"Blindness" may seem at first consideration to be easy to define. It is simply a complete lack of sensation entering through the eyes. Think of what the mind perceives from visual input to the back of the head; there are no visual receptors, no eyes in the back of the head, so all human beings are blind behind them.

When specialists and consumers define blindness, however, they rarely use this simple definition; the issue becomes very complex when the discussion turns to degrees of vision retained or lost.

This complexity arises because vision is a very complicated set of brain systems. When some part of this complex system is damaged, it is possible that the human brain becomes "blind" to certain kinds of input. Color blindness is an example. Most of the systems called "vision" function normally in a color blind individual, but these people are "blind" to specific colors.

When we leave the safe harbor of total blindness, we enter a sea of new distinctions and definitions; consider the following:

Visual Impairment:
Low Vision
Partial Sight:
Functional Vision:
Legal Blindness
Cortical Vision Impairment (CVI)
Light Perception
Object Perception
Inattentional Blindness
Visual Neglect

At this stage, I am not including the names of the experts who sent the quote. This is bacuse I do not know all the members full names, loactions and titles. If you would like to be credited with your quote, please contact me with personal details.

"In New York State, our definition of visual impairment is a functional one: Visual impairment including blindness means an impairment in vision that, even with correction, adversely affects a student's educational performance. The term includes both partial sight and blindness. Therefore, services can be based upon functional needs rather than numbers. However, the legal definition of blindness remains in registering students for federal quota funds. I like Susan's functional definition of blindness as the inability to use vision to guide independent mobility. This covers situations of fluctuating vision such as are encountered with CVI and other visual and cortical diagnoses related to light perception. The fact that many students demonstrate object perception in NONVISUAL ways (echolocation/"facial perception") will therefore not enter into the equation in terms of the definition of blindness. In other words, I think that for legal purposes we should retain the legal definition, and for functional purposes a functional definition."

"I feel that the definition for blindness is not as clear-cut as that of legal blindness, which has a necessary cutoff point, above which one is not legally blind. I would say that blindness goes from no light perception to light perception, without object perception, but after that, it seems to me that it would be difficult to come up with a clear definition. What degree of object perception qualifies someone as having moved from blindness to legal blindness? I think that is the question and I for one, don't know the answer.

"I think another important term to consider is "functional vision", which goes beyond the definition of legal blindness and illustrates the ability of a visually impaired individuals to use his or her remaining vision. People often function much differently than the acuity reported in their ophthalmologic tests -- a person who has 20/300 OS and 20/400 OD, might use his or her vision much more effectively that a person who measures 20/200 OU. One reason for this is how much and how diligently one used his or her vision before becoming visually impaired. In other words, good and avid readers generally do much better using their remaining vision than people who did little reading before their vision loss. This also might change whether a person can be termed as blind or legally blind -- that might beg the question: How much can one use their light-perception/object perception functionally?"

"I'll comment more on the other definitions later, but I agree with Jan and Lori that the 20/200 cutoff is too limiting to call blind. In Michigan, with bioptic systems, these folks are getting drivers licenses. I have kids with 20/400 acuity who are amazing visual travelers. I'm wondering whether we need to have these definitions at all, but if the group does, I'm thinking a definition that is more functional, than clinical, such unable to use vision to guide independent mobility. That's a definition that we use to qualify as multiply impaired. That opens the door for some of the quirkier situations we get like students with brain damage / cortical visual impairment that might test as visual in a clinical setting, but don't function all that well in real life.

"I am impressed with the ideas so far floating around on the topic. I agree that we need to include games and problem solving activities. I like the definitions proposed so far, except that I would like to see the definition of blindness be more restricted than 20/200 of 20 degree field. I have a student with a 5 degree field who is far from blind, although he does experience some difficulty with mobility and is learning to use a white cane. I also have a little student with 20/400 acuity, who is learning to read both print and braille, and uses a white cane part time (even though I would like to see her using it more than she does). Perhaps we could have a definition of legal blindness and another definition of blindness.

"My proposed definition of blindness - having light perception or less.

Blindness: A visual acuity of 20/200 or less in the better eye with the best correction and/or a visual field of 20 degrees or less.

Low vision: person who has difficulty accomplishing visual tasks even with prescribed corrective lenses, but can enhance his or her ability to accomplish these tasks with the use of compensatory visual strategies, low vision and other devices, and environmental modifications." - Anne Corn and Alan Koenig in Foundations of Low Vision: Clinical and Functional Perspectives