My favourite pair of eyeglasses had a terrible tendency of slipping off my nose when I looked down. The simple tool that finally has them staying put: ponytail holders.
I realised one day after tying my hair back with the elastic that it could offer some grip on my wide eyeglasses. A couple of twists of the elastic at the back of the arms and now the glasses are non-slip.
The elastic isn't even noticeable because it's behind your ear, but you can get clear elastics or, I guess, use rubber bands.
Either way, it's a solution to an annoying problem and quicker to try than adding shrink wrap to your glasses.