Name

Comparaison du signal de reflectivité obtenu en OCT Enface et en Angio OCT dans l'oedème maculaire cystoïde

Purpose: to compare and evaluate images of macular cysts with different degrees of reflectivity (from gray to black signal) as observed in B-scan Spectral Domain OCT (SD-OCT) and En Face OCT with decorrelation signal obtained with OCT-angiography (OCT-A) in eyes with cystoid macular edema (CME) secondary to diabetic retinopathy (DR) and retinal vein occlusion (RVO).

Methods: images from 3033 patients affected by CME secondary to diabetes or RVO examined with SD-OCT (Spectralis OCT, Heidelberg Engineering, Germany or Cirrus 5000 OCT, Zeiss, Germany), En Face OCT and OCT-A (Optovue XR Avanti, Optovue, USA) at the Eye Clinic Department, Hôpital Intercommunal, Créteil, France, and at the University Eye Clinic of Cagliari, “San Giovanni di Dio” Hospital, Italy, were retrospectively examined. The deep capillary plexus OCT-A images and the corresponding EnFace OCT images, both acquired with the same automatic segmentation, were overlapped to compose RGB color images as red and green channels, respectively, using ImageJ software (National Institutes of Health, Bethesda, MD). Then, linear regions of interest were traced on the color images to obtain the profiles of OCT-A and EnFace gray values. Data were exported to Excel to create the plots.

Results: we found 94 patients with DME and 27 patients with RVO showing intraretinal macular cystoid spaces with similar homogeneous, gray-looking content, and 73 patients with DME and 113 patients with RVO showing  macular cystoid spaces with homogeneous, black-looking content, as observed at SD-OCT, EnFace and OCT-A scans. Interestingly, the limits of macular cystoid spaces are clearly detectable with OCT-A. 

Discussion: the analysis of red and green profiles demonstrated a clearly visible overlapping between the average OCT-A and En Face signal observed around cystoid spaces (Figure 1, zones A-D), that could be attributed to a relationship between the dynamic vascularization and structural density of the tissue. In fact, OCT-A profiles show sharp peaks, whereas EnFace profiles show somewhat parallel, but smoother changes. A similar overlapping of red and green plots was also found inside the cystoid spaces (Figure 1, zones B-C), where microvessels are not visible, although here the red and green signals are of lower intensity, but still significantly higher than the background level.

Conclusions: this is the first investigation which characterizes and correlates OCT-A and enface signals on images of macular cystoid spaces in DR and RVO. We found a constant overlapping between the vascular signal (OCT-A) and the structural signal (EnFace OCT) both outside and inside the cystoid spaces examined in our population affected by diabetic retinopathy and retinal vascular occlusion.. Since OCT-A is a technique that employs motion contrast to detect erythrocyte movements in retinal blood vessels, the low intensity OCT-A signals observed inside cystoid spaces, pose a relevant question about their nature, as to whether they are due to the presence of corpusculated content or must be considered OCT-A artifacts.