New frontier in vision research: Light pulse morphology affects retinal imaging

A new study has found that the eye’s response to light depends not only on the intensity of the light, but also on the way that light is pushed energetically in a very short period of time. This finding opens up new areas of vision research.

Vision is a complex perceptual process that encompasses physics, biochemistry, physiology, neurology and many other disciplines. Simply put, the retina receives light, and the visual nerve transmits electrical impulses to the brain, where they are imaged.

Previously, scientists only know that the visual effect and the amount of energy per unit time into the eye light, or the number of photons related. This new study finds that it also has to do with the way energy is delivered faster or slower on a very microscopic timeline.

Geoffrey Gaulier of the Department of Applied Physics at the University of Geneva (UNIGE) in Switzerland, the study’s first author, said, “The process of visual sensing starts with the retinal cells taking the first step. When the retina is exposed to light, the retinal cells undergo a deformation. This triggers a complex mechanism that generates neural impulses within the visual nerve.”

People feel that the process of imaging the eye is a momentary effort. But when analyzed carefully, each stage takes a certain amount of time.

To understand how long it takes for the first step, physicists measured the answer from retinal cells in a laboratory petri dish. The researchers isolated the retinal cells and placed them in a laboratory cuvette and tested them with a laser and found that the retinal cells responded within 50 femtoseconds.

The difference between one femtosecond and one second is the same as the difference between one second and the age of the universe,” said Jean-Pierre Wolf, a physicist at the University of Geneva (UNIGE) in Switzerland, one of the study’s lead authors. This speed is too fast. We want to understand if such a fast response is the result of cells being isolated and seen in vitro, or do they also respond so fast in living tissue?”

To further answer this question, this new study found biologists to help. They put invisible lenses on mice and observed their electroretinogram (electroretinogram) signals. Wolfe says, “This method, without invasive surgery, was able to measure the strength of the signal transmitted to the optic nerve.”

When light strikes the retina, with the help of an electronic amplifier, the researchers can see the voltage that appears across the cornea. The results showed that the first steps of vision occurred as fast in the mice as they would have if the retinal cells had been isolated from the body.

Then, the researchers changed the shape of the light pulse to see how the retina responded. “We sent the same energy, the same number of photons, but changed the shape of the light pulses. Some are shorter, some are longer, some are in the shape of a slice and so on.” Golyer said.

The shape of the light pulse means that even if the same number of photons are delivered per unit time, there are many differences in the microscopic timeline, such that these energies can be pushed more at a time with longer intervals, or they can be pushed less at a time with shorter intervals, or they can be pushed intensively many times in a short period of time, intensively again after an interval, and so on. The retina responds differently to these different light pulses.

The researchers also tested using various colors of light pushed in different orders and found that the order in which the colors were pushed in time also affected the retina’s response.

Wolfe said that the retina’s response is different, meaning that the current it passes to the brain also appears to be different in strength. That means that even if light of the same energy enters the eye, the way the energy is pushed along the microscopic timeline, and the order in which the light colors appear, may affect the final visual image.

“Understanding this information helps us to improve the imaging of the eye.” Alternatively, researchers could develop new diagnostic and therapeutic approaches to eye diseases in response.

The study was published April 28 in the journal Science Advances.