'Blindness' is the condition of lacking
visual perception due to
physiological or
psychological factors.
Various scales have been developed to describe the extent of
vision loss and define "blindness."
[1] 'Total blindness' is the complete lack of form and light perception and is clinically recorded as "NLP," an abbreviation for "no light perception."
''Blindness'' is frequently used to describe severe
visual impairment with vision. Those described as having only "light perception" can see no more than the ability to tell light from dark. A person with only "light projection" can tell the general direction of a light source.
In order to determine which people may need special assistance because of their visual disabilities, various governmental jurisdictions have formulated more complex definitions referred to as 'legal blindness'.
[2] In
North America and most of
Europe, legal blindness is defined as
visual acuity (vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet (6 m) from an object to see it with the same degree of clarity as a normally sighted person could from 200 feet (60 m). In many areas, people with average acuity who nonetheless have a
visual field of less than 20
degrees (the norm being 180 degrees) are also classified as being legally blind.
Approximately ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to relatively good acuity.
Low vision is sometimes used to describe visual acuities from 20/70 to 20/200.
[1]
By the 10th Revision of the
WHO International Statistical Classification of Diseases, Injuries and Causes of Death, ''low vision'' is defined as visual acuity of less than 6/18, but equal to or better than 3/60, or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction. ''Blindness'' is defined as visual acuity of less than 3/60, or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.
[2][3]
Legal blindness
In 1934, the
American Medical Association adopted the following definition of blindness:
:''"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."''
[3]
The
United States Congress included this definition as part of the
Aid to the Blind program in the
Social Security Act passed in 1935
. 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
[4] which currently states:
:''"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."''
[5]
Kuwait is one of many nations that share the same criteria for legal blindness
[6].
Epidemiology
In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness
[7]. Of this number, 58% were over the age of 65
. In 1994-1995, 1.3 million Americans reported legal blindness
[8].
In November 2004 article 'Magnitude and causes of visual impairment', the
WHO estimated that in 2002 there were 161 million (about 2.6% of the world population) visually impaired people in the world, of whom 124 million (about 2%) had low vision and 37 million (about 0.6%) were blind.
[9]
Causes of blindness
Artist's depiction of blind people
Serious visual impairment has a variety of causes:
Diseases
Most visual impairment is caused by
disease and
malnutrition. According to WHO estimates in 2002, the most common causes of blindness around the world are:
★
cataracts (47.8%),
★
glaucoma (12.3%),
★
uveitis (10.2%),
★ age-related
macular degeneration (AMD) (8.7%),
★
trachoma (3.6%),
★
corneal opacity (5.1%), and
★
diabetic retinopathy (4.8%), among other causes.
People in developing countries are significantly more likely to experience visual impairment as a consequence of treatable or preventable conditions than are their counterparts in the developed world. While vision impairment is most common in people over age 60 across all regions, children in poorer communities are more likely to be affected by blinding diseases than are their more affluent peers.
The link between
poverty and treatable visual impairment is most obvious when conducting regional comparisons of cause. Most adult visual impairment in
North America and
Western Europe is related to age-related macular degeneration and diabetic retinopathy. While both of these conditions are subject to treatment, neither can be cured. Another common cause is
retinopathy of prematurity.
In developing countries, wherein people have shorter life expectancies, cataracts and water-borne parasites—both of which can be treated effectively—are most often the culprits (see
River blindness, for example). Of the estimated 40 million blind people located around the world, 70–80% can have some or all of their sight restored through treatment.
In developed countries where parasitic diseases are less common and
cataract surgery is more available, age-related macular degeneration, glaucoma, and diabetic retinopathy are usually the leading causes of blindness
[10].
Abnormalities and injuries
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.
People with injuries to the
occipital lobe of the
brain can, despite having undamaged eyes and
optic nerves, still be legally or totally blind.
Genetic defects
People with
albinism often suffer from visual impairment to the extent that many are legally blind, though few of them actually cannot see.
Leber's congenital amaurosis can cause total blindness or severe sight loss from birth or early childhood.
Recent advances in
mapping the
human genome have identified other genetic causes of
low vision or blindness. One such example is
Bardet-Biedl syndrome.
Poisoning
A small portion of all cases of blindness are caused by the intake of certain chemicals. A well-known example is
methanol [ Methanol ]
, found in
methylated spirits, which are sometimes used by
alcoholics as a cheap substitute for regular
alcoholic beverages.
