I have one pair of Chanel sunnies that go straight across and those Lens Crafters put a prescription in no problem. I had a second pair that they also put my prescription in (but shouldn't have because of the lens curve) and it altered my vision and the lenses popped out all the time. My vision is middle of the road, not too bad, not great so the lenses weren't super thick or anything. I guess what I am saying is, I learned the hard way that yes it can physically be done in all shapes of glasses, but if a reputable place advises you not to do it, this may be in your best interest. I ended up with a pair of crap sunnies that cost me over $350 before the prescription lenses went in! I now have the one pair that are straight across with a prescription, and I ended up needing to buy a new pair which I wear "blind" or with contacts. If you want I can post pics of both sets so you can get an idea of what I mean by straight, as I am not sure my description has been the best! LOL! sorry long post!