Blindness, what is blindness?

About Blindness:

When can be said that a person is blind?

The usually accepted legal definition of blindness is visual acuity of less than 20/16 with correction or a field of less than 20 degrees. Kenneth Jernigan once asked a group of high school learners when they think a person is blind. One of them replied that a person is blind if he/ she cannot see. He asked the student if she really meant what she said. She replied that she did. He then asked her whether she would consider a person blind who could see light but who could not see objects, a person who would bump into things unless she used a cane, a dog, or some other travel aid and who would, if she depended solely on the use of her eyesight, walk directly into a telephone pole or fire plug. After some hesitation the student said that she would consider such a person to be blind. He agreed with her and then went on to point out the obvious-that she literally did not mean that the definition of blindness was to be unable to see.

He told this student of a man he had known who had normal (20/20) visual acuity in both eyes but who had such an extreme case of sensitivity to light that he literally could not keep his eyes open at all. The slightest amount of light caused such excruciating pain that the only way he could open his eyes was by prying them open with his fingers. Nevertheless, this person, despite the excruciating pain he felt while doing it, could read the eye chart without difficulty. The readings showed that he had normal sight. The student then agrees that even a person with normal sight can still be in the physical, literal sense of the word being blind. He then asked her whether if a sighted person were put into a vault which was absolutely dark so that he could see nothing whatever, it would be accurate to refer to that sighted person as a blind man. She then replied no.For a third time Kenneth Jernigan agreed with her. He then asked her to examine what they had established. They came to the following conclusions:
1. To be blind does not mean that one cannot see.
2. It is possible for an individual to have perfect sight and yet be physically and literally blind.
3. It is possible for an individual not to be able to see at all and still be a sighted person.

Kenneth Jernigan came to the conclusion that one is blind to the extent that the individual must devise alternative techniques to do efficiently those things which he would do if he had normal vision. An individual may properly be said to be blind or a blind personwhen he has to devise so many alternative techniques that is, if he is to function efficiently that his pattern of daily living is substantially altered.
Source: A Definition of Blindness, Kenneth Jernigan