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 tobe ambushpredators 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.