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
Oct 25, 2009 |
5 / 5 (23) |
1
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 ...
The unicycling clown phenomenon: Talking, walking and driving with cell phone users
Medicine & Health / Psychology & Psychiatry
Oct 19, 2009 |
5 / 5 (1) |
0
Everyone tends to float off into space once in a while and fail to see what is sitting there right in front of them. Recently researchers decided to put the theory of "inattentional blindness" to the test: the unicycling ...
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. ...
More infants surviving pre-term births results in higher rates of eye problems
Oct 12, 2009 |
not rated yet |
0
As more extremely pre-term infants survive in Sweden, an increasing number of babies are experiencing vision problems caused by abnormalities involving the retina, according to a report in the October issue of Archives of ...
Cancer drug is no different in effectiveness as gold standard treatment for macular degeneration
Oct 09, 2009 |
not rated yet |
0
Investigators from Boston University School of Medicine (BUSM) and the VA Boston Healthcare System have shown, at 6 months in a small group of patients, that there is no difference in efficacy between Bevacizumab (Avastin) ...
Researchers discover novel circulation in human eye, new glaucoma treatment target
Oct 05, 2009 |
4 / 5 (1) |
0
Researchers at the University of Toronto, St. Michael's Hospital and Sunnybrook Health Sciences Centre have discovered a previously unidentified form of circulation within the human eye which may provide important new insights ...
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 ...
Out of darkness, sight: How the brain learns to see
Medicine & Health / Neuroscience
Sep 17, 2009 |
4.9 / 5 (17) |
0
(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 |
5 / 5 (11) |
0
(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.
Virtual maps for the blind
Sep 10, 2009 |
5 / 5 (1) |
0
The blind and visually impaired often rely on others to provide cues and information on navigating through their environments. The problem with this method is that it doesn't give them the tools to venture out on their own, ...
Study predicts 40 percent increase in blindness in Nigeria by 2020
Sep 08, 2009 |
5 / 5 (1) |
0
By 2020, 1.4 million Nigerians over age 40 will lose their sight, and the vast majority of the causes are either preventable or treatable, according to the Nigeria National Blindness and Visual Impairment Study Group.
Portuguese award goes to Helen Keller nonprofit
Sep 05, 2009 |
5 / 5 (1) |
0
(AP) -- The Helen Keller International nonprofit organization has won a $1.4 million prize from a Portuguese foundation for its work in preventing blindness in the developing world, the foundation said Friday.
Delays in UK child brain tumor diagnosis
Aug 07, 2009 |
not rated yet |
0
Significant numbers of children in the UK are suffering from preventable levels of disability, particularly blindness, and premature death because of poor diagnosis of brain tumours.
More insulin-producing cells, at the flip of a 'switch'
Aug 06, 2009 |
5 / 5 (1) |
0
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, ...
Developing gene therapy to fight blindness
Jul 29, 2009 |
5 / 5 (1) |
0
An international team of scientists and clinicians from the United States and Saudi Arabia are working to develop gene therapy for treating a rare, hereditary retinal disease. The therapy has been shown to restore lost vision ...
