What happens when light hits the spot where your optic nerve meets the retina (the lining inside your eye)? That spot has no light receptors. It creates a gap in your vision called the blind spot. You draw a dot and a cross on a card. Hold the card at arm's length and close one eye. Slowly bring the card closer while staring at the cross. At a certain distance the dot vanishes completely. Move closer and it reappears. Your brain fills in the gap so you never notice it in daily life. You can even measure the size of your blind spot using simple math.