Repeatability and Reproducibility of Foveal Avascular Zone Area Measurement on Normal Eyes by Different Optical Coherence Tomography Angiography Instruments

Optical coherence tomography angiography in diabetic retinopathy: A major review

Diabetic retinopathy (DR) is characterized by retinal vasculopathy and is a leading cause of visual impairment. Optical coherence tomography angiography (OCTA) is an innovative imaging technology that can detect various pathologies and quantifiable changes in retinal microvasculature. We briefly describe its functional principles and advantages over fluorescein angiography and perform a comprehensive review on its clinical applications in the screening or management of people with prediabetes, diabetes without clinical retinopathy (NDR), nonproliferative DR (NPDR), proliferative DR (PDR), and diabetic macular edema (DME). OCTA reveals early microvascular alterations in prediabetic and NDR eyes, which may coexist with sub-clinical neuroretinal dysfunction. Its applications in NPDR include measuring ischemia, detecting retinal neovascularization, and timing of early treatment through predicting the risk of retinopathy worsening or development of DME. In PDR, OCTA helps characterize the flow within neovascular complexes and evaluate their progression or regression in response to treatment. In eyes with DME, OCTA perfusion parameters may be of predictive value regarding the visual and anatomical gains associated with treatment. We further discussed the limitations of OCTA and the benefits of its incorporation into an updated DR severity scale.

Morphological characteristics of the foveal avascular zone in pathological myopia and its relationship with macular structure and microcirculation

PURPOSE

To explore the characteristics of macular structure, microcirculation, and foveal avascular zone (FAZ) morphology in pathological myopia and to research the associations between these factors and pathological myopia.

METHODS

This is a cross-sectional study. The study included 103 eyes with non-high myopia and 206 eyes with high myopia (139 with simple high myopia and 67 with pathological myopia). Macular structural and microcirculation parameters were determined using optical coherence tomography angiography (OCTA). The FAZ morphological parameters were measured manually using Image J software. Correlations between pathological myopia and various factors were analyzed.

RESULTS

Patients with pathological myopia had a thinner retinal thickness (RT) and choroidal thickness (CT) and a lower retinal superficial vascular density (SVD), retinal deep vascular complex density (DVD), choriocapillaris perfusion area (CCPA), and choroidal vascularity index (CVI) (all P < 0.05). Patients with pathological myopia had a larger FAZ area, perimeter, major axis, minor axis, acircularity index (AI), and lower circularity index (CI) (all P < 0.01). The axial length (AL), the major axis of the superficial FAZ, CI, and AI were significantly correlated with myopia severity (all P < 0.05).

CONCLUSIONS

Patients with pathological myopia exhibited worse macular microcirculation and thinner macular retina and choroid. The FAZ in pathological myopia was larger and more irregular. The AL, CI, and AI were significantly associated with myopia severity. Thus, CI and AI might serve as new indicators for monitoring the progression of myopia. Further investigations should be performed.

TRIAL REGISTRATION

Clinical Trials.gov Identifier: ChiCTR2100046590.

Repeatability and reproducibility of quantitative OCT angiography measurements from table-top and portable Flex Spectralis devices

PURPOSE

The recent development of a portable investigational handheld OCT-angiography (OCTA) device has allowed for expansion of imaging into the operating room (OR) in addition to standard in-clinic imaging. The aim of this study was to assess intravisit repeatability and intervisit reproducibility of retinal microvasculature measures and central retinal thickness for in-clinic table-top and portable OR compatible OCTA devices.

METHODS

Repeated 10 × 10 OCTA images were acquired in 20 healthy adult participants on two separate visit days using Spectralis spectral-domain OCTA table-top and investigational armature suspended Flex systems. Intravisit and intervisit intraclass correlation coefficients and average absolute percent difference were calculated for quantitative microvasculature measures and CRT.

RESULTS

120 OCTA images were acquired from 20 subjects (n = 20, mean age 26.7 ± 1.61 years, range 24-30 years) with both devices across two separate imaging days. FAZ and CRT measurements had near complete intravisit and intervisit agreement with ICCs between .97 and 1 for both table-top (FAZ ICC .97, .97; CRT ICC .98-1, .98-.99) and Flex (FAZ ICC .97, .95; CRT ICC .99-1, .98-.99) devices. Vessel density measures demonstrated greater variance with only fair to strong agreement (ICC .32-.75) and average absolute percent differences ranging from 2.96 to 6.63%.

CONCLUSION

FAZ and CRT measures for both devices demonstrated high repeatability and reproducibility; retinal vessel density measures demonstrated less. Differences of less than 7% for retinal microvasculature measurements across time and devices are most likely attributable to expectable variance between repeat scans.

Reproducibility of peripapillary, optic nerve head and macular vessel density by OCT-A according to glaucoma severity staging

OBJECTIVE

To assess the reproducibility of peripapillary, optic nerve head (ONH-PP) and macular vessel density (VD) by Spectral Domain optical coherence tomography angiography (SD OCT-A) in glaucoma patients and healthy subjects.

