blindness

(medicine) Loss or absence of the ability to perceive visual images. The condition of a person having less than 1/10 (20/200 on the Snellen test) normal vision.

For more information on blindness, visit Britannica.com.

Surprisingly, blindness rarely means total absence of light perception. Most definitions of blindness are based on measurement of visual acuity (the ability to read letters at a certain distance) and assessment of the ability of the person to carry out tasks needing vision. In the UK, the National Assistance Act 1948 states that a person can be certified as blind if they are ‘so blind that they cannot do any work for which eyesight is essential’. This rather circular definition refers to ‘any work’ and not just the person's normal job or one for which he has been specially trained.

Visual acuity is usually tested by asking the patient to read letters of various sizes on a chart viewed from a distance of 6 m or 20 feet (the Snellen method). Acuity is expressed as a fraction, the number on top referring to the distance at which a normal person can read a particular size of letter and the lower number the distance at which the subject being tested can read that size of letter. Hence ‘normal’ visual acuity is 6/6 (European) or 20/20 (American). A person should be certified blind if the visual acuity (while wearing corrective glasses) is 3/60 or below (when a letter that can be recognized from 60 metres by a normal person can be identified only from 3 metres or closer). A person should also be certified blind if their acuity is between 3/60 and 6/60 but they have completely lost the peripheral part of their visual field, hence restricting their vision to the central part of the field. Indeed, if the more useful lower part of the visual field is lost then someone with better than 6/60 acuity can be certified blind.

There is no legal definition of partial sight in the UK, but a person can be certified as partially sighted if they are ‘substantially and permanently handicapped by defective vision caused by congenital defect or illness or injury’. All certification must be done by a consultant ophthalmologist. The help from Social Services should be the same for both legally blind and partially sighted groups but Social Security benefits and tax concessions differ.

Definitions of blindness are not the same around the world and the vast majority depend on measured visual acuity with no allowance for any functional deficits. Consequently comparison of the incidence of blindness world-wide is inexact. The World Health Organisation has proposed categories of visual impairment but these have not yet been widely adopted.

The common causes of blindness vary in different countries according to the general levels of economic and physical health. The high rate of blindness in developing countries is mainly due to malnutrition and infectious diseases, coupled with the scarcity of medical care. Moorfields Eye Hospital was founded in London in 1805 to treat the ‘Egyptian ophthalmia’, a mixture of trachoma and purulent ophthalmitis brought back by British troops from Aboukir after their withdrawal from Egypt in 1803. The disease quickly spread throughout the country when the disbanded soldiers returned to their homes, taking the infection with them. Nowadays the condition is treatable with tetracycline eye ointment and tetracycline taken orally.

Causes of blindness

Lack of vitamin A has a direct effect on the eye, causing clouding and softening of the cornea (keratomalacia), but also increases the risk and severity of infections, so that measles can be a blinding or even fatal disease in children who are deficient in vitamin A. Night-blindness due to lack of vitamin A may occur in famines, and cure of this condition by eating liver, which is rich in vitamin A, has been known for over 3000 years.

Another cause of night-blindness is pigmentary degeneration of the retina (retinitis pigmentosa) which, combined with partial loss of the visual field, eventually contracting down to ‘tunnel vision’, can be most disabling. This condition is mainly inherited as an autosomal recessive condition (showing itself only when both parents carry the mutant gene), but other forms occur. A high proportion of the population of the Atlantic island Tristan da Cunha was recently discovered to be affected when they were evacuated because of volcanic activity. The disorder is progressive and untreatable.

Trachoma, an infectious disease, affects some 500 million people world-wide, of whom 7 million are blind and 10 million visually impaired. The infectious agents are bacteria known as Chlamydia.

River blindness (onchocerciasis) is the next commonest infection, where microfilarial parasites, spread by black flies, which breed in the tropical, sub-Saharan belt across the whole of Africa and at similar latitudes in Mexico, Brazil, and Ecuador, invade the retina and the supporting, vascularized middle layer of the eyeball, the choroid. Treatment was revolutionized in 1987 when ivermectin, already used in veterinary medicine, was registered for human therapy.

