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#REDIRECT [[Visual impairment]]
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'''Blindness''' is the condition of poor [[visual perception]].

Various scales have been developed to describe the extent of [[vision loss]] and define blindness.<ref name="ICO">International Council of Ophthalmology. [http://www.icoph.org/pdf/visualstandardsreport.pdf "International Standards: Visual Standards — Aspects and Ranges of Vision Loss with Emphasis on Population Surveys."] April 2002.</ref> Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for "no light perception."<ref name="ICO"/> Blindness is frequently used to describe severe [[visual impairment]] with some remaining 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]]. The [[World Health Organization]] defines ''low vision'' as visual acuity of less than 20/60 (6/18), but equal to or better than 20/200 (6/60), or 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 a visual field loss to less than 10 degrees, in the better eye with best possible correction.<ref>http://www3.who.int/icd/currentversion/fr-icd.htm</ref><ref name=WHO2013>{{cite web| title = Visual impairment and blindness Fact Sheet N°282| publisher = [[World Health Organization]]| date=October 2013| url = http://www.who.int/mediacentre/factsheets/fs282/en/index.html| accessdate=4 May 2014}}</ref>

<!-- Epidemiology -->
As of 2012 there were 285 million visually impaired people in the world, of which 246 million had low vision and 39 million were blind.<ref name=WHO2013/> The majority of people with poor vision are in the [[developing world]] and are over the age of 50 years.<ref name=WHO2013/>

{{TOC limit|3}}
==Signs and symptoms==<!--"Legally-blind" redirects to this section-->
Blindness is defined by the [[World Health Organization]] as vision in a person's best eye of less than 20/500 or a [[visual field]] of less than 10 degrees.<ref>{{cite journal|last=Maberley|first=DA|author2=Hollands, H|author3=Chuo, J|author4=Tam, G|author5=Konkal, J|author6=Roesch, M|author7=Veselinovic, A|author8=Witzigmann, M|author9=Bassett, K|title=The prevalence of low vision and blindness in Canada.|journal=Eye (London, England)|date=March 2006|volume=20|issue=3|pages=341–6|pmid=15905873|doi=10.1038/sj.eye.6701879}}</ref> This definition was set in 1972, and there is ongoing discussion as to whether it should be altered somewhat.<ref>http://www.who.int/blindness/Change%20the%20Definition%20of%20Blindness.pdf</ref>

Blind people with undamaged eyes may still register light non-visually for the purpose of [[Circadian rhythm|circadian]] [[Entrainment (chronobiology)|entrainment]] to the 24-hour light/dark cycle. Light signals for this purpose travel through the [[retinohypothalamic tract]] and are not affected by optic nerve damage beyond where the retinohypothalamic tract exits.

===United States===
In 1934, the [[American Medical Association]] adopted the following definition of blindness: <blockquote>
"Central visual acuity of 20/200 or less in the better eye with corrective glasses or central visual acuity of more than 20/200 if there is a visual field defect in which the peripheral field is contracted to such an extent that the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye."<ref name="Koestler">Koestler, F. A., (1976). ''The unseen minority: a social history of blindness in the United States.'' New York: David McKay.</ref>
</blockquote>

The [[United States Congress]] included this definition as part of the Aid to the Blind program in the [[Social Security (United States)#Creation: The Social Security Act|Social Security Act]] passed in 1935.<ref name="Koestler"/><ref name="Corn">Corn, AL; Spungin, SJ. [http://www.coe.ufl.edu/copsse/docs/IB-10/1/IB-10.pdf "Free and Appropriate Public Education and the Personnel Crisis for Students with Visual Impairments and Blindness."] Center on Personnel Studies in Special Education. April 2003.</ref> In 1972, the Aid to the Blind program and two others combined under Title XVI of the Social Security Act to form the [[Supplemental Security Income]] program<ref>http://www.ssa.gov/history/pdf/80chap12.pdf</ref> which currently states: <blockquote>
"An individual shall be considered to be blind for purposes of this title if he has central visual acuity of 20/200 or less in the better eye with the use of a correcting lens. An eye which is accompanied by a limitation in the fields of vision such that the widest diameter of the visual field subtends an angle no greater than 20 degrees shall be considered for purposes of the first sentence of this subsection as having a central visual acuity of 20/200 or less. An individual shall also be considered to be blind for purposes of this title if he is blind as defined under a State plan approved under title X or XVI as in effect for October 1972 and received aid under such plan (on the basis of blindness) for December 1973, so long as he is continuously blind as so defined."<ref>Social Security Act. [http://www.ssa.gov/OP_Home/ssact/title16b/1614.htm "Sec. 1614. Meaning of terms."] Retrieved 17 February 2006.</ref>
</blockquote>

