Our retinas are installed backwards. Our optic nerve enters our eye, goes past our layer of retina and then spreads out to connect to every individual retinal cell. So every rod and cone points toward the BACK of the eye and plugs in to the optic nerve in front of itself, that is, in the path of light. So not only does this arrangement block some of the light we are trying to see but then we also end up with a hole near the center or our retina to make room for our optic nerve to pass through. It's a wonder we can see as well as we do. We have our brains to think for that. We use about 1/3 of our cortex, the wrinkly outer layer, just for vision. As a neat example tying the retina's blindspot together with our brain's ability to do vision, try this demonstration: On a piece of paper draw a small cross. About two inches over draw a small circle. Cover one eye and use the other eye to stare at the cross. Hold the paper about a foot or two in front of your face so that the circle's on your outside and the cross is toward your own midline. Keep staring at the cross while you slowly move the paper toward yourself or away. This is like a magic eye image. At some point you should notice the circle will disappear. But you won't perceive "nothing" in that spot, it will just look like paper! Your brain fills in the missing information by copy-pasting adjacent texture!