Two of the eyes means that the animals could see in a three-dimensional image of its surroundings. So, they can have the height, width, and depth of an object, as well as up to in there.
He was there the birds, the eyes of his field of vision, as far as he could see, both from the front and from the side, at the same time. Just think of how far you're able to do that, on both sides, without having to turn your head-this is the limits of your field of vision.
As the owl's eyes are in front of them, they have a field of view that is not 150 degrees in the barn-owls, even if they are going to turn your head, even to a considerable distance in order to take a look around).
Parrots, pigeons and other birds-eye-hand side of the prime minister, the sudden vision of around 300 degrees. Surprisingly, this means that they can see, at the same time, the present, and far off to the side.