Imaging of Parafoveal Surface Macrophages in Thyroid Eye Disease

Abstract

Purpose : Retinal macrophages play key roles in the regulation of immune reactions and tissue repair. Using clinical OCT, we examined the association of parafoveal surface macrophage density and capillary density in thyroid eye disease (TED) patients with low and high clinical activity scores (CAS).

Methods : 33 TED patients (33 eyes) and 13 healthy control subjects (13 eyes) were imaged using a clinical SD-OCT system (Avanti RTVue-XR; Optovue). 23 of the 33 TED patients had a CAS <=3 and 10 had CAS > 3. Ten 3x3mm scans centered at the fovea were acquired and averaged (PMID: 28068370). Axial length was obtained for ocular magnification correction of images. Automated macrophage identification was performed on a 3µm OCT-Reflectance (OCT-R) slab located above the ILM surface using MATLAB (Fig 1, Left Column) (PMID: 32574351). The OCT-A full vascular slab, located between ILM and 9μm below the OPL was used for capillary density measurements and foveal avascular zone (FAZ) delineation. (Fig 1, Middle Column) (PMID: 31106029). Macrophage density maps were generated for each subject to provide quantitative visualization of cell distribution across the 3x3mm scan area (Fig 1, Right Column).

Results : Surface macrophages within the FAZ were identified in 31% of controls, 87% of low CAS and 100% of high CAS groups. A statistically significant difference in macrophage density within the FAZ was observed between the control and TED groups (Kruskal-Wallis tests, P= 0.0005), with mean±SDs of 1±1, 6±7 and 14±6 cells/mm² in the controls, low CAS and high CAS, respectively. Linear regression showed no significant correlation between macrophage density within the FAZ and capillary density (r= -0.1; P= 0.495).

Conclusions : Clinical OCT is capable of imaging parafoveal surface macrophages in TED patients and healthy controls. Our findings suggest that the concentration of macrophages within the FAZ reflects the inflammatory burden in TED.

This is a 2021 ARVO Annual Meeting abstract.

 

In vivo imaging of parafoveal macrophages (left column) and the underlying microvasculature (middle column) in a healthy control (top row), TED patient with low CAS (middle row) and TED patient with high CAS (bottom row) using clinical OCT. A1, B1 & C1) 3 µm OCT-R slab located above the ILM surface, showing the presence of macrophages. A2, B2 & C2) Corresponding OCT-A full vascular layer. A3, B3 & C3) Overlay of macrophage density map and OCT-A. Higher macrophage density within the FAZ is associated with higher CAS in TED.