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Filtering blebs vary in appearance, vascularity, wall thickness, presence of conjunctival microscysts, fluid-filled cystic space and fibrosis. Leung et al. (146) investigated bleb morphology and development using non-invasive, non-contact, time-domain optical coherence tomography (OCT). A series of 14 Chinese patients undergoing trabeculectomy with mitomycin C (2-3 minutes) were enrolled and imaged using the Visante System developed by Carl Zeiss Meditec, Inc. A 1310 nm superluminescent diode yielded an axial resolution of 18 microns. The authors developed criteria for OCT assessment of blebs through their observation of the blebs they enrolled. Diffuse blebs were characterized by pockets of fluid collections, thin bleb wall thickness, and visible suprascleral fluid. Cystic blebs had a large hyporeflective spaces. Non-functioning flat blebs or encapsulated blebs have no subconjunctival fluid and thick bleb walls. OCT offers several advantages over UBM for assessment of bleb morphology, particularly in the early stages of bleb formation. OCT is non contact and avoids the potential changes in anatomy that may be caused by UBM imaging. It is highly likely that the improved resolution of the OCT will allow for better identification of conjunctival microcysts and the role that they play in filtration. This use of this technology will improve our understanding of the healing stages of trabeculectomy and interventions that can improve filtration.