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From Nordan Symposia
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==Origin==
[http://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], from [http://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]
==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
:b : of or relating to sightless persons
*2a : unable or unwilling to [[discern]] or [[judge]] <blind to a lover's faults>
:b : unquestioning <blind [[loyalty]]>
*3a : having no regard to [[rational]] [[discrimination]], [[guidance]], or restriction <blind [[choice]]>
:b : lacking a directing or controlling [[consciousness]] <blind [[chance]]>
:c : drunk 1a
*4a : made or done without sight of certain objects or [[knowledge]] of certain [[facts]] that could serve for [[guidance]] or cause bias <a blind taste test> — compare double-blind, single-blind
:b : having no [[knowledge]] of [[information]] that may cause bias during the course of an [[experiment]] or test <physicians blind to whether the test drug is administered>
*5: defective: as a : lacking a growing point or producing leaves instead of flowers
:b : lacking a complete or legible address <blind mail>
*6a : difficult to [[discern]], make out, or discover
:b : hidden from [[sight]] : covered <blind seam>
*7: having but one opening or outlet <blind sockets>
*8: having no opening for [[light]] or passage : blank <blind wall>
==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]].
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.
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.
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]
[[Category: Health]]
==Origin==
[http://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], from [http://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]
==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
:b : of or relating to sightless persons
*2a : unable or unwilling to [[discern]] or [[judge]] <blind to a lover's faults>
:b : unquestioning <blind [[loyalty]]>
*3a : having no regard to [[rational]] [[discrimination]], [[guidance]], or restriction <blind [[choice]]>
:b : lacking a directing or controlling [[consciousness]] <blind [[chance]]>
:c : drunk 1a
*4a : made or done without sight of certain objects or [[knowledge]] of certain [[facts]] that could serve for [[guidance]] or cause bias <a blind taste test> — compare double-blind, single-blind
:b : having no [[knowledge]] of [[information]] that may cause bias during the course of an [[experiment]] or test <physicians blind to whether the test drug is administered>
*5: defective: as a : lacking a growing point or producing leaves instead of flowers
:b : lacking a complete or legible address <blind mail>
*6a : difficult to [[discern]], make out, or discover
:b : hidden from [[sight]] : covered <blind seam>
*7: having but one opening or outlet <blind sockets>
*8: having no opening for [[light]] or passage : blank <blind wall>
==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]].
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.
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.
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]
[[Category: Health]]
