Non-Invasive Three Dimensional (3D) Virtual Casting of the Functioning Human Intrascleral Venous Plexus During Active Aqueous Outflow

Abstract

 

Purpose:

 

Aqueous exiting the eye via the trabecular meshwork/Schlemm’s canal (SC) passes through the deep and intrascleral venous plexus (ISVP) or directly through aqueous veins. The purpose of this study was to visualize the human aqueous outflow system 360 degrees in 3D during active aqueous outflow.

 

Methods:

 

During perfusion at different pressures, the outflow pathways of 7 donor eyes were imaged with a modified Bioptigen spectral-domain optical coherence tomography system (Bioptigen Inc, USA; SuperLum LTD, Ireland). Thirty-six scans (3 equally distributed in each clock hour), each covering a 2 x 3 x 2 mm volume (512 frames, each 512 x 1024 pixels), were obtained from each eye (Figures A and B). All image data were black/white inverted, and the background subtracted (Subtract Background algorithm, ImageJ 1.40g, http://rsb.info.nih.gov/ij/). Contrast was adjusted to isolate the ISVP.

 

Results:

 

SC, collector channels, the deep and ISVP, and episcleral veins were observed in different regions of limbus. Aqueous veins could be observed extending from SC towards the ISVP (B). Individual scan ISVP castings were rendered (C) and assembled in 3D space (D) in Amira 4.1 (Visage Imaging Inc. USA). A 360-degree casting of the ISVP was obtained in all perfused eyes. The ISVP tended to be dense and overlapping in the superior and inferior quadrants, and thinner in the lateral quadrants.

 

Conclusions:

 

The human aqueous outflow pathway can be imaged using SD-OCT. The more superficial structures of the aqueous outflow pathway present with sufficient contrast as to be optically isolated and non-invasively cast in-situ 360 degrees in cadaver eye perfusion models. This approach may be useful as a model in future studies of human aqueous outflow.  

 

Keywords: aqueous • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • anterior segment