Abstract
Purpose :
Flow signal interpretation in optical coherence tomography angiography (OCTA) can be confounded by artifacts.The aim of this study was to investigate whether hyperreflective foci (HRF) exhibit flow projection artifact on OCTA, and to study the efficacy of commercial projection artifact removal software (PAR-OCTA, Optovue, Inc), and a custom projection resolved OCTA (PR-OCTA) in distinguishing these artifacts from true flow in retinal angiomatous proliferation (RAP).
Methods :
Five eyes with intraretinal HRF and dry age-related macular degeneration (AMD) representing retinal pigment epithlial (RPE) migration, five eyes with actively leaking treatment-naïve RAP appearing as HRF on OCT, and ten eyes with diabetic hard exudates were analyzed. We examined flow signal on OCTA cross-sections using PAR, and performed PR-OCTA to study the effect of increasingly stringent projection removal thresholds. The region of interest (ROI) was selected, and flow signal analysis was performed using the "color histogram" feature in imageJ (NIH, Bethesda, MD). Flow signal intensity was quantified by calculating the percentage of red pixels (R) representing flow in the ROI, compared to green (G) and blue (B) pixels.
Results :
PAR-OCTA cross sections revealed persistent flow signal in HRF in all eyes. In RAP lesions, PR-OCTA detected intransigent flow, irrespective of the strength of flow removal threshold. Mean R in the five RAP lesions at the most stringent PR-OCTA threshold remained higher than mean G and B (40.96 % vs 29.52 and 29.52 %, respectively) denoting the persistence of flow. In contrast, increasing the PR-OCTA threshold in pigment migration and in hard exudate lesions removed the flow signal. For RPE migration and hard exudates, there was a statistically significant decrease in mean R with increasing threshold (ANOVA, p = 0.017 and 0.0029, respectively).
Conclusions :
PAR-OCTA is not completely effective at removing artifactual flow in hard exudates and HRF related to RPE migration. Custom built PR-OCTA, using a sliding scale of threshold, allowed us to distinguish true flow in RAP from artifactual flow in avascular HRF. Further studies are needed to validate the optimum threshold for projection artifact removal, which would also maintain true flow in RAP and the small intraretinal capillaries.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.