Revisiting convergence: scallop eyes (Introduction)

by David Turell @, Tuesday, December 05, 2017, 14:35 (9 days ago) @ David Turell

Amazing eyes, built like reflecting telescopes with mirrors made of minerals focusing on a two-layered retina:

https://cosmosmagazine.com/biology/eyes-of-the-scallop

"Researchers have obtained a detailed view of a scallop’s visual system - a sophisticated arrangement of up to 200 eyes they say is strikingly similar to a reflecting telescope. Just as the complex optics of other animals, like lobsters, have informed telescope design, these results may pave the way to the construction of novel bio-inspired optical devices for imaging and sensing applications.

"Most animals use lenses to focus light onto their retina, a light-sensitive layer of tissue coating the inner portion of the eye, though certain marine organisms (including the Pecten scallop) have adopted mirrors to create images.

"Benjamin Palmer and colleagues at the Weizmann Institute of Science in Rehovot, Israel, investigated the complex organization of the scallop’s mirror. Using various microscopic imaging approaches, the scientists found that spatial vision in the scallop is achieved through the mirror's layered structure located at the back of each eye, which is fine-tuned to reflect wavelengths of light that penetrate its habitat.

"What’s more, the mirror is tiled with a mosaic of square-shaped crystals, minimizing surface defects for a clearer picture. The mirror forms images on a double-layered retina, to separately image both peripheral and central fields of view. The researchers note their work demonstrates the remarkable control the scallop exerts over the growth and arrangement of crystals to make a highly reflective mirror capable of forming functional images."

From the original article:

"Fine-tuned for image formation

"We typically think of eyes as having one or more lenses for focusing incoming light onto a surface such as our retina. However, light can also be focused using arrays of mirrors, as is commonly done in telescopes. A biological example of this is the scallop, which can have up to 200 reflecting eyes that focus light onto two retinas. Palmer et al. find that spatial vision in the scallop is achieved through precise control of the size, shape, and packing density of the tiles of guanine that together make up an image-forming mirror at the back of each of the eyes.

Science, this issue p. 1172

"Abstract

"Scallops possess a visual system comprising up to 200 eyes, each containing a concave mirror rather than a lens to focus light. The hierarchical organization of the multilayered mirror is controlled for image formation, from the component guanine crystals at the nanoscale to the complex three-dimensional morphology at the millimeter level. The layered structure of the mirror is tuned to reflect the wavelengths of light penetrating the scallop’s habitat and is tiled with a mosaic of square guanine crystals, which reduces optical aberrations. The mirror forms images on a double-layered retina used for separately imaging the peripheral and central fields of view. The tiled, off-axis mirror of the scallop eye bears a striking resemblance to the segmented mirrors of reflecting telescopes."

http://science.sciencemag.org/content/358/6367/1172

Comment: An other superb example of convergence. Evolution is set up as an extremely inventive process producing advanced complexity.


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