Conversion of Flow-restrictive Ahmed Glaucoma Valve to a Nonrestrictive Drainage Implant by Slicing the Valve Leaflets: An In Vitro Study.

PRECIS

With a newly designed blade, slicing of the Ahmed glaucoma valve (AGV) leaflets helped to convert the flow-restrictive AGV into a non-flow-restrictive device. Flow characteristics by our in-vitro study confirmed the loss of resistance of AGV valve leaflets.

PURPOSE

To describe a new blade to destroy the valve leaflets of AGV and to report the in-vitro flow characteristics of AGV after valve destruction.

METHODS

All the newly opened AGV implants and the Aurolab aqueous drainage implants (AADI, used as controls) were tested by connecting to a 27-G cannula, open manometer, digital manometer, and automated infusion pump. Data logging was done using a digital manometer at 4 Hz using computerized software. When the AGV's flow characterization reached the steady phase, their valve functionality was destroyed by disrupting the valve leaflets, using a specially designed blade. The flow characteristics after valve slicing were compared with that of AADI.

RESULTS

A total of 5 FP7 AGVs and 2 AADIs were tested. After initial resistance to flow (5, 8 mm Hg) observed in the case of AADI for 1 to 3 hours, it dropped to 1 mm Hg in both the implants. The flow-restrictive AGV showed 3 distinct phases in the flow characterization. The first phase included the transient phase followed by the steady phase wherein the pressure was 11.2±2.6 (min 7, max 14) mm Hg. The pressure resistance of the AGV dropped significantly (P<0.001) to a mean of 0.4±0.54 mm Hg (1 mm Hg in 2 devices and 0 mm Hg in 3 devices) after the valve functionality was destroyed. The average time taken for this drop in pressure resistance after valve slicing was 10.2±3.0 minutes (min 7, max 15).

CONCLUSIONS

It was possible to convert the flow-restrictive AGV into a non-flow-restrictive device by destroying the functionality of the valve leaflets. The pressure of the AGVs was similar to AADI after destroying its valve functionality.