These contact lenses give people infrared vision - even with their eyes closed

Science fiction technology uses nanoparticles to convert infrared light into visible light that people can see.

People have a new way to see infrared light without the need for clumsy night vision glasses. Researchers have made the first contact lenses to transmit infrared vision - and the devices work even when people's eyes are closed.

The team behind the invention, led by scientists from the University of Science and Technology of China (USTC) in Hefei, gave the lenses their power by filling them with nanoparticles that convert near-infrared light in the range of 800-1,600 nanometers into visible light with a shorter wavelength that humans can see, in the range of 400-700 nanometers. According to researchers' estimates, lenses cost about 200 USD per pair.

The technology, which was described in detail in Cell on May 22, is "incredibly cool, like something from a science fiction movie," says Xiaomin Li, a chemist at Fudan University in Shanghai, China. This opens up "new opportunities for understanding the world around us," he adds.

Pros and cons

Near-infrared light is outside the wavelength range that people can usually detect. Some animals may feel infrared light, although probably not well enough to form images.

Night vision gogles allow people to see infrared radiation, but they are bulky and require a power source to work. New lenses avoid these limitations and also offer richer, multi-colored infrared images that are not usually made by night vision glasses that work on a monochrome green scale.

Nevertheless, lenses have their drawbacks. Since built-in nanoparticles scatter light, the images created by the lenses are blurred. The team partially corrected this by introducing technology into glasses with additional lenses that redirect light. Moreover, unlike night vision glasses, which amplify light to detect low-level infrared signals, lenses allow users to see only intense infrared signals, such as those emitted by light-emitting diodes (LEDs).

For these reasons, some critics do not believe that lenses will be useful. "I can't think of a single application that wouldn't be fundamentally easier with infrared glasses," says Glen Jeffrey, a neurobiologist at University College London who specializes in eye health. "Evolution avoided it for a good reason."

Nevertheless, the authors believe that their lenses can be further optimized and foresee several possible applications for the invention. For example, carriers will be able to read anti-counterfeit signs that emit infrared wavelengths, but are otherwise invisible to the human eye, says co-author Yuqian Ma, a neurobiologist from USTC.

Lee, who did not participate in the work, offers another possibility: lenses can be worn by doctors conducting near-infrared fluorescence for direct detection and removal of cancerous lesions "not relying on bulky traditional equipment".

"Delicing moment"

To create contact lenses, scientists relied on previous studies in which they gave mice infrared vision by introducing nanoparticles into the retina of animals. This time they took a less invasive approach and added nanoparticles of rare earth metals, including ytterbium and erbium, to polymer building block soup to form soft lenses, and then tested them for safety.

According to Ma, the main task was to pack enough nanoparticles into lenses to convert enough infrared light into detectable visible light without otherwise changing the optical properties of lenses, including their transparency.

Tests on mice showed that animals wearing lenses usually chose a dark box, which was considered "safe", instead of the one illuminated by infrared light, while mice without lenses did not prefer any box. People wearing lenses could see the flickering infrared light from the LED well enough to both catch Morse code signals and feel the direction from which the signals come from. Lens performance even improved when participants closed their eyes, because near-infrared light easily penetrates the eyelids, while visible light, which could interfere with the formation of the image, does so to a lesser extent.

"Seeing how people wear contact lenses and successfully seeing infrared flashes was undoubtedly an exciting moment," says Ma.

Now the team plans to find ways to shove more nanoparticles into lenses and hopes to develop particles that can transform light with higher efficiency to increase the sensitivity of the technology. "We have overcome the physiological limitations of human vision, as if opening a completely new window to the world," says Ma.