Visually impaired : A person who is visually impaired has a decreased ability to see, even with corrective lenses, that adversely affects his visual access or interferes with processing visual information. The visual challenges an individual may have can range from not being able to see newspaper print to not being able to read print at all. Other challenges may include not being able to recognize a friend in a room until she is standing within arm’s reach or until she identifies herself.
Blindness: The term “blindness” is typically used to describe individuals with no usable vision or only the ability to perceive light.
Legally Blind : The term “legally blind” is a definition used to determine if individuals are eligible for government or other benefits as determined by the classification of legal blindness. Persons classified as legally blind have a central visual acuity of 20/200 or worse in the better eye with the best possible correction and/or a visual field of 20 degrees or less. For example, someone with an acuity of 20/200 may see something at 20 feet the same as what someone with normal vision can see at 200 feet
Low Vision : A person with normal vision typically has a visual acuity of 20/20 in both eyes and a visual field of approximately 160 to 180 degrees. An individual with low vision may have a visual acuity of 20/70 or worse and a visual field of 20 to 40 degrees or less. Individuals with low vision can often use optical devices, nonoptical devices, and environmental modifications to increase their visual functioning
Source : AFB (American for The Blind)