Vision of dogs: what and how our pets see
Many people know that dogs understand everything, just can’t say it. Anyone who has ever seen a dog’s eye will not deny this. But what does the dog really feel, and how does the surrounding world, in particular, people see it?
Let’s start with an important and very interesting question: do dogs distinguish colors. Many believe, based on old data, that dogs see our world in black and white. This is not true. According to recent studies by scientists from the United States, dogs have colored vision, but different from human. Why? There are fewer cones in the dog’s retina than in the human eye, and it is cones that are responsible for color perception. The human retina contains 3 types of cones, each of which responds to a different color range. Some are sensitive to long-wave radiation: red and orange, others to medium-wave: yellow and green, and others to blue, blue, and purple. A feature of the retina of dogs is that they do not have cones sensitive to red color, due to this they cannot catch the difference between yellow-green and orange-red colors. This feature of canine vision is similar to color blindness in humans
What a person perceives as blue-green, the dog can see in white. But dogs are much better than people distinguish all shades of gray. This is not only because the dog’s retina has more rods, i.e. photosensitive cells responsible for the quality of vision at dusk, but also due to the fact that the sticks themselves are more sensitive than human ones. Due to this, dogs see in the dark at 3, maybe even 4 times better than humans. No wonder they say that dogs are transient animals, i.e. they are the average between day and night. Let’s try to conditionally divide the dog’s retina into 2 parts – the upper and lower. The upper part helps to see better against a dark background due to the fact that there is a reflective membrane behind the photoreceptors of the upper part, therefore, the light entering the eye is reflected by the membrane. These same reflected rays are immediately captured by cones and rods, and instead of one ray it turns out, as it were, two. The lower part of the retina contains a dark pigment that absorbs “unnecessary” light rays and thanks to this the dog sees perfectly in bright light. Perhaps someone will ask a question: who sees better, a dog or a person? The answer is simple. There are many differences in the structure of the human and canine eyes. For example, a person has a “yellow spot” in his eye that contains cones and is located in the center of the retina, on the optical axis of the eye. The rays of light, straight, not distorted when passing through the cornea and lens, fall on cones. The sticks are on the rest of the retina. Dogs do not have this spot, so their visual acuity is 3 times lower than human. An interesting fact: if we wanted to check the dog’s eyesight on the checklist in the ophthalmologist’s office, she would be able to distinguish only the third line, and a person with good eyesight would be able to read the tenth.
Do not think that dogs are shortsighted; by the way, they have a weak farsightedness, up to +0.5 diopters – an indicator of most adults. The thing is that, like for all predators for a dog, visual acuity is not needed. Here it is more important to see equally well at any time of the day and determine the object of hunting. It is from here that dogs have the ability to see a moving object better than a motionless one: due to the greater number of sticks in the eye, a dog can see a moving object at a distance of 800-900 m, and a motionless one with only 600 m. The consequence of this is that you cannot run away from dogs – You will be perceived as prey.
Also, the dog can more accurately determine the distance. Perhaps this is due to the fact that the sticks are located near the optical axis of the eye, where people have a “yellow spot”. At close range, the dog sees it vaguely, it needs a distance of at least 30-35 cm, and a person can focus his vision on an object from a distance of several centimeters.
An interesting question about the field of view of the dog, because it is also different from the human. The field of view of the human eye is a circle, and the field of view of the dog is “stretched” to the sides. The axes of the eyes in humans are parallel, and in dogs such that the optical axes diverge by 20 degrees. It is thanks to this that the field of view of the dog is 240-250, and a person has 60-70 degrees less. These figures are not taken into account such important characteristics as the structure of the skull, the location of the eyes and the shape of the nose. Let us give an example, in dogs with wide faces and a short nose, the angle of divergence of the eyes is small, therefore, their lateral vision is limited. Narrow-faced hunting dogs with an extended nose have a large angle of divergence of the eyes, therefore, their field of view is wide. There is an opinion that wild dogs have better vision. There is no exact data on this subject, but all wild animals have better vision. For example, the vision of monkeys is 3 times better than that of humans. And the number of sticks in the retina of a wolf is higher than that of a dog, therefore, their eyesight is sharper, although wolves, like dogs, do not distinguish red.