===United Kingdom===
In the [[UK]], the Certificate of Vision Impairment (CVI) is used to certify patients as severely sight impaired or sight impaired.<ref>[http://www.dh.gov.uk/en/Healthcare/Primarycare/Optical/DH_4074843 "Identification and notification of sight loss"]</ref> The accompanying guidance for clinical staff states: "The National Assistance Act 1948 states that a person can be certified as severely sight impaired if they are “so blind as to be unable to perform any work for which eye sight is essential” (National Assistance Act Section 64(1)). The test is whether a person cannot do any work for which eyesight is essential, not just his or her normal job or one particular job."<ref name="dh.gov.uk">[http://www.dh.gov.uk/prod_consum_dh/groups/dh_digitalassets/documents/digitalasset/dh_078294.pdf "Certificate of Vision Impairment: Explanatory Notes for Consultant Ophthalmologists and Hospital Eye Clinic Staff"]</ref>

In practice, the definition depends on individuals' [[visual acuity]] and the extent to which their [[field of vision]] is restricted. The [[Department of Health]] identifies three groups of people who may be classified as severely visually impaired.<ref name="dh.gov.uk"/>
#Those below 3/60 (equivalent to 20/400 in US notation) [[Snellen]] (most people below 3/60 are severely sight impaired),
#Those better than 3/60 but below 6/60 Snellen (people who have a very contracted field of vision only),
#Those 6/60 Snellen or above (people in this group who have a contracted [[field of vision]] especially if the contraction is in the lower part of the field),

The Department of Health also state that a person is more likely to be classified as severely visually impaired if their eyesight has failed recently or if they are an older individual, both groups being perceived as less able to adapt to their vision loss.<ref name="dh.gov.uk"/>

===Other===
[[Kuwait]] is one of many nations that share the 6/60 criteria for legal blindness.<ref name="Al-Merjan">{{cite journal | last1 = Al-Merjan | first1 = JI | last2 = Pandova | first2 = MG |last3 = Al-Ghanim | first3 = M | last4 = Al-Wayel | first4 = A | last5 = Al-Mutairi | first5 = S |title = Registered blindness and low vision in Kuwait | journal = Ophthalmic epidemiology | volume = 12 | issue = 4 | pages = 251–7 | year = 2005 | pmid = 16033746 | doi = 10.1080/09286580591005813}}</ref>

===Comorbidities===
{{expand section|date=June 2012}}
Blindness can occur in combination with such conditions as [[intellectual disability]], [[autism spectrum disorders]], [[cerebral palsy]], [[hearing impairment]]s, and [[epilepsy]].<ref name="lighthouse">{{cite web|url=http://www.lighthouse.org/about-low-vision-blindness/causes-of-blindness/|title=Causes of Blindness|publisher=Lighthouse International|accessdate=27 May 2010}}</ref><ref name="autism">{{cite web|url=http://www.ncecbvi.org/autism.htm|title=Autism and Blindness|publisher=Nerbraska Center for the Education of Children who are Blind or Visually Impaired|accessdate=27 May 2010}}</ref> In a study of 228 visually impaired children in [[Atlanta metropolitan area|metropolitan Atlanta]] between 1991 and 1993, 154 (68%) had an additional disability besides visual impairment.<ref name="lighthouse"/> Blindness in combination with hearing loss is known as [[deafblindness]].

It has been estimated that over half of totally blind people have [[non-24-hour sleep–wake disorder]], a condition in which a person's [[circadian rhythm]], normally slightly longer than 24 hours, is not [[Entrainment (chronobiology)|entrained]] (re-set) to the light/dark cycle.<ref name="AASM2008">{{cite web |url=http://www.aasmnet.org/resources/factsheets/crsd.pdf |title=Circadian Rhythm Sleep Disorder |accessdate=2009-08-08 |year=2008 |format=PDF |publisher=American Academy of Sleep Medicine}}</ref><ref>{{cite journal |author=Sack RL, Lewy AJ, Blood ML, Keith LD, Nakagawa H |title=Circadian rhythm abnormalities in totally blind people: incidence and clinical significance |journal=J. Clin. Endocrinol. Metab. |volume=75 |issue=1 |pages=127–34 |date=July 1992 |pmid=1619000 |url=http://jcem.endojournals.org/cgi/pmidlookup?view=long&pmid=1619000 |doi=10.1210/jc.75.1.127}}</ref>

