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.
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.
“Quoted from Wikipedia“
When you meet a blind person, don’t be at ill of ease, it will help if you remember the following points.
They are ordinary person, just blind. You don’t need to raise your voice or address them as if they were children. Don’t ask their companion what they want — “Cream in the coffee?” — Ask them directly.
- They will most probably be using a long white cane to walk indecently: or they may ask to take your arm. Let them decide, and please don’t grab their cane or arm, let them take yours. Let them keep a half-step behind you to anticipate curbs and and steps.
- They would want to know who’s in the room with them. Speak when you enter. Introduce him/her to the others including children and tell them if there’s a cat or dog in the room.
- The door to a room or a cabinet or to a car that is left partially open is a hazard to the blind.
- At dinner they will not have trouble with ordinary table skills.
- You don’t have to avoid the words like “see”, they use them too.
- They won’t want pity, but don’t talk about “the wonderful compensations” of blindness. Their sense of smell, taste, touch, hearing did not improve when they became blind, they rely on them more and therefore may get more information through those senses then you do — thats all.
- If they are your houseguest, show them the bathroom, closet, dresser, window, the light switch too. They would like to know if lights are on or off.
- They wil discuss blindness with you if you are curious but its an old story to them. They have as many other interest as you do.
- Don’t think of them as just blind person, they are just people who happen to be blind.
- You don’t have to remember some “politically correct” term, “visually impaired”, “sight challenge”, etc. Keep it simple and honest, just say blind.
The traffic law require drivers to yield the right of way when they see the extended white cane. Only the blind will usually carry white cane. You see more blind person today walking alone, not because there are more of them, but because they have learned to make their own way.