Preferential Vulnerability of Capillary Occlusion in Sickle Cell Retinopathy

Abstract

Purpose : Capillary occlusion, leading to ischemic retinopathy, is a hallmark of sickle cell disease (SCD). However, the site of greatest vulnerability to capillary occlusion is controversial. In this study, we assessed the extent of peri-arteriolar and peri-venular non-perfusion in SCD patients with retinopathy using OCT-A as a clue to any preferential vulnerability.

Methods : Seventeen healthy controls (17 eyes) and 14 SCD patients (14 eyes) were imaged using a clinical SD-OCT system (Avanti RTVue-XR; Optovue). SCD patients were divided further into two subgroups according to their genotypes (5 HbSC and 9 HbSS). Ten 3x3mm OCT-A scans centered 9 degrees temporal to the fovea were acquired and averaged for each control and SCD patient (PMID: 28068370) (Fig. Top row). Peri-vascular capillary densities were measured using full vascular OCT-A slabs. First, arterioles and venules on the OCT-A were extracted using global thresholding (MATLAB, The MathWorks Inc., Natick, MA). Next, a 300 µm region of interest centered along the skeletonized arterioles and venules was generated. Peri-vascular capillary density measurements were performed on two pairs of adjacent arterioles and venules with similar caliber and length (Fig. Bottom row. Only one pair is shown). Arterioles and venules were pre-identified using the color fundus image. Axial length was obtained for ocular magnification correction of each measurement.

Results : Median ± interquartile range of peri-vascular capillary density (%) in controls, SCD HbSC, and SCD HbSS respectively, were 46.7±7.9, 41.8±15.3, and 40.6±15.7 for arterioles; and 51.5±5.2, 49.7±6.6, and 49.7±2.9 for venules. Peri-arteriolar capillary density was significantly different among groups (Kruskal-Wallis test, p = 0.003). Peri-arteriolar capillary density was significantly lower in the SCD HbSS group compared to the control group (pairwise comparison, p = 0.021). Peri-venular capillary density among groups showed no significant differences (Kruskal-Wallis test, p = 0.257).

Conclusions : Peri-vascular capillary density using OCT-A can be helpful for determining specific occlusive vulnerability. Our findings suggest that the most vulnerable site of vaso-occlusion is located adjacent to the arteriolar–capillary junctions. Further investigation into the regional variations of the vaso-occlusive events has the potential to enhance our understanding of the disease pathophysiology, severity, and treatment effect.

This is a 2021 Imaging in the Eye Conference abstract.