There are two definitions of visual impairment a legal one and an educational one because of their learning abilities. Determining if a visual impaired person is legally involved involves assessment of visual acuity and field of vision. Visual impaired individual who are blind ar so severely impaired that they must learn Braille or audio tapes.
Low vision refers to the students who can read some and see only with a large magnifying glass.
Only a small percentage of individuals who are legally blind have absolutely no vision at all.