Changes

==Origin==

==Origin==

[https://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], from [https://nordan.daynal.org/wiki/index.php?title=English#ca._600-1100.09THE_OLD_ENGLISH.2C_OR_ANGLO-SAXON_PERIOD Old English]; akin to Old High German blint blind, Old English blandan to mix  

[https://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], from [https://nordan.daynal.org/wiki/index.php?title=English#ca._600-1100.09THE_OLD_ENGLISH.2C_OR_ANGLO-SAXON_PERIOD Old English]; akin to Old High German blint blind, Old English blandan to mix  

*[http://en.wikipedia.org/wiki/12th_century before 12th Century]

*[https://en.wikipedia.org/wiki/12th_century before 12th Century]

==Definitions==

==Definitions==

*1a (1) : sightless (2) : having less than 1⁄10 of normal [[vision]] in the more [[efficient]] eye when refractive defects are fully corrected by lenses  

*1a (1) : sightless (2) : having less than 1⁄10 of normal [[vision]] in the more [[efficient]] eye when refractive defects are fully corrected by lenses  

*8: having no opening for [[light]] or passage : blank <blind wall>  

*8: having no opening for [[light]] or passage : blank <blind wall>  

==Description==

==Description==

'''Blindness''' is the condition of lacking [[visual]] [[perception]] due to [http://en.wikipedia.org/wiki/Physiology physiological] or [http://en.wikipedia.org/wiki/Neurology neurological] [[factors]].

'''Blindness''' is the condition of lacking [[visual]] [[perception]] due to [https://en.wikipedia.org/wiki/Physiology physiological] or [https://en.wikipedia.org/wiki/Neurology neurological] [[factors]].

Various [[scale]]s have been [[developed]] to describe the extent of [[vision]] loss and define blindness. Total blindness is the complete lack of [[form]] and [[visual]] light [[perception]] and is clinically recorded as NLP, an abbreviation for "no light perception." Blindness is frequently used to describe severe visual impairment with residual [[vision]]. Those described as having only [[light]] [[perception]] have no more sight than the [[ability]] to tell light from [[dark]] and the general direction of a [[light]] [[source]].

Various [[scale]]s have been [[developed]] to describe the extent of [[vision]] loss and define blindness. Total blindness is the complete lack of [[form]] and [[visual]] light [[perception]] and is clinically recorded as NLP, an abbreviation for "no light perception." Blindness is frequently used to describe severe visual impairment with residual [[vision]]. Those described as having only [[light]] [[perception]] have no more sight than the [[ability]] to tell light from [[dark]] and the general direction of a [[light]] [[source]].

In order to determine which people may need special [[assistance]] because of their visual disabilities, various governmental [[jurisdictions]] have formulated more [[complex]] definitions referred to as legal blindness. In North America and 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 (6.1 m) from an object to see it—with corrective lenses—with the same [[degree]] of [[clarity]] as a normally sighted person could from 200 feet (61 m). 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]], have no [[vision]]. The rest have some vision, from [[light]] [[perception]] alone to relatively good acuity. Low [[vision]] is sometimes used to describe visual acuities from 20/70 to 20/200.

In order to determine which people may need special [[assistance]] because of their visual disabilities, various governmental [[jurisdictions]] have formulated more [[complex]] definitions referred to as legal blindness. In North America and 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 (6.1 m) from an object to see it—with corrective lenses—with the same [[degree]] of [[clarity]] as a normally sighted person could from 200 feet (61 m). 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]], have no [[vision]]. The rest have some vision, from [[light]] [[perception]] alone to relatively good acuity. Low [[vision]] is sometimes used to describe visual acuities from 20/70 to 20/200.

By the 10th Revision of the [http://en.wikipedia.org/wiki/World_Health_Organization WHO] International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 20/60 (6/18), but equal to or better than 20/200 (6/60), 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 20/400 (6/120), or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.

By the 10th Revision of the [https://en.wikipedia.org/wiki/World_Health_Organization WHO] International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 20/60 (6/18), but equal to or better than 20/200 (6/60), 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 20/400 (6/120), or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.

Blind people with undamaged eyes may still register light non-visually for the [[purpose]] of [http://en.wikipedia.org/wiki/Circadian_rhythm circadian entrainment] to the 24-hour light/dark cycle. Light signals for this [[purpose]] travel through the retinohypothalamic tract, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.[http://en.wikipedia.org/wiki/Blindness]

Blind people with undamaged eyes may still register light non-visually for the [[purpose]] of [https://en.wikipedia.org/wiki/Circadian_rhythm circadian entrainment] to the 24-hour light/dark cycle. Light signals for this [[purpose]] travel through the retinohypothalamic tract, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.[https://en.wikipedia.org/wiki/Blindness]

==See also==

==See also==

*'''''[[Deafness]]'''''

*'''''[[Deafness]]'''''

[[Category: Health]]

[[Category: Health]]