Blindness

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
popularity132 comments 0

Driving with central visual field loss

Vision researchers in Boston have published the second paper of a study designed to determine if a driver who suffers from loss of central vision is able to detect pedestrians in a timely manner when driving. Central visual ...

Sep 02, 2015
popularity24 comments 0

'Awakenings' author, neurologist Oliver Sacks dies at 82

There was the blind man who had the disastrous experience of regaining his sight. The surgeon who developed a sudden passion for music after being struck by lightning. And most famously, the man who mistook his wife for a ...

Aug 30, 2015
popularity15 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
popularity168 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 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

New role for an old protein: Cancer causer

A protein known to play a role in transporting the molecular contents of normal cells into and out of various intracellular compartments can also turn such cells cancerous by stimulating a key growth-control pathway.

Study reveals the genetic start-up of a human embryo

An international team of scientists led from Sweden's Karolinska Institutet has for the first time mapped all the genes that are activated in the first few days of a fertilized human egg. The study, which is being published ...