==Causes==
[[File:Caoguia2006.jpg|thumb|A blind man is assisted by a [[guide dog]] in Brasília, Brazil.]]
Serious [[visual impairment]] has a variety of causes:

===Diseases===
According to [[World Health Organization|WHO]] estimates, the most common causes of blindness (excluding [[refractive error]]) around the world in 2002 were:
#[[cataract]]s (47.9%),
#[[glaucoma]] (12.3%),
#age-related [[macular degeneration]] (8.7%),
#[[corneal opacification]] (5.1%), and
#[[diabetic retinopathy]] (4.8%),
#[[childhood blindness]] (3.9%)(according to the WHO, sufficient data for precise description is not available,<ref>{{cite journal|year=1993|last1=Gilbert|first1=C|last2=Foster|first2=A|last3=Négrel|first3=AD|last4=Thylefors|first4=B|title=Childhood blindness: A new form for recording causes of visual loss in children|volume=71|issue=5|pages=485–489|journal=Bulletin of the World Health Organization|pmid=8261552|pmc=2393473}}</ref>)
#[[trachoma]] (3.6%)
#[[onchocerciasis]] (0.8%).<ref>{{cite web|url=http://www.who.int/blindness/causes/en/|title=Causes of blindness and visual impairment|publisher=[[World Health Organization]]|accessdate=19 February 2009}}</ref>

====Developing countries====
In terms of the worldwide prevalence of blindness, it is present on a much greater scale in developing world countries than in developed world countries. According to numbers from the WHO, 90% of blind people live in the developing world.<ref name=WHO2013/> Of these, cataract is responsible for 65%> or more than 22 million cases of blindness and glaucoma is responsible for 6 million cases, while leprosy and onchocerciasis each blind approximately 1 million individuals worldwide.

The number of individuals blind from trachoma has dropped dramatically in the past 10 years from 6 million to 1.3 million, putting it in seventh place on the list of causes of blindness worldwide. Xerophthalmia is estimated to affect 5 million children each year; 500,000 develop active corneal involvement, and half of these go blind. Central corneal ulceration is also a significant cause of monocular blindness worldwide, accounting for an estimated 850,000 cases of corneal blindness every year in the Indian subcontinent alone. As a result, corneal scarring from all causes now is the fourth greatest cause of global blindness. (Vaughan & Asbury's General Ophthalmology, 17e)

[[File:68-4062-1 (ATED).jpg|thumb|The burden of [[onchocerciasis]]: children leading blind adults in Africa]]
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.

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 (see [[Onchocerciasis|river blindness]], for example). Of the estimated 40 million blind people located around the world, 70–80% can have some or all of their sight restored through treatment.{{Citation needed|date=March 2011}}

====Developed countries====
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 [[macular degeneration]] and [[diabetic retinopathy]]. While both of these conditions are subject to treatment, neither can be cured.

In developed countries where parasitic diseases are less common and [[cataract surgery]] is more available, age-related macular degeneration, glaucoma, and diabetic retinopathy are usually the leading causes of blindness.<ref name="Bunce">{{cite journal | last1 = Bunce | first1 = C | last2 = Wormald | first2 = R | title = Leading causes of certification for blindness and partial sight in England & Wales | journal = BMC Public Health | volume = 6 | page = 58 | year = 2006 | pmid = 16524463 | pmc = 1420283 | doi = 10.1186/1471-2458-6-58 }}</ref>

===Pregnancy-related===
Childhood blindness can be caused by conditions related to pregnancy, such as [[congenital rubella syndrome]] and [[retinopathy of prematurity]].

===Abnormalities and other injuries===
[[File:Re-educating wounded. Blind French soldiers learning to make baskets. American Red Cross., 1917 - 1919 - NARA - 533674.tif|thumb|Re-educating wounded. Blind French soldiers learning to make baskets, World War I.]]
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]]. Injuries and cataracts affect the eye itself, while abnormalities such as [[optic nerve hypoplasia]] affect the nerve bundle that sends signals from the eye to the back of the brain, which can lead to decreased visual acuity.

