View source for Visual impairment

{{Short description|Decreased ability to see}}
{{Redirect|Blindness}}
{{Infobox medical condition (new)
| name          = Visual impairment
| synonyms      = Vision impairment, vision loss
| image         = Snellen chart.svg
| image_size    = 200px
| caption       = A typical [[Snellen chart]] that is frequently used for [[visual acuity]] testing
| alt           = Lines of letters of decreasing size
| field         = [[Ophthalmology]]
| symptoms      = Decreased ability to [[visual perception|see]]<ref name=WHO2014/><ref name=CDC2011/>
| complications = [[Non-24-hour sleep–wake disorder]], [[falls in older adults]]<ref>{{cite journal | vauthors = Auger RR, Burgess HJ, Emens JS, Deriy LV, Thomas SM, Sharkey KM | title = Clinical Practice Guideline for the Treatment of Intrinsic Circadian Rhythm Sleep-Wake Disorders: Advanced Sleep-Wake Phase Disorder (ASWPD), Delayed Sleep-Wake Phase Disorder (DSWPD), Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD), and Irregular Sleep-Wake Rhythm Disorder (ISWRD). An Update for 2015: An American Academy of Sleep Medicine Clinical Practice Guideline | journal = Journal of Clinical Sleep Medicine | volume = 11 | issue = 10 | pages = 1199–236 | date = October 2015 | pmid = 26414986 | pmc = 4582061 | doi = 10.5664/jcsm.5100 }}</ref><ref>{{cite journal |last1=Blaylock |first1=SE |last2=Vogtle |first2=LK |title=Falls prevention interventions for older adults with low vision: A scoping review |journal=Canadian Journal of Occupational Therapy |date=June 2017 |volume=84 |issue=3 |pages=139–147 |doi=10.1177/0008417417711460 |pmid=28730900|s2cid=7567143 }}</ref>
| onset         = 
| duration      = 
| causes        = Uncorrected [[refractive errors]], [[cataract]]s, [[glaucoma]]<ref name=WHO2014/>
| risks         = 
| diagnosis     = [[Eye examination]]<ref name=CDC2011/>
| differential  = 
| prevention    = 
| treatment     = [[Vision rehabilitation]], changes in the environment, assistive devices ([[eyeglasses]], [[white cane]])<ref name=CDC2011/>
| medication    = 
| prognosis     = 
| frequency     = 940 million / 13% (2015)<ref name=GBD2015Pre/>
| deaths        = 
}}
<!-- Definition -->
'''Visual''' or '''vision impairment''' ('''VI''' or '''VIP''') is the partial or total inability of [[visual perception]]. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficulties with normal daily tasks, including reading and walking.<ref>{{Cite web |date=2021-08-10 |title=Vision Impairment and Blindness {{!}} Examination-Based Studies {{!}} Information on Data Sources {{!}} Vision and Eye Health Surveillance System {{!}} Vision Health Initiative (VHI) {{!}} CDC |url=https://www.cdc.gov/visionhealth/vehss/data/studies/vision-impairment-and-blindness.html |access-date=2022-03-03 |website=www.cdc.gov |language=en-us}}</ref> The terms ''low vision'' and ''blindness'' are often used for levels of impairment which are difficult or impossible to correct and significantly impact daily life.<ref>{{Cite journal |last1=Jeon |first1=Byoung-Jin |last2=Cha |first2=Tae-hyun |date=June 2013 |title=The Effects of Balance of Low Vision Patients on Activities of Daily Living |journal=Journal of Physical Therapy Science |volume=25 |issue=6 |pages=693–696 |doi=10.1589/jpts.25.693 |issn=0915-5287 |pmc=3804998 |pmid=24259832}}</ref> In addition to the various permanent conditions, fleeting temporary vision impairment, [[amaurosis fugax]], may occur, and may indicate serious medical problems.<ref>{{cite web |title=Visually Impaired People (VIP) - Education & Engagement |url=https://www.bats.org.uk/our-work/education-engagement/visually-impaired-people-vip |publisher=Bat ConservationTrust |access-date=2023-01-16 |language=en}}</ref><ref>{{cite web |title=Home page |url=https://warringtonvip.co.uk/ |website= |publisher=Warrington VIP Centre |access-date=2023-01-16 }}</ref><ref>{{cite journal |last1=Rountree |first1=Helen |title=Working with a VIP (Visually Impaired Person) |journal=IH World |date=Autumn 2018 |volume=45 |url=https://ihworld.com/ih-journal/issues/issue-45/working-with-a-vip-visually-impaired-person/ |access-date=2023-01-16  |language=en}}</ref>

<!-- Cause and diagnosis-->
The most common causes of visual impairment globally are uncorrected [[refractive errors]] (43%), [[cataract]]s (33%), and [[glaucoma]] (2%).<ref name=WHO2014/> Refractive errors include [[near-sightedness]], [[far-sightedness]], [[presbyopia]], and [[astigmatism (eye)|astigmatism]].<ref name=WHO2014/> Cataracts are the most common cause of blindness.<ref name=WHO2014/> Other disorders that may cause visual problems include [[age-related macular degeneration]], [[diabetic retinopathy]], [[corneal opacification|corneal clouding]], [[childhood blindness]], and a number of [[infection]]s.<ref name=WHO2012Data>{{cite book|title=GLOBAL DATA ON VISUAL IMPAIRMENTS 2010|date=2012|publisher=WHO|page=6|url=https://www.who.int/blindness/GLOBALDATAFINALforweb.pdf?ua=1|url-status=live|archive-url=https://web.archive.org/web/20150331221058/http://www.who.int/blindness/GLOBALDATAFINALforweb.pdf?ua=1|archive-date=2015-03-31}}</ref> Visual impairment can also be caused by problems in the [[Human brain|brain]] due to [[stroke]], [[premature birth]], or trauma, among others.<ref name=Leh2012/> These cases are known as [[cortical visual impairment]].<ref name=Leh2012>{{cite journal | vauthors = Lehman SS | title = Cortical visual impairment in children: identification, evaluation and diagnosis | journal = Current Opinion in Ophthalmology | volume = 23 | issue = 5 | pages = 384–7 | date = September 2012 | pmid = 22805225 | doi = 10.1097/ICU.0b013e3283566b4b | s2cid = 33865357 }}</ref> Screening for vision problems in children may improve future vision and educational achievement.<ref>{{cite journal | vauthors = Mathers M, Keyes M, Wright M | title = A review of the evidence on the effectiveness of children's vision screening | journal = Child | volume = 36 | issue = 6 | pages = 756–80 | date = November 2010 | pmid = 20645997 | doi = 10.1111/j.1365-2214.2010.01109.x }}</ref> Screening adults without symptoms is of uncertain benefit.<ref name=USPSTF2016>{{cite journal | vauthors = Siu AL, Bibbins-Domingo K, Grossman DC, Baumann LC, Davidson KW, Ebell M, García FA, Gillman M, Herzstein J, Kemper AR, Krist AH, Kurth AE, Owens DK, Phillips WR, Phipps MG, Pignone MP | display-authors = 6 | title = Screening for Impaired Visual Acuity in Older Adults: US Preventive Services Task Force Recommendation Statement | journal = JAMA | volume = 315 | issue = 9 | pages = 908–14 | date = March 2016 | pmid = 26934260 | doi = 10.1001/jama.2016.0763 | author-link3 = Kirsten Bibbins-Domingo | doi-access = free }}</ref> Diagnosis is by an [[eye exam]].<ref name=CDC2011>{{cite web|title=Blindness and Vision Impairment|url=https://www.cdc.gov/healthcommunication/ToolsTemplates/EntertainmentEd/Tips/Blindness.html|access-date=23 May 2015|date=February 8, 2011|url-status=dead|archive-url=https://web.archive.org/web/20150429145832/http://www.cdc.gov/healthcommunication/toolstemplates/entertainmented/tips/blindness.html|archive-date=29 April 2015}}</ref>

<!-- Prevention and treatment -->
The [[World Health Organization]] (WHO) estimates that 80% of visual impairment is either preventable or curable with treatment.<ref name=WHO2014/> This includes cataracts, the infections [[onchocerciasis|river blindness]] and [[trachoma]], glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness.<ref name=WHO2015Cause>{{cite web|title=Causes of blindness and visual impairment|url=https://www.who.int/blindness/causes/en/|access-date=23 May 2015|url-status=dead|archive-url=https://web.archive.org/web/20150605165934/http://www.who.int/blindness/causes/en/|archive-date=5 June 2015}}</ref> Many people with significant visual impairment benefit from [[vision rehabilitation]], changes in their environment, and assistive devices.<ref name=CDC2011/>

