Dogs see the world around them a little differently to you. The anatomy of a dog’s eye has adapted to suit their role as a predator and the human eye has adapted for better fine focus vision and more colour. Dogs also perceive what they see differently because they are lower to the ground.
Dogs, like humans, have binocular vision and are quite good at depth perception. This is different in prey animals, for example, horses that have a 360degree field of vision but not much depth perception. Some spiders have eight eyes and a complete field of vision.
When light enters the eye it is converted into an electrical charge that goes to the brain as an image. It is the cells in the retina at the back of the eye called rods and cones that capture the light. Dogs have a lot of rod cells and fewer cones. Humans have a lot of cones and fewer rods.
Rods are useful for night vision. Dogs also have an extra reflective layer in their eye called the tapetum. This allows light that passes through the retina to bounce back and be absorbed by the retina improving night vision. A dog’s ability to see in low light and in the dark is seven times better than humans. Your dog can see in the dark.
Having a majority of rods in the retina also means that dogs are superior motion detectors. It has been shown that a German Shepherd dog can detect motion 1km away. If the same object is not moving, the dog can only see it as far as 500m away.
Dogs see a 60Hz television screen as a rapid flicker of single images (like a home made cartoon). When they watch a high definition 120Hz television they can see the smooth image like we see.
Cones in the retina are helpful for colour vision and light vision. Humans, having more cones have more highly developed colour vision and light vision.
Humans have three types of cones for colour; red, green and blue. Dogs have only blue and red. Dogs see red and green colours as different shades of grey.
Human eyes can detect different shades of brightness, which dogs see as the same.
A dog’s visual acuity or focus is inferior to a human. Dogs do not have a fovea, a small area on the retina where images are fine focused. Dogs have 20/75 vision, so they see what a human with 20/20 vision would see on an eye chart if the human was standing 75 feet from the chart instead of 20 feet from the chart. A dog’s focus is about half to a quarter that of humans.
Dogs lack fine detail vision but have excellent night vision and motion detection.
Next time you are walking your dog, try to imagine what he can see from down low with slightly blurry vision but great awareness of moving objects up to a kilometre away and less of a variety of colours but able to see things in dim light and darkness.
Would you trade lack of fine detail vision for night vision?