Reproducibility of retinal erythrocyte velocity using human erythrocyte-mediated angiograms

Abstract

Purpose : Erythrocyte-mediated angiography (EMA) is a novel technique that allows for direct visualization of indocyanine green (ICG)-labeled ghost erythrocytes for in vivo determination of retinal erythrocyte velocity. Retinal erythrocyte velocities may be an important biomarker in the development of ocular diseases. Due to the innovative nature of EMA, no data exists on the reliability and reproducibility of retinal erythrocyte velocity measurements obtained from erythrocyte-mediated angiograms. As part of a prospective human study, we aimed to evaluate the repeatability of retinal erythrocyte velocity both within and across EMA sessions.

Methods : EMA was performed using a Heidelberg Retinal Angiograph 2 (Heidelberg Engineering, Germany). 10 to 20-second angiograms of the retina were obtained at 24.6 frames per second. After image registration, graders tracked erythrocytes flowing within vessels, and erythrocyte velocity was obtained using a custom MATLAB script. Intrasession variability, or the reproducibility of erythrocyte velocity within a single EMA session, was determined using 10 vessels (3 arteries and 7 veins, 6 eyes of 5 subjects) imaged twice within the same EMA session. Intersession variability, or the reproducibility of erythrocyte velocity across time, was determined using 10 vessels (3 arteries and 7 veins, 8 eyes of 5 subjects) imaged in the same subject in two separate EMA sessions, separated by at least 60 days. The region of the vessel for velocity measurement was limited to no more than 100 pixels, approximately 1 mm. Diameters of retinal vessels were determined using conventional liquid ICG angiograms obtained at the conclusion of each EMA session.

Results : Average percent difference in mean erythrocyte velocities within a single EMA session was 4.34% (3.13%). Average percent difference in mean erythrocyte velocities across two EMA sessions separated by at least 60 days (mean 348 days) was 6.69% (4.32%). Absolute erythrocyte velocity was 7.26 (0.98) mm/s in a 40.57 (4.08) µm arteriole and 5.81 (1.76) mm/s in a 43.37 (8.25) µm venule.

Conclusions : Mean erythrocyte velocity in this sample is 7.26 mm/s in arterioles and 5.81 mm/s in venules. Intrasession variability of erythrocyte velocity using EMA is 4.34%, and intersession variability is 6.69%, suggesting that erythrocyte-mediated angiography generates reproducible erythrocyte velocity measurements.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Erythrocyte flowing in an arteriole.