<!-- Epidemiology and society -->
{{as of|2015}}, there were 940 million people with some degree of vision loss.<ref name=GBD2015Pre>{{cite journal | vauthors = Vos T, Allen C, Arora M, Barber RM, Bhutta ZA, Brown A, etal | collaboration = GBD 2015 Disease and Injury Incidence and Prevalence Collaborators| title = Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990-2015: a systematic analysis for the Global Burden of Disease Study 2015 | journal = Lancet | volume = 388 | issue = 10053 | pages = 1545–1602 | date = October 2016 | pmid = 27733282 | pmc = 5055577 | doi = 10.1016/S0140-6736(16)31678-6 }}</ref> 246 million had low vision and 39 million were blind.<ref name=WHO2014/> The majority of people with poor vision are in the [[developing world]] and are over the age of 50 years.<ref name=WHO2014>{{cite web|title=Visual impairment and blindness Fact Sheet N°282 |url=https://www.who.int/mediacentre/factsheets/fs282/en/ |access-date=23 May 2015 |date=August 2014|url-status=dead|archive-url= https://web.archive.org/web/20150512062236/http://www.who.int/mediacentre/factsheets/fs282/en/ |archive-date=12 May 2015}}</ref> Rates of visual impairment have decreased since the 1990s.<ref name=WHO2014/> Visual impairments have considerable economic costs, both directly due to the cost of treatment and indirectly due to decreased ability to work.<ref>{{cite journal | vauthors = Rein DB | title = Vision problems are a leading source of modifiable health expenditures | journal = Investigative Ophthalmology & Visual Science | volume = 54 | issue = 14 | pages = ORSF18-22 | date = December 2013 | pmid = 24335062 | doi = 10.1167/iovs.13-12818 | doi-access = free }}</ref>
{{TOC limit|3}}

==Classification==
{{See also|Low vision assessment}}
In 2010, the WHO definition for visual impairment was changed and now follows the [[ICD-11]]. The previous definition, which used "best corrected visual acuity," was changed to "presenting visual acuity". This change was made as newer studies showed that best-corrected vision overlooks a larger proportion of the population who have visual impairment due to uncorrected refractive errors, and/or lack of access to medical or surgical treatment.<ref>{{Cite web |title=World report on vision |url=https://www.who.int/publications-detail-redirect/9789241516570 |access-date=2022-03-03 |website=World Health Organization |language=en}}</ref>

Distance vision impairment:
* Category 0: No or mild visual impairment – presenting visual acuity better than 6/18
* Category 1: Moderate visual impairment – presenting visual acuity worse than 6/18 and better than 6/60
* Category 2: Severe visual impairment – presenting visual acuity worse than 6/60 and better than 3/60
* Category 3: Blindness – presenting visual acuity worse than 3/60 and better than 1/60
* Category 4: Blindness – presenting visual acuity worse than 1/60 with light perception
* Category 5: Blindness – irreversible blindness with no light perception
Near vision impairment:
* Near visual acuity worse than N6 or M 0.8 at 40&nbsp;cm.

===United Kingdom===
Severely sight-impaired
* Defined as having central visual acuity of less than 3/60 with normal fields of vision, or gross visual field restriction.
* Unable to see at {{convert|3|m|0}} what the normally sighted person sees at {{convert|60|m}}.

Sight impaired
* Able to see at {{convert|3|m|0}}, but not at {{convert|6|m}}, what the normally sighted person sees at {{convert|60|m}}
* Less severe visual impairment is not captured by registration data, and its prevalence is difficult to quantify

Low vision
* A visual acuity of less than 6/18 but greater than 3/60.
* Not eligible to drive and may have difficulty recognising faces across a street, watching television, or choosing clean, unstained, coordinated clothing.<ref>Cupples, M., Hart, P., Johnston, A., & Jackson, A. (2011) Improving healthcare access for people with visual impairment and blindness [[BMJ (Clinical Research Ed.)]]</ref>

In the UK, the Certificate of Vision Impairment (CVI) is used to certify people as being severely sight-impaired or sight-impaired.<ref>{{cite web | url = http://www.dh.gov.uk/en/Healthcare/Primarycare/Optical/DH_4074843 | title = Identification and notification of sight loss | archive-url = https://web.archive.org/web/20110503235348/http://www.dh.gov.uk/en/Healthcare/Primarycare/Optical/DH_4074843 | archive-date=2011-05-03 }}</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'". Certification is based on whether a person can do any work for which eyesight is essential, not just one particular job (such as their job before becoming blind).<ref name="dh.gov.uk">{{cite web | url = http://www.dh.gov.uk/prod_consum_dh/groups/dh_digitalassets/documents/digitalasset/dh_078294.pdf | title = Certificate of Vision Impairment: Explanatory Notes for Consultant Ophthalmologists and Hospital Eye Clinic Staff | archive-url = https://web.archive.org/web/20120916114153/http://www.dh.gov.uk/prod_consum_dh/groups/dh_digitalassets/documents/digitalasset/dh_078294.pdf | archive-date=2012-09-16 }}</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 chart|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 states 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"/>

===United States===
In the United States, any person with vision that cannot be corrected to better than 20/200 in the better eye, or who has 20 [[visual angle|degrees]] ([[angular diameter|diameter]]) or less of visual field remaining, is considered legally blind or eligible for disability classification and possible inclusion in certain government sponsored programs.

The terms ''partially sighted'', ''low vision'', ''legally blind'' and ''totally blind'' are used by schools, colleges, and other educational institutions to describe students with visual impairments.<ref>{{cite web | url = http://www.nichcy.org/ | title = National Dissemination Center for Children with Disabilities | archive-url = https://web.archive.org/web/20070911232205/http://www.nichcy.org/ | archive-date=2007-09-11 }}</ref> They are defined as follows:
* ''Partially sighted'' indicates some type of visual problem, with a need for the person to receive special education in some cases.
* ''Low vision'' generally refers to a severe visual impairment, not necessarily limited to distance vision. Low vision applies to all individuals with sight who are unable to read the newspaper at a normal viewing distance, even with the aid of eyeglasses or contact lenses. They use a combination of vision and other senses to learn, although they may require adaptations in lighting or the size of print, and, sometimes, [[braille]].
* ''Legally blind'' indicates that a person has less than 20/200 vision in the better eye after best correction (contact lenses or glasses), or a field of vision of less than 20 degrees in the better eye.
* ''Totally blind'' students learn via braille or other non-visual media.

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">{{cite book | vauthors = Koestler FA | date = 1976 | title = The unseen minority: a social history of blindness in the United States. | location = New York | publisher = David McKay }}</ref>
}}

The [[United States Congress]] included this definition as part of the Aid to the Blind program in the [[Social Security Act]] passed in 1935.<ref name="Koestler"/><ref name="Corn">{{cite web | vauthors = Corn AL, Spungin SJ | url = http://www.coe.ufl.edu/copsse/docs/IB-10/1/IB-10.pdf | title = Free and Appropriate Public Education and the Personnel Crisis for Students with Visual Impairments and Blindness | publisher = Center on Personnel Studies in Special Education | date = April 2003 |archive-url=https://web.archive.org/web/20100604163643/http://www.education.ufl.edu/copsse/docs/IB-10/1/IB-10.pdf |archive-date=Jun 4, 2010 |url-status=dead}}</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>{{cite web |url=http://www.ssa.gov/history/pdf/80chap12.pdf |title=Supplemental Security Income |access-date=2015-05-23 |url-status=live |archive-url= https://web.archive.org/web/20150924120114/http://www.ssa.gov/history/pdf/80chap12.pdf |archive-date=2015-09-24 }}</ref> which 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>{{cite web | author = Social Security Act | url = http://www.ssa.gov/OP_Home/ssact/title16b/1614.htm | title = Sec. 1614. Meaning of terms | archive-url = https://web.archive.org/web/20150523170519/http://www.ssa.gov/OP_Home/ssact/title16b/1614.htm | archive-date=2015-05-23 }}</ref>
}}

===Temporary vision impairment===
{{Main|Amaurosis fugax}}
Vision impairment for a few seconds or minutes may occur due to any of a variety of causes, some serious and requiring medical attention.

==Health effects==

=== General functioning ===
Visual impairments may take many forms and be of varying degrees. Visual acuity alone is not always a good predictor of an individual's function. Someone with relatively good acuity (e.g., 20/40) can have difficulty with daily functioning, while someone with worse acuity (e.g., 20/200) may function reasonably well if they have low visual demands.

Best-corrected visual acuity differs from presenting visual acuity; a person with a "normal" best corrected acuity can have "poor" presenting acuity (e.g. individual who has uncorrected refractive error). Thus, measuring an individual's general functioning depends on one's situational and contextual factors, as well as access to treatment.<ref name="Vision impairment and blindness">{{Cite web |title=Blindness and vision impairment |url=https://www.who.int/news-room/fact-sheets/detail/blindness-and-visual-impairment |access-date=2022-03-07 |website=World Health Organization |language=en}}</ref>

The [[American Medical Association]] has estimated that the loss of one eye equals 25% impairment of the visual system and 24% impairment of the whole person;<ref name=colenbrander/><ref>{{cite web | url = http://www.useironline.org/Prevention.htm | title = Eye Trauma Epidemiology and Prevention | archive-url = https://web.archive.org/web/20060528033458/http://www.useironline.org/Prevention.htm | archive-date=2006-05-28 }}</ref> total loss of vision in both eyes is considered to be 100% visual impairment and 85% impairment of the whole person.<ref name=colenbrander/>

Some people who fall into this category can use their considerable residual vision&nbsp;– their remaining sight&nbsp;– to complete daily tasks without relying on alternative methods. The role of a low vision specialist (optometrist or ophthalmologist) is to maximize the functional level of a patient's vision by optical or non-optical means. Primarily, this is by use of magnification in the form of telescopic systems for distance vision and optical or electronic magnification for near tasks.

People with significantly reduced acuity may benefit from training conducted by individuals trained in the provision of technical aids. Low [[Vision Rehabilitation|vision rehabilitation]] professionals, some of whom are connected to an agency for the blind, can provide advice on lighting and contrast to maximize remaining vision. These professionals also have access to non-visual aids and can instruct patients in their use.

