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Monday, June 29, 2009

Terminology definitions of various degrees of blindness

Many of my family members and friends have asked the difference between the terminology of light perception, legal blindness, etc... I found the below that can help to differentiate the difference terms used with defining blindness. Thank you to visionaware.org for this.

The term "low vision," also known as "partial sight," can be defined in several ways:

  • Low vision is a condition caused by eye disease, in which visual acuity is 20/70 or poorer in the better-seeing eye and cannot be corrected or improved with regular eyeglasses. (Scheiman, Scheiman, and Whittaker)
  • Low vision is uncorrectable vision loss that interferes with daily activities. It is better defined in terms of function, rather than [numerical] test results. (Massof and Lidoff)
  • In other words, low vision is "not enough vision to do whatever it is you need to do," which can vary from person to person.

You may also want to know what the term "visual acuity" means, as well as the meaning of "legally blind."

Visual Acuity

Visual acuity is a number that indicates the sharpness or clarity of vision. In the United States, the Snellen Eye Chart is a test that is commonly used by ophthalmologists and optometrists to measure a person's distance visual acuity. It contains rows of letters, numbers, or symbols printed in standardized graded sizes. The 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 can also be used.

  • If you can read line 8 (directly above the red bar) 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.
  • If you can only read the big "E" on line 1 of the chart 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.

Legal Blindness

In the United States, "legal blindness" is a definition developed by the federal government to determine eligibility for disability benefits and tax exemption programs. It's not a term that tells us very much about a person's ability to function, nor what an individual can and cannot see. In the United States, the criteria for legal blindness are:

  • Visual acuity of 20/200 or less in the better-seeing eye with best conventional correction (meaning regular glasses or contact lenses); or
  • A visual field (the total area an individual can see without moving the eyes from side to side) of 20 degrees or less (often known as "tunnel vision") in the better-seeing eye.

Light Perception

Light perception describes the ability to perceive the difference between light and dark, or daylight and nighttime. An individual can have severely reduced vision and still be able to determine the difference between light and dark.

Light Projection

Light projection describes the ability to determine the general source and direction of a light. Again, an individual can have severely reduced vision and still be able to determine the general source and direction of a light.

Total blindness

Total blindness is the complete lack of light perception, light projection, 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.

1 comment:

  1. Hello Jen:

    This is Maureen Duffy, the Editorial Director of VisionAWARE.org. I'm so pleased to know that our information was helpful to you.

    I'm reading your blog with great interest. If there is any other information you need, please let me know. There are some good parent Listservs and related professionals I can refer you to if you wish.

    Just know that you're not alone on your journey.

    Best,
    Maureen

    Maureen A. Duffy, CVRT
    Editorial Director
    AWARE (Associates for World Action in Rehabilitation & Education)
    Phone: 914-528-5120
    e-mail: maureen.duffy@visionaware.org
    www.visionaware.org
    "Self-Help for Vision Loss"
    www.twitter.com/visionaware

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