Longitudinal in vivo changes in radial peripapillary capillaries and optic nerve head structure in non-human primates with early experimental glaucoma

Abstract

Purpose : There is conflicting evidence as to whether a loss of radial peripapillary capillaries (RPCs) precedes neuronal loss in glaucoma. We examined the time-course of in vivo changes in RPCs, optic nerve head (ONH) geometry, and retinal nerve fiber layer thickness (RNFLT) in a monkey model of experimental glaucoma (EG).

Methods : Spectral domain optical coherence tomography images (48-line 20° radial B-scans, 12° circular scans; Spectralis HRA+OCT) centered on the ONH were acquired before and approximately every 2 weeks after inducing unilateral EG in 8 rhesus monkeys. Mean anterior lamina cribrosa surface depth (ALCSD) and minimum rim width (MRW) were quantified from manually segmented radial scans. Adaptive optics scanning laser ophthalmoscope images of perfused RPCs were acquired on the temporal half of the ONH and used to quantify RPC density at all time points. RPC density and RNFLT were calculated globally and in 60° sectors centered on the fovea to Bruch’s Membrane Opening axis. Intraocular pressure (IOP) was measured (Tonopen) prior to imaging. For all metrics, the time of first significant change (global or sectoral) was defined as the first time-point that values fell outside of the 95% confidence interval established from control eye data.

Results : In EG eyes, mean IOP was 14.3 ± 2.8 mmHg at baseline and increased by 12.4 ± 6.6 mmHg at the first time of measured ONH or retinal change. Baseline values of mean ALCSD and MRW in EG eyes were 194.9 ± 21.3 μm and 349.8 ± 57.9 μm, respectively. Mean ALCSD or MRW were the first parameters to change in 7 EG eyes, while RPC density changed first in the 8^th. At their first points of change, the ALCSD was posteriorly deformed by 100.2 ± 101.2 μm and MRW thinned by 82.3 ± 65.9 μm, on average. Baseline values of RNFLT and RPC density in EG eyes were 116.1 ± 8.5 μm and 14.3 ± 2.2%, respectively. RNFL thinning occurred before a decrease in RPC density in 4 EG eyes. RPC density decreased prior to RNFL thinning in 3 EG eyes. A simultaneous change in RNFLT and RPC density occurred in 1 EG eye.

Conclusions : This longitudinal study illustrates that circumpapillary RNFLT or RPC density decrease in early glaucoma. These data suggest that vascular factors may make some eyes more susceptible to axonal loss in early stages of the disease.

This is a 2020 ARVO Annual Meeting abstract.