By Amy Shojai, contributing writer
My dad is color blind and has difficulty distinguishing between reds and greens. He’s a talented artist, and over the years has taught himself to compensate for this condition termed deuteranopia.
Are dogs color blind, like my dad? According to veterinarian Cynthia Carlson, for NBC News, for many years we assumed that dogs could see only in shades of black, gray and white. She says dogs do see color, but not in the same way as people do. Veterinary ophthalmologist Dr. Christopher Murphy and Paul Miller, DVM wrote in their paper “Vision in Dogs” that the differences are in the light-receptor cells contained in the retina at the back of the dog’s eye.
How Do Eyes See Color?
Dog eyes are structured like and function similar to our own. The retina acts like a movie screen where light is focused and translated into the colors and shapes that the brain then translates into images. Drs. Murphy and Miller explain that both people and dogs share the same types of specialized light-sensory equipment, called rods and cones.
The rods respond to shades of black and white. Dogs have many more rods than people do in the central part of their eyes. Rods are most sensitive to changes in light which is useful for motion detection. That likely would have helped dogs tracking varmints – or Frisbees.
It is the cones – cells primarily responsible for visual acuity or sharpness – that determine how well we see and also detect color.
WebMD explains that people (and primates) normally have three kinds of cones, and these photoreceptor cells respond best to red, green and blue. This three-color system – called trichromatic vision – allows humans to detect different hues and their combinations, including yellows, oranges and purples and a variety of shades in between.
How Do Dogs See Color?
Dr. Gerald Jacobs, Professor of Psychology at the University of Santa Barbara has been studying color-sight detection, including studies and tests to find out how dogs can see color. In one test published by Visual Neuroscience, dogs were presented with three circles of different colors and taught to choose the one that was different. When dogs couldn’t see a particular color, they couldn’t pick out the odd circle. But dogs presented with colors they could detect were able to point out the one that was different. By using color samples of different brightness or hue, researchers figured out what colors dogs see well, and which ones they have trouble detecting.
The results of Dr. Jacobs’ studies show that dogs do see in color, but rather than trichromatic three color receptors of most humans, dogs see in dichromatic vision – like my dad.
The cones in your dog’s eyes are most responsive to green and blue, but they’re missing the red-responsive receptor. So by this definition, dogs are partially color blind.
Why Does Seeing Color Matter?
Murphy and Miller note that the green, orange, red and yellow we see probably looks like different yellowish hues to the dog, while blue-green, blue and violet look like various shades of blue-gray. That makes sense when we consider dog ancestors probably didn’t need to see red colors, and dealt with the blues, greens and shaded browns and grays of hunting prey through vegetation.
What does it mean for your dog today? If squirrels start to wear red riding hoods, it could be a cloak of invisibility and spell trouble for canine fun! Offering your dog a bright green toy that to him looks neon-bright could be a new way to treat him. On the other paw, a contrasting color – maybe a blue ball – may be easier for him to find in the grass during play.