I have long been told that dogs only see in black and white with little way to see colors, but is this true? Are dogs color blind?
While there is actually much more to just a yes or no answer, it is true that their spectrum of colors is relatively limited because of their eye structure. Canine eye structure evolved to make them effective nocturnal hunters and has more rods than cones which does allow them to discern between certain shades but not all.
What Causes Color Blindness?
Color blindness results from an inability to differentiate between colors or to see specific colors altogether. It is the result of an abnormality in the receptors that sense colors. Eyes are made up of two receptors in the retina, rods, and cones. The retina contains millions of light-sensing cells.
Rods work in low light and detect movement and cones work in bright light to control color perception. The retina converts light into electrical impulses and these signals are conveyed via the optic nerve to the brain. The most common types of human colorblindness occur because a person is missing one of the three types of cones and is most prevalent in Northern European populations.
Colorblind individuals that are missing one type of cone cannot recognize certain light wavelengths (most commonly red and green) but can still discern other wavelengths. This is the same situation for dogs since they naturally have only two types of cones.
Are Dogs Color Blind?
The answer to “are dogs color blind?” is yes. However, this does not mean to say that dogs see only shades of grey. Dogs see colors although they are not as rich or plentiful as the colors that we see. Canine vision structure resembles that of a red-green colorblind person. This goes against popular belief suggesting that a dog’s world is black and white. Dogs can differentiate between certain colors, though their vision is not as vivid, and they cannot distinguish between shades as well.
Whereas humans have more cones than rods, dogs have more rods. This is the primary difference in color perception. Humans have three types of cones and dogs only have two. Because of this, dog color vision is often labeled as dichromatic.
The dichromatic arrangement is common among non-primate mammal species including squirrels, pigs, and cats. Research from the Neitz Color Vision Lab at the University of Washington found that there were no differences in color vision among the different breeds of dogs. This suggests that all domestic dogs have the same cone pigment types and nervous system connections that make color vision possible.
Humans as well as other primates have trichromatic vision, meaning they have three different types of cones. Some animals such as birds and fish have four cones and are tetrachromatic, meaning they have an even broader range of the color spectrum than humans.
In humans, there are generally two forms of color blindness:
- An inability to distinguish between red and green
- An inability to differentiate between blue and yellow.
Most dogs can distinguish between yellow and blue, but they cannot see red and green well. A dog’s visible spectrum begins with a deep brown and transitions into light brown, yellow, grey, light blue, and dark blue.
Therefore, people can usually identify three color combinations (red, blue, and green) while dogs can recognize two (yellow and blue). A dog’s color vision resembles that of a person suffering from deuteranopia who has red-green color blindness according to research from the Neitz Lab. Blue and purple are perceived as one hue, red, yellow, and green comprise a second hue, and cyan and magenta are perceived as a neutral hue (grey).
Dogs are still able to see green and red objects, but they cannot distinguish red, yellow, or green objects based on their color. They may be able to distinguish between a yellow object and a green object based on the perceived difference in brightness between the two objects.
A recent journal study found that dogs could distinguish images of bright red cats from a mottled green background. However, when the color contrast decreased, the dogs were no longer able to distinguish between the mild red cat and the green background.
Sight is not the primary sense for dogs. They evolved to rely on their sophisticated sense of smell that is 1,000 times as effective as humans to help them navigate their surroundings. However, in contrast to other dichromatic animals, they can make pure-color discriminations. Besides red-green colorblindness, no further degree of colorblindness has been recorded in dogs.
How Dogs See
Optic Nerve
The optic nerve is the most important part of the dog’s eye function. Connecting the eye to the brain, it carries electrical signals to the brain where they are processed to form images.
Retina
The retina is the innermost layer of the eye that allows it to receive light and send signals through the optic nerve to the brain, shaping vision.
Cones
Cones are light processing cells in the retina that allow for color vision. They work in bright light and are responsible for processing fine detail in vision. In dogs, cones are outnumbered by rods.
Rods
Rods are millions of photoreceptors cells that help process light coming into the eyes. They allow dogs to capture movement and see in dim light situations. In dogs, rods outnumber cones.
Canine Eye Structure and Night Vision
Studies have shown that there are important differences in eye structure between humans and dogs mostly because of evolution. Canine vision evolved to help dogs hunt at night, so they adapted to see well in the dark and sense movement.
Their dichromatic vision evolved to aid in identifying predators and prey and enhancing contrasts between colorful animals and the green background of the trees that is not present in their visual spectrum. Their limited vision makes certain colorful objects bolder and filters out less important details.
According to the AKC chief veterinary officer, dog eyes have a larger lens and corneal surface and a reflexive membrane that assists in night vision. Dogs cannot see when it is very dark or there is no light. They have many light-sensitive rods that collect light in the retina.
The high level of rods in the retina collect the light and the tapetum lucidum (a thin tissue behind the retina) amplifies the light back to the lens which is fixed on what the dogs are seeing. The tapetum increases the probability of visual stimulation of the photoreceptors by reflecting light assisting in vision in dim-lit situations. The layer is visible in cats, dogs, birds, and fish and is responsible for the shining appearance in the eyes in the dark.
Dogs & Nearsightedness
Because of canine dichromatic vision, the lower number of cones results in decreased color absorption and less visual detail compared to humans, primates, and tetrachromatic birds and fish. Compared to the sharp vision of humans, dogs are very nearsighted.
They have a visual acuity of 20/80 so that something that people can see from 80 feet can be seen by dogs only within 20 feet. A dog’s visual acuity is anywhere from 4-8 times worse than a human’s. this means that dogs have a worse depth perception compared to humans.
Dogs also have a wide peripheral vision ranging from 240 to 270 degrees. Where dogs’ vision differs is in their motion detection, depth perception, and visual perspective that allow them to detect movement better than people at night. Dogs can detect motion at 80 images captured per second compared to only 60 images per second for humans.
Dogs are relatively poor at differentiating between differences in brightness or shades of colors. Researchers say that people are twice as likely to differentiate between shades as dogs. Still, even with only two types of cones, dogs can differentiate between 10,000 different shades of colors in their spectrum.
Conclusion
While there is actually much more to the question about are dogs color blind, we do know that its essentially true. Their spectrum of colors is relatively limited because of their eye structure. Canine eye structure evolved to make them effective nocturnal hunters and has more rods than cones. This means they can only discern between shades of yellow and blue. This makes their vision like that of a red-green colorblind person.
Perhaps it explains why dogs like to eat bananas and love blue or yellow toys best!
Dogs are nearsighted and the sharpness of the images they see is relatively lower than humans. However, in some ways, dogs have a better sense of vision than us. They can detect motion faster than humans and have a wider peripheral vision.
Ironically, the most popular colors selected for dog toys are red and safety orange. The next time that we are selecting the next toy for our best friend, make sure to select a color like blue or yellow that a dog can genuinely appreciate.
Color considerations could also play an important role in ensuring the security of our pets. We should select colors that dogs cannot distinguish well when constructing outdoor fences and installing markers for special outdoor railing to deter them from biting or digging through.
Finally, dogs have long served in service roles for the disabled population which requires the use of vision. Understanding the strengths and limitations of canine vision will better help train service dogs to better fulfill their duties.
For anyone interested in more information, please visit the following online resources:
https://www.petmd.com/dog/general-health/what-colors-do-dogs-see