"Legal blindness" is a definition used by the United States government to determine eligibility for vocational training, rehabilitation, schooling, disability benefits, low vision devices, and tax exemption programs. It's not a functional low vision definition and doesn't tell us very much at all about what a person can and cannot see.
Part 1 of the U.S. definition of legal blindness states this about visual acuity:
A visual acuity of 20/200 or less in the better-seeing eye with best conventional correction (meaning with regular glasses or contact lenses).
This is a 20/200 visual acuity measurement, correlated with the Snellen Eye Chart:
If you can only read line 1 (the big "E") from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/200 with best correction.
Update: In 2007, the Social Security Administration updated the criteria for measuring legal blindness when using newer low vision test charts with lines that can measure visual acuity between 20/100 and 20/200. Under the new criteria, if a person's visual acuity is measured with one of the newer charts, and they cannot read any of the letters on the 20/100 line, they will qualify as legally blind, based on a visual acuity of 20/200 or less.
Part 2 of the U.S. definition of legal blindness states this about visual field:
OR a visual field (the total area an individual can see without moving the eyes from side to side) of 20 degrees or less (also called tunnel vision) in the better-seeing eye.
For more information on the definitions of legal blindness, you can read Disability Evaluation Under Social Security, a publication from the Social Security Administration.
Using Low Vision Optical and Non-Optical Devices
To learn more about the many different types of reading options that are available, see Reading, Writing, and Vision Loss on the VisionAware website.
What Can I Still Do If I Am Legally Blind?
Much like low vision, there are many different definitions of visual impairment. "Visual impairment" is a general term that describes a wide range of visual function, from low vision through total blindness.
Here is an example of the variations in the term "visual impairment" or "visually impaired" from the World Health Organization Levels of Visual Impairment:
Moderate Visual Impairment:
- Snellen visual acuity = 20/70 to 20/160
- Severe Visual Impairment:
- Snellen visual acuity = 20/200 to 20/400
- OR visual field of 20 degrees or less
Profound Visual Impairment:
- Snellen visual acuity = 20/500 to 20/1000
- OR visual field of 10 degrees or less
Like the term "legal blindness," "visual impairment" is not a functional definition that tells us very much about what a person can and cannot see. It is a classification system, rather than a definition.
Light Perception and Light Projection
These terms describe the ability to perceive the difference between light and dark, or daylight and nighttime. A person can have severely reduced vision and still be able to determine the difference between light and dark, or the general source and direction of a light.
The stereotypical assumption – that people who are blind or have low vision live in a type of "blackness" that sighted people see when they close their eyes – is generally not accurate.
Although every person sees differently, including persons with low vision, an individual who has light perception/projection can perceive the presence or absence of light. Some people describe light perception as knowing when a room light is on or off, or being able to walk toward a lighted lamp on a table in an otherwise darkened room.
Total blindness is the complete lack of light perception and form perception, and is recorded as "NLP," an abbreviation for "no light perception."
Few people today are totally without sight. In fact, 85% of all individuals with eye disorders have some remaining sight; approximately 15% are totally blind.
Source: Maureen A. Duffy, Making Life More Livable: Simple Adaptations for Living at Home After Vision Loss (New York, NY: AFB Press, American Foundation for the Blind, 2015), p. 11. © 2015 by American Foundation for the Blind. All Rights Reserved.