Abstract
Recently introduced microincisional glaucoma surgeries that enhance conventional outflow offer a favorable risk profile over traditional surgeries, but can be unpredictable. Two paramount challenges are the lack of an adequate training model for angle surgeries and the absence of an intraoperative quantification of surgical success. To address both, we developed an ex vivo training system and a differential, quantitative canalography method that uses slope-adjusted fluorescence intensities of two different chromophores to avoid quenching. We assessed outflow enhancement by trabecular micro-bypass (TMB) implantation or by ab interno trabeculectomy (AIT). In this porcine model, TMB resulted in an insignificant (p > 0.05) outflow increase of 13 ± 5%, 14 ± 8%, 9 ± 3%, and 24 ± 9% in the inferonasal, superonasal, superotemporal, and inferotemporal quadrant, respectively. AIT caused a 100 ± 50% (p = 0.002), 75 ± 28% (p = 0.002), 19 ± 8%, and 40 ± 21% increase in those quadrants. The direct gonioscopy and tactile feedback provided a surgical experience that was very similar to that in human patients. Despite the more narrow and discontinuous circumferential drainage elements in the pig with potential for underperformance or partial stent obstruction, unequivocal patterns of focal outflow enhancement by TMB were seen in this training model. AIT achieved extensive access to outflow pathways beyond the surgical site itself.
Highlights
® becular meshwork micro-bypass stent (TMB, iStent G1, Glaukos Corporation, Laguna Hills, CA, USA) and trabectome-mediated ab interno trabeculectomy (AIT, trabectome, Neomedix, Tustin, California, USA) are the only MIGS approved by the Food and Drug Administration of the United States (USFDA)
The trabecular meshwork, a complex sieve-like tissue that permits fluid passage by giant vacuoles, variable pores, and transcytosis[17], has long been considered to be the principal cause of decreased outflow in primary open angle glaucoma[9] with most of the resistance thought to be residing in the juxtacanalicular tissue or the inner wall of Schlemm’s canal[18,19]
The procedures discussed here are considered minimally invasive, they are difficult to learn because they are performed on a scale that is approximately 200-fold smaller than that of traditional glaucoma surgery
Summary
® becular meshwork micro-bypass stent (TMB, iStent G1, Glaukos Corporation, Laguna Hills, CA, USA) and trabectome-mediated ab interno trabeculectomy (AIT, trabectome, Neomedix, Tustin, California, USA) are the only MIGS approved by the Food and Drug Administration of the United States (USFDA). Past studies have quantified the bulk outflow of aqueous humor[11] or modeled focal outflow mathematically[12] Tracers, such as cationized ferritin[13] and fluorescent beads[14,15], allow to highlight areas of high flow through the TM, but either have cytotoxic effects[16] or do not permit the examination of elements downstream of the TM. The purpose of this study was to develop a well calibrated, quantitative, differential canalography technique to assess conventional outflow enhancement. We hypothesized that this method could highlight outflow enhancement obtained by TMB and AIT. We developed a MIGS training model using enucleated pig eyes
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