actually go through the eyelids and reach the retina and this is why even when you close your eyes you will see some light where's the challenge if we want to penetrate penetrate tissue and get images 350 years ago microscopy was invented right that really revolutionized medicine or any previous before that point there was no technology that allows us to see cells with the Y field optical microscopy we can see cells now we're at micron resolution however you have to cut the tissue into very thin slices like ten