Abstract: Objective To describe the evolution of filtering channels after CO2 laser-assisted sclerectomy surgery (CLASS) with ultrasonic biomicroscopy(UBM), and to evaluate the mechanism of lowering intraocular pressure in CLASS. Design Cohort study. Participants Continuous 25 patients (25 eyes) with open angle glaucoma performed CLASS from 2016 to 2017. Methods On 1, 3, 6, 12 months after CLASS, UBM were performed at the operation area of surgical eyes. And the best corrected visual acuity, intraocular pressure, visual field were also examined. Main Outcome Measures Morphology of the filtering blebs, thickness of the trabeculo-Descemet membrane (TDM), the size of the scleral reservoir (anteroposterior extent and height) and correlation coefficient between scleral reservoir size and intraocular pressure. Results On 1 month after CLASS surgery, L-type and H-type filtering blebs was 19 eyes (76%), 6 eyes (24%), respectively. On 12 months after surgery, L-type and H-type filtering blebs was 11 eyes (44%), 14 eyes (56%), respectively. On 1, 12 month after surgery, 4 eyes (16%),17 eyes (68%) showed a filtering bleb height＜1 mm, respectively. On 1, 12 month after surgery, the TDM thickness was (0.104±0.026) mm, (0.100±0.019) mm, respectively. The anteroposterior length of scleral reservoir was (2.12±1.04) mm, (1.81±0.74) mm, respectively. The height of scleral reservoir were (0.52±0.18) mm, (0.46±0.17) mm, respectively. On 12 month after surgery, the anteroposterior length and height of scleral reservoir were negatively correlated with intraocular pressure (r=-0.432, -0.523, all P＜0.05). Conclusions The filtering bleb height, scleral reservoir size gradually decreases after CLASS. The scleral reservoir stabilized on 3 months after CLASS, and the filtering blebs morphology stabilized on 6 months after CLASS. By 12 months after CLASS, the main aqueous humor drainage pathway has changed from subconjunctival filtration to internal drainage. (Ophthalmol CHN, 2020, 29: 309-314)

Key words: CO2 laser-assisted sclerectomy surgery, filtering bleb morphology, ultrasound biomicroscopy (UBM)