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Facts about Low Vision Visual Acuity and Low Vision A Functional Definition of Low Vision Low Vision vs. Legal Blindness Visual Impairment Light Perception and Light Projection Total Blindness

Most surveys and studies indicate that the majority of people in the United States with vision loss are adults who are not totally blind; instead, they have what is referred to as low vision. You may have heard the terms "partial sight" or "partial blindness" also used to describe low vision. Those descriptions are no longer in general use, however.

Here is one definition of low vision, related to visual acuity:

Visual acuity is a number that indicates the sharpness or clarity of vision. A visual acuity measurement of 20/70 means that a person with 20/70 vision who is 20 feet from an eye chart sees what a person with unimpaired (or 20/20) vision can see from 70 feet away.

20/70 can best be understood by examining a standard eye testing chart that you may have used in your own doctor's office during an eye examination.

In the United States, the Snellen Eye Chart (pictured left) is a test that ophthalmologists and optometrists use to measure a person's distance visual acuity. It contains rows of letters, numbers, or symbols printed in standardized graded sizes.

Your eye doctor will ask you to read or identify each line or row at a fixed distance (usually 20 feet), although a 10-foot testing distance is also used.

If you can read line 8 (D E F P O T E C) from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/20 with best correction.

If the smallest print you can read is line 3 (T O Z) from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/70 with best correction.

Please note: An actual Snellen Eye Chart is much larger than the one depicted here; therefore, it's not recommended that you use this chart to test your own (or a friend's or family member's) visual acuity.

Not all eye care professionals agree with an exclusively numerical (or visual acuity) description of low vision. Here's another more functional definition of low vision:

"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:

This is a 20/200 visual acuity measurement, correlated with the Snellen Eye Chart (pictured above):

Part 2 of the U.S. definition of legal blindness states this about visual field:

This is a representation of a constricted visual field:

For more information on the definitions of legal blindness, you can read Disability Evaluation Under Social Security, a publication from the Social Security Administration.

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:

Severe Visual Impairment:

Profound Visual Impairment:

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.

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.

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.

Low vision optical devices can make it possible for you to do various tasks, such as reading, doing crafts, and preparing meals. To help you understand the different types of devices and options that are available, see Reading with Low Vision Optical Devices.

Living room image source: From 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.

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Low Vision and Legal Blindness Terms and Descriptions ...

This entry was posted on August 4, 2016 at 9:42 am and is filed under Eye Sight & Vision. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed. |