Blindness
Overview
 
Blindness is the condition of lacking visual perception
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...

 due to physiological
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 or neurological
Neurology
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,...

 factors.

Various scales have been developed to describe the extent of vision loss
Vision loss
Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically .-Ranges of vision loss:...

 and define blindness. Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for "no light perception." Blindness is frequently used to describe severe visual impairment
Visual impairment
Visual impairment is vision loss 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...

 with residual vision.
Discussions
Encyclopedia
Blindness is the condition of lacking visual perception
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...

 due to physiological
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 or neurological
Neurology
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,...

 factors.

Various scales have been developed to describe the extent of vision loss
Vision loss
Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically .-Ranges of vision loss:...

 and define blindness. Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for "no light perception." Blindness is frequently used to describe severe visual impairment
Visual impairment
Visual impairment is vision loss 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...

 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. In North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and most of Europe
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 watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, legal blindness is defined as visual acuity
Visual acuity
Visual acuity is acuteness or clearness of 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 lens
Corrective lens
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...

es—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
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...

 of less than 20 degrees
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...

 (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
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 Low vision is a subspecialty within...

 is sometimes used to describe visual acuities from 20/70 to 20/200.

By the 10th Revision of the WHO
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

 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.

Blind people with undamaged eyes may still register light non-visually for the purpose of circadian
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

 entrainment
Entrainment (chronobiology)
Entrainment, within the study of chronobiology, occurs when rhythmic physiological or behavioral events match their period and phase to that of an environmental oscillation. A common example is the entrainment of circadian rhythms to the daily light–dark cycle, which ultimately is determined by...

 to the 24-hour light/dark cycle. Light signals for this purpose travel through the retinohypothalamic tract
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...

, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.

Classification

In 1934, the American Medical Association
American Medical Association
The American Medical Association , founded in 1847 and incorporated in 1897, is the largest association of medical doctors and medical students in the United States.-Scope and operations:...

 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.


The United States Congress
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, 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 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
Supplemental Security Income
Supplemental Security Income is a United States government program that provides stipends to low-income people who are either aged , blind, or disabled. Although administered by the Social Security Administration, SSI is funded from the U.S. Treasury general funds, not the Social Security trust fund...

 program 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.


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
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...

 using a number IV target size. If the doctor or facility performing the test is approved by the Social Security Administration
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...

, this is the official US determination for legal blindness due to field loss in conditions like retinitis pigmentosa
Retinitis pigmentosa
Retinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. 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...

.

Kuwait
Kuwait
The State of Kuwait is a sovereign Arab state situated in the north-east of the Arabian Peninsula in Western Asia. It is bordered by Saudi Arabia to the south at Khafji, and Iraq to the north at Basra. It lies on the north-western shore of the Persian Gulf. The name Kuwait is derived from the...

 is one of many nations that share the same criteria for legal blindness.

In the UK, the Certificate of Vision Impairment (CVI) is used to certify patients as severely sight impaired or sight impaired. The accompanying guidance for clinical staff states:

The National Assistance Act 1948 states that a person can be certified as severely sight impaired if they are “so blind as to be unable to perform any work for which eye sight is essential” (National Assistance Act Section 64(1)). The test is whether a person cannot do any work for which eyesight is essential, not just his or her normal job or one particular job.


In practice, the definition depends on individuals' visual acuity
Visual acuity
Visual acuity is acuteness or clearness of 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.
  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.

Causes

Serious visual impairment has a variety of causes:

Diseases

According to WHO
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

 estimates, the most common causes of blindness around the world in 2002 were:
  1. cataract
    Cataract
    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...

    s (47.9%),
  2. glaucoma
    Glaucoma
    Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

     (12.3%),
  3. age-related macular degeneration
    Macular degeneration
    Age-related macular degeneration is a medical condition which usually affects older adults and 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 blindness and visual impairment in older adults...

     (8.7%),
  4. cornea
    Cornea
    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, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

    l opacity (5.1%), and
  5. diabetic retinopathy
    Diabetic retinopathy
    Diabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness....

     (4.8%),
  6. childhood blindness (3.9%),
  7. trachoma
    Trachoma
    Trachoma is an infectious disease causing a characteristic roughening of the inner surface of the eyelids. Also called granular conjunctivitis and Egyptian ophthalmia, it is the leading cause of infectious blindness in the world...

