What does this mean?

Question

wat does the 20/20 thing mean my doctor said i have 80/80 something like that i dont understand how that works

yes im talkin bout eye sights here

Answer 1

there is no "80/80".

here is a cut-and-pasted blog entry about acuity from my blog:

WHAT IS 20/20?
I get this question all the time, and I'm always amazed at what patients think it is and/or what they've been told that it is. 1st let me tell you what it is NOT:

1) It is not your prescription. You cannot have a prescription of 20/20 or 20/50 or 20/70 or 20/anything.

2) Its not "perfect" vision. Its only average vision for a normal, healthy human eye. Most healthy eyes should be able to see better than 20/20.

3) Its not a comparison to anyone else's vision. For example I get told all the time by patients that they heard that if they have 20/40 vision its the same as having 20/20 vision but being closer...? Some jibe about "you see at 20 feet what a normal person sees at 40 feet"...No.

20/20 is an angular measurement of letter size. Thats it. The top "20" is the test distance...in the U.S. its 20 feet (in Europe they use meters, so average vision for the human eye is 6/6, with the top "6" being 6 meters). The BOTTOM "20" is the harder one to explain:

The denominator of any Snellen acuity is "the distance at which the letter subtends 5 seconds of arc". Yeah...wait, what? LOL seriously, its confusing. Remember that I started all of this by saying that we're talking about an angular measurement of letter size. If a circle has 360 degrees in it, and each degree is further divided into 60 seconds, then the denominator of the acuity is the distance that the letter size in question produces an angle that equals 5 of those seconds of one degree. Its not an easy thing to wrap your brain around.

The reason we have to use angles like that instead of talking about a 6" letter or a 5" letter or whatever, is b/c obviously a 6" letter looks really small at 200 yards, and really big if your nose is 2" away from it. We as a profession needed a way to "standardize" the vision measurements with varying test distances. The way to do that is to talk about the angles, not the letter sizes.

"Snellen" letters are generally the standard...its an optotype that is easy to distinguish.

Answer 2

20/20 is a way of measuring your vision. The first 20 refers to the test distance (20 feet from the chart), the second 20 specifies the smallest letters you could correctly identify.

In theory, the smallest thing that a human eye can see subtends 1 degree of arc. So the "20" letter is the size of 1 degree at 20 ft, the "40" letter is the 1 degree at 40 ft and so on.

If your uncorrected vision is 20/80 it means that you were tested at 20 ft and the smallest letter you could identify was the "80" letter.

Answer 3

20/20 means you see what you're supposed to see from 20 ft away. If you are 20/80, it means you see what you should see from a distance of 80 feet when you are 20 feet from it.

Answer 4

20/20 means when you stand 20 feet away from the chart you can see what " normal' people see.standing 20 feet.. so if your 80/80 you stand 80 feet away from the chart you can see what normal people can see standing 80 feet away from the chart. i hope you understand that . go to the site--- howstuffworks. and it will tell you more or type in 20/20 eyesight and it will explain it better ...

Answer 5

Now how can I even try to add anything to Princeidoc's answer? :) He's got it right on!

Answer 6

20/20 eye sight ?
i don't understand wat u r tryin 2 say -_-