July 2013
Volume 13, Issue 9
Free
Vision Sciences Society Annual Meeting Abstract  |   July 2013
Pupil shape is adaptive for many species.
Author Affiliations
  • William Sprague
    School of Optometry, Vision Science Program, University of California, Berkeley
  • Zachary Helft
    School of Optometry, Vision Science Program, University of California, Berkeley
  • Jared Parnell
    Department of Physics, Durham University
  • Jurgen Schmoll
    Department of Physics, Durham University
  • Gordon Love
    Department of Physics, Durham University
  • Martin Banks
    School of Optometry, Vision Science Program, University of California, Berkeley
Journal of Vision July 2013, Vol.13, 607. doi:10.1167/13.9.607
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      William Sprague, Zachary Helft, Jared Parnell, Jurgen Schmoll, Gordon Love, Martin Banks; Pupil shape is adaptive for many species.. Journal of Vision 2013;13(9):607. doi: 10.1167/13.9.607.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Pupil shape varies considerably across species, though most are circular or elliptical.

Elliptical pupils are always elongated vertically or horizontally relative to the

head. We examined the usefulness of elongated pupils: specifically, why horizontal

elongation is useful to some species and vertical elongation to others. Walls (1942)

proposed that such pupils are adaptive for nocturnality, providing more control

over retinal illumination. Malmström and Kröger (2006) proposed that they

preserve image quality in eyes with multifocal lenses. However, these proposals do

not explain why pupil orientation varies across species. We propose a new theory

based on the visual requirements of different species in their environments. We

examined pupil shape in over 200 animals and related it to activity time, foraging

mode, and height. Clear correlations emerged. Round pupils occur in tall or diurnal

predators. Vertical elongation occurs in short, nocturnal predators; these animals

usually have forward-facing eyes and stereovision. Horizontally elongated pupils

occur in prey animals; they tend to have lateral eyes. We argue that vertical pupils

are well suited for using stereopsis to estimate distances of vertical contours and

using depth-of-field blur for distances of horizontal contours. In an analysis of image

formation, we found that the potential usefulness of blur is inversely related to

height. This may explain why vertical-slit pupils are more common in short than

tall predators. For horizontally elongated pupils, our optical analyses show that the

elongation expands field of view horizontally allowing these terrestrial prey animals

to see objects near the ground plane both in front of and behind them. Our analyses

also show that horizontal elongation allows sharper imaging of horizontal contours

on the ground in different directions, particularly directions well off the optic axis.

We conclude that elongated pupils evolved to optimize visual information near the

ground plane in predators and prey.

Meeting abstract presented at VSS 2013

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