METHODS

Cross-sectional study assessing 63 eyes of 63 subjects, including 33 glaucoma patients and 30 healthy subjects. Glaucoma was classified in mild, moderate, or advanced. Two consecutive scans were acquired by Spectralis Module OCT-A (Heidelberg, Germany), and provided images of the superficial vascular complex (SVC), nerve fiber layer vascular plexus (NFLVP), superficial vascular plexus (SVP); deep vascular complex (DVC), intermediate capillary plexus (ICP) and deep capillary plexus (DCP). VD (%) was calculated by AngioTool. Intraclass correlation coefficients (ICCs) and coefficients of variation (CV) were calculated.

RESULTS

Among ONH-PP VD, better ICC presented advanced (0.83-0.97) and moderate glaucoma (0.86-0.96) compared with mild glaucoma (0.64-0.86). For the macular VD reproducibility, ICC results for superficial retinal layers were better for mild glaucoma (0.94-0.96) followed by moderated (0.88-0.93) and advanced glaucoma (0.85-0.91), and for deeper retinal layers ICC was better for moderate glaucoma (0.96-0.95) followed by advanced (0.80-0.86) and mild glaucoma (0.74-0.91). CVs ranged from 2.2%% to 10.94%. Among healthy subjects, ICCs for the ONH-PP VD measurements (0.91-0.99) and for the macular VD measurements (0.93-0.97) were excellent in all layers, with CVs from 1.65% to 10.33%.

CONCLUSIONS

SD OCT-A used to quantify macular and ONH-PP VD showed excellent and good reproducibility in most layers of the retina, both in healthy subjects and in glaucoma patients regardless of the severity of the disease.

Peripapillary and macular vascular parameters by optical coherence tomography angiography in primary congenital glaucoma

OBJECTIVE

To evaluate the differences in peripapillary and macular vascular parameters by optical coherence tomography angiography (OCTA) between patients with primary congenital glaucoma (PCG) and healthy controls; and to determine their diagnostic accuracy.

MATERIAL AND METHODS

Observational, cross-sectional study including 39 eyes with PCG and 78 healthy eyes. Only one eye per patient was included. All included patients underwent a comprehensive ophthalmic examination and peripapillary and macular analysis were performed by AngioplexTM OCTA (Cirrus HD-OCT 5000) with a 4.5 × 4.5 mm optic nerve head scan and 6 × 6 mm macular scan. Global data and quadrant data from peripapillary vascular parameters and global data and circular sectors data from macular superficial plexus parameters were compared between groups. The glaucoma discrimination capability of these parameters was calculated as areas under the receiver operating characteristics curve (AUC ROC).

RESULTS

Mean age was 14.1 ± 8.7 years for the PCG patients and 11.7 ± 6.2 years for controls (p = 0.093). All vascular peripapillary measurements (global and quadrants; all p < 0.001) and all macular measurements (p < 0.042) excepting perfusion density in the inner circle (p = 0.087), were reduced in the PCG group compared to controls. According to AUC ROC, peripapillary (all ≥ 0.706) and macular parameters (all ≥ 0.699) showed good diagnostic capacity. AUC ROC for the most discriminatory measurements corresponding to blood flux index (0.887) and whole macula vascular density (0.855) were similar (p = 0.085).

CONCLUSION

Peripapillary and macular vascular parameters by OCTA are decreased in patients with PCG, showing a good capacity to discriminate between normal and glaucomatous eyes.

Automated measurement of the foveal avascular zone in healthy eyes on Heidelberg spectralis optical coherence tomography angiography

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) which is an evolution of the 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 (ICP) 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. 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 ICP.

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.

Optical coherence tomography (OCT) angiolytics: a review of OCT angiography quantitative biomarkers

Optical coherence tomography angiography (OCTA) provides a non-invasive method to obtain angiography of the chorioretinal vasculature leading to its recent widespread adoption. With a growing number of studies exploring the use of OCTA, various biomarkers quantifying the vascular characteristics have come to light. In the current report, we summarize the biomarkers currently described for retinal and choroidal vasculature using OCTA systems and the methods used to obtain them. Further, we present a critical review of these methods and key findings in common retinal diseases and appraise future directions, including applications of artificial intelligence in OCTA .

Evaluation of the Optic Disc and Macula in Healthy Children Using Optical Coherence Tomography Angiography

Objectives

To perform the measurements of the optic disc and macula in healthy children using optical coherence tomography angiography (OCTA) in order to determine the normative data values and compare these by age, gender, spherical equivalent (SE), and axial length (AL).

Materials and Methods

A total of 146 eyes belonging to 146 healthy children (74 girls, 72 boys) aged 6 to 16 years were included in this prospective study. Refraction and biometry measurements were performed. Retinal nerve fiber layer thickness (RNFLT), central macular volume, and central macular thickness (CMT) were measured by optical coherence tomography (OCT) after dilatation. Using the OCTA device, foveal avascular zone (FAZ) area, vascular density (VD) of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) of the macula, and the VD of the radial peripapillary capillary plexus (RPCP) of the optic disc were recorded.

