The basic premise is that opticians often over prescribe glasses. I've had this personally, an optician prescribed me glasses that were 0.75 dipole too strong for computer use, as the way they test (unless you ask otherwise) is for long distance vision (i.e. driving), not for 50cm in front of your eyes.
The theory is that your eye muscles become lazy as they don't need to work so hard, and you get used to that, so you need glasses to see clearly. If you look at distance text that is ever so slightly out of focus, eventually your vision system will figure out how to correct for that blur, and you will be able to see in focus. If you rinse and repeat, changing ever few months to a slightly weaker prescription (e.g. a reduction of 0.25) you can greatly reduce the strength of glasses you need.
I've only just started, but there are other comments on HN about people who have done this.