Why do we have a blind spot in our vision?
Images are formed on the retina at the back of the eye. On one portion of the retina, there are no receptors. This area is where the optic nerve leaves the eye. Because our eye (and brain) want us to have the clearest most complete image possible when we see, it is not normally apparent that we have a blind spot.
You can find your blind spot by playing a fun trick on yourself. Take a piece of paper and draw a dark circle on the left side of the paper, and an X on the right side of the paper. Put your hand over your right eye and focus on the X with your left eye, while you move the paper further and closer from your eyes.Do not let your eyes wander from the X. You will still be aware of the dot in your peripheral vision, and as you move the paper further and closer from your eye you will find an area in which the dot disappears momentarily from vision. This is your blind spot.
We don’t normally notice this blind spot because it is off to the side and our mind fills in the blanks. A good demonstration of this is to take another piece of paper. Draw the X again on the right, but on the left draw two thick lines in a row, not quite connecting to each other. Move the paper back and forth to your eye as you did before. In your blind spot, instead of making the lines disappear (like the dot did) your brain will connect the two lines making one long line.