Rat optic nerve head anatomy within 3D histomorphometric reconstructions of normal control eyes

Abstract

The purpose of this study is to three-dimensionally (3D) characterize the principal macroscopic and microscopic relationships within the rat optic nerve head (ONH) and quantify them in normal control eyes. Perfusion-fixed, trephinated ONH from 8 normal control eyes of 8 Brown Norway Rats were 3D histomorphometrically reconstructed, visualized, delineated and parameterized. The rat ONH consists of 2 scleral openings, (a superior neurovascular and inferior arterial) separated by a thin connective tissue strip we have termed the “scleral sling”. Within the superior opening, the nerve abuts a prominent extension of Bruch's Membrane (BM) superiorly and is surrounded by a vascular plexus, as it passes through the sclera, that is a continuous from the choroid into and through the dural sheath and contains the central retinal vein (CRV), (inferiorly). The inferior scleral opening contains the central retinal artery and three long posterior ciliary arteries which obliquely pass through the sclera to obtain the choroid. Bruch's Membrane Opening (BMO) is irregular and vertically elongated, enclosing the nerve (superiorly) and CRV and CRA (inferiorly). Overall mean BMO Depth, BMO Area, Choroidal Thickness and peripapillary Scleral Thickness were 29 μm, 56.5 × 103 μm2, 57 μm and 104 μm respectively. Mean anterior scleral canal opening (ASCO) and posterior scleral canal opening (PSCO) radii were 201 ± 15 μm and 204 ± 16 μm, respectively. Mean optic nerve area at the ASCO and PSCO were 46.3 × 103 ± 4.4 × 103 μm2 and 44.1 × 103 ± 4.5 × 103 μm2 respectively. In conclusion, the 3D complexity of the rat ONH and the extent to which it differs from the primate have been under-appreciated within previous 2D studies. Properly understood, these anatomic differences may provide new insights into the relative susceptibilities of the rat and primate ONH to elevated intraocular pressure.

Expansions of the neurovascular scleral canal and contained optic nerve occur early in the hypertonic saline rat experimental glaucoma model

“…The purpose of the present report is to 3-D characterize overall and animal specific, global and regional EG versus Control eye differences within the 8 rats of our previous report (Pazos et al, 2015). …”

“…Supplemental Figures 1–3 (corresponding to figures 1–3 of our previous publication (Pazos et al, 2015)) review the macroscopic and microscopic relationships of the rat ONH. See our previous report (Pazos et al, 2015) for more detailed illustration of the 3D relationships among the neural, vascular and connective components of the rat ONH.…”

“…Supplemental Figures 1–3 (corresponding to figures 1–3 of our previous publication (Pazos et al, 2015)) review the macroscopic and microscopic relationships of the rat ONH. See our previous report (Pazos et al, 2015) for more detailed illustration of the 3D relationships among the neural, vascular and connective components of the rat ONH. Throughout the present report, all right and left eye data are presented in right eye orientation and all parameters are italicized to distinguish the behavior of measured parameters from the behavior of the underlying anatomy they characterize (not italicized).…”

“…For each 3-D ONH reconstruction, a plane satisfying a least-squares error restraint was fit to the 80 BMO points (Pazos et al, 2015), creating a BMO reference plane which served as the reference plane for a series of subsequent measurements (Supplemental Figure 4) and the base for the second peripheral anterior scleral reference plane (Supplemental Figure 6). The following parameters have been previously described (Pazos et al, 2015) and are illustrated in Supplemental Figures 4–7: BMO and the neurovascular canal parameters: ASCO and PSCO Areas, Radii and Depths, Horizontal/Vertical (H/V) Diameter Ratios for BMO, ASCO and PSCO; Optic Nerve cross-sectional parameters: Optic Nerve cross sectional area, radii and shape (H/V diameter ratios) at the level of ASCO ( ON-ASCO ) and PSCO ( ON-PSCO ) as well as the Optic Nerve Volume ; Scleral and Choroidal Parameters: Scleral Sling Depth, Scleral Depth, Scleral Thickness and Choroidal Thickness .…”

“…In an initial publication (Pazos et al, 2015), we described the 3D histomorphometric anatomy of the 8 Control rat ONHs and characterized the differences between the normal control rat and primate ONH (Figures 1 – 7 of our previous report) (Pazos et al, 2015). That study was the first to describe the rat ONH as consisting of two scleral openings (a neurovascular and arterial) and clarify that the central retinal artery (CRA) does not accompany the central retinal vein (CRV) within the neurovascular canal, but passes through a separate, large, irregular opening, inferior to it, accompanied by the long posterior ciliary arteries (LCPAs) and their dense intra-scleral branches.…”