Two Eyes in One

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Science  10 Sep 2010:
Vol. 329, Issue 5997, pp. 1259
DOI: 10.1126/science.329.5997.1259-a
CREDIT: STOWASSER ET AL., CURR. BIOL. 20, 1482 (2010).

Nearly 500 million years ago, schizochroal trilobites roamed the oceans, guided by compound eyes with bifocal lenses. In extant animals, the structures of the eye range from those with accommodating lenses (us) to those with multilayered retinas, such as the complex eyes of jumping spiders. Now, to add to these varieties, Stowasser et al. have described a bifocal lens in the larva of the sunburst diving beetle Thermonectus marmoratus. Of its six pairs of eyes, the E2 eyes are tubular and face directly forward. They contain two retinas that are positioned at unequal distances from the lens, with photoreceptors oriented either parallel or perpendicular to the light path. Using a microscope to observe images formed by isolated lenses, the authors measured optical performance and determined that two distinct and well-focused images are produced on the proximal and distal retinas, indicating a true bifocal lens. Moreover, the images are separated vertically, leading to an improved contrast for each of the focused images.

Curr. Biol. 20, 1482 (2010).

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