[[Cortical blindness]] results from injuries to the [[occipital lobe]] of the [[Human brain|brain]] that prevent the brain from correctly receiving or interpreting signals from the [[optic nerve]]. Symptoms of cortical blindness vary greatly across individuals and may be more severe in periods of exhaustion or stress. It is common for people with cortical blindness to have poorer vision later in the day.

===Genetic defects===
People with [[albinism]] often have vision loss to the extent that many are legally blind, though few of them actually cannot see. [[Leber's congenital amaurosis]] can cause total blindness or severe sight loss from birth or early childhood.

Recent advances in [[genetic map|mapping]] of the [[human genome]] have identified other genetic causes of [[low vision]] or blindness. One such example is [[Bardet-Biedl syndrome]].

===Poisoning===
Rarely, blindness is caused by the intake of certain chemicals. A well-known example is [[methanol]], which is only mildly toxic and minimally intoxicating, and breaks down into the substances [[formaldehyde]] and [[formic acid]] which in turn can cause blindness, an array of other health complications, and death.<ref name="Methanol">{{cite web
| title = Methanol
| work = Symptoms of Methanol Poisoning
| publisher = Canada Safety Council
| year = 2005
| url = http://www.safety-council.org/info/OSH/methanol.htm
| doi =
| accessdate=27 March 2007 |archiveurl = http://web.archive.org/web/20070220004549/http://www.safety-council.org/info/OSH/methanol.htm <!-- Bot retrieved archive --> |archivedate = 20 February 2007}}</ref> When competing with [[ethanol]] for metabolism, ethanol is metabolized first, and the onset of toxisity is delayed. Methanol is commonly found in [[methylated spirits]], [[Denatured alcohol|denatured ethyl alcohol]], to avoid paying taxes on selling ethanol intended for human consumption. Methylated spirits are sometimes used by [[Alcoholism|alcoholics]] as a desperate and cheap substitute for regular ethanol [[alcoholic beverages]].

===Willful actions===
Blinding has been used as an act of vengeance and [[torture]] in some instances, to deprive a person of a major sense by which they can navigate or interact within the world, act fully independently, and be aware of events surrounding them. An example from the classical realm is [[Oedipus]], who gouges out his own eyes after realizing that he fulfilled the awful prophecy spoken of him. Having crushed the Bulgarians, the Byzantine Emperor [[Basil II]] blinded as many as 15,000 prisoners taken in the battle, before releasing them.<ref>Finlay, George (1856). ''History of the Byzantine Empire from DCCXVI to MLVII'', 2nd Edition, Published by W. Blackwood, p. 444–445.</ref>

In 2003, a Pakistani anti-terrorism court sentenced a man to be blinded after he carried out an acid attack against his fiancee that resulted in her blinding.<ref>{{Cite news|title=Eye-for-eye in Pakistan acid case|url=http://news.bbc.co.uk/2/hi/south_asia/3313207.stm|publisher=BBC News|date=12 December 2003|accessdate=2008-06-30}}</ref> The same sentence was given in 2009 for the man who blinded [[Ameneh Bahrami]].

==Management==
[[File:Tommy Edison blind cooking.jpg|thumb|Tommy Edison, a blind film critic, demonstrates for his viewers how a blind person can cook alone.]]

===Mobility===
[[File:Long cane folded.jpg|thumb|Folded long cane]]
Many people with serious visual impairments can travel independently, using a wide range of tools and techniques. Orientation and mobility specialists are professionals who are specifically trained to teach people with visual impairments how to travel safely, confidently, and independently in the home and the community. These professionals can also help blind people to practice travelling on specific routes which they may use often, such as the route from one's house to a convenience store. Becoming familiar with an environment or route can make it much easier for a blind person to navigate successfully.

Tools such as the [[white cane]] with a red tip - the [[international symbols|international symbol]] of blindness - may also be used to improve mobility. A long cane is used to extend the user's range of touch sensation. It is usually swung in a low sweeping motion, across the intended path of travel, to detect obstacles. However, techniques for cane travel can vary depending on the user and/or the situation. 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. The choice depends on the individual's vision, motivation, and other factors.

A small number of people employ [[guide dog]]s to assist in mobility. These dogs are trained to navigate around various obstacles, and to indicate when it becomes necessary to go up or down a step. However, the helpfulness of guide dogs is limited by the inability of dogs to understand complex directions. The human half of the guide dog team does the directing, based upon skills acquired through previous mobility training. In this sense, the handler might be likened to an aircraft's navigator, who must know how to get from one place to another, and the dog to the pilot, who gets them there safely.

