Abstract
Purpose :
Rabbits are a commonly used as a model for glaucoma research, however, the dynamic aqueous outflow pathway has not been clearly defined. We aim to describe rabbit aqueous outflow in vivo using an angiographic imaging methodology.
Methods :
Under an approved AACUC protocol, 4 normal Dutch Belted rabbits were anesthetized with an intravenous combination of ketamine and xylazine, and 1 eye of each rabbit was injected intracamerally with 5 µL of 2.5 mg/mL indocyanine green (ICG) (Akorn, Inc., Lake Forest, Illinois). Aqueous outflow vasculature was imaged at 10 minute intervals following ICG injection up to 40 minutes with the confocal scanning laser ophthalmoscopic feature of the Spectralis HRA+OCT (Heidelberg Engineering, Germany). Optical coherence tomography images were simultaneously acquired.
Results :
Perilimbal vessels (i.e. trabecular plexus, Figure 1) appear to fill with aqueous as early as 10 minutes and are seen 360 degrees around the limbus. Aqueous from the trabecular plexus drains posteriorly to radially oriented episcleral outflow vessels which are heavily concentrated at the 12 o’clock position over the superior rectus muscle, and to a lesser degree at the 6 o’clock position over the inferior rectus muscle. Real time videos show the aqueous flow to be pulsatile. Aqueous draining posteriorly from the trabecular plexus appears to also drain into deeper, radially oriented, larger diameter intrascleral vessels (i.e. intrascleral plexus). Two rabbits showed a single large diameter drainage vessel emanating from the aqueous plexus in the superior nasal quadrant. Fellow eyes of rabbits exhibited no ICG signal, suggesting signal detected was due to aqueous drainage and not due to ICG in the systemic circulation.
Conclusions :
In vivo aqueous angiography is an effective technique to understand the outflow vasculature of normal rabbit. This imaging methodology may be extended to evaluate glaucoma therapies that are designed to enhance aqueous outflow.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.