Retinal capillary and choriocapillaris velocimetry in normal eyes by optical coherence tomography angiography

Abstract

Purpose : To investigate the distribution of retinal capillary and choriocapillaris (CC) blood flow velocity in normal eyes, we performed swept-source optical coherence tomography angiography (SS-OCTA) using modified scanning protocols.

Methods : A prospective SS-OCTA imaging study was performed using a SS-OCTA instrument (PLEX® Elite 9000, ZEISS, Dublin, CA) with a 1050 nm center wavelength, a 200 kHz A-line rate, and motion tracking. A new scanning protocol was designed and implemented on the device using a 200x200 scan pattern covering 2x2mm with 10 repetitions at each B-scan position for the estimation of capillary velocimetry. The time interval between the adjacent B scans was ~1ms which gives a distinguishable velocity range from 0 mm/s to ~0.5mm/s according to the theoretical analysis. The mean frequency (MF) of the signal was calculated by the eigen-decomposition (ED) approach representing the mean blood flow velocity within the scanned tissue volume. Depth-resolved retinal and CC layers were segmented to investigate the speed variations in different plexuses, including the superficial retinal layer (SRL), deep retinal layer (DRL), and CC layers. The images were colorized to demonstrate the flow speed with variations from red (fast flow) to blue (slow flow). To maintain consistency, a fixed display range ([0, 700 Hz]) which was only determined by the time interval of the scanning protocol was applied to all the color images.

Results : 55 normal eyes with an age range between 20 to 90 years were recruited in this study. The MF has the ability of differentiating the flow speed at the capillary level (Fig.1) in the retina and CC. A strong negative linear relationship was shown to exist between MF and age in the SRL (P < 0.001, r=-0.63) and CC (P < 0.001, r=-0.66). A moderate negative linear relationship was shown to exist between the MF and age in the DRL (P < 0.001, r=-0.46).

Conclusions : The blood flow speed within capillaries of normal eyes decreased with increasing age in both retina and choriocapillaris. This capillary velocimetry strategy may provide additional functional parameters to help in the diagnosis, prognosis, and management of ocular diseases.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Fig1. Examples of mean frequency (MF) values compared with OCTA enface images.

 

Fig2. Relationship between the MF and age in Retina and chorodial layers. (A) Superfacial retina layer, (B) deep retina layer, (C) Choroidallcapillary layer.