Assessment of Filtration Bleb and Endplate Positioning Using Magnetic Resonance Imaging in Eyes Implanted with Long-Tube Glaucoma Drainage Devices

Abstract

BackgroundTo evaluate ocular fluid filtration and endplate positioning in glaucomatous eyes with long-tube glaucoma drainage devices (GDDs) using magnetic resonance imaging (MRI) and the effects of various factors on postoperative intraocular pressure (IOP).MethodsThis observational case series included 27 consecutive glaucomatous eyes (18 men, 7 women; mean age ± standard error, 63.0±2.0 years) who underwent GDD implantation (n = 8 Ahmed Glaucoma Valves [AGV] and n = 19 Baerveldt Glaucoma Implants [BGI]). Tubes were inserted into the pars plana in 23 eyes and anterior chamber in 4 eyes. Six months postoperatively, high-resolution orbital images were obtained using 3-Tesla MRI with head-array coils, and the filtering bleb volume, bleb height, and distances between the anterior endplate edge and corneal center or limbus or between the endplate and orbital wall were measured.ResultsIn MR images obtained by three-dimensional fast imaging employing steady-state acquisition (3D-FIESTA) sequences, the shunt endplate was identified as low-intensity signal, and the filtering bleb was identified as high-intensity signals above and below the endplate in all eyes. The 6-month-postoperative IOP level was correlated negatively with bleb volume (r = -0.4510, P = 0.0182) and bleb height (r = -0.3954, P = 0.0412). The postoperative IOP was significantly (P = 0.0026) lower in BGI-implanted eyes (12.2±0.7 mmHg) than AGV-implanted eyes (16.7±1.2 mmHg); bleb volume was significantly (P = 0.0093) larger in BGI-implanted eyes (478.8±84.2 mm3) than AGV-implanted eyes (161.1±52.3 mm3). Other parameters did not differ.ConclusionsThe presence of intraorbital/periocular accumulation of ocular fluid affects postoperative IOP levels in eyes implanted with long-tube GDDs. Larger filtering blebs after BGI than AGI implantations explain lower postoperative IOP levels achieved with BGI than AGV. The findings will contribute to better understanding of IOP reducing mechanism of long-tube GDDs.

Evaluation of Bleb Fluid After Baerveldt Glaucoma Implantation Using Magnetic Resonance Imaging

“…These previous case series have demonstrated that filtering bleb volume is negatively correlated with postoperative IOP 7 , 8 . However, one study included eight cases with Ahmed glaucoma valve and Molteno implants 7 , whereas another study included 27 cases with Ahmed glaucoma valve and Baerveldt glaucoma implant with a 350-mm 2 or 250-mm 2 endplate 8 . IOP-lowering effect of these implants is affected by the size 9 – 11 , material 12 , and internal valve of the endplate 10 , 11 .…”

“…High-resolution orbital images were obtained using a 3 Tesla scanner (Discovery MR 750 3.0 T; GE Healthcare, Milwaukee, WI) in combination with a 32-element phased-array head coil with fast imaging sequences employing steady-state acquisition cycled phases (FIESTA-C). The imaging parameters were as follows: repetition time, 5.6 ms; echo time, 2.7 ms; field-of-view, 180 mm; matrix size, 320 × 288; and a slice thickness of 0.6 mm with an overlap thickness of 0.3 mm, resulting in an in-plane resolution of 0.56 mm × 0.63 mm 8 . Images of the coronal plane were obtained perpendicular to the plane containing both optic nerves.…”

“…Unlike the filtering bleb that results from trabeculectomies, the bleb fluid structure created by Baerveldt glaucoma implantation cannot be assessed by the instruments used in standard ophthalmic examinations such as anterior-segment optical coherence tomography or ultrasound biomicroscopy because of its posterior location. Magnetic resonance imaging (MRI) is a useful tool for noninvasively evaluating bleb fluid structure after tube-shunt surgery 5 – 8 . T2-weighted images can be used to visualize and quantify the bleb fluid around the endplate, and the bleb image is shown as a dark circumlunar band (endplate) surrounded by a pocket of water density (bleb fluid) 7 .…”

“…T2-weighted images can be used to visualize and quantify the bleb fluid around the endplate, and the bleb image is shown as a dark circumlunar band (endplate) surrounded by a pocket of water density (bleb fluid) 7 . A recent cross-sectional study using 3 Tesla MRI showed that the bleb structure consists of two fluid layers divided by the endplate 8 . These previous case series have demonstrated that filtering bleb volume is negatively correlated with postoperative IOP 7 , 8 .…”

“…A recent cross-sectional study using 3 Tesla MRI showed that the bleb structure consists of two fluid layers divided by the endplate 8 . These previous case series have demonstrated that filtering bleb volume is negatively correlated with postoperative IOP 7 , 8 . However, one study included eight cases with Ahmed glaucoma valve and Molteno implants 7 , whereas another study included 27 cases with Ahmed glaucoma valve and Baerveldt glaucoma implant with a 350-mm 2 or 250-mm 2 endplate 8 .…”