Blindness is the condition of lacking visual perception
due to physiological of neural factors.
Various scales have been developed to describe the extent of vision
loss and define
blindness is the complete lack of form and visual light perception and is
clinically recorded as "NLP," an abbreviation for "no light perception."
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. A person with only "light projection"
can tell 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 America and most of
Europse, legal blindness is defined as visual acioty (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 itówith vision correctionówith 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
visiion 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.