=== Mobility ===
Older adults with visual impairment are at an increased risk of physical inactivity,<ref>{{Cite journal |last1=Sengupta |first1=Sabyasachi |last2=Nguyen |first2=Angeline M. |last3=van Landingham |first3=Suzanne W. |last4=Solomon |first4=Sharon D. |last5=Do |first5=Diana V. |last6=Ferrucci |first6=Luigi |last7=Friedman |first7=David S. |last8=Ramulu |first8=Pradeep Y. |date=2015-01-30 |title=Evaluation of real-world mobility in age-related macular degeneration |journal=BMC Ophthalmology |volume=15 |pages=9 |doi=10.1186/1471-2415-15-9 |issn=1471-2415 |pmc=4328075 |pmid=25636376 |doi-access=free }}</ref><ref>{{Cite journal |last1=Willis |first1=Jeffrey R. |last2=Jefferys |first2=Joan L. |last3=Vitale |first3=Susan |last4=Ramulu |first4=Pradeep Y. |date=March 2012 |title=Visual impairment, uncorrected refractive error, and accelerometer-defined physical activity in the United States |journal=Archives of Ophthalmology |volume=130 |issue=3 |pages=329–335 |doi=10.1001/archopthalmol.2011.1773 |issn=1538-3601 |pmid=22411662|doi-access=free }}</ref> slower gait speeds,<ref>{{Cite journal |last1=CLARK-CARTER |first1=D. D. |last2=HEYES |first2=A. D. |last3=HOWARTH |first3=C. I. |date=1986-06-01 |title=The efficiency and walking speed of visually impaired people |url=https://doi.org/10.1080/00140138608968314 |journal=Ergonomics |volume=29 |issue=6 |pages=779–789 |doi=10.1080/00140138608968314 |issn=0014-0139 |pmid=3743536|url-access=subscription }}</ref><ref>{{Cite journal |last1=Patel |first1=Ilesh |last2=Turano |first2=Kathleen A. |last3=Broman |first3=Aimee T. |last4=Bandeen-Roche |first4=Karen |last5=Muñoz |first5=Beatriz |last6=West |first6=Sheila K. |author-link6=Sheila West |date=2006-01-01 |title=Measures of Visual Function and Percentage of Preferred Walking Speed in Older Adults: The Salisbury Eye Evaluation Project |url=https://iovs.arvojournals.org/article.aspx?articleid=2124540 |journal=Investigative Ophthalmology & Visual Science |language=en |volume=47 |issue=1 |pages=65–71 |doi=10.1167/iovs.05-0582 |issn=1552-5783 |pmid=16384945|url-access=subscription |doi-access=free }}</ref><ref>{{Cite journal |last1=Huang |first1=Xiaoting |last2=Chen |first2=Zhixuan |last3=Merchant |first3=Reshma |last4=Lim |first4=Moses |date=2017-10-17 |title=Impact of vision impairment on gait speed relating to eventual risk of developing sarcopenia |journal=International Journal of Integrated Care |language=en |volume=17 |issue=5 |pages=A557 |doi=10.5334/ijic.3877 |issn=1568-4156|doi-access=free }}</ref> and fear of falls.<ref>{{Cite journal |last1=Ramulu |first1=Pradeep Y. |last2=van Landingham |first2=Suzanne W. |last3=Massof |first3=Robert W. |last4=Chan |first4=Emilie S. |last5=Ferrucci |first5=Luigi |last6=Friedman |first6=David S. |date=July 2012 |title=Fear of falling and visual field loss from glaucoma |journal=Ophthalmology |volume=119 |issue=7 |pages=1352–1358 |doi=10.1016/j.ophtha.2012.01.037 |issn=1549-4713 |pmc=3389306 |pmid=22480738}}</ref>

Physical activity is a useful predictor of overall well-being, and routine physical activity reduces the risk of developing chronic diseases and disability.<ref>{{Cite journal |last1=Warburton |first1=D. E. |last2=Gledhill |first2=N. |last3=Quinney |first3=A. |date=April 2001 |title=Musculoskeletal fitness and health |url=https://pubmed.ncbi.nlm.nih.gov/11312417/ |journal=Canadian Journal of Applied Physiology |volume=26 |issue=2 |pages=217–237 |doi=10.1139/h01-013 |issn=1066-7814 |pmid=11312417}}</ref><ref>{{Cite journal |last1=Warburton |first1=D. E. |last2=Glendhill |first2=N. |last3=Quinney |first3=A. |date=April 2001 |title=The effects of changes in musculoskeletal fitness on health |url=https://pubmed.ncbi.nlm.nih.gov/11312416/ |journal=Canadian Journal of Applied Physiology |volume=26 |issue=2 |pages=161–216 |doi=10.1139/h01-012 |issn=1066-7814 |pmid=11312416}}</ref> Older adults with visual impairment (including glaucoma, age-related macular degeneration, and diabetic retinopathy) have decreased physical activity as measured with self-reports and accelerometers.<ref>{{Cite journal |last1=Heinemann |first1=A. W. |last2=Colorez |first2=A. |last3=Frank |first3=S. |last4=Taylor |first4=D. |date=April 1988 |title=Leisure activity participation of elderly individuals with low vision |url=https://pubmed.ncbi.nlm.nih.gov/3360359/ |journal=The Gerontologist |volume=28 |issue=2 |pages=181–184 |doi=10.1093/geront/28.2.181 |issn=0016-9013 |pmid=3360359}}</ref><ref>{{Cite journal |last1=Ong |first1=Sharon R. |last2=Crowston |first2=Jonathan G. |last3=Loprinzi |first3=Paul D. |last4=Ramulu |first4=Pradeep Y. |date=August 2018 |title=Physical activity, visual impairment, and eye disease |journal=Eye |volume=32 |issue=8 |pages=1296–1303 |doi=10.1038/s41433-018-0081-8 |issn=0950-222X |pmc=6085324 |pmid=29610523}}</ref> The US [[National Health and Nutrition Examination Survey]] (NHANES) showed that people with corrected visual acuity of less than 20/40 spent significantly less time in moderate to vigorous physical activity.<ref>{{Cite journal |last1=Willis |first1=Jeffrey R. |last2=Vitale |first2=Susan E. |last3=Agrawal |first3=Yuri |last4=Ramulu |first4=Pradeep Y. |date=August 2013 |title=Visual impairment, uncorrected refractive error, and objectively measured balance in the United States |journal=JAMA Ophthalmology |volume=131 |issue=8 |pages=1049–1056 |doi=10.1001/jamaophthalmol.2013.316 |issn=2168-6173 |pmid=23744090|doi-access=free }}</ref> Age-related macular degeneration is also associated with a 50% decrease in physical activity–however physical activity is protective against age-related macular degeneration progression.<ref>{{Cite journal |last1=Seddon |first1=Johanna M. |last2=Cote |first2=Jennifer |last3=Davis |first3=Nancy |last4=Rosner |first4=Bernard |date=June 2003 |title=Progression of age-related macular degeneration: association with body mass index, waist circumference, and waist-hip ratio |journal=Archives of Ophthalmology |volume=121 |issue=6 |pages=785–792 |doi=10.1001/archopht.121.6.785 |issn=0003-9950 |pmid=12796248|doi-access=free }}</ref><ref>{{Cite journal |last1=Knudtson |first1=M. D. |last2=Klein |first2=R. |last3=Klein |first3=B. E. K. |date=December 2006 |title=Physical activity and the 15-year cumulative incidence of age-related macular degeneration: the Beaver Dam Eye Study |journal=The British Journal of Ophthalmology |volume=90 |issue=12 |pages=1461–1463 |doi=10.1136/bjo.2006.103796 |issn=0007-1161 |pmc=1857544 |pmid=17077116}}</ref>

In terms of mobility, those with visual impairment have a slower gait speed than those without visual impairment; however, the rate of decline remains proportional with increasing age in both groups. Additionally, the visually impaired also have greater difficulty walking a quarter mile (400&nbsp;m) and walking up stairs, as compared to those with normal vision.<ref>{{Cite journal |last1=Swenor |first1=B. K. |last2=Munoz |first2=B. |last3=West |first3=S. K. |date=2014-02-01 |title=A Longitudinal Study of the Association Between Visual Impairment and Mobility Performance in Older Adults: The Salisbury Eye Evaluation Study |journal=American Journal of Epidemiology |language=en |volume=179 |issue=3 |pages=313–322 |doi=10.1093/aje/kwt257 |issn=0002-9262 |pmc=3954103 |pmid=24148711}}</ref>

=== Cognitive ===
Older adults with vision loss are at an increased risk of memory loss, cognitive impairment, and cognitive decline.<ref>{{Cite journal |last1=Zheng |first1=D. Diane |last2=Swenor |first2=Bonnielin K. |last3=Christ |first3=Sharon L. |last4=West |first4=Sheila K. |last5=Lam |first5=Byron L. |last6=Lee |first6=David J. |date=2018-09-01 |title=Longitudinal Associations Between Visual Impairment and Cognitive Functioning: The Salisbury Eye Evaluation Study |url=https://doi.org/10.1001/jamaophthalmol.2018.2493 |journal=JAMA Ophthalmology |volume=136 |issue=9 |pages=989–995 |doi=10.1001/jamaophthalmol.2018.2493 |pmid=29955805 |pmc=6142982 |issn=2168-6165}}</ref>

