Blindness is the condition of lacking visual perception Visual perception is the ability to interpret information and surroundings from visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision . The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in psychology, cognitive due to physiological Physiology is the science of the functioning of living systems. It is a subcategory of biology. In physiology, the scientific method is applied to determine how organisms, organ systems, organs, cells and biomolecules carry out the chemical or physical function that they have in a living system. The word physiology is from Ancient Greek: φύσις or neurological Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue, such as muscle. The corresponding surgical specialty factors.

Various scales have been developed to describe the extent of vision loss Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically (i.e. over a long period of time) and define blindness.^[1] Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for "no light perception."^[1] Blindness is frequently used to describe severe visual impairment Visual impairment is vision loss (of a person) to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, medication, or surgery. This with residual vision. Those described as having only light perception have no more sight than the ability to tell light from dark and the general direction of a light source Light is electromagnetic radiation of a wavelength that is visible to the human eye . In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.

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 North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the southeast and most of Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus region (Specification of borders) and the Black Sea to the southeast. Europe is bordered by the, legal blindness is defined as visual acuity Visual acuity is acuteness or clearness of vision, especially form vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain (vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet (6.1 m) from an object to see it—with corrective lenses A corrective lens is a lens worn in front of the eye, mainly used to treat myopia, hyperopia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract—with the same degree of clarity as a normally sighted person could from 200 feet (61 m). In many areas, people with average acuity who nonetheless have a visual field The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while 'field of view' "refers to the physical objects and light sources in the of less than 20 degrees A degree , usually denoted by ° (the degree symbol), is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians. When that angle is with respect to a reference meridian, it indicates a location along a great circle of a sphere, such as Earth (see Geographic coordinate system), Mars, or the (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 Low vision is a subspecialty within the professions of optometry and ophthalmology dealing with individuals who have reduced vision even when using the best possible spectacle or contact lens correction available. It can be a result of either congenital disease or acquired factors (such as in some forms of optic atrophy) is sometimes used to describe visual acuities from 20/70 to 20/200.^[3]

By the 10th Revision of the WHO The World Health Organization is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. Established on 7 April 1948, and headquartered in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health Organization, which had been an agency of the International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 20/60 (6/18), but equal to or better than 20/200 (6/60), or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction. Blindness is defined as visual acuity of less than 20/400 (6/120), or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.^[4][5]

Blind people with undamaged eyes may still register light non-visually for the purpose of circadian A circadian rhythm is a roughly 24-hour cycle in the biochemical, physiological, or behavioural processes of living entities, including plants, animals, fungi and cyanobacteria . The term "circadian" comes from the Latin circa, "around", and diem or dies, "day", meaning literally "approximately one day". The entrainment In chronobiology, entrainment of a circadian system is the alignment of its own period and phase to the period and phase of an external rhythm. A common example is the entrainment of endogenous circadian rhythms to the daily light-dark cycle. Of the several possible cues, called zeitgeber (German for time-giver, synchronizer), which can contribute to the 24-hour light/dark cycle. Light signals for this purpose travel through the retinohypothalamic tract The retinohypothalamic tract is a photic input pathway involved in the circadian rhythms of mammals. The origin of the retinohypothalamic tract is the intrinsically photosensitive Retinal Ganglion Cells , which contain the photopigment melanopsin. The axons of the ipRGCs belonging to the retinohypothalamic tract project directly to the, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.

Classification

In 1934, the American Medical Association The American Medical Association , founded in 1847 and incorporated in 1897, is the largest association of physicians and medical students in the United States 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.^[6]

The United States Congress The United States Congress is the bicameral legislature of the federal government of the United States of America, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C included this definition as part of the Aid to the Blind program in the Social Security Act In the United States, Social Security refers to the federal Old-Age, Survivors, and Disability Insurance program passed in 1935.^[6][7] 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 Supplemental Security Income is a monthly stipend provided to aged (legally deemed to be 65 or older), blind, or disabled persons based on need, paid by the United States Government. The program is administered by the Social Security Administration. Payments are made from the US Treasury general funds, not the Social Security trust funds. The program^[8] 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.^[9]

In the United States, legal blindness due to acuity loss is most often measured by a regular eye doctor with an eye chart.

