Importance: Susac syndrome (SuS) is a rare neurological condition that remains poorly understood and can lead to encephalopathy, branch retinal artery occlusions and vestibulopathy.

Objective: To determine whether there is subclinical microvascular involvement in the superficial and deep layers of the retina of patients with SuS and to evaluate the utility of OCTA as a diagnostic tool. 
 
Study Design:  Prospective cross-sectional study approved by the local ethics committee (H18-02488) conducted between 2019 to 2020. 
 
Setting: Vancouver Eye Care Centre, British Columbia, Canada

Participants: We enrolled 18 eyes of 9 SuS patients (diagnosed according to the EuSac Consortium) and 18 eyes of 9 age- similar healthy controls. 12 eyes (2 males and 5 females) of SuS patients were affected by previous BRAOs (SuS-A), 6 eyes (2 males and 1 female) were clinically unaffected (SuS-U). Mean age of all SuS patients was 46±12 years (range 31-69) and healthy controls were 47±13 years (range 31-68) of age.

Interventions/Exposures: Eyes of all patients with Susac syndrome determined by conventional fluorescein angiography (FA), and 18 eyes of healthy controls were enrolled prospectively to undergo measurements with an OCT-A system (Plexelite 9000, ZEISS). Three 6x6mm images, centered at the fovea were captured. 

Main Outcome and Measures: Analysis was conducted of various parameters including vessel density, skeleton density, fractal dimension, axis ratio, and measurements of the foveal avascular zone in both the deep and superficial layers of the retina. Comparisons were made using ANOVA, with post-hoc Tukey HSD.    


Results: Eccentricity (EC) and axis ratio (AR) in superficial and deep retinal layers were significantly higher in SuS patients compared to healthy controls (EC: SuS 0.61±0.11, controls 0.51±0.10, p=0.003; AR: SuS 1.57±0.28, controls 1.39±0.11, p=0.005). EC was significantly higher in superficial (p=0.027) and deep retinal layers (p=0.047), AR only in superficial retinal layers (p=0.018). Skeleton density (SD) of superficial and deep retinal layers was significantly lower in SuS patients when compared to healthy controls (SuS 0.11±0.01 vs. controls 0.12±0.01, p=0.027). Vessel density of the inner ring (VDI) in the superficial layers was significantly lower in SuS patients when compared to healthy controls (SuS 0.39±0.04 vs. controls 0.42±0.02, p=0.041), but not in post hoc analyses when comparing the different subgroups. The remaining VD values, although consistently higher in healthy controls, were not significantly different between the tested groups.

Investigating microangiopathy using optical coherence tomography angiography in patients with Susac syndrome

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