Patchy proteins form a perfect lens

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Science  11 Aug 2017:
Vol. 357, Issue 6351, pp. 546-547
DOI: 10.1126/science.aao1456

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Most lenses are imperfect: They fail to focus all rays to the same convergence point. In 1854, James Clerk Maxwell proposed a solution for this optical aberration (1). He argued that if the refractive index would decrease parabolically from the center of a spherical lens to its edge, rays would follow curved paths and focus each point on the spherical surface to the opposite point on the same surface. The eyes of fishes and decapod squid are such parabolic lenses, but it has remained unclear how the required molecular architecture is achieved. On page 564 of this issue, Cai et al. (2) report that in squid eyes, globular proteins of different sizes form a gel of varying density, thereby building up a refractive index gradient. The findings suggest a role of such protein polydispersity not only in squid and fish lenses, but also in those of vertebrates other than fish, and provide a novel route to smart materials.