From 1976 the total number of people registered blind in Britain has risen, but this rise is limited to those over 75 years old. Fifty per cent of all 75-85-year-olds registered with impaired vision in this country suffer from age-related macular degeneration (ARMD). Cataracts are now second as a cause of blindness, at around 40%, but these are essentially treatable by surgery except in those cases where extraction of the cataract reveals underlying, untreatable ARMD.

Damage to the retina caused by glaucoma (increased pressure in the eyeball) and by diabetes (diabetic retinopathy) make up almost all the remaining causes of blindness. Glaucoma is insidious in onset: acuity in the central visual field is not seriously affected and a diagnosis may not be made until much of the peripheral retina has been destroyed. Diabetic retinopathy is most prevalent and severe in long-standing insulin-dependent diabetes. This emphasizes the importance of striving for optimal diabetic control. Routine screening checks for both glaucoma and diabetic retinopathy are essential, but manpower and economic considerations have led to much of this work being transferred to orthoptists and optometrists. Retinal detachment (separation of the retina from the pigment epithelium behind it) is a rarer cause of blindness.

There is a long history of visual upsets from staring directly at the sun. The high energy optically concentrated at the central part of the retina for only seconds can produce prolonged after-images and even permanent loss of central vision. This is an occupational hazard for astronomers, and for members of the public who sun-gaze in a misguided attempt to strengthen their eyes or when under the influence of hallucinogenic drugs. There is a particular hazard during solar eclipses because the reduced total amount of light makes it easier to hold fixation on the sun, but the intensity on the remaining illuminated part of the retina is just as high (and just as damaging) as when there is no eclipse: hence the term ‘eclipse blindness’.

Possibilities for treatment

Given the immense social importance of vision, there is intense effort to develop new treatments for blinding conditions. These are focusing not only on the conventional approach of developing new vaccines to prevent infection and new drugs to treat specific conditions, but also on more innovative approaches. For instance, attempts have been made to implant an array of electrodes over the surface of the visual cortex, coupled to a video camera or an optical letter reader, in the hope of bypassing the eye and providing visual sensation by direct stimulation of the cortex. Unfortunately, such stimulation produces only the sensation of tiny pin-points of light, which appear to move with movements of the eyes. A more promising approach is the implantation of a thin sheet of light-sensitive electrodes into the retina, to take the place of degenerated receptors and provide direct stimulation to the fibres of the optic nerve.

Cortical blindness

Damage to the visual cortex in the occipital lobe of the cerebral hemispheres can also cause blindness — cortical blindness. When fixation is maintained on a point in space, a particular region of the visual field is blind (a ‘scotoma’) whether either eye is open, or both (because the cortex receives signals from corresponding regions of the two retinae). Cortical blindness can occur, for example, after a stroke affecting the posterior cerebral artery, which supplies blood to that part of the brain. If extensive damage occurs in one hemisphere, the opposite side of the visual field becomes blind (hemianopia). Often, a small region around the fixation point is spared. This ‘macular sparing’ is thought to be due to the fact that so much of the visual cortex is devoted to the central part of the retina that some part of this region has a high chance of surviving. Interestingly, even when the occipital visual cortex is bilaterally destroyed, resulting in total blindness with no light perception, the patient does not feel enveloped in darkness: rather, the outside world simply does not exist visually (as for the world behind our heads). This contrasts with blindness resulting from retinal damage (for instance from total bilateral retinal detachment), when the patient complains of being in complete darkness. Indeed, the cortically blind patients are subjectively unaware of their disability — blind to their blindness.

