Dual-wavelength polarimetry for monitoring glucose in the presence of varying birefringence.

In a continuing effort to develop a noninvasive means of monitoring glucose levels using the aqueous humor of the eye, a dual-wavelength system is developed to show that varying birefringence, similar to what is seen with a moving cornea, can be compensated. In this work, a dual-wavelength, closed-loop system is designed and a model is developed to extract the glucose concentration information. The system and model are tested using various concentrations of glucose in a birefringent test cell subject to motion artifact. The results show that for a static, nonmoving sample, glucose can be predicted to within 10 mg/dl for the entire physiologic range (0 to 600 mg/dl) for either laser wavelength (523 or 635 nm). In the presence of moving birefringence, each individual wavelength produces 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 20 mg/dL. The approach shows that multiple wavelengths can be used to drastically reduce the error in the presence of a moving birefringent sample and thus may have the potential to be used to noninvasively monitor glucose levels in vivo in the presence of moving corneal birefringence.