Legal blindness due to visual field being less than 20 degrees is measured by a visual field test A visual field test is an examination that may be performed to analyze a patient's visual field. The exam may be performed by a technician in one of several ways. The test may be performed by a technician directly, with the assistance of a machine, or completely by an automated machine. Machine based tests aid diagnostics by allowing a detailed using a number IV target size. If the doctor or facility performing the test is approved by the Social Security Administration The United States Social Security Administration is an independent agency of the United States federal government that administers Social Security, a social insurance program consisting of retirement, disability, and survivors' benefits. To qualify for these benefits, most American workers pay Social Security taxes on their earnings; future, this is the official US determination for legal blindness due to field loss in conditions like retinitis pigmentosa Retinitis pigmentosa is a group of genetic eye conditions. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some sight all their lives . Others go completely blind from RP, in some cases as early as.

Kuwait The State of Kuwait is a sovereign Arab emirate situated in the northeast of the Arabian Peninsula in Western Asia. It is bordered by Saudi Arabia to the south and Iraq to the north and lies on the northwestern shore of the Persian Gulf. The name Kuwait is derived from the Arabic "akwat", the plural of "kout", meaning fortress is one of many nations that share the same criteria for legal blindness.^[10]

In the UK The United Kingdom of Great Britain and Northern Ireland[note 7] is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of the island of Ireland, and many small islands. Northern Ireland is the only part of the UK with a land, the Certificate of Vision Impairment (CVI) is used to certify patients as severely sight impaired or sight impaired.^[11] 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 as to be unable to perform any work for which eye sight is essential” (National Assistance Act Section 64(1)). The test is whether a person cannot do any work for which eyesight is essential, not just his or her normal job or one particular job.^[12].

In practice, the definition depends on individuals' visual acuity Visual acuity is acuteness or clearness of vision, especially form vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain and the extent to which their field of vision is restricted. The Department of Health identifies three groups of patients who may be classified as severely visually impaired.^[12].

1. Those below 3/60 Snellen (most people below 3/60 are severely sight impaired),
2. Those better than 3/60 but below 6/60 Snellen (people who have a very contracted field of vision only),
3. Those 6/60 Snellen or above (people in this group who have a contracted field of vision especially if the contraction is in the lower part of the field),

The Department of Health also state that a person is more likely to be classified as severely visually impaired if their eyesight has failed recently or if they are an older individual, both groups being perceived as less able to adapt to their vision loss.^[12].

Causes

Serious visual impairment has a variety of causes:

Diseases

According to WHO The World Health Organization is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. Established on 7 April 1948, and headquartered in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health Organization, which had been an agency of the estimates, the most common causes of blindness around the world in 2002 were:

1. cataracts A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light. Early in the development of age-related cataract the power of the lens may be increased, causing near-sightedness , and the gradual yellowing and opacification of the (47.9%),
2. glaucoma Glaucoma is a disease in which the optic nerve is damaged, leading to progressive, irreversible loss of vision. It is often, but not always, associated with increased pressure of the fluid in the eye (12.3%),
3. age-related macular degeneration Age related macular degeneration is a medical condition which usually affects older adults that results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of visual impairment in older adults (>50 years). Macular degeneration can make it (8.7%),
4. corneal The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. While the cornea contributes most of the eye' opacity (5.1%), and
5. diabetic retinopathy Diabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness. It is an ocular manifestation of systemic disease which affects up to 80% of all patients who have had diabetes for 10 years or more. Despite these intimidating statistics, research indicates that at least 90% of these new (4.8%),
6. childhood blindness (3.9%),
7. trachoma Trachoma is an infectious eye disease, and the leading cause of the world's infectious blindness. Globally, 84 million people suffer from active infection and nearly 8 million people are visually impaired as a result of this disease. Globally this disease results in considerable disability (3.6%)
8. onchocerciasis Onchocerciasis , also known as river blindness and Robles' Disease, is a parasitic disease caused by infection with the nematode Onchocerca volvulus. Onchocerciasis is the world's second-leading infectious cause of blindness. It is not the nematode but its endosymbiont, Wolbachia pipientis, that causes the severe inflammatory response that leaves (0.8%).^[13]

