[Ultrasound biomicroscopy long-term study of filtering belbs]

To study aspect of filtering blebs by Ultrasound Biomicroscopy (UBM) and to compare it to intraocular pressure (IOP), to type of surgery performed and to the measurement of the anterior chamber angle after glaucoma surgery.

An observational study, conducted between January and December 2010 on 46 eyes of 42 patients who underwent glaucoma surgery. 17 combined surgeries (14 non-penetrating deep sclerectomy (NPDS) with phacoemulsification and 3 trabeculectomy with phacoemulsification) and 29 filtering surgeries alone (16 NPDS and 13 trabeculectomy) were performed by the same surgeon with application of mitomycin C for 1.30 minutes during surgery. After surgery, IOP was controlled at day 5, day 30 and at UBM realisation. Filtering blebs were classified according to Yamamoto's study: functional blebs (L: Low-reflective) and non-functional blebs (H: High-reflective, E: Encapsulated and F: Flattened).

Mean follow-up was 21 months (± 3.7). We noted a significant decrease in IOP, mean preoperative IOP 23.2mmHg (± 9.4), mean post operative IOP 14.7mmHg (± 3.3) (P<0.001). We identified 36 functional blebs (36L type) and 10 non-functional blebs (including 1 H, 7 F and 2 E). There was no significant morphological differences between filtering blebs after combined surgery and filtering surgery alone (P=0.072). We did not find any morphological difference between filtering blebs after trabeculectomy and NPSD (P=0.394). Blebs are significantly more functional with an IOP less or equal to 6mmHg after surgery (P=0.028). We didn't find any difference between efficacy of filtering blebs and depth of the anterior chamber angle.

Our study reports 78% of functional blebs after glaucoma surgery (mean duration of 21 months). Type of surgery does not seem to interfere with the long-term morphological type of the bleb, however the immediate postoperative IOP less than or equal to 6mmHg is a factor of good prognosis. UBM appears to be an interesting tool for monitoring patients undergoing glaucoma surgery.