Originally Posted by 5263
btw, that is what I tested at to enter Navy Flight school...back in the day.
Still tested at 20/20 this yr at 52.
Yep, that's as good as it gets. The reasons are extremely boring to 99% of people who don't care about anatomy, so I won't bother listing them, but in essence it comes down to the fact that we simply don't need
greater vision, so the parts of our eye aren't made to suit that lack of need.
Hawks, eagles and falcons in comparison max out around 20/4 or 20/2. The reason these numbers don't exactly scale is because you need a different measurement mechanism. For humans, visual acuity really only is beneficial for having great resolution at distance, that is, being able to discriminate objects at distance. For athletes, that's not very useful since this has nothing to do with depth. If a baseball player can see that a white object is flying at him, that's all he needs. He doesn't need to make out the writing, as long as he can tell it's a baseball and has enough depth perception to know where it is, he's good (that's entirely separate, howeveer).
Fighter pilots, and others in the military however, need to be able to discriminate between similar looking objects at a distance. So for them, 20/10 vision is far more relevant than it is for someone who just happens to have above normal visual acuity. In the bird example, the hawk needs to be able to see that at 400 feet away that a 2" mouse is indeed a mouse even though it may not be moving. That puts just how absurd that level of acuity and resolution is into perspective. Us mortal humans have no need for that ability, hence why most laser surgery places won't even count it as plastic surgery even if you request it. It offers you nothing other than the risks associated with the surgery. Wikipedia puts it nicely:
Some people may suffer from other visual problems, such as color blindness, reduced contrast, or inability to track fast-moving objects and still have normal visual acuity. Thus, normal visual acuity does not mean normal vision. The reason visual acuity is very widely used is that it is a test that corresponds very well with the normal daily activities a person can handle, and evaluate their impairment to do them.