To be considered legally blind means to meet certain criteria as set forth by laws in regards to a person's vision. In the United States, the definition for legally blind was adopted in 1934 as set forth by the American Medical Association. The definition of legally blind entails that a person has a vision that is 20/200 in a person's best eye with correction. Also, the visual field is limited to less than 20 degrees.
The definition for legally blind, in medical terms, does not mean a person cannot see, but rather has limited eyesight that can hinder certain activities. An example could be that a person under the provisions of being legally blind must stand within 20 feet in order to seen an object that a person with perfect 20/20 vision can see from a distance of 200 feet.
The United States Government uses the American Medical Association definition for legal blindness for the purpose of being to determine special kinds of benefits to be issued to such people being so impaired. This definition of legally blind allows for the government to provide special kinds of aids to people suffering from such conditions, such as financial assistance, Seeing Eye dogs, or special technology to assist them in everyday activities.
Conversely, the US Government also uses the definition for legally blind to have certain restrictions. The most common may be with driving privileges and the issuing of driver's licenses. People that are legally blind may be limited to driving to only certain times of the day and with the help of certain visions aids.