Well, generally speaking, it is actually kind of annoying to have salt water over sunglasses. What is more, salt water can just be harmful your sunglasses. So you need to take some measures to remove it off. First, you should prepare undiluted white distilled vinegar, for it can be good for removing salt water over sunglasses. And then, you can just soak the glass item in the white vinegar for a while. And then, just use some soft cloth with vinegar to wipe the glass. Of course, you should do this very carefully, so that it will not hurt your sunglasses. Finally, just dry the glass piece with a lint-free cloth. Anyway, just take care of your sunglasses to avoid being unclean, or scratched.