If you can persist on doing eye exercise for a long time, you can improve your eyesight. But most people are too lazy so they can't persist on doing it. So they seems to achieve nothing in the end. Besides, it is possible for children to improve their eyesight because their eyes are under development. And the eyes are more flexible. As to adults, it is difficult to improve their eyesight because all the organs are mature and began to degenerate as they age.