Differential Canalograms Detect Outflow Changes from Trabecular Micro-Bypass Stents and Ab Interno Trabeculectomy

Abstract

The increasing prevalence of glaucoma, a leading cause of blindness, makes the development of safer and more effective treatment more urgent. Recently introduced microincisional glaucoma surgeries that enhance conventional outflow offer a favorable risk profile but can be unpredictable. Two paramount challenges are the lack of an adequate surgical training model for new surgeries and the absence of pre-or intraoperative guidance to sites of reduced flow. To address both, we developed an ex vivo training system and a differential, quantitative canalography method to assess outflow enhancement by trabecular micro-bypass (TMB) implantation or by ab interno trabeculectomy (AIT). TMB resulted in insignificant (p>0.05) outflow increases of 13{+/-}5%, 14{+/-}8%, 9{+/-}3%, and 24{+/-}9% in the inferonasal, superonasal, superotemporal, and inferotemporal quadrants. AIT caused a 100{+/-}50% (p=0.002), 75{+/-}28% (p=0.002), 19{+/-}8%, and 40{+/-}21% increase in those quadrants. AIT eyes had a 7.5 (p=0.01), 5.7 (p=0.004), 2.3, and 1.8-fold greater outflow enhancement than matching quadrants of paired TMB-implanted eyes. Quantitative canalography demonstrated that TMB, when successful, provided focal outflow enhancements, while AIT achieved a more extensive access to outflow pathways including and beyond the surgical site itself.