An ultrasound biomicroscopic study of filtering blebs after mitomycin C trabeculectomy

Purposes: To investigate the relation between filtering bleb function and ultrasound biomicroscopic images, and to establish a new classification system for filtering blebs according to these images. Methods: After trabeculectomy with mitomycin C, the filtering blebs of 117 eyes from 117 patients with various types of glaucoma were examined using ultrasound biomicroscopy. Four parameters of the images - intrableb reflectivity, visibility of the route under the scleral flap, formation of a cavernous fluid-filled space, and bleb height - were correlated with the level of intraocular pressure (IOP). Results: Reflectivity inside the bleb and visibility of a route under the scleral flap were highly associated with IOP control. Blebs were classified into four categories according to the four measured parameters: type L (low-reflective), type H (high-reflective), type E (encapsulated), and type F (flattened). Eyes with good IOP control had mainly type L blebs. Type E and type F blebs were seen mostly in eyes requiring additional medication. Conclusion: The structure inside a filtering bleb is visible by ultrasound biomicroscopy, and bleb function is significantly associated with its ultrasound biomicroscopic image in eyes trabeculectomized with adjunctive mitomycin C.