The definition of vision impairment includes people who are blind and people who have very limited vision.

Vision impairment or low vision is a severe reduction in vision that cannot be corrected with standard glasses or contact lenses and reduces a person's ability to function at certain or all tasks. Disease, damage or injury causing vision impairment can occur to any part of the visual system, such as the eye, the visual pathway to the brain or visual centre of the brain. 

Total blindness is the inability to tell light from dark, or the total inability to see.  Legal blindness refers to a best-corrected central vision of 20/200 or worse in the better eye or a visual acuity of better than 20/200 but with a visual field no greater than 20° (e.g., side vision that is so reduced that it appears as if the person is looking through a tunnel).