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Purpose: To investigate the outflow characteristics of silicone tubes with intraluminal stents used in membrane-tube (MT) type glaucoma shunt devices (MT-device). Methods: The silicone tubes used in MicroMT (internal diameter of 100 µm with 7-0 nylon intraluminal stent) and Finetube MT (internal diameter of 200 µm with 5-0 nylon intraluminal stent) were connected to a syringe-pump that delivered a continuous flow of distilled water at flow rates of 2, 5, 10, and 25 µl/min. The pressures and resistances of tubes were measured at a steady flow rate with full-length, half-length, and absence of intraluminal stents. Results: At flow rates between 2 and 25 µl/min, the mean outflow resistance of tubes ranged from 3.0 ± 1.9 to 3.8 ± 1.7 mmHg/µl/min with a full-length intraluminal stent, 1.8 ± 1.1 to 2.2 ± 1.1 mmHg/µl/min with a half-length intraluminal stent, and 0.1 ± 0 to 0.2 ± 0 mmHg/µl/min without an intraluminal stent. At a physiologic state with a flow rate of 2 µl/min and episcleral venous pressure of 6 mmHg, the mean pressures of tubes were expected to be 13.2 ± 3.0, 10.5 ± 2.4, and 6.4 ± 0.2 mmHg in MicroMT with full-length, half-length, and absence of intraluminal stents, respectively, and 12.5 ± 3.9, 9.6 ± 2.4, and 6.2 ± 0.2 mmHg in Finetube MT with full-length, half-length, and absence of intraluminal stents, respectively. Variance of the pressure decreased according to the intraluminal stent retraction (P < 0.01). Conclusion: The tubes with intraluminal stents used in the MT-device showed safe (with a minimal risk of postoperative ocular hypotony) and effective (sufficient for intraocular pressure control) outflow characteristics. |