=== Social and psychological ===
Studies demonstrate an association between older adults with visual impairment and a poor mental health;<ref name="Brunes 24">{{Cite journal |last1=Brunes |first1=Audun |last2=B. Hansen |first2=Marianne |last3=Heir |first3=Trond |date=2019-02-01 |title=Loneliness among adults with visual impairment: prevalence, associated factors, and relationship to life satisfaction |journal=Health and Quality of Life Outcomes |volume=17 |issue=1 |pages=24 |doi=10.1186/s12955-019-1096-y |issn=1477-7525 |pmc=6359849 |pmid=30709406 |doi-access=free }}</ref><ref>{{Cite journal |last1=Demmin |first1=Docia L |last2=Silverstein |first2=Steven M |date=2020-12-03 |title=Visual Impairment and Mental Health: Unmet Needs and Treatment Options |journal=Clinical Ophthalmology |volume=14 |pages=4229–4251 |doi=10.2147/OPTH.S258783 |issn=1177-5467 |pmc=7721280 |pmid=33299297 |doi-access=free }}</ref><ref name="Aa 849–854">{{Cite journal |last1=Aa |first1=Hilde P. A. van der |last2=Comijs |first2=Hannie C. |last3=Penninx |first3=Brenda W. J. H. |last4=Rens |first4=Ger H. M. B. van |last5=Nispen |first5=Ruth M. A. van |date=2015-02-01 |title=Major Depressive and Anxiety Disorders in Visually Impaired Older Adults |url=https://iovs.arvojournals.org/article.aspx?articleid=2212840 |journal=Investigative Ophthalmology & Visual Science |language=en |volume=56 |issue=2 |pages=849–854 |doi=10.1167/iovs.14-15848 |pmid=25604690 |issn=1552-5783|url-access=subscription }}</ref><ref>{{Cite web |last=CDC |date=2021-09-27 |title=Protect Your Vision |url=https://www.cdc.gov/visionhealth/resources/features/vision-loss-mental-health.html |access-date=2022-03-07 |website=Centers for Disease Control and Prevention |language=en-us}}</ref> discrimination was identified as one of the causes of this association.<ref name="Jackson 825–832">{{Cite journal |last1=Jackson |first1=Sarah E. |last2=Hackett |first2=Ruth A. |last3=Pardhan |first3=Shahina |author-link3=Shahina Pardhan |last4=Smith |first4=Lee |last5=Steptoe |first5=Andrew |date=2019-07-01 |title=Association of Perceived Discrimination With Emotional Well-being in Older Adults With Visual Impairment |url=https://doi.org/10.1001/jamaophthalmol.2019.1230 |journal=JAMA Ophthalmology |volume=137 |issue=7 |pages=825–832 |doi=10.1001/jamaophthalmol.2019.1230 |issn=2168-6165 |pmc=6547384 |pmid=31145413}}</ref>&nbsp;Older adults with visual impairment have a 1.5-fold risk of reporting perceived discrimination and of these individuals, there was a 2-fold risk of loneliness and 4-fold risk of reporting a lower quality of life.<ref name="Jackson 825–832"/>&nbsp; Among adults with visual impairment, the prevalence of moderate loneliness is 28.7% (18.2% in the general population), and the prevalence of severe loneliness is 19.7% (2.7% in the general population).<ref name="Brunes 24"/>&nbsp; The risk of depression and anxiety is also increased in the visually impaired; 32.2% report depressive symptoms (12.01% in the general population), and 15.61% report anxiety symptoms (10.69% in the general population).<ref name="Aa 849–854"/>

The subjects making the most use of rehabilitation instruments, who lived alone, and preserved their mobility and occupation, were the least depressed, with the lowest risk of suicide and the highest level of social integration.

Those with worsening sight and the prognosis of eventual blindness are at comparatively high risk of suicide and thus may need supportive services. Many studies have demonstrated how rapid acceptance of the serious visual impairment has led to better, more productive compliance with rehabilitation programs. Moreover, psychological distress has been reported to be at its highest when sight loss is not complete, but the prognosis is unfavorable. Therefore, early intervention is imperative for enabling successful psychological adjustment.<ref>{{cite journal | vauthors = De Leo D, Hickey PA, Meneghel G, Cantor CH | title = Blindness, fear of sight loss, and suicide | journal = Psychosomatics | volume = 40 | issue = 4 | pages = 339–44 | date = 1999 | pmid = 10402881 | doi = 10.1016/S0033-3182(99)71229-6 | doi-access = free | pmc = 2448359 }}</ref>

===Associated conditions===
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|access-date=27 May 2010|url-status=dead|archive-url=https://web.archive.org/web/20100612060146/http://www.lighthouse.org/about-low-vision-blindness/causes-of-blindness/|archive-date=12 June 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|archive-url=https://web.archive.org/web/20080808120836/http://www.ncecbvi.org/autism.htm|archive-date=8 August 2008|access-date=27 May 2010}}</ref> Blindness in combination with hearing loss is known as [[deafblindness]].

It has been estimated that over half of completely 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]] (synchronized) to the light{{ndash}}dark cycle.<ref name="AASM2008">{{cite web |url=http://www.aasmnet.org/resources/factsheets/crsd.pdf |title=Circadian Rhythm Sleep Disorder |access-date=2009-08-08 |year=2008 |publisher=American Academy of Sleep Medicine |url-status=dead|archive-url=https://web.archive.org/web/20100826121447/http://www.aasmnet.org/Resources/FactSheets/CRSD.pdf |archive-date=2010-08-26 }}</ref><ref>{{cite journal | vauthors = Sack RL, Lewy AJ, Blood ML, Keith LD, Nakagawa H | title = Circadian rhythm abnormalities in totally blind people: incidence and clinical significance | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 75 | issue = 1 | pages = 127–34 | date = July 1992 | doi = 10.1210/jcem.75.1.1619000 | pmid = 1619000 | url = http://jcem.endojournals.org/cgi/pmidlookup?view=long&pmid=1619000 | url-access = subscription }}</ref>

==Cause==
[[File:Number-of-people-with-blindness-due-to-each-cause.png|thumb|alt=Charts showing the estimated number of people with blindness from each cause: cataract, glaucoma, refraction disorders, age-related macular degeneration, malaria, river blindness, trachoma, and others|The estimated number of people with blindness from each cause: cataract, glaucoma, refraction disorders, age-related macular degeneration, malaria, river blindness, trachoma, and others.<ref>{{cite web |title=Number of people with blindness, broken down by cause |url=https://ourworldindata.org/grapher/number-of-people-with-blindness-due-to-each-cause |publisher=[[Our World in Data]] |access-date=11 June 2025}}</ref>]]
The most common causes of visual impairment globally in 2010 were:
# [[Refractive error]] (42%)
# [[Cataract]] (33%)
# [[Glaucoma]] (2%)
# [[Age-related macular degeneration]] (1%)
# [[Corneal opacification]] (1%)
# [[Diabetic retinopathy]] (1%)
# [[Childhood blindness]]
# [[Trachoma]] (1%)
# Undetermined (18%)<ref name=WHO2012Data/>

The most common causes of blindness worldwide in 2010 were:
# Cataracts (51%)
# Glaucoma (8%)
# Age-related macular degeneration (5%)
# Corneal opacification (4%)
# Childhood blindness (4%)
# Refractive errors (3%)
# Trachoma (3%)
# Diabetic retinopathy (1%)
# Undetermined (21%)<ref name=WHO2012Data/>

About 90% of people who are visually impaired live in the [[developing world]].<ref name=WHO2014/> Age-related macular degeneration, glaucoma, and diabetic retinopathy are the leading causes of blindness in the developed world.<ref name="Bunce">{{cite journal | vauthors = Bunce C, Wormald R | title = Leading causes of certification for blindness and partial sight in England & Wales | journal = BMC Public Health | volume = 6 | pages = 58 | date = March 2006 | pmid = 16524463 | pmc = 1420283 | doi = 10.1186/1471-2458-6-58 | doi-access = free }}</ref>

Among working-age adults who are newly blind in England and Wales the most common causes in 2010 were:<ref>{{cite journal | vauthors = Liew G, Michaelides M, Bunce C | title = A comparison of the causes of blindness certifications in England and Wales in working age adults (16-64 years), 1999-2000 with 2009-2010 | journal = BMJ Open | volume = 4 | issue = 2 | pages = e004015 | date = February 2014 | pmid = 24525390 | pmc = 3927710 | doi = 10.1136/bmjopen-2013-004015 }}</ref>
# Hereditary retinal disorders (20.2%)
# Diabetic retinopathy (14.4%)
# Optic atrophy (14.1%)
# Glaucoma (5.9%)
# Congenital abnormalities (5.1%)
# Disorders of the visual cortex (4.1%)
# Cerebrovascular disease (3.2%)
# Degeneration of the macula and posterior pole (3.0%)
# Myopia (2.8%)
# Corneal disorders (2.6%)
# Malignant neoplasms of the brain and nervous system (1.5%)
# Retinal detachment (1.4%)

