I have used the brand called Sun Shield available at both WalMart and Walgreen's.
They come in two styles - "fit over flip up frame" and "clip on" which clips to the edges of the eyeglass frame in four locations.
The clip-on type require a bit of manual dexterity to be removing and adding, but the flip-up allow easy switching between regular vision and sun protection.
They both come in several shapes to better fit the different shapes of prescription eyeglasses, so you have to do a little fitting.
I like the good fit I got with the clip-on and my particular eyeglass frames.