Sorry, C. M. Coolidge, but man’s best friend would probably really suck at poker. For one, dogs can’t see red. Two, their vision is so awful that they’d probably have trouble even making out the numbers.
See for yourself: WolframAlpha, every nerd’s favorite search engine, has a web app that lets you look at life through a dogs’ eyes.
Where people have three specialized receptors in our eyes to distinguish colors, dogs only have two: this leaves them red-green color blind (we think). Life’s Little Mysteries:
To see blue and yellow, dogs and humans alike rely on neurons inside the eye’s retina. These neurons are excited in response to yellow light detected in the cone cells (which are also inside the retina), but the neurons’ activity gets suppressed when blue light hits the cones. A dog’s brain interprets the excitation or suppression of these neurons as the sensation of yellow or blue, respectively. However, in dogs and color-blind individuals, red light and green light both have a neutral effect on the neurons. With no signal to interpret these colors, the dogs’ brains don’t perceive any color. Where you see red or green, they see shades of gray.
“A human would be missing the sensations of red and green,” Neitz told Life’s Little Mysteries . “But whether or not the dog’s sensations are missing red and green, or if their brains assign colors differently, is unclear.”
Aside from the color issue, dogs’ sight is pretty bad. Using a custom eye test for dogs, researchers have found that dogs basically have 20/75 vision compared to a person’s 20/20 vision, says Psychology Today.
To give you a feeling about how poor this vision is, you should know that if your visual acuity is worse than 20/40 you would fail the standard vision test given when you apply for a driver’s license in the United States and would be required to wear glasses. A dog’s vision is considerably worse than this.
More from Smithsonian.com: