In Vitro Analysis of Pressure Resistance in the Paul Glaucoma Implant and Ahmed ClearPath 250 With and Without Polypropylene Thread Inside the Tube.

PURPOSE

Pressure resistance characteristics of the Paul glaucoma implant (PGI) and Ahmed ClearPath 250 (ACP), with and without the insertion of polypropylene thread in their tubes, were evaluated.

METHODS

The in vitro flow pressure was evaluated at varying flow rates, both with and without threads (6-0 for PGI and 4-0 or 3-0 for ACP). Cross-sectional areas of the tube lumen and thread were measured to calculate pressure resistance using the Hagen-Poiseuille equation.

RESULTS

For the PGI without the thread, the pressure remained relatively low and constant across all flow rates. In contrast, with the insertion of a 6-0 thread, there was a significant increase in pressure resistance, with the pressure increasing from 7.5 mm Hg at 1 µL/min to 43.8 mm Hg at 5 µL/min. For the ACP, the pressure resistance remained relatively constant across all flow rates without a thread and with either 4-0 or 3-0 threads. However, the pressure was higher with 3-0 threads compared with a 4-0 thread. The actual measured pressures agreed well with theoretical values in the no-thread conditions, but were consistently higher than the theoretical values in the threaded conditions.

CONCLUSIONS

Inserting polypropylene threads into the tubes of nonvalved glaucoma drainage devices significantly affects pressure resistance with various degree.

TRANSLATIONAL RELEVANCE

PGI with a 6-0 polypropylene thread may not require external tube ligation to prevent hypotony, whereas ACP with a 4-0 thread likely requires additional ligation. Using a 3-0 thread in ACP may enhance pressure resistance sufficiently to avoid tube ligation, but this requires careful clinical consideration.