Correlating longitudinal Optical Coherence Tomography (OCT) structural change to retrolaminar myelin-related protein alteration in non-human primate (NHP) early experimental glaucoma (EG)

Abstract

Purpose : OCT peripapillary retinal nerve fiber layer thickness (pRNFLT) change detection is a standard tool in the management of both human glaucoma and NHP unilateral EG. Here, using a novel approach for consistent anatomical comparisons, we employ quantitative immunohistochemistry (qIHC) to test the hypothesis that retrolaminar myelin-related protein expression alterations correlate to longitudinal OCT structural change in NHP early EG.

Methods : Data from n=4 unilateral early EG NHPs (<30% EG pRNFLT loss) were included. For each EG eye, longitudinal OCT pRNFLT change relative to baseline was quantified within 12 Fovea-BMO (FoBMO axis) 30° sectors (Fig 1). For each NHP, the optic nerve head (ONH) of the EG and Control (C) eye was trephined, (10 mm), 5 µm serial vertical paraffin sections were cut, their clinical location was anatomically estimated (Fig 1a), and n=4 adjacent sections were selected to represent similar FoBMO sectors in both eyes. Sections from all 4 NHPs were deparaffinized and stained with anti 2',3'-Cyclic-nucleotide 3'-phosphodiesterase, (CNPase, a myelin associated enzyme). Localized retrolaminar signal intensity in each section was quantified within the first 4 retrolaminar 50 µm bands of 12 anatomically consistent horizontal regions (Fig 1b). For each NHP, EG vs C eye differences in CNPase intensity within each region and EG vs C CNPase intensity % differences were correlated with longitudinal percent change in OCT pRNFLT in the same OCT sector (Fig 2) using a linear mixed effect model.

Results : CNPase intensity decreased significantly in EG versus C eyes in 26 of 48 qIHC regions where early OCT RNFLT loss had occurred (p < 0.05). pRNFLT % change and EG versus C CNPase % intensity difference in the same FoBMO 30° sector were correlated (p=0.01, linear mixed effect model, R²=0.46, Fig 2b). EG eyes showed a 49% reduction in CNPase intensity at 0% pRNFLT change.

Conclusions : To our knowledge, this is the first attempt to anatomically link qIHC EG vs C protein expression differences to longitudinally detected OCT pRNFLT change in NHP early EG and demonstrate that myelin loss may occur before RNFLT loss. Linking protein expression change to OCT pRNFLT change may enhance the interpretation of OCT findings and inform our understanding of the pathophysiology of glaucoma.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.