     (3.6%)
  8. onchocerciasis
    Onchocerciasis
    Onchocerciasis , also known as river blindness and Robles' disease, is a parasitic disease caused by infection by Onchocerca volvulus, a nematode . Onchocerciasis is the world's second-leading infectious cause of blindness. It is not the nematode, but its endosymbiont, Wolbachia pipientis, that...

     (0.8%).


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
Poverty is the lack of a certain amount of material possessions or money. Absolute poverty or destitution is inability to afford basic human needs, which commonly includes clean and fresh water, nutrition, health care, education, clothing and shelter. About 1.7 billion people are estimated to live...

 and treatable visual impairment is most obvious when conducting regional comparisons of cause. Most adult visual impairment in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and Western Europe
Western Europe
Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...

 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
Onchocerciasis , also known as river blindness and Robles' disease, is a parasitic disease caused by infection by Onchocerca volvulus, a nematode . Onchocerciasis is the world's second-leading infectious cause of blindness. It is not the nematode, but its endosymbiont, Wolbachia pipientis, that...

, 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
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 time lead to the development of the cataract and loss of transparency, causing impairment or loss of vision...

 is more available, age-related macular degeneration, glaucoma, and diabetic retinopathy are usually the leading causes of blindness.

Childhood blindness can be caused by conditions related to pregnancy, such as congenital rubella syndrome
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...

 and retinopathy of prematurity
Retinopathy of prematurity
Retinopathy of prematurity , previously known as retrolental fibroplasia , 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...

.

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
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. Injuries and cataracts affect the eye itself, while abnormalities such as optic nerve hypoplasia
Optic nerve hypoplasia
Optic nerve hypoplasia is a medical condition arising from the underdevelopment of the optic nerve. This condition is the most common congenital optic nerve anomaly. The optic disc appears abnormally small, because 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
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...

 of the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

 can, despite having undamaged eyes and optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

s, still be legally or totally blind.

Genetic defects

People with albinism
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...

 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
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.It was first described by Theodor Leber in the 19th century...

 can cause total blindness or severe sight loss from birth or early childhood.

Recent advances in mapping of the human genome
Human genome
The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs plus the small mitochondrial DNA. 22 of the 23 chromosomes are autosomal chromosome pairs, while the remaining pair is sex-determining...

 have identified other genetic causes of low vision
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 Low vision is a subspecialty within...

 or blindness. One such example is Bardet-Biedl syndrome
Bardet-Biedl syndrome
The Bardet–Biedl syndrome is a ciliopathic human genetic disorder that produces many effects and affects many body systems. It is characterized principally by obesity, retinitis pigmentosa, polydactyly, mental retardation, hypogonadism, and renal failure in some cases.-Summary of the...

.

Poisoning

Rarely, blindness is caused by the intake of certain chemicals. A well-known example is methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

, which is only mildly toxic and minimally intoxicating, but when not competing with ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 for metabolism, methanol breaks down into the substances formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

 and formic acid
Formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...

 which in turn can cause blindness, an array of other health complications, and death. 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
Alcoholism
Alcoholism is a broad term for problems with alcohol, and is generally used to mean compulsive and uncontrolled consumption of alcoholic beverages, usually to the detriment of the drinker's health, personal relationships, and social standing...

 as a desperate and cheap substitute for regular ethanol alcoholic beverages.

Willful actions

Blinding has been used as an act of vengeance and torture
Torture
Torture is the act of inflicting severe pain as a means of punishment, revenge, forcing information or a confession, or simply as an act of cruelty. Throughout history, torture has often been used as a method of political re-education, interrogation, punishment, and coercion...

 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
Oedipus
Oedipus was a mythical Greek king of Thebes. He fulfilled a prophecy that said he would kill his father and marry his mother, and thus brought disaster on his city and family...

, who gouges out his own eyes after realizing that he fulfilled the awful prophecy spoken of him. Having crushed the Bulgarians, the Byzantine Emperor Basil II
Basil II
Basil II , known in his time as Basil the Porphyrogenitus and Basil the Young to distinguish him from his ancestor Basil I the Macedonian, was a Byzantine emperor from the Macedonian dynasty who reigned from 10 January 976 to 15 December 1025.The first part of his long reign was dominated...

 blinded as many as 15,000 prisoners taken in the battle, before releasing them.

