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A New Technique to Detect Ocular Pathologies Based on Electrical Measurement Implemented on Programmable Logic

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3 Author(s)
Bellotti, M.I. ; Lab. de Cavitacion y Biotecnologia, Inst. Balseiro/CAB, San Carlos de Bariloche, Argentina ; Dellavale, D. ; Bonetto, F.J.

We developed a technique that detects superficial ocular pathologies based on the measurement of electrical impedance spectra. The sensor used is a small microelectrode made of platinum insulated from a cylindrical counterelectrode built of surgical stainless steel. The sensor has the shape of a truncated cone made of acrylic with dimensions identical to that of a standard Goldman prism. The sensor is applied to normal and pathological subject eyes with a constant force provided by a commercial tonometer. The circuit is closed through the lacrimal layer and the epithelial and endothelial cells. We measure the electrical impedance with a programmable logic device in which we implemented all the significant functions. These are the synthesis of the seventeen sines for the excitation, one lock-in, and delta-sigma modulators for the digital-to-analog converter and analog-to-digital converter requirements. A simple analog circuit filters the output, implements a voltage divider, and acts as current limiter in order not to damage the cells. We convert the measurements to resistance and capacitance as a function of frequencies. Consistent results are obtained for left and right eyes of the normal subjects. Significant differences are detected between the results for normal eyes and pathological eyes.

Published in:

Instrumentation and Measurement, IEEE Transactions on  (Volume:61 ,  Issue: 12 )