Limits...
Why do animal eyes have pupils of different shapes?

Banks MS, Sprague WW, Schmoll J, Parnell JA, Love GD - Sci Adv (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Vision Science Graduate Program, University of California, Berkeley, Berkeley, CA 94720, USA. ; School of Optometry, University of California, Berkeley, Berkeley, CA 94720, USA.

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.

No MeSH data available.


Related in: MedlinePlus

Pupil shape and image quality in the model sheep eye.(A) Schematic sheep eyes viewed from above. The upper plot is for a circular pupil and the lower plot for a horizontally elongated pupil with the same area. The black curves represent, from left to right, the anterior and posterior surfaces of the cornea (radius 11.66 and 13 mm, thickness 0.8 mm, refractive index 1.382), the anterior and posterior surfaces of the lens (radius 9.17 and −8.12 mm, thickness 9 mm, refractive index 1.516), and the retina (radius 12 mm). The red and green dashed curves respectively represent the focal surfaces for vertical and horizontal contours. (B) Widths of sections through the PSF for different pupils and retinal positions. The upper and lower plots were computed with circular (2.8 × 2.8 mm) and horizontally elongated (8 × 1 mm) pupils, respectively. The optic axis is in the center of each circular plot. Black concentric dashed circles represent different eccentricities. Colors correspond to the SD of the PSF (a measure of the spread of the PSF cross section) for vertical (left) and horizontal cross sections (right); lighter red corresponds to the smallest SD (that is, the sharpest image) and darker red corresponds to the largest SD (least sharp image). (C) Throughput for circular and horizontal pupils. The contour lines represent regions of constant throughput: red, blue, green, and yellow for 80, 60, 40, and 20%, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4643806&req=5

Figure 4: Pupil shape and image quality in the model sheep eye.(A) Schematic sheep eyes viewed from above. The upper plot is for a circular pupil and the lower plot for a horizontally elongated pupil with the same area. The black curves represent, from left to right, the anterior and posterior surfaces of the cornea (radius 11.66 and 13 mm, thickness 0.8 mm, refractive index 1.382), the anterior and posterior surfaces of the lens (radius 9.17 and −8.12 mm, thickness 9 mm, refractive index 1.516), and the retina (radius 12 mm). The red and green dashed curves respectively represent the focal surfaces for vertical and horizontal contours. (B) Widths of sections through the PSF for different pupils and retinal positions. The upper and lower plots were computed with circular (2.8 × 2.8 mm) and horizontally elongated (8 × 1 mm) pupils, respectively. The optic axis is in the center of each circular plot. Black concentric dashed circles represent different eccentricities. Colors correspond to the SD of the PSF (a measure of the spread of the PSF cross section) for vertical (left) and horizontal cross sections (right); lighter red corresponds to the smallest SD (that is, the sharpest image) and darker red corresponds to the largest SD (least sharp image). (C) Throughput for circular and horizontal pupils. The contour lines represent regions of constant throughput: red, blue, green, and yellow for 80, 60, 40, and 20%, respectively.

Mentions: To gain insight into why horizontal pupils are so common among terrestrial prey (the great majority of whom also have lateral eyes), we examined how pupil shape affects image quality and field of view by using a published model of the sheep eye (38). Figure 4A shows in plan view the focal surfaces for line objects at infinite distance and different horizontal eccentricities: red for vertical lines and green for horizontal lines. The difference between the red and green lines is a manifestation of astigmatism of oblique incidence. Horizontal lines are focused more myopically (that is, the focal surface is closer to the front of the eye) relative to vertical lines, particularly when the pupil is horizontally elongated. As an object moves toward a non-accommodating eye, the surface of best focus moves toward the back of the eye, so horizontal contours at nearer distances and displaced from the optic axis are better focused than vertical contours. To investigate image quality, we took vertical or horizontal cross sections through the point spread functions (PSFs) and calculated the spread of those sections. The upper and lower halves of Fig. 4B show the results for circular and horizontal pupils, respectively, and the left and right halves, the results for horizontal and vertical cross sections, respectively. The reduced vertical extent of horizontally elongated pupils increases depth of field for horizontal contours and thereby reduces blur for such contours. Thus, horizontal pupils minimize the blur of horizontal contours caused by astigmatism of oblique incidence. As the distance to imaged contours decreases (for example, nearer points on the ground), the horizontal strip of high image quality in the lower left panel widens, whereas the corresponding region in the upper left panel does not. By reducing blur for horizontals, the horizontally elongated pupil improves image quality for features in the ground ahead of and behind the animal. This is surely advantageous for visual guidance of locomotion across uneven terrain while also yielding greater dynamic range in the amount of light striking the retina. The results for vertically elongated pupils (not shown) are the same as for horizontally elongated pupils but rotated by 90°. Thus, a vertical pupil would reduce the blur of vertical contours above and below the animal’s head.


