Why are pupils sometimes red in pictures?

Why are pupils sometimes red in pictures?

See the inside of your eye!

Take a look at the pictures above and below.

Red pupils

What do you notice?

That's right, the people in the pictures all have spooky red pupils. Do you know what it is?

It's a picture of the inside of your eye!

Your pupil is an opening that lets light enter your eye. It usually appears black because the inside of our eye is usually dark. When a camera flash goes off, it can send light into our pupils. At the back of your eye is the retina. This is a layer of cells that respond to light entering your eye and tell your brain what you're seeing. Blood vessels behind the retina are red. They cause the red colour you see in the picture.

Red pupils_Rob

Red pupils show the blood vessels behind the retina

So the red eye in your picture is really a picture of the inside of your eye. Pretty exciting, right?

Some nocturnal animals have a reflective layer called the tapetum lucidum at the back of their eye. This helps them to see at night. In photos it looks a strange, silvery colour, like this:

Tapetum lucidum_Flick_Niall McAuley_cropped

Nocturnal animals sometimes have 'eyeshine' caused by the tapetum lucidum (c) Niall McAuley

You know what to do next time you see red eyes on a picture. Tell everyone why it happens!

Main image (c) Wispfox