What do animals see?
In order to ‘see,’ there are three structures (eyeball, the optic nerve travelling from the eye to the brain, and visual cortex of the brain) that are required to communicate information and produce an image. Nerve cells in the retina of the eye called cones are responsible for colour vision, and cells called rods are for night vision.
The type of vision that an animal experiences depends on the species. Many species of birds are active mostly in the day time, and may have bright plumage, so have larger numbers of cones in their retinas. In nocturnal birds, almost 100% of the receptors are rods.
Dogs and cats have night vision far superior to humans thanks to two things: more rods in their retinas, as well as a reflective structure known as the tapetum, to gather light. It is light reflected from the tapetum that we see when lights shine on an animal at night. It has also been proposed that the tapetum shifts the wavelength of the light in the cat. This brightens a blue-black evening or night sky and enhances the contrast between the sky and objects silhouetted against it.
The high number of rods also gives them a superior ability to detect motion, making them good hunters. This ability to detect motion is the visual “skill” that lasts the longest as our pets age, so we often observe our elderly dogs can still spot a fleeing squirrel, but they can’t see a toy lying in front of them.
The old belief that dogs are colour blind has been proven wrong. In dogs, the 2 types of cones stimulated by light photons are blue-violet (blue) and yellow-green (yellow). Blue-green and red appear as a shade of grey (so dogs have partial colour blindness to red and green). However, dogs can perceive more shades of grey than humans. Check out this site for a picture of what your dog sees compared to you- https://veterinaryvision.com/resources/what-do-dogs-and-cats-see/ .
In cats, the types of cones that have been identified are also yellow-green and blue.
25% of all dogs are myopic (near-sighted). Myopia is most common in the German Shepherd dog, Rottweiler, Collie, Labrador Retriever, Miniature Schnauzer, Toy Poodle and English Springer Spaniel. Interestingly, one study showed 53% of the German Shepherds in veterinary practices were myopic, where only 15% in guide dog programs were myopic!
When dogs and cats lose their vision, they adapt very well because they have other senses that are far superior to ours, mainly their hearing and sense of smell, as well as sensory hairs on their faces and limbs that help them to navigate in their environments.
What do they see when watching TV? Scientific studies have shown that dogs are able to detect dancing lights at higher frequency than man. Old 60-Hz television models will quickly flash individual images for our dogs, while the new 120-Hz televisions will produce a continuous image…..newer TV’s have made watching “Homeward Bound” a much smoother experience for our dogs and cats!
If you have concerns about your pets’ vision, please contact your veterinarian or visit the Eastern Shore Veterinary Hospital to book an appointment.
65th Convention of the Canadian Veterinary Medical Association, 2013
67th Convention of the Canadian Veterinary Medical Association, 2015
Kerry L. Ketring, DVM, DACVO
Written by Dr. Fran Minty, June 2016