There is a difference between the world seen by dog eyes and the world seen by human eyes. Dogs see a lot of things that are blurry, but dogs have good vision at night.
The human eye has three types of retinal cells that allow us to see all colors of light in the visible spectrum. In contrast, there are two types of retinal cone cells in the dog's retina, which can recognize short wavelengths and medium and long wavelengths of light waves, which means that they can only perceive blue light and red and yellow light. Because of the small number of cone cells, the colors in the dog's eyes are very monotonous, unlike the colorful world in human eyes. According to Ishihara's color blindness test, dogs are found to have the same reaction as red-green blind humans.
Dogs see a lot of things blurry, and their visual sensitivity is 4 to 8 times lower than humans, meaning that if humans can see
Dogs seem to be a little nearsighted, but in fact, if the object is about 35-55 cm away from the dog, the dog often does not see very well. So if looking for a closer still object, the dog usually needs to use other senses to help it "search" it, which is just said that the need to sniff to locate.
Dogs have a wider field of vision. Dogs have a large number of optic rod cells in their eyes, which can see objects at rest within 600 meters and objects in constant motion at 800-900 meters. Optic rod cells are sensitive to low light response, sensitive to the perception of moving objects, so when it is darker, the dog's vision is rather much better than people.
This is why there is a watchdog, right, it can see the danger at night that humans can not see. At the same time, the dog's field of vision is also more open compared to humans. The human field of vision is fan-shaped, the two eyes are parallel to the visual axis, while the dog's field of vision is more extended to the sides, while the visual axis to about 20 ° spread out. Thus, a dog's field of vision can reach 240°-250°, nearly 60°-70° larger than a human's.