Actually, you can replace your clear lens with prescription one if your glasses frame is not so big. Just take your glasses to any optcian and they will know whether your glasses lens can be replaced or not.
If you like your glasses frame, you can take your eyeglasses to the eyeglasses store and replace the clear lenses with prescription lenses. However, I do not know how to make already clear lenses into prescription lenses. Maybe you can ask for a help from optician.