A Novel Study Quantifying Intrinsic Dimensional Variation Among Glaucoma Drainage Devices

Purpose Variation among aqueous humor outflow from venting slits performed on glaucoma drainage device tubing often occurs even when physician technique and equipment are held constant. Our hypothesis is that there are dimensional differences within the tubing, even among the same make and model of glaucoma drainage device (GDD) implants. Methods Prior to surgical implantation, excess glaucoma drainage tubing was collected for analysis. The tubing samples were sliced horizontally, and the external tube, internal lumen, and wall dimension measurements were collected microscopically. Groups were divided based upon brand and model and then statistically analyzed using an independent t-test. A total of 28 tubes were analyzed, consisting of 7 Molteno and 21 Baerveldt implants. Results The mean external diameter for the Molteno group was 656 ± 20µm, significantly larger than the Baerveldt external diameter of 620 ± 13µm (P<0.05). The mean internal diameter among Molteno lumens was 344 ± 13µm, also statistically larger than the mean internal diameter of 309 ± 18µm for Baerveldt tubes (P<0.05). The Molteno luminal wall width varied significantly less than the Baerveldt wall, 18% versus 28%, respectively (P<0.05). The tubings' wall widths variation translated into highly significant off-centered lumens among both brands. Conclusion Our findings suggest that there are significant variations among glaucoma implant dimensions between and within the multiple makes and models. The discrepancies among tubal wall thickness and off-centered lumens are undetectable to the naked eye. Importantly, this may result in significant aqueous humor outflow variation following the creation of venting slits secondary to the found irregular luminal diameters and tube wall thicknesses.