Abstract
Purpose :
Refractory glaucoma treated with a GDD often uses the venting slit technique. The incision of uniform lumen venting slits can allow for good intraocular pressure (IOP) regulation in the early post-operative period. However, a large variation of IOP has been observed among patients where technique and equipment are standardized. Our quality-control study tested the hypothesis that this discrepancy is due to intrinsic implant dimensional inconsistencies producing variation in outflow from the venting slits.
Methods :
Following GDD implantation, the trimmed excess tubing was collected for investigation. Baerveldt and Molteno GDD’s were analyzed (n=20). Prior to measurement, each sample was carefully cut to a length of 2mm to prevent tubal distortion. Using a microscope (Olympus BX60) and measurement program (DinoCapture 2.0), the dimensions were recorded down to ± 5µm specificity with two measurements of each sample’s luminal diameter, external diameter, and wall thickness. An independent T-test was used for statistical analysis to assess for variation within and between brands.
Results :
Between brands, the implants were similar in total outer diameter as the Molteno-245 and Baerveldt-350 tubes measured 606 ± 17µm and 615 ± 8µm (mean ± standard deviation), respectively. The Molteno lumen diameters were larger (313 ± 27µm) compared to the Baerveldt (284 ± 7µm). Lastly, the Molteno walls were thinner compared to the Baerveldt, measuring 145 ± 20.6µm and 169 ± 18µm, respectively. Findings of high variation in wall thickness around the travel of the outer circumference were common (Figure 1 and 2).
Conclusions :
Our results support the hypothesis that there is a large variation among the dimensions of GDD tubing, even in the same make and model as indicated by the large standard deviations (SD). Notably, the Molteno tubes had nearly twice the SD across all three dimensions compared to the Baerveldt brand. Additionally, the variation in wall thickness translated into off-centered lumens, as illustrated by Figure 2. These internal dimension inconsistences with GDD implants prevent ophthalmologists from cutting knowingly accurate venting slit depths into the tubing. This likely leads to the variable drainage from venting slits and variable post-operative intraocular pressures, even when the same technique of making a venting slit and same brand and model of GDD are used.
This is a 2020 ARVO Annual Meeting abstract.