Determination of Bleb Capsule Porosity With an Experimental Glaucoma Drainage Device and Measurement System

Abstract

IMPORTANCE Control of intraocular pressure after implantation of a glaucoma drainage device (GDD) depends on the porosity of the capsule that forms around the plate of the GDD.OBJECTIVE To compare capsular porosity after insertion of 2 different GDDs using a novel implant and measurement system. DESIGN, SETTING, AND SUBJECTSWe performed an experimental interventional study at an eye research facility in a tertiary eye care center. Testing was performed on 22 adult New Zealand white rabbits that received the experimental GDD or an existing GDD.INTERVENTIONS A new experimental GDD, the Center for Eye Research Australia (CERA) implant, was created using computer-aided design and a 3-dimensional printer. The CERA GDDs were implanted in the eyes of rabbits randomized into 1 of the following 3 groups: with no connection to the anterior chamber (n = 7), with connection to the anterior chamber for 1 week (n = 5), and with connection to the anterior chamber for 4 weeks (n = 5). In a control group (n = 5), a pediatric GDD was implanted without connection to the anterior chamber. We measured the capsular porosity using a pressure-gated picoliter pump at a driving pressure of 12 mm Hg. The animals were killed humanely for histologic study. MAIN OUTCOMES AND MEASURESPorosity of the fibrous capsule around the implant. RESULTSWe found no difference in mean (SEM) capsular porosity between the CERA (3.39 [0.76; 95% CI, 1.43-5.48] μL/min) and pediatric (4.52 [0.52; 95% CI, 3.19-5.95] μL/min) GDDs (P = .28, unpaired t test) at 4 weeks without aqueous exposure. Mean (SEM) capsular porosity of CERA GDDs connected to the anterior chamber at 1 week was 2.46 (0.36; 95% CI, 1.55-3.44) μL/min but decreased to 0.67 (0.07; 95% CI, 0.49-0.86) μL/min at 4 weeks (P = .001, unpaired t test). CONCLUSIONS AND RELEVANCEOur experimental method permits direct measurement of capsular porosity of an in situ GDD. In a comparison between an experimental (CERA) and an existing GDD, no differences were identified in capsular porosity or histologic reaction between the implants. These results suggest that the CERA GDD model can be used to test key components of glaucoma surgery and implant design.

Porosity of Bleb Capsule declines rapidly with Fluid Challenge

“…1112 The GDD was left in situ for 28 (±2) days without exposure to aqueous. By testing the implants at 28 days, the initial inflammatory process is likely to have resolved and the effect of “fluid stress” is thus (mostly) isolated from the surgical trauma and foreign body reaction.…”

“…The measurement system to record porosity employed in this study has been developed by us and been shown to be reliable and repeatable. 12 …”

“…1112 Briefly, an experimental glaucoma drainage device (“CERA GDD”) was implanted in one eye under general anesthesia. The right eye had a limbal conjunctival incision made in the superotemporal quadrant, and the implant was placed and secured there.…”

“…Using this model, porosity of the bleb capsule has been studied in the New Zealand White (NZW) rabbit model. 1112 In short, all NZW rabbits had thick capsules with very low porosity at 4 weeks when the implant had been connected to the anterior chamber and the plate had been bathed in aqueous. Histologically, bleb capsules have been reported to have marked subconjunctival/bleb capsule condensation of collagen which is (relatively) impervious.…”

Blebs, Barriers, and Bagpipes: Why is It so Hard?

“…We did this by additive 3D printing via a number of prototypes and eventually landed on a particular type and shape, using a biologically stable and compatible polymer. 6 …”