Blindness

Surge in traffic deaths outpaces increase in travel

Traffic deaths surged about 8 percent in the first nine months of last year, continuing an alarming upward spiral that may be partially explained by more Americans on the roads due to the economic recovery, according to National ...

Jan 13, 2017
popularity0 comments 1

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

Latest Spotlight News

Every meal triggers inflammation

When we eat, we do not just take in nutrients – we also consume a significant quantity of bacteria. The body is faced with the challenge of simultaneously distributing the ingested glucose and fighting these bacteria. This ...

Researchers identify source of opioids' side effects

A commercially available drug may help drastically reduce two side effects of opioid painkillers—a growing tolerance and a paradoxical increased sensitivity to pain—without affecting the drugs' ability to reduce pain, ...

Who needs stress? We all do. Here's why

If you could do something to decrease your risk of memory failure, to increase your self-confidence, to be a better public speaker, to improve your brain, to help you deal with back pain, to bust out of your comfort zone, ...

Can coffee perk up heart health, too?

The caffeine in your morning cup of joe may do more than jolt you awake—it may also help dampen the type of inflammation that's linked to heart disease risk factors, a new study suggests.