Results

The mean age of the study group was 11.27±3 years, the mean AL was 23.39±1.18 mm and the mean SE was -1.31±1.61 diopters. The mean FAZ area was 0.3±0.09 mm2, the mean SCP-VD was 43.88±3.4%, the mean DCP-VD was 39.6±3.55%, and the mean RPCP-VD was 52.47±3.42%. When the relationship between the OCTA measurements and the SE and AL values were analyzed, there was no statistical significance (p>0.05). When age and OCTA measurements were compared, only DCP-VD values were found to significantly decrease with increasing age (p=0.015). There was no significant difference in OCTA measurements based on gender (p>0.05). Similarly, no statistical age-based differences were observed in RNFLT, CMV and CMT values (p>0.05).

Conclusion

With its short procedure time and no dye requirement, OCTA can be safely used in the evaluation of the optic disc and macular perfusion in children. Determination of normative values in children will be useful in detecting pathologic changes in tissue in patients with retinal diseases.

Repeatability of Manual Measurement of Foveal Avascular Zone Area in Optical Coherence Tomography Angiography Images in High Myopia

PURPOSE

To analyze the repeatability of manual measurement of foveal avascular zone (FAZ) area in an optical coherence tomography angiography (OCTA) image in high myopia.

METHODS

This study comprised patients with high myopia and controls. Two consecutive FAZ areas of the superficial and deep capillary plexus were obtained using OCTA. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were assessed, and univariate and multivariate generalized linear mixed models were conducted to identify factors related to repeatability.

RESULTS

Thirty eyes with high myopia and 34 eyes of healthy subjects were included in the study. The mean age in high myopia and control subjects was 55.5 and 60.8 years, respectively, the mean spherical equivalent was -9.98 and -0.55 diopters, and the mean axial length was 28.0 and 23.9 mm. The ICCs of FAZ area of the superficial capillary plexus (SCP) were 0.891 and 0.919, while the CVs were 8.8% and 8.5%. In measurement of the deep capillary plexus, the ICCs were 0.788 and 0.907, while the CVs were 11.2% and 11.0%, which were acceptable but exhibited lower repeatability than those of SCP. Multivariate analyses showed that older age (p = 0.030) and greater axial length (p = 0.005) were significantly associated with lower repeatability of SCP FAZ area measurements. In addition, greater axial length (p = 0.044) was a significant factor for lower repeatability of deep capillary plexus FAZ area measurements.

CONCLUSIONS

Manual measurement of FAZ area using OCTA exhibited relatively good repeatability for high myopia. Age and axial length affected repeatability and should be considered when analyzing FAZ areas in high myopia patients.

Repeatability of Macular and Optic Nerve Head Measurements by Optical Coherence Tomography Angiography in Healthy Children

Aims: To evaluate the repeatability of the peripapillary and macular vascular parameters using optical coherence tomography angiography (OCT-A) in healthy children.Materials and methods: Cross-sectional study including 34 eyes of 34 healthy children. After a complete medical examination, two consecutive OCT-A exams were done using AngioPlex Cirrus 5000 (Carl Zeiss Meditec, Dublin, CA, USA) in the same session. The scan area used was 6 × 6 mm for the analysis of the superficial vascular plexus (SVP) in the macula, and 4.5 × 4.5 mm for the peripapillary plexus. To study the repeatability of the measurements, the intraclass correlation coefficient (ICC) and the coefficient of variation (CV) of each pair of exams were calculated.Results: The mean age of the children included was 10.77 ± 2.49 years (range 6 to 15 years). Good and excellent ICCs were obtained for all the parameters considered. Peripapillary vascular parameters showed greater reproducibility than macular ones (global peripapillary perfusion density (pPD): ICC = 0.834 CV = 0.89% vs. whole macular area PD (w-mPD): ICC = 0.697 CV = 3.49%; global peripapillary flux index (FI): ICC = 0.858 CV = 1.28%; whole macular area vascular density (VD): ICC = 0.699 CV = 3.30%). Amongst the macular parameters, the characteristics of the foveal avascular zone (FAZ) were the ones showing higher rates of repeatability (FAZ circularity: ICC = 0.858 CV = 8.83%).Conclusion: OCT-A is a non-invasive, time-efficient technology that may be useful in the evaluation of the retinal and peripapillary vascular network in healthy children. The repeatability of the measures will allow the follow-up and evaluation of any change occurring in the macular or optic nerve perfusion.

The foveal avascular zone area in healthy eyes measured by ocular coherence tomography angiography using a full spectrum probabilistic algorithm

PURPOSE

Report the foveal avascular zone (FAZ) area imaged by OCT angiography (OCTA) using a full spectrum probabilistic algorithm in eyes of healthy individuals from Costa Rica without any ocular or systemic pathology.