Willful actions
Blinding has been used as an act of vengeance and
torture in some instances, to deprive a person of a major sense by which they can navigate or interact within the world, act fully independently, and be aware of events surrounding them.
Blindness prevention
There exist a number of organizations, such as
International Agency for the Prevention of Blindness,
ORBIS International, and
Seva Foundation, who have developed programs aimed at preventing blindness.
Adaptive techniques
Visually impaired and blind people have devised a number of techniques that allow them to complete daily activities using their remaining senses. These might include the following:
★ Adaptive
computer software that allows people with visual impairments to interact with their computer via audio or screen magnifiers.
★ Adaptive
mobile phones that allows people with visual impairments to interact with their phones via audio or screen magnifiers. These mobile phones uses software called Mobile Speak a screen reader from Code Factory http://www.codefactory.es. It provides audio feedback to every functionality on the phone.
★ Adaptations of
banknotes so that the value can be determined by touch. For example:
★
★ In some currencies, such as the
euro,
pound sterling and
Australian dollar, the size of a note increases with its value.
★
★ Many
banknotes from around the world have a tactile feature to indicate denomination in the upper right corner. This
tactile feature is a series of raised dots, but it is not standard
Braille [5].
★
★ It is also possible to fold notes in different ways to assist recognition.
★ Labeling and tagging clothing and other personal items
★ Placing different types of food at different positions on a dinner plate
★ Marking controls of household appliances
Most people, once they have been visually impaired for long enough, devise their own adaptive strategies in all areas of personal and professional management.
For corrective surgery of blindness, see
acquired vision.
Tools
Watch for the blind
Designers, both visually impaired and sighted, have developed a number of tools for use by blind people.
Mobility
Many people with serious visual impairments can travel independently assisted by
tactile paving and/or using a
white cane with a red tip - the
international symbol of blindness.
A long cane is used to extend the user's range of touch sensation, swung in a low sweeping motion across the intended path of travel to detect obstacles. However, some visually impaired persons do not carry these kinds of canes, opting instead for the shorter, lighter identification (ID) cane. Still others require a support cane. The choice depends on the individual's vision, motivation, and other factors.
Each of these is painted white for maximum visibility, and to denote visual impairment on the part of the user. In addition to making rules about who can and cannot use a cane, some governments mandate the
right-of-way be given to users of white canes or
guide dogs.
A small number of people employ
guide dogs. Although the dogs can be trained to navigate various obstacles, they are not capable of interpreting street signs. The human half of the guide dog team does the directing, based upon skills acquired through previous mobility training. The handler might be likened to an aircraft's navigator, who must know how to get from one place to another, and the dog is the pilot, who gets them there safely.
Orientation and Mobility Specialist 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.
Reading and magnification
Most blind and visually impaired people read print, either of a regular size or enlarged through the use of magnification devices. A variety of
magnifying glasses, some of which are handheld, and some of which rest on desktops, can make reading easier for those with decreased visual acuity.
The rest read
Braille (or the infrequently used
Moon type), or rely on talking books and readers or
reading machines. They use computers with special hardware such as scanners and
refreshable Braille displays as well as software written specifically for the blind, like optical character recognition applications and screen reading software.
Some people access these materials through agencies for the blind, such as the
National Library Service for the Blind and Physically Handicapped in the United States, the
National Library for the Blind or the
RNIB in the United Kingdom.
Closed-circuit televisions, equipment that enlarges and contrasts textual items, are a more
high-tech alternative to traditional magnification devices. So too are modern
web browsers, which can increase the size of text on some web pages through browser controls or through user-controlled
style sheets.
Computers
Access technology such as
Freedom Scientific's
JAWS for Windows screen reading software enable the blind to use mainstream computer applications. Most legally blind people (70% of them across all ages, according to the
Seattle Lighthouse for the Blind) do not use computers. Only a small fraction of this population, when compared to the sighted community, have
Internet access. This bleak outlook is changing, however, as availability of assistive technology increases, accompanied by concerted efforts to ensure the accessibility of information technology to all potential users, including the blind.
Linux distributions (as
Live CDs) for the blind include
Oralux and
Adriane Knoppix, the latter developed in part by
Adriane Knopper who has a visual impairment. The Macintosh OS also comes with a built-in screen reader, called
VoiceOver. Later versions of
Microsoft Windows include an Accessibility Wizard & Magnifier for those with partial vision.