In terms of the worldwide prevalence of blindness, the vastly greater number of people in the developing world and the greater likelihood of their being affected mean that the causes of blindness in those areas are numerically more important. Cataract is responsible for more than 22 million cases of blindness and glaucoma 6 million, while leprosy and onchocerciasis each blind approximately 1 million individuals worldwide. The number of individuals blind from trachoma has dropped dramatically in the past 10 years from 6 million to 1.3 million, putting it in seventh place on the list of causes of blindness worldwide. Xerophthalmia is estimated to affect 5 million children each year; 500,000 develop active corneal involvement, and half of these go blind. Central corneal ulceration is also a significant cause of monocular blindness worldwide, accounting for an estimated 850,000 cases of corneal blindness every year in the Indian subcontinent alone. As a result, corneal scarring from all causes now is the fourth greatest cause of global blindness (Vaughan & Asbury's General Ophthalmology, 17e)

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 Poverty is the lack of basic human needs, such as clean water, nutrition, health care, education, clothing and shelter, because of the inability to afford them. This is also referred to as absolute poverty or destitution. Relative poverty is the condition of having fewer resources or less income than others within a society or country, or compared and treatable visual impairment is most obvious when conducting regional comparisons of cause. Most adult visual impairment in North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the southeast and Western Europe Western Europe is a loose term for the collection of countries in the westernmost region of Europe, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a cultural entity—the region lying west of Central Europe. Another definition was created during the Cold War is related to age-related macular degeneration and diabetic retinopathy. While both of these conditions are subject to treatment, neither can be cured.

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 Onchocerciasis , also known as river blindness and Robles' Disease, is a parasitic disease caused by infection with the nematode Onchocerca volvulus. Onchocerciasis is the world's second-leading infectious cause of blindness. It is not the nematode but its endosymbiont, Wolbachia pipientis, that causes the severe inflammatory response that leaves, 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 Cataract surgery is the removal of the natural lens of the eye that has developed an opacification, which is referred to as a cataract. Metabolic changes of the crystalline lens fibers over the time lead to the development of the cataract and loss of transparency, causing impairment or loss of vision. During cataract surgery, a patient's cloudy is more available, age-related macular degeneration, glaucoma, and diabetic retinopathy are usually the leading causes of blindness.^[14]

Childhood blindness can be caused by conditions related to pregnancy, such as congenital rubella syndrome Congenital rubella syndrome can occur in a developing fetus of a pregnant woman who has contracted rubella during her first trimester. If infection occurs 0-28 days before conception, there is a 43% chance the infant will be affected. If the infection occurs 0-12 weeks after conception, there is a 51% chance the infant will be affected. If the and retinopathy of prematurity Retinopathy of prematurity , previously known as retrolental fibroplasia (RLF), is an eye disease that affects prematurely born babies. It is thought to be caused by disorganized growth of retinal blood vessels which may result in scarring and retinal detachment. ROP can be mild and may resolve spontaneously, but may lead to blindness in serious.

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 ^ b. English is the de facto language of American government and the sole language spoken at home by 80% of Americans age five and older. Spanish is the second most commonly spoken language. Injuries and cataracts affect the eye itself, while abnormalities such as optic nerve hypoplasia Optic nerve hypoplasia is a medical condition that results in underdevelopment of the optic nerve(s). This condition is the most common congenital optic disc anomaly in which the optic disc appears abnormally small, due to the fact that not all the optic nerve axons have developed properly 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 The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1 . Human V1 is located on the medial side of the occipital lobe within the calcarine sulcus; the full extent of V1 often continues onto the of the brain The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the skull and close to the primary can, despite having undamaged eyes and optic nerves The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibres are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system, still be legally or totally blind.

Genetic defects

People with albinism Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin. Albinism results from inheritance of recessive gene alleles and is known to affect all vertebrates, including humans. The most common term used for an often have vision loss to the extent that many are legally blind, though few of them actually cannot see. Leber's congenital amaurosis Leber's congenital amaurosis is a rare inherited eye disease that appears at birth or in the first few months of life, and affects around 1 in 80,000 of the population can cause total blindness or severe sight loss from birth or early childhood.

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

Poisoning

Rarely, blindness is caused by the intake of certain chemicals. A well-known example is methanol, which is only mildly toxic and minimally intoxicating, but when not competing with ethanol for metabolism, methanol breaks down into the substances formaldehyde and formic acid which in turn can cause blindness, an array of other health complications, and death.^[15] Methanol is commonly found in methylated spirits, denatured ethyl alcohol, to avoid paying taxes on selling ethanol intended for human consumption. Methylated spirits are sometimes used by alcoholics as a desperate and cheap substitute for regular ethanol alcoholic beverages.

