Blindness is the condition of missing visual perception due to physiological or neurological factors.
Various scales have been developed to explain the extent of vision loss and define "blindness”. Total blindness is the entire lack of form and visual light perception and is clinically recorded as "NLP," an abbreviation for "no light perception”. Blindness is normally used to describe severe visual impairment with residual vision. Those described as having only "light perception" have no more sight than the capacity to tell light from dark. A person with only "light projection" can tell the common 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 difficult 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 improved eye with best correction possible. This means that a officially 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 usually sighted person could from 200 feet (61 m). In many areas, people with average acuity who nevertheless have a visual field of less than 20 degrees (the norm being 180 degrees) are also classified as being legally blind. About ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to comparatively good acuity. Low vision is sometimes used to illustrate visual acuities from 20/70 to 20/200.
Various scales have been developed to explain the extent of vision loss and define "blindness”. Total blindness is the entire lack of form and visual light perception and is clinically recorded as "NLP," an abbreviation for "no light perception”. Blindness is normally used to describe severe visual impairment with residual vision. Those described as having only "light perception" have no more sight than the capacity to tell light from dark. A person with only "light projection" can tell the common 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 difficult 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 improved eye with best correction possible. This means that a officially 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 usually sighted person could from 200 feet (61 m). In many areas, people with average acuity who nevertheless have a visual field of less than 20 degrees (the norm being 180 degrees) are also classified as being legally blind. About ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to comparatively good acuity. Low vision is sometimes used to illustrate visual acuities from 20/70 to 20/200.
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