76.3 Friday, Jan. 6 Optical coherence tomography (OCT) reveals that scallop eyes may have bifocal optics SPEISER, DI*; GAGNON, YL; CHHETRI, RK; OLDENBURG, AL; JOHNSEN, S; Univ. of California, Santa Barbara; Duke University; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill; Duke University firstname.lastname@example.org
Eyes that use a single focusing mechanism to form multiple images are quite rare in nature. In these eyes, two images formed simultaneously by a multi-focal lens fall separately on stacked retinas. Scallop eyes contain a pair of stacked retinas, but these eyes, unlike any known multi-focal eye, are thought to use a mirror, not a lens, to focus light. It is possible that scallops employ bifocal optics to place a focused image on each of their retinas, but if they do, they must do so through a novel, mirror-based mechanism. Complicating matters is the observation that the scallop proximal retina lies against the mirror, a position too close to receive an image by reflection. To ascertain whether or not scallops gather spatial information with both of their retinas using bifocal optics, we re-evaluated scallop eye morphology using optical coherence tomography (OCT), an imaging method that allows the non-invasive cross-sectioning of live, intact biological samples through the use of interferometry with broadband near-infrared light. By using this cutting-edge imaging technique, which avoids the artifacts introduced by the more invasive classical methods of morphological examination, we have produced the most accurate account of scallop eye morphology to date. Using OCT, we have made several discoveries concerning the eyes of the bay scallop Argopecten irradians: 1) there is a gap between the proximal retina and mirror; 2) the lens has a more elliptical front surface than previously thought; and 3) the pupil is narrower than previously thought. By combining this new morphological information with ray-tracing models, we provide evidence that bifocal optics likely allow both scallop retinas to receive spatial information.