METHODS

Retrospective chart review of consecutive healthy patients that were evaluated from January 2018 to October 2018 that underwent OCTA of the macular area. The OCTA consisted of a 10° × 10° cube of 512 A scans separated by 6 µm each with an automated real time mode of 5. The FAZ area of the superficial vascular complex (SVC), the deep vascular complex (DVC), superficial vascular plexus (SVP), intermediate vascular plexus (IVP) and the deep vascular plexus (DVP) were measured manually by 2 different observers at 3 different times.

RESULTS

A total of 234 eyes of 121 patients were included in this study. Mean age was 50 years (range, 15-89), 85 patients (70%) were female. Inter- and intra-observer agreements were excellent. The mean FAZ areas in the different layers were 0.258 ± 0.0035 mm² for the SVC, 0.205 ± 0.01 mm² for the DVC, 0.415 ± 0.01 mm² for the SVP, 0.305 ± 0.01 mm² for the ICP and 0.420 ± 0.01 mm² for the DCP. The mean FAZ areas in most of the measured layers increased with age and decreased with CMT. Gender and spherical equivalence were not correlated with FAZ area.

CONCLUSION

Manual measurements of the FAZ imaged by OCT-A using a full spectrum probabilistic algorithm are widely reproducible both by the same observer and between observers. The FAZ increases with age and decreases with CMT in normal individuals.

Morphological changes in and quantitative analysis of macular retinal microvasculature by optical coherence tomography angiography in hypertensive retinopathy

Hypertension is a serious global health problem. Hypertensive retinopathy is generally considered to be a predictor of vascular disease elsewhere in the human body. In the past few decades, a variety of grading systems have been proposed for hypertensive retinopathy. However, these grading systems have some limitations. This study utilized optical coherence tomography angiography (OCTA) to investigate the morphological changes and macular retinal microvasculature in depth among 100 patients with hypertensive retinopathy and 66 healthy participants. Five main pathological changes were discovered in hypertensive retinopathy, as follows: focal capillary sparsity, scattered microangioma, focal macular arch ring defects, focal capillary disorder, and focal capillary nonperfusion at the levels of the superficial and deep vascular networks. In addition, we have found that the number of various pathological changes shows an increasing trend as hypertensive retinopathy progresses and may be related to renal damage. Finally, deep vessel density tended to decrease with progressive stages of hypertensive retinopathy and could be the best indicator to predict the risk of hypertensive retinopathy. Our study, therefore, proposes 3 stages of hypertensive retinopathy without macular edema according to the pathophysiology found by OCTA: stage 1 (only focal capillary sparsity), taking the place of KWB grade I; stage 2 (focal capillary sparsity and scattered microangioma), taking the place of KWB grade II; and stage 3 (focal capillary sparsity, scattered microangioma, focal capillary disorder, and nonperfusion), taking the place of KWB grade III. Hence, OCTA may be a potentially useful tool for evaluating the pathophysiology and staging of hypertensive retinopathy. Further longitudinal prospective studies are needed to confirm our findings.

Improved Automated Foveal Avascular Zone Measurement in Cirrus Optical Coherence Tomography Angiography Using the Level Sets Macro

Purpose

To evaluate automated measurements of the foveal avascular zone (FAZ) using the Level Sets macro (LSM) in ImageJ as compared with the Cirrus optical coherence tomography angiography (OCTA) inbuilt algorithm and the Kanno–Saitama macro (KSM).

Methods

The eyes of healthy volunteers were scanned four times consecutively on the Zeiss Cirrus HD-OCT 5000 system. The FAZ metrics (area, perimeter, and circularity) were measured manually and automatically by the Cirrus inbuilt algorithm, the KSM, and the LSM. The accuracy and repeatability of all methods and agreement between automated and manual methods were evaluated.

Results

The LSM segmented the FAZ with an average Dice coefficient of 0.9243. Compared with the KSM and the Cirrus inbuilt algorithm, the LSM outperformed them by 0.02 and 0.19, respectively, for Dice coefficients. Both the LSM (intraclass correlation coefficient [ICC] = 0.908; coefficient of variation [CoV] = 9.664%) and manual methods (ICC ≥ 0.921, CoV ≤ 8.727%) showed excellent repeatability for the FAZ area, whereas the other methods presented moderate to good repeatability (ICC ≤ 0.789, CoV ≥ 15.788%). Agreement with manual FAZ area measurement was excellent for both the LSM and KSM but not for the Cirrus inbuilt algorithm (LSM, ICC = 0.930; KSM, ICC = 0.928; Cirrus, ICC = 0.254).

Conclusions

The LSM exhibited greater accuracy and reliability compared to the KSM and inbuilt automated methods and may be an improved and accessible option for automated FAZ segmentation.

Translational Relevance

The LSM may be a suitable automated and customizable tool for FAZ quantification of Cirrus HD-OCT 5000 images, providing results comparable to those for manual measurement.

