A lens resembling an octopus eye has been created by US researchers, nature.com reported.
The sphere consists of hundreds of thousands of layers of plastic and could revolutionize cameras, telescopes and spectacles.
Traditional glass lenses use a curved surface to focus incoming light towards a central point. The stronger the lens, the more curved its surface must be and therefore the thicker and heavier it is. In nature, eyes avoid this problem by using materials whose density varies in a certain way.
Light is bent, or refracted, when it travels between two substances that have different densities (or refractive indices), such as air and water. The greater the difference between the two materials, the more the light is refracted. So a flat object that has a greater refractive index towards its edges can focus light like a curved lens.
Many biological lenses consist of up to hundreds of thousands of nanolayers, each of which has a slightly different refractive index. The layers form a smooth density gradient that helps to focus light.
In human eyes, this lens is made up of about 22,000 layers. But animals that live in water, which has a high refractive index compared with air, need stronger lenses. The octopus eye, for example, can focus light five times more strongly than a human eye.

When too much sand has accumulated, an avalanche occurs and the dunes start to "sing".

From Marco Polo onwards explorers have told stories about strange sounds they have heard in the desert.
It is known that the sounds are produced by sand dunes when they avalanche, but the exact mechanism behind the phenomenon has remained a mystery.
Now, Bruno Andreotti from the University of Paris-7 has proposed that the sounds come from vibrations in the sand bed that have been excited by collisions between grains of sand.
"Singing dunes are one of the most puzzling and impressive natural phenomena I have ever encountered," says Andreotti. "The sounds produced can be heard up to 10 kilometers away and resemble a drum or a low-flying jet." The sounds can be as loud as 105 decibels and have frequencies between about 95 and 105 Hertz.
The French physicist took his equipment from Paris to the Atlantic Sahara in Morocco, which contains more than 10,000 crescent shaped dunes known as barchans.
The wind in the desert can erode the back of these dunes, causing sand to build up at the top of the dune. When too much sand has accumulated, an avalanche occurs and the dunes start to "sing".
Andreotti simultaneously measured vibrations in the sand bed and acoustic emissions in the air, and then extracted information about the frequency, amplitude and the phase of these signals.
He found that the vibrations in the sand behaved like slow-moving elastic sound waves that were localized at the surface of the dune and had amplitude that was about a quarter of the diameter of an individual grain of sand.
"The sounds result from avalanches in which the grains drum on one another, exciting elastic waves on the dune surface, with the vibration of the sand bed tending to synchronize the collisions," he told PhysicsWeb. "In many ways the surface of the sand bed acts like the membrane in a loudspeaker."
Andreotti now plans to study the effect in more detail in the laboratory and with computer simulations. The results could also be relevant to the behaviour of granular materials in general.

New study from Ohio State University provides the first laboratory evidence that certain antioxidants found in dark leafy green vegetables can indeed help prevent cataracts, said Science Daily online.
Vitamin manufacturers often add the antioxidants lutein and zeaxanthin to their products, but until now there has been no biochemical evidence to support the claim that these substances help protect the eyes, said Joshua Bomser, a study co-author and an assistant professor of nutrition at Ohio State University. Some studies have suggested that these antioxidants boost eye health.
Results from laboratory experiments on human lens cells showed that lutein and zeaxanthin, antioxidants found in plants such as kale, spinach and collard greens, helped to protect the cells from exposure to ultraviolet light a leading cause of cataract formation.
The researchers compared the effects of these antioxidants to vitamin E, an antioxidant also thought to reduce the onset of eye diseases.
Adding lutein and zeaxanthin to the cell cultures provided double the protection from UVB damage these antioxidants reduced signs of damage by 50 to 60 percent, compared to vitamin E, which reduced the same signs of damage by 25 to 32 percent.
Lutein and zeaxanthin were nearly 10 times more powerful than vitamin E in protecting the cells from UV-induced damage.
The researchers treated human eye lens cells with varying concentrations of lutein, zeaxanthin or vitamin E. They then exposed these cells, along with a batch of untreated cells, to doses of ultraviolet-beta radiation for 10 seconds. UVB radiation is thought to be the primary environmental culprit in causing skin cancer as well as initiating cataract disease.
Adding lutein and zeaxanthin to the cell cultures provided double the protection from UVB damage these antioxidants reduced signs of damage by 50 to 60 percent, compared to vitamin E, which reduced the same signs of damage by 25 to 32 percent.
The researchers also found that it took far less lutein and zeaxanthin as vitamin E about 10 times less to get this protective effect.
What researchers don't know, however, is how these two antioxidants get into the eye. It's what Bomser hopes to learn next.