The terms partially sighted, low vision, legally blind, and totally blind are used in the educational context to describe students with visual impairments. They are defined as follows:
“Partially sighted” indicates some type of visual problem has resulted in a need for special education;
“Low vision” generally refers to a severe visual impairment, not necessarily limited to distance vision. Low vision applies to all individuals with sight who are unable to read the newspaper at a normal viewing distance, even with the aid of eyeglasses or contact lenses. They use a combination of vision and other senses to learn, although they may require adaptations in lighting or the size of print, and, sometimes, braille;
“Legally blind” indicates that a person has less than 20/200 vision in the better eye or a very limited field of vision (20 degrees at its widest point); and
Totally blind students learn via braille or other non-visual media.
Visual impairment is the consequence of a functional loss of vision, rather than the eye disorder itself. Eye disorders which can lead to visual impairments can include retinal degeneration, albinism, cataracts, glaucoma, muscular problems that result in visual disturbances, corneal disorders, diabetic retinopathy, congenital disorders, and infection.
This information was sourced from the National Dissemination Centre for children with disabilities http://nichcy.org/disability/specific/visualimpairment