What Do Our Pets See?
Dr. Dennis Selig, Tribune-Review/Pittsburgh Tribune-Review
Ever wonder what your dog or cat sees as he or she gazes upon their world? Do they see colors and, if so, which ones? Can they see great distances or only close up? What about night vision?
The answers to some of these questions might surprise you but, by knowing what your pet's vision should be, this information may guide you and help you recognize if it is having vision difficulties.
Human vs. canine
We have a good idea of what dogs and cats see, because we know the make-up of their retinas. The retina, which lines the inside of the eye, is made up of light-sensitive cells called rods and cones. Cones provide color perception and detailed vision; rods detect motion and vision in dim light.
Dogs have 10 times more rods than humans and therefore can see better in the dark and can detect subtle movements better than humans. Enhancing their night vision is a thin reflective tissue behind the retina called the tapetum lucidum. This tissue reflects light back through the retina, giving the rods and cones a second opportunity to absorb the light. We have all seen the tapedum in action: It's the bright green to yellow reflection seen in a dog's eyes when a bright light shines on them at night.
Also because of the large number of rods in their retinas, dogs see moving objects much better than stationary items; in a study, dogs could recognize moving objects more than 2,500 feet away but could recognize the same object, when stationary, at less than 1,500 feet. This motion-detecting characteristic offers a clear advantage for canines stalking prey, especially at twilight, or guarding territory against intruders at night.
Dr. Ralph Hamor, a veterinarian specializing in ophthalmology, said: "So much of dog behavior deals with posture and appropriateness. Small changes in your body posture mean a lot to your dog." They see and interpret body language of other animals and humans and are far more skilled than we are at this form of nonverbal communication.
The trade-off in the large ratio of rods to cones in a dog's retina is dogs can't distinguish the full spectrum of colors and probably see colors similar to a red-green color-blind human. Dr. C.J. Miller at the University of Wisconsin School of Veterinary Medicine reports dogs have two types of cones in their retinas: One that is maximally sensitive to violet-blue wavelengths and one that is sensitive to yellow-green light. …