Dogs' eyesight is very different from that of humans. Dogs see the world in fewer colors than we do, but that doesn't mean our canine friends are completely colorblind. However, although dogs' visual worlds are not as clear or colorful as ours, their ability to see movement is superior.
HOW SHARP IS DOG VISION?
Besides missing some of the hues perceived by the human eye, dog vision lacks some of the acuity of human vision.
In a 2017 study published in the journal PLOS One and conducted at Linköping University in Sweden, researchers designed a dog visual acuity test similar to the tests ophthalmologists give humans.
The dogs were rewarded with rewards for accurately identifying images that contained vertical or horizontal lines with constantly decreasing spacing between them, rather than distinguishing letters that were shrinking in size.
The researchers found that the dogs—or at least the hounds, pugs, and the only Shetland sheepdog that participated in the experiments—are very nearsighted.
The results of the experiment show that in well-lit conditions the dogs have roughly 20/50 vision.
This means they must be 20 feet (6 meters) away from a person and 50 feet (15 m) away from the same object to be able to see something.
WHAT COLORS CAN DOGS SEE?
The human eye works thanks to three types of color-sensing cells called cones.
By comparing the way each of these cones is excited by incoming visible light, our brains distinguish red wavelengths from green wavelengths and blue wavelengths from yellow wavelengths.
Dogs' eyes, like most other mammals, contain only two types of cones.
These allow their brains to distinguish blue from yellow, but not red from green.
Dogs are not completely colorblind, but their eyes are structured similarly to humans with red-green color blindness, lacking the third type of cone normally found in humans.
Jay Neitz, a color vision scientist at the University of Washington, who conducts many of the modern experiments on color perception in dogs, said;
Assuming that dogs' brains interpret signals from cone cells in the same way that color-blind people's brains do, we can get an idea of what dogs see, he said.
Dogs and humans need neurons in the part of the eye called the retina to see blue and yellow.
These neurons are excited in response to the yellow light detected in the cone cells (also found inside the retina), but when the blue light hits the cones, the activity of the neurons is suppressed.
A dog's brain interprets the stimulation or suppression of these neurons as feeling yellow or blue, respectively.
However, both red light and green light have a neutral effect on neurons in dogs and colorblind people.
Since there is no signal to interpret these colors, the brains of dogs do not perceive any color. Where you see red or green, they see shades of gray.
“A person would miss out on their red and green feelings,” Neitz said. "But it's unclear whether the dog's senses are missing red and green, or whether their brains assign colors differently," he said.
Also, like people with color blindness, dogs can use other cues to distinguish the color we call "red" from the color we call "green."
“Often, there are good clues to help them understand; for example, red objects tend to be darker than green objects.” Said.
There is some evidence that dogs can see colors that humans cannot.
A study published in 2014 in the journal Proceedings of the Royal Society B found that the lenses in a dog's eyes transmit significant amounts of ultraviolet light, whereas these wavelengths are blocked by human lenses.
This suggests that dogs can see more blue light than we can.