A recent study published in Cell outlined the development and testing of a new technology called upconversion contact lenses (UCLs) that allow for near-infrared (NIR) color vision in humans.
Give me some background.
The human eye can only detect light with wavelengths from 380-700 nm, which is called the visible light spectrum.
- NIR light sits just beyond the red end of the visible light spectrum (800-2,500 nm wavelengths), and consequently is invisible to the human eye.
Note: Infrared goggles (often known as night vision goggles) allow people to see infrared radiation.
- However: This technology is currently limited to head-mounted eyewear that can be bulky, often requires a power source, and operates only on a green scale.
Is this the first study to use upconversion technology?
No, in fact the UCLs were designed as a follow up to prior analyses.
Previously, the research team from this study designed ocular injectable retinal photoreceptor-binding upconversion nanoparticles (pbUCNPs) that enabled NIR light sensation and pattern vision in mice.
- How it works: The pbUCNPs act as miniature energy transducers that can transform mammalian invisible NIR light in vivo into short wavelength visible emissions.
As such: Investigators sought to design and test wearable contact lenses that make NIR wavelengths visible to humans as a less invasive option to the injectable nanoparticles.
Talk about these UCLs.
The UCLs have the above-mentioned pbUCNPs built into flexible, non-toxic polymers often used in standard soft contact lenses—making them wearable and comfortable—with over 90% transparency across most wavelengths.
- The nanoparticles were made from ytterbium and erbium, though nanoparticle integration into polymeric materials can alter optical properties.
In addition: Trichromatic UCLs (tUCLs) were developed wherein the nanoparticles were engineered to to color code different NIR wavelengths:
- 808 nm wavelengths were converted to green light
- 980 nm wavelengths were converted to blue light
- 1,532 nm wavelengths were converted to red light
Now let’s get to the study.
The UCLs were tested in both mice and human models as follows:
- Mice were given the choice of a “safe” dark box or an infrared-illuminated box to test whether the mice wearing UCLs showed a preference
- Humans were tested on whether they could detect flickering Morse-code like signals and perceive the direction of incoming NIR light
And the findings?
Mice wearing the UCLs could recognize NIR temporal and spatial information and tended to choose the “safe” dark box, while mice that didn’t wear the lenses showed no preference.
- Further: The pupils of mice wearing UCLs constricted in the presence of infrared light, and brain imaging demonstrated that infrared light caused their visual processing centers to activate.
Moreover: Human participants wearing the UCLs could discern NIR information, such as temporal coding and spatial images.
- Participants wearing the tUCLs could discriminate between the three colors, demonstrating that they had NIR spatiotemporal color vision.
Tell me more.
Interestingly: UCL performance improved when participants closed their eyes, potentially because NIR light can penetrate the eyelids, so visible light may have interfered with image formation when their eyes were open.
Any limitations?
Due to their close proximity to the retina and the light-scattering properties of the nanoparticles, the UCLs created blurry images.
As such: Investigators also developed wearable spectacles using the same nanoparticle technology, which allowed participants to perceive higher-resolution infrared information.
- In addition: Currently the UCLs can only detect NIR wavelengths projected from an LED source, but the research team is working to increase the sensitivity of the nanoparticles so they can detect lower levels of infrared light.
Expert opinion?
“Overall, this concept-proving study confirms that human supervision ability can be achieved by wearable nano-biomaterials and paves the way to numerous applications of human NIR spatiotemporal color vision,” the study authors highlighted.
While this research is promising, the technology is still in the early stages of development and will likely require significantly more time before it is available for practical use.
Tie it all together for me.
These findings demonstrate the proof of concept of wearable transparent UCLs with high NIR-conversion efficiency and biocompatibility.
- How: The UCLs allowed for NIR spatiotemporal vision and the tUCLs converted multispectral NIR light, making it possible for humans to identify the distinct NIR spectra of images.
Moving forward: These findings are the early steps in the development of wearable polymeric materials for non-invasive NIR vision—aiding humans in perceiving and transmitting temporal, spatial, and color dimensions of NIR light.