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.
Other aids
People may use talking
thermometers, enlarged or marked oven dials, talking watches, talking clocks, talking
scales, talking
calculators, talking
compasses and other talking equipment.
Social attitudes towards blindness
Moche Portrait of Blind Man. 300 A.D.
The story of the
Blind Men and an Elephant uses blindness as a symbol of limited perception and perspective. Stories such as ''
The Cricket on the Hearth'' by
Charles Dickens provided yet another view of blindness, wherein those affected by it were ignorant of their surroundings and easily deceived.
H. G. Wells' story
The Country of the Blind explores what would happen if a sighted man found himself trapped in a country of blind people to emphasise societies atttitude to blind people by turning the situation on its head.
The authors of modern educational materials (see:
blindness and education for further reading on that subject), as well as those treating
blindness in literature, have worked to paint a different picture of blind people as three-dimensional individuals with a range of abilities, talents, and even character flaws.
The
Moche people of ancient
Peru depicted the blind in their ceramics.
[11]
Young mammals
Statements that this or that species of
mammals are "born blind" refers to them being born with their eyes closed and their eyelids fused together; the eyes open later. One example is the
rabbit.
In humans the eyelids are fused for a while before birth, but open again before the normal birth time, but very premature babies are sometimes born with their eyes fused shut, and opening later.
References
1. International Council of Ophthalmology. "International Standards: Visual Standards — Aspects and Ranges of Vision Loss with Emphasis on Population Surveys." April 2002.
2. Belote, Larry. "Low Vision Education and Training: Defining the Boundaries of Low Vision Patients." ''A Personal Guide to the VA Visual Impairment Services Program.'' Retrieved March 31, 2006.
3. Koestler, F. A., (1976). ''The unseen minority: a social history of blindness in the United States.'' New York: David McKay.
4. Corn, AL; Spungin, SJ. "Free and Appropriate Public Education and the Personnel Crisis for Students with Visual Impairments and Blindness." Center on Personnel Studies in Special Education. April 2003.
5. Social Security Act. "Sec. 1614. Meaning of terms." Retrieved Feb 17, 2006.
6. Al-Merjan JI, Pandova MG, Al-Ghanim M, Al-Wayel A, Al-Mutairi S. "Registered blindness and low vision in Kuwait." ''Ophthalmic Epidemiol.'' 2005 Aug;12(4):251-7. PMID 16033746.
7. Kirchner, C., Stephen, G. & Chandu, F. (1987). "Estimated 1987 prevalence of non-institutionalized 'severe visual impairment' by age base on 1977 estimated rates: U. S.", 1987. ''AER Yearbook.''
8. American Foundation for the Blind. "Statistics and Sources for Professionals." Retrieved April 1, 2006.
9. World Health Organization
10. Bunce C, Wormald R. "Leading Causes of Certification for Blindness and Partial Sight in England & Wales." ''BMC Public Health.'' 2006 Mar 8;6(1):58 [Epub ahead of print]. PMID 16524463.
11. Berrin, Katherine & Larco Museum. ''The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera.'' New York: Thames and Hudson, 1997.
See also
★
Accessibility
★
Amaurosis
★
Blind musicians
★
Blindness and education
★
Braille
★
Color blindness
★
Cortical blindness
★
Deafblind
★
Inattentional blindness
★
List of eye diseases
★
Night blindness
★
Scotoma
★
Snow blindness
★
Stereoblindness
★
Web accessibility
External links
★
Access Watch: Blind users review accessibility of mainstream software
★
The Chicago Lighthouse for People Who Are Blind or Visually Impaired
★
AccessWorld Technology and People Who Are Blind or Visually Impaired
★
American Council of the Blind
★
American Foundation for the Blind
★
Blind Access Journal: Visual impairment in the real world
★
Christian Blind Mission
★
VISION 2020: The Right to Sight
★
International Agency for the Prevention of Blindness (IAPB)
★
International Braille Research Center
★
Journal of Visual Impairment & Blindness
★
Literature Bibliography and Resources List
★
National Braille Press
★
National Federation of the Blind: Civil rights and consumer advocacy
★
National Library for the Blind
★
National Library Service for the Blind and Physically Handicapped
★
Recording for the Blind and Dyslexic
★
Royal National Institute for the Blind
★
Scottish Sensory Centre
★
SMCCB Vision Links
★
WHO Fact Sheet on Visual Impairment
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