===Cataracts===

[[Cataracts]] are the greying or opacity of the crystalline lens, which can be caused in children by intrauterine infections, metabolic disorders, and genetically transmitted syndromes.<ref name="Althomali, T. 2012">{{cite journal | vauthors = Althomali T | year = 2012 | title = Management of congenital cataract | journal = Saudi Journal for Health Sciences | volume = 1 | issue = 3| page = 115 | doi=10.4103/2278-0521.106079| doi-access = free }}</ref> Cataracts are the leading cause of child and adult blindness that doubles in prevalence with every ten years after the age of 40.<ref name="Brian, G. 2001">{{cite journal | vauthors = Brian G, Taylor H | title = Cataract blindness--challenges for the 21st century | journal = Bulletin of the World Health Organization | volume = 79 | issue = 3 | pages = 249–56 | year = 2001 | pmid = 11285671 | pmc = 2566371 }}</ref> Consequently, today cataracts are more common among adults than in children.<ref name="Althomali, T. 2012"/> That is, people face higher chances of developing cataracts as they age. Nonetheless, cataracts tend to have a greater financial and emotional toll upon children as they must undergo expensive diagnosis, long-term rehabilitation, and visual assistance.<ref>{{cite journal | vauthors = Wirth MG, Russell-Eggitt IM, Craig JE, Elder JE, Mackey DA | title = Aetiology of congenital and paediatric cataract in an Australian population | journal = The British Journal of Ophthalmology | volume = 86 | issue = 7 | pages = 782–6 | date = July 2002 | pmid = 12084750 | pmc = 1771196 | doi = 10.1136/bjo.86.7.782 }}</ref> Also, according to the Saudi Journal for Health Sciences, sometimes people experience irreversible amblyopia<ref name="Althomali, T. 2012"/> after pediatric cataract surgery because the cataracts prevented the normal maturation of vision before operation.<ref name="Rashad, M. A. 2012"/> Despite the great progress in treatment, cataracts remain a global problem in both economically developed and developing countries.<ref name="Althomali, T. 2012" /> At present, with the variant outcomes as well as the unequal access to cataract surgery, the best way to reduce the risk of developing cataracts is to avoid smoking and extensive exposure to sun light (i.e. UV-B rays).<ref name="Brian, G. 2001"/>

===Glaucoma===
[[Glaucoma]] is an eye disease often characterized by increased pressure within the eye or intraocular pressure (IOP).<ref name="go.galegroup.com">{{cite journal | last = Krader | first = Cheryl Guttman | name-list-style = vanc | title = Etiology Determines IOP Treatment: Customized Approach Needed for Managing Elevated Pressure in Patients with Uveitis. | journal = Ophthalmology Times | date = 15 May 2012 | volume = 24 | publisher = Academic OneFile }}<{{cite web |url=http://go.galegroup.com/ps/i.do?id=GALE%7CA294505910&v=2.1&it=r&p=AONE&sw=w&asid=e8aa73e119058ee89d879915b9226421 |title=Gale - Institution Finder |access-date=2014-05-05 |url-status=live |archive-url=https://web.archive.org/web/20140421065542/http://go.galegroup.com/ps/i.do?id=GALE%7CA294505910&v=2.1&u=cuny_centraloff&it=r&p=AONE&sw=w&asid=e8aa73e119058ee89d879915b9226421 |archive-date=2014-04-21 }}>.</ref> Glaucoma causes visual field loss as well as severs the optic nerve.<ref name="glaucoma.org">Glaucoma Research Foundation. "High Eye Pressure and Glaucoma." Glaucoma Research Foundation. N.p., 5 Sept. 2013. Web.<{{cite web |url=http://www.glaucoma.org/gleams/high-eye-pressure-and-glaucoma.php |title=High Eye Pressure and Glaucoma |access-date=2014-05-05 |url-status=live |archive-url=https://web.archive.org/web/20170902095935/http://www.glaucoma.org/gleams/high-eye-pressure-and-glaucoma.php |archive-date=2017-09-02 }}>.</ref> Early diagnosis and treatment of glaucoma in patients is imperative because glaucoma is triggered by non-specific levels of IOP.<ref name="glaucoma.org"/> Also, another challenge in accurately diagnosing glaucoma is that the disease has four causes: 1) inflammatory ocular hypertension syndrome (IOHS); 2) severe uveitic angle closure; 3) corticosteroid-induced; and 4) a heterogonous mechanism associated with structural change and chronic inflammation.<ref name="go.galegroup.com"/> In addition, often [[pediatric glaucoma]] differs greatly in cause and management from the glaucoma developed by adults.<ref name="Meszaros, Liz 2013">{{cite journal | last = Meszaros | first = Liz | name-list-style = vanc | title = Pediatric, Adult Glaucoma Differ in Management: Patient Populations Not Same, so Diagnosis/clinical Approach Should Reflect Their Uniqueness. | journal = Ophthalmology Times | date = 15 September 2013 | volume = 11 | publisher = Academic OneFile | url=http://go.galegroup.com/ps/i.do?id=GALE%7CA348978213&v=2.1&it=r&p=AONE&sw=w&asid=543a017fba673f928c486fc78c826e1d |url-status=live |archive-url=https://web.archive.org/web/20140421081812/http://go.galegroup.com/ps/i.do?id=GALE%7CA348978213&v=2.1&u=cuny_centraloff&it=r&p=AONE&sw=w&asid=543a017fba673f928c486fc78c826e1d |archive-date=2014-04-21 }}</ref> Currently, the best sign of pediatric glaucoma is an IOP of 21&nbsp;mm Hg or greater present within a child.<ref name="Meszaros, Liz 2013"/> One of the most common causes of pediatric glaucoma is cataract removal surgery, which leads to an incidence rate of about 12.2% among infants and 58.7% among 10-year-olds.<ref name="Meszaros, Liz 2013"/>

===Infections===
[[File:68-4062-1 (ATED).jpg|thumb|alt=Black and white photo of children leading a line of adults across a dry landscape|The burden of [[onchocerciasis]]: children leading blind adults in Africa]]
Childhood blindness can be caused by conditions related to pregnancy, such as [[congenital rubella syndrome]] and [[retinopathy of prematurity]]. Leprosy and onchocerciasis each blind approximately 1 million individuals in the developing world.

The number of individuals blind from [[trachoma]] has decreased 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.

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 is now the fourth greatest cause of global blindness.<ref>(Vaughan & Asbury's General Ophthalmology, 17e)</ref>

===Injuries===
[[File:Re-educating wounded. Blind French soldiers learning to make baskets. American Red Cross., 1917 - 1919 - NARA - 533674.jpg|thumb|alt=Black and white photo of three men weaving wicker baskets|Re-educating wounded. Blind French soldiers learning to make baskets, World War I.]]
[[Eye injury|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.

Blinding has been used as an [[blinding (punishment)|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, pp. 444–445.</ref> Contemporary examples include the addition of methods such as [[acid throwing]] as a form of [[disfigurement]].

===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 congenital amaurosis]] can cause total blindness or severe sight loss from birth or early childhood. [[Retinitis pigmentosa]] is characterized by decreased peripheral vision and trouble seeing at night.

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===
The intake of certain chemicals rarely causes blindness. 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 | access-date=27 March 2007 |archive-url = https://web.archive.org/web/20070220004549/http://www.safety-council.org/info/OSH/methanol.htm <!-- Bot retrieved archive --> |archive-date = 20 February 2007}}</ref> When competing with [[ethanol]] for metabolism, ethanol is metabolized first, and the onset of toxicity 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 [[surrogate alcohol|desperate and cheap substitute]] for regular ethanol [[alcoholic beverages]].

