Aqueous Angiography: Visualization of Aqueous Humor Outflow in Bovine Eyes.

Abstract

 

Purpose

 

Minimally invasive glaucoma (MIGS) surgeries are performed to lower intraocular pressure (IOP) often by trabecular meshwork (TM) bypass to improve aqueous humor outflow (AHO). While capable of lowering IOP, variable success has been seen with one hypothesis being segmental (non-360 degrees uniform) AHO past the trabecular meshwork. We have described aqueous angiography as a real-time, physiologic, and comprehensive AHO imaging technique in pig/human eyes. Here we characterize aqueous angiography in bovine eyes which are more freshly obtained in our location and test additional fluorescent tracers.

 

Methods

 

Bovine enucleated eyes were obtained (within 6 hours of death from local abattoirs). Eyes were orientated based upon their inferior oblique insertions and pre-perfused with Balanced Salt Solution (BSS). Fluorescein (2.5% in BSS) and/or indocyanine green (ICG; 0.25%), as per AAO guidelines for capsular stain, were introduced intracamerally via a Lewicky AC maintainer through a 1mm side-port wound at 30 or 80 mmHg. With an angiographer, infrared and fluorescent (488 or 795 nm; aqueous angiography) images were acquired. Concurrent OCT was performed, and fixable fluorescent dextrans were introduced into the eye for histological analysis of angiographically positive and negative areas.

 

Results

 

Aqueous angiography with fluorescein (Fig. 1) and ICG (Fig. 2) yielded high quality images although fluorescein images had slightly better signal-to-noise ratio. Segmental patterns were observed. High IOP did not lead to blockage of AHO. To demonstrate that aqueous angiography signal occurred in AHO lumens as opposed to surface staining, concurrent OCT showed that angiographically positive but not negative areas had intrascleral lumens. Additionally, conducting aqueous angiography with fluorescent dextrans led to their trapping in AHO pathways.

 

Conclusions

 

Aqueous angiography is a real-time, physiologic, and comprehensive AHO imaging technique that works in bovine eyes. ICG functions as an alternative to fluorescein. This is important as all tracers ultimately accumulate on the ocular surface because episcleral veins eventually surface in enucleated eyes. As such, a second tracer is necessary for scientific studies (pharmacologic or surgical) as a way to perform aqueous angiography before and after interventions.