Assessment of Closing Pressure in Silicone Ahmed FP7 Glaucoma Valves
2008; Lippincott Williams & Wilkins; Volume: 17; Issue: 6 Linguagem: Inglês
10.1097/ijg.0b013e3181622532
ISSN1536-481X
AutoresEdward B. Moss, Graham E. Trope,
Tópico(s)Retinal and Macular Surgery
ResumoPurpose To measure closing pressure in a series of new Model FP7 silicone Ahmed Glaucoma Valves (AGVs), using an in vitro gravity-driven system, in which closing pressure was measured directly from a dual manometer/pressure reservoir. Method A straight length of tubing served as an open manometer, which connected via a 3-way stopcock to the inlet of the AGV submerged under 1.5 cm of balanced saline solution (BSS). Six AGV were assessed in 5 sequential trials and the mean inlet pressure at 90 minutes was recorded as the closing pressure. After testing, a single valve was primed a second time using greater force and retested. Control trials were performed with a submerged 26-G cannula opening directly into the BSS bath. Results At 90 minutes, the 6 valves equilibrated at a mean inlet pressure of 7.1 mm Hg, with a range from 1.4 to 13.5 mm Hg. Closing pressures at or less than 5 mm Hg were measured in half (3/6) of the valves tested. The average flow of BSS across the valves in the final 30 minutes was less than 1.5×10−2 μL/min. In the single valve reperfused under greater pressure, the closing pressure increased. Conclusions Model FP7 AGVs, in vitro, exhibit significant variability in closing pressure, with half closing at intraocular pressures considered potentially problematic in clinical situations. The results of the high-pressure perfusion experiment suggest that more research into the priming process is required so a precise description can be developed for surgeons.
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