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Correcting colour blindness with metasurface contact lenses

Ultra-thin optical devices known as metasurfaces have been successfully incorporated into contact lenses to correct the most common form of colour blindness.

The device is specifically designed for people with deuteranomaly, which makes it difficult to differentiate between red and green.

Colour blindness is a common condition - affecting around 8 per cent of men and 1 in 200 women - that occurs due to the way light-sensitive cells found in the retina of the eye respond to certain colours.

“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, Israel, and a member of the research team that has developed the new contact lens.

“Our contact lenses use metasurfaces based on nano metric-size gold ellipses to create a customised, compact and durable way to address these deficiencies.”

L-R original image, as perceived by a person with deuteranomaly, scene viewed with the new contact lenses

The researchers state that based on simulations of colour vision deficiency, their new metasurface-based contact lens can restore lost colour contrast and improve colour 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 colour vision deficiency and even other eye disorders, the researchers said.

“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 the problem, the researchers turned to metasurfaces; artificially fabricated thin films designed with specific optical properties.

While metasurfaces are conventionally made on flat surfaces, the researchers adapted them so they could fit 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 found that its light-manipulation properties did not change after being transferred to the curved surface, indicating that the process was successful.

Although clinical testing will be needed before the contact lenses can be marketed, the researchers believe manufacturers could embed the metasurface during the moulding stage of contact lens fabrication or thermally fuse them to a rigid contact lens.

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