Finite element modeling of retinal prosthesis mechanics

Abstract

Epiretinal prostheses used to treat degenerative retina diseases apply stimulus via an electrode array fixed to the ganglion cell side of the retina. Mechanical pressure applied by these arrays to the retina, both during initial insertion and throughout chronic use, could cause sufficient retinal damage to reduce the device's effectiveness. In order to understand and minimize potential mechanical damage, we have used finite element analysis to model mechanical interactions between an electrode array and the retina in both acute and chronic loading configurations. Modeling indicates that an acute tacking force distributes stress primarily underneath the tack site and heel edge of the array, while more moderate chronic stresses are distributed more evenly underneath the array. Retinal damage in a canine model chronically implanted with a similar array occurred in correlating locations, and model predictions correlate well with benchtop eyewall compression tests. This model provides retinal prosthesis researchers with a tool to optimize the mechanical electrode array design, but the techniques used here represent a unique effort to combine a modifiable device and soft biological tissues in the same model and those techniques could be extended to other devices that come into mechanical contact with soft neural tissues.

Interphase gap as a means to reduce electrical stimulation thresholds for epiretinal prostheses

“…In Argus II patients, electrodes farther from the retina and/or macula generally require more stimulus current to evoke visual phosphenes [4, 5]. Because the array is affixed to the retina with a single retinal tack [6, 7], it is often difficult to obtain a tight MEA-retina interface. This is due to a number of factors, such as intersubject variability in eye curvature.…”

Parylene-Based Electrochemical-MEMS Transducers

“…However, the magnitude of this mechanical interaction has not been quantitatively studied and is currently unknown. There is evidence that suggests that micronewton-to-millinewton forces can be expected [18]- [21]; however, measurement of these interfacial forces in situ requires novel sensor technology. Polymer-MEMS sensors based on EI transduction offer a novel approach with many advantages, including improved mechanical matching to tissue (in contrast to rigid materials such as silicon and glass), small footprint, low power consumption, simple construction, and excellent sensitivity [22].…”

Fine-resolution maps of acoustic properties at 250 MHz of unstained fixed murine retinal layers

“…We therefore hypothesize that a more comprehensive assessment of material properties rather than estimations from single parameters such as c, will lead to a more precise and realistic characterization of the elastic properties of ocular tissues at small length scales. These material properties are for example required for in-silico studies involving numerical models such as the finite-element modeling used by Basinger et al (2009). Moreover, ocular tissue elastic properties may be associated with several disease conditions such as keratoconus (Andreassen et al, 1980) and high myopia and straphyloma (McBrien et al, 2009).…”