Assessment of intraorbital bleb formation and endplate positioning by using magnetic resonance imaging in eyes implanted with long tube glaucoma drainage devices

Abstract

Purpose: To evaluate the intraorbital status of ocular fluid filtration and endplate positioning in glaucoma eyes that implanted with long tube glaucoma drainage devices (GDDs), by using magnetic resonance imaging (MRI). Possible effects of various MRI-measured factors on post-surgical intraocular pressure (IOP) level also were assessed.

Methods: This prospective study included consecutive 27 refractory glaucoma eyes of 25 subjects (mean age ± SEM, 63.0±2.0 years; 18 males and 7 females) who were received GDD implantation surgeries; 8 and 19 eyes were implanted with Ahmed Glaucoma Valve (AGV) (plate size, 184 mm²) and Baerveldt Glaucoma Implant (BGI) (plate size, 250 or 350 mm²), respectively. Tube was inserted into posterior chamber or pars plana in 23 eyes and anterior chamber in 4 eyes. In each subject, high-resolution orbital images were obtained using 3-T MRI(Signa HDxt3.0T, GE Healthcare, Milwaukee, USA) with a head array coil, at 6 months after the surgery. Filtering bleb volume, depth of anterior endplate edge from the central corneal surface, and distance between endplate and orbital wall were measured on obtained MRI images using image analysis software Image J.

Results: In T2-weighted MRI images, the shunt endplate and filtering bleb were clearly identified as low and high intensity signals, respectively, in all eyes. Post-surgical IOP level at 6 months was negatively correlated with filtering bleb volume (r=-0.4510 and p=0.0182, Spearman’s correlation analysis), while 2 other MRI-measured parameters did not correlate with post-surgical IOP. Post-surgical IOP level was significantly lower in BGI-implanted eyes (12.2±0.7 mmHg, mean ± SEM) than AGV-implanted eyes (16.8±1.2 mmHg) (p=0.0026, Mann-Whitney U test); filtering bleb volume was significantly larger in BGI-implanted eyes (478±114 mm³) than AGV-implanted eyes (161±52 mm³) (p=0.0093, Mann-Whitney U test).

Conclusions: Presence of intraorbital-periocular accumulation of ocular fluid is a parameter that affects post-surgical IOP level in eyes implanted with long tube GDDs. Larger filtering bleb formed after BGI than AGI implantations explains lower post-surgical IOP levels achieved with BGI than AGV.