Measurement of Retinal Blood Flow Parameters in Steady State Sickle Cell Disease Using Doppler Optical Coherence Tomography

Abstract

Purpose : In sickle cell disease (SCD), red blood cell (RBC) polymerization and aggregation causes alterations in retinal hemodynamics and tissue perfusion. Chronic sickling is hypothesized to contribute to hypoxic conditions that may induce vasodilation. Arteriovenous shunting is thought to contribute to reduced capillary resistance and increased blood flow. The purpose of this study was to quantify microvascular retinal blood flow (RBF) parameters in SCD using a prototype Doppler OCT flowmeter (Topcon Corp., Tokyo, Japan).

Methods : 18 steady state SCD (22 eyes, 4 Hemoglobin SC, 18 Hemoglobin SS) and 18 age-matched controls (29 eyes, Hemoglobin AA) were included in this cross-sectional observational study. Doppler OCT was employed to quantify the average velocity (mm/s), blood flow rate (μL/min), and vessel diameter (μm) in a total of 156 vessels (82 arteries, 74 veins) located within 2.0-3.5 mm from the optic disc. The 1 mm D-OCT scan was located perpendicular to the selected vessel in the superotemporal (ST) or inferotemporal (IT) arcades. Statistical tests were used to quantify RBF parameters and their correlation with hematocrit levels measured within one week of imaging.

Results : Vessel diameter and flow rate in ST arteries were significantly elevated in subjects with HbSS disease compared to controls (Table 1, Kruskal Wallis Test, p<0.001 and p<0.001, respectively). In ST veins, hematocrit was negatively correlated with velocity after controlling for vessel diameter (Figure 1, ρ=-0.541, p=0.046 in vessels with lumen diameters ≥ 133 μm and ρ=-0.829, p=0.021 in vessels with diameters < 133 μm). Velocity, flow rate, and vessel diameter were significantly different between HbSS disease and controls (p=0.012, p=0.004, and p=0.011). There were no significant differences in RBF parameters between vessels in the ST and IT arcades in SCD patients.

Conclusions : SCD subjects with HbSS disease exhibited significantly increased vessel diameters and RBF rates in ST vessels compared to controls. These hemodynamic changes hypothetically constitute a compensatory mechanism for insufficient retinal oxygenation due to RBC sickling and increased endothelial shear stress. Blood velocity was found to be correlated with hematocrit only in vessels with low shear rates (veins). Additional data is needed to determine whether there are differences in RBF parameters between HbSS and HbSC disease.

This abstract was presented at the 2023 ARVO Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.