When damage is restricted to the primary visual cortex (not extending into the surrounding cortical areas) some patients are still able to detect certain forms of visual stimulation (especially moving objects and sudden changes in brightness) in the ‘blind’ part of the visual field. Amazingly, if the stimulus is not very intense or rapidly moving, they are often unaware of their residual visual capacity, but can reliably ‘guess’ whether, for instance, the stimulus has moved, and even in which direction. This bizarre dissociation of vision from consciousness is known as ‘blindsight’. Recent research even suggests that the facial expression of faces ‘seen’ in the blind part of the field can be recognized. Blindsight is not magic! Even when the primary visual cortex is damaged, information from the eyes still reaches parts of the midbrain and other visual parts of the cerebral cortex. These secondary pathways presumably mediate the impoverished visual performance.

If a stroke or injury leaves the primary visual cortex intact but destroys visual areas further forward in the occipital lobe of the cerebral hemispheres, remarkable disorders of visual perception, without frank blindness, can occur. These include the inability to see movement, even though stationary objects are quite normally perceived (akinetopsia), and a lack of perceived colour, despite normal perception of shape and movement (achromatopsia). These observations are entirely compatible with evidence from experiments in animals in which the activity of nerve cells has been recorded with microelectrodes, as well as with studies using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to detect activity in the normal human brain caused by different forms of visual stimulation. These experimental approaches have shown that the primary visual cortex is surrounded by a patchwork of other areas in which neurons are devoted to the analysis of one aspect or another of the visual image — motion in some areas, colour in others, etc.

Damage further forward, in the lower part of the temporal lobe, can precipitate even more curious failures of perceptual interpretation, generally known as visual agnosias (from the Greek for lack of knowledge). Not uncommon, especially after damage on the right side, is prosopagnosia — an inability to recognize faces, sometimes even of family members, although other aspects of object identification (even knowing that a face is a face) are intact. In extreme cases, the poor patient has great difficulty in recognizing a wide variety of everyday objects (until he or she touches them), even though all basic aspects of vision (acuity, colour vision, detection of movement, etc.) are unaffected.

Injury to the rear part of the corpus callosum — the great cable of millions of nerve fibres that links the two hemispheres — or to regions at the junction of the occipital and temporal lobes can cause specific disorders of visual integration (associational disturbances), such as word blindness (alexia).

Provision for the visually disabled

The reaction of the public to handicapped and disabled people remains capricious, and often prejudiced. The deaf have long been figures of fun: they are often ignored and easily retreat into solitude. However, the blind generally receive more sympathy, even admiration. Social Services for the blind unfortunately are not uniformly good throughout the UK. However, some national organizations such as the Royal National Institute for the Blind and Guide Dogs for the Blind give great help and provide funds for research into blindness as well. In 1835 Louis Braille introduced his system of raised writing, where projecting dots represent a letter or number and are interpreted by touch, but it took 30 years to gain acceptance. In this electronic age there are many devices which can make an enormous difference to the blind person's quality of life. One is a computer that reads out text audibly as it appears on screen. This can be set to speeds as fast as the subject can comprehend the speech. A braille printer and labelling machine help, for example, to identify foodstuffs in the kitchen or deep-freeze, or to catalogue a CD library. Microwave units can respond to and speak instructions and will defrost different foods correctly once they have been weighed. For contact with the outside world there are talking newspapers, which can be sent by compressed e-mail, or put on to the Internet. A CD-ROM of all British daily newspapers is available weekly. Never has so much been available for blind people who can afford it.

— Peter Fells, Colin Blakemore

Bibliography

• Cullinon, T. R. (1987). The epidemiology of blindness. In Clinical ophthalmology, (ed. S. Miller), p. 571. Wright, Bristol.
• Walsh, F. B. and Hoyt, W. F. (1969). Clinical neuro-ophthalmology, Vol. 1, (3rd edn), pp. 87-120. Williams and Wilkins, Baltimore

See also blind spot; eyes; optometry; orthoptics; vision.

noun

The condition of not being able to see: sightlessness. See see/not see.