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. The same sentence was given in 2009 for the man who blinded Ameneh Bahrami
Ameneh Bahrami
Ameneh Bahrami is an Iranian woman blinded in an acid attack. She became the focus of international controversy after demanding that her attacker, Majid Movahedi, be punished by being similarly blinded...

.

Comorbidities

Blindness can occur in combination with such conditions as mental retardation
Mental retardation
Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...

, autism spectrum disorders, cerebral palsy
Cerebral palsy
Cerebral palsy is an umbrella term encompassing a group of non-progressive, non-contagious motor conditions that cause physical disability in human development, chiefly in the various areas of body movement....

, hearing impairment
Hearing impairment
-Definition:Deafness is the inability for the ear to interpret certain or all frequencies of sound.-Environmental Situations:Deafness can be caused by environmental situations such as noise, trauma, or other ear defections...

s, and epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

. In a study of 228 visually impaired children in metropolitan Atlanta between 1991 and 1993, 154 (68%) had an additional disability besides visual impairment. Blindness in combination with hearing loss is known as deafblindness
Deafblindness
Deafblindness is the condition of little or no useful sight and little or no useful hearing. Educationally, individuals are considered to be deafblind when the combination of their hearing and vision loss causes such severe communication and other developmental and educational needs that they...

.

Management

A 2008 study published in the New England Journal of Medicine tested the effect of using gene therapy to help restore the sight of patients with a rare form of inherited blindness, known as Leber's congenital amaurosis
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.It was first described by Theodor Leber in the 19th century...

 or LCA. Leber's Congenital Amaurosis damages the light receptors in the retina and usually begins affecting sight in early childhood, with worsening vision until complete blindness around the age of 30.

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

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

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
White cane
A white cane is used by many people who are blind or visually impaired, both as a mobility tool and as a courtesy to others. Not all modern white canes are designed to fulfill the same primary function, however: There are at least five varieties of this tool, each serving a slightly different...

 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 dog
Guide dog
Guide dogs are assistance dogs trained to lead blind and visually impaired people around obstacles.Although the dogs can be trained to navigate various obstacles, they are partially color blind and are not capable of interpreting street signs...

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

Some blind people use GPS for the visually impaired
GPS for the visually impaired
There have been many attempts to integrate Global Positioning System into a navigation-assistance system for the blind. GPS was introduced in the late 1980s and since then there have been several research projects to increase it's usefulness for the visually impaired.Satellite navigation...

 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.

Technology to allow blind people to drive motor vehicles is currently being developed.

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
Tactile paving
Tactile paving is a system of textured ground surface indicators found on many footpaths, stairs and train station platforms to assist blind and vision impaired pedestrians.Tactile warnings provide a distinctive surface pattern of "truncated domes" or cones...

 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

Most visually impaired people who are not totally blind read print, either of a regular size or enlarged by magnification devices. Many also read large-print, which is easier for them to read without such devices. A variety of magnifying glass
Magnifying glass
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle ....

es, some handheld, and some on desktops, can make reading easier for them.

Others read Braille
Braille
The Braille system is a method that is widely used by blind people to read and write, and was the first digital form of writing.Braille was devised in 1825 by Louis Braille, a blind Frenchman. Each Braille character, or cell, is made up of six dot positions, arranged in a rectangle containing two...

 (or the infrequently used Moon type
Moon type
The Moon System of Embossed Reading is a writing system for the blind, using embossed symbols mostly derived from the Roman alphabet...

), or rely on talking books and readers or reading machine
Reading machine
A reading machine is a piece of Assistive Technology that allows blind people to access printed materials. It scans text, converts the image into text by means of optical character recognition and uses a speech synthesizer to read out what it has found....

s, which convert printed text to speech or Braille
Braille
The Braille system is a method that is widely used by blind people to read and write, and was the first digital form of writing.Braille was devised in 1825 by Louis Braille, a blind Frenchman. Each Braille character, or cell, is made up of six dot positions, arranged in a rectangle containing two...

