Imaging of scar tissue in the filtering bleb by anterior-segment polarization-sensitive OCT

Abstract

Purpose : Wound healing and scarring in filtering bleb created by trabeculectomy have important roles in decreased functioning of the filtering bleb, although these changes cannot be detected in standard imaging methods. The purpose of this study is to demonstrate anterior-segment polarization-sensitive optical coherence tomography (AS-PS-OCT) for visualization of the filtering bleb and healthy anterior eye segment.

Methods : A prototype AS-PS-OCT with a swept source at 1.3 µm wavelength was developed. Anterior segment around the angle was measured in four healthy human eyes, and filtering blebs of two glaucomatous human eyes that had nonfunctioning filtering bleb were measured. PS-OCT data were processed using Cloude-Pottier decomposition to estimate unbiased local phase retardation of birefringent tissue and to calculate entropy that shows randomness of polarization property. In addition, attenuation coefficient image was calculated and used to create composite images with the phase retardation or entropy images.

Results : In all healthy eyes, conjunctiva and sclera showed weak and moderate phase retardations, respectively (Fig. 1(c)). The composite image in Fig. 1(d) was effective to visualize both light scattering and birefringence of the tissues in Fig. 1(b) and (c), respectively. Entropy images in Fig. 1(e) and (f) showed low, moderate and high randomness of polarization properties in conjunctiva, sclera and uvea, respectively. In all glaucomatous eyes, regions with high phase retardation were found in the bleb wall, indicating scar tissue with highly organized collagen fibers. In Fig. 2(c) and (d), not only the large scar tissue at the adhesion between the bleb wall and scleral flap but also fine and diffuse scar tissues were found in the bleb wall.

Conclusions : AS-PS-OCT with the advanced signal processing provides additional contrast in both healthy tissue and scarred filtering bleb. The composite images using the attenuation coefficient enabled comprehensive understanding of the tissue properties in light scattering and birefringence.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Figure 1: Images of the healthy anterior eye segment. OCT intensity (a), attenuation coefficient (b), local phase retardation (c), composite image (d) of (b) and (c), entropy (e), composite image (f) of (b) and (e) are shown.

 

Figure 2: Images of the filtering bleb. The notation is same as Fig. 1.