- Telescopic Contact Lens Helps AMD Patients See
SAN DIEGO, and LAUSANNE, Switzerland, June 27, 2013 — A slim, telescopic contact lens that switches between normal and magnified vision using liquid crystal eyeglasses could provide a relatively unobtrusive way to enhance the sight of patients with age-related macular degeneration (AMD).
Contact lenses correct many people’s eyesight but do nothing to improve the blurry vision of those suffering from AMD, the leading cause of blindness among older adults in the western world. Simply correcting the eye’s focus with contacts cannot restore the central vision lost from a retina damaged by AMD.
Visual aids that magnify incoming light help AMD patients see by spreading light around to undamaged parts of the retina, but these optical aids use either bulky spectacle-mounted telescopes that interfere with social interactions, or microtelescopes that require surgery to implant into the patient’s eye.
“For a visual aid to be accepted it needs to be highly convenient and unobtrusive,” said Eric Tremblay of École Polytechnique Fédérale de Lausanne in Switzerland, who worked with an international team of researchers led by University of California, San Diego professor Joseph Ford to develop the device. A contact lens is an “attractive compromise” between the head-mounted telescopes and surgically implanted microtelescopes, Tremblay says.
The lens system developed by Ford’s team uses tightly fitting mirror surfaces to make a telescope that has been integrated into a nearly 1-mm-thick contact lens. The lens has a dual modality: the center of the lens provides unmagnified vision, while the ring-shaped telescope located at the periphery of the regular contact lens magnifies the view 2.8 times.
Five views of the switchable telescopic contact lens developed by an international team of researchers led by University of California, San Diego professor Joseph Ford. (a) From front. (b) From back. (c) On the mechanical model eye. (d) With liquid crystal glasses. Here, the glasses block the unmagnified central portion of the lens. (e) With liquid crystal glasses. Here, the central portion is not blocked. Images courtesy of Optics Express.
To switch between the magnified view and normal vision, users would wear a modified pair of liquid crystal glasses originally made for viewing 3-D televisions. These glasses selectively block either the magnifying portion of the contact lens or its unmagnified center by electrically changing the orientation of polarized light to allow light with one orientation or the other to pass through the glasses to the lens.
The design was tested both with computer modeling and lens fabrication. A life-sized model eye also was created to capture images through the team’s contact lens-eyeglasses system.
In constructing the lens, the researchers relied on a robust material commonly used in early contact lenses called polymethyl methacrylate (PMAA). The material’s robustness was needed to place tiny grooves into the lens for aberrant color correction caused by the lens’ shape, which is designed to conform to the human eye.
Tests showed that the magnified image quality through the lens was clear and provided a much larger field of view than other magnification approaches, but refinements are necessary before the proof-of-concept system could be ready for commercial use.
The grooves used to correct color were discovered to degrade image quality and contrast, and also made the lens unwearable unless it is surrounded by a smooth, soft “skirt,” something commonly used with rigid contact lenses today. The researchers also said that PMAA is not ideal for contact lenses because it is gas-impermeable, limiting wear to short periods of time.
Images captured through the contact lens and mechanical model eye. (c) Outdoor image taken with model eye alone. (d) Outdoor image taken with model eye and contact lens. This image shows why each of the two magnification states (normal and 2.8×) should be used one at a time: here, neither section of the lens is being blocked by the glasses, and the result is an image with greatly reduced contrast. (e) Outdoor image taken with just the magnified outer portion of the contact lens (2.8×).
Ford’s team is now pursuing a similar design that will still be switchable, but that will use gas-permeable materials and will correct aberrant color without the need for grooves to bend light. Their hope is to offer a design that improves performance and enhances sight for people with AMD, at least until a more permanent remedy is available.
“In the future, it will hopefully be possible to go after the core of the problem with effective treatments or retinal prosthetics,” Tremblay said. “The ideal is really for magnifiers to become unnecessary. Until we get there, however, contact lenses may provide a way to make AMD a little less debilitating.”
The research — funded as part of a larger DARPA research project called “Soldier Centric Imaging with Computational Cameras,” or SCENICC — was published in Optics Express (doi: 10.1364/OE.21.015980).
For more information, visit: www.ucsd.edu or www.epfl.ch
- color correction
- The reduction in longitudinal, lateral and secondary chromatic aberrations in a lens or lens system.
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