Modeling the corneal birefringence of the eye toward the development of a polarimetric glucose sensor

Optical polarimetry for monitoring glucose concentration in the aqueous humor of the eye as a potential noninvasive means of assessing blood glucose has promise, but the realization of such an approach has been limited by noise from time-varying corneal birefringence due to motion artifact. Modeling the corneal birefringence of the eye is critically important toward understanding the overall effect of this noise source compared to other changes in the signal, and can aid in design of the polarimetric system. To this end, an eye model is introduced in this work that includes spatially varying birefringence properties of the cornea. The degree of birefringence and the fast axis orientation is calculated as a function of beam position on the anterior chamber. It is shown that the minimum change in polarization vector orientation occurs for beam position near the midpoint between the corneal apex and limbus. In addition, the relative wavelength independence of motion artifact is shown in the same region. The direct consequence of these findings are that a multiwavelength polarimetric system can potentially be utilized to eliminate the effect of time-varying corneal birefringence, and that eye coupling is optimal at the midpoint between the apex and limbus.