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Y. Mandel, S. Laufer, B. Rubinsky; Assesing Corneal Endothelial Electrical Properties by External Electrodes: Experimental and Finite Element Model Study. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3942.
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The goal of this study was to develop a method to asses the passive electrical properties of the corneal endothel. The corneal endothelial electrical properties are related to its anatomical integrity and function. Minimally invasive methods that can asses the electrical properties of the endothel are of great importance for evaluation patients with endothelial dysfunction.
Procine corneas where preserved in normal saline not more than 48 hours before electrical properties measurements. Complex impedance was measure by CH Instruments , Electrochemical Analyzer using two electrodes configuration in frequency range of 100Hz-100kHz. Impedance was measured in cross sectional as well as tangential configuration on the endothelial and epithelial sides. Impedance loci were ploted with Cole-Cole configuration. Curves were fitted using Matlab software.Finite element model was constructed by Comsol Multiphysiscs using DC as well as AC model and measured the current density when 5 mico amper current was injected in various electrode geometrical relationships. In a simplified model the epithalical layer was missing. The stroma was modeled as 5 ohm·cm2 while the endothelial layer was modelde as a resistor with parallel set of resistors and capacitors with various resistivity and capacitance.
Electrode impedance measured in normal saline at 1kHz was less than 100 Ohms The results of the complex impedance measurements were presented in a Cole-Cole model and demonstrated a depressed semi circle. The cornea demonstrated a typical relaxation at the 1kHz frequency zone. However, when the epithelial layer was scrapped the relaxation disappeared. No relaxation was found on a 1 day endothelial layer in eyes that were kept in normal saline solution. The finite element model demonstrated that most of the current is delivered by the stroma. However, part of the current cross the endothelium into the anterior chamber. The proportion of current that passes the endothelium is dependent on the electrode gemoterical relationships as well as the ratio between the stroma and the endothel
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