. They use computers with special hardware such as scanners
Image scanner
In computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop scanner where the document is placed on a glass...

 and refreshable Braille display
Refreshable Braille display
A refreshable Braille display or Braille terminal is an electro-mechanical device for displaying Braille characters, usually by means of raising dots through holes in a flat surface. Blind computer users, who cannot use a normal computer monitor, use it to read text output...

s as well as software written specifically for the blind, such as optical character recognition
Optical character recognition
Optical character recognition, usually abbreviated to OCR, is the mechanical or electronic translation of scanned images of handwritten, typewritten or printed text into machine-encoded text. It is widely used to convert books and documents into electronic files, to computerize a record-keeping...

 applications and screen reader
Screen reader
A screen reader is a software application that attempts to identify and interpret what is being displayed on the screen . This interpretation is then re-presented to the user with text-to-speech, sound icons, or a Braille output device...

s.

Some people access these materials through agencies for the blind, such as the National Library Service for the Blind and Physically Handicapped
National Library Service for the Blind and Physically Handicapped
The National Library Service for the Blind and Physically Handicapped is a free library program of braille and audio materials circulated to eligible borrowers in the United States by postage-free mail. The program is a service sponsored by the Library of Congress. People may be eligible for the...

 in the United States, the National Library for the Blind
National Library for the Blind
The National Library for the Blind was a public library in the United Kingdom, founded 1882, which aimed to ensure that people with sight problems have the same access to library services as sighted people. NLB was taken over by RNIB on 1 January 2007.-Origins:The Lending Library for the Blind...

 or the RNIB in the United Kingdom.

Closed-circuit television
Closed-circuit television
Closed-circuit television is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors....

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

There are also over 100 radio reading service
Radio reading service
A radio reading service or reading service for the blind is a service of many universities, community groups and public radio stations, where a narrator reads books, newspapers and magazines aloud for the benefit of the blind and vision-impaired. It is most often carried on a subcarrier, with...

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

Computers

Access technology such as screen reader
Screen reader
A screen reader is a software application that attempts to identify and interpret what is being displayed on the screen . This interpretation is then re-presented to the user with text-to-speech, sound icons, or a Braille output device...

s, screen magnifier
Screen magnifier
A screen magnifier is software that interfaces with a computer's graphical output to present enlarged screen content. It is a type of assistive technology suitable for visually impaired people with some functional vision; visually impaired people with little or no functional vision usually use a...

s and refreshable Braille display
Refreshable Braille display
A refreshable Braille display or Braille terminal is an electro-mechanical device for displaying Braille characters, usually by means of raising dots through holes in a flat surface. Blind computer users, who cannot use a normal computer monitor, use it to read text output...

s enable the blind to use mainstream computer applications and mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

s. The availability of assistive technology is increasing, accompanied by concerted efforts to ensure the accessibility of information technology to all potential users, including the blind. Later versions of Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 include an Accessibility Wizard & Magnifier for those with partial vision, and Microsoft Narrator
Microsoft Narrator
Narrator is a light-duty screen reader utility included in Microsoft Windows. Narrator reads dialog boxes and window controls in a number of the more basic applications for Windows....

, a simple screen reader. Linux distribution
Linux distribution
A Linux distribution is a member of the family of Unix-like operating systems built on top of the Linux kernel. Such distributions are operating systems including a large collection of software applications such as word processors, spreadsheets, media players, and database applications...

s (as live CD
Live CD
A live CD, live DVD, or live disc is a CD or DVD containing a bootable computer operating system. Live CDs are unique in that they have the ability to run a complete, modern operating system on a computer lacking mutable secondary storage, such as a hard disk drive...

s) for the blind include Oralux
Oralux
Oralux is an association whose objective is to foster digital accessibility using solutions based upon Free Software and open standards. The association proposes Voxin, an easily installable add-on which provides yet another text-to-speech to blind users of Linux....

 and Adriane Knoppix, the latter developed in part by Adriane Knopper
Klaus Knopper
Klaus Knopper is a German electrical engineer and free software developer. "My nationality from my passport is austrian, not german, though I will absolutely not complain about being listed as "german engineer", because I was born and have lived in Germany all of my life", - says Klaus...

 who has a visual impairment. Mac OS also comes with a built-in screen reader, called VoiceOver
VoiceOver
VoiceOver is a screen reader built into Apple Inc.'s Mac OS X, iOS and iPod operating systems. By using VoiceOver, the user can access their Macintosh or iOS device based on spoken descriptions and, in the case of the Mac, the keyboard. The feature is designed to increase accessibility for blind...

