Longitudinal Changes in RNFL and GCIPL Thicknesses in Rhesus Macaques with Chronic Ocular Hypertension

Abstract

Purpose : Retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thicknesses are primary structural biomarkers used in clinical management of glaucoma for diagnosis and longitudinal monitoring. In this study we compare the thickness change of RNFL and GCIPL in a rhesus macaque model with laser-induced chronic ocular hypertension as the eyes transition from health to early structural changes.

Methods : Laser photocoagulation of the trabecular meshwork was employed to induce chronic IOP elevation in one eye of each of three adult rhesus macaques. The RNFL and GCIPL thicknesses were longitudinally measured using spectral-domain OCT (Bioptigen Envisu; Leica, Chicago, IL). Images were obtained both at intrinsic IOP levels and at 15 mmHg which was achieved through anterior chamber cannulation. The Iowa Segmentation software (Retinal Image Analysis Lab, Iowa Institute for Biomedical Imaging, Iowa City, IA) was used to analyze the scans. Linear mixed effect models were used to determine differences in the rate of change. To standardize the difference in RNFL and GCIPL dynamic range measurements, percent change from baseline was also compared.

Results : Peak IOP range during the follow up period was 31-34mmHg in the experimental eyes of the 3 animals and 16-17mmHg in the control eyes. Significant rate of RNFL thickness change was detected in naïve (p=0.001) and fixed IOP (p=0.001) settings in the experimental eye and non-significant for GCIPL thickness measurements (p=0.339, 0.358, respectively; Figure, Table). The overall rate of change was faster in the experimental eye then the control eye for RNFL (p<0.001, 0.047 for naïve and fixed IOP) but not for GCIPL (p=0.932, 0.451). The overall rate of change by percent (all eyes) was faster for RNFL compared with GCIPL under both naïve (p<0.001) and fixed IOP (p=0.017) conditions. The rate of change for either the RNFL or the GCIPL was independent of the IOP value at the time of image acquisition (p=0.465, 0.663, respectively).

Conclusions : Moderately high IOP at the time of image acquisition does not affect RNFL or GCIPL thickness measurements. RNFL thickness decline more rapidly than GCIPL thickness at early stages of experimental glaucoma, even when accounting for the different dynamic range of the parameters, making it a better indicator of disease change at this stage of the disease.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.