Superficial and Deep Foveal Avascular Zone Area Measurement in Healthy Subjects Using Two Different Spectral Domain Optical Coherence Tomography Angiography Devices

Purpose

To compare the area of the foveal avascular zone (FAZ) in the superficial and deep retinal layers using two different spectral-domain optical coherence tomography angiography (OCTA) devices.

Methods

A cross-sectional comparative study was conducted to obtain macular OCTA images from healthy subjects using Optovue RTVue XR Avanti (Optovue, Inc, Fremont, CA) and Spectralis HRA+OCTA (Heidelberg Engineering, Heidelberg, Germany). Two independent trained graders measured the FAZ area using automated slab segmentation. The FAZ area in the superficial and deep retinal layers were compared.

Results

Twenty-three eyes of 23 subjects were included. The graders agreement was excellent (>0.86) for all measurements. The mean FAZ area was significantly larger at the superficial retinal layer as compared to the deep retinal layer on both devices (0.31 ± 0.08 mm2 vs 0.26 ± 0.08 mm2 in Optovue and 0.55 ± 0.16 mm2 vs 0.36 ± 0.13 mm2 in Spectralis, both P< 0.001). The mean FAZ area was significantly greater in the superficial and deep retinal layers using Spectralis as compared to Optovue measurements (P< 0.001 for both comparisons).

Conclusion

In contrast to previous reports, the FAZ area was larger in the superficial retina as compared to deep retinal layers using updated software versions. Measurements from different devices cannot be used interchangeably.

Assessing the Influence of OCT-A Device and Scan Size on Retinal Vascular Metrics

Purpose

The purpose of this study was to investigate the effect of device and scan size on quantitative optical coherence tomography angiography (OCT-A) metrics.

Methods

The 3 × 3 mm scans from Optovue AngioVue and Zeiss AngioPlex systems were included for 18 eyes of 18 subjects without ocular pathology. The foveal avascular zone (FAZ) was segmented manually by two observers, from which estimates of FAZ area (using both the nominal image scale and the axial length corrected image scale) and acircularity were derived. Three scan sizes (3 mm, 6 mm HD, and 8 mm) from the AngioVue system were included for 15 eyes of 15 subjects without ocular pathology. For each subject, larger image sizes were resized to the same resolution as 3 × 3 mm scans, aligned, then cropped to a common area. FAZ area, FAZ acircularity, average and total parafoveal intercapillary area, vessel density, and vessel end points were computed.

Results

Between the devices used here, there were no significant differences in FAZ acircularity (P = 0.88) or FAZ area using scaled (P = 0.11) or unscaled images (P = 0.069). Although there was no significant difference in FAZ area across scan sizes (P = 0.30), vessel morphometry metrics were all significantly influenced by scan size.

Conclusions

The scan devices and sizes used here do not affect FAZ area measures derived from manual segmentations. In contrast, vessel morphometry metrics are affected by scan size. As individual differences in axial length induce differences in absolute scan size, extreme care should be taken when interpreting metrics of vessel morphometry, both between and within OCT-A devices.

Translational Relevance

A better characterization of the confounds surrounding OCT-A retinal vasculature metrics can lead to improved application of these metrics as biomarkers for retinal and systemic diseases.

Magnification Effect of Foveal Avascular Zone Measurement Using Optical Coherence Tomography Angiography

Purpose

The aim of this study was to evaluate the foveal avascular zone (FAZ) of healthy subjects and examine the magnification effect.

Methods

A total of 33 healthy volunteers were enrolled and all subjects were eligible for analysis. Optical coherence tomography angiography (OCTA) examination scanned 3 × 3 mm of the macular area. The FAZ area was measured on the superficial OCTA en face image with and without correction by axial length. The relationship between changes in the FAZ area after correction with the axial length was examined.

Results

The mean age was 21.9 ± 0.6 years. The mean axial length was 24.87 ± 1.17 mm and mean spherical equivalent (SE) value was -3.64 ± 2.83 diopters (D). The FAZ area was 0.26 ± 0.10 mm² before the axial length correction and 0.27 ± 0.10 mm² after the correction. In the eyes that had an axial length longer than or equal to 26 mm or SE less than or equal to -6 D, the FAZ area after correction was significantly larger than that before correction (p < 0.01). The change of FAZ area after correction with axial length was significantly correlated with the axial length (R ² = 0.88, p < 0.01) or SE value (R ² = 0.55, p < 0.01).

Conclusion

FAZ areas were comparable to previous reports. In high myopic cases, the magnification effect needs to be considered when evaluating the FAZ area.

Factors Affecting Repeatability of Foveal Avascular Zone Measurement Using Optical Coherence Tomography Angiography in Pathologic Eyes

Purpose

To determine factors that may affect the repeatability of the foveal avascular zone (FAZ) measurement obtained using optical coherence tomography angiography (OCTA) including instrument type, image segmentation, image quality, and fundus pathology.

