20/200. Legal blindness varies with the jurisdiction but the two most common discriminators are a best corrected acuity of 20/200 in the best eye and/or a visual field with less than 10 degrees of extent in all directions in the better eye. Some also consider permanent doubling of vision in all directions of gaze to be legal blindness.
20/200 corrected. For most purposes, a person is considered "legally blind' if the best they are able to see with all corrective assistance (glasses, etc.) is 20/200, which means that for them, looking at something 20 feet away is like someone with normal vision looking at something 200 feet away. However, there are many types of vision problems, and legal rules are also stricter for driving and other activities.