Intraluminal Stent Optimization for the Baerveldt Glaucoma Implant: An Experimental Study

Our laboratory study determined the approximate suture diameter for use in intraluminal stenting of the Baerveldt glaucoma implant (BGI) to prevent postoperative hypotony. Commercial 3-0 monofilament nylon sutures which are commonly used may vary significantly outside of this diameter.

Postoperative hypotony is a complication of surgical treatment of glaucoma using the BGI. One method utilized to prevent early postoperative hypotony is intraluminal stenting of the implant with monofilament sutures. The present study attempted to determine optimal stent diameter in microns for 3-0 monofilament sutures to reduce outflow and thereby reduce the risk of postoperative hypotony using the BGI.

A laboratory bench model of the anterior chamber was utilized to measure the outflow rate of balanced salt solution through the BGI at pressures of 20 and 40 mm Hg while utilizing commercially available 3-0 monofilament nylon stents of various diameters. The BGI tube has an inner diameter of 300 µm. In addition, 3-0 nylon sutures were studied for variability by measuring the diameters at 10 equally spaced points along the length of each sample using a digital micrometer.

Average experimental flow rates decreased with increasing intraluminal stent diameter and increased with increasing pressure. An intraluminal stent diameter of 250 µm yielded a flow rate of 40 µL/min at a nominal pressure of 20 mm Hg. Diameters of the tested 3-0 monofilament nylon sutures were all within the United States Pharmacopeia diameter range of 200 to 250 µm, but diameters varied significantly depending on the manufacturer.

In our laboratory model, the optimal stent diameter to reduce aqueous flow to a level approaching the normal aqueous production is at least 250 µm. Secondarily, commercially available 3-0 monofilament nylon suture materials showed variable diameters within the United States Pharmacopeia diameter range.