Abstract
Purpose :
Changes in retinal blood flow are dynamic and range from normal physiological changes associated with a cardiac pulse to abnormal changes associated with acute or chronic diseases. Detailed assessment of temporal traits of retinal blood flow including differential assessment of arterial flow and venous flow may offer benefits to research and clinical diagnostics.
Methods :
The XyCAM RI investigational device was used to acquire data from either the left or right (randomly chosen) eye of 15 subjects. Four imaging sessions were conducted on each subject, wherein each imaging sessions involved acquisition of laser speckle images over 6 seconds at a rate of 82 frames/second. Data was processed by the XyCAM RI in sliding batches of 11 frames each to generate retinal blood flow maps, and averaged over the four sessions. As illustrated in Figure 1, flow values were averaged over all pixels in one arterial segment and a proximal venous segment to obtain volumetric flow indices (VFI) for the vessel and its temporal profile over the first cardiac cycle was assessed. Other indices computed include blood volume (V), fractional change of V during the cardiac cycle (ΔV/V), blood velocity index (BVI), and ratios of arterial metrics to corresponding venous metrics (AVR).
Results :
Table 1 provides salient observations in the assessed arteries and veins of 15 subjects. Further, the XyCAM RI was able to successfully determine that the peak in the venous flow lagged the peak in arterial flow by 6.46% ± 2.65% of the duration of the cardiac cycles. There was also a significant (p<0.001, paired two sided student t-test) difference in the ratio of rise time to fall time of flow in arteries (0.60 ± 0.12) and veins (0.69 ± 0.13). Observed AVR for peak VFI in the artery-vein pairs was 1.00 ± 0.07 suggesting that blood flow in the region supplied by these vessels is conserved. However, the AVR for peak BVI was 1.69 ± 0.63 and AVR for ΔV/V was 1.61 ± 0.22.
Conclusions :
Preliminary results from our investigation validate the ability of the XyCAM RI to elucidate differential blood flow dynamics in retinal arteries and veins at a high temporal resolution and may offer avenues for development of early biomarkers for ophthalmic or systemic diseases with vascular symptoms in the retina.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.