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Telescopic contact lens helps AMD patients see

EuroPhotonics
Sep 2013
SAN DIEGO, and LAUSANNE, Switzerland – A slim, telescopic contact lens that switches between normal and magnified vision in combination with liquid crystal eyeglasses could provide a relatively unobtrusive way to enhance the sight of patients with age-related macular degeneration (AMD).

Contact lenses can correct eyesight, but they do nothing to help AMD, the leading cause of blindness among older adults in the Western world. Simply correcting the blur with contacts cannot restore the central vision lost from a retina damaged by AMD.


Five views of the new switchable telescopic contact lens. (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.


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 must be surgically implanted directly into the 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 head-mounted telescopes and implanted microtelescopes, Tremblay said.

The 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 with a dual modality: The center provides unmagnified vision, while the ring-shaped telescope at the periphery of the regular contact lens magnifies the view 2.8 times.

To switch between the magnified view and normal vision, users wear a modified pair of liquid crystal glasses originally made for viewing 3-D TVs. 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.


Images captured through the contact lens and mechanical model eye: (a) Outdoor image taken with model eye alone. (b) This outdoor image, taken with model eye and contact lens, 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. (c) Outdoor image taken with just the magnified outer portion of the contact lens (2.8×). OE = optoelectronic.


The design was tested both with computer modeling and lens fabrication. A life-sized model eye was created to capture images through the system.

To construct the lens, the researchers used a robust material common in early contact lenses called polymethyl methacrylate (PMAA), into which they placed tiny grooves to correct for aberrant color caused by the lens’ shape, which conforms 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 degraded image quality and contrast, and also made the lens unwearable unless it is surrounded by a smooth, soft “skirt,” something often used with rigid contact lenses today. PMAA is not currently ideal for contact lenses because it is gas-impermeable, limiting wear to short periods of time. The team is pursuing a similar design that will still be switchable, but that will use gas-permeable materials and correct aberrant color without the need for grooves.

“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 was published in Optics Express (doi: 10.1364/OE.21.015980).


GLOSSARY
color correction
The reduction in longitudinal, lateral and secondary chromatic aberrations in a lens or lens system.
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