Porosity of Bleb Capsule declines rapidly with Fluid Challenge

Abstract

IntroductionThe porosity of the fibrous capsule around a glaucoma drainage device (GDD) may be the most important functional attribute. The factors that determine capsular porosity are not well understood. Failed GDD surgeries are usually associated with thick impervious capsules and components of aqueous have been implicated in this process.PurposeIn this study, we interrogated the effect of passage of nonaqueous fluid on capsular porosity in mature (but aqueous naïve) blebs in a previously reported GDD model (the “Center for Eye Research Australia Implant”).Materials and methodsThe study was performed at two centers using 17 New Zealand White (NZW) rabbits. An experimental GDD was implanted into the subconjunctival space but without connection to the anterior chamber. After 28 days, balanced salt solution (BSS) was passed through the implant for 30 to 40 minutes at 12 mm Hg. Capsular porosity was measured as flow (μL/min) at a constant pressure. Porosity of the capsule was retested at 3 and 6 days.ResultsThere was a marked reduction in capsular porosity within 3 days of exposure to BSS (fluid challenge). Even though the baseline porosity was significantly different in the two groups (3.00 ± 0.5 μL/min and 29.67 ± 12.12 μL/min, p < 0.001), the effect of passage of BSS was similar. Capsular porosity fell by approximately 80% in both groups from baseline after single BSS challenge. Capsular thickness was significantly less in Advanced Eye Center (AEC) rabbits at baseline. There was no change in the capsular thickness before and after single fluid challenge.ConclusionPassage of BSS at physiological pressures for under 40 minutes caused marked reduction in the porosity of the fibrous capsule within 3 days. This was not associated with any significant thickening of the fibrous capsule within this time frame.How to cite this articlePandav SS, Ross CM, Thattaruthody F, Nada R, Singh N, Gautam N, Beirne S, Wallace GG, Sherwood MB, Crowston JG, Coote M. Porosity of Bleb Capsule declines rapidly with Fluid Challenge. J Curr Glaucoma Pract 2016;10(3):91-96.

Evaluation of the Ultrastructural and In Vitro Flow Properties of the PRESERFLO MicroShunt

“…Maintaining the anatomy of the Tenon capsule seems to be an important factor in controlling the outflow in the early postoperative period with this device. The sequence of AH outflow control by the subconjunctival tissue response might well be as follows: the mere presence of the fluid, 33 as well as the presence of inflammatory mediators (cytokines) in the AH of primary open-angle glaucoma patients 34 that initiates the fibrovascular response of the tissues to form the filtering bleb that ultimately modulates AH absorption, takes a few weeks to occur. 1 In the very early postoperative period when the fibrovascular response has not yet been initiated, the resistance to flow offered by the Tenon capsule against the amount of AH delivered by the implant (directly proportional to the preoperative intraocular pressure but restricted by its length and diameter) might be the main factor involved in the prevention of hypotony.…”

An Ex-Press implant versus trabeculectomy in a fibrotic bleb with late failure after previous trabeculectomy

“…If the bleb is revived by needling with use of antimetabolites as mitomycin C (MMC) that is usually used during the operation, the associated increase in IOP will be controlled if the revision occurred early within the first three months after surgery [4] . However, likelihood of success is less if the bleb revision is delayed [5][6] . If the bleb revision fails, alternative surgeries include a second trabeculectomy or an aqueous implant surgery [7][8] .…”

<p>Recommendations for the management of elevated intraocular pressure due to bleb fibrosis after XEN gel stent implantation</p>

“…The natural wound healing process after filtration surgery may result in decreased aqueous outflow due to subconjunctival and episcleral fibrosis. Furthermore, the mere presence of fluid or a pressure head in the subconjunctival space stimulates a cellular reaction that reduces tissue porosity 6. The aqueous in glaucoma patients and others with elevated IOP contains higher levels of inflammatory cytokines PGE2 and TGFβ, substances that play a key role in inflammation and postoperative fibrosis 7,8.…”