Blindness

New study validates new approach to high blood pressure

It truly could be mind over matter after all. University Hospitals Case Medical Center's Richard Josephson, MD, recently released trial results in a study published in Psychosomatic Medicine that discusses mindfulness-based stress ...

Aug 05, 2014
popularity 4 / 5 (2) | comments 0

Blindness 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 corrective lenses—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 20/60 (6/18), but equal to or better than 20/200 (6/60), 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 20/400 (6/120), or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.

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 and are not affected by optic nerve damage beyond where the retinohypothalamic tract exits.

This text uses material from Wikipedia licensed under CC BY-SA

Latest Spotlight News

Children with autism have extra synapses in brain

Children and adolescents with autism have a surplus of synapses in the brain, and this excess is due to a slowdown in a normal brain "pruning" process during development, according to a study by neuroscientists ...

Learning to play the piano? Sleep on it!

According to researchers at the University of Montreal, the regions of the brain below the cortex play an important role as we train our bodies' movements and, critically, they interact more effectively after ...

How 'wriggling' skin cancer cells go on the move

(Medical Xpress)—Scientists at King's College London have discovered a new way that melanoma skin cancer cells can invade healthy tissue and spread round the body, according to research published in Nature Co ...