These images illustrate the effect a metasurface-based contact lens would have on a person with deuteranomaly. The left image shows the original scenario while the middle image is how the scene would look to a person with deuteranomaly. The image on the right represents the scene viewed with deuteranomaly and corrected with the new contact lenses. Image credit: Sharon Karepov, Tel Aviv University
You may have a problem in observing green or red light at the traffic or you may be surprised when someone says ‘look! that tree is reddish’ as you see them other than reddish and your doctor had suggested you with the expensive and bulky equipment to eliminate this blindness. But now this problem is solved and this solution will let you wear your own lens that will eliminate color blindness.
Metasurfaces, ultra-thin optical devices, have been successfully incorporated into contact lenses to correct deuteranomaly- which is the most common class of color vision deficiency.
Typically, humans can distinguish around 1 million colors but for some these numbers is not the same as to others as their color perception is limited in certain ranges of the electromagnetic spectrum. For those types of a person when any light source with a specific wavelength of light hits on their eye, the response of the light-sensitive cone photoreceptor cells at the back of the eye is attenuated. For instance, for a person with deuteranomaly, signals from the cells that are sensitive to green-yellow light (known as medium-type cone photoreceptors) are dulled and the brain receives too many signals from longer wavelengths associated with yellow-red light. As a result, the person with this form of color blindness struggles to tell red and green wavelengths apart.
Researchers involving Sharon Karepov and Tal Ellenbogen from Tel Aviv University in Israel have now incorporated plasmonic metasurfaces into standard contact lenses and they were able to restore lost color contrast and improve color perception by up to a factor of 10. This design has offered a potential route to combating a particular form of color blindness. The team embed large-scale, plasmonic metasurfaces into off-the-shelf rigid gas permeable contact lenses and study their ability to serve as visual aids for color vision deficiency. In this study, the team specifically addresses deuteranomaly, which is the most common class of color vision deficiency.
The research was published in Optics Letters, a publication of OSA, The Optical Society.
"Problems with distinguishing red from green interrupt simple daily routines such as deciding whether a banana is ripe," said Sharon Karepov from Tel Aviv University in Israel, a member of the research team. "Our contact lenses use metasurfaces based on nano-metric size gold ellipses to create a customized, compact, and durable way to address these deficiencies."
Researcher Sharon Karepov said, "Glasses based on this correction concept are commercially available, however, they are significantly bulkier than contact lenses." Karepov added, "Because the proposed optical element is ultrathin and can be embedded into any rigid contact lens, both deuteranomaly and other vision disorders such as refractive errors can be treated within a single contact lens."
As the traditional metasurfaces are usually fabricated on flat surfaces, the challenge to this team was to design a manufacturing operation capable of incorporating the gold nanostructures onto the curved surface of a contact lens. To do this the research team developed a technique to transfer metasurfaces from their initial flat substrates to curved surfaces such as contact lenses and tested the optical response of the metasurface after every step of the new fabrication procedure and acquired microscopy images to examine the structure of the metasurface. The result was as they desired and expected: the metasurface’s light manipulation properties did not change after transfer to the curved surface, indicating that the fabrication process was successful.
Then they used a standard simulation of color perception to quantify the deuteranomaly color perception before and after introducing the optical element. The research team found newly designed device could shift incorrectly-recognized colors closer to the original hues and that lost visual contrast in red-green color blindness could essentially be restored. In mathematical terms, they claimed that they have achieved an improvement of up to a factor of 10.
Karepov said, "Our contact lenses use metasurfaces based on nano-metric size gold ellipses to create a customized, compact and durable way to address these deficiencies." He also added, "We developed a technique to transfer metasurfaces from their initial flat substrate to other surfaces such as contact lenses and this new fabrication process opens the door for embedding metasurfaces into other non-flat substrates as well."
Though the team got an unprecedented result, the new lens still needs to pass clinical-stage tests. About the production of this kind of lens, the researchers highlighted that manufacturers could potentially embed the metasurfaces during the molding stage of contact lens fabrication or thermally fuse them to a rigid lens.