What does this mean?!

What does this mean?

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

2 weeks ago
yes im talkin bout eye sights here

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.