Background The existing classifications for evaluating glaucoma filtering blebs rely mostly on external blebcharacteristics and the postoperative control of intraocular pressure (lOP). Internal bleb structures are not carefullyobserved. This study aimed to analyze and compare glaucoma filtering bleb morphology using slit-lamp-adapted opticalcoherence tomography (SL-OCT) and ultrasound biomicroscopy (UBM), and to classify blebs according to results andintraocular pressure.Methods We followed 29 eyes of 21 male patients and 40 eyes of 32 female patients who underwent glaucoma filtering surgery in Sixth Peoples Hospital of Shanghai, between 2002 and 2006. The blebs were imaged using SL-OCT and UBM and classified according to the intrableb morphology and control of lOP after surgery. A Fishers exact test was used to compare the sensitivity for predicting a functioning bleb differed significantly between SL-OCT and UBM. A Fishers exact test was also used for morphological analysis of the trabeculectomy blebs based on SL-OCT.Results In the 69 eyes, there were 45 (65.2%) functioning blebs and 24 (34.8%) non-functioning blebs. We classified the blebs into four categories on the basis of SL-OCT images: diffuse, cystic, encapsulated and flat. Diffuse and cystic blebs were typically functional, whereas the other two types were always non-functional. The sensitivity of SL-OCT for predicting a functioning bleb was 92.7% (38/41 eyes) and specificity of predicting a non-functioning bleb was 83.3% (20/24 eyes). By contrast, sensitivity of UBM was 66.7% (30/45 eyes) and specificity was 75.0% (18/24 eyes). The sensitivity for predicting a functioning bleb differed significantly between the two techniques (P=0.003).Conclusions SL-OCT provides high-axial-resolution images of anterior segment structures. The non-contact approach of SL-OCT enables visualization of intrableb structures at any time after surgery. SL-OCT has greater sensitivity and specificity than UBM in evaluating filtering bleb function. The morphological classification supported the assessment of bleb function and could provide objective data for evaluating the outcome of antiglaucoma surgery or the need for a second procedure.