===Other===
* [[Amblyopia]]: is a category of vision loss or visual impairment that is caused by factors unrelated to refractive errors or coexisting ocular diseases.<ref name="Rashad, M. A. 2012">{{cite journal | vauthors = Rashad MA | title = Pharmacological enhancement of treatment for amblyopia | journal = Clinical Ophthalmology | volume = 6 | pages = 409–16 | year = 2012 | pmid = 22536029 | pmc = 3334227 | doi = 10.2147/opth.s29941 | doi-access = free }}</ref> Amblyopia is the condition when a child's visual systems fail to mature normally because the child either has been born premature, measles, congenital rubella syndrome, vitamin A deficiency, or meningitis.<ref name="Gilbert, C. 2001">{{cite journal | vauthors = Gilbert C, Foster A | title = Childhood blindness in the context of VISION 2020--the right to sight | journal = Bulletin of the World Health Organization | volume = 79 | issue = 3 | pages = 227–32 | year = 2001 | pmid = 11285667 | pmc = 2566382 }}</ref> If left untreated during childhood, amblyopia is currently incurable in adulthood because surgical treatment effectiveness changes as a child matures.<ref name="Gilbert, C. 2001"/> Consequently, amblyopia is the world's leading cause of child monocular vision loss, which is the damage or loss of vision in one eye.<ref name="Rashad, M. A. 2012"/> In the best case scenario, which is very rare, properly treated amblyopia patients can regain 20/40 acuity.<ref name="Rashad, M. A. 2012"/>
* [[Corneal opacification]]
* [[Degenerative myopia]]
* [[Diabetic retinopathy]] is one of the manifestations of microvascular complications of diabetes, which is characterized by blindness or reduced acuity. That is, diabetic retinopathy describes the retinal and vitreous hemorrhages or retinal capillary blockage caused by the increase of A1C,<ref name="Morello, C. M 2007">{{cite journal | vauthors = Morello CM | title = Etiology and natural history of diabetic retinopathy: an overview | journal = American Journal of Health-System Pharmacy | volume = 64 | issue = 17 Suppl 12 | pages = S3–7 | date = September 2007 | pmid = 17720892 | doi = 10.2146/ajhp070330 }}</ref> which a measurement of blood glucose or sugar level.<ref>{{cite web |url=http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/a1c/ |title=A1C and eAG |access-date=2014-05-05 |url-status=live |archive-url= https://web.archive.org/web/20140603145010/http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/a1c/ |archive-date=2014-06-03 }}</ref> In fact, as A1C increases, people tend to be at greater risk of developing diabetic retinopathy than developing other microvascular complications associated with diabetes (e.g. chronic hyperglycemia, diabetic neuropathy, and diabetic nephropathy).<ref name="Morello, C. M 2007"/> Despite the fact that only 8% of adults 40 years and older experience vision-threatening diabetic retinopathy (e.g. nonproliferative diabetic retinopathy or NPDR and proliferative diabetic retinopathy or PDR), this eye disease accounted for 17% of cases of blindness in 2002.<ref name="Morello, C. M 2007"/>
* [[Retinitis pigmentosa]]
* [[Retinopathy of prematurity]] (ROP): The most common cause of blindness in infants worldwide, ROP can result in a range of visual impairment. In its most severe form, it causes retinal detachment, with attendant visual loss. Treatment is aimed mainly at prevention, via laser or [[Avastin]] therapy. Premature birth or very low birth weight has been shown to have a high correlation with this cause of visual impairment.<ref>{{cite journal |last1=Leung |first1=Myra Ps |last2=Thompson |first2=Benjamin |last3=Black |first3=Joanna |last4=Dai |first4=Shuan |last5=Alsweiler |first5=Jane M |date=2018 |title=The effects of preterm birth on visual development, Clinical and Experimental Optometry |url=https://pubmed.ncbi.nlm.nih.gov/28868651/ |journal= Clinical and Experimental Optometry |volume=101 |issue=1 |publisher= |pages=4-12 |doi=10.1111/cxo.12578 |access-date=16 February 2025|hdl=2292/44033 |hdl-access=free }}</ref>
* [[Stargardt's disease]]
* [[Uveitis]]: is a group of 30 intraocular inflammatory diseases<ref name="sciencedirect.com">{{cite journal | vauthors = Jabs DA, Busingye J | title = Approach to the diagnosis of the uveitides | journal = American Journal of Ophthalmology | volume = 156 | issue = 2 | pages = 228–36 | date = August 2013 | pmid = 23668682 | pmc = 3720682 | doi = 10.1016/j.ajo.2013.03.027 }}</ref> caused by infections, systemic diseases, organ-specific autoimmune processes, cancer, or trauma.<ref name="Rao, Narsing 2013">{{cite journal | vauthors = Rao NA | title = Uveitis in developing countries | journal = Indian Journal of Ophthalmology | volume = 61 | issue = 6 | pages = 253–4 | date = June 2013 | pmid = 23803475 | pmc = 3744776 | doi = 10.4103/0301-4738.114090 | doi-access = free }}</ref> That is, uveitis refers to a complex category of ocular diseases that can cause blindness if either left untreated or improperly diagnosed.<ref name="Rao, Narsing 2013"/> The current challenge of accurately diagnosing uveitis is that often the cause of a specific ocular inflammation is either unknown or multi-layered.<ref name="sciencedirect.com"/> Consequently, about 3–10% of those with uveitis in developed countries, and about 25% of those with uveitis in developing countries, become blind from incorrect diagnosis and ineffectual prescription of drugs, antibiotics, or steroids.<ref name="Rao, Narsing 2013"/> In addition, uveitis is a diverse category of eye diseases that are subdivided as granulomatous (or tumorous) or non-granulomatous anterior, intermediate, posterior, or pan uveitis.<ref name="Rao, Narsing 2013"/> In other words, uveitis diseases tend to be classified by their anatomic location in the eye (e.g. uveal tract, retina, or lens), as well as can create complication that can cause cataracts, glaucoma, retinal damage, age-related macular degeneration or diabetic retinopathy.<ref name="Rao, Narsing 2013"/>
* [[Xerophthalmia]], often due to [[vitamin A deficiency]], is estimated to affect 5 million children each year; 500,000 develop active corneal involvement, and half of these go blind.

==Diagnosis==
[[File:Exploring-Eye-Movements-in-Patients-with-Glaucoma-When-Viewing-a-Driving-Scene-pone.0009710.s001.ogv|thumb|alt=Video tracing eye movements while driving along urban street|Scientists track eye movements in glaucoma patients to check vision impairment while driving.]]
People must be examined by a specialist in low vision care before other rehabilitation training to rule out potential medical or surgical correction for the problem and to establish a careful baseline refraction and prescription of both normal and low vision glasses and optical aids. Only a doctor is qualified to evaluate the visual functioning of a compromised visual system effectively.<ref>{{cite web | url = http://www.aoa.org/x5240.xml | title = American Optometric Association web site | archive-url = https://web.archive.org/web/20130605031811/http://aoa.org/x5240.xml | archive-date=2013-06-05 }}</ref> The [[American Medical Association]] provides an approach to evaluating visual loss as it affects an individual's ability to perform activities of daily living.<ref name=colenbrander>{{cite web | url = http://www.ski.org/Colenbrander/Images/AMA_Guides_Vision5_01.pdf | title = AMA Guides | archive-url = https://web.archive.org/web/20060502000817/http://www.ski.org/Colenbrander/Images/AMA_Guides_Vision5_01.pdf | archive-date=2006-05-02 }}</ref>

Screening adults who have no symptoms is of uncertain benefit.<ref name=USPSTF2016/>

==Prevention==
The World Health Organization estimates that 80% of visual loss is either preventable or curable with treatment.<ref name=WHO2014/> This includes cataracts, onchocerciasis, trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness.<ref name=WHO2015Cause/> The Centers for Disease Control and Prevention estimates that half of blindness in the United States is preventable.<ref name=CDC2011/>

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

===Mobility===
[[File:Long cane folded.jpg|thumb|alt=White cane with red band, folded into four segments|Folded long cane]]
[[File:Caoguia2006.jpg|thumb|alt=Man walks through mall, holding onto harnessed yellow lab|A blind man is assisted by a [[guide dog]] in Brasília, Brazil.]]
[[File:Blind girl feels shape of vehicle near Mana village, Uttarakhand.jpg|thumb|alt=Indian woman touches a large brown vehicle|Blind girl feels shape of vehicle near [[Mana, India|Mana village, Uttarakhand]].]]
[[File:Visually impaired girl negotiating a rock while rock climbing.jpg|thumb|upright|alt=Girl wedged between two bolders, climbing|Visually impaired girl negotiating a rock while rock climbing]]
Many people with serious visual impairments can travel independently, using a wide range of tools and techniques. [[Orientation and Mobility|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 on 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 | vauthors = Thaler L, Arnott SR, Goodale MA | title = Neural correlates of natural human echolocation in early and late blind echolocation experts | journal = PLOS ONE | volume = 6 | issue = 5 | pages = e20162 | year = 2011 | pmid = 21633496 | pmc = 3102086 | doi = 10.1371/journal.pone.0020162 | bibcode = 2011PLoSO...620162T | doi-access = free }}</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
 |access-date = 14 March 2014
 |url-status  = live
 |archive-url = https://web.archive.org/web/20140315184642/http://www.uwo.ca/bmi/news/bmi_news/bat_man.html
 |archive-date = 15 March 2014
}}</ref>

Government actions are sometimes taken to make public places more accessible to blind people. Public transportation is freely available to blind people 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|upright|alt=Watch with tactile hands and braille digits|[[Braille watch]]]]
Most visually impaired people who are not completely 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|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 [[high-tech|higher-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 and mobile technology===
Access technology such as [[screen reader]]s, [[screen magnifier]]s, and [[refreshable Braille display|refreshable braille display]]s enables 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 [[Vinux]] and [[Adriane Knoppix]], the latter developed in part by [[Klaus Knopper|Adriane Knopper]] who has a visual impairment. macOS and iOS also come with a built-in screen reader called [[VoiceOver]], while [[Google TalkBack]] is built into most Android devices.

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|alt=Raised bumps on a Canadian banknote|A [[Canadian currency tactile feature|tactile feature]] on a [[Banknotes of the Canadian dollar|Canadian banknote]]]]
[[File:Roca seta -mushroom rock- (Los Barruecos).jpg|thumb|Scaled-down palpable model of mountain for blind tourists]]
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, 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>{{cite web | url = http://www.bankofcanada.ca/en/banknotes/accessibility.html | title = Accessibility features – Bank Notes | publisher = Bank of Canada | archive-url = https://web.archive.org/web/20110429132719/http://www.bankofcanada.ca/en/banknotes/accessibility.html | archive-date = April 29, 2011 }}</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 adaptive strategies in all areas of personal and professional management.

For the blind, there are books in braille, audiobooks, text-to-speech computer programs, machines, and [[e-book readers]]. Low vision people can make use of these tools as well as [[large-print]] reading materials and e-book readers that provide large [[font]] sizes.

Computers are important tools of integration for the visually impaired person. They allow, using standard or specific programs, screen magnification and conversion of text into sound or touch (braille line), and are useful for all levels of visual impairment. [[Optical character recognition|OCR]] scanners can, in conjunction with text-to-speech software, read the contents of books and documents aloud via computer. Vendors also build closed-circuit televisions that electronically magnify paper, and even change its contrast and color, for visually impaired users. For more information, consult [[assistive technology]].

