The significance of ultrasound biomicroscopy in the objective assessment of post-trabeculectomy bleb success

Purpose: To compare clinical characteristics and ultrasound biomicroscopy (UBM) measurements of cases with functional and non-functional blebs, and to identify potential risk factors capable of affecting UBM parameters. Methods: Thirty-one patients aged 40–79 were included. Following trabeculectomy, cases were divided into two groups as those with functional bleb (Group 1, n = 20) and those with non-functional bleb (Group 2, n = 11). UBM was performed. Results: In Group 1 compared to Group 2, lower postoperative intraocular pressure (IOP) (12.1 ± 1.7 vs 27.2 ± 3.2 mmHg, p < 0.001), greater bleb height (1.0 ± 0.2 vs 0.5 ± 0.3 mm, p < 0.001), greater scleral route visibility [16/20 (80%) vs 4/11 (36.4%), p = 0.023] and lower bleb reflectivity (1.8 ± 0.2 vs 2.4 ± 0.4, p = 0.015) were observed. In Group 1, as postoperative IOP decreased, bleb height and scleral route visibility increased ( r = −0.387, p = 0.029 for bleb height; r = −0.374, p = 0.033 for scleral route), and bleb reflectivity decreased ( r = 0.359, p = 0.042). In Group 1, as duration of preoperative antiglaucoma drug use increased, bleb reflectivity increased ( r = 0.348, p = 0.046). Preoperative IOP and number of preoperative antiglaucoma drug use had no effect on UBM parameters in groups ( p > 0.05). Conclusion: UBM is useful in assessing bleb success. Lower bleb reflectivity, greater bleb height and greater scleral route visibility indicate that the bleb is functional. To the best of our knowledge, this is the first study investigating effects of preoperative IOP, number and duration of preoperative antiglaucoma drug use on UBM parameters. In cases with functional bleb, duration of preoperative drug use affects only bleb reflectivity, while postoperative IOP affects bleb height, scleral route visibility and bleb reflectivity.