How Your Dogs Eyes Differ from Yours

September 23, 2019 Written by: Aiden Doane

“Fetch that red ball.”

“Bring me your green rope.”

Have you had any success with these play commands?

Even though your dog is super smart, it’s difficult to teach him differences in colors. His color vision doesn’t align with most people’s, says Steve Roberts, DVM, ophthalmologist, and owner of the Animal Eye Center in Loveland, Colorado. 

“In the social structure of a dog, color is not as important as it is to us,” says Dr. Roberts. “As far as physical structure, dogs have rod and cone cells like people, but dogs (as well as most animals) don’t have cones that are good at detecting red-colored light.”

So basically, he says, dogs are red-green color blind. However, their cones are quite sensitive to blue and green light. 

Physical Differences 

The variations in the construction of the two eyes aren’t always black and white. For example, because of the variety of physical sizes of dogs, they also have a disparity in the size of their eyes. To put that in perspective, larger dog breeds have about the same size eyes as humans.

Dr. Roberts says the basic structure of the eye is similar, but the diameter of the cornea in a dog is larger than a human’s resulting in a larger iris. A dog’s pupil is capable of dilating or opening to a larger diameter than a person’s and the lens measures three-to-four times that of a human. 

Another difference humans don’t have, that’s seen in both domestic and wild animals, he explains, is the reflective layer behind the retina called the tapetum lucidum. This layer reflects light back across the retina and out of the eye giving the animal the eye shine that can be detected at night when shining a light toward him.

Dogs track movement better than people because of their visual streak, a feature humans don’t have. It’s a horizontal band across the retina, above the optic nerve head, that contains a high concentration of cone receptors, clarifies Dr. Roberts.

“This visual streak allows dogs to be good at detecting subtle horizontal movements,” clarifies Dr. Roberts. “They may not immediately recognize exactly what the moving object is, but they can track the movement and quickly adjust their movements to approach and attempt to catch the moving object.”

Canines also have different structures that produce and remove the watery fluid within the eye and an extra set of muscles behind the eye. These muscles allow a dog to retract the entire eye ball deeper into the eye socket, something humans can’t do, he says.

Structural Differences

Your “best friend” has less sharpness of vision than you do. Where perfect sight for us is 20:20, for your dog, it’s 20:70-20:80.

“That means they see about one-third to one-fourth of the detail that we do,” describes Dr. Roberts. 

Because the visual acuity or sharpness of vision in a dog is less than that of a person, minor scratches on their goggles won’t bother a dog as much as they would a person. However, if you look through a scratched pair of Rex Specs and feel that the dog’s vision is being impacted by more than 30-50 percent, then the dog is likely also being affected and the lenses should be replaced, Dr. Roberts explains.

Do dogs see better at night than we do?

“Because the dog’s eye is designed to let more light enter the eye, their night vision is superior to that of a person. At least as far as seeing an overall image, with shape recognition and motion detection,” says Dr. Roberts.

Dogs do better in the dark than humans because of their rod-dominated retina. Their rod photoreceptors function at a low level of light while their cones do well at bright light levels. All these differences have created a system in dogs that is better suited for low light activities than people are.

If you had to use your backyard as a bathroom at night, you’d probably have an eye structure similar to a dog.

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