legal blindness

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A degree of visual acuity that is low enough to determine that a person needs special assistance.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun vision that is 20/200 or worse in both eyes (20/200 vision is the ability to see at 20 feet what a normal eye can see at 200 feet)