[[GPS for the visually impaired|GPS devices]] can also be used as a mobility aid. Such software can assist blind people with orientation and navigation, but it is not a replacement for traditional mobility tools such as white canes and guide dogs.

Some blind people are skilled at [[human echolocation|echolocating]] silent objects simply by producing mouth clicks and listening to the returning echoes. It has been shown that blind echolocation experts use what is normally the "visual" part of their brain to process the echoes.<ref name=Thaler2011>{{cite journal |journal=PLoS ONE |year=2011 |volume=6 |issue=5 |pages=e20162 |title= Neural correlates of natural human echolocation in early and late blind echolocation experts |author=Thaler L, Arnott SR, Goodale MA. |doi=10.1371/journal.pone.0020162 |pmid=21633496|bibcode = 2011PLoSO...6E0162T |pmc=3102086}}</ref><ref name="Reader">{{citation
| title = Bat Man
| publisher = Reader's Digest
| date= June 2012
|url=http://www.uwo.ca/bmi/news/bmi_news/bat_man.html
|accessdate=14 March 2014}}</ref>

Technology to allow blind people to drive motor vehicles is currently being developed.<ref>{{cite news|url=http://www.boston.com/business/technology/articles/2011/01/28/blind_driver_to_debut_new_technologies_at_daytona/?page=full|title=Blind driver to debut new technologies at Daytona|agency=Associated Press|date=28 January 2011|accessdate=27 October 2012}}</ref>

Government actions are sometimes taken to make public places more accessible to blind people. Public transportation is freely available to the blind in many cities. [[Tactile paving]] and [[Pedestrian crossing#enhancements for disabled people|audible traffic signals]] can make it easier and safer for visually impaired pedestrians to cross streets. In addition to making rules about who can and cannot use a cane, some governments mandate the [[Priority (right of way)|right-of-way]] be given to users of white canes or guide dogs.

===Reading and magnification===
[[File:Watch for the blind2.jpg|thumb|[[Braille watch]]]]
Most visually impaired people who are not totally blind read print, either of a regular size or enlarged by magnification devices. Many also read [[large-print]], which is easier for them to read without such devices. A variety of [[magnifying glass]]es, some handheld, and some on desktops, can make reading easier for them.

Others read [[Braille]] (or the infrequently used [[Moon type]]), or rely on [[audiobook|talking books]] and readers or [[reading machine]]s, which convert printed text to speech or [[Braille]]. They use computers with special hardware such as [[image scanner|scanners]] and [[refreshable Braille display]]s as well as software written specifically for the blind, such as [[optical character recognition]] applications and [[screen reader]]s.

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.

[[Closed-circuit television]]s, equipment that enlarges and contrasts textual items, are a more [[high-tech]] alternative to traditional magnification devices.

There are also over 100 [[radio reading service]]s throughout the world that provide people with vision impairments with readings from periodicals over the radio. The International Association of Audio Information Services provides links to all of these organizations.

===Computers===
Access technology such as [[screen reader]]s, [[screen magnifier]]s and [[refreshable Braille display]]s enable the blind to use mainstream computer applications and [[mobile phone]]s. The availability of assistive technology is increasing, accompanied by concerted efforts to ensure the accessibility of information technology to all potential users, including the blind. Later versions of [[Microsoft Windows]] include an Accessibility Wizard & Magnifier for those with partial vision, and [[Microsoft Narrator]], a simple screen reader. [[Linux distribution]]s (as [[live CD]]s) for the blind include [[Oralux]] and [[Adriane Knoppix]], the latter developed in part by [[Klaus Knopper|Adriane Knopper]] who has a visual impairment. Mac OS also comes with a built-in screen reader, called [[VoiceOver]].

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 in [[sensory substitution]] are beginning to provide access to arbitrary live views from a [[camera]].

