There are two types of cells present on the retina at the back of each eye where the image is formed. Rods provide the ability to see under relatively poor lighting conditions, whereas cones are required for effective colour vision, being stimulated by bright light.




Dogs have a much higher ratio of rods to cones than we do, which means that they have much better night-time vision, being able to see in conditions which appear to be pitch black to us, but conversely, they are not able to see as well in colour.