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
One shot of gene therapy and children with congenital blindness can now see
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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 ...
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(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 ...
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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.
New study shows brain's ability to reorganize
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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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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. ...
Researchers create first model for retina receptors
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A team of scientists at the University of Oklahoma Health Sciences Center has created the first genetic research model for a microscopic part of the eye that when missing causes blindness. The research appears in a recent ...
Vigorous exercise may help prevent vision loss
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There's another reason to dust off those running shoes. Vigorous exercise may help prevent vision loss, according to a pair of studies from the U.S. Department of Energy's Lawrence Berkeley National Laboratory. The studies ...
Researchers develop camera for the blind
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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.
Scientists increases understanding of two types of blindness
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Though based on mouse studies, the research bolsters the idea that humans suffering from these and other eye conditions may be able to help preserve function by adding antioxidants to their diet, and explains why this would ...
Study suggests new approach to common cause of blindness
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Researchers at the University of North Carolina at Chapel Hill School of Medicine in collaboration with lead investigators at the University of Kentucky have identified a new target for the diagnosis and treatment of age-related ...
Blind can take wheel with new vehicle
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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.
Diet could reduce onset of eye disease by 20 percent
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University of Liverpool scientists claim that the degeneration of sight, caused by a common eye disease, could be reduced by up to 20% by increasing the amount of fruit, vegetables and nuts in the diet.
Shining light on diabetes-related blindness
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A group of scientists in California is trying to develop a cheaper, less invasive way to spot the early stages of retinal damage from diabetic retinopathy, the leading cause of blindness in American adults, before it leads ...
Genetic sleuth solves glaucoma mystery
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Dr. Michael Walter is one good gumshoe. The University of Alberta medical geneticist has cracked the case of WDR36, a gene linked to glaucoma.
