Unlike some animals, we humans cannot see in the dark, we lack the necessary infrared perspective. However, material scientists have now developed novel night vision contact lenses that convert infrared light in visible light. People and mice who wear these contact lenses can see both in the light and in the dark – even with their eyes closed. In contrast to night vision glasses, the contact lenses do not need any power source and are convenient to wear, the team reports. A second version of the contact lenses makes the infrared light even multicolored visible light. In the future, this could help both color blinds to see and enable useful visual aids for security technology.
The retina of our eyes can only recognize radiation in the wavelength range between 400 and 700 nanometers. This light spectrum ranges from blue to red. The short-wave UV light and the long-wave infrared light are usually invisible to us. Night vision devices that convert infrared light into visible light can, however, enlarge our point of view and enable us to see something in the dark. So far, there are only such devices as binoculars or glasses that are relatively chunky and impractical or require an external power source.
Infrared is visible from infrared
Researchers around Yuqian Ma from the Chinese University of Science and Technology in Hefei have now developed night vision contact lenses that offer more comfort and are versatile. To do this, they used the flexible polymer material phema, which is also used for the production of soft standard contact lenses, and combined it with special nanoparticles consisting of gold, sodium gadolinium fluoride as well as ytterbium and inheritance ion (Au/Naglf4: YB3+He3+). These only 45 nanometers small particles absorb near infrared light in the range between 800 and 1600 nanometers and convert it into light with wavelengths visible to us. In earlier studies, the team had already injected these particles into the retina of mice and thus enabled them to get infrared.
Now MA and his colleagues have installed the particles into contact lenses and tested their function in a number of experiments in different lighting conditions on humans and mice. The tests showed that the night vision contact lenses have similar mechanical and chemical properties and offer comfort similar to normal contact lenses. The behavior of the mice equipped with such infrared contact lenses suggests that they can actually see infrared wave lengths. For example, they preferred a box with infrared lighting compared to a dark box. In addition, the pupils of the contact lens carriers were narrowed in the infrared light and in their brain the visual processing center in the cortex was actively active, as corresponding tests showed.
See in the dark
People equipped with the new contact lenses could also see in the dark. For example, they recognized the Morse pattern flashing infrared signals, letters and geometric patterns and from which direction these signals came. “It is completely clear: the subject cannot see anything without the contact lenses, but if it puts on it, it can clearly recognize the flickering of the infrared light,” reports senior author Tian Xue from the Chinese University of Science and Technology. The normal vision in the light was not affected by the transparent contact lenses. Accordingly, mice and people with the visual aids can see both in the light and in the dark.
The night vision works even better with eyes closed, as the tests showed. “The light permeability of the mouse eyes was 0.388 percent for 535-nanometer light and 23.292 percent for 980 nanometer infrared light,” writes the team. The same showed itself in humans: “The sensitivity to near infrared light increased by 3.7 times when the test subjects closed their eyes, while sensitivity to visible light decreased by 4.5 times.” When the eyes are closed, the infrared signal is stronger because the disturbing noise signal of normal light decreases, the team explains. “If the contact lens carrier closes the eyes, it can receive the flickering information even better, since near infrared light penetrates the eyelid more effectively than visible light, so that there is fewer interference due to visible light,” summarizes XUE.
Practical use for color blind and safety technology
The material scientists then optimized their contact lenses. To do this, they added the nanoparticles to Thulium and neodymium ions (TM3+ and nd3+). Together with the ions already contained, these can convert different infrared wave lengths into different visible wavelengths and thus different colors. For example, the contact lenses transferred infrared wavelengths of 980 nanometers into blue light, wavelengths of 808 nanometers in green light and wavelengths of 1532 nanometers in red light. This makes more details visible in the “translated” infrared images. As the researchers explain, a similar color coding technology could also be suitable as visual aid for color-blind people, for example in red-green weakness: “By converting red visible light into something like green visible light, this technology could make the invisible for color blind people visible,” says XUE.
In the future, the visual aids could also be useful. “There are many possible uses for this material. For example, flickering infrared light could be used to transfer information in the areas of security, rescue, encryption or counterfeiting,” explains XUE. To do this, the sensitivity and dissolution of the contact lenses must first be further improved. So far, they only detect infrared radiation that is projected by an LED light source. In the future, however, they should also recognize less intensive infrared light. In addition, the contact lenses have so far not been able to record fine details, since the light is converted close to the retina and is scattered. Optimized nanoparticles could prevent this spread in the future. “We hope to establish a contact lens with more precise spatial resolution and greater sensitivity in the future through working with material scientists and optic experts,” says XUE.
Source: Yuqian Ma (Chinese University of Science and Technology) et al.; Cell, DOI: 10.1016/J.CELL.2025.04.019
