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Joel G. Thomas, Ashley N. Selner, John R. Hetling; Exogenous Currents Delivered To The Eye As A Potential Therapy: Computational Model Comparing Two Electrode Geometries In Rat. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1864.
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Multiple groups are investigating the delivery of exogenous electrical currents to the eye as a potential therapy for retinal degenerative disease. To guide experimental work aimed at optimizing parameters of current delivery for therapeutic effect, it is of interest to know the spatial distribution of currents in the eye. Several electrode geometries have been used to deliver these currents; here, two representative geometries were simulated to evaluate current density (CD) at the retina.
A computational model of electrodes in contact with a rat head (comprised of skull, brain, muscle, adipose tissue, and detailed eye), was built in SolidWorks and imported into ANSYS for electromagnetic finite element analysis. Geometries were G1) concentric ring electrodes in a contact lens, and G2) pellet electrodes located at the corneal pole and in the mouth. Simulations passed equal (4 micro Amps) current between the electrode pair for each geometry.
Spatial maps of CD at the photoreceptor layer were generated for both geometries. Summary statistics were calculated from each map (all values in mA m-2). G1: range = 10.1 - 0.01, mean = 1.7, variance = 0.01. G2: range = 122 - 363, mean = 207, variance = 1.5. The mean value of CD for G2 was more than 100x higher than for G1. For G1, the CD over the central half of the retinal area was uniformly <0.1 % of the typical values for the peripheral half.
The CD at the photoreceptor layer was significantly higher, and more spatially uniform, when using electrode geometry G2, as compared to G1. Both geometries resulted in maximum CD at the peripheral retina, and minimum at the posterior pole. For experimental investigation of the effects, and mechanism of action, of exogenous electrical currents applied to the retina, achieving a spatially-uniform delivery of current may simplify interpretation of electrophysiological, histological, and biochemical measures of retinal health.
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