Comparison of intensity, phase retardation, and local birefringence images for filtering blebs using polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomography (PS-OCT) allows the recording of depth-resolved polarimetric measurements. It has been reported that phase retardation and local birefringence images can noninvasively detect fibrotic area in blebs after glaucoma surgery. Evaluation of scar fibrosis in blebs is important not only for predicting bleb function, but also for planning revision trabeculectomy. Herein, we characterize the intensity, phase retardation, and local birefringence images of blebs using PS-OCT. A total of 85 blebs from 85 patients who had undergone trabeculectomy were examined. Both phase retardation and local birefringence images detected fibrotic changes in blebs after glaucoma surgery. Phase retardation images detected slight fibrotic change during the early stage after surgery, whereas local birefringence images showed localized fibrotic tissue. There are two main patterns of local birefringence image changes in blebs: plate-like birefringence changes and diffuse changes. The area of plate-like birefringence change was significantly larger in poorly functioning blebs and is thus correlated with bleb function. These data suggest that the plate-like fibrotic change evaluation by PS-OCT may be useful not only for noninvasive evaluation of fibrotic scar tissue in blebs, but also for developing strategies for revision trabeculectomy.