Abstract
Purpose :
Through the use of fluorescently-labeled erythrocytes, Erythrocyte Mediated Angiography (EMA) allows for direct observation of retinal blood flow in vivo (Tracey et al., Scientific Reports, 2019). We present a novel technique for quantifying capillary blood flow velocity (BFV) in the superficial vascular plexus (SVP), the intermediate capillary plexus (ICP), and the deep capillary plexus (DCP) in humans and non-human primates (NHPs) using EMA.
Methods :
Human red blood cells (RBCs) loaded with 1 mM indocyanine green and rhesus macaque RBCs loaded with up to 10 mM carboxyfluorescein succinimidyl ester (CFSE) were prepared for autologous injection. RBCs were injected intravenously, and a Heidelberg Spectralis was used to acquire angiograms and perform optical coherence tomography angiography (OCTA) at the macula. High intraocular pressure (IOP) was induced in the NHPs by using a tight lid speculum. RBCs in capillaries were tracked using a custom MATLAB script. To identify the corresponding vascular plexus, overlays were made using a time-lapse stack of EMA frames and en-faceOCTA images of the SVP, ICP, and DCP (Figure 1). Two-tailed, unpaired t-tests were used to compare velocities in different plexuses or conditions.
Results :
Mean retinal capillary BFV in each plexus was quantified in 6 eyes of 4 humans and 4 eyes of 2 NHPs (Table 1). Mean BFV in the NHPs was significantly lower when IOP was increased as compared to the baseline velocities for the SVP, ICP, and DCP (p<0.01, p<0.01, and p<0.01, respectively).
Conclusions :
Adequate capillary blood flow is essential to supporting the metabolic functions of retinal tissue. However, our understanding of flow dynamics in the various retinal capillary networks is limited. To our knowledge, we are the first to measure absolute retinal capillary BFV in the SVP, ICP, and DCP in humans and NHPs. Additionally, we found a significant decrease in BFV across the three vascular plexuses when IOP was increased in the NHPs. Retinal capillary velocities are highly dependent on ocular perfusion, both IOP and blood pressure. The ability to quantify blood flow in retinal capillaries may further the understanding of disease progression as a result of impaired ocular flow.
This is a 2021 ARVO Annual Meeting abstract.