Researchers have given people a taste of superhuman vision after creating contact lenses that allow them to see infrared light, a band of the electromagnetic spectrum that is invisible to the naked eye.
Unlike night vision goggles, the contact lenses need no power source, and because they are transparent, wearers can see infrared and all the normal visible colours of light at the same time.
Prof Tian Xue, a neuroscientist at the University of Science and Technology of China, said the work paved the way for a range of contact lenses, glasses and other wearable devices that give people “super-vision”. The technology could also help people with colour blindness, he added.
The lenses are the latest breakthrough driven by the team’s desire to extend human vision beyond its natural, narrow range. The wavelengths of light that humans can see make up less than one hundredth of a per cent of the electromagnetic spectrum.
Dr Yuqian Ma, a researcher on the project, said: “Over half of the solar radiation energy, existing as infrared light, remains imperceptible to humans.”
The rainbow of colours visible to humans spans wavelengths from 400 to 700 nanometres (a nanometre is a millionth of a millimetre). But many other animals sense the world differently. Birds, bees, reindeer and mice can see ultraviolet light, wavelengths too short for humans to perceive. Meanwhile, some snakes and vampire bats have organs that detect far-infrared, or thermal radiation, which helps them hunt for prey.
To extend humans’ range of vision and enhance our experience of the world, the scientists developed what are called upconversion nanoparticles. The particles absorb infrared light and re-emit it as visible light. For the study, the scientists chose particles that absorb near-infrared light, comprising wavelengths that are just too long for humans to perceive, and converted it into visible red, green or blue light.
In previous work, the research team gave mice near-infrared vision by injecting upconversion nanoparticles under the retina, the light-sensitive membrane at the back of the eye. But noting that this “may not be readily accepted by humans,” they searched for a less invasive strategy.
Writing in the journal Cell, the scientists describe how they made soft contact lenses seeded with upconversion nanoparticles. When worn, people could see Morse code-like signals flashed from an infrared LED and tell what direction infrared light came from.
Their infrared vision improved when they closed their eyes, because eyelids block visible light more than infrared, so there was less visible light to interfere.
The lenses are not sensitive enough to see natural low levels of infrared light, and because warm objects radiate mostly in the far-infrared, the lenses do not provide thermal vision. But future work will focus on making lenses that are more effective, the scientists say.
Xue said: “If materials scientists can develop upconversion nanoparticles with higher efficiency, it may become possible to see surrounding infrared light using contact lenses.”
Even without full infrared vision, Xue sees applications. For example, secret messages sent by infrared light would only be visible to people wearing the contact lenses, he said.
A similar approach might help people with colour blindness by converting wavelengths they cannot see into hues they can.
