Abstract
Purpose :
Visual thresholds and circumpapillary retinal nerve fiber layer (RNFL) thickness both are dependent on the underlying retinal ganglion cell (RGC) content, and are clinically used for the diagnosis and evaluation of progression of optic neuropathies. The purpose of this study was to determine the relationship between endpoint in vivo measures and retrobulbar RGC axonal counts in the non-human primate model of experimental glaucoma.
Methods :
Intraocular pressure was elevated by laser scarring the trabecular meshwork in 8 non-human primates. Both experimental and control eyes were monitored with standard automated perimetry (SAP 24-2, full thresholds), and optical coherence tomography (OCT). At varying endpoints, SAP thresholds were converted to RGC counts using the eccentricity dependent non-linear model, accounting for individual differences in retinal scaling . Global RNFL thickness was determined from an elliptical scan path 550µm from the Bruch’s membrane opening. Post-mortem complete axon counts were determined from thin optic nerve sections imaged with light microscopy using 100X magnification.
Results :
The optic nerves of control eyes had an average of 1,309,496±160,025 axons. RGC estimates from SAP were on average 73,316 less than that established from total retrobulbar axon counts (95% limits of agreement = -365,187, 218,553). The slope of the regression comparing the two RGC counts (R2 = 0.89, slope = 0.96) was not significantly different from 1 (p = 0.44). RNFL thickness was linearly related to retrobulbar axon counts (R2 = 0.85, slope = 15322.9 axons/µm), and RGC estimates from SAP (R2 = 0.92, slope = 15740 RGCs/µm).
Conclusions :
Estimates of global retinal ganglion cell counts from visual thresholds are an accurate representation of the retrobulbar axonal count. This relationship is also reflected in objective measures of RNFL thickness, a measure often used as a surrogate of axonal counts.
This is a 2021 ARVO Annual Meeting abstract.