Patients and Methods

This prospective single-center study enrolled 43 subjects (85 eyes) with retinal vasculopathy, macular edema, optic pathology or normal contralateral eye. The macula was imaged twice using Optovue Angiovue and once using Cirrus Angioplex to obtain 3x3mm OCTA images centered on the fovea. Images were generated by the same operator within 30 mins. The FAZ size for the entire retinal thickness ("overall FAZ") was measured automatically using the OCTA software. The FAZ size of the superficial and deep retinal vascular plexus layers was measured manually using the enface OCTA images of the segmented layers and Image J analysis. Intraclass correlations coefficient (ICC) was calculated to determine repeatability.

Results

For the overall FAZ measurement, repeatability was excellent (ICC 0.953 right eye, 0.938, left eye) using the same machine (intra-instrument) and somewhat lower but still good to excellent (ICC 0.803 right eye, 0.917 left eye) using machines made by different vendors (inter-instrument). For the segmented layers, intra-instrument repeatability of FAZ measurement was excellent (ICC > 0.95) for both plexus layers. Inter-instrument repeatability was good for the superficial plexus layer (ICC 0.86 right eye, 0.88 left eye) but reduced for the deep plexus layer (ICC 0.63 right eye, 0.57 left eye). Suboptimal image quality and presence of retinal vasculopathy and macular edema tended to reduce FAZ repeatability but to a lesser degree.

Conclusion

Inter- and intra-instrument repeatability of the overall FAZ measurement was high using commercial OCTA instruments and only mildly reduced by suboptimal image quality and fundus pathology. For segmented layers, intra-instrument repeatability remained high but inter-instrument repeatability was reduced for the deep plexus layer.

OCT Angiography Study of the Macula in Patients with Diabetic Macular Edema Treated with Intravitreal Aflibercept

Purpose: To compare foveal avascular zone density (FAZ) in the superficial (SCP) and deep (DCP) capillary plexus and vessel density (VD) in the macula in eyes with diabetic macular edema (DME) treated with intravitreal aflibercept.Methods: Patients with DME were imaged at baseline, and 30 days after the 1^st, 2^nd and 3^rd intravitreal aflibercept injection. Images were analyzed for the FAZ area in the SCP and DCP in each visit and VD.Results: Twenty eyes were enrolled. FAZ was 0.304 ± 0.131 mm² in the SCP and 0.738 ± 0.5836 mm² in the DCP at baseline. SCP FAZ was not significantly different whereas, FAZ in the DCP decreased (p = .035) after treatment. VD in the center was 20.62 ± 4.31 at baseline and decreased by 8% (p = .002). Parafoveal VD remained unchanged with treatment.Conclusion: DCP ischemia may improve after aflibercept treatment. Central macular vessel density was found to decrease post-treatment, but the clinical relevance needs further investigation.

Reliability of foveal avascular zone metrics automatically measured by Cirrus optical coherence tomography angiography in healthy subjects

PURPOSE

To investigate the reliability of the foveal avascular zone (FAZ) metrics automatically measured using Cirrus optical coherence tomography angiography (OCTA) embedded algorithm compared to human manual measurement.

METHODS

Thirty-five eyes of 35 healthy subjects were enrolled and scanned four times continuously on Zeiss Cirrus HD-OCT 5000. The FAZ metrics (area, circularity and perimeter) of the superficial capillary plexus were measured automatically using the embedded tool and manually measured by the two independent observers using ImageJ. The repeatability of the four scans within all methods of measurements was calculated. The agreement of the manual vs automated measurement was also analyzed.

RESULTS

The repeatability of the automated algorithm was only poor to moderate (intraclass correlation coefficients [ICCs] for the area, perimeter and circularity were 0.600, 0.405 and 0.221, respectively) while the repeatability of the manually measured FAZ area and perimeter was good [([ICCs] ranged from 0.845 to 0.877) except the circularity (ICC = 0.538 to 0.608)]. The ranges of 95% limits of agreement between the manual measurements by the two observers were only 20% to 31% of those of automated-manual agreement. The Cirrus inbuilt algorithm obviously outlined the border of FAZ wrongly in 22.9% cases.

CONCLUSION

Caution should be taken when using the automated measurement results of FAZ metrics in Cirrus OCTA, because of the low repeatability and poor agreement compared with the manual measurement.

Reproducibility of Foveal Avascular Zone and Superficial Macular Retinal Vasculature Measurements in Healthy Eyes Determined by Two Different Scanning Protocols of Optical Coherence Tomography Angiography

PURPOSE

To assess the reproducibility of quantitative measurements of the foveal avascular zone (FAZ) and retinal vasculature determined by different scanning protocols of optical coherence tomography angiography (OCTA) in healthy volunteers.

