Blindness
hideBlindness is the condition of lacking visual perception due to physiological or neurological factors.
Various scales have been developed to describe the extent of vision loss and define blindness. 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 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 and most of Europe, legal blindness is defined as visual acuity (vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet (6.1 m) from an object to see it—with 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 of less than 20 degrees (the norm being 180 degrees) are also classified as being legally blind. Approximately ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to relatively good acuity. Low vision is sometimes used to describe visual acuities from 20/70 to 20/200.
By the 10th Revision of the WHO International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 6/18 (20/60), but equal to or better than 3/60 (20/400), or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction. Blindness is defined as visual acuity of less than 3/60 (20/400), or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.
It should be noted that blind people with undamaged eyes may still register light non-visually for the purpose of circadian entrainment to the 24-hour light/dark cycle. Light signals for this purpose travel through the retinohypothalamic tract, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.
For more information about Blindness, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with blindness
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Medicine & Health / Neuroscience
Nov 18, 2009 |
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(PhysOrg.com) -- Visually impaired people appear to be fearless, navigating busy sidewalks and crosswalks, safely finding their way using nothing more than a cane as a guide. The reason they can do this, researchers suggest, ...
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Electronics / Consumer & Gadgets
Nov 11, 2009 |
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Intel Corporation today announced the Intel Reader, a mobile handheld device designed to increase independence for people who have trouble reading standard print.
Study finds many people with hemianopia have difficulty detecting pedestrians while driving
Nov 12, 2009 |
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Schepens Eye Research Institute scientists have found that--when tested in a driving simulator--patients with hemianopia (blindness in one half of the visual field in both eyes) have significantly more difficulty detecting ...
Search results for blindness
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Dec 04, 2009 |
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Humans and mice have previously unknown and potentially critical differences in one of the genes responsible for Duchenne muscular dystrophy (DMD). Researchers writing in the open access journal BMC Biology have found that t ...
Scientists rescue visual function in rats using induced pluripotent stem cells
Dec 03, 2009 |
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An international team of scientists has rescued visual function in laboratory rats with eye disease by using cells similar to stem cells. The research shows the potential for stem cell-based therapies to treat ...
Diabetes cases to double and costs to triple by 2034
Nov 27, 2009 |
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In the next 25 years, the number of Americans living with diabetes will nearly double, increasing from 23.7 million in 2009 to 44.1 million in 2034. Over the same period, spending on diabetes will almost triple, rising from ...
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Nov 24, 2009 |
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Suddenly seeing floaters or flashes of light may indicate a serious eye problem that - if untreated - could lead to blindness, a new study shows.
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Nov 24, 2009 |
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A first-of-its-kind consensus statement on diabetes surgery is published online today in the Annals of Surgery. The report illustrates the findings of the first international consensus conference -- Diabetes Surgery Summit ...
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German scientist Paul Ehrlich found what he coined the "magic bullet" in the early 20th century upon developing the world’s first effective treatment of syphilis.
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Nov 19, 2009 |
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Embryonic stem cell therapy got a step closer to the clinic Thursday after US researchers said they filed a request for government approval of human trials.
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Nov 09, 2009 |
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(PhysOrg.com) -- UConn researchers have developed a tiny wireless device that can be inserted under a patient?s skin to monitor blood glucose levels over a period of several months.
Cataract surgery does not appear associated with worsening of age-related macular degeneration
Nov 09, 2009 |
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Age-related macular degeneration does not appear to progress at a higher rate among individuals who have had surgery to treat cataract, contrary to previous reports that treating one cause of vision loss worsens the other, ...
The world's most common operation
Nov 09, 2009 |
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As many as 10 million people around the world suffer from cataracts. Thomas Kohnen of the Goethe University in Frankfurt and his coauthors discuss cataract surgery with the implantation of an artificial lens in the current ...
List of search results for blindness
