Infrared contact lens helps people see in the dark, even with their eyes closed

Many people have wished for night vision on a dark walk home. But have you ever wondered if it's possible to see with your eyes closed?

Both are feasible with a contact lens that allows the wearer to see light that's usually invisible to our eyes — and can pass through our eyelids.

The infrared lens, which was developed by researchers in China, was unveiled in the journal Cell today.

Tian Xue, a neuroscientist at the University of Science and Technology of China and study co-author, said the material had the potential to give people "super-vision".

But in the shorter term, the team's ambitions are more modest.

"Flickering infrared light could be used to transmit information in security, rescue, encryption or anti-counterfeiting settings," Professor Xue said in a press release.

Finding unseen wavelengths

Our eye cells only register light in a small proportion of the electromagnetic spectrum.

If we could see longer wavelengths — just outside the visible spectrum into the near-infrared — we'd be able to see humans and other warm-blooded animals "glow" faintly as they emit infrared light.

Devices like night-vision goggles often work by tuning into near-infrared wavelengths, sometimes accompanied by an infrared light source to illuminate the surrounding area.

But these devices usually need an external power source to work, making them bulky.

They also tend to have a very limited of field of view, according to Paul Martin, a researcher in ophthalmology at the University of Sydney.

While it's possible to buy "infrared" contact lenses online, typically marketed for cheating at card games, these lenses don't allow users to see infrared light.

Instead, Professor Martin said they filter out higher wavelengths of light to make it easier to see light at a desired wavelength — usually, one tuned to an invisible ink sold with the contact lenses.

Converting infrared light into visible light

Researchers around the world, including in Australia, have been working on less cumbersome materials that can perform "wavelength shifting": absorbing invisible infrared light and re-emitting it as light we can see.

The researchers behind the new study had previously developed particles roughly the size of a small virus by mixing gold atoms with a few other elements, including the metals ytterbium and erbium.

The team injected these particles into the eyes of mice and found it gave them infrared vision. But they wanted to make the process less invasive before testing it on humans.

In the newest study, the researchers mixed their nanoparticles with polymers used in commercial contact lenses, and moulded this mixture into contacts.

They found people wearing the contact lenses could see visible light as normal. But they could also see a flashing infrared light — even when their eyes were shut.

Our eyelids have evolved to block visible light, but infrared light can pass right through them.

In fact, Professor Xue said participants were better at detecting the infrared flashes when their eyes were shut, because there was less interference from visible light.

The researchers could tweak their nanoparticles to convert specific infrared wavelengths into specific visible wavelengths, so the participants could see different shades of infrared light in different visible colours.

They tested this by showing the study participants different letters made from infrared light, which the participants could read in different colours.

Professor Martin, who was not involved with the research, called the study a "marvellous technical tour de force".

"One big and exciting promise of the present study is that the contact lenses or glasses could become a new basis for human-worn surveillance devices."

See-in-the-dark contacts aren't ready yet

While the research is promising, Professor Martin believes these contact lenses are a long way away from practical use.

People using the lenses could see infrared light, but they weren't granted fine night vision.

The researchers did build their nanoparticles into wearable spectacles, which gave people crisper infrared vision, but they still needed a bright source of infrared light for the glasses to work.

"The nanoparticles in the contact lens or glasses are not sensitive enough to detect the very low intensity of infrared radiation emitted by warm-blooded animals," Professor Martin said.

Professor Xue said that the team was working on improving the nanoparticles' sensitivity so that they could make higher-resolution contact lenses.