Dogs do not see the world entirely in black and white, despite the persistence of the popular myth. Their vision includes colour, although the range they perceive is more limited than that of humans.
Scientists believe dogs can distinguish blue and yellow, but their eyes lack the receptors needed to clearly identify colours in the red and green parts of the spectrum.
How dogs perceive colour
Most humans have three types of cone-shaped receptor cells in the retina, allowing them to see a broad spectrum of colours from red to violet.
Dogs have only two types of cone receptors, meaning their colour vision is more restricted. A red or orange object may appear to a dog as a shade of tan, while green may also look brownish or muted.
Blue objects, however, are likely to appear broadly similar to both dogs and humans.
Researchers have tested canine colour vision by training dogs to touch illuminated coloured discs with their noses in exchange for treats. When the dogs repeatedly failed to distinguish between certain colours, scientists concluded that they could reliably identify only yellow and blue.
Dogs see less clearly at a distance
Dogs are also believed to have lower visual acuity than humans.
Normal human eyesight is commonly described as 20/20, while a typical dog’s vision is estimated to be closer to 20/75. This means that an object a person can see clearly from 75 feet away may need to be only 20 feet away for a dog to see it with similar clarity.
Visual ability can also vary between breeds. Dogs bred to hunt by sight, including greyhounds, may have sharper vision than breeds such as bulldogs.
Better vision in dim light
Although dogs see fewer colours and less detail, their eyes are better adapted to darker conditions.
Dog retinas contain a higher proportion of rod cells, which perform better in low light than cone cells. Scientists therefore believe dogs may see almost as effectively at dawn or dusk as they do during the middle of the day.
Dogs also have a reflective layer of tissue behind the retina known as the tapetum lucidum. It collects and reflects available light, helping the animal see in dim conditions.
This tissue is responsible for the glow often seen in dogs’ eyes when they are illuminated by vehicle headlights or a camera flash.
Vision adapted for hunting
Dogs share this form of vision with several other mammals, including cats and foxes.
Scientists believe this visual system developed because predators needed to detect the movement of prey in twilight or darkness. As many mammals evolved to hunt or forage in low-light conditions, they retained strong night vision but lost the ability to distinguish the wider range of colours seen by birds, reptiles and primates.
Dogs compensate for their more limited colour vision with other highly developed senses. They can hear higher-frequency sounds from greater distances, while their sense of smell is considerably stronger than that of humans.
With information from Independent
