Too strong of Glasses - how bad is it really?

I used to occasionally try on other people's glasses in high school, but forgot about it for 15 years until last year I'd done it at work. A guy with about -2 prescrition let me borrow his extra pair, and I liked it! Now over those years I'd had regular eye exams, but always had 20/20 and been given a script of around +0.5 -0.75 @ 90 in each eye, never buying glasses (no insurance or need). Well at last year's exam I decided to fill it online since they were so cheap. On a whim I substracted -2 from the sphere; if I couldn't stand it, hey, what's 20 bucks? Well long story short I now also own pairs -4 and -6 too strong, and for the most part, can see well thru them after a brief 'learning' period (except the -6 I can't read anyting closer than my PC monitor) and like the effects. Sometimes when I wear the stronger ones I get eyestrain, but can handle the -2s all day and -4s for a long time.

I also just ordered glasses with the right script and I don't like them as much, otherwise, I'd stop this silliness.

I have two questions, #1, is this illegal? and, #2, will I damage my eyes - serious disease, or just refractive errors like myopia, astigmatism increase, or earlier loss of near vision? The internet-and what little I can make of studies - is full of conflicting info about that question #2 so I am asking a real person (afraid to ask my own eye doc on this year's visit during which my script hadn't worsened...yet).
Thanks for hearing my strange request, Buddy J.

[Sandy Feldman, MD, MS]

Dear Buddy77,

Wearing glasses that are too strong for you may cause you too strain your eyes constantly.

Dr. Feldman

Sandy T. Feldman, M.D., M.S.
ClearView Eye and Laser Medical Center
San Diego, California