Medical research

Study: Stem cells may aid vision in blind people

The first use of embryonic stem cells in humans eased a degenerative form of blindness in two volunteers and showed no signs of any adverse effects, according to a study published by The Lancet on Monday.

Ophthalmology

What are eye floaters?

Spots, flashes of light or darkness on any side of your vision could be a sign of eye floaters. Most often noticeable when looking at a plain, bright background, such as a blue sky or a white wall, eye floaters are a symptom ...

Medical research

A possible cure for river blindness and elephantiasis

An international team of researchers has found what might be a cure for river blindness and elephantiasis. In their paper published in the journal Science Translational Medicine, the group describes their search for a drug ...

Ophthalmology

Blindness and sight loss to double by 2050

Blindness and severe vision impairment is predicted to affect almost 900 million people worldwide by 2050—up from around 338 million today, according to a new pre-print study accepted by The Lancet and highlighted on World ...

Ophthalmology

Giant hogweed can cause burns and blindness

(PhysOrg.com) -- The U.S Department of Agriculture is warning residents in a variety of states to be on the lookout for the Heracleum Mantegazzianum, or giant hogweed. This plant in native to Central Asia but has turned up ...

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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