News tagged with blindness

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Curing cataracts without surgery?

Cataracts are very common. The Centers for Disease Control and Prevention estimates that 20.5 million Americans age 40 and over have them. Cataracts slowly cloud your vision, and people struggling with them say it's like ...

Nov 16, 2015
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Resveratrol impacts Alzheimer's disease biomarker

The largest nationwide clinical trial to study high-dose resveratrol long-term in people with mild to moderate Alzheimer's disease found that a biomarker that declines when the disease progresses was stabilized in people ...

Sep 11, 2015
popularity320 comments 3

We've all got a blind spot, but it can be shrunk

You've probably never noticed, but the human eye includes an unavoidable blind spot. That's because the optic nerve that sends visual signals to the brain must pass through the retina, which creates a hole in that light-sensitive ...

Aug 31, 2015
popularity133 comments 0

Self-control saps memory, study says

You're driving on a busy road and you intend to switch lanes when you suddenly realize that there's a car in your blind spot. You have to put a stop to your lane change—and quickly.

Aug 26, 2015
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New nanotechnology drug to control blindness

The Mexican company "Medical and Surgical Center for Retina" has created a way to deliver drugs in order to avoid risks and painful treatments in people with secondary blindness due to chronic degenerative blindness such ...

Jun 25, 2015
popularity108 comments 0


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 vision correction—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 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.

It should be noted that 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, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.

This text uses material from Wikipedia, licensed under CC BY-SA

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