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Mark Disclafani; Optimization of Stent Diameter for Use with Baerveldt Glaucoma Implants: a Laboratory Study.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4964.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine optimum stent diameter for immediate post-operative pressure control using a Baerveldt Glaucoma Implant (BGI), when the stent method is used at the time of implantation of such non-valved devices. We previously determined (ARVO, 2016) that 5-0, 4-0, and 3-0 monofilament nylon stents do not reduce flow to the physiologic rate of 2.75 +/- 0.63 ul/min (Brubaker, 1991).
Methods: Laboratory setup included a custom model eye (University of South Florida Invention Disclosure, M. DiSclafani, 2015 ), made water-tight and connected to a source of balanced salt solution (BSS, at controlled elevation); a digital manometer ( Dwyer Instruments Model 490A-1 ); and a BGI (tube inner diameter 300 microns). Uniform diameter of experimental stents was documented with a digital micrometer (Mitituyo Model IP 65, 1- micron accuracy). Height of the BSS source was controlled to create pressures ranging from 20 to 40 mm Hg , and stents with diameters > 200 u ( the USP diameter of 3-0 nylon) were tested. Flow rates were measured though the BGI tubing, either unblocked or partially occluded by stents with diameters of 226, 235, and 250 u. The BGI plate was left uncovered and unobstructed; resistance due to Tenon’s capsule and/or conjunctiva, as expected clinically, was therefore not accounted for.
Results: Flow rates increased with pressure and decreased with diameter of stent.At 40 mm Hg pressure, rates (ul/min) ranged from 204 +/-10 for the 226 stent to 72 +/-12 for the 250 stent. At 20 mm Hg, rates ranged from 68 +/-9 for the 226 stent to 20 +/-1 for the 250 stent. Differences in rates were statistically significant at p<0.01 level or better by Student’s T test.
Conclusions: A monofilament stent to be used with the BGI needs a diameter of at least 250 u in order to reduce flow to a level that approaches the Brubaker physiologic level. Such stents are not currently available commercially; 3-0 USP monofilament suture diameter is 200u, and 2-0 USP diameter is 300u. A customized stent for BGI use is needed.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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