Related topics: eye , retina , vision loss
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
New study shows brain's ability to reorganize
Medicine & Health / Neuroscience
Nov 18, 2009 |
4.6 / 5 (11) |
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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, ...
One shot of gene therapy and children with congenital blindness can now see
Oct 25, 2009 |
5 / 5 (23) |
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Born with a retinal disease that made him legally blind, and would eventually leave him totally sightless, the nine-year-old boy used to sit in the back of the classroom, relying on the large print on an electronic ...
Out of darkness, sight: How the brain learns to see
Medicine & Health / Neuroscience
Sep 17, 2009 |
4.9 / 5 (17) |
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(PhysOrg.com) -- Cases of restored vision after a lifetime of blindness, though exceedingly rare, provide a unique opportunity to address several fundamental questions regarding brain function. After being ...
Color blindness cured in monkeys
Sep 16, 2009 |
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(PhysOrg.com) -- Researchers from the University of Washington and the University of Florida used gene therapy to cure two squirrel monkeys of color blindness — the most common genetic disorder in people.
Stimulating sight: New retinal implant developed
Sep 23, 2009 |
4.9 / 5 (19) |
2
(PhysOrg.com) -- Inspired by the success of cochlear implants that can restore hearing to some deaf people, researchers at MIT are working on a retinal implant that could one day help blind people regain a ...
Researchers discover mechanism that helps humans see in bright and low light
Medicine & Health / Neuroscience
Oct 13, 2009 |
4.9 / 5 (9) |
0
Ever wonder how your eyes adjust during a blackout? When we go from light to near total darkness, cells in the retina must quickly adjust. Vision scientists at Washington University School of Medicine in St. ...
The changing pattern of childhood blindness in developing countries
Dec 08, 2009 |
not rated yet |
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"Changing patterns of global childhood blindness suggest a reassessment of research, training, and programmatic needs," says a team of eye specialists from India, Malawi, and Tanzania.
Rigorous visual training teaches the brain to see again after stroke (w/Video)
Medicine & Health / Neuroscience
Mar 31, 2009 |
not rated yet |
1
By doing a set of vigorous visual exercises on a computer every day for several months, patients who had gone partially blind as a result of suffering a stroke were able to regain some vision, according to ...
Researchers develop camera for the blind
Jan 12, 2009 |
5 / 5 (5) |
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(PhysOrg.com) -- Elizabeth Goldring smiles as she shows a visitor photos she's taken — and can see — with her blind eye.
Blind can take wheel with new vehicle
Jul 15, 2009 |
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A student team in the Virginia Tech College of Engineering is providing the blind with an opportunity many never thought possible: The opportunity to drive.
Intel Reader Transforms Printed Text to Spoken Word (w/ Video)
Electronics / Consumer & Gadgets
Nov 11, 2009 |
4.5 / 5 (2) |
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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.
More insulin-producing cells, at the flip of a 'switch'
Aug 06, 2009 |
5 / 5 (1) |
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Researchers have found a way in mice to convert another type of pancreas cell into the critical insulin-producing beta cells that are lost in those with type I diabetes. The secret ingredient is a single transcription factor, ...
Researchers to implant pig cells in diabetics
Jul 23, 2009 |
5 / 5 (1) |
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(AP) -- A New Zealand biotech company began a trial Thursday that will implant cells from newborn pigs into eight human volunteers as an experimental treatment for their diabetes.
Type of vitamin B1 could treat common cause of blindness
Apr 23, 2009 |
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University of Texas Medical Branch at Galveston researchers have discovered that a form of vitamin B1 could become a new and effective treatment for one of the world's leading causes of blindness.
Stem cell therapy makes cloudy corneas clear
Apr 09, 2009 |
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Stem cells collected from human corneas restore transparency and don't trigger a rejection response when injected into eyes that are scarred and hazy, according to experiments conducted in mice by researchers at the University ...
