Quantification of Focal Outflow Enhancement using Differential Canalograms

Abstract

Purpose : To quantify focal changes of conventional outflow caused by ab interno trabeculectomy (AIT).

Methods : Gonioscopic, plasma-mediated ab interno trabeculectomy (AIT; Trabectome, Neomedix, Tustin, CA) was established in enucleated pig eyes. We developed a program to automatically quantify outflow changes (R, package eye-canalogram, github.com) using a fluorescent tracer reperfusion technique. Trabecular meshwork (TM) ablation was demonstrated with fluorescent microspheres in 6 eyes before formal outflow quantification was performed with two dye reperfusion canalograms (fluorescein followed by Texas red) in 6 further eyes. Eyes were perfused with a central, intracameral needle at 15 mmHg. Canalograms and histology were correlated for each eye.

Results : The pig eye provided a model with high similarity to AIT in human patients. Histology indicated ablation of TM and unroofing of most Schlemm’s canal segments. Microspheres highlighted additional circumferential and radial outflow beyond the immediate area of ablation. Differential canalograms showed that AIT caused an increase in outflow of 17±5 fold inferonasally (IN), 14±3 fold superonasally (SN) and also an increase in the opposite quadrants with a 2±1 fold increase superotemporally (ST) and 3±3 inferotemporally (IT). Perilimbal specific flow image analysis showed an accelerated nasal filling with additional perilimbal flow directed into adjacent quadrants.

Conclusions : In this quantitative canalography model, supraphysiological outflow enhancement by AIT could be measured in the area of TM ablation and beyond. These new tools are now available as open source software to aid the investigation of outflow tract bioengineering and design of new devices.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.