.

The movement towards greater web accessibility
Web accessibility
Web accessibility refers to the inclusive practice of making websites usable by people of all abilities and disabilities. When sites are correctly designed, developed and edited, all users can have equal access to information and functionality...

 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
Sensory substitution
Sensory substitution means to transform the characteristics of one sensory modality into stimuli of another sensory modality. It is hoped that sensory substitution systems can help handicapped people by restoring their ability to perceive a certain defective sensory modality by using sensory...

 are beginning to provide access to arbitrary live views from a camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...

.

Modified visual output that includes large print and/or clear simple graphics can be of benefit to users with some residual vision.

Other aids and techniques

Blind people may use talking equipment such as thermometer
Thermometer
Developed during the 16th and 17th centuries, a thermometer is a device that measures temperature or temperature gradient using a variety of different principles. A thermometer has two important elements: the temperature sensor Developed during the 16th and 17th centuries, a thermometer (from the...

s, watches, clocks, scales
Weighing scale
A weighing scale is a measuring instrument for determining the weight or mass of an object. A spring scale measures weight by the distance a spring deflects under its load...

, calculator
Calculator
An electronic calculator is a small, portable, usually inexpensive electronic device used to perform the basic operations of arithmetic. Modern calculators are more portable than most computers, though most PDAs are comparable in size to handheld calculators.The first solid-state electronic...

s, and compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

es. They may also enlarge or mark dials on devices such as ovens and thermostats to make them usable. Other techniques used by blind people to assist them in daily activities include:
  • Adaptations of coin
    Coin
    A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....

    s and banknote
    Banknote
    A banknote is a kind of negotiable instrument, a promissory note made by a bank payable to the bearer on demand, used as money, and in many jurisdictions is legal tender. In addition to coins, banknotes make up the cash or bearer forms of all modern fiat money...

    s so that the value can be determined by touch. For example:
    • In some currencies, such as the euro
      Euro
      The euro is the official currency of the eurozone: 17 of the 27 member states of the European Union. It is also the currency used by the Institutions of the European Union. The eurozone consists of Austria, Belgium, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg,...

      , the pound sterling
      Pound sterling
      The pound sterling , commonly called the pound, is the official currency of the United Kingdom, its Crown Dependencies and the British Overseas Territories of South Georgia and the South Sandwich Islands, British Antarctic Territory and Tristan da Cunha. It is subdivided into 100 pence...

       and the Indian rupee
      Indian rupee
      The Indian rupee is the official currency of the Republic of India. The issuance of the currency is controlled by the Reserve Bank of India....

      , 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
      Canadian currency tactile feature
      The Canadian currency tactile feature is a feature on the current "Canadian Journey" series of Canadian banknotes. The feature indicates the banknote denomination in the upper right corner of the face side of the bill using a series of raised dots. It was suggested by Bruno Thériault, an...

       is a system of raised dots in one corner, based on Braille cells but not standard Braille
      Braille
      The Braille system is a method that is widely used by blind people to read and write, and was the first digital form of writing.Braille was devised in 1825 by Louis Braille, a blind Frenchman. Each Braille character, or cell, is made up of six dot positions, arranged in a rectangle containing two...

      .
    • 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
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

 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. In order of frequency the leading causes were cataract
Cataract
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...

, uncorrected refractive errors (near sighted, far sighted, or an astigmatism
Astigmatism
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances...

), glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

, and age-related macular degeneration.
In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness. Of this number, 58% were over the age of 65. In 1994-1995, 1.3 million Americans reported legal blindness.

In literature and the arts

In Greek myth, Tiresias
Tiresias
In Greek mythology, Tiresias was a blind prophet of Thebes, famous for clairvoyance and for being transformed into a woman for seven years. He was the son of the shepherd Everes and the nymph Chariclo; Tiresias participated fully in seven generations at Thebes, beginning as advisor to Cadmus...

 was a prophet famous for his clairvoyance
Clairvoyance
The term clairvoyance is used to refer to the ability to gain information about an object, person, location or physical event through means other than the known human senses, a form of extra-sensory perception...

