I used to have a prescription of 150 (I'm not sure how the system of reading the prescription is in your country). I couldn't read anything from signs and all that. I had trouble seeing from the back of the classroom. Then I began to use contact lenses. My prescription went up to 250, back in high school! This peeved me to no end. I began to feel that the contacts were causing my poor vision, so I trashed them.
I lost my glasses too in a taxicab, so I stopped using them for a long time. I noticed that my eyes were in a state of "hyperuse" when I was wearing glasses-- everything is too clear, at least that was my observation! While without glasses, I can focus on one area and cancel out the clarity in the rest, everything is really sharp when they are on. This caused (and still causes, when I wear glasses) my eyes to be tired.
After a bit, I began doing a regimen based on the
Bates method to help relax and exercise the eyes. This helped a lot in eye tension. I also used these eyedrops made from coleus plant.
My eyesight is greatly improved (with a prescription down to 75-- I can read reasonably sized signs), but is slowly becoming a bit bad again, perhaps because I have stopped doing the exercises and the drops for a few years now. I have glasses, but only when I travel for critical signage.
I will actually get back to them, after being reminded. It takes some discipline, some personal observation as to what works, and attention to personal patterns. I can't guarantee this will work, but it's always worth a shot. I'm not sure what the scientific consensus on the Bates method is, but it really improved my vision, and that matters a lot for me.