Without getting to technical. You can actually see the blood vessels in your own eye. It's something your eyes actually see all the time but your brain cancels it out because of sensory adaptation.
For example if you've ever forgot you had your eye glasses or wrist watch on. You've experienced sensory adaptation. Your mind is just use to it and forgets its there.
So lets get to this pretty cool effect. What you'll see is something like this image. But not made of solid lines. More like shadows.
Put a small hole in a sheet of paper. Or form a tiny hole with your finger like this image. Close one eye and hold this tiny hole over the other eye. Close enough to look through the hole.
Now stare at something bright through the hole like this white image. Then move the hole in front of your eye very quickly. Don't move it far. Just kind of vibrate the hole. Go ahead and try.
Here's a short video of how to move the hole in front of your eye. Very small and fast movement. Go back to the white image on the previous page and give it a try. Experiment with different directions
Do you see it? Pretty cool huh.