** Update 2019: I have pretty much confirmed, at least for myself, that getting stronger glasses each year was the cause of my myopia.  I stopped going to eye exams and getting stronger glasses since 7th grade, which is over 15 years ago now.  I also made deliberate effort to never wear my glasses except when needed to read far.  During that time, I only went back once at the end of college to replace broken glasses, and that prescription ended up being pretty much the same as eight years prior.  Another seven years later, today, after going back to replace broken glasses, my prescription still ended up being close to what it was over a decade ago.  

My eyes went from 0 to -5.00 diopters from 4th to 7th grade in a matter of 3 years, during which doctors gave me stronger glasses every year.  Eight years later after avoiding eye doctors for so long, my replacement glasses ended up still only -5.25 diopters.  Now, my newest prescription 7 years after that is -6.00 diopters, of which I currently have to practically argue with the eye doctor not to prescribe the full amount and restart the worsening cycle.  It's a bit too much a coincidence to think it had nothing to do with when I stopped upping the prescription every year.