Hydrodynamic properties of glaucoma drainage implants in vitro

Purpose. To develop and demonstrate a test protocol for glaucoma drainage implants. Methods. Implant devices were requested from all manufacturers representing commercially available devices. Two manufacturers did not respond. A stepping motor pump, water manometer and pressure transducer measured the drainage implant perfusing Balanced Salt Solution at 34°C. Real-time pressure at two different flow rates (High and Normal, equivalent to ~2.5 and 5.0 (iL/min) was measured on each device. Opening and/or running pressures were obtained. Facilities of outflow were calculated at steady state flow. Results (in mmHg). At high flow rates the two Ahmeds opened at 14.0, 16.0 and partially closed at 6.4,7.7. The Krupins had a biphasic response, one device partially opened at 6.5 then fully opened at 9.8. The other fully opened at 14.2. Neither closed after opening. The Bacrveldts had a low running pressure of 1.7, 2.7 versus the open control of 1.3. The Optimeds also had a low running pressure of 2.3, 2.5 versus the open control. At normal flow rates the Ahmeds opened at 11.1,12.8. One Krupin partially opened at 6.0 then fully opened at 11.6 while the other fully opened at 5.7. Neither Krupin closed after opening. The Baerveldts had a low running pressure of 1.1, 1.7 at normal flow as did the Optimeds at 1.4, 1.7. Conclusions. We have demonstrated a valid and unbiased protocol for testing glaucoma drainage implants. Based on our pilot study, the Ahrned has measurable opening pressure and true opening valve effect, but only a relative closing pressure. The Krupin was more variable, one device had partial and full opening behavior while neither showed a closing pressure. The Baerveldts and Optimeds showed only low running resistances at our jested flow rates.