As an phenomenon of the moment, tunnel vision is a temporary condition that can come on in times of stress, especially when combined with anger. One's peripheral vision is obscured by a red or black "fog" as one's eyes become half-closed, perhaps for protection of your delicate sight organs. The head is often lowered, and the mouth may fall open slightly and be accompanied by labored breathing. It becomes difficult to concentrate on anything not directly before you. In this angry state one may be more likely to perpetrate violence. It is often accompanied by a feeling of going cold (or hot) all over, all at once.
Another, less violent form of tunnel vision may also be present in austistic individuals who manifest it in a tendency to focus on one aspect of an object or situation to the exclusion of all else. This interferes with one's ability to grasp the larger picture and thus function as a "normal" member of society.
Finally, there is a form of tunnel vision which literally allows a person to clearly see only a spot before them. It is commonly caused by glaucoma or by Retinitis pigmentosa (retinal dystrophy).
As a result of these conditions, various tendencies to see (or recognize) only one aspect of a situation is known as tunnel vision; to see the bad and ignore the good in someone, something, or some situation, for example. This could easily be the other way around as well, which would be not being able to see the bad in some situation.
References:
- Stephen M. Edelson, Stimulus Overselectivity: Tunnel Vision in Autism. 1995. (http://www.autism.org/tunvsn.html)
- Guide Dog Association of New South Wales and A.C.T. Tunnel vision. 2002.(http://www.guidedogs.com.au/vision/vision_tunnel.htm)