Morphometric Analysis of Retinal Ganglion Cell Axons in Normal and Glaucomatous Brown Norway Rats Optic Nerves

• Type of Material: Article
• Authors: Vidisha Goyal, Georgia Institute of Technology; Thomas A Read, Georgia Institute of Technology; Dillon M Brown, Georgia Institute of Technology; Luke Brawer, Georgia Institute of Technology; Kaitlyn Bateh, Georgia Institute of Technology; Bailey G Hannon, Georgia Institute of Technology; Andrew Feola, Emory University; Christopher Ethier, Emory University
• Language: English
• Date: 2023-03-01
• Publisher: ASSOC RESEARCH VISION OPHTHALMOLOGY INC
• Publication Version: Final Published Version
• Copyright Statement: 2023 The Authors
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1167/tvst.12.3.8
• Title of Journal or Parent Work: TRANSLATIONAL VISION SCIENCE & TECHNOLOGY
• Volume: 12
• Issue: 3
• Start Page: 8
• End Page: 8
• Grant/Funding Information: Supported by NIH R01 EY025286 (CRE), 5T32 EY007092-32 (BGH), Department of Veteran Affairs R&D Service Career Development Award (RX002342; AJF), NIH NEI EY030871 (AJF), and Georgia Research Alliance (CRE).
• Keywords: RGC axon morphology; DIAMETER; NUMBER; Life Sciences & Biomedicine; Science & Technology; brown norway rats; reference database; Ophthalmology; HISTOMORPHOMETRY
• Research Categories: Health Sciences, Opthamology; Engineering, Electronics and Electrical; Engineering, Mechanical; Engineering, Biomedical

Abstract

Purpose: A reference atlas of optic nerve (ON) retinal ganglion cell (RGC) axons could facilitate studies of neuro-ophthalmic diseases by detecting subtle RGC axonal changes. Here we construct an RGC axonal atlas for normotensive eyes in Brown Norway rats, widely used in glaucoma research, and also develop/evaluate several novel metrics of axonal damage in hypertensive eyes. Methods: Light micrographs of entire ON cross-sections from hypertensive and normotensive eyes were processed through a deep learning-based algorithm, AxoNet2.0, to determine axonal morphological properties and were semiquantitatively scored using the Morrison grading scale (MGS) to provide a damage score independent of AxoNet2.0 outcomes. To construct atlases, ONs were conformally mapped onto an ON “template,” and axonal morphometric data was computed for each region. We also developed damage metrics based on myelin morphometry. Results: In normotensive eyes, average axon density was ∼0.3 axons/μm2 (i.e., ∼80,000 axons in an ON). We measured axoplasm diameter, eccentricity, cross-sectional area, and myelin g-ratio and thickness. Most morphological parameters exhibited a wide range of coefficients of variation (CoV); however, myelin thickness CoV was only ∼2% in normotensive eyes. In hypertensive eyes, increased myelin thickness correlated strongly with MGS (P < 0.0001). Conclusions: We present the first comprehensive normative RGC axon morphometric atlas for Brown Norway rat eyes. We suggest objective, repeatable damage metrics based on RGC axon myelin thickness for hypertensive eyes. Translational Relevance: These tools can evaluate regional changes in RGCs and overall levels of damage in glaucoma studies using Brown Norway rats.