(from the American Optometric Association)
Quote: 20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.
20/20 does not necessarily mean perfect vision. 20/20 vision only indicates the sharpness or clarity of vision at a distance.
...then let's see. (Ha.) 20/100= the 20 is you, looking at something 20 feet away; the 100 is a person with normal vision seeing with the same clarity but standing 100 feet away. So if you have better than 20/20, would that be expressed as, say, 20/10? So that you at 20 feet away see the object with the same level of clarity as someone standing 10 feet away from it. ??