In adults with low vision, there is no conclusive evidence supporting one form of reading aid over another.<ref name="Virgili"/> In several studies, stand-mounted devices allowed faster reading than hand-held or portable optical aids.<ref name="Virgili">{{cite journal | vauthors = Virgili G, Acosta R, Bentley SA, Giacomelli G, Allcock C, Evans JR | title = Reading aids for adults with low vision | journal = The Cochrane Database of Systematic Reviews | volume = 2018 | pages = CD003303 | date = April 2018 | issue = 4 | pmid = 29664159 | pmc = 6494537 | doi = 10.1002/14651858.CD003303.pub4 }}</ref> While electronic aids may allow faster reading for individuals with low vision, portability, ease of use, and affordability must be considered for people.<ref name=Virgili/>

Children with low vision sometimes have reading delays, but do benefit from phonics-based beginning reading instruction methods. Engaging phonics instruction is multisensory, highly motivating, and hands-on. Typically, students are first taught the most frequent sounds of the alphabet letters, especially the so-called short vowel sounds, then taught to blend sounds with three-letter consonant-vowel-consonant words such as cat, red, sit, hot, and sun. Hands-on (or kinesthetically appealing) VERY enlarged print materials, such as those found in "The Big Collection of Phonics Flipbooks" by Lynn Gordon (Scholastic, 2010), help teach word families and blend skills to beginning readers with low vision. Beginning reading instructional materials should focus primarily on the lower-case letters, not the capital letters (even though they are larger), because reading text requires familiarity (mostly) with lower-case letters. Phonics-based beginning reading should also be supplemented with phonemic awareness lessons, writing opportunities, and many read-alouds (literature read to children daily) to stimulate motivation, vocabulary development, concept development, and comprehension skill development. Many children with low vision can be successfully included in regular education environments. Parents may need to be vigilant to ensure that the school provides the teacher and students with appropriate low vision resources, for example, technology in the classroom, classroom aide time, modified educational materials, and consultation assistance with low vision experts.

==Epidemiology==
The [[World Health Organization|WHO]] estimates that in 2012, there were 285 million visually impaired people in the world, of whom 246 million had low vision and 39 million were blind.<ref name=WHO2014/>

Of those who are blind, 90% live in the developing world.<ref name="ReferenceA">{{cite web | vauthors = Bosanquet N, Mehta P | title = Evidence base to support the UK Vision Strategy. | publisher = [[RNIB]] and [[The Guide Dogs for the Blind Association]] | citeseerx = 10.1.1.649.6742 | url = https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.649.6742&rep=rep1&type=pdf | access-date=August 27, 2023}}</ref> Worldwide for each blind person, an average of 3.4 people have low vision, with country and regional variation ranging from 2.4 to 5.5.<ref name="WHO">World Health Organization{{full citation needed|date=February 2012}}</ref>

'''By age''': visual impairment is unequally distributed across age groups. More than 82% of all people who are blind are 50 years of age and older, although they represent only 19% of the world's population. Due to the expected number of years lived in blindness (blind years), childhood blindness remains a significant problem, with an estimated 1.4 million blind children below age 15.

'''By gender''': available studies consistently indicate that in every region of the world, and at all ages, females have a significantly higher risk of being visually impaired than males.<ref>{{Cite journal|last1=Esteban|first1=J. J. Navarro|last2=Martínez|first2=M. Solera|last3=Navalón|first3=P. García|last4=Serrano|first4=O. Piñar|last5=Patiño|first5=J. R. Cerrillo|last6=Purón|first6=M. E. Calle|last7=Martínez-Vizcaíno|first7=V.|date=February 2008|title=Visual impairment and quality of life: gender differences in the elderly in Cuenca, Spain|url=https://pubmed.ncbi.nlm.nih.gov/18026851/|journal=Quality of Life Research|volume=17|issue=1|pages=37–45|doi=10.1007/s11136-007-9280-7|issn=0962-9343|pmid=18026851|s2cid=24556942}}</ref><ref>{{Cite journal|last1=Woldeyes|first1=Alemayehu|last2=Adamu|first2=Yilkal|date=July 2008|title=Gender differences in adult blindness and low vision, Central Ethiopia|url=https://pubmed.ncbi.nlm.nih.gov/19271384/|journal=Ethiopian Medical Journal|volume=46|issue=3|pages=211–218|issn=0014-1755|pmid=19271384}}</ref><ref>{{Cite journal|last1=Rius Ulldemolins|first1=Anna|last2=Benach|first2=Joan|last3=Guisasola|first3=Laura|last4=Artazcoz|first4=Lucía|date=2019-08-01|title=Why are there gender inequalities in visual impairment?|url=https://pubmed.ncbi.nlm.nih.gov/30500932/#:~:text=Conclusions:%20Strong%20gender%20inequalities%20were,related%20to%20their%20gender%20socialization|journal=European Journal of Public Health|volume=29|issue=4|pages=661–666|doi=10.1093/eurpub/cky245|issn=1464-360X|pmid=30500932|hdl=2117/130141|hdl-access=free}}</ref><ref>{{Cite journal|last1=Mousa|first1=Ahmed|last2=Courtright|first2=Paul|last3=Kazanjian|first3=Arminee|last4=Bassett|first4=Ken|date=2014-06-01|title=Prevalence of Visual Impairment and Blindness in Upper Egypt: A Gender-based Perspective|url=https://doi.org/10.3109/09286586.2014.906629|journal=Ophthalmic Epidemiology|volume=21|issue=3|pages=190–196|doi=10.3109/09286586.2014.906629|issn=0928-6586|pmid=24746251|s2cid=22521634|url-access=subscription}}</ref><ref>{{Cite journal|last1=Ulldemolins|first1=Anna Rius|last2=Lansingh|first2=Van C.|last3=Valencia|first3=Laura Guisasola|last4=Carter|first4=Marissa J.|last5=Eckert|first5=Kristen A.|date=September 2012|title=Social inequalities in blindness and visual impairment: a review of social determinants|journal=Indian Journal of Ophthalmology|volume=60|issue=5|pages=368–375|doi=10.4103/0301-4738.100529|issn=1998-3689|pmc=3491260|pmid=22944744 |doi-access=free }}</ref><ref>{{Cite journal|last1=Doyal|first1=Lesley|last2=Das-Bhaumik|first2=Raja G.|date=2018|title=Sex, gender and blindness: a new framework for equity|journal=BMJ Open Ophthalmology|volume=3|issue=1|pages=e000135|doi=10.1136/bmjophth-2017-000135|issn=2397-3269|pmc=6146307|pmid=30246151}}</ref>

'''By geography''': visual impairment is not distributed uniformly throughout the world. More than 90% of the world's visually impaired live in developing countries.<ref name="WHO"/>

Since the estimates of the 1990s, new data based on the 2002 global population show a reduction in the number of people who are blind or visually impaired, and those who are blind from the effects of infectious diseases, but an increase in the number of people who are blind from conditions related to longer life spans.<ref name="WHO"/>

In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness.<ref name="Kirchner">{{cite book | vauthors = Kirchner C, Stephen G, Chandu F | date = 1987 | chapter = Estimated 1987 prevalence of non-institutionalized 'severe visual impairment' by age based on 1977 estimated rates: U. S.", 1987. | title = 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">{{cite web | url = http://www.afb.org/Section.asp?SectionID=15&DocumentID=1367#prev | title = Statistics and Sources for Professionals | publisher = American Foundation for the Blind | archive-url = https://web.archive.org/web/20080807030614/http://www.afb.org/Section.asp?SectionID=15&DocumentID=1367 | archive-date=2008-08-07 }}</ref> The [[Royal National Institute of Blind People]] estimates that there are over 2 million people in the UK with sight loss, while 320,000 are registered as Sight Impaired or Severely Sight Impaired.<ref>{{cite web|url=https://www.rnib.org.uk/professionals/research-and-data/key-information-and-statistics-on-sight-loss-in-the-uk/|title=Key information and statistics on sight loss in the UK|publisher=[[Royal National Institute of Blind People]]|access-date=30 May 2025}}</ref>

==Society and culture==
{{See also|List of blind people|Blind musicians}}

===Legal definition===
[[File:RU road sign 8.15.svg|upright|thumb|Blind pedestrians - [[Road signs in Russia|Road sign in Russia]]]]
[[File:Bangladesh road sign B43.svg|upright|thumb|Blind pedestrians - [[Road signs in Bangladesh|Road sign in Bangladesh]]]]
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 |access-date=January 22, 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140127023130/http://www.ssdiqualify.org/defining-boundaries-low-vision-patients/ |archive-date=January 27, 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{{snd}}with [[corrective lens]]es{{snd}}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 fifteen percent of those deemed legally blind, by any measure, have no light or form perception. 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.visionaware.org/info/your-eye-condition/eye-health/low-vision/low-vision-terms-and-descriptions/1235|title=Low Vision and Legal Blindness Terms and Descriptions|publisher=American Foundation for the Blind|access-date=2017-02-28|url-status=dead|archive-url=https://web.archive.org/web/20170301010338/http://www.visionaware.org/info/your-eye-condition/eye-health/low-vision/low-vision-terms-and-descriptions/1235|archive-date=2017-03-01}}</ref>

===Literature and art===
{{see also|Cultural depictions of blindness|Visual impairment in art}}

====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|alt=Oil painting of woman with head tilted down, possibly with eyes closed|''Blind Woman'' by [[Diego Velázquez]]]]
[[File:José de Ribera 018.jpg|upright|thumb|alt=Man with eyes closed holds and feels a marble bust|''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 society's attitude to blind people by turning the situation on its head.

