Oz: Laser system lets the eye see the invisible color Olo

A team of researchers in the USA has made the invisible visible: they have developed a new color. A special technique is required to be able to see it. This in turn could be used in medical research in the future.

The team from the University of California at Berkeley (UC Berkeley) has named its creation Olo. It describes it as "a blue-green color of unparalleled saturation".

"It was like a deeply saturated turquoise", enthuses Austin Roorda, an optometrist at UC Berkeley, "the most saturated natural color simply paled in comparison." Unfortunately, no one can see this color.

This is what Oz does: it makes Olo visible. Oz uses weak laser doses to activate specific photoreceptors in the eye. This is the only way to see the color. The developers chose the name regarding the novel "The Wizard of Oz" – "because it was as if we traveled to the Land of Oz to see this brilliant color that we had never seen before", said James Carl Fong, lead author of the study, which was published in the journal Science Advances.

The human eye has different photoreceptors

The human visual system consists of two different photoreceptors: rods for light-dark vision and cones for color perception. There are three types of the latter: S cones (for short) detect shorter wavelengths, i.e. blue light. M cones are responsible for medium wavelengths, i.e. the green range. Finally, the L cones detect longer wavelengths, i.e. red.

However, the ranges of the M and L cones overlap, so that 85 percent of the light activates both. "There is no wavelength in the world that can only stimulate the M cone," said senior author Ren Ng. "I wondered what it would look like if you could only stimulate all the M cones. Would it be the greenest green you've ever seen?"

The Oz system is designed to make this possible by activating only the M cones. To achieve this, the retina of an observer must first be scanned to record the individual distribution of the S, M and L cones. To achieve this, the team uses a camera system developed at the University of Washington in Seattle to image the human retina.

Oz activates M cones

With the map of the retina, Oz can then specifically activate the M cones and thus represent Olo – the name can be read as a binary code for the cones: Only M cones are active (1), S and L cones are not (0). So far, however, only five people have benefited from this.

"We have developed a system that can track, target and stimulate photoreceptor cells with such high precision that we can now answer fundamental [...] questions about the nature of human color vision", said Fong. "It gives us a way to study the human retina at a new scale that was previously impossible in the field."

It is hoped that Oz can be used to study eye diseases and vision loss: Many vision disorders caused by diseases, for example, are related to the loss of cones. Oz can be used to simulate the loss of cones in healthy people.

The team is also investigating whether it is possible to use Oz to enable people with color blindness to see all the colors of the rainbow or to enable normal people to see the rarely occurring tetrachromatic vision. People with tetrachromacy have four different cones and can therefore perceive significantly more colors. Ultimately, Oz could help us understand how the brain perceives the complex world around us.

(wpl)