Willful actions

Blinding has been used as an act of vengeance and torture in some instances, to deprive a person of a major sense by which they can navigate or interact within the world, act fully independently, and be aware of events surrounding them. An example from the classical realm is Oedipus, who gouges out his own eyes after realizing that he fulfilled the awful prophecy spoken of him.

In 2003, a Pakistani anti-terrorism court sentenced a man to be blinded after he carried out an acid attack against his fiancee that resulted in her blinding.^[16] The same sentence was given in 2009 for the man who blinded Ameneh Bahrami.

Comorbidities

Blindness can occur in combination with such conditions as mental retardation, autism, cerebral palsy, hearing impairments, and epilepsy.^[17][18] In a study of 228 visually impaired children in metropolitan Atlanta between 1991 and 1993, 154 (68%) had an additional disability besides visual impairment.^[17] Blindness in combination with hearing loss is known as deafblindness.

Management

A 2008 study published in the New England Journal of Medicine^[19] tested the effect of using gene therapy to help restore the sight of patients with a rare form of inherited blindness, known as Leber Congenital Amaurosis or LCA. Leber Congenital Amaurosis damages the light receptors in the retina and usually begins affecting sight in early childhood, with worsening vision until complete blindness around the age of 30.

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

Two experimental treatments for retinal problems include a cybernetic replacement and transplant of fetal retinal cells.^[20]

Adaptive techniques and aids

Mobility

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

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

In addition, some blind people use software using GPS technology 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.

Government actions are sometimes taken to make public places more accessible to blind people. Public transportation is freely available to the blind in many cities. Tactile paving and audible traffic signals can make it easier and safer for visually impaired pedestrians to cross streets.^{[citation needed]} 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.

Reading and magnification

Most visually impaired people who are not totally blind read print, either of a regular size or enlarged by magnification devices. Many also read large-print, which is easier for them to read without such devices. A variety of magnifying glasses, some handheld, and some on desktops, can make reading easier for them.

Others read Braille (or the infrequently used Moon type), or rely on talking books and readers or reading machines, which convert printed text to speech or Braille. They use computers with special hardware such as scanners and refreshable Braille displays as well as software written specifically for the blind, such as optical character recognition applications and screen readers.

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.

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

Computers

Access technology such as screen readers, screen magnifiers and refreshable Braille displays enable the blind to use mainstream computer applications and mobile phones. 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 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. Mac OS also comes with a built-in screen reader, called VoiceOver.

The movement towards greater web accessibility is opening a far wider number of websites to adaptive technology, making the web a more inviting place for visually impaired surfers.

Experimental approaches in sensory substitution are beginning to provide access to arbitrary live views from a camera.

Other aids and techniques

Blind people may use talking equipment such as thermometers, watches, clocks, scales, calculators, and compasses. 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 coins and banknotes so that the value can be determined by touch. For example:
  • In some currencies, such as the euro, the pound sterling and the Indian rupee, the size of a note increases with its value.
  • On US coins, pennies and dimes, and nickels and quarters are similar in size. The larger denominations (dimes and quarters) have ridges along the sides (historically used to prevent the "shaving" of precious metals from the coins), which can now be used for identification.
  • Some currencies' banknotes have a tactile feature to indicate denomination. For example, the Canadian currency tactile feature is a system of raised dots in one corner, based on Braille cells but not standard Braille.^[21]
  • It is also possible to fold notes in different ways to assist recognition.
• Labeling and tagging clothing and other personal items
• Placing different types of food at different positions on a dinner plate
• Marking controls of household appliances

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

Epidemiology

The WHO estimates that in 2002 there were 161 million visually impaired people in the world (about 2.6% of the total population). Of this number 124 million (about 2%) had low vision and 37 million (about 0.6%) were blind.^[22] In order of frequency the leading causes were cataract, uncorrected refractive errors (near sighted, far sighted, or an astigmatism), glaucoma, and age-related macular degeneration.^[23] In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness.^[24] Of this number, 58% were over the age of 65.^[24] In 1994-1995, 1.3 million Americans reported legal blindness.^[25]

Society and culture

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 in order 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" is an area where someone cannot see, e.g. where a car driver cannot see because parts of his car's bodywork are in the way.

Sports

Blind and partially sighted people participate in sports such as swimming, snow skiing and athletics. Some sports have been invented or adapted for the blind such as goalball, association football, cricket, and golf.^[26] The worldwide authority on sports for the blind is the International Blind Sports Federation.^[27] People with vision impairments have participated in the Paralympic Games since the 1976 summer Paralympics in Toronto.^[28]

In other animals

Statements that certain 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. Other animals such as the blind mole rat are truly blind and rely on other senses.