Definition: sightlessness
Antonyms: sight, sightedness

Jewish law is very cognizant of the need to show consideration to the blind. Thus, while it is generally required to say the Amidah prayer standing and facing Jerusalem, a blind person need only direct his thoughts to Heaven, without having to find someone to point him in the right direction. Furthermore, while a person who has been blind from birth cannot act as the cantor for the morning Shema prayer, because it deals with the luminaries in the heavens, he can recite the prayers on his own. A blind person may also be called up to the Torah reading, even though he will only hear the words read and not see them. While he is required to say the prayers over the new Moon (kiddush levanah) and the blessings over the Hanukkah lights, a blind person does not recite the blessing over the Havdalah candle.

In general, unlike deaf-mutes (see ḥeresh, Shoteh, and Katan), the blind are regarded in Jewish law as fully normal and only restricted insofar as warranted by their physical limitations.

Lack or loss of ability to see. Diagnosed in an animal on the absence of a menace reflex, walking into obstructions and failure to indicate awareness of a soundless movement in its visual field, e.g. a falling cotton ball or feather.

• Appaloosa night b. — see appaloosa.
• bright b. — toxic retinopathy in sheep grazing bracken; characterized by blindness, dilated pupils, poor pupillary light reflex, retinal degeneration.
• central b. — due to a lesion of the optic cortex; the pupillary light reflex still functions. Called also cortical blindness.
• cortical b. — see central blindness (above).
• day b. — defective vision in bright light. See also hemeralopia.
• inherited congenital b. — occurs in a number of breeds of cattle in which there are several defects in the eyes including irideremia, microphakia, ectopia lentis and cataract.
• night b. — failure or imperfection of vision in conditions of diminished illumination; a characteristic of progressive retinal atrophy.
• peripheral b. — blindness due to a lesion in the optical apparatus peripheral to the optical cortex, including lesions in the optic chiasma, optic nerve, retina, anterior and posterior chambers, lens and cornea. With the exception of obvious lesions in the eyeball this is characterized by dilatation of the pupil and absence of the pupillary light reflex.

Quotes:

"In the country of the blind, the one-eyed man is King." - Michael Apostolius

"Blindness hatred is blind, as well as love." - Thomas Fuller

"But who would rush at a benighted man, and give him two black eyes for being blind?" - Thomas Hood

"There is a condition worse than blindness, and that is, seeing something that isn't there." - L. Ron Hubbard

"We may remark in passing that to be blind and beloved may, in this world where nothing is perfect, be among the most strangely exquisite forms of happiness. The supreme happiness in life is the assurance of being loved; of being loved for oneself, even in spite of oneself; and this assurance the blind man possesses. In his affliction, to be served is to be caressed. Does he lack anything? no. Possessing love he is not deprived of light. A love, moreover, that is wholly pure. There can be no blindness where there is this certainty." - Victor Hugo

"What a blind person needs is not a teacher but another self." - Helen Keller

See more famous quotes about Blindness

This article is about the visual condition. For other uses, see Blindness (disambiguation).

Blindness
Classification and external resources
A white cane, the international symbol of blindness
ICD-10	H54.0, H54.1, H54.4
ICD-9	369
DiseasesDB	28256

Blindness is the condition of lacking visual perception due to physiological or neurological 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 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 with residual vision. Those described as having only light perception have no more sight than the ability to tell light from dark and the general direction of a light source.

In order to determine which people may need special assistance because of their visual disabilities, various governmental jurisdictions have formulated more complex definitions referred to as legal blindness.^[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 (6.1 m) from an object to see it—with corrective lenses—with the same degree of clarity as a normally sighted person could from 200 feet (61 m). In many areas, people with average acuity who nonetheless have a visual field of less than 20 degrees (the norm being 180 degrees) are also classified as being legally blind. Approximately ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to relatively good acuity. Low vision is sometimes used to describe visual acuities from 20/70 to 20/200.^[3]

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 (20/60), but equal to or better than 3/60 (20/400), 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 (20/400), or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.^[4][5]

It should be noted that blind people with undamaged eyes may still register light non-visually for the purpose of circadian entrainment to the 24-hour light/dark cycle. Light signals for this purpose travel through the retinohypothalamic tract, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.

