Does your dog really see the world in shades of gray or does he or she have access to color perception? How do dogs see? Can they really see emotions on their owner’s face? And from what distance will a dog understand that he or she is being given a non-verbal signal? Let’s look at the features of canine vision to better understand your pet’s behavior and reactions.
The structure of the dog’s eye is determined by tasks of the type
Before we start comparing the anatomy of the eyeball of a dog and a human, let’s remember that canines are primarily hunters, focused on pursuing prey and protecting their territory. Therefore, for them, it is not the clarity of details that is important, but the fixation of movement in the visual field, regardless of the time of day.
The principle of operation of the visual analyzer
The general mechanism of operation is identical in humans and dogs. The light wave penetrates the cornea and the pupil opening, is refracted by the lens body and is focused on the retina.
The dog has a third eyelid. A thin skin membrane is located in the inner corner of the eye and moves horizontally across the cornea, helping to remove dust, small debris, and additionally moisturize the eye with tears.
In ophthalmological terms, dogs have normal emmetropic vision. This means slight myopia, if we draw an analogy with humans:
- it is difficult for them to see an object if the distance is closer than 25 cm;
- approximately -0.05 diopter;
- A dog will see a moving object from a distance of 900 meters, and a static object only from 600 meters.
That is why pets determine the location of food pieces scattered right in front of their muzzles by smell. Moreover, the degree of “myopia” depends on the breed. The acuity of canine vision is estimated at 20/70. For dogs engaged in service or participating in competitions, corrective contact lenses have been invented that allow pets to more clearly distinguish the actions and commands of a human partner.
Color Wave Recognition
Canines have dichromatic vision, but their perception of the world is not in shades of gray. Unlike the human eye, a dog’s retina is dominated by photoreceptors called “rods”, which are responsible for twilight and night vision. But there are significantly fewer “cone” receptors, which are used to recognize colors in daylight. The “cones” in a dog’s retina are sensitive to blue and green, but they do not distinguish red. At the same time, animals can focus on the brightness of the shade, this property is used by trainers when it is necessary, for example, to teach a dog to distinguish traffic lights.
How does a dog see at night, in the dark?
Since the number of rod photoreceptors in canines is almost 3 times greater than in humans, the dog’s retina perceives light much more effectively. In addition, dogs have a reflective layer, the tapetum, located behind the retina and increasing the efficiency of collecting light waves in dog eyes by 40%. This allows the dog to see moving objects better in the dark.
Depth perception
Canines are predators, evolutionarily they are characterized by the location of the eyes on the frontal part of the muzzle. The visual fields of the eyes overlap, obtaining the effect of binocular vision. Thanks to this, predators are able to perceive the “depth of the picture”. In dogs, the binocular view is – 30 o – 60 o, in different breeds, depending on the structure of the muzzle, binocular vision will differ:
- with a short muzzle – the angle of binocular vision is larger;
- In greyhounds and other long-nosed dogs whose eyes are set further apart, the angle is smaller.
The human eye perceives depth of an image much better, our binocular vision is about 140o. This explains why dogs will only see movements from a long distance, but will not recognize a person until they hear and smell them – especially if the owner is wearing new clothes.
Peripheral vision
Evolution has given the retina of the dog’s eye an important feature for a hunter – the so-called “visual stripe”. These are visual cells with a high density of distribution in the area. Thanks to this, the dog is able to clearly see objects at a distance even with the corner of the eye. In long-muzzled breeds, the visual stripe is more pronounced. For canines, the angle of peripheral vision is 240 o, the visual field is oval. For comparison: the human eye covers only 180 o, and the shape of the visual field is a circle.
Thanks to the evolutionary peculiarities of the development of the visual apparatus, dogs are able to distinguish even with their peripheral vision the owner’s signals given by hand at a distance of up to 1.5 km. They mostly ignore stationary objects, but if they notice movement even “out of the corner of their eye” – they actively begin to pursue.
Facial expression recognition
Unlike hounds and long-muzzled fellow sighthounds, brachycephalic dogs may lack the “visual stripe” cell complex on the retina. However, in the central part of the retina, their eyes have a concentrated cluster of visual cells with a density that exceeds the “visual stripe” of their fellows by 3 times! This makes the visual perception of short-muzzled dogs closer to that of humans. Due to this feature, pugs, Pekingese, and other brachycephalic dogs are more interested in the facial expressions of their owner and are able to sense their mood from their facial expression.
Watching TV
It is believed that dogs with short muzzles are more inclined to watch TV. The ability of dogs’ eyes to perceive images is 80 frames per second. Human programs use a frame rate of 60 Hz or 24 frames per second. In the dog’s perception, the image on the screen is just blurry spots. Modern television equipment is capable of giving an image with a frequency of 100 Hz, which will allow the dog to see the image. For such TVs, they even began to develop special video programs for the entertainment of pets.