Abstract
Purpose :
Filtering blebs from glaucoma drainage devices (GDD) form too posteriorly for direct observation. The purpose of this study was to evaluate magnetic resonance imaging (MRI) features of different GDD and explore clinical correlations.
Methods :
Cross-sectional study of ocular, GDD and bleb morphology using a 3-Tesla MRI scanner (Philips Medical Systems, Netherlands) with an 8-channel head coil in consecutive glaucoma patients implanted with one of 4 distinct GDD: Ahmed Glaucoma Valve FP7 (AGV) and Ahmed ClearPath 350mm2 (ACP; both New World Medical, USA), Baerveldt Glaucoma Implant 350mm2 (BGI; Abbott Medical Optics, USA) and Paul Glaucoma Implant (PGI; Advanced Ophthalmic Innovations, Singapore). Forty-four patients were recruited but 13 were excluded due to inability to undergo quality MRI. Clinical data was retrieved from patient files. Statistical analysis was performed with Prism 8 (GraphPad Software, San Diego, CA).
Results :
A total of 36 eyes from 30 patients aged 57±20 years (mean±SD) were included in this study. Seven eyes had been implanted with the AGV (19%), 8 with ACP (22%), 5 with BGI (14%) and 16 with PGI (44%). Orbital MRI was performed 2,4±2,1 months after GDD implantation. Average total bleb volume was 563±390mm3, with no significant difference among different GDD (p=0,1223). Bleb volume did not correlate with intraocular pressure (IOP) at any timepoint (pre-operative, time of MRI, last follow-up; p>0,1524, all comparisons), with time from surgery to MRI (p=0,5590) or with axial length (p=0,3398). A double-layered bleb was observed in 94% of eyes (n=34), the layers separated by the GDD endplate. Inferior blebs (between the sclera and the endplate undersurface) were significantly larger with the PGI than with the remaining GDD (380±205 vs. 193±161mm3; p=0,0043) and also larger with non-valved GDD (BGI, PGI and ACP, collectively) versus the AGV (318±202 vs. 101±64mm3; p=0,0086). Flattening of the scleral bed underneath the endplate was a common finding in eyes with non-valved GDD (n=15, 52%; absent in all AGV patients) and was associated with larger blebs (observed in 78% of blebs in volume quartile 75-100; p=0,0049).
Conclusions :
Double-layered blebs are a common finding with GDD filtering blebs. Bleb morphology seems to be independent of IOP or time from surgery, but dependent on the type of GDD, with non-valved devices (particularly the PGI) forming larger inferior blebs which commonly flatten the underlying sclera.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.