StemCell Therapy

Blindness is the condition of poor visual perception.

Various scales have been developed to describe the extent of vision loss and define blindness.[1] Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for "no light perception."[1] Blindness is frequently used to describe severe visual impairment with some remaining 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. The World Health Organization defines low vision as visual acuity of less than 20/60 (6/18), but equal to or better than 20/200 (6/60), or 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 a visual field loss to less than 10 degrees, in the better eye with best possible correction.[2][3]

As of 2012 there were 285 million visually impaired people in the world, of which 246 million had low vision and 39 million were blind.[3] The majority of people with poor vision are in the developing world and are over the age of 50 years.[3]

Blindness is defined by the World Health Organization as vision in a person's best eye of less than 20/500 or a visual field of less than 10 degrees.[4] This definition was set in 1972, and there is ongoing discussion as to whether it should be altered somewhat.[5]

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.

In 1934, the American Medical Association adopted the following definition of blindness:

"Central visual acuity of 20/200 or less in the better eye with corrective glasses or central visual acuity of more than 20/200 if there is a visual field defect in which the peripheral field is contracted to such an extent that the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye."[6]

The United States Congress included this definition as part of the Aid to the Blind program in the Social Security Act passed in 1935.[6][7] In 1972, the Aid to the Blind program and two others combined under Title XVI of the Social Security Act to form the Supplemental Security Income program[8] which currently states:

"An individual shall be considered to be blind for purposes of this title if he has central visual acuity of 20/200 or less in the better eye with the use of a correcting lens. An eye which is accompanied by a limitation in the fields of vision such that the widest diameter of the visual field subtends an angle no greater than 20 degrees shall be considered for purposes of the first sentence of this subsection as having a central visual acuity of 20/200 or less. An individual shall also be considered to be blind for purposes of this title if he is blind as defined under a State plan approved under title X or XVI as in effect for October 1972 and received aid under such plan (on the basis of blindness) for December 1973, so long as he is continuously blind as so defined."[9]

In the UK, the Certificate of Vision Impairment (CVI) is used to certify patients as severely sight impaired or sight impaired.[10] The accompanying guidance for clinical staff states: "The National Assistance Act 1948 states that a person can be certified as severely sight impaired if they are so blind as to be unable to perform any work for which eye sight is essential (National Assistance Act Section 64(1)). The test is whether a person cannot do any work for which eyesight is essential, not just his or her normal job or one particular job."[11]

See the rest here:
Blindness - Wikipedia, the free encyclopedia

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