I'm not really thinking about taking a backup pair of regular glasses, but taking a regular pair and a pair of sunglasses (one would be worn). Right now, my regular glasses weigh .75 ounces, my sunglasses are 1 ounce, and the case I am used to carrying them in is about 4.5 ounces. On a cloudy day, I'm carrying over 5 ounces in glasses and case in my pack, which I'd like to cut down. I think a lighter case would be a start, because I really love my sunglasses.
_________________________
...then we might find something that we weren't looking for, which might be just what we were looking for, really. - Milne