By Shirley Ha, HBSc., O.D.
A team of Swiss and U.S. researchers has built a revolutionary telescopic contact lens tethered to a pair of liquid crystal eyeglasses that can switch between normal and magnified vision[i].The unprecedented contact lens system, which uses the special eyeglasses as will be explained below, could become a visual aid for those struggling with degenerative eye diseases such as age-related macular degeneration (AMD), a leading cause of irreversible central vision loss and legal blindness in older adults.
Current vision rehabilitation devices, such as external, spectacle-mounted telescopes and the more recent Implantable Miniature Telescope (IMT), magnify images in front of the eye and project them onto the healthy areas of the retina. The problem is that external, spectacle-mounted telescopes are often seen as protrusive and unattractive, while IMTs require invasive eye surgery for implantation.
“For a visual aid to be accepted, it needs to be highly convenient and unobtrusive; a contact lens is an attractive compromise,” says Eric Tremblay at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland[ii].
Together with colleagues from the University of California at San Diego, Tremblay developed the 1-mm centre thickness, 8-mm diameter prototype contact lens. It has a clear central aperture of 2.2-mm for normal, unmagnified vision and an outer ring of 1.17-mm thick optics for the telescopic 2.8x magnification.
The researchers used their “origami” lens design to achieve longer effective focal lengths or zooming power[iii]. They did this by precision diamond-turning a series of tiny, reflective and non-reflective annular concentric aluminum surfaces into the lens periphery. Instead of light moving through a lens system that is several times thicker, the “folded” aspheric reflectors bounce the light internally back and forth in a pre-determined zigzag pattern within the lens periphery before projecting the final magnified image onto the retina.
To make the two independent optical paths switchable, the team applied orthogonal polarization films over the central and annular apertures and modified a pair of Samsung 3D TV glasses with liquid crystal sensors that can electrically toggle on and off the polarization in the contact lens. Instead of seeing the regular and magnified vision simultaneously, the user can selectively switch to or block either the regular, unmagnified stream in the centre or the telescopic stream on the periphery.
In its first round of experimental demonstration, the prototype telescopic contact lens design is still very basic. It is made of polymethyl methacrylate (PMMA), an outdated contact lens polymer that cannot be worn for any extended period of time because of its oxygen impermeability to the eye. Although diffractive optics are grooved into the PMMA material to fix the axial chromatic aberration that the contact lens curvature creates, the grooves make the contact lens unwearable. While the retinal field of view could be made larger than other magnifiers, the image quality and contrast captured by a life-sized optomechanical eye are degraded by higher-order diffraction from the same diffractive grooves.
The researchers are already working out the bugs. They are currently partnering with contact lens manufacturer Paragon Vision Sciences to develop an upgraded model of the telescopic contact lens using modern, rigid gas-permeable (RGP) materials that can be worn for longer periods of time. The redesign will have improved “all-refractive”, rather than diffractive, optics to enhance contrast and image quality. The team of researchers plans to begin clinical trials to test their new design on AMD patients as early as November.
Other ongoing collaborations include one with Rockwell Collins Inc., a large, U.S.-based international communication solutions company, to develop glasses with additional control and interaction, such as a wink trigger that can switch between normal and magnified vision when the gesture is registered. The researchers also believe they can eventually incorporate the liquid crystal sensors directly into the contact lens with an external remote, like the recently commercialized SENSIMED Triggerfish® system for monitoring glaucoma.
But don’t expect to see variable-focus, high-power zoom anytime soon. It will be some time before these telescopic contact lens systems become readily available to the average consumer. Funded by the U.S. Department of Defense’s Defense Advanced Research Projects Agency (DARPA), the technology could also become the future soldier’s eagle vision, helping to identify allies or enemies at far distances, or as a deadly accurate weapon-target locking device.
Eventually, this innovative breakthrough, which extends functioning vision with a contact lens that can be worn comfortably, will become available to people in the general population who suffer from permanent sight loss such as AMD.
[i] TREMBLAY, Eric J., STAMENOV, Igor, BEER, R. Dirk, ARIANPOUR, Ashkan, FORD, Joseph E. “Switchable telescopic contact lens”, Optics Express, vol. 21, No. 13, July 2013
[ii] Business Wire: “A Telescope For Your Eye: New Contact Lens Design May Improve Sight of Patients with Macular Degeneration”, June 27, 2013.
[iii] Jacobs School of Engineering, UC San Diego: “Concentric Multi-Reflection Lenses for Ultra-Thin Cameras (aka Origami Optics)”.