Evaluation of Automatically Quantified Foveal Avascular Zone Metrics for Diagnosis of Diabetic Retinopathy Using Optical Coherence Tomography Angiography
Yansha LuJoseph M. SimonettJie WangMiao ZhangThomas S. HwangAhmed M. HagagDavid HuangDengwang LiYali Jia
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Abstract:
To describe an automated algorithm to quantify the foveal avascular zone (FAZ), using optical coherence tomography angiography (OCTA), and to compare its performance for diagnosis of diabetic retinopathy (DR) and association with best-corrected visual acuity (BCVA) to that of extrafoveal avascular area (EAA).We obtained 3 × 3-mm macular OCTA scans in diabetic patients with various levels of DR and healthy controls. An algorithm based on a generalized gradient vector flow (GGVF) snake model detected the FAZ, and metrics assessing FAZ size and irregularity were calculated. We compared the automated FAZ segmentation to manual delineation and tested the within-visit repeatability of FAZ metrics. The correlations of two conventional FAZ metrics, two novel FAZ metrics, and EAA with DR severity and BCVA, as determined by Early Treatment Diabetic Retinopathy Study (ETDRS) charts, were assessed.Sixty-six eyes from 66 diabetic patients and 19 control eyes from 19 healthy participants were included. The agreement between manual and automated FAZ delineation had a Jaccard index > 0.82, and the repeatability of automated FAZ detection was excellent in eyes at all levels of DR severity. FAZ metrics that incorporated both FAZ size and shape irregularity had the strongest correlation with clinical DR grade and BCVA. Of all the tested OCTA metrics, EAA had the greatest sensitivity in differentiating diabetic eyes without clinical evidence of retinopathy, mild to moderate nonproliferative DR (NPDR), and severe NPDR to proliferative DR from healthy controls.The GGVF snake algorithm tested in this study can accurately and reliably detect the FAZ, using OCTA data at all DR severity grades, and may be used to obtain clinically useful information from OCTA data regarding macular ischemia in patients with diabetes. While FAZ metrics can provide clinically useful information regarding macular ischemia, and possibly visual acuity potential, EAA measurements may be a better biomarker for DR.Keywords:
Foveal avascular zone
Repeatability
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<b><i>Purpose:</i></b> The aim of this study was to evaluate the repeatability and reproducibility of foveal avascular zone (FAZ) area measurements using AngioPlex spectral domain optical coherence tomography (OCT) angiography in normal subjects. <b><i>Methods:</i></b> Twenty-two healthy subjects (25 eyes) underwent FAZ area measurements with AngioPlex OCT. Each volunteer was separately examined 3 consecutive times by the 2 experienced observers. The FAZ area was measured using ImageJ software. Intraobserver repeatability was evaluated by calculating the coefficient of variation (CoV) and intraclass correlation coefficient (ICC). Interobserver reproducibility was also assessed using the Bland-Altman test and concordance correlation coefficient (CCC). <b><i>Results:</i></b> The FAZ areas were measured as 0.373 ± 0.109 and 0.377 ± 0.112 mm<sup>2</sup> by observers 1 and 2, respectively. The repeatability assessment of the FAZ area measurements yielded CoV values of 0.029 and 0.034 and ICC values of 0.997 and 0.996 by observers 1 and 2, respectively. The mean difference between the 2 observers was 0.004. CCC values ranged from 0.9705 to 0.9844. <b><i>Conclusions:</i></b> The FAZ area measurements obtained using AngioPlex OCT showed a good repeatability and reproducibility in healthy subjects. Excellent reliability makes AngioPlex OCT a valid device for measuring the FAZ area.
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ABSTRACT Purpose To develop and evaluate an automated method to measure the foveal avascular zone (FAZ) area in healthy eyes on Heidelberg Spectralis Optical Coherence Tomography Angiography (HS-OCTA). This method is referred to as the modified Kanno-Saitama macro (mKSM) and it is an evolution of the original Kanno-Saitama macro (KSM) approach. Methods This cross-sectional study included 29 eyes of 25 healthy volunteers who underwent HS-OCTA at the macular area twice at the same time. Regardless of the quality of the images, all of them were included. Macular data on the superficial vascular plexus, intermediate capillary plexus and deep capillary plexus were processed by mKSM. The FAZ area was measured twice automatically using the mKSM and KSM and twice manually by two independent examiners. Results From 174 images, KSM could not measure correctly 31% while mKSM could successfully measure all of them. Intrascan intraclass coefficient ranged from 0,948 to 0,993 for manual measurements and was 1 for mKSM method, which means that mKSM FAZ area value is always the same for the same OCTA image. Despite that the difference between human examiners is smaller than between human examiners and mKSM according to Bland-Altman plots, the scatterplots show a strong correlation between human and automatic measurements. The best results are obtained in intermediate capillary plexus. Conclusions With mKSM, the automated determination of the FAZ area in HS-OCTA is feasible and less human-dependent. It solves the inability of KSM to measure the FAZ area in suboptimal quality images which are frequent in daily clinical practice. Therefore, the mKSM processing could contribute to our understanding of the three vascular plexuses.
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Abstract Background: To analyze the microvascular parameters using optical coherence tomography angiography (OCTA) in non-infectious posterior uveitis (PU) patients. Methods: In this cross-sectional study, OCTA images of patients with non-infectious PU were evaluated. The vessel densities (VD) in the superficial and deep capillary plexuses (SCP & DCP), foveal avascular zone (FAZ) area were measured and compared to healthy controls. Results: The study cohort comprised 64 patients with age and gender-matched groups. The VD in the SCP was 43.9±3.9% in the whole image; 18.4±4.8% in the fovea, 43.9±4.6% in the parafoveal area, and 43.4±9.7% in the perifoveal zone, in eyes with uveitis. These were respectively 48.8±2.9%, 22.9±6.9%, 50.9±3.0%, and 49.2±3.1% in the control group (p=0.0001, 0.043, 0.0001, 0.01, respectively). The changes in the DCP in eyes with uveitis were not significant. In the uveitis group, the FAZ was significantly enlarged compared to controls (0.37±0.1 microns vs. 0.24±0.2 microns, p=0.046). Conclusion: OCTA depicted significant changes including decreased VD in the SCP and enlarged FAZ in non-infectious PU.
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