Contents 1 Classification 2 Causes 2.1 Diseases 2.2 Abnormalities and injuries 2.3 Genetic defects 2.4 Poisoning 2.5 Willful actions 3 Management 3.1 Adaptive techniques 3.2 Tools 4 Epidemiology 5 Society and culture 5.1 Metaphorical uses 5.2 Sports 6 In other animals 7 See also 8 References 9 External links

Classification

The examples and perspective in this section deal primarily with the United States and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page.

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.^[6]

The United States Congress included this definition as part of the Aid to the Blind program in the Social Security Act 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 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 US, 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 using a number IV target size. If the doctor or facility performing the test is approved by the Social Security Administration, this is the official US determination for legal blindness due to field loss in conditions like retinitis pigmentosa.

Kuwait is one of many nations that share the same criteria for legal blindness.^[10]

Causes

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 (47.9%),
• glaucoma (12.3%),
• age-related macular degeneration (8.7%),
• corneal opacity (5.1%), and
• diabetic retinopathy (4.8%), among other causes.^[11]

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.

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.^[12]

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 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.^[13] 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 man named Mohammad Sajid was sentenced to be blinded under Islamic Qisas law, for blinding his fiancee after her parents called off the engagement.^[14] The same sentence was given in 2009 for the man who blinded Ameneh Bahrami.

Management

A 2008 study published in the New England Journal of Medicine^[15] 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.^[16]

Adaptive techniques

A tactile feature on a Canadian banknote.

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 and mobile phone software that allows people with visual impairments to interact with their computers and/or phones via screen readers or screen magnifiers.
• 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 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.^[17]
  • 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

Designers, both visually impaired and sighted, have developed a number of tools for use by blind people.

Mobility

Folded long cane.

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

Tools such as the white cane with a red tip - the international 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 is the pilot, who gets them there safely.

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. 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

Watch for the blind

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.

The rest 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. 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.

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 and Screen magnifiers enable the blind to use mainstream computer applications. 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

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.

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.^[18] 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.^[19] In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness.^[20] Of this number, 58% were over the age of 65.^[20] In 1994-1995, 1.3 million Americans reported legal blindness.^[21]

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 where 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.

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, cricket and golf.^[22] The worldwide authority on sports for the blind is the International Blind Sports Federation.^[23] People with vision impairments have participated in the Paralympic Games since the 1976 summer Paralympics in Toronto.^[24]

In other animals

Main article: Blind 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

• Accessibility
• Amaurosis
• Blindism
• Blind artists
• Blind musicians
• Blindness and education
• Braille
• Color blindness
• Cortical blindness
• Deafblind
• GPS for the visually impaired
• Inattentional blindness
• List of eye diseases
• List of blind people
• Night blindness
• Scotoma
• Seeing is Believing (organization)
• Snow blindness
• Slate and stylus
• Stereoblindness
• Tactile alphabets for the blind
• Tactile graphic
• Tangible symbol systems
• Web accessibility

