One group says cats and snakes have oval pupils to reduce the light that gets in during the day. Another group says that there's no definite reason. Consequently, they have sensitive retinas. According to Pedersen, the oval pupil shape protects the retina during the daytime. A cat can close a slit more completely than a round pupil and that is why the shape is oval.
Tigers have round pupils and domestic cats, oval ones.
Back in 1916, R.I. Pocock of the London Zoo took a look at cats. He found that tigers, lions, jaguars, and leopards have round pupils. Whereas, domestic cats and most little cats have oval ones. It turns out that all cats with a well-developed hyoid can purr but do not roar and they have oval pupils. The big cats have a hyoid in which one 'bone' fails to develop into a bone.