Blindness is the condition of lacking visual perception Visual perception is the ability to interpret information from visible light reaching the eye. The resulting perception is also known as eyesight, sight or vision. The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in psychology, cognitive science, due to physiological Physiology is the study of the mechanical, physical, and biochemical functions of living organisms. Physiology has traditionally been divided between plant physiology and animal and all living things physiology but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about or neurological Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue, such as muscle. The corresponding surgical specialty factors.

Various scales have been developed to describe the extent of vision loss Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically (i.e. over a long period of time). The effects of visual loss can, before the acquisition of alternative adaptations and skills, be devastating; especially when a person's vision disappears over a short period of time and define blindness.[1] Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for "no light perception."[1] Blindness is frequently used to describe severe visual impairment In the U.S., the terms partially sighted, low vision, legally blind, and totally blind are used in the educational context to describe students with visual impairments. They are defined as follows: with residual vision. Those described as having only light perception have no more sight than the ability to tell light from dark. A person with only light projection can tell the general direction of a light source.

In order to determine which people may need special assistance because of their visual disabilities, various governmental jurisdictions have formulated more complex definitions referred to as legal blindness Blindness is the condition of lacking visual perception due to physiological or neurological factors.[2] In North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the and most of Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, and by the Caucasus Mountains to the southeast. Europe is washed upon to the north by the Arctic Ocean and, legal blindness is defined as visual acuity VA is a quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is varied. It is the most common clinical measurement of visual function. In the term "20/20 vision" the numerator refers to the distance in feet from which a person can reliably distinguish a (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 vision correction—with the same degree of clarity as a normally sighted person could from 200 feet (61 m). In many areas, people with average acuity who nonetheless have a visual field The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while field of view "refers to the physical objects and light sources in the external of less than 20 degrees A degree , usually denoted by ° (the degree symbol), is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians. When that angle is with respect to a reference meridian, it indicates a location along a great circle of a sphere, such as Earth (see Geographic coordinate system), Mars, or the (the norm being 180 degrees) are also classified as being legally blind. Approximately ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to relatively good acuity. Low vision Low vision is a subspecialty within the professions of optometry and ophthalmology and opticianry dealing with individuals who have less than normal vision even with the most accurate conventional prescription available. It can be a result of either congenital or acquired factors. An example of the former is Leber's congenital amaurosis and of the is sometimes used to describe visual acuities from 20/70 to 20/200.[3]

By the 10th Revision of the WHO The World Health Organization is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. Established on 7 April 1948, and headquartered in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health Organization, which had been an agency of the International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 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 A circadian rhythm is a roughly-24-hour cycle in the biochemical, physiological or behavioral processes of living entities, including plants, animals, fungi and cyanobacteria . The term "circadian", coined by Franz Halberg, comes from the Latin circa, "around," and diem or dies, "day", meaning literally " entrainment In chronobiology, entrainment of a circadian system is the alignment of its own period and phase to the period and phase of an external rhythm. A common example is the entrainment of endogenous circadian rhythms to the daily light-dark cycle. Of the several possible cues, called zeitgeber (German for time-giver, synchronizer), which can contribute to the 24-hour light/dark cycle. Light signals for this purpose travel through the retinohypothalamic tract The retinohypothalamic tract is a photic input pathway involved in the circadian rhythms of mammals. The origin of the RHT is the intrinsically photosensitive Retinal Ganglion Cells (ipRGC), which contain the photopigment melanopsin. The axons of the ipRGCs belonging to the RHT project directly to the suprachiasmatic nuclei (SCN) via the optic (RHT), so a damaged optic nerve beyond where the RHT exits it is no hindrance.

Contents

Legal blindness

The examples and perspective in this section deal primarily with the United States The United States of America is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the 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 The American Medical Association , founded in 1847 and incorporated 1897, is the largest association of physicians and medical students in the United States. The AMA's mission claims to promote the art and science of medicine for the betterment of the public health, to advance the interests of physicians and their patients, to promote public (AMA) adopted the following definition of blindness:

Central visual acuity of 20/200 or less in the better eye with corrective glasses or central visual acuity of more than 20/200 if there is a visual field defect in which the peripheral field is contracted to such an extent that the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye.[6]

The United States Congress The United States Congress is the bicameral legislature of the federal government of the United States of America, consisting of two houses, the Senate and the House of Representatives. Both senators and representatives are chosen through direct election included this definition as part of the Aid to the Blind program in the Social Security Act Social Security in the United States currently refers to the federal Old-Age, Survivors, and Disability Insurance program passed in 1935.[6][7] In 1972, the Aid to the Blind program and two others combined under Title XVI of the Social Security Act to form the Supplemental Security Income 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]

Kuwait The State of Kuwait is a sovereign Arab emirate bordered by Saudi Arabia to the south and Iraq to the north and west. The name is a diminutive of an Arabic word meaning "fortress built near water." It has a population of 3.1 million and an area of 17,818 km². Kuwait is a constitutional monarchy with a parliamentary system of government, is one of many nations that share the same criteria for legal blindness.[10]

