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Yu Zhao, Charles DeBoer, Mandheerej Nandra, James Weiland, Mark Humayun, Yu-Chong Tai; An Optimal Power Coil Configuration to Minimize Surgical Cut for Intraocular Retinal Prostheses. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1056.
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© ARVO (1962-2015); The Authors (2016-present)
Power coils used in current telemetries powering the epiretinal, subretinal and suprachoroidal prosthetic devices, such as microfabricated planar coil with metal electroplating and wire-wound coil, are not suitable/ideal for intraocular implantation as they are usually thick, rigid and large. For intraocular implantation, we propose a foil coil as an optimized configuration. It demonstrates not only better electrical performance, but also superior mechanical flexibility and bendability allowing the surgeon to implant through a minimal incision.
The lens capsule is a possible intraocular implantation site for the telemetry coils, which also sets the size and mass constraints. This implantation is similar to the common intraocular lens implantation. While making the best use of the coil winding window, it is still necessary to make the coil flexible for minimally invasive surgical implantation. Flexural stiffness, i.e., resistance to bending, equals to the product of the Young’s modulus E and second moment of area I reflecting the material stiffness and its geometrical cross section, respectively. Given same constructing metal, second moment of area varies with cross-sectional size and geometry (Fig. 1). The long-span high-aspect ratio foil strip can achieve smallest I and therefore the most flexibility. The strip was fabricated using a parylene-metal-parylene sandwich structure. The thermally deposited metal is thin (0.25 μ m) and patterned to form a 1-mm-wide stripe to fit into lens capsule. After the foil was dry-peeled off from the silicon substrate and manually wound into a circular coil, the original width of the encapsulated metal foil becomes the equivalent thickness of the coil.
To demonstrate the surgical feasibility, the coil was implanted into the lens capsule of a porcine eye (Fig. 2). The coil was compressed and inserted into a porcine lens capsule through a capsulorhexis. After implantation the forceps were withdrawn and the coil regained its circular shape (dotted circle in the middle panel). By observing the implanted coil after removal of the iris, the full recovery of the coil shape was achieved in vitro.
Foil coil configuration has been theoretically proven and experimentally demonstrated to be more bendable, thus less invasive during implantation. The resulting smaller surgical incision has the potential to reduce post operative recovery time.
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