Modified visual output that includes large print and/or clear simple graphics can be of benefit to users with some residual vision.<ref name="dynamicdiversity">Gregor, P., Newell, A.F., Zajicek, M. (2002). Designing for Dynamic Diversity – interfaces for older people. Proceedings of the fifth international ACM conference on Assistive technologies. Edinburgh, Scotland. Session: Solutions for aging. Pages 151–156.</ref>

===Other aids and techniques===
[[File:Banknote feature.JPG|right|thumb|A [[Canadian currency tactile feature|tactile feature]] on a [[Banknotes of the Canadian dollar|Canadian banknote]]]]
Blind people may use talking equipment such as [[thermometer]]s, watches, clocks, [[weighing scale|scales]], [[calculator]]s, and [[compass]]es. They may also enlarge or mark dials on devices such as ovens and thermostats to make them usable. Other techniques used by blind people to assist them in daily activities include:

*Adaptations of [[coin]]s and [[banknote]]s so that the value can be determined by touch. For example:
** In some currencies, such as the [[euro]], the [[pound sterling]] and the [[Indian rupee]], the size of a note increases with its value.
** On US coins, pennies and dimes, and nickels and quarters are similar in size. The larger denominations (dimes and quarters) have ridges along the sides (historically used to prevent the "shaving" of precious metals from the coins), which can now be used for identification.
** Some currencies' [[banknotes]] have a tactile feature to indicate denomination. For example, the [[Canadian currency tactile feature]] is a system of raised dots in one corner, based on Braille cells but not standard [[Braille]].<ref>[http://www.bankofcanada.ca/en/banknotes/accessibility.html Accessibility features - Bank Notes - Bank of Canada]{{dead link|date=July 2012}}</ref>
** 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 controls of household appliances

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

==Epidemiology==
The [[World Health Organization|WHO]] estimates that in 2012 there were 285 million visually impaired people in the world, of which 246 million had low vision and 39 million were blind.<ref name=WHO2013/> In order of frequency the leading causes were uncorrected [[refractive errors]] ([[near sighted]], [[far sighted]], or an [[astigmatism]]), [[cataract]], and [[glaucoma]].<ref name=WHO2013/>

In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness.<ref name="Kirchner">Kirchner, C., Stephen, G. & Chandu, F. (1987). "Estimated 1987 prevalence of non-institutionalized 'severe visual impairment' by age base on 1977 estimated rates: U. S.", 1987. ''AER Yearbook.''</ref> Of this number, 58% were over the age of 65.<ref name="Kirchner"/> In 1994-1995, 1.3 million Americans reported legal blindness.<ref name="AFB">[http://www.afb.org/Section.asp?SectionID=15&DocumentID=1367#prev "Statistics and Sources for Professionals." American Foundation for the Blind]</ref>

==Society and culture==
===Legal definition===
To determine which people qualify for special assistance because of their visual disabilities, various governments have specific definitions for legal blindness.<ref name="ssdiqualify.org">{{cite web |title=Defining the Boundaries of Low Vision Patients |url=http://www.ssdiqualify.org/defining-boundaries-low-vision-patients/ |publisher=SSDI Qualify|accessdate=January 22, 2014}}</ref> 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 {{convert|20|ft|m}} from an object to see it—with [[corrective lens]]es—with the same degree of clarity as a normally sighted person could from {{convert|200|ft|m}}. In many areas, people with average acuity who nonetheless have a [[visual field]] of less than 20 [[degree (angle)|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.<ref>{{cite web|url=http://www.afb.org/Section.asp?SectionID=26&TopicID=144 |title=Living with Low Vision |publisher=American Foundation for the Blind|accessdate=2012-07-18}}</ref>

===Literature and art===
{{see also|Blindness in literature}}

====Antiquity====
The [[Moche (culture)|Moche]] people of ancient [[Peru]] depicted the blind in their ceramics.<ref>Berrin, Katherine & Larco Museum. ''The Spirit of Ancient Peru:Treasures from the [[Larco Museum|Museo Arqueológico Rafael Larco Herrera]].'' New York: [[Thames and Hudson]], 1997.</ref>

In Greek myth, [[Tiresias]] was a prophet famous for his [[clairvoyance]]. According to one myth, he was blinded by the Gods as punishment for revealing their secrets, while another holds that he was blinded as punishment after he saw Athena naked while she was bathing. In [[the Odyssey]], the one-eyed Cyclops [[Polyphemus]] captures [[Odysseus]], who blinds Polyphemus to escape. In Norse mythology, [[Loki]] tricks the blind God [[Höðr]] into killing his brother [[Baldr]], the God of happiness.

