Microvascular Architecture of the Rabbit Eye: A Scanning Electron Microscopic Study of Vascular Corrosion Casts

Abstract

ABSTRACT. The microvasculature of the eyes of 5 rabbits was investigated using scanning electron microscopy on corrosion casts. The study revealed that the pars plana vessels draining blood from the iris and ciliary body coursed directly into the anterior vortex venous system constituting the scleral venous plexus (the venous circle of Hovius). The episcleral vasculature was found to possess a specialized morphology, with channels draining the aqueous humor. The capillaries of the third palpebral, bulbar and palpebral conjunctiva formed a single-layered capillary network approximately parallel to the epithelium and formed a well-developed venous plexus in the stroma. The retina was found to be merangiotic, meaning that vessels were present only in a small part of the retina, extending in a horizontal direction to form bands on either side of the optic disc. Channels representing the aqueous veins that drained blood mixed with aqueous humor were found to derive directly from the suprachoroidal space and communicate with the scleral venous plexus via the anterior vortex veins. The functional significance of the microvasculature of the iris, cilia, retina and choroid is discussed in this report as well. The elaborate microvasculature of the conjunctiva may be a prerequisite for the exchange of nutrients and gasses between the cornea and the vessels across the conjunctival epithelium when the eyelids are shut during sleep, and possibly for the dynamics of eye drop delivery. The scleral venous plexus in rabbits may be analogous to the scleral venous sinus (Schlemm's canal) in rats, primates and humans.

Hyperspectral Computed Tomographic Imaging Spectroscopy of Vascular Oxygen Gradients in the Rabbit Retina In Vivo

“…The presence of gradients in apparently random locations may correlate with feeding vessels that merge from below the plane of the image and are not visible. Anatomical studies have demonstrated deep penetrating vessels within the thick nerve fiber layer of the rabbit [34]–[38]. The intravascular gradients may be a reflection of variations in local metabolic activity and represent a novel method of studying microvascular oxygen transport completely non-invasively.…”

“…This physiology provides an excellent animal model to calibrate our spectral measurements over a wide range of in vivo hemoglobin oxygen saturation. In addition, the well described anatomy of retinal vessels provides an ideal imaging target in vivo [34]–[38]. Specifically, the largest retinal vessels (100–200 micron diameter) in rabbits lay on top of a non-pigmented nerve fiber layer (Figure 1).…”

Effect of acute intraocular pressure elevation on blood flow velocity and resistance in the rabbit ophthalmic artery

“…However, the measurements of blood flow velocities in other orbital blood vessels were much more difficult in the rabbits using the CDI technique 7 . The tortuous orientations and variable sizes of short and long posterior ciliary arteries in rabbits complicated their identifications 24,25 . In this study, we found that it was difficult to visualize the posterior ciliary arteries as well as the small central retinal artery in the rabbits with the 17–5 MHz automatic frequency adjusting ultrasound transducer.…”

Acute Variations in Retinal Vascular Oxygen Content in a Rabbit Model of Retinal Venous Occlusion

“…The anatomy of the rabbit retina has been described extensively in previous work. [33]–[36] The vascular distribution within the rabbit retina is localized (to the medullary rays) and corresponding arteries and veins are easily imaged with conventional fundus photography. Previous studies from our lab have demonstrated that argon laser photothrombosis can induce retinal vein occlusion (RVO) and the commonly observed clinical sequelae including intraretinal hemorrhages, leakage, capillary non-perfusion, and collateral circulation.…”