OutƒPow Facility in Tube Shunt Fenestration

Abstract

Aim: Determination of the effect of varying fenestration technique, and simulated patch graft on outflow facility for Baerveldt tube.Materials and methods: Silicone tubing similar to Baerveldt implant (AMO, Santa Ana, CA) with different fenestrations techniques was connected to a digital manometer in a closed system with a fluid-filled syringe on a stand to adjust pressure. The venting slits included: (A) 4 piercings with 7-0 TG140-8 needle; (B) a 2-mm slit with a 15º blade; (C) 4 piercings with a 15º blade; (D) 9-0 Nylon on CS140-6 needle with suture stenting the fenestration.

How Many Fenestrations Should I Make When Placing a Baerveldt Glaucoma Implant? A Laboratory Study

“…Like other reports evaluating glaucoma tube shunt fenestrations, our results varied widely between each trial. [ 7 , 8 ] This may be due to microscopic variations in surgical technique resulting in a variety of differences in microarchitecture between fenestrations [Figure 2]. We found that fenestrations with the 7-0 Vicryl TG140-8 needle could take the form of a uniplanar, biplanar, or triplanar structure.…”

“…Olayanju et al characterized the outflow facility of a tube system with constant intraocular pressure and fenestrated with varying needles and blades. [ 8 ] They found that the outflow facility (mL/min/mmHg) was mainly dependent on intraocular pressure and did not significantly change by external weight on the tube (e.g., scleral patch graft). However, they made the observation that the microarchitecture of the fenestrations was widely variable; the same external forces (e.g., scleral patch graft) could either reinforce fenestration closure or hold the fenestrations open.…”

“…In theory, the scleral patch graft may apply external pressure to the tubing, either facilitating flow or blocking the fenestrations. [ 8 ] However, prior studies (Olayanju et al) simulated the presence of the patch graft with external weights and found no significant difference in outflow facility of the tubing.…”

“…Moreover, only a few published experiments evaluating the number of fenestrations and their effects on outflow facility and IOP in in vitro and ex vivo systems have been performed, with equivocal results. [ 7 , 8 ] In an in vitro study of a ligated BGI with four fenestrations using a 7-0 Vicryl TG140-8 needle, the volume of fluid egress was found to positively correlate with simulated IOP. [ 8 ] In an ex vivo study of porcine eyes, three fenestrations with a 7-0 Vicryl TG140-8 needle led to a significantly lower final IOP compared to a single fenestration after 15 min with an initial IOP of 50 mmHg.…”

“…[ 7 , 8 ] In an in vitro study of a ligated BGI with four fenestrations using a 7-0 Vicryl TG140-8 needle, the volume of fluid egress was found to positively correlate with simulated IOP. [ 8 ] In an ex vivo study of porcine eyes, three fenestrations with a 7-0 Vicryl TG140-8 needle led to a significantly lower final IOP compared to a single fenestration after 15 min with an initial IOP of 50 mmHg. [ 7 ] Additional studies are needed to evaluate the wide spectrum of fenestration possibilities and their effects on fluid egress.…”