How do you improve your eyesight?

Visit an optician and get a decent pair of glasses. Not being nasty at all but that's your only real option if your eyes are, like mine and for want of a better word... defective. There is laser surgery but as far as I know it only exists as a choice for a vey specific kind of eye defect (mild shortsightedness I believe) and even then it is only effective for a few years.
Bottom line is there is no way to correct your eyesight to be perfect by diet, exercise or any other method. It may, and that's a big may, be possible to have your eyes replaced with perfect ones but that's extreme, highly risky and incredibly expensive.