Your brain is really, really good at filling in blind spots. There is a big one where your optic nerve connects to the back of your eye, you can even see it you

Your brain is really, really good at filling in blind spots. There is a big one where your optic nerve connects to the back of your eye, you can even see it yourself. http://pbskids.org/zoom/activities/sci/blindspot.html http://pbskids.org/zoom/activities/sci/blindspot.html In order to keep from overwhelming the brain with irrelevant optical data, there is a lot of processing going on, and one of the things that happens is a filling in of places where there's no stimulus coming from that part of the eye. It's possible you have blind spots and don't know it. Also, only UV-blocking sunglasses will keep you from getting cataracts.