Metasurfaces Correct Color Blindness

Color blindness: The left 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. (Source: S. Karepov, Tel Aviv U.)

Researchers have incor­porated ultra-thin meta­surfaces into off-the-shelf contact lenses to correct deuter­anomaly, a form of red-green color blindness. The new customizable contact lens could offer a convenient and comfortable way to help people who experience various forms of color blindness. “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.”

Karepov and colleagues report that, based on simulations of color vision deficiency, their new metasurface-based contact lens can restore lost color contrast and improve color perception up to a factor of 10. The approach used to introduce new and tailor-designed func­tionalities to contact lenses could be expanded to help other forms of color vision deficiency and even other eye disorders, according to the researchers.

Deuteranomaly, which occurs mostly in men, is a condition in which the photo­receptor responsible for detecting green light responds to light associated with redder colors. Scientists have known for more than 100 years that this vision problem can be improved by reducing detection of the exces­sively perceived color but achieving this correction in a comfortable and compact device is challenging. “Glasses based on this correction concept are commer­cially available, however, they are signi­ficantly bulkier than contact lenses,” said Karepov. “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.”

To solve this problem, the researchers turned to metasurfaces. Meta­surfaces made of nanoscale gold ellipses have been extensively studied in the past few decades and can be designed to achieve specific effects on the light transmitted through them. However, the researchers needed a way to get meta­surfaces, which are conven­tionally made on flat surfaces, onto the curved surfaces of contact lenses. “We developed a technique to transfer meta­surfaces from their initial flat substrate to other surfaces such as contact lenses,” said Karepov. “This new fabri­cation process opens the door for embedding meta­surfaces into other non-flat substrates as well.”

The researchers tested the optical response of the meta­surface after every step of the new fabrication procedure and acquired micro­scopy images to closely examine the structure of the metasurface. Their measurements showed that the meta­surface’s light mani­pulation properties did not change after transfer to the curved surface, indicating that the process was successful. The researchers then used a standard simulation of color perception to quantify the deuter­anomaly color perception before and after intro­ducing the optical element. They found an improvement of up to a factor of 10 and showed that visual contrast lost due to deuter­anomaly was essen­tially fully restored.

Although clinical testing would be needed before the contact lenses could be marketed, the researchers say that manu­facturers could embed the meta­surface during the molding stage of contact lens fabri­cation or thermally fuse them to a rigid contact lens. They plan to keep studying and improving the metasurface transfer process and test it for other appli­cations. (Source: OSA)

Reference: S. Karepov & T. Ellenbogen: Metasurface-based contact lenses for color vision deficiency, Opt. Lett. 45, 1379 (2020); DOI: 10.1364/OL.384970

Link: Light Matter Interaction Center, Tel Aviv University, Tel Aviv, Israel

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