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Introduction
Since its inception, optical coherence tomography angiography (OCTA) has inspired a steady rise in the number of studies capitalizing on its ability to provide a depth-resolved, contrast-free imaging of the retinal vasculature. This technology has been shown to be particularly useful in evaluating the microvascular changes associated with diabetes.1,2 The commercially available Angiovue software on the Avanti RTVue XR device (Optovue, Fremont, CA) uses a split-spectrum amplitude-decorrelation algorithm (SSADA), which reduces the effect of bulk-motion to improve signal-to-noise ratio in the axial direction.3 The SSADA algorithm, which compares only amplitude information between consecutive OCT B-scans, also splits the OCT spectrum into 11 sub-bands, further improving the signal-to-noise ratio but decreasing axial resolution of the final image.4 Another commercially available OCTA instrument, the Zeiss Cirrus HD-OCT 5000 (Zeiss Meditec, Dublin, CA) with Angioplex, is based on optical microangiography (OMAG), which compares both amplitude and phase differences between consecutive B-scans.5,6
The software currently available in these two OCTA devices automatically segments the retinal capillaries into two slabs: the superficial capillary plexus (SCP) and the deep capillary plexus (DCP), and a majority of the diabetic retinopathy (DR) literature evaluated only these two plexuses.7–14 However, previous work has demonstrated the existence of a physiologically distinct middle capillary plexus (MCP).15–18 As a consequence, the MCP is visualized, in part, within both slabs. Previously, we have demonstrated a manual segmentation procedure on Angioview software to elucidate and qualitatively evaluate the distinct MCP.19
In this study, we aim to assess the feasibility of using customized segmentation strategies to reveal the MCP using the Zeiss Angioplex OCTA in a cohort of patients with varying levels of DR. We then compare the capillary plexuses derived from the two devices (Optovue and Zeiss) in terms of motion artifacts, preservation of pathological changes, and quantitative parameters (including full-thickness foveal avascular zone [FAZ] and vessel length density) at each capillary plexus layer.
Patients and Methods
Participants
This prospective, observational study was approved by the institutional review board at Northwestern University, complied with the Health Insurance Portability and Accountability Act, and followed the tenets of the Declaration of Helsinki. The study period was between September 2016 and January 2017. Informed consent was obtained from all subjects. Patients were recruited during their routine ophthalmologic examinations in the Department...