetiske defekter

Mennesker som er albino har ofte redusert syn to the extent that many are legally blind, though few of them actually cannot see.

Tilpasningsteknikker

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 banknotes so that the value can be determined by touch. For example:
    • In some currencies, such as the euro and pound sterling, the physical size of a note increases with value.
    • A lot of banknotes from around the world have a tactile feature to indicate denomination in the upper right corner. This tactile feature is a series of raised dots, but it is not standard Braille *.
    • 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.

Redskaper

Watch for the blind2.jpg Designere har utviklet en rekke hjelpeverktøy for blinde mennesker.

Mobilitet

Mennesker med meget redusert syn kan forflytte seg uten hjelp ved hjelp av en hvit stokk, det internasjonale symbolet for blindhet.

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 redusert syn 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.

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.

Lesning og forstørrelse

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 synsstyrke.

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 RNIB in the United Kingdom.

Closed-circuit televisions, equipment that enlarge and contrast textual items, are a more high-tech alternative 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.

Datamaskiner

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, 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 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 seeing with sound project are beginning to provide access to arbitrary live views from a camera.

Andre hjelpemidler

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

Samfunnets holdninger overfor blindhet

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 Dickens provided yet another view of blindhet, wherein those affected by it were ignorant of their surroundings and easily deceived.

The authors of modern educational materials (see: blindhet and education for further reading on that subject), as well as those treating blindhet 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.

Se også

Eksterne lenker

Blindhet | Øyesykdommer

Slepota | Dallineb | Blindheit | Blindness | Ceguera | Blindeco | Cécité | Cecità | עיוורון | Blindheid | 失明 | Ślepota | Cegueira | Sljepilo | Blindness | Sokeus | 失明

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Blindhet".

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