In order to be considered legally blind, someone must have vision of 20/200 (6/60) in his or her best eye with correction, and/or have a visual field which is limited to 20 degrees or less, in contrast with the 180 degree visual field enjoyed by people with healthy eyes. This definition means that it is possible for someone to be able to see and to still be considered blind in the eyes of the law.
Governments have come up with a definition for legal blindness for the purpose of being able to determine who should receive special government benefits and assistance for blindness. Someone who is legally blind may be entitled to disability payments and other assistance, such as note takers in college classes, or aids such as seeing eye dogs, canes, and so forth which will help them navigate the world.
Being legally blind means that your best seeing eye cannot be corrected with glasses or contact lenses any better than 20/200. The best way to understand this is to think about a normal person with 20/20 vision. This person has the ability to stand 200 feet away from an object and see the finest detail, whereas the legally blind person would have to move all of the way up to 20 feet to see the same detail. A legally blind person has difficulty seeing objects very far away or very close. Source: http://vision.about.com/od/faqs/f/What-Does-It-Mean-To-Be-Legally-Blind.htm