Aqueous Angiography: A Real-Time, Physiologic, and Comprehensive Aqueous Humor Outflow Imaging Technique

Abstract

 

Purpose

 

Minimally invasive glaucoma surgeries (MIGS) attempt to enhance native aqueous humor outflow (AHO) in the eye to lower intraocular pressure (IOP). While results of trabecular meshwork (TM) bypass are promising, inconsistent success is seen. One hypothesis for this variability rests upon segmental (non-360 degrees uniform) AHO past the trabecular meshwork. We propose aqueous angiography, a real-time, physiologic, and comprehensive AHO imaging technique.

 

Methods

 

Pig (Fig. 1; n = 30) and human (Fig. 2; n = 2) enucleated eyes were obtained (within 30 and 40 hours of death respectively from abattoirs or San Diego Eye Bank). Eyes were orientated based upon their inferior oblique insertions and pre-perfused with Balanced Salt Solution (BSS). Fluorescein (2.5% in BSS), as per AAO guidelines for capsular stain, was introduced intracamerally via a Lewicky AC maintainer through a 1mm side-port wound at 30 or 80 mm Hg. With an angiographer infrared and fluorescent (488 nm; aqueous angiography) images were acquired. Image processing allowed for collection of pixel information segregated by location for statistical analyses. Concurrent OCT was performed, and fixable fluorescent dextrans were also introduced into the eye for histological analysis of angiographically positive and negative areas.

 

Results

 

Aqueous angiography yielded high quality images given excitation with a 488 nm laser. Segmental patterns (Figs. 1 and 2) were observed regardless of whether total angiographic information was analyzed or if the data was segregated toward proximal or distal areas of flow (p<.0001; Kruskal-Wallis test). Using various methods, no primary quadrant of flow was detected across the cohort of eyes. Regions of proximal flow did not necessarily correlate with regions of distal flow. High IOP (80 mm Hg) did not lead to blockage of AHO. By OCT, angiographically positive but not negative areas demonstrated intrascleral lumens. 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. Aqueous Angiography may have human intra-operative use for customized MIGS placement toward angiographically functional areas for improved surgical results and IOP lowering.