METHOD

All participants were scanned by two trained operators using an AngioPlex OCTA. Both angiography protocols (6 × 6 mm and 3 × 3 mm) were performed three times on the same eye by operator A and one additional time by operator B. The FAZ area and perimeter, retinal vessel length density (VLD) and perfusion density (PD) of different regions were analysed.

RESULTS

Fifty-two eyes from 52 subjects were recruited for this study. The repeated measurements of FAZ, VLD, and PD parameters obtained by the same operator, as well as by different operators, were not significantly different when the same protocol was used (p > 0.05). The intra- and inter-operator intraclass correlation coefficients (ICCs) of the FAZ and central VLD and PD parameters (range, 0.99-0.95) were better than the intra- and inter-operator ICCs of VLD and PD in the inner and outer rings (range, 0.86-0.90). The FAZ area, perimeter, and VLDs obtained by the 3 × 3 mm protocol were larger than those obtained by the 6 × 6 mm protocol (p < 0.01), but the PDs obtained by the 3 × 3 mm protocol were smaller than those obtained by the 6 × 6 mm protocol (p < 0.001). All of the corresponding parameters obtained by the two protocols were positively correlated (r = 0.64-0.99, p < 0.001).

CONCLUSION

Both the 6 × 6 and 3 × 3 mm protocols of the AngioPlex OCTA provide good reproducibility for assessing the FAZ and superficial retinal vasculature. However, the values obtained by these different protocols cannot be compared directly.

Association of Macular and Circumpapillary Microvasculature with Visual Field Sensitivity in Advanced Glaucoma

PURPOSE

To evaluate the association between optical coherence tomography angiography (OCTA) macular and circumpapillary vessel density and visual field mean deviation (MD) in advanced primary open angle glaucoma.

DESIGN

Cross-sectional study.

METHODS

Macula (superficial layer) and optic nerve head (ONH) with capillary density (CD) and without vessel density (VD) automated removal of large vessels OCTA of 34 eyes (34 patients, MD < -10 dB) were investigated as macula whole image VD (wiVD), parafoveal VD (pfVD), ONH wiVD, wiCD, circumpapillary VD, and cpCD. Spectral domain OCT circumpapillary retinal nerve fiber layer, macular ganglion cell complex, and ganglion cell inner plexiform layer were also analyzed.

RESULTS

Macular and ONH VD decreased significantly with worsening MD. Each 1-dB decrease in MD was associated with a reduction of 0.43% and 0.46% for macular wiVD and pfVD with R² of 0.28 and 0.27, respectively (all P < .01). The association between MD and VD was strongest for measures of ONH with large vessels removed, wiCD, and cpCD, followed by wiVD and circumpapillary VD with R² of 0.26, 0.22, 0.17, 0.14, and a VD reduction of 0.43%, 0.51%, 0.33%, and 0.40%, respectively (all P < .02). There was a reduction of 1.19 μm in Avanti parafoveal ganglion cell complex, 1.13 μm in Spectralis ganglion cell inner plexiform layer, and 1.01 μm in Spectralis circumpapillary retinal nerve fiber layer, with R² of 0.19 (P = .006), 0.23 (P = .002), and 0.24 (P = .002), respectively.

CONCLUSIONS

ONH and macula OCTA VD and thickness are associated with the severity of visual field damage in advanced primary open angle glaucoma.

[Foveal avascular zone and OCT angiography. An overview of current knowledge]

BACKGROUND

The foveal avascular zone (FAZ) has often been analyzed under different aspects in the last decades, mainly by fluorescence angiography (FA); however, the novel technology of optical coherence tomography angiography (OCTA) enables a non-invasive examination, visualization and quantitative analysis of the FAZ, which has recently led to many new findings, especially in a multidisciplinary manner. This article provides an overview of the investigation of the FAZ using OCTA and the new findings that have been obtained using OCTA in recent years.

METHODS

This article is based on a comprehensive literature review.

RESULTS

In many studies a good reproducibility and repeatability of the FAZ measurements by OCTA could be proven, also by comparing different OCTA devices. In patients with ocular pathologies and systemic diseases, e. g. after retinal vein occlusion or retinal surgery and in patients with diabetes mellitus without diabetic retinopathy, differences to healthy control groups and correlations to visual function could be shown. Moreover, in patients with neurological diseases, such as Alzheimer's dementia, changes of the FAZ could be identified.

CONCLUSION

The OCTA is a non-invasive technology, which enables a reliable visualization and reproducible quantification of the FAZ. The size of the FAZ seems to be altered in different retinal and systemic diseases, which also may correlate with visual function; however, long-term studies evaluating the diagnostic value of these changes in the course of the disease are currently lacking.

