The dog has a narrow vision of colors. He can see certain colors, but they are much less rich and varied than those which man distinguishes. A funny phenomenon, moreover, among dog toy manufacturers is that they sell most often brightly colored items, orange or red, while the dog does not distinguish them. For him it's dark gray or black. This is the reason why teachers sometimes think that their dogs have vision problems, or that they are not very awake, when in fact depending on the color of the ground, they may not distinguish these toys or any other object.
Everyone knows Snellen's picture hanging on the wall of all ophthalmologists and opticians. We must read the letters starting with the large print and as soon as we start to have trouble reading, the letters are confused and he for the dog, but an exercise was designed to test his vision. It is for the dog to show that he perceives the details of a drawing, in this case the same black and white vertical lines. Next to this table is another solid gray color. If the dog, using his muzzle, touches the striped pattern, he receives a reward. As the test progresses, the lines become smaller and smaller, and when they become fuzzy, the striped panel becomes identical to its plain gray neighbor. The dog no longer distinguishes between the two and this is the limit of his visual acuity. Even the dog that has recorded the best vision to date has obtained the score of 6/23, ie the reason that the dog no longer sees six meters away is still visible at a distance of twenty-three meters. for a normally seeing man.
It can be concluded that the dog's vision is very poor, beyond the perception of the nuances of the colors. Even if he receives a lot of information like the man, his brain does not focus as well and does not see all the details. He sees the contours of the objects but the details are blurred, even invisible.