Assessing Systemic and Retinopathy Severity in Sickle Cell Disease Using Transient and Permanent OCT-A Perfusion Indices

Abstract

Purpose : Transient and permanent vaso-occlusions are responsible for retinopathy and other end-organ injuries in sickle cell disease (SCD). HbSS genotype typically results in worse systemic disease, while HbSC produces more proliferative retinopathy. In this study, we compared transient and permanent OCT-A perfusion indices to evaluate systemic and retinopathy severity in SCD patients with different genotypes.

Methods : Fifty-four eyes in 54 SCD patients and 17 eyes of 17 race-matched unaffected controls were imaged at baseline and 1-hour apart using a clinical SD-OCT device (Avanti RTVue-XR; Optovue). SCD patients were divided into 4 subgroups by genotype (3 Trait, 13 HbSC, 34 HbSS, 4 HbS beta0 thalassemia). Ten macular 3x3mm full vascular layer OCT-A scans were registered and averaged at each session (Fig. A). Transient vaso-occlusion was evaluated using between-session intermittent perfusion index (IPI) based on a race-matched normative database as described previously (PMID: 34123506) (Fig. B). Permanent vaso-occlusion was evaluated using peri-vascular densities. Specifically, Peri-arteriolar to peri-venular capillary density ratio (AV ratio) on the averaged OCT-A scans were measured within 200 µm region of interest centered along the vessels (Fig. C).

Results : While median ± interquartile range of between-session IPI (%) in controls, SC trait, HbSC, HbSS, and HbS beta0 thalassemia were 0.006±0.009, 0.039±0.046, 0.205±0.300, 0.576±0.453, and 0.060±0.191, respectively (Kruskal-Wallis test, p < 0.0001), median ± interquartile range of AV ratios were 0.93±0.02, 0.93±0.01, 0.89±0.09, 0.91±0.05, and 0.89±0.04 (Kruskal-Wallis test, p = 0.005). Overall, worst IPI and AV Ratio were found in HbSS and HbSC, respectively. In the 3 HbSS patients who were imaged before treatment (IPI and capillary density (mean ± SD): 1.97±0.1 and 50.04±0.18%) and after treatment (IPI and capillary density (mean ± SD): 0.54±0.1 and 50.40±0.74%), IPI showed noticeably improvement with capillary density remained relatively stable.

Conclusions : OCT-A perfusion indices revealed transient and permanent occlusions in SCD with different genotypes. Our findings suggest that while IPI provides functional index of systemic disease activity, AV ratio is more predictive of retinopathy. Perivascular capillary density also revealed arterioles as the preferential site of vaso-occlusion in contrast to prior animal studies.

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