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Saturday, 26 July 2014

Legally Blind - What does that mean? Can you see or not?

Have you heard the term "Legally Blind" before? What does that mean? Is the person blind or not? Can they see? If you can see then you are not blind? By definition "blind" means not to see anything so surely a blind person cannot see at all?

What does it mean Legally Blind mean?

Generally the term "Legally Blind" is a term used to describe a person whose best corrected eyesight is at such a low level that their eyesight isn't deemed satisfactory to see properly. You can think of this as the gray area between actually seeing and seeing at such a poor level that the quality of sight isn't acceptable for most duties and task.

Some people in the legally blind category may detect light and shadows. Others may only see objects but couldn't read writing regardless of the size although some may be able to read with low vision magnifying glasses. So a legally blind person could possibly see people if close enough and know roughly where the head is but wouldn't be able to see your facial features etc. Very few people are in the total blindness category meaning they have no light perception.

The this isn't so clear then perhaps the following chart that I drew would help explain things more clearer.

How to measure Legal Blindness?


Legally blind is conducted by one of the two methods (which ever ends up being true):
  1. In Australia, North America and most of Europe legal blindness is defined as visual acuity (vision) of 20/200 (or 6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet (or 6 meters) from an object to see it with the same degree of clarity as a normally sighted person could from 200 feet (or 60 meters). This is the threshold / tipping point in order to be classified as Legally Blind.

    So a normal sighted person can see an object 60 meters away that a legally blind person would need to be 6 meters away.
  2. Another test performed to determine legal blindness is the eyesight range that you can see when looking straight (i.e. determining whether you have tunnel vision or not). In general when people look straight ahead, they can normally detect objects to either side, or above or below the direction in which they are looking. This measurement is called the visual field. In normal sighted people, this is measured as 170 degrees. A person is "legally blind" if the combined visual field for both eyes is less than 10 or 20 degrees depending on the country. For Australia it is 20 degrees.
Some people may claim they are legally blind if they are tested without their prescribed glasses or any corrective measures to their eyesight. This would be incorrect as you would need to measured by the best eye limits with the prescribed glasses or any corrective measures to your eye.

So if you were totally blind in one eye (no light perception) and with your other eye you can hardly see but with your glasses you perform better than visual acuity (vision) of 20/200 (or 6/60) and have better than 10 or 20 degree visual field then you wouldn't be classified as legally blind.

Why have the term Legally Blind?

Governments generally want to determine the "Legal Blindness" to determine the eligibility of social security benefits that a person may be entitled to because a person in this category would generally would find it difficult to work and generate an income to support them self. Such benefits is offered in most Western countries.

The above helps determine road safety too as clearly having tunnel vision or unable to see objects that normal people see at 60 meters away that you can't see 6 meters away would make driving cars etc a real hazard and dangerous on the road.



Please let me know if you spot any errors in the above and I will correct it.



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