Objectives: To analyze filtering blebs after trabeculectomy by means of in vivo confocal microscopy and to correlate the images with clinical bleb appearance and function. Method: In vivo confocal microscopy using the Heidelberg Retina Tomograph/ Rostock Cornea Module (Heidelberg Engineering, Heidelberg, Germany) was performed in 53 filtering blebs in 45 patients 6 days to 30 years postoperatively. Results: In vivo confocal microscopic findings significantly correlated with good bleb function included the number of epithelia lmicrocysts (P=.03), a large total stromal cyst area (P=.009), the absence of encapsulated stromal cysts (P=.002), minimal vascularization (P=.05), and the absence of tortuous conjunctival vessels (P=.01). In contrast, a hyperreflective condensed bleb stroma was significantly associated with bleb failure (P< .001). Bleb stroma mainly consisting of a rarified collagenlike network was significantly linked to trabeculectomy performed with mitomycin C (P=.001). Epithelial and stromal inflammation were observed at a median of 1 and 4 months after surgery, respectively. Conclusions: In vivo confocal microscopy using the Heidelberg Retina Tomograph/Rostock Cornea Module permits diagnostic imaging of filtering blebs and differentiation between good and insufficient bleb function. Moreover, the postoperative inflammatory reaction can be monitored directly for adapted postoperative anti-inflammatory treatment. Objectives: To analyze filtering blebs after trabeculectomy by means of in vivo confocal microscopy and to correlate the images with clinical bleb appearance and function. Method: In vivo confocal microscopy using the Heidelberg Retina Tomograph / Rostock Cornea Module (Heidelberg Engineering, Heidelberg, Germany) was performed in 53 filtering blebs in 45 patients for 6 days to 30 years postoperatively. Results: In vivo confocal microscopic observation: Significant correlated with good bleb function included the number of epithelial lmicrocysts (P = .03), a large total stromal cyst area (P = .009), the absence of encapsulated stromal cysts (P = .002), minimal vascularization (P = .05), and the absence of tortuous conjunctival vessels (P = .01). In contrast, a hyperreflective condensed bleb stroma was Significant associated with bleb failure (P <.001). Bleb stroma consisting of a rarified collagenlike network was significantly linked to trabeculectomy performed with mitomycin C (P = .001). Epithel ial and stromal inflammation were observed at a median of 1 and 4 months after surgery, respectively. Conclusions: In vivo confocal microscopy using the Heidelberg Retina Tomograph / Rostock Cornea Module permits diagnostic imaging of filtering blebs and differentiation between good and insufficient bleb function. , the postoperative inflammatory reaction can be monitored directly for adapted postoperative anti-inflammatory treatment.