PRéCIS:: Analysis of filtering bleb morphology using swept-source 3-dimensional anterior segment optical coherence tomography (3D AS-OCT) indicates that phacoemulsification can negatively impact the morphology of preexisting filtering blebs. PURPOSE: To identify the cross-sectional morphologic changes in successful filtering blebs after phacoemulsification using swept-source 3D AS-OCT. MATERIALS AND METHODS: In total, 30 phakic eyes of 29 patients with successful filtering blebs after primary trabeculectomy were included in this retrospective cohort study. Success was defined as intraocular pressure (IOP)≤15 mm Hg and a>20% reduction in IOP without glaucoma medication or additional glaucoma surgery after trabeculectomy. The subjects were classified into 2 groups according to whether they had undergone phacoemulsification or not after trabeculectomy: a phaco group and a control group. Filtering blebs were examined using swept-source 3D AS-OCT and evaluated for quantitative parameters, including maximum bleb height, maximum bleb wall thickness, and the ratio of the hyporeflective space of the bleb wall. RESULTS: Sixteen eyes were assigned to the phaco group and 14 eyes to the control group. The eyes in the control group showed no significant differences in IOP or in any of the 3D AS-OCT parameters at any of the follow-up timepoints. In the phaco group, the mean IOP increased significantly after phacoemulsification (P=0.003). Furthermore, the eyes in the phaco group showed a significant decrease in maximum bleb height (P=0.030), maximum bleb wall thickness (P=0.006), and the ratio of the hyporeflective space of the bleb wall (P=0.011) between prephacoemulsification and 1-year postphacoemulsification. CONCLUSION: Phacoemulsification can have a negative impact on filtering bleb morphology, which may lead to an IOP increase.