New contact lens enables vision in the dark

Night vision without bulky night vision devices: Chinese researchers say they have developed a contact lens that makes it possible to see in the dark.

The human eye perceives electromagnetic radiation in the range between 400 and 700 nanometers. To be able to see in the dark, it must be able to process infrared radiation with longer wavelengths.

This is made possible by the contact lens developed by the team led by Yuqian Ma from the Chinese University of Science and Technology in Hefei in the eastern Chinese province of Anhui. To achieve this, they have combined a material used for conventional soft contact lenses with 45 nanometer particles consisting of gold, sodium gadolinium fluoride, ytterbium, and erbium ions.

Nanoparticles convert infrared light

These nanoparticles can absorb light in the near-infrared range with wavelengths between 800 and 1600 nanometers and convert it into visible light, as the team describes in the scientific journal Cell. These upconversion contact lenses (UCLs) also work in the visible light range, which means that they extend the perceptible spectrum for the wearer. They are worn in a similar way to conventional contact lenses. The mechanical and chemical properties are also comparable.

The team tested the UCLs on mice and humans. The mice showed by their behavior that they could see in the dark. The human test subjects recognized patterns, letters or flashing infrared signals in the dark.

Better vision with eyes closed

“We also found that a subject with closed eyes can perceive these blinking signals even better because near-infrared light penetrates the eyelid better than visible light, so there is less interference with visible light,” said Tian Xue, one of the authors.

The team has been experimenting with the nanoparticles for some time. A few years ago, they injected them into the retinas of mice to allow them to see at night. However, the contact lenses are more practical because they are non-invasive.

The UCLs gave people super vision. “There are many potential applications for this material. For example, blinking infrared light could be used to transmit information in the fields of security, rescue, encryption or anti-counterfeiting,” said Xue. He sees further applications in the medical field: “By converting red visible light into something like green visible light, this technology could make the invisible visible to the colorblind.”

(wpl)