Epidemiology

In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness.[11] Of this number, 58% were over the age of 65.[11] In 1994-1995, 1.3 million Americans reported legal blindness.[12]

In the November 2004 article Magnitude and causes of visual impairment, the WHO The World Health Organization is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. Established on 7 April 1948, and headquartered in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health Organization, which had been an agency of the estimated that in 2002 there were 161 million (about 2.6% of the world population) visually impaired people in the world, of whom 124 million (about 2%) had low vision and 37 million (about 0.6%) were blind.[13]

Causes of blindness

Serious visual impairment has a variety of causes:

Diseases

Most visual impairment is caused by disease A disease or medical condition is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and signs. It may be caused by external factors, such as invading organisms, or it may be caused by internal dysfunctions, such as autoimmune diseases and malnutrition Malnutrition is a general term for a medical condition caused by an improper or inadequate diet and nutrition. A number of different nutrition disorders may arise, depending on which nutrients are under or overabundant in the diet. According to WHO The World Health Organization is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. Established on 7 April 1948, and headquartered in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health Organization, which had been an agency of the estimates in 2002, the most common causes of blindness around the world are:

People in developing countries are significantly more likely to experience visual impairment as a consequence of treatable or preventable conditions than are their counterparts in the developed world. While vision impairment is most common in people over age 60 across all regions, children in poorer communities are more likely to be affected by blinding diseases than are their more affluent peers.

The link between poverty Poverty is the shortage of common things such as food, clothing, shelter and safe drinking water, all of which determine the quality of life. It may also include the lack of access to opportunities such as education and employment which aid the escape from poverty and/or allow one to enjoy the respect of fellow citizens. According to Mollie and treatable visual impairment is most obvious when conducting regional comparisons of cause. Most adult visual impairment in North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the and Western Europe Western Europe refers to the countries generally in the westernmost half of Europe, but the definition is complex and carries political connotations. As a result, geographically eastern countries that steered clear of Soviet influence during the Cold War are usually included, while Western members of the former Eastern Bloc (Czech Republic, Poland) is related to age-related macular degeneration and diabetic retinopathy. While both of these conditions are subject to treatment, neither can be cured.

In developing countries, wherein people have shorter life expectancies, cataracts and water-borne parasites—both of which can be treated effectively—are most often the culprits (see River blindness Onchocerciasis , also known as river blindness, is the world's third leading infectious cause of blindness. It is caused by Onchocerca volvulus, a nematode that can live for up to fifteen years in the human body. It is transmitted to humans through the bite of a black fly. The worms spread throughout the body, and when they die, they cause intense, for example). Of the estimated 40 million blind people located around the world, 70–80% can have some or all of their sight restored through treatment.

In developed countries where parasitic diseases are less common and cataract surgery Cataract surgery is the removal of the natural lens of the eye that has developed an opacification, which is referred to as a cataract. Metabolic changes of the crystalline lens fibers over the time lead to the development of the cataract and loss of transparency, causing impairment or loss of vision. During cataract surgery, a patient's cloudy is more available, age-related macular degeneration, glaucoma, and diabetic retinopathy are usually the leading causes of blindness.[15]

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 The United States of America is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the. Injuries and cataracts affect the eye itself, while abnormalities such as optic nerve hypoplasia During the second month of pregnancy, a structure called the optic stalk develops into a pair of optic nerve bundles. These bundles send signals from the eyes to the occipital lobe of the brain, naturally undergo pruning as the fetus develops. In some individuals, however, either this pruning process is too complete, or the nerves simply fail to affect the nerve bundle that sends signals from the eye to the back of the brain, which can lead to decreased visual acuity.

People with injuries to the occipital lobe The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1 . Human V1 is located on the medial side of the occipital lobe within the calcarine sulcus; the full extent of V1 often continues onto the of the brain The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the skull and close to the primary can, despite having undamaged eyes and optic nerves The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibers are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system, still be legally or totally blind.

Genetic defects

People with albinism Albinism is a form of hypopigmentary congenital disorder, characterized by a partial (in hypomelanism, also known as hypomelanosis) or total (amelanism or amelanosis) lack of melanin pigment in the eyes, skin and hair, or more rarely in the eyes alone. Albinism results from inheritance of recessive alleles. The condition is known to affect mammals often suffer from visual impairment to the extent that many are legally blind, though few of them actually cannot see. Leber's congenital amaurosis Amaurosis refers to a loss of vision not associated with a lesion, and congenital refers to a condition present from birth . However, beyond these general descriptions, the presentation of LCA can vary, because it is associated with multiple genes can cause total blindness or severe sight loss from birth or early childhood.

