title: Why do animal eyes have pupils of different shapes?
abstract: There is a striking correlation between terrestrial species' pupil shape and ecological niche (that is, foraging mode and time of day they are active). Species with vertically elongated pupils are very likely to be ambush predators and active day and night. Species with horizontally elongated pupils are very likely to be prey and to have laterally placed eyes. Vertically elongated pupils create astigmatic depth of field such that images of vertical contours nearer or farther than the distance to which the eye is focused are sharp, whereas images of horizontal contours at different distances are blurred. This is advantageous for ambush predators to use stereopsis to estimate distances of vertical contours and defocus blur to estimate distances of horizontal contours. Horizontally elongated pupils create sharp images of horizontal contours ahead and behind, creating a horizontally panoramic view that facilitates detection of predators from various directions and forward locomotion across uneven terrain.
authors.affiliation: Vision Science Graduate Program, University of California, Berkeley, Berkeley, CA 94720, USA. ; School of Optometry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Martin S
authors.initials: MS
authors.lastname: Banks
authors.affiliation: Vision Science Graduate Program, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: William W
authors.initials: WW
authors.lastname: Sprague
authors.affiliation: Department of Physics and Biophysical Sciences Institute, Durham University, Durham DH1 3LE, UK.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schmoll
authors.affiliation: Department of Physics and Biophysical Sciences Institute, Durham University, Durham DH1 3LE, UK.
authors.forename: Jared A Q
authors.initials: JA
authors.lastname: Parnell
authors.affiliation: Department of Physics and Biophysical Sciences Institute, Durham University, Durham DH1 3LE, UK.
authors.forename: Gordon D
authors.initials: GD
authors.lastname: Love
keywords: anatomy; aperture; blur; chromatic aberration; depth of field; evolution; eye; pupil; stereopsis