Longitudinal Analysis of Retinal Perfusion in Mice Following Acute Ischemia-Reperfusion Injury

Abstract

Background and Purpose Retinal ischemia is a common pathology in many vision-threatening diseases. Optical coherence tomography angiography (OCTA) is a non-invasive imaging technique that provides images of microvasculature by measuring temporal variations in the intensity of reflected light. OCTA has been employed previously to assess changes in retinal perfusion during, or immediately after acute ischemia-reperfusion (I/R) injury, however, the longitudinal impact of I/R injury has yet to be fully explored. The goal of this study was to explore the longitudinal relationship between retinal perfusion, thickness, and retinal ganglion cell (RGC) loss using a model of acute I/R injury in mice.

Methods 24 adult female C57Bl/6 mice were divided evenly into groups receiving 15-, 30- or 45-minutes of retinal ischemia, induced by elevating intraocular pressure (IOP) with a cannula in the anterior chamber connected to a raised pressure reservoir. A non-ischemic repeatability group of 4 mice was used for comparison. Imaging sessions were performed at baseline and over a period of 10-days post-I/R injury. At all time points, perfusion density (PD) in the superficial (SVP), intermediate (ICP) and deep (DCP) capillary plexuses were computed from OCTA vascular volumes and ganglion cell complex (GCC) thickness was computed from peripapillary optical coherence tomography (OCT) B-scans. Following the last imaging session, immunohistochemistry (IHC) was performed to quantify cumulative RGC loss. Relevant statistics were performed.

Results Longitudinal changes in retinal perfusion and GCC thickness following acute I/R injury were tracked in vivo with OCTA and OCT. PD was decreased in all plexuses in the 15- and 30-minute elevated IOP groups, however, changes at all time points were not significant when compared to the repeatability group. No significant differences were found in GCC thickness and RGC density between repeatability/control and the 15- and 30-minute elevated IOP groups across all time points. Due to extensive retinal damage, PD in the 45-minute elevated IOP group was computed using a custom vascular volume that combined all capillary plexuses together. PD in the 45-minute elevated IOP group was significantly lower than the repeatability group at all time points post-I/R injury. GCC thickness in the 45-minute elevated IOP group was significantly increased at 1-day, then significantly decreased at 5-, 7- and 10-days post-I/R injury, when compared to all other groups. RGC density in the 45-minute elevated IOP group was significantly lower than all other groups. There was no significant difference in PD between the SVP, ICP and DCP any time point in the 15- and 30-minute elevated IOP groups.

Conclusion This research describes the in vivo use of OCTA and OCT in tracking the longitudinal changes in retinal PD and GCC thickness following acute I/R injury in mice. Data gathered from OCTA and OCT may be useful in enhancing our understanding of the time course of changes in retinal perfusion and thickness during disease. Our comparative analyses between ischemic durations and between the vascular plexuses may provide valuable insight into the pathogenesis of ischemic retinal disease.