Blind Spot
Blind Spot is a small area in each eye where you cannot see anything because no light sensors exist there.
A muffin tray has a grid of slots, but one slot in the middle has no cup. You fill every other slot with batter and bake. The done tray has muffins in every spot except that one bare gap. Your eye is like that tray: sensors cover most of it, but one small spot has none.
Explaining blind spot by grade level
Draw a dot on a card and hold it in front of one eye. Close the other eye and move the card slowly. At one spot, the dot goes away. That happens because one small part of your eye has no way to sense light.
Projects that explore blind spot
Every eye has a small area on the retina where no light receptors exist, called the blind spot. You can prove it by drawing a dot and a plus sign on paper, closing one eye, and slowly moving the paper toward your face. At a certain distance, the dot disappears because it falls on your blind spot.
Where the optic nerve meets the retina, there are no light receptors. That gap in your vision is your blind spot, and finding it takes just a card and steady hand. Draw a dot and a cross on a card, hold it at arm's length, and close one eye while staring at the cross. As you slowly bring the card closer, the dot vanishes completely — then reappears as you move closer still. Your brain fills in the gap so you never notice it in daily life, but you can even measure the blind spot's size using simple math.