The term legal blindness is used by the Internal Revenue Service and others to determine whether you are eligible for disability benefits or for certain other benefits or services. There are two definitions of legal blindness, depending upon whether you have lost central or peripheral vision. You are legally blind if central vision in your better eye, with the best correction possible with contacts or glasses, is no better than 20/200, or if peripheral vision is no greater than 20 degrees diameter (10 degrees radius) in your better eye.

You are not legally blind if you are blind in only one eye. Legal blindness does not necessarily mean total blindness. For example, you may still be able to read with special magnifying lenses and devices. If your peripheral vision is good, you may also be able to move about without difficulty even though your central vision is poor. On the other hand, you may be legally blind with respect to peripheral vision but be able to read even though you are not able to move about easily — especially in dim illumination such as at dusk or nighttime.