Gingles,
You do not seem to have a reply to your query of some weeks back. This is well known and should be explained in any Aviation Medicine document.
The blind spot is where the optic nerve enters the eyeball and does not respond to light, or sight is fuzzy at best.
You can locate and demonstrate it with a piece of card with two symbols on it, say an O and an X about 5cm apart. Hold the card about 60cm away, with the O-X axis horizontal, and focus on the O and observe that the X is visible, and remains so while moving the card towards the eye. When fairly close the X will disappear (or become too fuzzy to see). You will be able to see that other items outside the blind spot are still visible, ie, it is a spot, not a cut-off point. You have already seen this effect.
The function is important for pilots, since it is entirely possible for an object to be overlooked (pardon the expression) if it happens to fall into that place. Therefore if you are looking for air traffic, etc, you must scan continuously.