Poems and Thoughts    by Frank Maurer

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The Mystery of Why Domestic Cats Have Vertical Pupils. Have you ever wondered why domestic cats have vertical pupils, And in big cats like lions, tigers, jaguars, and pumas, the pupils are round? The summary is this in the evolutionary story of various life cycles-- ----Round pupils (humans, birds) give even focus across the entire depth of field during the day. ----Vertical pupils (cat, gecko) optimize depth perception, day and night. ----Horizontal pupils (goat, frog) optimize and give a panoramic field of view to detect predators. These various pupil shapes are adaptations to their lifestyle. Specifically, domestic cats are ambush predators And have a superior depth of field. This allows them to better judge distance to their prey. This pupil shape also helps cats to see side-to-side motions, Making their small rodent prey easier to spot with their movements. Unlike small domestic cats which are crepuscular actors, Big cats which hunt diurnally and with round pupils, Are capable of a clear focus across the entire long distance field of view. Having vertical pupils, also gives its bearer camouflage, As it breaks up the round shape of the eye, And thus makes it harder for its prey to see the hidden predator. There too, are geckos with vertical slits, having tiny round openings, Cuttlefish with distinctive 'W'-shaped pupils, And rays possessing crescent-shaped pupils. Such aquatic species are benefitted by both round and horizontal pupils. The other factors determining how an animal sees, Are the number and distribution of rods and cones, Working in concert with pupil shape; The shape of the lens is also important, for instance, In correcting chromatic aberration, resulting in excellent color vision. So, wonder less about the different pupil shapes, because you now know! Frank Maurer 5 January 2026 2200 Hours.