Visualization of Scleral Flap Patency in Glaucoma Filtering Blebs Using OCT

Abstract

PurposeTo investigate the use of anterior segment-optical coherence tomography (AS-OCT) to visualise the aqueous outflow pathway and patency of the scleral flap in glaucoma filtration surgery blebs. DesignCross-sectional study Subjects205 filtering blebs of 112 patients with glaucoma who had undergone trabeculectomy (Trab, n = 97) or deep sclerectomy surgery (DS, n = 108) with/without mitomycin-C (MMC). MethodsSwept source AS-OCT raster slices were used to image the Trab and DS blebs in sagittal and coronal planes using a standardised protocol. Bleb appearances were classified into four categories based on the scleral flap and sclerostomy/TDW appearance; A—sclerostomy/TDW not visible, B—sclerostomy/TDW visible but scleral flap indiscriminate from sclera, C—scleral flap distinct but edges adherent to surrounding sclera, D—scleral flap edges non adherent to surrounding sclera. Surgical outcomes were classified into complete success (CS; IOP ≤18mmHg with no medications), qualified success (IOP ≤18 with medications) and failure (IOP>18mmHg). ResultsThe proportions of complete success, qualified success and failure in the Trab and DS cohorts were 45.0% and 29.6%, 33.0% and 31.5%, and 22.0% and 38.9% respectively, with a median post-operative follow up of 8.4 years (SD 7.9, IQR 3.2-9.0). In qualified success and failed blebs, category C (Trab, 53.7%; DS, 52.5%) accounted for the majority of scleral flap appearances, followed by categories A and B. Category D (86.0%; 71.9%) accounted for the majority of appearances in Trab and DS blebs with complete success. There was a significantly greater proportion of MMC use in categories C and D compared to categories A and B in both Trab (p < 0.0001) and DS (p = 0.02) cohorts, demonstrating the association of intraoperative MMC use with increased patency of the scleral flap. ConclusionSwept source AS-OCT may be used to visualise the position and patency of the sclerostomy/TDW and scleral flap in relation to surrounding structures in both sagittal and coronal planes. While free scleral flap edges are primarily correlated with MMC use, it may also correlate with surgical success. AS-OCT may be used to complement subjective bleb grading at the slit-lamp in the assessment of filtering blebs.