The [[New Testament]] contains numerous instances of [[Miracles of Jesus|Jesus performing miracles]] to heal the blind. According to the Gospels, Jesus healed [[Healing the two blind men in Galilee|the two blind men of Galilee]], [[Blind man of Bethsaida|the blind man of Bethsaida]], [[Healing the blind near Jericho|the blind man of Jericho]] and [[Healing the blind at birth|the man who was born blind]].

The parable of the [[blind men and an elephant]] has crossed between many religious traditions and is part of [[Jainism|Jain]], [[Buddhist]], [[Sufi]] and [[Hindu]] lore. In various versions of the tale, a group of blind men (or men in the dark) touch an [[elephant]] to learn what it is like. Each one feels a different part, but only one part, such as the side or the tusk. They then compare notes and learn that they are in complete disagreement.

"[[Three Blind Mice]]" is a medieval [[English language|English]] [[nursery rhyme]] about three blind mice whose tails are cut off after chasing the farmer's wife. The work is explicitly incongruous, ending with the comment ''Did you ever see such a sight in your life, As three blind mice?''

====Modern times====
[[File:Velázquez Blind woman.jpg|upright|thumb|''Blind Woman'' by [[Diego Velázquez]]]]
[[File:José de Ribera 018.jpg|upright|thumb|''The Sense of Touch'' by [[Jusepe de Ribera]] depicts a blind man holding a marble head in his hands.]]
Poet [[John Milton]], who went blind in mid-life, composed [[On His Blindness]], a sonnet about coping with blindness. The work posits that ''[those] who best Bear [God]'s mild yoke, they serve him best.''

The Dutch painter and engraver [[Rembrandt]] often depicted scenes from the apocryphal [[Book of Tobit]], which tells the story of a blind patriarch who is healed by his son, Tobias, with the help of the archangel [[Raphael (archangel)|Raphael]].<ref>[[Julius Held]], ''Rembrandt and the Book of Tobit'', Gehenna Press, Northampton MA, 1964.</ref>

Slaver-turned-abolitionist [[John Newton]] composed the hymn [[Amazing Grace]] about a wretch who ''"once was lost, but now am found, Was blind, but now I see."'' Blindness, in this sense, is used both metaphorically (to refer to someone who was ignorant but later became knowledgeable) and literally, as a reference to those healed in the Bible. In the later years of his life, Newton himself would go blind.

[[H. G. Wells]]' story "[[The Country of the Blind]]" explores what would happen if a sighted man found himself trapped in a country of blind people to emphasise societies attitude to blind people by turning the situation on its head.

[[Bob Dylan]]'s anti-war song "[[Blowin' in the Wind]]" twice alludes to metaphorical blindness: ''How many times can a man turn his head // and pretend that he just doesn't see... How many times must a man look up // Before he can see the sky?''

Contemporary fiction contains numerous well-known [[:Category:Fictional blind characters|blind characters]]. Some of these characters can "see" by means of fictitious devices, such as the [[Marvel Comics]] superhero [[Daredevil (Marvel Comics)|Daredevil]], who can "see" via his super-human hearing acuity, or ''[[Star Trek]]'''s [[Geordi La Forge]], who can see with the aid of a [[VISOR]], a fictitious device that transmits optical signals to his brain.

===Sports===
Blind and partially sighted people participate in sports, such as [[Swimming (sport)|swimming]], [[snow skiing]] and [[athletics (sport)|athletics]]. Some sports have been invented or adapted for the blind, such as [[goalball]], [[Paralympic association football|association football]], [[blind cricket|cricket]], [[blind golf|golf]], and [[tennis]].<ref name="Vicsports">{{cite web|url=http://www.blindsports.org.au/|title=Blind Sports Victoria|accessdate=2008-03-04}}</ref> The worldwide authority on sports for the blind is the [[International Blind Sports Federation]].<ref name="Para">{{cite web|url=http://www.paralympic.org/paralympian/20014/2001430.htm|title=IBSA General Assembly Elects New Leadership|publisher=International Paralympic Committee|work=The Paralympian|date=April 2001|accessdate=2008-03-04}}</ref><ref name=tennis>{{cite news|last=Lin|first=Thomas|title=Hitting the Court, With an Ear on the Ball|url=http://www.nytimes.com/2012/06/05/science/a-game-of-tennis-tests-notions-of-blindness.html?_r=2&ref=science|work=Science|publisher=The New York Times|accessdate=6 June 2012|date=4 June 2012}}</ref> People with vision impairments have participated in the [[Paralympic Games]] since the [[1976 Summer Paralympics|1976 Toronto summer Paralympics]].<ref name="disserv">{{cite web|title=The history of people with disabilities in Australia - 100 years|publisher=Disability Services Australia|url=http://www.dsa.org.au/life_site/text/sport/index.html|accessdate=2008-03-04}}</ref>

