Abstract
Purpose :
Adaptive optics (AO) can be used to visualize autologously-reinjected, indocyanine green (ICG)-loaded erythrocytes (erythrocyte mediated angiography, EMA) in the living human eye. In this study, we introduce an improved approach to longitudinally map erythrocytes in stasis within the choriocapillaris.
Methods :
EMA was performed annually for four years in one subject, with images acquired at various timepoints after injection using a Heidelberg Spectralis Scanning Laser Ophthalmoscope (SLO). For three of the visits, AO imaging was performed on the same day as the EMA procedure to obtain higher resolution images of the erythrocytes in stasis. AO enhanced ICG angiography (AO-ICGA) was also performed to map out the choriocapillaris in the foveal region (PMID 30456310). All images were co-registered and locations of cells in stasis identified using both SLO and AO were combined for further analysis.
Results :
Erythrocytes in stasis were observed at all visits. Across the four-year follow-up, a total of 54 cells in stasis were identified by SLO and/or AO within the foveal choriocapillaris network mapped using AO-ICGA. Remarkably, 100% of these cells were localized to pixels corresponding to the choriocapillaris vessel lumens, which would be highly unlikely to occur by random chance (p<0.01, one-sided binomial test, with the probability of success set at 68% - the overall percentage of pixels that corresponded to choriocapillaris lumens). The observation of cells in stasis within the choriocapillaris (as opposed to retinal capillaries) was further corroborated using AO images acquired over a series of different focal planes throughout the retina (~35 µm step size). Interestingly, when comparing locations at which cells in stasis were observed over the four years, there were positions within the choriocapillaris network at which cells in stasis was observed across multiple visits, suggesting that these may be preferential sites of erythrocyte stasis within the choriocapillaris.
Conclusions :
The combination of AO with EMA enables erythrocytes to be mapped to the choriocapillaris network at fine spatial resolution, a first step towards unraveling the peculiarities of how cells flow through the choriocapillaris meshwork. We demonstrate, for the first time, longitudinal assessment of erythrocytes in stasis at the single capillary level.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.