Aqueous Angiography with Fluorescein and Indocyanine Green in Bovine Eyes

Abstract

PurposeWe characterize aqueous angiography as a real-time aqueous humor outflow imaging (AHO) modality in cow eyes with two tracers of different molecular characteristics.MethodsCow enucleated eyes (n = 31) were obtained and perfused with balanced salt solution via a Lewicky AC maintainer through a 1-mm side-port. Fluorescein (2.5%) or indocyanine green (ICG; 0.4%) were introduced intracamerally at 10 mm Hg individually or sequentially. With an angiographer, infrared and fluorescent images were acquired. Concurrent anterior segment optical coherence tomography (OCT) was performed, and fixable fluorescent dextrans were introduced into the eye for histologic analysis of angiographically positive and negative areas.ResultsAqueous angiography in cow eyes with fluorescein and ICG yielded high-quality images with segmental patterns. Over time, ICG maintained a better intraluminal presence. Angiographically positive, but not negative, areas demonstrated intrascleral lumens with anterior segment OCT. Aqueous angiography with fluorescent dextrans led to their trapping in AHO pathways. Sequential aqueous angiography with ICG followed by fluorescein in cow eyes demonstrated similar patterns.ConclusionsAqueous angiography in model cow eyes demonstrated segmental angiographic outflow patterns with either fluorescein or ICG as a tracer.Translational RelevanceFurther characterization of segmental AHO with aqueous angiography may allow for intelligent placement of trabecular bypass minimally invasive glaucoma surgeries for improved surgical results.

Aqueous Angiography in Living Nonhuman Primates Shows Segmental, Pulsatile, and Dynamic Angiographic Aqueous Humor Outflow

“…), the aggregate similar observations of segmental AHO by different laboratories using different tracers with various molecular properties provide increased support for the concept of segmental AHO. Regarding, fluorescein and ICG, using enucleated human and cow eyes, similarities were established 19 such that interventions could be placed between angiographies of the two dyes and assessed as a differential change 20 . In the future, more quantitative methods will need to be developed to both quantify more or less segmentalization as well as to provide local flow descriptors such as volume, delay, or rate.…”

“…Segmental patterns have been observed that may be relevant to trabecular bypass surgeries and their success via concepts of guiding surgical placement toward areas of greater or lesser flow in the eye. Comparisons between ICG and fluorescein aqueous angiography have shown sufficient similarity to conduct interventional studies where ICG is first used to determine a pattern followed by fluorescein after an intervention to query the effect 19, 20 . With this method, regions of initially poor angiographic flow have been shown to be capable of angiographic recruitment for enhanced flow using aqueous angiography-guided trabecular bypass in enucleated human eyes 20 .…”

Aqueous Angiography: Aqueous Humor Outflow Imaging in Live Human Subjects

“…Subsequently, fluorescent images were obtained on ICG capture mode (excitation wavelength: 786 nm and transmission filter > 800 nm) to establish a black pre-injection background 1–4 . Pharmaceutical grade ICG (ICGREEN 25 mg [NDC 17478-701-25], Akorn) was dissolved with 0.7 ml of the manufacturer solvent followed by 5.6 ml of balanced salt solution for a 0.4% concentration 2–5 . After introduction of ICG, fluorescent, cSLO-IR images, or video were acquired with the subject looking in different directions.…”

Structural and functional imaging of aqueous humour outflow: a review

“…Angiographic images were readily obtained, and multi‐model imaging was used to validate angiographic signal as AHO. First, AS‐OCT performed on (but not off) angiographic structures corresponded with intrascleral lumens that were consistent with AHO pathways . Second, fixable fluorescent tracers that could be trapped were present to a much greater extent in TM associated with angiographically positive compared to negative regions .…”

“…Aqueous angiography was also developed with the principle of starting with clinical (Spectralis HRA + OCT [Heidelberg Engineering, Heidelberg, Germany], indocyanine green [ICG], fluorescein and others) and operating room (AC maintainer, tubing and others) instrumentation for easier translation to patients. Bringing these supplies into the laboratory, aqueous angiography was first tested with post‐mortem pig, cow, and human eyes . Given that the Spectralis was a clinical instrument meant for adult humans with chins, enucleated eyes were secured to drilled holes in the eyes of Styrofoam heads commonly used in cosmetology schools because the models had chins.…”