Analysis of Foveal Microvascular Abnormalities in Diabetic Retinopathy Using Optical Coherence Tomography Angiography with Projection Artifact Removal

Abstract

Purpose To analyze foveal microvascular abnormalities in different stages of diabetic retinopathy (DR) using optical coherence tomography angiography (OCTA) with projection artifact removal (PAR). Methods We analyzed 93 eyes of 59 patients with diabetes—31 with no DR (no DR), 34 with mild to moderate nonproliferative DR (mild DR), and 28 with severe nonproliferative DR to proliferative DR (severe DR)—and 31 age-matched healthy controls. Sections measuring 3 × 3 mm2 centered on the fovea were obtained using OCTA. The area, perimeter, and acircularity index (AI) of the foveal avascular zone (FAZ), vessel density within a 300 μm wide region of the FAZ (FD-300), and parafoveal vessel density in the superficial capillary plexus (SCP) and deep capillary plexus (DCP) were calculated using novel built-in software with PAR. Results There was no statistically significant difference in the FAZ area (p=0.162). There was a statistically significant difference in the FAZ perimeter (p=0.010) and the AI (p < 0.001) between the four groups. There was a correlation between the AI and the increasing severity of DR (p=0.010). Statistically significant decreases of vessel density in the FD-300, SCP, and DCP were observed (all p < 0.001). There was a difference in parafoveal vessel density in the DCP between the healthy control eyes and the eyes with diabetes without DR (p=0.027). There was a significant correlation between vessel density and increasing severity of DR (p < 0.001). Conclusion Compared with the FAZ area, AI allows a more helpful quantitative assessment of the changes in the FAZ. Vessel density determined using OCTA with PAR might be a useful parameter indicating the progression of DR. Parafoveal vessel density in the DCP after PAR might be a potential early biomarker of DR before appearance of clinically evident retinopathy and needs further investigation.

Clinical validation of the RTVue optical coherence tomography angiography image quality indicators

“…However, the new SQI also takes motion artefacts and image defocus into consideration. Numerous previous studies have reported on the OCTA image quality using the SSI but more recent studies are using SQI . Direct comparison between these values for individual patient is not possible since users can no longer access the SSI values once the software is upgraded to Phase 7.0.…”

“…This threshold was also used in the Hwang et al study for quantification of capillary non‐perfusion in DR. A higher threshold of SSI ≥60 was used by other studies, such as Mastropasqua et al to analyse VR in patients with RVO complicated with macular oedema, and Golebiewska et al to assess OCTA features in children with type 1 DM. Conversely, in more recent studies using Optovue device, an SQI of ≥6 was used as the threshold for acceptable images . However, none of the above studies provided a scientific justification for the minimum SSI or SQI threshold chosen.…”

“…Numerous previous studies have reported on the OCTA image quality using the SSI but more recent studies are using SQI. 19,20 Direct comparison between these values for individual patient is not possible since users can no longer access the SSI values once the software is upgraded to Phase 7.0. We had the opportunity to do this comparative analysis because we routinely exported the SSI value for our scans prior to the upgrade.…”

“…The minimum cut-off SSI for acceptable OCTA image ranges from 40 to 60 in the current literature. For example, SSI ≥40 was used as the cut-off threshold in the Tang et al 21 study for evaluation of quantitative metrics in diabetic patients and the Cao et al 22 study evaluating patients with preclinical DR. SSI ≥50 was applied in the studies reported by Samara et al, 23 Wang et al 24 19,20 However, none of the above studies provided a scientific justification for the minimum SSI or SQI threshold chosen. A few studies have investigated which signal strength threshold should be used for excluding OCTA images from quantitative assessment.…”

Quantitative Analysis of Foveal Microvascular Differences in Diabetic Macular Edema with and without Subfoveal Neuroretinal Detachment

“…A series of parameters in the foveal area were obtained using the built-in AngioAnalytics software (version 2017.1.0.151; Optovue, Fremont, California, USA). In the FAZ quantitative analysis, the area, perimeter, and the acircularity index (AI) were evaluated as in a previous study [18]. The AI was measured using the following equation: AI = perimeter calculated/standard circular perimeter of the equal area.…”