Dogs have good eyesight but they see things differently to humans. And to cats or parrots! I have a page comparing dog and parrot eyesight which you can read by clicking this link.
For many years the experts thought that the dog saw everything in black and white. They thought they lacked colour vision but it has been known for a long time now that they were wrong. Dogs see colour but in pastel tints. This is because their ratio of rods to cones in the retina of the eye favours the rods much more so than for humans. Rods are photoreceptors which are responsible for vision at low light levels (scotopic vision). They do not mediate colour vision. Cones are active at higher light levels (photopic vision). They are capable of colour vision and are responsible for high spatial acuity.
When the retina has more rods than normal the eye is more geared up to see in lowlight conditions. This means that the anatomy of the dog’s eye has evolved for a daily cycle of activity during dawn and dusk as is the case for cats. It is called a crepuscular rhythm and you will see it in the majority of mammals.
Humans are not typical mammals in this respect because they are diurnal which means active during the day. The small number of cones in the retina of the dog’s eye tells us that they don’t see colour as well as humans but they can see some degree of coloration.
An expert on the eye, Gordon Walls, said that “To any such semi-nocturnal, rod-rich animal [as a dog] the richest of spectral lights could at best appear only as delicate pastel tints of uncertain identity.”
But, as mentioned, they can see colour and its weaker than for humans. In low-light conditions dogs are better than us. Not only do they have more rods but they have a reflective layer behind the retina as is the case cats. This is called the tapetum lucidum. It acts as a magnifier of light intensity enabling dogs to make more use of the little available light they have at dawn and dusk.
Another major difference between dogs and humans is that they are more sensitive to movement which is also apparent with cats. But they don’t see detail so well. This is why you see prey animals freezing when they become alarmed before trying to flee. They understand that the predator is unlikely to see them until they move. Cats, too, are incredibly sensitive to quick movements which is why they tend to slap at a hand that is moving quickly in front of their face.
Studies have found that if a dog’s caregiver remains motionless around 300 yards or metres away from their dog, they won’t detect them. But if they are about a mile away waving their hands around their sheepdog will see them. Dogs’ eyes are tuned up to pursue fleeing prey.
And lastly, also in line with domestic cats, the field of vision for hunting dogs is much wider and for humans. The greyhound, with a narrow head has a visual range of 270° while a more typical dog has a visual range of 250°. Flat-faced dogs have a narrower field of vision but still greater than for humans at around 180°.