Guest Author - Carla Ruschival
What is meant by legally blind and tunnel vision? What is light perception, travel vision and object perception? This handy guide simplifies these confusing terms.
A totally blind person is unable to see. He cannot tell day from night and cannot tell if a light is on in a room. Less than 10 per cent of all people with visual impairments are totally blind.
A legally blind person has a visual acuity of 20/200 or less in the better eye (as measured on the Snellen chart) with best correction (with glasses or contacts). If a person sees 20/200 without glasses, but with glasses can see 20/100, 20/70, 20/40, 20/20 etc., he is not legally blind. Also, if the person sees 20/200 or less in one eye, but can see better than 20/200 in the other eye, he is not legally blind.
Visual acuity refers to central vision, or the ability to see straight ahead. Visual field refers to peripheral vision, which can be thought of as side vision. Peripheral vision is what is used to see out of the corner of the eye.
A person may have a visual acuity of 20/20 and yet be legally blind. If the visual field (peripheral vision) is restricted to 20 degrees or less in the better eye with best correction (with glasses), then the person is legally blind. This is called tunnel vision, and means that the person can see straight ahead but cannot see things to either side.
A person with light perception can tell when it is daylight or dark or distinguish if a light is on or off in a room. People with light perception sometimes use their ability to see the windows in a room to help them navigate around the house, school or office, but they cannot read print.
The phrase travel vision is an unscientific term that means that the person's vision is good enough to help with mobility in some way. It may mean that he can see steps going up or down, see objects in his path such as telephone poles or cars, or tell a bus from a car. It is a term that is not measurable, so it is not normally used by ophthalmologists to describe vision.
Sometimes people with very poor vision will say they have object perception. This usually means that they can see large things such as trees, furniture etc. When I was young, I could see the general shape of a tree, including the trunk and the branches. I could tell that the branches were full of leaves in spring and summer because they created more shade than when they were bare in winter, but I could not see the individual leaves or see them moving in the breeze. Object perception is another term that is not measurable on an eye chart.
People who are totally blind, or who have light perception or object perception, are legally blind. But not all legally blind people fit into these categories. Many legally blind people can see to read some print, especially with the help of appropriate low vision aids.
All totally blind and legally blind people are visually impaired, but not all visually impaired people are legally blind. A person whose visual acuity is 20/60 or 20/70 is visually impaired, but he is not legally blind. This bevel of vision is usually below the required limit for obtaining a driver's license in most states.
