There are a lot of different pupil shapes among vertebrates (and some invertebrates, too).
The eye itself is kind of a weird misshapen organ, particularly in land animals where it has had to compensate for, you know, the fact that it originally evolved in the water. Light passes differently through water than it does in air, not to mention that now we have to worry about our lenses- which have to be moist to properly function- drying out.
But the focus (ha ha) today is on the pupil, the transparent bit inside the iris that allows light to enter the eye. Without it, our eyes would be functionless. With it, there are a whole bunch of different ways that animals can shape their vision- and their pupil- to their advantage.
Of course, no two scientists seem to agree on exactly what these advantages are.