Why Our Pets See Differently From Humans
Cats and Dogs are very perceptive. They’re quick, fast and it’s fascinating how quickly they can turn and run with greater agility that most humans. They’re lower to the ground than us humans, so they have a greater ability to find hidden spaces under beds, furniture and other little nooks and crannies that we’d never think of going into. So, how do dogs and cats see us and their surroundings?
Rumors have persisted for years that pets only see in black and white, or that they’re color blind. We can’t get inside their heads and actually see what they see. However, there are some scientific hints as to how cats and dogs respond to different types of light, indoors and out.
Visual Functions in Cats and Dogs
Visual function involves many things, such as, field of view, depth perception (how to determine distances), acuity (the ability to focus), motion perception, and color differentiation. The brain absorbs all of this information and determines how one sees.
Night Vision and Colors
Cats and Dogs are crepuscular, which means that they are mainly active during the twilight hours of sunset and sunrise. This is when their eyesight is extremely keen to pick up things. It can also help explain why they start craving food, especially cats, in the early evening and in the early morning.
While it was originally believed for many years that cats and dogs could only see in black and white, it’s now quite obvious that they can see certain colors.
Photopigments, Trichromatic and Dichromatic Vision
Humans have 3 cone photopigment populations, which are unstable pigments that experience a chemical change as they encounter light. Our peak absorbance is in red, blue, and green which makes us trichromatic, meaning that our retinas contain three kinds of color receptors.
Many animals are dichromatic, which means that they have 2 photopigment populations. So, cats and dogs do have color vision, although not nearly in the same vein as us humans. Based on behavioral tests, it’s believed that dogs are able to see red and blue, but have issues with red and green, which means that they should never get behind the wheel of a car.
Dogs are able to detect hand signals from a mile away, and yet they have greater difficulty with something right in front of them at a close range. If a dog, or any other member of the canine family, is looking straight ahead, it will have a visual field of view of 240 degrees compared to a cat’s which is 200 degrees.
Cats have better night vision compared to dogs; they can see objects and details as far as 200 feet in the distance. In terms of colors, cats are able to distinguish yellows, blues, and some shades of violet and green. Colors such as red and pink are different for them to distinguish.
This is often determined by cone photoreceptors, or cone cells, which are found in the retina. Cone cells normally function in conditions where bright light exists, and make up around 20% of the photoreceptors in a dog’s retina; humans normally have 100% cones.
Binocular and Peripheral Vision
Binocular vision (when the field of view of each eye overlaps) is a key element in depth perception. Cats usually have 140 degrees binocular vision, while dogs are known to have around 30 to 60 degrees. Both cats and dogs are able to see from the corners of their eyes. Dogs have greater ability over cats to observe any kind of movement with their peripheral vision.
Peripheral vision is determined by the placement of the eyes in the head. It also defines the amount of vision one has simultaneously with both eyes. Peripheral is a type of binocular vision which is important in helping to determine distance. For dogs, based on their head shape, they tend to have a visual field of 240 degrees, whereas a human will have 200 degrees. Cats and dogs will have a binocular field that is about half of what humans have.
Visual Resolution and Acuity in Cats and Dogs
Visual acuity is the value that is measured when you visit an optometrist and read an eye chart. Think of it as a study of the retina and your eye’s overall optics. For cats and dogs, visual acuity can be measured with retinoscopy.
A dog’s visual acuity is approximately 20-40% compared to that of humans. So, a dog would be able to distinguish something at 20 feet, where a human would be able to see it at around 60 to 90 feet.
The range is different when compared with cats. If a cat can see from 20 feet, a human is able to see anywhere from 100 to 200 feet way. This encompasses different structures of the eye, such as the cornea, the aqueous humor, the lens, and the vitreous. It also utilizes combined refractive powers allowing for an image to be clearly focused on the retina.
Dogs aren’t able to focus that clearly on objects that are closer than about ten inches away. Cats have a greater ability with near vision. Dogs and cats are geared more towards motion instead of focus. They often tend to be farsighted, which can explain why they’re always on the prowl and sniffing the ground in search of food or other critters.
How Smell Helps Cats and Dogs See
Aside from using their eyes, both cats and dogs are able to see by using their other senses.
For example, cats are able to hear ultrasonic pitches that are emitted by whatever animal they’re chasing, even if their vision is obscured. Sense of smell is also used to identify other creatures and people. If you’ve been gone for two or three days and you return home, you may smell different to your cats. This could be on if used a different type of soap while you were away, so they may be wary of your scent, even if they recognize you visually.
Dogs have a vomeronasal organ which is part of their septum, which helps enhance their sense of smell and determine specific odors. Not all dogs are the same though, depending on the breed of dog their sense of smell can be greater or lesser than that of a person.
It’s very important to keep your pets healthy, especially their eyes. Over time, dogs and cats can develop issues with their eyes, such as cataracts, corneal damage, eyelid mass, uveitis, glaucoma and conjunctivitis, to name a few. While it may not be noticeable at first, long lasting conditions can greatly affect your pet’s vision. Please contact us if you have any questions about your pets eyesight, or notice anything out of the ordinary that might be affecting your pet’s vision.