An Australian review concluded that sleeping on your stomach can increase eye fluid pressure, which can raise glaucoma risk and worsen nearsightedness. Further, glaucoma can cause partial vision loss, with blindness as a possible eventual outcome. Over time, you may develop other disorders like pain and tension in the muscles of your face, headache and postural abnormalities like lower back pain. Constant pressure on your jaws will deteriorate your teeth as well. The best is to sleep on your back and right.