Structural imaging of conjunctival filtering blebs in XEN gel implantation and trabeculectomy: a confocal and anterior segment optical coherence tomography study

Purpose To describe and compare the conjunctival filtering bleb features after XEN gel implantation and trabeculectomy using anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscopy (IVCM). Methods Fifty-two patients who underwent completely successful trabeculectomy (24 eyes) or completely successful XEN gel implantation (28 eyes) were consecutively enrolled. At the sixth-month follow-up, filtering blebs were analyzed with AS-OCT and IVCM. The main outcomes were the following: (i) bleb-wall epithelium cyst-like structure density and area (BECSD, BSCSA), (ii) bleb-wall sub-epithelium cyst-like structure density and area (BSCSD, BSCSA,), (iii) bleb-wall thickness (BT), (iv) bleb-wall epithelial thickness (BET), (v) bleb-wall reflectivity (BR), and (vi) bleb height (BH), for AS-OCT. Mean microcyst density (MMD) and area (MMA) and stromal meshwork reflectivity (SMR) were the IVCM outcomes. Results Six-month intraocular pressure was 11.46 +/- 3.09 and 10.06 +/- 3.39 mmHg in the XEN gel implantation and trabeculectomy, respectively (p > 0.05). At AS-OCT, XEN gel blebs showed lower BH, BT, BET, BR, (p < 0.001), and BECSA values (p < 0.005), and a higher BECSD (p < 0.05) compared with trabeculectomy blebs. At IVCM, MMA and SMR values were lower in the XEN gel implantation, compared with trabeculectomy (p < 0.05). BECSD and BSCSD negatively correlated with BR (p < 0.01; r = - 0.110; p < 0.01; r = - 0.249), whereas BR strongly correlated with SMR (p < 0.001; r = 0.819). Conclusion Successful filtering blebs after XEN gel implantation appeared flatter and thinner, with a higher number of epithelial cysts and a hypo-reflective bleb wall compared with trabeculectomy. These aspects may depend on the different intra-operative tissue manipulation and/or on different aqueous humor dynamics in the sub-conjunctiva between surgeries.