Recent advances in mapping Genetic linkage occurs when particular genetic loci or alleles for genes are inherited jointly. Genetic loci on the same chromosome are physically connected and tend to stay together during meiosis, and are thus genetically linked. This is called autosomal linkage. Alleles for genes on different chromosomes are usually not linked, due to of the human genome The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs. Twenty-two of these are autosomal chromosome pairs, while the remaining pair is sex-determining. The haploid human genome occupies a total of just over 3 billion DNA base pairs. The Human Genome Project produced a reference sequence of the euchromatic human have identified other genetic causes of low vision Low vision is a subspecialty within the professions of optometry and ophthalmology and opticianry dealing with individuals who have less than normal vision even with the most accurate conventional prescription available. It can be a result of either congenital or acquired factors. An example of the former is Leber's congenital amaurosis and of the or blindness. One such example is 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.

Poisoning

Rarely, blindness is caused by the intake of certain chemicals. A well-known example is methanol Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a toxic chemical with chemical formula C , which ironically is only mildly toxic and minimally intoxicating, but when not competing with ethanol Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs. In common usage, it is often referred to simply as for metabolism, methanol breaks down into the substances formaldehyde Formaldehyde is a chemical compound with the formula CH2O. It is the simplest aldehyde. Formaldehyde also exists as the cyclic trimer trioxane and the polymer paraformaldehyde. It exists in water as the hydrate H2C(OH)2. Aqueous solutions of formaldehyde are referred to as formalin. "100%" formalin consists of a saturated solution of and formic acid Formic acid is the simplest carboxylic acid. Its formula is H which in turn can cause blindness, an array of other health complications, and death.[16] 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. [17] The same sentence was given in 2009 for the man who blinded Ameneh Bahrami.

Treatments

A 2008 study published in the New England Journal of Medicine[18] 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.

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:

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. Most legally blind people (70% of them across all ages, according to the Seattle Lighthouse for the Blind) do not use computers. Only a small fraction of this population, when compared to the sighted community, have Internet access. This bleak outlook is changing, however, as availability of assistive technology increases, accompanied by concerted efforts to ensure the accessibility of information technology to all potential users, including the blind. 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. The Macintosh 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

People may use talking thermometers, enlarged or marked oven dials, talking watches, talking clocks, talking scales, talking calculators, talking compasses and other talking equipment.

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.[20] The worldwide authority on sports for the blind is the International Blind Sports Federation (IBSA).[21] People with vision impairments have participated in the Paralympic Games since the 1976 summer Paralympics in Toronto.[22]

Blindness in 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.

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.

See also

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. ^ 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.
  12. ^ American Foundation for the Blind. "Statistics and Sources for Professionals." Retrieved April 1, 2006.
  13. ^ "World Health Organization" (Web). World Health Organization. 2006. http://www.who.int/en/. Retrieved on December 16 2006.
  14. ^ "Causes of blindness and visual impairment". World Health Organization. http://www.who.int/blindness/causes/en/. Retrieved on 19 February 2009.
  15. ^ 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.
  16. ^ "Methanol" (Web). Symptoms of Methanol Poisoning. Canada Safety Council. 2005. http://www.safety-council.org/info/OSH/methanol.htm. Retrieved on March 27 2007.
  17. ^ "Eye-for-eye in Pakistan acid case". BBC News. 12 December, 2003. http://news.bbc.co.uk/2/hi/south_asia/3313207.stm. Retrieved on 2008-06-30.
  18. ^ 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.
  19. ^ Accessibility features - Bank Notes - Bank of Canada
  20. ^ "Blind Sports Victoria". http://www.blindsports.org.au/. Retrieved on 2008-03-04.
  21. ^ "IBSA General Assembly Elects New Leadership". The Paralympian. International Paralympic Committee. April 2001. http://www.paralympic.org/paralympian/20014/2001430.htm. Retrieved on 2008-03-04.
  22. ^ "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 on 2008-03-04.

External links

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Eye disease · pathology of the eye (H00-H59, 360-379)
Adnexa eyelid: inflammation (Stye, Chalazion, Blepharitis) · Entropion · Ectropion · Lagophthalmos · Blepharochalasis · Ptosis · Blepharophimosis · Xanthelasma · Trichiasis · Madarosis

lacrimal system: Dacryoadenitis · Epiphora · Dacryocystitis

orbit: Exophthalmos · Enophthalmos
Eyeball
Conjunctiva Conjunctivitis (Allergic conjunctivitis) · Pterygium · Pinguecula · Subconjunctival hemorrhage
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
Iris and ciliary body Iritis · Uveitis (Intermediate uveitis) · Iridocyclitis · Hyphema · Rubeosis iridis · Persistent pupillary membrane · Iridodialysis · Synechia
Lens Cataract · Aphakia · Ectopia lentis
Choroid Choroideremia · Choroiditis (Chorioretinitis)
Retina Retinitis (Chorioretinitis, Cytomegalovirus retinitis) · Retinal detachment · Retinoschisis · 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
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
Eye infections Trachoma · Onchocerciasis
Other Nystagmus · Glaucoma/Ocular hypertension · Floater · Leber's hereditary optic neuropathy · Red eye · Keratomycosis · Xerophthalmia · Phthisis bulbi
See also

Categories: Blindness

 

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