The human eye is one of nature's most complex and sophisticated creations. The really amazing part of what your eye does is the transformation of light into electrical impulses.
This is done by the photoreceptor cells in your retina.
There are two kinds of these cells. The rods and the cones. Your cones are responsible for all the colorful and vivid images you see.
They are concentrated at the center of the retina, so when you look straight ahead, you see what the cones are showing you.
The rods only see black & white. But they are more sensitive to light, and much better at detecting movement.
This gives rise to some interesting phenomena. You're outside on a beautiful night. And then, out of the corner of your eye, you see a bright star. But when you turn that way, the star is gone.
This is because what you saw from the corner of your eye was shown to you by the rods.
When you turned, the star moved to the field of the cones, who, of course are not sensitive enough to show you that star. So in a way, now you are not seeing that which is already there.
The eye truly sees a lot more than you realize.
So think about the last time you saw something out of the corner of your eye. A blurred image or a moving object. You turned towards it and it was gone. Next time, don't turn.
Your rods are trying to show you something.