Quantitative Evaluation of Phase Retardation in Filtering Blebs Using Polarization-Sensitive Optical Coherence Tomography

PURPOSE. Polarization-sensitive optical coherence tomography (PS-OCT) can detect and evaluate scar fibrosis of the filtering blebs after glaucoma surgery. Although the change in phase retardation reportedly reflects bleb function, quantitative assessment of phase retardation in ocular tissues has not been conducted. We aimed to establish quantitative methods to investigate changes in phase retardation in the blebs after surgery using PS-OCT. METHODS. Twenty-two blebs of 22 patients who had undergone glaucoma filtration surgery were consecutively examined for 4 months. Phase retardation was measured by PS-OCT and quantitatively analyzed to evaluate its relationship with bleb function based on intraocular pressure and medication use. Cross-sectional re-evaluation was also performed for a previous data set of 153 blebs of 122 patients. RESULTS. In consecutive measurements, all blebs showed a low phase retardation value and good bleb function until 2 weeks. One month postoperatively, the phase retardation value was significantly increased, whereas bleb function was still good. The phase retardation value at 1 month postoperatively was significantly correlated with bleb function at 4 months postoperatively. While 55.6% of blebs with a high phase retardation value at 1 month subsequently lost function, only 7.7% with a low phase retardation value had bleb failure. In the cross-sectional re-evaluation, the quantitatively evaluated phase retardation value was highly correlated with bleb function (b = 0.770, P < 0.001). CONCLUSIONS. An increase in phase retardation preceded deterioration of bleb function. The change in phase retardation may provide a prognostic metric for bleb function in the early stage after surgery.