I'm told there are indeed eye-strengthening exercises. Cover one eye (not tightly, don't press on it) and focus alternately on a close object, a medium distance object, and a far-off object. Repeat for a minute or two, then repeat with the other eye. Then shut both eyes for a few minutes to rest the muscles.
There are various books on the "Bates Method" available, which covers various ways to "improve your eyesight without glasses". Most largish bookstores should carry at least one book on the subject.