eye's blind spot

 
Draw two 1/4 inch spots about 4 inches apart on a sheet of paper. Or use the dots below this paragraph. Have the dots at arm's length. Close the right eye. Look at the right spot as you slowly bring the dots closer. The left dot disappears when the paper is about 1 foot away. You may have to rotate the paper slightly or slant your head slightly.
 

 
The back of the eye is covered with a layer of light sensitive cells. The electrical signals from all those cells are sent to the brain through a bundle of nerve fibers. The place in the layer where the bundle is connected contains no ligh; sensitive cell. When the image of the dot falls on that area the dot disappears.