In Vivo Angiographic Study of Rabbit Aqueous Outflow following Ab Interno Gelatin Stent Implantation

Abstract

Purpose : An ab interno gelatin stent (XEN 45, Allergan plc) provides a minimally invasive approach to glaucoma filtration surgery by facilitating aqueous drainage to the subconjunctival space. Using a rabbit model, we aim to describe the dynamic aqueous outflow pathway following the stent implantation and examine how normal outflow is altered using aqueous angiography.

Methods : Five normotensive New Zealand White rabbits received a gelatin stent in left eyes, followed by 10 μg mitomycin-C subconjunctivally. At up to 2 weeks post-implantation, the implanted eyes were injected intracamerally with 5 μL of 2.5 mg/mL indocyanine green (ICG) (Akorn, Inc.). Aqueous outflow vasculature was serially imaged following ICG injection up to 60 minutes with the confocal scanning laser ophthalmoscopic feature of the Spectralis HRA+OCT (Heidelberg Engineering, Germany). Optical coherence tomography images were simultaneously acquired.

Results : Unlike normal aqueous drainage, which begins at the circumferential trabecular plexus as early as 10 minutes post-ICG injection (Figure 1A) and drains posteriorly to radially oriented episcleral outflow vessels which are heavily concentrated at the 12 o’clock position over the superior rectus muscle, rabbits with the gelatin stent showed preferential drainage directly into the subconjunctival bleb as early as 30 seconds post-ICG injection in the aqueous humor (Figure 1B). In 2 of the rabbits, additional outflow to the trabecular plexus was observed at later timepoints. OCT imaging of the bleb showed enlarged superficial conjunctival vessels that were reminiscent of lymphatic outflow lumens (Figure 1C).

Conclusions : In vivo aqueous angiography is an effective technique to understand the outflow vasculature of normal and glaucoma filtration rabbit models. The redirection of aqueous from normal outflow vasculature to a subconjunctival bleb with a gelatin stent suggests an efficient glaucoma filtration mechanism for lowering intraocular pressure.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure 1. Normal rabbit aqueous outflow includes trabecular plexus, intrascleral plexus, and episcleral outflow vessels (A). Outflow with a gelatin stent 1 week post-implantation shows preferential outflow to the subconjunctival bleb (B) and outflow from the bleb is at least partially through the enlarged drainage vessels, which are thought to be lymphatic vessels (C).