Question: Does every 'picture' you look at leave a tiny etching on your retina like a photo negative?

  1. No.

    The retina is a series of light detectors. It actually works more like a digital camera than film. These detectors are called rods and cones. The cones detect colour and the rods are best for low light, i.e. seeing in the dark. When an image passes across the retina the rods and cones send a signal to the brain to say if they saw any light and the brain combines the signals to form what you see.

    The reason it sometimes seems like images are ‘burned’ or ‘etched’ onto you retina is because the rods and cones sort of get stuck sending the same signal if they see something very bright. So when you look away from the bright thing they keep sending the same signal to the brain for a little while afterwards.