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GRIN (Gradient Refractory INdex) polymer lens nearly identical to human eye lens

Case Western Reserve University : 16 November, 2012  (Special Report)
A multi-layered polymer gradient refractive index (GRIN) lens inspired by the human eye could one day provide a more natural alternative to implantable eye lenses and consumer vision products.

GRIN (Gradient Refractory INdex) polymer lens nearly identical to human eye lens

The work, conducted by scientists at Case Western Reserve University, Rose-Hulman Institute of Technology, the US Naval Research Laboratory and PolymerPlus, provides a new material approach for fabricating synthetic polymer lenses. Using a multilayer-film coextrusion technique - a common method used for producing multilayer structures - the team stacked thousands of nanoscale layers, each with a slightly different refractive index. These layers were laminated and shaped into GRIN optics.

In GRIN, light gets bent, or refracted, by varying degrees as it passes through a lens or other transparent material. In contrast, traditional lenses such as optical telescopes and microscopes bend light one way or another using their surface shape or single index of refraction.

These light-gathering polymer lenses, 3.5 times more powerful than glass, are the first commercial nanolayered product to come out of many years of R&D at Case Western Reserve University. To create the lenses, a 4000-layer film is coextruded, and then 200 layers of film are stacked to create an 800,000-nanolayer sheet. Courtesy of Michael Ponting.

Current-generation intraocular replacement lenses, like those used to treat cataracts, use their shape to focus light to a precise prescription, similar to glasses and contacts. Such lenses never achieve the same performance of natural lenses because they lack the ability to incrementally change the refraction of light. This single-refraction replacement lens can create aberrations and other unwanted optical effects.

“The human eye is a GRIN lens,” said Michael Ponting, polymer scientist and president of PolymerPlus, an Ohio-based Case Western Reserve spinoff. “As light passes from the front of the human eye lens to the back, light rays are refracted by varying degrees. It’s a very efficient means of controlling the pathway of light without relying on complicated optics, and one that we attempted to mimic.”

The lens design was previously created by scientists at the University of Granada, in Spain, and Advanced Medical Optics for aging human eyes, but the technology did not exist to replicate the gradual evolution of refraction.

The new approach, modeled on nature’s example, produces a lens that gradually varies its refractive index. It also provides the freedom to stack any combination of the nanolayered films, enabling the fabrication of GRIN optics previously unattainable through other methods.

Fabricated lens images (a and d) and measured geometry surface profiles (b/c and e/f) of the aspheric anterior and posterior bio-inspired human eye GRIN lenses. Courtesy of Optics Express.

“Applying naturally occurring material architectures, similar to those found in the layers of butterfly wing scales, human tendons and even in the human eye, to multilayered plastic systems has enabled discoveries and products with enhanced mechanical strength, novel reflective properties and optics with enhanced power,” Ponting said.

GRIN optics may find use in miniaturised medical imaging devices or implantable lenses.

The GRIN technology could also enable optical systems with fewer components such as ground- and aerial-based military surveillance products. It has moved from Case Western Reserve’s research lab to PolymerPlus for commercialization.

The research was first published in Optics Express. 

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