I'd suggest that your glasses don't really fit - if they did they'd be much more stable. I'm fortunate that my current pair don't move at all because they fit so well around my ears, and they're photochromic as well so I don't need special sunglasses. If you do want proper running prescription glasses however then look at www.optilabs.com - they're much better quality than a lot of what the high street opticians offer, and cheaper too. I've used their prescription fishing glasses all over the world for years, and they're superb.