. According to one myth, he was blinded by the Gods as punishment for revealing their secrets, while another holds that he was blinded as punishment after he saw Athena naked while she was bathing. In the Odyssey, the one-eyed Cyclops Polyphemus
Polyphemus
Polyphemus is the gigantic one-eyed son of Poseidon and Thoosa in Greek mythology, one of the Cyclopes. His name means "much spoken of" or "famous". Polyphemus plays a pivotal role in Homer's Odyssey.-In Homer's Odyssey:...

 captures Odysseus
Odysseus
Odysseus or Ulysses was a legendary Greek king of Ithaca and the hero of Homer's epic poem the Odyssey. Odysseus also plays a key role in Homer's Iliad and other works in the Epic Cycle....

, who blinds Polyphemus in order to escape. In Norse mythology, Loki
Loki
In Norse mythology, Loki or Loke is a god or jötunn . Loki is the son of Fárbauti and Laufey, and the brother of Helblindi and Býleistr. By the jötunn Angrboða, Loki is the father of Hel, the wolf Fenrir, and the world serpent Jörmungandr. By his wife Sigyn, Loki is the father of Nari or Narfi...

 tricks the blind God Höðr
Höðr
Höðr is the brother of Baldr in Norse mythology. Guided by Loki he shot the mistletoe missile which was to slay the otherwise invulnerable Baldr....

 into killing his brother Baldr, the God of happiness.

The New Testament
New Testament
The New Testament is the second major division of the Christian biblical canon, the first such division being the much longer Old Testament....

 contains numerous instances of Jesus performing miracles
Miracles of Jesus
The miracles of Jesus are the supernatural deeds of Jesus, as recorded in Gospels, in the course of his ministry. According to the Gospel of John, only some of these were recorded. states that "Jesus did many other things as well...

 to heal the blind. According to the Gospels, Jesus healed the two blind men of Galilee
Healing the two blind men in Galilee
Jesus healing two blind men is one of the miracles of Jesus in the Gospels , immediately following the account of the Daughter of Jairus miracle...

, the blind man of Bethsaida, the blind man of Jericho and the man who was born blind
Healing the blind at birth
Healing the blind at birth is one of the miracles of Jesus in the Gospels .According to the Gospel, Jesus saw a man blind from birth. His disciples asked him, "Rabbi, who sinned, this man or his parents, that he was born blind?"Jesus replied:...

.

The parable of the blind men and an elephant
Blind Men and an Elephant
The story of the blind men and an elephant originated in India from where it is widely diffused. It has been used to illustrate a range of truths and fallacies...

 has crossed between many religious traditions and is part of Jain
Jainism
Jainism is an Indian religion that prescribes a path of non-violence towards all living beings. Its philosophy and practice emphasize the necessity of self-effort to move the soul towards divine consciousness and liberation. Any soul that has conquered its own inner enemies and achieved the state...

, Buddhist, Sufi and Hindu
Hindu
Hindu refers to an identity associated with the philosophical, religious and cultural systems that are indigenous to the Indian subcontinent. As used in the Constitution of India, the word "Hindu" is also attributed to all persons professing any Indian religion...

 lore. In various versions of the tale, a group of blind men (or men in the dark) touch an elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...

 to learn what it is like. Each one feels a different part, but only one part, such as the side or the tusk. They then compare notes and learn that they are in complete disagreement.
Poet John Milton
John Milton
John Milton was an English poet, polemicist, a scholarly man of letters, and a civil servant for the Commonwealth of England under Oliver Cromwell...

, who went blind in mid-life, composed On His Blindness
On His Blindness
On His Blindness is one of the best known of the sonnets of John Milton. It may have been written as early as 1652, although most scholars believe it was composed sometime between June and October of 1655, when Milton's blindness was essentially complete....

, a sonnet about coping with blindness. The work posits that [those] who best Bear [God]'s mild yoke, they serve him best.

The Dutch painter and engraver Rembrandt often depicted scenes from the apocryphal Book of Tobit
Book of Tobit
The Book of Tobit is a book of scripture that is part of the Catholic and Orthodox biblical canon, pronounced canonical by the Council of Carthage of 397 and confirmed for Roman Catholics by the Council of Trent...

, which tells the story of a blind patriarch who is healed by his son, Tobias, with the help of the archangel Raphael
Raphael (archangel)
Raphael is an archangel of Judaism, Christianity, and Islam, who in the Judeo-Christian tradition performs all manners of healing....

.

