Artist’s view of femtosecond laser pulses showing up in an eye. Credit: © Scientify – UNIGE
Scientists at the UNIGE have actually revealed that the reaction of the retina to light depends not just on the strength of the light viewed by the eye, however likewise on its temporal shape and the order in which the colors are arranged.
Vision is a complicated procedure that has actually been effectively analyzed by numerous disciplines – physics, biochemistry, physiology, neurology, etc. The retina catches light, the optic nerve sends electrical impulses to the brain, which eventually produces the understanding of an image. Although this procedure takes a while, current research studies have actually revealed that the very first phase of vision, the understanding of light itself, is very quick. But the analysis of this definitive action was performed on particles in service in the lab.
Scientists from the University of Geneva (UNIGE), in cooperation with EPFL and the University Hospitals of Geneva (HUG), Switzerland, recreated the experiment on mice, in order to observe the processing of light by a living organism in all its intricacy. This non-invasive research study reveals that light energy alone does not specify the reaction of the retina. Its shape –brief or long– likewise has an influence on the signal sent out to the brain to form an image. This discovery, released in the journal Science Advances, opens a brand-new field of research study into vision, diagnostics, and potentially brand-new alleviative possibilities.
The cellular system of vision has actually been effectively studied thanks to the cooperation of a number of disciplines. “In the eye, the first stage of vision is based on a small molecule – the retinal – which, on contact with light, changes shape,” discusses Geoffrey Gaulier, scientist at the Applied Physics Department of the UNIGE Faculty of Science and very first author of the research study. “When the retinal alters its geometric form, it triggers a complex mechanism that will result in a nerve impulse generated in the optic nerve.”
This procedure takes a while in between the minute the eye views the light and the minute the brain translates it. Physicists took a look at the extremely first particle in the chain, retinal, to see the length of time it required to change its shape. They separated this particle in a cuvette and subjected it to laser pulses to evaluate its response speed. To their excellent surprise, the particle responded in about 50 femtoseconds!
“By way of comparison, one femtosecond compared to one second is the equivalent of one second compared to the age of the Universe,” explains Jean-Pierre Wolf, teacher at the UNIGE Physics Section and the last author of the research study. “This is so fast that we wondered whether this speed could be achieved by the molecule only when it was isolated, or whether it possessed the same speed in a living organism in all its complexity.”
Light strength and shape specify the eye’s level of sensitivity
To research study this very first phase of vision in information, the researchers contacted biologists, especially Ivan Rodriguez and Pedro Herrera, teachers at the UNIGE Faculties of Science and Medicine, respectively, who positioned a contact lens and carried out an electroretinogram on mice. “This method, which is totally non-invasive, makes it possible to measure the intensity of the signal sent to the optic nerve,” continues Jean-Pierre Wolf. When the light hits the retina, they had the ability to observe an electrical voltage at the cornea, thanks to an electronic amplifier. And their outcomes revealed that this phase accompanied the very same severe speed as when the particle is separated!
The group continued the research study by differing the shape of the pulses in time. “We always send the same energy, the same number of photons, but we change the shape of the light pulse. Sometimes the pulse is short, sometimes long, sometimes sliced, etc,” discusses Geoffrey Gaulier. Indeed, altering the shape needs to not cause any variation in the reaction of the retina, since previously it was believed that just the variety of photons caught by the eye contributed. “But this is not the case!” states the Geneva-based scientist. This result might be described with the aid of computer system simulations carried out in the group of Ursula Röthlisberger from EPFL.
The researchers observed that the eye did not respond in the very same method depending upon the shape of the light, despite the fact that the light energy equaled. “We also discovered that the eye’s reaction differed according to the order in which the colors were varied, for example as in a temporal rainbow, even though they follow each other extremely quickly,” continues Jean-Pierre Wolf. In short, the retina thinks that there is basically light depending upon the shape of the light, while the energy is comparable, and for that reason sends out a more powerful or weaker present to the brain depending upon its reaction.
This discovery, which was made in the context of a Swiss National Science Foundation (SNSF) Sinergia job, opens a brand-new field of research study into vision. “Now that we know that the shape of light plays a role in perception, we can use this new knowledge to make the eye work differently,” proposes Jean-Pierre Wolf. Areas of examination into brand-new possibilities for detecting or potentially dealing with eye weak points can now be established.
Reference: “Ultrafast pulse shaping modulates perceived visual brightness in living animals” by Geoffrey Gaulier, Quentin Dietschi, Swarnendu Bhattacharyya, Cédric Schmidt, Matteo Montagnese, Adrien Chauvet, Sylvain Hermelin, Florence Chiodini, Luigi Bonacina, Pedro L. Herrera, Ursula Rothlisberger, Ivan Rodriguez and Jean-Pierre Wolf, 28 April 2021, Science.
DOI: 10.1126/sciadv.abe1911