The theme of blind animals has been a powerful one in literature. Peter Schaffer's Tony-Award winning play, Equus, tells the story of a boy who blinds six horses. 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. Jacob Appel's prize-winning story, "Rods and Cones," describes the disruption that a blind rabbit causes in a married couple's life. In non-fiction, a recent classic is Linda Kay Hardie's essay, "Lessons Learned from a Blind Cat," in Cat Women: Female Writers on their Feline Friends.

See also

• Blindism
• Blindness and education
• Color blindness
• Cortical blindness
• Eye disease
• List of blind people
• Nyctalopia
• Stereoblindness
• Tactile alphabets
• Tactile graphic
• Tangible symbol systems
• World Blind Union

References

1. ^ ^{a b} 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. ^ Living with Low Vision - American Foundation for the Blind
4. ^ http://www3.who.int/icd/currentversion/fr-icd.htm
5. ^ WHO | Magnitude and causes of visual impairment
6. ^ ^{a b} Koestler, F. A., (1976). The unseen minority: a social history of blindness in the United States. New York: David McKay.
7. ^ 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.
8. ^ http://www.ssa.gov/history/pdf/80chap12.pdf
9. ^ Social Security Act. "Sec. 1614. Meaning of terms." Retrieved February 17, 2006.
10. ^ 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.
11. ^ "Identification and notification of sight loss" Retrieved April 26, 2010.
12. ^ ^{a b c} "Certificate of Vision Impairment: Explanatory Notes for Consultant Ophthalmologists and Hospital Eye Clinic Staff" retrieved April 26, 2010.
13. ^ "Causes of blindness and visual impairment". World Health Organization. http://www.who.int/blindness/causes/en/. Retrieved 19 February 2009.
14. ^ Bunce C, Wormald R. "Leading Causes of Certification for Blindness and Partial Sight in England & Wales." BMC Public Health. 2006 March 8;6(1):58 [Epub ahead of print]. PMID 16524463.
15. ^ "Methanol" (Web). Symptoms of Methanol Poisoning. Canada Safety Council. 2005. http://www.safety-council.org/info/OSH/methanol.htm. Retrieved March 27, 2007.
16. ^ "Eye-for-eye in Pakistan acid case". BBC News. 12 December 2003. http://news.bbc.co.uk/2/hi/south_asia/3313207.stm. Retrieved 2008-06-30.
17. ^ ^{a b} "Causes of Blindness". Lighthouse International. http://www.lighthouse.org/about-low-vision-blindness/causes-of-blindness/. Retrieved 27 May 2010.
18. ^ "Autism and Blindness". Nerbraska Center for the Education of Children who are Blind or Visually Impaired. http://www.ncecbvi.org/autism.htm. Retrieved 27 May 2010.
19. ^ Bainbridge JW, Smith AJ, Barker SS, et al. (May 2008). "Effect of gene therapy on visual function in Leber's congenital amaurosis". N. Engl. J. Med. 358 (21): 2231–9. doi:10.1056/NEJMoa0802268. PMID 18441371. http://content.nejm.org/cgi/content/abstract/NEJMoa0802268.
20. ^ by Jon Hamilton. All Things Considered, National Public Radio. 20 Oct 2009.
21. ^ Accessibility features - Bank Notes - Bank of Canada
22. ^ "World Health Organization" (Web). World Health Organization. 2006. http://www.who.int/en/. Retrieved December 16, 2006.
23. ^ "WHO | Visual impairment and blindness". http://www.who.int/mediacentre/factsheets/fs282/en/index.html.
24. ^ ^{a b} 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.
25. ^ American Foundation for the Blind. "Statistics and Sources for Professionals." Retrieved April 1, 2006.
26. ^ "Blind Sports Victoria". http://www.blindsports.org.au/. Retrieved 2008-03-04.
27. ^ "IBSA General Assembly Elects New Leadership". The Paralympian. International Paralympic Committee. April 2001. http://www.paralympic.org/paralympian/20014/2001430.htm. Retrieved 2008-03-04.
28. ^ "The history of people with disabilities in Australia - 100 years". Disability Services Australia. http://www.dsa.org.au/life_site/text/sport/index.html. Retrieved 2008-03-04.

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