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. ^ "Causes of blindness and visual impairment". World Health Organization. http://www.who.int/blindness/causes/en/. Retrieved 19 February 2009. 
12. ^ 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.
13. ^ "Methanol" (Web). Symptoms of Methanol Poisoning. Canada Safety Council. 2005. http://www.safety-council.org/info/OSH/methanol.htm. Retrieved March 27, 2007. 
14. ^ "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. 
15. ^ 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. 
16. ^ Bionic Eye Opens New World Of Sight For Blind by Jon Hamilton. All Things Considered, National Public Radio. 20 Oct 2009.
17. ^ Accessibility features - Bank Notes - Bank of Canada
18. ^ "World Health Organization" (Web). World Health Organization. 2006. http://www.who.int/en/. Retrieved December 16, 2006. 
19. ^ "WHO | Visual impairment and blindness". http://www.who.int/mediacentre/factsheets/fs282/en/index.html. 
20. ^ ^{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.
21. ^ American Foundation for the Blind. "Statistics and Sources for Professionals." Retrieved April 1, 2006.
22. ^ "Blind Sports Victoria". http://www.blindsports.org.au/. Retrieved 2008-03-04. 
23. ^ "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. 
24. ^ "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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v • d • e Eye disease · pathology of the eye (H00-H59, 360-379) Adnexa eyelid: inflammation (Stye, Chalazion, Blepharitis) · Entropion · Ectropion · Lagophthalmos · Blepharochalasis · Ptosis · Blepharophimosis · Xanthelasma · eyelash (Trichiasis, Madarosis) lacrimal system: Dacryoadenitis · Epiphora · Dacryocystitis · Xerophthalmia orbit: Exophthalmos · Enophthalmos conjunctiva: Conjunctivitis (Allergic conjunctivitis) · Pterygium · Pinguecula · Subconjunctival hemorrhage Globe Fibrous tunic sclera: Scleritis cornea: Keratitis (Herpetic keratitis, Acanthamoeba keratitis, Fungal keratitis) · Corneal ulcer · Snow blindness · Thygeson's superficial punctate keratopathy · Corneal dystrophy (Fuchs', Meesmann) · Keratoconus · Keratoconjunctivitis sicca · Arc eye · Keratoconjunctivitis · Corneal neovascularization  · Kayser-Fleischer ring · Arcus senilis · Band keratopathy Vascular tunic Iris and ciliary body Iritis · Uveitis (Intermediate uveitis) · Iridocyclitis · Hyphema · Rubeosis iridis · Persistent pupillary membrane · Iridodialysis · Synechia Choroid Choroideremia · Choroiditis (Chorioretinitis) Lens Cataract · Aphakia · Ectopia lentis Retina Retinitis (Chorioretinitis, Cytomegalovirus retinitis) · Retinal detachment · Retinoschisis · Ocular ischemic syndrome/Central retinal vein occlusion · Retinopathy (Bietti's crystalline dystrophy, Coats disease, Diabetic retinopathy, Hypertensive retinopathy, Retinopathy of prematurity) · Macular degeneration · Retinitis pigmentosa · Retinal haemorrhage · Central serous retinopathy · Macular edema · Epiretinal membrane · Macular pucker · Vitelliform macular dystrophy · Leber's congenital amaurosis · Birdshot chorioretinopathy Other Glaucoma/Ocular hypertension · Floater · Leber's hereditary optic neuropathy · Red eye · Keratomycosis · Phthisis bulbi Pathways Optic nerve and visual pathways Optic neuritis · Papilledema · Optic atrophy · Leber's hereditary optic neuropathy · Dominant optic atrophy · Optic disc drusen · Glaucoma · Toxic and nutritional optic neuropathy · Anterior ischemic optic neuropathy Ocular muscles, binocular movement, accommodation and refraction Paralytic strabismus: Ophthalmoparesis · Progressive external ophthalmoplegia · Palsy (III, IV, VI) · Kearns-Sayre syndrome Other strabismus: Esotropia/Exotropia · Hypertropia · Heterophoria (Esophoria, Exophoria) · Brown's syndrome · Duane syndrome Other binocular: Conjugate gaze palsy · Convergence insufficiency · Internuclear ophthalmoplegia · One and a half syndrome Refractive error: Hyperopia/Myopia · Astigmatism · Anisometropia/Aniseikonia · Presbyopia Visual disturbances and blindness Amblyopia · Leber's congenital amaurosis  · Subjective (Asthenopia, Hemeralopia, Photophobia, Scintillating scotoma) · Diplopia · Scotoma · Anopsia (Binasal hemianopsia, Bitemporal hemianopsia, Homonymous hemianopsia, Quadrantanopia) · Color blindness (Achromatopsia, Dichromacy, Monochromacy) · Nyctalopia (Oguchi disease) · Blindness/Low vision Pupil Anisocoria · Argyll Robertson pupil · Marcus Gunn pupil · Adie syndrome · Miosis · Mydriasis · Cycloplegia Other Nystagmus Eye infections Trachoma · Onchocerciasis eye navs: anat/adnexa anat/pathways/physio/dev, noncongen/congen/neoplasia, eponymous signs, proc

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