Examining the Effects of Chromatic Aberration, Object Distance, and Eye Shape on Image-Formation in the Mirror-Based Eyes of the Bay Scallop Argopecten irradians.


Journal Article

The eyes of scallops form images using a concave spherical mirror and contain two separate retinas, one layered on top of the other. Behavioral and electrophysiological studies indicate that the images formed by these eyes have angular resolutions of about 2°. Based on previous ray-tracing models, it has been thought that the more distal of the two retinas lies near the focal point of the mirror and that the proximal retina, positioned closer to the mirror at the back of the eye, receives light that is out-of-focus. Here, we propose three mechanisms through which both retinas may receive focused light: (1) chromatic aberration produced by the lens may cause the focal points for longer and shorter wavelengths to fall near the distal and proximal retinas, respectively; (2) focused light from near and far objects may fall on the distal and proximal retinas, respectively; and (3) the eyes of scallops may be dynamic structures that change shape to determine which retina receives focused light. To test our hypotheses, we used optical coherence tomography (OCT), a method of near-infrared optical depth-ranging, to acquire virtual cross-sections of live, intact eyes from the bay scallop Argopecten irradians Next, we used a custom-built ray-tracing model to estimate the qualities of the images that fall on an eye's distal and proximal retinas as functions of the wavelengths of light entering the eye (400-700 nm), object distances (0.01-1 m), and the overall shape of the eye. When we assume 550 nm wavelength light and object distances greater than 0.01 m, our model predicts that the angular resolutions of the distal and proximal retinas are 2° and 7°, respectively. Our model also predicts that neither chromatic aberration nor differences in object distance lead to focused light falling on the distal and proximal retinas simultaneously. However, if scallops can manipulate the shapes of their eyes, perhaps through muscle contractions, we speculate that they may be able to influence the qualities of the images that fall on their proximal retinas and-to a lesser extent-those that fall on their distal retinas as well.

Full Text

Duke Authors

Cited Authors

  • Speiser, DI; Gagnon, YL; Chhetri, RK; Oldenburg, AL; Johnsen, S

Published Date

  • November 2016

Published In

Volume / Issue

  • 56 / 5

Start / End Page

  • 796 - 808

PubMed ID

  • 27549200

Pubmed Central ID

  • 27549200

Electronic International Standard Serial Number (EISSN)

  • 1557-7023

International Standard Serial Number (ISSN)

  • 1540-7063

Digital Object Identifier (DOI)

  • 10.1093/icb/icw099


  • eng