Blindness

New glaucoma culprit is found

Glaucoma, a leading cause of irreversible blindness, is associated with elevated pressure in the eye. This elevated pressure essentially is due to a plumbing problem. Fluid builds up in the eye, increasing ...

Sep 15, 2014
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A second look at glaucoma surgery

New research led by Queen's University professor Robert Campbell (Ophthalmology) has revealed using anti-inflammatory medications after glaucoma laser surgery is not helpful or necessary.

5 hours ago
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Optogenetics has 'completely changed neuroscience'

It's getting harder to find the line between science and science fiction. One of the hot research techniques these days, "optogenetics," uses gene therapy to deliver light-sensitive proteins to specific cells. Then researchers ...

Sep 16, 2014
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Pre-diabetes, diabetes rates fuel national health crisis

Americans are getting fatter, and older. These converging trends are putting the USA on the path to an alarming health crisis: Nearly half of adults have either pre-diabetes or diabetes, raising their risk of heart attacks, ...

Sep 16, 2014
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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

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