As an optometrist I hate these type of questions. I was taught you can't, but my personal experience is slightly different.
From my personal experience, yes, you can improve your eyesight. It takes long and apparently don't last long if you don't work on that all the time but you can. I also don't claim it works for everyone, it did work for me.
I improved my eyesight from over -4 to around -2, it took years. Now I'm back to about -3. I also have many other issues with my eyes that did not improve much but the prescription and visual acuity and ability did improve a lot. I still have eye fatigue issue which require progressives but there was a time I could read a lot without glasses without strain.
A lot of things can effect your eyesight and you must treat them, it is not only your eyes. Eye exercises alone don't help much at all, you must work on other things too. Everyone is different and have to focus on other things as well.
Personally, I don't think it worth the effort. I mean I'm very happy with the improvement, I see better and can cope better without correction comparing to the worst time, but to be completely honest, there is not much difference because I'm still very much dependent on eyesight correction on day to day basis. Even at my best I really forced myself not to wear glasses when not really needed, although it was more convenient just to wear them.
I may return to working on eyesight improvement, but I have much more important things to focus on.