Dual wavelength polarimetry for monitoring glucose in the presence of varying birefringence
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In a continuing effort to develop a noninvasive means of monitoring glucose levels using the aqueous humor of the eye, a dual wavelength system has been developed in order to show that varying birefringence, similar to what is seen with a moving cornea, can be compensated. In this paper a dual wavelength, closed-loop, system was designed and a model was developed to extract the glucose concentration information. The system and model were tested using various concentrations of glucose in a birefringent test cell subject to motion artifact. The results show that for a static, non-moving sample, glucose can be predicted to within 10 mg/dl for the entire physiologic range (0-600mg/dl) for either laser wavelength (523nm or 635nm). In the presence of moving birefringence, each individual wavelength produced standard errors on the order of a few thousand mg/dL. However, when the two wavelengths are combined into the developed model, this error is less than 20mg/dL. The approach shows that multiple wavelengths can be used to drastically reduce the error in the presence of a moving birefringent sample. This research also shows promising preliminary results that the error is less than 25mg/dl in presence of a motion induced cornea birefringence artifact in NZW rabbits?? eyes.