The horizontal pupil also enhances the image quality of horizontal planes and this enhanced view at ground level is also an advantage when running at speed to escape. This allows them panoramic vision along the ground to help detect potential predators as early as possible. Having a horizontal pupil enhances the amount of light they can receive in front of and behind them while reducing the amount of light from above and below. Having eyes towards the side of their head helps them to see nearly all around them. They need to check all around for prey and they need to flee rapidly in case of attack. Grazing animals have different problems to deal with. This modelling showed that the vertically elongated pupils in ambush predators enhances their ability to judge distance accurately without having to move their head, which could give away their presence to potential prey. We produced a computer model of eyes which simulates how images appear with different pupil shapes, in order to explain how orientation could benefit different animals. They are also very likely to be prey animals such as sheep and goats. In contrast, horizontally elongated pupils are nearly always found in grazing animals, which have eyes on the sides of their head. The difference between foxes and wolves is down to the fact wolves are not ambush predators вЂ“ instead they hunt in packs, chasing down their prey. Foxes and domestic cats are clear examples of this. They also tend to have eyes on the front of their heads. We found animals with vertically elongated pupils are very likely to be ambush predators which hide until they strike their prey from relatively close distance. This has been described before, but we went one step further to quantify the relationship. One of the most interesting factors we found is that the orientation of the pupil can be linked to an animalвЂ™s ecological niche. Our work has focused on the visual benefits of vertical and horizontal pupils in mammals and snakes. This is particularly useful for animals that are active both day and night, allowing for much better vision in low light conditions. For instance, a domestic cat can change its pupil area by a factor of 135 from fully dilated to fully constricted, whereas humans, with a round pupil, can only change area by a factor of 15.

The established theory for this is that elongated pupils allow greater control of the amount of light entering the eye. Goats, sheep, horses, domestic cats, and numerous other animals have pupils which vary from fully circular in faint light to narrow slits or rectangles in bright light. In a new study published in the journal Science Advances, colleagues from Durham, Berkeley and I explain why these pupil shapes have developed. ItвЂ™s a question that has long interested scientists working on vision and optics. But it isnвЂ™t just canines вЂ“across the animal kingdom, pupils come in all shapes and sizes. But look at their eyes вЂ“ where wolves have rounded pupils like humans, foxes instead have a thin vertical line. Wolves and foxes are closely related and share many of the same characteristics.

Sheep eyeballs