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Definition/Explanation of “Legally Blind”

by: Southwest Low Vision 1-888-534-4321

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What does it mean to be legally blind? Is it the same as having low vision? Does it mean that these individuals are completely without sight? The terms legally blind and low vision are often used interchangeably, but there is an important difference between the two. The term “legally blind” was created to set government eligibility assistance guidelines for people with visual impairments.

In 1934, the American Medical Association defined “legally blind” as having “central visual acuity of 20/200 or less in the better eye with corrective glasses or central visual acuity of more than 20/200 if there is a visual field defect in which the peripheral field is contracted to such an extent that the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye” (quoted by Koestler, 1976).

To put this into understandable terms, having a visual acuity of 20/200 means that even with the most powerful corrective lenses available, this person can be no further than 20 feet away from the object to see the details that a person with normal vision (20/20) can see from 200 feet away. One very important point to remember is that even when the legally blind person is 20 feet away from the object, others with unimpaired vision cannot assume that this person can see all the details that they are able to see. Additionally, a person with normal vision has a total visual field of 180 degrees for peripheral vision while someone who is legally blind only has the ability to see objects that are located within a 20 degrees visual field.