I think Aldous Huxley wrote a book on the topic?? maybe I'm wrong, but I'm pretty sure there is a book on it, try making a search.
IMO if you did the exercises regularly leading up to an eye test it would give you an edge and you might pass when you would otherwise have failed. By extension of that it you did the exercises regularly all the time your eye sight might be that slight bit better. However, IMO the margins are very small and you would be only kidding yourself if you could have better sight with glasses / contacts, at worst it could be dangerous. In particular I think with fatigue your sight might revert to form...
Nevertheless, I think that exercising you eyes will give you every chance of keeping up the strength of vision you presently have.