Local birefringence imaging of ocular tissue by multifunctional Jones matrix OCT

Abstract

 

Purpose

 

Polarization sensitive (PS-) OCT has been utilized to visualize the birefringence of ocular tissue. However, PS-OCT did not directly visualized the birefringence, but visualized phase retardation (PR). PR is a depth-oriented cumulative effect to light originated from the tissue birefringence. Although it was frequently believed that the depth derivative of PR is the birefringence, it is true only if the polarization axis orientation, i.e., the orientation of the fibrous structure, of tissue is uniform along the depth. This condition is satisfied with nerve fiber layer, but no for other tissues.<br /> <br /> We present a new type of PS-OCT, so called Jones matrix (JM-) OCT, which is capable of correctly visualizing tissue birefringence even the axis orientation is not uniform. The limitation of PR imaging and the advantages of birefringence are extensively discusses in experimentally and theoretically.

 

Methods

 

A custom-built JM-OCT was utilized. This device uses a 1060 nm probe, the measurement speed is 100,000 A-lines/s and the depth resolution is 6.2 uμm. Volumetric scanning was performed to cover 6 mm x 6 mm area for 6.6 s. In this method, a depth- cumulative Jones matrixes are obtained first. Subsequently, depth-localized Jones matrixes and the tissue birefringence are derived. This raw birefringence is significantly distorted by measurement noise. So it is corrected by using a numerical estimation algorithm based on Bayesian theory. This process finally provides 3-D distribution of fully quantitative tissue birefringence. 14 cases were examined, which includes dry- and wet-AMD, polypoidal choroidal vasculopathy (PCV), and also pathologic myopia.

 

Results

 

Fig. 1 shows an example of PCV with a huge fibrosis. Its PR image (b) shows a non-uniform pattern in the fibrotic region, while this region is appeared with uniformly high birefringence (green) in the birefringence image (c). Since the fiber orientation in this region is not uniform, the appearance of PR might be an artifact, while the birefringence image is rational. In Fig. 2(c), the sclera of pathologic myopic eye is appeared with two distinctive domains of birefringence (low-blue and high-green). This domain structure is not clearly shown in PR (b).

 

Conclusions

 

The local birefringence images clearly visualized birefringence domains of posterior eye.  

 

OCT (a), PR (b) and birefringence tomography (c) of PCV.

 

 

Fig. 2: A case of pathologic myopia.