I did a pirate bust several years ago with one blind eye. I painted the eye normally, and then put several thin, transparent coats of off-white acrylic over the eye to simulate a cataract. The underlying eye is visible through the "mist" of the white. I then did a scar from the forehead to the top of the cheek using some lighter flesh tones (to explain the eye damage).
Think of a few great movies that have characters with damaged eyes and go for that look. My inspiration was Ragnar in The Vikings (Kirk Douglas).
good luck.