"AM I LEGALLY BLIND?"

Many people THINK they are legally blind when they take one look at the thickness of their glasses, or take another look across the room without their glasses on, and can barely see the wall! Officially, at least in the United States, you are legally blind in an eye if you cannot see 20/200 or better with the BEST correction in place or your central field of vision is reduced to 20 or less. Eye doctors are asked quite often by patients whether or not they are "legally" blind without their glasses or contacts on. In reality, legal blindness cannot be measured or determined unless the patient has his or her glasses ON! So the question is invalid. Are we confused yet? I thought so.

Despite its invalidity, the question is a reasonable one and one that has not been all that easy to answer. Let's go back to the civil war. In 1862, Dr. Hermann Snellen designed a system for describing human vision. He found that certain letters of the alphabet, when of a certain size, could be seen easily at a particular distance by the average normal eye. This relationship-size of letters viewed from a specific distance-has become a standard way for recording visual acuity. It was determined that a letter that was approximately 8.75 millimeters tall could be identified by most "normal" people at a distance of 20 feet. Therefore, the Snellen fraction of 20/20 became the standard for "normal" vision and it meant that at 20 feet the person could identify a letter that was 8.75 mm tall, or "size 20". The top number of the fraction is always 20, because it represents the testing distance, and the bottom number identifies the smallest letter a person can see at 20 feet. If that size is 17.5 millimeters (or twice the size of a size 20 letter) then the Snellen fraction for that person would be 20/40. Doing OK so far? Another way to look at your acuity measurement is to say that if a person sees 20/20 he could identify a letter from 100 feet away that a person with 20/100 vision could only see at 20 feet.

What has all this got to do with legal blindness? Well, I'm not sure, except to say that most countries in the world use some type of Snellen fraction to determine if "vision is not sufficient for the ordinary affairs of life" or "too low to permit normal school education". In 1902 Hugo Magnus, a one-time professor of ophthalmology in Germany, wrote a book on "visual economics" proposing that visual acuity, visual field, and muscle function, as well as ability to compete and earning power, should play a role in determining what level of vision should be considered "blindness". Most of these attempts to quantify the functional implications of visual impairment were for disability compensation purposes. In the United States our best example of this was in the 1935 passage of the Social Security Act with its benefits for the blind. First specified in this act was the current "legal" blindness standard based on 20/200 best corrected acuity, with an amendment the following year to add the alternative definition of a residual visual field of 20 degrees in diameter or less. So, try this: you could have 20/20 vision and STILL be legally blind if your side vision was reduced to a central 20 degrees!

In any case, legal blindness is quite rare and just because you wear thick glasses or strong contact lenses it does NOT mean that you are legally blind. For that matter, it is very unlikely, no matter how bad your UNCORRECTED vision gets, that you will ever become legally blind. There, now quit worrying and go get some sleep.

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