Needle Perforations of Molteno Tubes

Abstract

To investigate the effects of needle perforation of proximal Molteno tubes on intraluminal pressure in a constant flow system.

Balanced salt solution was infused at a rate of 2 μL/min through nonexpansile silicon tubing attached to a manometric reservoir, pressure transducer, and an occluded proximal Molteno glaucoma drainage device tube. As the intraluminal pressure rose to approximately 30 mm Hg, the tube was perforated once with needles ranging in size from 23G to 29.5 G (disposable insulin syringe). Intraluminal pressure was measured continuously throughout each test run for an average of 71 minutes each.

The average stable intraluminal pressure ranged from 25 mm Hg for 29.5-G perforation to 15 mm Hg for 23-G perforation. The lowest single pressure recorded ranged from 3 mm Hg for 23-G perforations to 17 mm Hg for 29.5-G perforations. Pressures of less than 15 mm Hg were recorded in more than 60% of the 23-G and 25-G perforations, less than 20% of the 27-G perforations, and none of the 29.5-G perforations.

At a flow rate of 2μL/min of balanced salt solution, 23-G and 25-G needle perforations of silicone glaucoma drainage device tubes produce intraluminal pressures in vitro, which may result in low intraocular pressures. Immediate postoperative hypotony risk can be reduced if a smaller needle perforation is used.