Actually, the term is "horizontally elongated". And a 2015 study by researchers at UC Berkeley and Durham University conclude that pupil features are determined by whether an animal is predator or prey. Goats (and horses and deer) are typically prey. Read how their pupils help them avoid being caught.
Ivy has an eye on each side of her head that are light-colored, almost hazel. Her pupil is dark and horizontally elongated, not round like ours. The bottom of her pupil tends to stay parallel with the ground, no matter if her head is raised or lowered.
Here are some reasons why:
- the eyes on the sides of her head give her a much greater field of vision. She is able to see forward, sideways and towards her back.
- a wider pupil rather than taller takes advantage of light, while not being blinded by the sun
- maintaining the pupil orientation lets her graze without sacrificing her ability to spot a predator
- unofficially, I think it helps her (and Mac) find their preferred snack in a field full of vines, ivy, briars and weeds!