Besides just the cones, there are other photoreceptors known as rods. Rods can only detect black and white, but they also process movement extremely well and help to see in the dark. A dogs photoreceptors are mostly rods. This means they can see exceptionally well in low light conditions and see different shades of grey to a higher degree than we can. They can also differinciate the tiniest movements you make. If you’ve ever stood still with your dog in the back yard at night in a shaded area, and caught him by suprise, your dog has probably barked at you. This is because while you are standing still, he doesn’t know who you are. Once you move, even wiggle your finger, he knows its you. This is helpful to an animal that hunts in the dark! On top of having an eye full of rods, they also have a reflective layer that helps to reflect light, helping them to see even better in the dark. This reflective layer is the glow that we see when we shine a light on a dogs eyes in the dark. As a matter of fact, it is believed that a dog can see in 4 times lower light levels than we can because of this reflective layer.
Another thing that comes into factor when talking about a dogs vision abilities is that they can see 240 to 250 degrees around them without moving their eyes. Our field of vision is only 180 degrees. So even if you are standing diagonally behind your dog, chances are he sees you.
Even though dogs are able to see all of these different things with their eyes, vision is not their primary sense. Actually, dogs are considered