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

Abstract

Abstract. 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.

Birefringence of the central cornea in children assessed with scanning laser polarimetry

“…5,[12][13][14][15][16][17][18][19] Although being relatively constant over the central area for any given eye, 20 corneal birefringence varies widely among individuals and eyes in both its amount (corneal retardance) and orientation (corneal azimuth). 21,22 Since light must pass through this major birefringent ocular medium before reaching the retina or any other polarization-sensitive structure of interest within the eye, polarization-related changes caused by the cornea must be dealt with.…”

Dual-wavelength polarimetric glucose sensing in the presence of birefringence and motion artifact using anterior chamber of the eye phantoms

“…9,19 The input beam diameter was fixed at 1 mm. The values used for n o and n e are 1.3760 and 1.3744 (i.e., jΔnj ¼ 1.6 × 10 −3 ).…”

“…This time-varying birefringence is the most significant source of noise when attempting polarimetric glucose sensing in the anterior chamber of the eye, wherein it confounds the signature of the optical activity of glucose by contributing a significant change in the state of polarization of the probing light. 9 Our group has quantified the effect of corneal birefringence on glucose sensing through the eye both theoretically and experimentally. 19 Although a simplified model was used in this previous work, it was clear from the research that time-varying corneal birefringence is a significant source of noise in the system.…”

“…6 As mentioned, the fibrous structure of the stroma makes the cornea birefringent, which varies spatially across the surface of the cornea. [7][8][9] Birefringence in structured materials such as linear retarders is characterized by Δn ¼ ðn e − n o Þ, which is the difference between the extraordinary and ordinary refractive indices (i.e., n e and n o , respectively). 10 In the case of the cornea, individual constituent collagen fibrils can be regarded as linear retarders with the direction of the fast axis oriented perpendicular to the fibril orientation.…”

A non-invasive photoacoustic and ultrasonic method for the measurement of glucose solution concentration

“…8,9 Cote et al also studied the correlation between the glucose levels with the depressing interference from corneal in Polarimetry. [10][11][12] But there are still two key issues not being solved for non-invasive blood glucose monitoring methodology. One is the specificity of blood glucose, the other is poor signal to noise ratio.…”