Dynamics of Microvascular Intermittent Flow in Sickle Cell Retinopathy Revealed by Serial OCT-Angiography

Abstract

Purpose : Pathophysiology of sickle cell retinopathy (SCR) involves transient occlusion of microcirculatory networks that precipitate ischemic damage. We assessed these perfusion changes between a baseline imaging session and a 1-hour follow-up in SCR patients compared to controls.

Methods : Seven controls and 9 SCR patients were imaged at two sessions 1-hour apart using an SD-OCT system (Avant RTVue-XR; Optovue). Ten 3x3mm OCT-A scans centered at the fovea were obtained at each session. Scans were registered per subject and averaged per session using ImageJ (PMID:28068370). Analysis was conducted on a full vascular slab. Within-session intermittent flow during the first session was qualitatively identified, defined as capillaries with perfusion in one scan and without perfusion during a subsequent or prior scan.
Between-session changes were measured by calculating the difference in capillary perfusion pixel intensity between sessions for controls (Fig. A & B). Bland-Altman analysis generated a normative variation of pixel intensity between sessions. Difference in perfusion pixel intensity of SCR patients was subsequently calculated. Between-session changes in SCR patients were determined using the normative variation, with regions of non-perfusion defined as change < 0.01st percentile and re-perfusion as change > the 99.99th percentile (Fig. C).

Results : Within-session intermittent flow surrounding the FAZ was seen in 2 of 7 controls and in all 9 SCR patients. Between-session capillary perfusion changes of the entire scan area showed a median (IQR) of 0.49% (0.17-0.82) in SCR, with similar levels of non-perfusion: 0.26% (0.06-0.42) and re-perfusion: 0.23% (0.07-0.37). Greater capillary perfusion alterations were seen in patients with HbSS: 0.82% (0.49-0.83) compared to HbSC: 0.11% (0.08-0.14) and sickle cell trait: 0.59%. Statistical significance was found between HbSS and HbSC on two-tailed Wilcoxon rank sum test (P=0.0357).

Conclusions : Serial OCT-A reveals intermittent flow and capillary perfusion change in retinal microvasculature for SCR patients without intervention. Increased intermittent flow in HbSS compared to HbSC is also consistent with increased systemic vaso-occlusive symptoms documented for the former. Further assessment may reveal alteration of intermittent flow in response to disease progression or pharmacological intervention.

This is a 2020 ARVO Annual Meeting abstract.