The Legal blindness reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Legal blindness

Legal blindness is defined either as vision of 20/200 or less in the better eye with correction, or as a visual field of less than 20 degrees.

What Do Those Numbers Mean?

‘Normal vision’ is defined as acuity of 20/20; people with 20/200 vision can theoretically see an object with the same degree of clarity at 20 feet as someone with typical acuity can at 200. In reality, however, an individual’s usable vision is more dependent upon the eye condition she has, and upon the circumstances under which she is operating visually (e.g. low light or poor contrast), than on what numbers her ophthalmologist charts while she is in the office.

A normal visual field is 180 degrees. 20 degrees, then, is considered “tunnel vision.”

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