Related topics: gene therapy · retina

How blind cavefish make their way in the dark

A team of researchers affiliated with several institutions in China, working with one colleague from the U.K and one from the U.S., has uncovered the means by which blind cavefish are able to find their way around in the ...

Far-infrared detector KID reaches highest possible sensitivity

Astronomy has a blind spot in the area of far-infrared radiation compared to most other wavelengths. A far-infrared space telescope can only utilize its full sensitivity with an actively cooled mirror at temperatures below ...

Actual greenhouse gas volumes exceed official reports

Wayne Christian wanted to brag, he said, rocking in his burgundy leather chair atop the dais of the powerful Railroad Commission of Texas. Colleagues and staff were doing "a darn good job," and people who "gripe about the ...

New digital tools to track illegal wildlife trade online

As governments around the world turned to lockdowns and travel restrictions to prevent the spread of the COVID-19 virus, smugglers used social media to find new ways to connect with potential customers.

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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 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