Determination of absolute erythrocyte velocity and flow in the human retinal microvasculature by direct visualization of ICG-labelled erythrocytes

Abstract

Purpose : Erythrocyte velocity in the retinal microvasculature may be an important biomarker for ocular disease. Erythrocyte-mediated angiography (EMA) utilizing Indocyanine Green (ICG) labelled erythrocyte ghosts allows for the direct visualization of erythrocytes and determination of retinal erythrocyte velocity. We performed a prospective human study aimed to measure the absolute erythrocyte velocity in the retinal microvasculature using EMA.

Methods : A Heidelberg Retinal Angiograph 2 (Heidelberg Engineering, Germany) was used to acquire 12-20 second angiograms of patients undergoing EMA at 24.6 frames per second. After image registration, three graders examined each angiogram frame by frame and determined the velocity of individual ICG labelled erythrocytes in peripapillary vessels of 30-65 microns in average diameter. Arteries and veins were distinguished by the direction of the erythrocyte movement. Average measured erythrocyte velocity was determined. The bottom quartile of measured velocities was assumed to be the diastolic velocity. Vessel flow was determined by multiplying the velocity by the cross-sectional area.

Results : 20 Erythrocyte Mediated angiograms of 16 vessels of 11 individuals (5 females and 6 males) were analyzed. The average age of participants was 58.8 +/- 5.9 years. The average vessel caliber was 43.76 +/- 7.66 microns. Diastolic venous velocity ranged from 3.21 to 6.38 mm/s with an average of 4.81 +/- 1.04 mm/s. Diastolic arterial velocity ranged from 3.59 to 8.95 mm/s with an average of 7.68 +/-2.50 mm/s. Overall measured venous velocity ranged from 4.71 to 8.07 mm/s with an average of 6.47 +/- 1.16 mm/s and overall measured arterial velocity ranged from 5.09 to 8.95 mm/s with an average of 7.02 +/11.44 mm/s. Average diastolic venous flow was 0.51 +/- 0.25 microliters per minute and average diastolic arterial flow was .0.53 +/- 0.18 microliters per minute.

Conclusions : Using erythrocyte mediated angiography, the average diastolic erythrocyte velocity in this sample was determined to be 4.81 +/- 1.04 mm/s in human retinal venules and 7.68 +/- 2.50 mm/s in arterioles. Deterrmination of systolic velocities was limited by frame rate.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Three consecutive erythrocyte mediated angiography frames (A-C) with tracked erythrocyte circled in red.