The central blind spot is a very annoying defect in the eye for anyone who enjoys astronomy.
It exists because the central portion of the eye is loaded with cones, which are sensitive to color, but are unable to function in the dark.
At night, if you look directly at a faint object in the sky, you will not see it, but if you look slightly to one side of it, it will appear. This is not easy to do, because as soon as you put your attention to the object, you will tend to look directly at it again, and lose it.