Characterization of the Canine Retinal Vasculature With Optical Coherence Tomography Angiography: Comparisons With Histology and Fluorescein Angiography.

Ana Ripolles-Garcia,Gustavo D Aguirre,Yineng Chen,Gui-Shuang Ying,William A Beltran,Nicolas Cuenca,Gordon Ruthel

doi:10.3389/fnana.2021.785249

Abstract

Purpose: To present a methodology for quantification of the canine retinal vasculature imaged by optical coherence tomography angiography (OCTA) and validate this approach by comparison with fluorescein angiography (FA) and confocal imaging of retinal wholemounts labelled by immunohistochemistry (IHC).Methods: Six normal adult dogs underwent retinal OCTA imaging in both eyes. The images extracted from the different microvascular plexuses at eight retinal locations spanning the central and mid-peripheral fundus were analyzed using the AngioTool software. FA was performed in one eye and was compared to the OCTA images. Six eyes from three dogs were processed by IHC to examine the retinal vasculature.Results: A total of four retinal plexuses were identified by OCTA in the canine retina, and their density and topographical pattern varied with eccentricity. OCTA offered improved resolution over FA with the advantage of allowing imaging of the individual plexuses. Detection by OCTA of small vessels within the deep capillary plexus was possible and approached the level of resolution achieved with ex vivo imaging of the retinal vasculature by confocal microscopy/IHC. The plexuses herein described are analogous to human retinal vasculature.Conclusion: OCTA can be used to image and quantify non-invasively the vascular retinal networks of the canine retina. We provide normative data in eight different retinal locations that can be imaged non-invasively with this technology. This could support analysis of retinal vascular changes associated with disease and following therapeutic intervention.

Highlights

The retina is a complex and highly metabolic extracranial part of the central nervous system that requires a continuous and self-regulated blood supply (Harris et al, 1998; Yu and Cringle, 2001)
The second vascular network spanned from the ILM to the ganglion cell layer (GCL)/inner plexiform layer (IPL) border, was formed by large arterioles, venules and their connecting capillaries, and branched from the optic nerve head (ONH) to the mid-periphery
Since the topographical pattern and location of these plexuses within the retinal layers is analogous to that found in human retinas, we propose that the same nomenclature (RPCP, SVP, Intermediate Capillary Plexus (ICP), and Deep Capillary Plexus (DCP)) outlined by Campbell et al (2017) be used in all future description of canine retinas (Cuenca et al, 2020)

Summary

Introduction

The retina is a complex and highly metabolic extracranial part of the central nervous system that requires a continuous and self-regulated blood supply (Harris et al, 1998; Yu and Cringle, 2001). Oxygenation is ensured by a well-organised retinal and choroidal vascular network. The choriocapillaris, a network of capillary vessels located under the retinal pigmented epithelium, is the main source of oxygen for the outer retina, and retinal vessels are the main supply for the inner retina (Michaelson, 1954). While choroidal vasculature has been maintained throughout evolution in vertebrates, the retinal vasculature pattern differs widely between species (Rochon-Duvigneaud, 1943). The canine retina is classified as holangiotic as its blood vessels extend from the optic nerve head to the far periphery. In the temporally located area centralis, they converge toward the highly specialized fovea-like area (Peichl, 1992; Beltran et al, 2014)

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