Is there a spot your eye can't see?

Close your eyes for a moment, then open them slowly. Look around at the lamp, the window and the soft edge of your blanket. It feels as if your eyes can see every bit of it.

Yet here is a curious question to wonder about tonight. Is there a spot your eye can't see? Let's find out together.

When you look at something, light bounces off it and slips into your eye through the dark round hole in the middle. That light travels all the way to the back of your eye, because that is where seeing begins.

A thin, soft layer lines the back of your eye. It is your retina, which means the seeing layer inside your eye. Your retina is full of tiny light catchers, packed close together like grains of sand, and each one catches a bit of the light that lands on it.

Your eye cannot make sense of the picture on its own. So every light catcher in your retina sends a quick message to your brain. Your brain puts all those messages together into the picture you see.

All those messages travel together in one thick bundle, like many threads twisted into a rope. The rope leaves the back of your eye through one small round place and runs to your brain. It fills up all the room in that place. Can you guess what has no room to be there?

Your retina has no light catchers in that spot at all! When light lands there, nothing catches it, so no message goes to your brain. That patch is your blind spot, which means the one place in your eye that cannot see.

So yes, each of your two eyes has its own blind spot, right where the rope leaves. You never notice a dark hole, though, because your other eye sees that very part for it.

Retina, blind spot. Light lands on the light catchers of your retina, but where the message rope leaves your eye there are none, so that small patch is your blind spot.

Now close your eyes and let all your tiny light catchers rest until morning.