In Frank Baum’s original novel, The Wonderful Wizard of Oz, it is said that the Esmeralda city is a bright green tone that visitors must wear glasses with green color to protect their eyes from the “brightness and glory” of the city.
The glasses are one of the many magicians; The city seen through glasses with green color, of course, it would only look greener.
But using a new technique called “Oz”, scientists from the University of California, Berkeley, have found a way to manipulate the human eye to see a new color: a green color blue of incomparable saturation that the research team has called “OLO”.
“It was like a deeply saturated bluish green … the most saturated natural color was pale in comparison,” said Austin Roorda, a professor of optometry and vision sciences at the Herbert Wertheim School of Optometry & Vision Science of UC Berkeley, and one of the creators of Oz.
OZ works using small doses of laser light to individually control up to 1,000 photoreceptors in the eye at the same time. Using OZ, the equipment can show people not only a more impressive green than anything in nature, but also other colors, lines, moving points and babies and fish.
The platform could also be used to answer basic questions about human view and loss of vision.
“We chose Oz to be the name because it was as if we were on a trip to the land of Oz to see this bright color that we had never seen before,” said James Carl Fong, a doctoral student in Electrical Engineering and Computer Science (EEC) in UC Berkeley.
“We have created a system that can trace, point and stimulate photoreceptor cells with such high precision that we can now answer very basic, but also very stimulating, questions about the nature of the vision of human color,” said Fong. “It gives us a way to study the human retina to a new scale that has never been possible in practice.”
The OZ technique is described in a new study published last week in the magazine Scientific advances. The work was partly funded by federal subsidies of the National Health Institutes and the Office of Scientific Research of the Air Force.
Without exploiting photoreceptors
Humans can see in color thanks to three different types of “cone” cells of photoreceptors embedded in the retina. Each type of cone is sensitive to the different wavelengths of the light: the cones s detect shorter and more blue wavelengths; M conos detect wavelengths of greenish medium; and the cones l detect longer and redst wavelengths.
However, due to an evolutionary peculiarity, the light wavelengths that activate the cones m and L are almost completely overlap. This means that 85% of the light that activates the cones M also activates the cones L.
“There is no wavelength in the world that can stimulate only the cone,” said the senior author of the Ren NG study, a professor of EEC at UC Berkeley, “I began to ask myself how it would see if I could stimulate all cone cells.
To find out, NG was associated with Roorda, who had created a technology that used small laser light microdosis to attack and activate individual photoreceptors. Roorda calls the technology “a microscope to look at the retina”, and ophthalmologists already use it to study eye disease.
But for a human to perceive a completely new color, NG and Roorda would need to find a way to activate not only a cone cell, but thousands of them.
A movie screen of the size of a nail
Fong began working on the OZ project in 2018 as a undergraduate engineering student, and has created much of the software complex necessary to translate images and colors in thousands of small laser pulses aimed at the human retina.
“I joined after meeting this other student who was working with Ren, who told me they were shooting lasers in people’s eyes to make impossible colors,” Fong said.
For Oz to work, he first needs a map of the unique disposition of cone, m and l cells in the retina of an individual. To obtain these maps, the researchers collaborated with Ramkumar knows and Vimal Prahbhu Pandiyan at the University of Washington, who have developed an optical system that can imagine the human retina and identify each cone cell.
With the cone map of an individual in the hand, the OZ system can be programmed to quickly scan a laser beam on a small retina patch, without small energy pulses when the beam reaches a cone that wants to activate and otherwise stay.
The laser beam is just a color, the same tone as a green laser pointer, but when activating a combination of cone, m and l cells, it can cheat in view to see images in complete technicolor. Or, by mainly activating cone cells m, Oz can show people the color.
“If you look at your index nail along the arm, it is approximately the screen size,” said Roorda. “But if we could, we would have filled all the visual space like an imax.”
The ‘wow’ experience
Hannah Doyle, a doctoral student at EECS and co-leader of the author of the article, designed and conducted human experiments with OZ. Five human subjects had the opportunity to see the color, including Roorda and NG, which were aware of the purpose of the study, but not the details of what they would see.
In an experiment, Doyle asked the participants to compare OLO with other colors. They described it as bluish green or peacock green, and reported that it was much more saturated than the closest monochromatic color.
“The most saturated colors you can experience in nature are monochromatic. The light of a green laser pointer is an example,” said Roorda. “When I set Olo against another monochromatic light, I really had that experience ‘wow’.”
Doyle also tried to “nerve” the oz laser, directing it very slightly out of the goal so that the pulses of light hit random cones instead of only mons. The participants immediately stopped seeing Olo and began to see the regular laser green.
“It was not subject to this document, but I have seen Olo since then, and it is very striking. You know you are looking at something very green,” Doyle said. “When the laser becomes nervous, the normal color of the laser seems yellow because the difference is very marked.”
Try the nature of color vision
OZ is not only useful for projecting small films in the eye. The research team is already finding ways to use the technique to study eye disease and loss of vision.
“Many diseases that cause visual disabilities involve lost cone cells,” Doyle said. “An application that I am exploring now is to use this cone by activation of the cone to simulate the loss of cone in healthy subjects.”
They are also exploring whether OZ could help people with color blindness to see all the colors of the rainbow, or if the technique could be used to allow humans to see in tetrachromatic color, as if they had four sets of cone cells.
It can also help answer more fundamental questions about how the brain makes sense of the complex world that surrounds us.
“We discover that we can recreate a normal visual experience simply manipulating cells, not launching an image, but simply stimulating photoreceptors. And we discover that we can also expand that visual experience, what we did with Olo,” said Roorda. “It is still a mystery if, if you expand the signals or generate new sensory contributions, can the brain make sense and appreciate them? And, you know, I like to believe that you can.
The additional authors of the study include congli Wang, Alexandra E. Boehm, Sophie R. Herbeck, Brian P. Schmidt, Pavan Tiruveedhula, John E. Vanston and William S. Tuten of UC Berkeley. This work was supported by a Hellman Scholarship, FHL Vive Center Seed Grant, Office of Scientific Research Subsidies of the Air Force (FA9550-20-1-0195, FA9550-21-1-0230), National Institutes for Health Subsid Burroughs donkey donkey.