Why do animal eyes have pupils of different shapes?

Banks MS, Sprague WW, Schmoll J, Parnell JA, Love GD - Sci Adv (2015)

Pupil shape and image quality in the model sheep eye.(A) Schematic sheep eyes viewed from above. The upper plot is for a circular pupil and the lower plot for a horizontally elongated pupil with the same area. The black curves represent, from left to right, the anterior and posterior surfaces of the cornea (radius 11.66 and 13 mm, thickness 0.8 mm, refractive index 1.382), the anterior and posterior surfaces of the lens (radius 9.17 and −8.12 mm, thickness 9 mm, refractive index 1.516), and the retina (radius 12 mm). The red and green dashed curves respectively represent the focal surfaces for vertical and horizontal contours. (B) Widths of sections through the PSF for different pupils and retinal positions. The upper and lower plots were computed with circular (2.8 × 2.8 mm) and horizontally elongated (8 × 1 mm) pupils, respectively. The optic axis is in the center of each circular plot. Black concentric dashed circles represent different eccentricities. Colors correspond to the SD of the PSF (a measure of the spread of the PSF cross section) for vertical (left) and horizontal cross sections (right); lighter red corresponds to the smallest SD (that is, the sharpest image) and darker red corresponds to the largest SD (least sharp image). (C) Throughput for circular and horizontal pupils. The contour lines represent regions of constant throughput: red, blue, green, and yellow for 80, 60, 40, and 20%, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643806&req=5

Figure 4: Pupil shape and image quality in the model sheep eye.(A) Schematic sheep eyes viewed from above. The upper plot is for a circular pupil and the lower plot for a horizontally elongated pupil with the same area. The black curves represent, from left to right, the anterior and posterior surfaces of the cornea (radius 11.66 and 13 mm, thickness 0.8 mm, refractive index 1.382), the anterior and posterior surfaces of the lens (radius 9.17 and −8.12 mm, thickness 9 mm, refractive index 1.516), and the retina (radius 12 mm). The red and green dashed curves respectively represent the focal surfaces for vertical and horizontal contours. (B) Widths of sections through the PSF for different pupils and retinal positions. The upper and lower plots were computed with circular (2.8 × 2.8 mm) and horizontally elongated (8 × 1 mm) pupils, respectively. The optic axis is in the center of each circular plot. Black concentric dashed circles represent different eccentricities. Colors correspond to the SD of the PSF (a measure of the spread of the PSF cross section) for vertical (left) and horizontal cross sections (right); lighter red corresponds to the smallest SD (that is, the sharpest image) and darker red corresponds to the largest SD (least sharp image). (C) Throughput for circular and horizontal pupils. The contour lines represent regions of constant throughput: red, blue, green, and yellow for 80, 60, 40, and 20%, respectively.
Mentions: To gain insight into why horizontal pupils are so common among terrestrial prey (the great majority of whom also have lateral eyes), we examined how pupil shape affects image quality and field of view by using a published model of the sheep eye (38). Figure 4A shows in plan view the focal surfaces for line objects at infinite distance and different horizontal eccentricities: red for vertical lines and green for horizontal lines. The difference between the red and green lines is a manifestation of astigmatism of oblique incidence. Horizontal lines are focused more myopically (that is, the focal surface is closer to the front of the eye) relative to vertical lines, particularly when the pupil is horizontally elongated. As an object moves toward a non-accommodating eye, the surface of best focus moves toward the back of the eye, so horizontal contours at nearer distances and displaced from the optic axis are better focused than vertical contours. To investigate image quality, we took vertical or horizontal cross sections through the point spread functions (PSFs) and calculated the spread of those sections. The upper and lower halves of Fig. 4B show the results for circular and horizontal pupils, respectively, and the left and right halves, the results for horizontal and vertical cross sections, respectively. The reduced vertical extent of horizontally elongated pupils increases depth of field for horizontal contours and thereby reduces blur for such contours. Thus, horizontal pupils minimize the blur of horizontal contours caused by astigmatism of oblique incidence. As the distance to imaged contours decreases (for example, nearer points on the ground), the horizontal strip of high image quality in the lower left panel widens, whereas the corresponding region in the upper left panel does not. By reducing blur for horizontals, the horizontally elongated pupil improves image quality for features in the ground ahead of and behind the animal. This is surely advantageous for visual guidance of locomotion across uneven terrain while also yielding greater dynamic range in the amount of light striking the retina. The results for vertically elongated pupils (not shown) are the same as for horizontally elongated pupils but rotated by 90°. Thus, a vertical pupil would reduce the blur of vertical contours above and below the animal’s head.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Vision Science Graduate Program, University of California, Berkeley, Berkeley, CA 94720, USA. ; School of Optometry, University of California, Berkeley, Berkeley, CA 94720, USA.

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.

No MeSH data available.


Related in: MedlinePlus