The Measurement of Flow Resistance in Drainage Implants Using Various Tube Ligation Methods

ABSTRACT

PURPOSE: To evaluate the flow resistance though the tube in a glaucoma drainage implant using various tube ligation methods. METHODS: To measure the flow resistance, the following tube ligation methods were designed and tested: Type 1: no ligation of Ahmed valve tube. Type 2: ligation of Ahmed valve tube with 8-0 Vicryl. Type 3: ligation of Molteno tube and a 6-0 Vicryl as an intra-luminal stent with 8-0 Vicryl. Type 4: ligation of Ahmed valve tube and three strands of 8-0 nylon as extra-luminal stents with 8-0 Vicryl. Type 5: ligation of Ahmed valve tube and a 6-0 Prolene as an extra-luminal stent with 8-0 Vicryl followed by removal of the Prolene for partial ligation. RESULTS: The pressure was maintained under 0.143 mm Hg in type 1. In type 2, the pressure increased to 6.688 mm Hg and dropped to approximately 6.384 mm Hg. In type 3, the pressure was maintained at 5.396 mm Hg which decreased to 3.572 mm Hg after stent removal. In type 4, the pressure was maintained at 5.700 mm Hg which dropped to 5.472 mm Hg after the 1st stent removal, to 5.016 mm Hg after the 2nd stent removal and to 4.180 mm Hg after the 3rd stent removal. In type 5, the pressure increased to 6.384 mm Hg and decreased to 5.624 mm Hg. CONCLUSIONS: The tube ligation along with extra-luminal stents followed by staged removal may provide prevention of hypotony and staged control of intraocular pressure after a glaucoma implant operation.