What causes red-eye in photos?
Normally the inside of your eyes look black (the pupil of the eye being the window to the interior), but red-eye essentially reveals that given enough light, they’re balls of transparent jelly with red walls. Here’s why. A camera flash happens faster than the iris of the eye can close the pupil (you can see the pupil’s of people’s eyes getting smaller if you happen to be looking at their eyes when they walk from a dark room into a sunny outdoors). The lens of the eye focuses the light from the flash onto the retina at the back of the eyeball, which is red because of all the blood vessels in it. People with blue or grey eyes get worse red-eye because their pupils have less melanin in them (the pigmentation that makes brown eyes brown and moles on your skin dark). Some animals, such as cats, have green- or yellow-eye instead of red. This is because they have a light-reflecting layer behind the retina, to help their night vision. It affects the colour of the reflected light. You can do va
