Everyone has a blind spot in each eye. The nerves in the back of human eyes actually come forward into the eye. They collect together, then exit the eye through a small gap off-center of the back of the eye. At this gap there are no optical receptors, so there is a blind spot. The brain, being the fairly clever thing that it is, tries to compensate for this.
If you want to see this for yourself, try the following simple test: Get a piece of paper. Draw two black dots on it next to each other and about two inches apart. Close one eye and focus on the same dot. For example, if you close your left eye, stare at the left dot. If you hold the paper flat in front of you, and get it just the right distance from your face, the other dot will disappear. This is because your brain kind of 'assumes' that the blind spot contains more or less the same kind of image as what is around it.
A side note: squid do not have this problem. Their optical nerves exit out the back ot the eye so there is no blind spot. This fact has been used as an argument against the divine perfection of Man, and caused quite a stir when discovered. | 
