Double-Layered Blebs Common With Glaucoma Drainage Devices

Double-layered blebs are a common finding with glaucoma drainage device (GDD) implants, according to a study published in Acta Ophthalmologica. These blebs typically form around the endplate, creating a double-layered configuration on imaging scans. The Paul Glaucoma Implant (PGI) device produces larger blebs than other GDDs, according to the report.

Researchers conducted a prospective observational study at a single center between 2019 and 2022, consisting of 36 eyes from 30 consecutive patients (mean age, 57.1 years) with glaucoma who underwent standardized GDD implantation followed by magnetic resonance imaging (MRI) at least 1 month following surgery. 

In total, 7 eyes (19%) were implanted with the Ahmed Glaucoma Valve (AGV), 5 eyes (14%) with Baerveldt Glaucoma Implant (BGI), 16 eyes (44%) with PGI and 8 eyes (22%) with Ahmed ClearPath (ACP). No significant differences were noted between groups regarding age, sex, glaucoma diagnosis, prior surgeries, baseline IOP or medication.

The researchers obtained MRI scans 85±66 days after surgery. They observed a double-layered bleb configuration in 94% of the eyes (n=34). The mean total bleb volume was 563±390mm³ and the bleb volume was inversely correlated with early post-operative IOP (day 7; r_s=−0.3326, P =.0475), but it positively correlated with IOP at 12 months (r_s=0.3592, P =.0341), the report shows. 

There was no significant difference in total bleb volume between GDD types (P =.1223). The inferior bleb volume was significantly larger in the PGI group compared with the other GDD groups (380±205 vs 193±161mm³; P =.0043). The distance from the endplate to the optic nerve was 9.5±4.0mm, which was similar in all of the GDD groups (P =.2519).

Most documented complications occurred early in the postoperative period and were self-limited. No serious sight threatening complications were reported.

“We conclude that GDDs overwhelmingly form a double-layered bleb, which should correspond, tridimensionally, to an encircling bleb around the device endplate. We also report that bleb volume may correlate with IOP control dynamically, with early bleb expansion being associated with lower IOP but larger blebs ultimately predicting higher long-term IOP,” according to the researchers. “Furthermore, we posit that an unstented and unvalved GDD such as the PGI produces larger blebs due to higher early outflow. Finally, a standardized 10mm implantation distance from the limbus seems to ensure a safe distance of the endplate to the optic nerve, regardless of the device.”

Study limitations include the relatively small sample size of patients, significantly more eyes were implanted with PGI devices, and the time from GDD implantation from MRI varied both within and across GDD subgroups.