Our pet's eyes

Our cats and dogs have certain anatomic differences in their eyes. This makes them see the world in a different way as we do.

The location of the orbit in the head tells the position of the eyes and also the amplitude of the field of vision. Non-predators species such as horses, sheep, pigs or cows have their eyes in the side of their head; this gives them a very good panoramic vision. The carnivorous, such as cats and dogs have the ocular globes in the frontal part of the head, so if they lose panoramic vision, they have a very developed binocular vision, formed up by the superposition of the field of vision of both eyes, and have a visual field angle of between 200 and 270 degrees. Depending on the race, this is inferior to herbivorous’ but noticeably superior to humans’, that only reaches 100-120 degrees.

Photoreceptors are the cells of the retina that make the process of the reception of visual stimulus, there are two kinds: the cones that perceive colours and details, and the sticks that detect movement and are sensitive to lower intensities of light. Dogs and casts have many more sticks than humans do, but many less cones, so their vision in the darkness is quite good and they are better at detecting moving images than fixed ones. This fact justifies that our dogs see perfectly the ball we throw several metres distance away (it is far and in movement), and however, they can’t find it when it is completely static few centimetres from them. In the same way, every dog is able to identify visually their owners by the way in which they move, but they can’t see their features with sharpness.

Dogs don’t see in black and white but in colour. These animals have bi-chromatic vision and they are able to distinguish blue and yellow colours and the different tones of grey. This means that they can’t differentiate yellow and orange, green and red, green and grey. So guide-dogs do not differentiate the colours in a traffic-light, but the brightness and the position of the light. This, besides the traffic noise and flood, allows them to know the right moment to cross the road.

Finally, cats can only differentiate blue and green colours and probable, the red one, and they are specially adapted for the night vision, it is estimated that is five times superior to ours, on the other hand, when they are hunting or running after a toy, they are able to concentrate themselves on their prey and take the rest of the objects inside their visual area out. They see their object with sharpness and the rest ones with a kind of blurred mass around.