Slaver-turned-abolitionist John Newton
John Newton
John Henry Newton was a British sailor and Anglican clergyman. Starting his career on the sea at a young age, he became involved with the slave trade for a few years. After experiencing a religious conversion, he became a minister, hymn-writer, and later a prominent supporter of the abolition of...

 composed the hymn Amazing Grace
Amazing Grace
"Amazing Grace" is a Christian hymn with words written by the English poet and clergyman John Newton , published in 1779. With a message that forgiveness and redemption are possible regardless of the sins people commit and that the soul can be delivered from despair through the mercy of God,...

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

"Three Blind Mice
Three Blind Mice
Three Blind Mice is an English nursery rhyme and musical round. It has a Roud Folk Song Index number of 3753.-Lyrics:The modern words are:-Variations and uses:Amateur music composer Thomas Oliphant noted in 1843 that:...

" is a medieval English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 nursery rhyme
Nursery rhyme
The term nursery rhyme is used for "traditional" poems for young children in Britain and many other countries, but usage only dates from the 19th century and in North America the older ‘Mother Goose Rhymes’ is still often used.-Lullabies:...

 about three blind mice whose tails are cut off after chasing the farmer's wife. The work is explicitly incongruous, ending with the comment Did you ever see such a sight in your life, As three blind mice?

Bob Dylan
Bob Dylan
Bob Dylan is an American singer-songwriter, musician, poet, film director and painter. He has been a major and profoundly influential figure in popular music and culture for five decades. Much of his most celebrated work dates from the 1960s when he was an informal chronicler and a seemingly...

's anti-war song "Blowin' in the Wind
Blowin' in the Wind
"Blowin' in the Wind" is a song written by Bob Dylan and released on his album The Freewheelin' Bob Dylan in 1963. Although it has been described as a protest song, it poses a series of questions about peace, war and freedom...

" twice alludes to metaphorical blindness: How many times can a man turn his head // and pretend that he just doesn't see... How many times must a man look up // Before he can see the sky?
Contemporary fiction contains numerous well-known blind characters. Some of these characters can "see" by means of fictitious devices, such as the Marvel Comics
Marvel Comics
Marvel Worldwide, Inc., commonly referred to as Marvel Comics and formerly Marvel Publishing, Inc. and Marvel Comics Group, is an American company that publishes comic books and related media...

 superhero Daredevil
Daredevil (Marvel Comics)
Daredevil is a fictional character, a superhero in comic books published by Marvel Comics. The character was created by writer-editor Stan Lee and artist Bill Everett, with an unspecified amount of input from Jack Kirby, and first appeared in Daredevil #1 .Living in the Hell's Kitchen neighborhood...

, who can "see" via his super-human hearing acuity, or Star Trek
Star Trek
Star Trek is an American science fiction entertainment franchise created by Gene Roddenberry. The core of Star Trek is its six television series: The Original Series, The Animated Series, The Next Generation, Deep Space Nine, Voyager, and Enterprise...

s Geordi La Forge
Geordi La Forge
Lieutenant Commander Geordi La Forge is a regular character in the television series Star Trek: The Next Generation and its feature films, played by LeVar Burton...

, who can see with the aid of a VISOR
Visor
A visor is a surface that protects the eyes, such as shading them from the sun or other bright light or protecting them from objects....

, a fictitious device that transmits optical signals to his brain.

Sports

Blind and partially sighted people participate in sports such as swimming
Swimming (sport)
Swimming is a sport governed by the Fédération Internationale de Natation .-History: Competitive swimming in Europe began around 1800 BCE, mostly in the form of the freestyle. In 1873 Steve Bowyer introduced the trudgen to Western swimming competitions, after copying the front crawl used by Native...

, snow skiing and athletics. Some sports have been invented or adapted for the blind such as goalball
Goalball
Goalball is a team sport designed for blind athletes. It was devised by Hanz Lorenzen , and Sepp Reindle , in 1946 in an effort to help in the rehabilitation of visually impaired World War II veterans...

, association football, cricket
Blind cricket
Blind cricket is a version of the sport of cricket adapted for blind and partially sighted players. It has governed by the World Blind Cricket Council since 1996...

