Abstract
Purpose :
Glaucoma is a multifactorial optic neuropathy resulting in progressive retinal ganglion cell loss. In vivo imaging studies have suggested that there is a reduction in perfused capillary density prior to thinning of the retinal nerve fiber layer. However, it is unknown if these in vivo changes reflect a disruption of vascular flow, a loss of capillary volume, or both. The purpose of this study was to determine the circumpapillary vasculature to tissue ratio in control and experimental glaucoma eyes using serial block-face scanning electron microscopy (SBF-SEM).
Methods :
4 macaque monkeys with unilateral laser-induced experimental glaucoma were euthanized at different endpoints. Animals were perfusion fixed, and retinal tissue from 6 sectors (superonasal, nasal, inferonasal, inferotemporal, temporal, and superotemporal) within 500μm of the optic nerve head rim was dissected and processed for SBF-SEM imaging. Nominally, a 200x200µm block face was imaged at 500nm intervals using a Tescan Mira3 SEM equipped with a Gatan 3View serial sectional system. Capillaries in the nerve fiber layer were marked using Image-Pro image analysis software and used to determine the vascular and tissue volume.
Results :
Endpoint circumpapillary retinal nerve fiber layer (RNFL) thickness for the four experimental eyes were 49, 52, 76, and 84μm. The average vascular volume and tissue volume were less in the glaucoma eyes (1.5±1.1 x10-5μL and 23.6±12.4 x10-4μL) compared to the control eyes (2.5±1.7 x10-5μL, p=0.02, and 41.0±12.9 x10-4μL, p<0.01). The vascular volume density was not significantly different (p =0.6) between experimental glaucoma eyes (0.59±0.09%) and control eyes (0.63±0.07%). For the samples analyzed, the vascular volume was linearly related to RNFL tissue volume (slope=0.0063, R2 = 0.76).
Conclusions :
This study suggests that in the non-human primate experimental glaucoma model, a constant circumpapillary vascular volume density is maintained. It is possible that the initial loss of vascular flow reported using in-vivo techniques might predict the extent of nerve fiber layer loss.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.