I've tried this before and I was disappointed. I ended up buying three different (cheap) pairs on Amazon and trying them on at home. I guess it wasn't a complete waste of time, because I liked one of them and bought two more of the same brand!
Is there a line you like specifically? Oakeleys, Ray Bans, Quays? I would narrow down brand and search on the vendor's website and then compare to other discounted outlets like Nordstrom Rack or Amazon. I personally love these as they are sleek and subtle.
I second Warby Parker! I ordered regular prescription glasses from them and was able to try on different pairs before purchasing that they shipped to me. Their customer service was top notch
I'll have to check Warby Parker out- I am very light sensitive (photophobia) due to my severe chronic migraines and live in sunglasses. Finding affordable prescription sunglasses so I can simply go grocery shopping or go out for gas is a must in my life LOL. :) Thank you!