Optic Nerve
Optic Nerve is the cord in your head that sends what your eyes see to your brain.
Think of it this way
A security camera on a wall picks up a scene. A wire runs from the camera to a small screen across the room. The screen shows what the camera sees. Your optic nerve is that wire — it carries signals from your eye to your brain, where the image is read.
Explaining optic nerve by grade level
Draw a dot on a card and hold it in front of one eye. Move the card slowly and the dot will vanish at one spot. That spot is where the cord to your brain plugs in. There are no seeing parts at that one spot.