, and golf
Blind golf
Blind golf is a version of the sport of golf adapted for blind and partially sighted players.-History:The earliest record of blind golf is from the 1920s in the USA: Clint Russell of Duluth, Minnesota, who lost his sight when a tire exploded in his face, began playing blind golf in 1925...

. The worldwide authority on sports for the blind is the International Blind Sports Federation. People with vision impairments have participated in the Paralympic Games
Paralympic Games
The Paralympic Games are a major international multi-sport event where athletes with a physical disability compete; this includes athletes with mobility disabilities, amputations, blindness, and Cerebral Palsy. There are Winter and Summer Paralympic Games, which are held immediately following their...

 since the 1976 summer Paralympics in Toronto
1976 Summer Paralympics
The 1976 Summer Paralympics were the fifth Paralympic Games to be held. They were held in Toronto, in the province of Ontario, Canada from August 3 to 11, 1976...

.

Metaphorical uses

The word "blind" (adjective and verb) is often used to signify a lack of knowledge of something. For example, a blind date is a date in which the people involved have not previously met; a blind experiment is one in which information is kept from either the experimenter or the participant to mitigate the placebo effect
Placebo effect
Placebo effect may refer to:* Placebo effect, the tendency of any medication or treatment, even an inert or ineffective one, to exhibit results simply because the recipient believes that it will work...

 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
Blind spot (vision)
A blind spot, also known as a scotoma, is an obscuration of the visual field. A particular blind spot known as the blindspot, or physiological blind spot, or punctum caecum in medical literature, is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on...

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

In other animals

Statements that certain species of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s are "born blind" refers to them being born with their eyes closed and their eyelids fused together; the eyes open later. One example is the rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...

. 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
Blind mole rat
The genus Spalax contains the blind, fossorial, or subterranean mole rats, which are one of several types of rodents that are called mole rats. The hystricognath mole rats of the family Bathyergidae are completely unrelated, but some other forms are also in the family Spalacidae...

 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
Equus (play)
Equus is a play by Peter Shaffer written in 1973, telling the story of a psychiatrist who attempts to treat a young man who has a pathological religious fascination with horses....

, tells the story of a boy who blinds six horses. Theodore Taylor
Theodore Taylor (author)
Theodore Taylor was an American author of more than 50 fiction and non-fiction books for young adult readers, including The Cay, The Weirdo , Ice Drift, Timothy of the Cay, The Bomb, Sniper, and Rogue...

's classic young adult novel, The Trouble With Tuck, is about a teenage girl, Helen, who trains her blind dog to follow and trust a seeing-eye dog.

See also

  • Blindism
    Blindism
    Blindisms are stereotyped behaviors sometimes found in visually impaired toddlers or children. Blindism behaviors range from body rocking, head swaying, eye rubbing, head banging, spinning to finger flicking...

  • Blindness and education
    Blindness and education
    The subject of blindness and education has included evolving approaches and public perceptions of how best to address the special needs of blind students...

  • Color blindness
    Color blindness
    Color blindness or color vision deficiency is the inability or decreased ability to see color, or perceive color differences, under lighting conditions when color vision is not normally impaired...

  • Cortical blindness
    Cortical blindness
    Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the visual area in the brain's occipital cortex. This damage is most often caused by loss of blood flow to the occipital cortex from either unilateral or bilateral posterior cerebral artery...

  • Eye disease
  • List of blind people
  • Nyctalopia
    Nyctalopia
    Nyctalopia is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition...

  • Stereoblindness
    Stereoblindness
    Stereoblindness is the inability to see in 3D using stereo vision, resulting in inability to perceive stereoscopic depth by combining and comparing images from the two eyes...

  • Tactile alphabets
  • Tactile graphic
    Tactile graphic
    Tactile graphics are images that use raised surfaces so that a visually impaired person can feel them. They are used to convey non-textual information such as maps, paintings, graphs and diagrams.Tactile graphics can be seen as a subset of accessible images...

  • Tangible symbol systems
    Tangible symbol systems
    Tangible symbols are objects or pictures that are used as symbols by individuals who are not able to communicate using more conventional symbol systems. Tangible symbols bear an obvious and concrete relationship to the visual or tactile properties of the entities that they represent...

  • World Blind Union
    World Blind Union
    The World Blind Union is an organisation of blind and partially sighted persons of the world, representing 180 million blind and visually impaired persons from about 600 different organisations in 158 countries....


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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