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Author’s Name(s): William Herspiegel, James Armstrong, Anastasiya Vinokurtseva, Taylor Lukasik, Len Pinchuk, Cindy Hutnik, Iqbal Ike Ahmed, David Yan

Author’s Disclosure Block: William Herspiegel: Glaukos, Other financial or material interest; James Armstrong: none; Anastasiya Vinokurtseva: none; Taylor Lukasik: none; Len Pinchuk: President/CEO Innovia LLC; Cindy Hutnik: none; Iqbal Ike Ahmed: Consultant for Santen and Glaukos; David Yan: Consulting and honorariums for Abbvie 

Abstract Body

Purpose: To measure the increase in outflow resistance of theSIBSmicroshunt when different suture lengths, sizes and material are inserted to partially occlude the lumen. Study Design: In-vitro experiment. Methods:  The SIBS microshunt proximal end was fixed and sealed within a 21g blunt tip cannula connected to a gravity perfusion system. The distal tip was submerged just below the surface within a f luid filled covered collection beaker. Flow through the microshunt was quantified through changes in mass of the collection beaker. Each 5-minute trial was replicated 4 times per condition in each of five different microshunts. Various sutures were inserted into the distal end of the microshunt’s lumen and f low resistance was measured in various partly occluded states (4mm or 8mm of suture length inserted,9-0 or 10-0 suture size, Vicryl (Ethicon: CS140-6 or BV100-3) or nylon suture (Ethilon: CS160-6 or BV100-4). Perfusion pressures were set at 15, 20, or 25 mmHg by adjusting the reservoir heights to 20.4, 27.2 and 33.4 cmH20 respectively. The 4 mm occlusion with 10-0 nylon test condition was repeated with sutures from different lots to investigate the effects of suture manufacturing variability. Results: Resistance of non-occluded SIBS microshunts (n=5) was 1.77±0.02 mmHg/ul/min, closely matching the theoretical value of 1.76 mmHg/ul/min at 21℃ from the Hagen-Poiseuille formula. Occlusion with a 4mm 10-0 suture increased resistance to 3.34±0.21 mmHg/ul/min for nylon and 3.58±0.12 for Vicryl. Occlusion with an 8mm 10-0 suture increased resistance to 4.58±0.30 for nylon and 5.10±0.22 for Vicryl. Occlusion with a 4mm 9-0 suture increased resistance to 5.17±0.27 for nylon and 5.08±0.30 for Vicryl. Occlusion with an 8mm 9-0 suture increased resistance to 7.29±0.36 for nylon and 7.92±0.53 for Vicryl. Resistance differed significantly between 4 vs. 8mm occlusion lengths (p<0.0001), 10-0 vs. 9-0 suture diameters (p<0.0001), different microshunts (p<0.0001), and 4mm 10-0 nylon sutures from different lots (p<0.05). No difference was observed between suture materials (p>0.05). Conclusion: Resistance of non-occluded microshunts as measured by the perfusion model closely matched theoretical values. Occlusion with either nylon or Vicryl sutures caused substantial increases in resistance, depending on suture diameter and length, compared to a non-occluded microshunt. Occlusion with an 8mm 10-0 suture of either material resulted in a similar increase in resistance to that of a 4mm 9-0 suture. These ripcord conditions are comparable to the theoretical resistance of the 45-um gelatin microstent (7.3 mmHg/ul/min) which was designed to minimize postoperative hypotony