[[José Saramago]]'s novel [[Blindness (novel)|''Blindness'']] describes a sudden mass blindness epidemic, and the main story follows the first group to lose their vision and how they have to adapt to their new disability amidst a decaying society.

[[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 extraordinary abilities or devices, such as the [[Marvel Comics]] superhero [[Daredevil (Marvel Comics character)|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 fictional device that transmits optical signals to his brain.

===Blind culture ===
People who are not blind often imagine that people who are blind share a cultural identity in the way that other minority groups with shared experiences have a distinct culture.<ref>{{cite journal |last1=Himes |first1=Joseph S. |title=Some Concepts of Blindness in American Culture |journal=Social Casework |date=9 May 2018 |volume=31 |issue=10 |pages=410–416 |doi=10.1177/104438945003101002|s2cid=150116014 |doi-access=free }}</ref> Various blind commentators have responded to this perception by explaining that more commonly, blind people integrate with the broader community and culture, and often do not identify blindness as a defining part of their culture.<ref>{{cite journal |last1=Weisleder |first1=Pedro |title=No Such Thing as a 'Blind Culture' |journal=Journal of Child Neurology |date=24 April 2012 |volume=27 |issue=6 |pages=819–820 |doi=10.1177/0883073812441249|pmid=22532546 |s2cid=41588734 }}</ref><ref>{{cite web |last1=Hopfe |first1=Alyssa |title=The Culture of Blindness |url=http://www.blindcanadians.ca/publications/cbm/14/culture-blindness |website=www.blindcanadians.ca |publisher=Alliance for Equality of Blind Canadians |language=en |date=July 1999}}</ref><ref>{{cite web |last1=Pierce |first1=Barbara |title=No Such Thing as Blind Culture |url=https://www.nfb.org/Images/nfb/Publications/bm/bm08/bm0810/bm081007.htm |website=www.nfb.org |publisher=Braille Monitor |date=November 2008}}</ref>

People who are blind share the common cultural experience of the many misconceptions sighted people have about living with blindness.<ref>{{cite web |title=A 20/20 Perspective on Blind Culture |url=http://www.thepittpulse.org/home/2018/1/18/a-2020-perspective-on-blind-culture |website=The Pitt Pulse |date=18 January 2018|archive-url=https://web.archive.org/web/20190518161853/http://www.thepittpulse.org/home/2018/1/18/a-2020-perspective-on-blind-culture|archive-date=May 18, 2019|url-status=dead}}</ref>

===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]], [[tennis]], [[bowling]], and [[beep baseball]].<ref name="Vicsports">{{cite web|url=http://www.blindsports.org.au/|title=Blind Sports Victoria|access-date=2008-03-04|url-status=live|archive-url=https://web.archive.org/web/20080221014751/http://www.blindsports.org.au/|archive-date=2008-02-21}}</ref><ref name=Atlantic>{{cite web|url=https://www.theatlantic.com/health/archive/2016/03/blind-athletes/475041/ |title=The Competitive World of Blind Sports |last=Chodosh |first=Sara | name-list-style = vanc |work=The Atlantic |date=24 March 2016 |access-date=29 July 2018}}</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|access-date=2008-03-04|url-status=dead|archive-url=https://web.archive.org/web/20070918225825/http://www.paralympic.org/paralympian/20014/2001430.htm|archive-date=2007-09-18}}</ref><ref name="tennis">{{cite news |last=Lin |first=Thomas |name-list-style=vanc |date=4 June 2012 |title=Hitting the Court, With an Ear on the Ball |work=Science |publisher=The New York Times |url=https://www.nytimes.com/2012/06/05/science/a-game-of-tennis-tests-notions-of-blindness.html |url-status=live |url-access=limited |access-date=6 June 2012 |archive-url=https://web.archive.org/web/20150509102622/http://www.nytimes.com/2012/06/05/science/a-game-of-tennis-tests-notions-of-blindness.html |archive-date=9 May 2015}}</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|access-date=2008-03-04|url-status=dead|archive-url=https://web.archive.org/web/20110207212725/http://www.dsa.org.au/life_site/text/sport/index.html|archive-date=2011-02-07}}</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; metaphorically, a topic on which an individual is unaware of their own biases, and therefore of the resulting distortions of their own judgements (see [[Bias blind spot]]).

==Research==
{{Main|Visual prosthesis}}
A 2008 study 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 | vauthors = Bainbridge JW, Smith AJ, Barker SS, Robbie S, Henderson R, Balaggan K, Viswanathan A, Holder GE, Stockman A, Tyler N, Petersen-Jones S, Bhattacharya SS, Thrasher AJ, Fitzke FW, Carter BJ, Rubin GS, Moore AT, Ali RR | display-authors = 6 | title = Effect of gene therapy on visual function in Leber's congenital amaurosis | journal = The New England Journal of Medicine | volume = 358 | issue = 21 | pages = 2231–9 | date = May 2008 | pmid = 18441371 | doi = 10.1056/NEJMoa0802268 | url = http://cvrl.ioo.ucl.ac.uk/people/stockman/pubs/2008%20gene%20therapy%20b%20et%20al.pdf | publisher = [[Massachusetts Medical Society]] | hdl = 10261/271174 }}</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. All three patients, aged 19, 22, and 25, responded well to the treatment and reported improved vision following the procedure.

Two experimental treatments for retinal problems include a cybernetic replacement and transplant of fetal retinal cells.<ref>{{cite news |url=https://www.npr.org/templates/story/story.php?storyId=113968653 |title=Bionic Eye Opens New World Of Sight For Blind |first=Jon |last=Hamilton | name-list-style = vanc |date=20 October 2009 |access-date=9 March 2019 |work=[[NPR]]}}</ref>

There is no high-quality evidence on the effect of assistive technologies on educational outcomes and quality of life in children with low vision {{as of|2015|lc=y}},<ref>{{cite journal | vauthors = Thomas R, Barker L, Rubin G, Dahlmann-Noor A | title = Assistive technology for children and young people with low vision | journal = The Cochrane Database of Systematic Reviews | issue = 6 | pages = CD011350 | date = June 2015 | volume = 2015 | pmid = 26086876 | doi = 10.1002/14651858.CD011350.pub2 | collaboration = Cochrane Eyes and Vision Group | pmc = 10638521 }}</ref> nor is there evidence on magnifying reading aids in children.<ref>{{cite journal | vauthors = Barker L, Thomas R, Rubin G, Dahlmann-Noor A | title = Optical reading aids for children and young people with low vision | journal = The Cochrane Database of Systematic Reviews | issue = 3 | pages = CD010987 | date = March 2015 | volume = 2015 | pmid = 25738963 | pmc = 6769181 | doi = 10.1002/14651858.CD010987.pub2 | collaboration = Cochrane Eyes and Vision Group }}</ref> Low-vision rehabilitation does not appear to have an important impact on health-related quality of life, though some low-vision rehabilitation interventions, particularly psychological therapies and methods of enhancing vision, may improve vision-related quality of life in people with sight loss.<ref>{{cite journal | vauthors = van Nispen RM, Virgili G, Hoeben M, Langelaan M, Klevering J, Keunen JE, van Rens GH | title = Low vision rehabilitation for better quality of life in visually impaired adults | journal = The Cochrane Database of Systematic Reviews | volume = 1 | pages = CD006543 | date = January 2020 | issue = 1 | pmid = 31985055 | pmc = 6984642 | doi = 10.1002/14651858.CD006543.pub2 | collaboration = Cochrane Eyes and Vision Group }}</ref>

==Other animals==
{{Main|Blindness in animals}}
Statements that certain species of [[mammal]]s are "born blind" refer to them being born with their eyes closed and their eyelids fused; 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 open 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 ==
{{div col|colwidth=25em}}
* [[Accessibility]]
* [[Accessible Books Consortium]]
* [[Acoustic wayfinding]]
* [[Acute visual loss]]
* [[Blindness and education]]
* [[Bookshare]]
* [[Braille technology]]
* [[Braille trail]]
* [[Color blindness]]
* [[Diplopia]]
* [[Disability rights movement]]
* [[Nyctalopia]]
* [[Recovery from blindness]]
* [[Retinal regeneration]]
* [[Sensory tourism]]
* [[Sighted guide]]
* [[Stereoblindness]]
* [[Swedish interactive thresholding algorithm]]
* [[Tactile alphabet]]
* [[Tactile graphic]]
* [[Tangible symbol systems]]
* [[Tōdōza]]/[[Goze]] - The low vision guild in medieval Japan.
* [[Vision disorder]]
* [[Visual agnosia]]
* [[Visual impairment due to intracranial pressure]]
* [[World Blind Union]]
{{div col end}}

== References ==
{{Reflist}}

== External links ==
{{Commons category}}
* {{cite EB1911|wstitle=Blindness}}
* [https://uclpress.co.uk/book/vision-impairment/ Vision Impairment: Science, art and lived experience]

{{Spoken Wikipedia|En-Visual impairment-article.ogg|date=2020-07-12}}
{{Medical condition classification and resources
| ICD10 = {{ICD10|H|54|0|h|53}}, {{ICD10|H|54|1|h|53}}, {{ICD10|H|54|4|h|53}}
| ICD9 = {{ICD9|369}}
| MeSH=D001766
| Width = 100
| ICDO =
| OMIM =
| DiseasesDB = 28256
| MedlinePlus =003040
| eMedicineSubj =
| eMedicineTopic =
}}
{{Eye pathology}}
{{Authority control}}

{{DEFAULTSORT:Visual impairment}}
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