Research ArticleLIFE SCIENCES

Why do animal eyes have pupils of different shapes?

See allHide authors and affiliations

Science Advances  07 Aug 2015:
Vol. 1, no. 7, e1500391
DOI: 10.1126/sciadv.1500391

You are currently viewing the abstract.

View Full Text


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.

  • pupil
  • eye
  • aperture
  • stereopsis
  • depth of field
  • blur
  • chromatic aberration
  • evolution
  • anatomy

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

View Full Text