The purpose of this study was to compare a novel anterior segment optical coherence tomography (AS-OCT) bleb grading system with a clinical bleb grading system (Moorfields) and both with intraocular pressure (IOP) levels following trabeculectomy surgery. The authors developed a novel AS-OCT grading system based on bleb size and internal reflectivity. An imaging centre was tasked with masked grading of AS-OCT images acquired by multiple surgical sites at postoperative week two, postoperative months (POM) four, six and 12, respectively. The Moorfields Bleb Grading System (MBGS) was used by another independent imaging centre to grade clinical photos. The results of the two grading systems were compared and correlated with IOP. Blebs of 124 eyes were assessed in this study. Higher AS-OCT bleb grades were significantly associated with: decreased bleb height at POM4, 6, and 12 (P<0.001, 0.001, and 0.0001), increased central bleb vascularity at POM4 and 12 (P=0.0026; 0.036) and decreased maximal bleb area at POM6 and 12 (P=0.026; 0.01). A higher AS-OCT bleb grade correlated with a higher IOP at POM4 and 6 (P=0.004; 0.02), though no longer significant at POM12 (P=0.1). Increased maximum bleb vascularity was associated with increased IOP at POM4 (P=0.003) though none of the remaining MBGS parameters correlated significantly with IOP. Eyes with a final IOP of 12mmHg had significantly lower AS-OCT bleb grades at POM6 (P=0.045). The authors conclude that their novel AS-OCT bleb grading system correlated well with a number of Moorfields Bleb Grading System variables throughout the one-year postoperative period. Although the AS-OCT grades also correlated well with IOP throughout most of the postoperative period, AS-OCT was limited in its ability to predict final IOP.