===Metaphorical uses===
The word "blind" (adjective and verb) is often used to signify a lack of knowledge of something. For example, a blind date is a date in which the people involved have not previously met; a [[blind experiment]] is one in which information is kept from either the experimenter or the participant to mitigate the [[placebo effect]] or [[observer bias]]. The expression "blind leading the blind" refers to incapable people leading other incapable people. Being blind to something means not understanding or being aware of it. A "[[blind spot (vision)|blind spot]]" is an area where someone cannot see, for example, where a car driver cannot see because parts of his car's bodywork are in the way.

==Research==
{{Main|Visual prosthesis}}
A 2008 study published in ''[[The New England Journal of Medicine]]'' tested the effect of using [[gene therapy]] to help restore the sight of patients with a rare form of inherited blindness, known as [[Leber's congenital amaurosis]] or LCA.<ref>{{Cite journal|author=Bainbridge JW, Smith AJ, Barker SS, et al.|title=Effect of gene therapy on visual function in Leber's congenital amaurosis |journal=N. Engl. J. Med. |volume=358 |issue=21 |pages=2231–9|date=May 2008 |pmid=18441371 |doi=10.1056/NEJMoa0802268 |url=http://content.nejm.org/cgi/content/abstract/NEJMoa0802268}}</ref> Leber's Congenital Amaurosis damages the light receptors in the retina and usually begins affecting sight in early childhood, with worsening vision until complete blindness around the age of 30.

The study used a common cold virus to deliver a normal version of the gene called [[RPE65]] directly into the eyes of affected patients. Remarkably, all 3 patients, aged 19, 22 and 25, responded well to the treatment and reported improved vision following the procedure. Due to the age of the patients and the degenerative nature of LCA, the improvement of vision in gene therapy patients is encouraging for researchers. It is hoped that gene therapy may be even more effective in younger LCA patients who have experienced limited vision loss, as well as in other blind or partially blind individuals.

Two experimental treatments for retinal problems include a cybernetic replacement and transplant of fetal retinal cells.<ref>[http://www.npr.org/templates/story/story.php?storyId=113968653 Bionic Eye Opens New World Of Sight For Blind] by Jon Hamilton. All Things Considered, National Public Radio. 20 October 2009.</ref>

==Other animals==
{{Main|Blind animals}}
Statements that certain species of [[mammal]]s are "born blind" refers to them being born with their eyes closed and their eyelids fused together; the eyes open later. One example is the [[rabbit]]. In humans, the eyelids are fused for a while before birth, but open again before the normal birth time; however, very premature babies are sometimes born with their eyes fused shut, and opening later. Other animals, such as the [[blind mole rat]], are truly blind and rely on other senses.{{Citation needed|date=August 2010}}

The theme of blind animals has been a powerful one in literature. [[Peter Shaffer]]'s Tony-Award winning play, [[Equus (play)|''Equus'']], tells the story of a boy who blinds six horses. [[Theodore Taylor (author)|Theodore Taylor]]'s classic young adult novel, ''[[The Trouble With Tuck]]'', is about a teenage girl, Helen, who trains her blind dog to follow and trust a seeing-eye dog.

==See also==
{{Portal|Disability}}
*[[Blindness and education]]
*[[Color blindness]]
*[[List of blind people]]
*[[Nyctalopia]]
*[[Recovery from blindness]]
*[[Stereoblindness]]
*[[Tactile alphabet]]
*[[Tactile graphic]]
*[[Tangible symbol systems]]
*[[World Blind Union]]

==References==
{{Reflist|30em}}

==External links==
{{wikiquote|Blindness}}
*{{Wiktionary-inline|blindness|blind}}
<!--This section should only link to blindness web directories; Wpedia isn't a directory of blindness organisations etc.see Wikipedia:External links-->
*{{dmoz|Health/Conditions_and_Diseases/Eye_Disorders/Blindness|Blindness}}
*[http://www.nyise.org/blind.htm Blindness Resource Center] from The New York Institute for Special Education

{{Eye pathology}}


[[Category:Blindness| ]]
[[Category:Blindness| ]]

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