ANSWERS: 3
  • 20/20 is a rating (this happens to be average) for ONE EYE. When you get a refraction, the doctor will give you 20/20 OD, 20/20 OS, or something like that. OD is your right eye, OS your left. The first number is the reference, originally 20 feet, and the second is the measurement of your visual accuity based on the _Snellen_ chart. (That's right, the familiar "read the smallest line without squinting" chart). Visual acuity is defined as: "Sharpness of vision, especially as tested with a Snellen chart. Normal visual acuity based on the Snellen chart is 20/20." by http://dictionary.reference.com, and an in-depth definition (with metric conversions!) is here: http://www.mdsupport.org/library/acuity.html If you had 200/10, that would be 20/1 on the Snellen chart, and you'd have a telescope for one eye, and be presumably blind in the other! I was diagnosed with 20/20, 20/15 when I was 10 years old. Now I have 20/200, 20/200, and am severely nearsighted (and a "prime candidate" for LASIK surgery, I've been told). Although legally blind without corrective lenses, WITH corrective lenses (particularly slightly over-powered contact lenses, usually -5.5 diopters), my _acuity_ is quite good. I'm seriously considering LASIK, especially since it's getting really, really cheap.
  • An average person sees between 20/16 and 20/20. A hawk sees at about 20/10 and an eagle sees at 20/6. Perhaps you mean that your vision is 20/200. This is typical for someone with about -3.00 D to -4.00 of near-sightedness. People with -5.00 D to -6.00 D would see about 400/20 (an equivalent to 200/10). Seeing 200/10 would be about 6 times better than the limits of the human eye. It has been postulated that with perfect optics, the human retina could attain the same acuity that an eagle achieves (20/6 or 200/60). See the other explanation for what the numerator and denominator in the fraction represent.

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