There are
different degrees of blindness. Various scales have been developed to
describe the extent of vision loss. Totally blind people can’t tell light from
dark. Total blindness is the complete lack of form and visual light perception;
doctors refer to this as NLP, or no light perception.

Partially blind people
have limited vision. Legally blind, usually refers to partially blind, not
total blindness. A legally blind person has 20/200 vision or worse with glasses
or contacts, or a visual field of less than 20 degrees.

Approximately 10%
of those deemed legally blind have no vision (NLP). The rest have some vision,
from light perception (the ability to tell light from dark, and the general
direction of a light source) to relatively good vision (with 20/200 vision, a
person could tell a car from a refrigerator).

Low Vision is sometimes
used to describe vision from 20/70 – 20/200. Vision not well enough to drive,
but good enough to watch TV. Low vision is not legally blind.

There are different
causes of blindness from birth defects to accidents, but disease (such as
macular degeneration and glaucoma) is the most common cause.