Quantitative analysis of the macula with optical coherence tomography angiography in normal Japanese subjects: The Taiwa Study

This study evaluated age-related changes in the superficial and deep retinal capillary plexus (SCP and DCP, respectively) and in the foveal avascular zone (FAZ). SCP and DCP perfusion density (PD) were measured in optical coherence tomography angiography (OCTA) macular scans of 145 eyes of 145 healthy Japanese subjects, and findings were compared with SCP FAZ and clinical data. We found that age was negatively correlated with SCP and DCP PD (r = -0.17, P = 0.04 and r = -0.20, P = 0.02, respectively) and positively correlated with FAZ area (r = 0.18, P = 0.03). SCP and DCP PD were correlated with each other (r = 0.67, P < 0.001). FAZ area was negatively correlated with SCP PD, DCP PD and central macular thickness (CMT) (r = -0.18, P = 0.03; r = -0.25, P < 0.01; and r = -0.39, P < 0.001, respectively). FAZ was larger and CMT was lower (P = 0.01 and P < 0.001, respectively) in women than men. SCP and DCP PD were positively correlated with estimated glomerular filtration rate (r = 0.17, P = 0.03 and r = 0.24, P < 0.01, respectively). Multiple regression analysis confirmed that age independently affected DCP PD and FAZ (P = 0.02 and P < 0.01, respectively) and that CMT independently affected FAZ area (P < 0.001). Thus, normal subjects showed age-related decreases in macular PD and renal function. FAZ and CMT were related, suggesting that age-related changes in macular thickness also affect capillary vasculature.

The Utility of Frame Averaging for Automated Algorithms in Analyzing Retinal Vascular Biomarkers in AngioVue OCTA

Purpose

This study proposes an optical coherence tomography angiography (OCTA) frame-averaging method and investigates the effects of the number of frames acquired and averaged on metrics quantifying the foveal avascular zone (FAZ), vessel morphology, and parafoveal intercapillary area (PICA).

Methods

Ten OCTA frames were acquired for each of the 19 subjects without known retinal disease using the AngioVue OCTA system. For each subject, acquired frames were ranked by an image quality metric. A subset of frames was then registered and averaged. The effects of the number of frames acquired and averaged on FAZ segmentation and metrics of FAZ geometry, vessel morphology, and PICA were analyzed.

Results

Frame averaging increased the accuracy of the automatically segmented FAZ region; for example, the absolute error in FAZ area decreased from 0.026 mm² (1 frame) to 0.005 mm² (5 frames). Averaging multiple frames exponentially decreased the estimated number of vessel endpoints and increased the average vessel length with a 32% decrease in number of endpoints and 14% increase in average vessel length when averaging five frames compared with one. Frame averaging also improved the precision of PICA estimates.

Conclusions

Averaging multiple OCTA frames using the Optovue AngioVue system reduced error in FAZ segmentation and improved the robustness of OCTA vessel morphology and perfusion metrics. The study demonstrated limited benefit in acquiring and averaging more than five frames.

Translational Relevance

Averaging multiple OCTA frames improved the robustness of OCTA foveal biomarkers with limited benefit when averaging more than five frames.

Repeatability, reproducibility and agreement of foveal avascular zone measurements using three different optical coherence tomography angiography devices

Purpose

To evaluate the repeatability, the reproducibility and the agreement of foveal avascular zone (FAZ) measurements using three different optical coherence tomography angiography (OCT-A) devices.

Procedures

This prospective study included 24 eyes of 24 healthy volunteers. OCT-A imaging was performed using RTVue XR Avanti, Canon OCT-HS100 and Spectralis OCT-A. Repeated measurements were performed under the same conditions on two separate days, and the area of the FAZ was determined and analyzed using the above devices.

Results

All three devices showed a high ICC and there was no significant difference between the ICCs (pairwise comparison) of the three devices (Optovue–Canon (p = 0.66); Canon–Heidelberg (p = 0.21); Heidelberg–Optovue (p = 0.37). Agreement analysis of the three devices revealed a significant elevation of FAZ area values with the Heidelberg device and a slight underestimation of the FAZ area with the Canon device. Nevertheless, overall we found a high level of agreement between all of the three devices (ICC ≥ 0.958 (0.905–0.982)).

Conclusions

Good reproducibility and repeatability were observed for all three devices. However, the agreement analysis revealed slight, but significant differences, which might limit alternating use of these devices for clinical research and follow-up examinations.

Variability of Foveal Avascular Zone Metrics Derived From Optical Coherence Tomography Angiography Images

Purpose

To characterize sources of inter- and intrasubject variability in quantitative foveal avascular zone (FAZ) metrics.

Methods

Two 3×3-mm optical coherence tomography angiography scans (centered on the fovea) were acquired in both eyes of 175 subjects. An image of the superficial plexus was extracted from each scan and segmented twice by a single observer. Four quantitative FAZ morphology metrics (area, axis ratio, acircularity, major horizontal axis angle) were calculated, and a variance components analysis was performed.

Results

Mean (±SD) age was 27.9 ± 11.9 years, and 55% were female. Area had the largest amount of variance resulting from intersubject differences (93.1%). In contrast, there was large interocular variance for axis ratio, acircularity, and major horizontal axis angle (55.0%, 53.7%, 70.7%, respectively), though only axis ratio showed significant asymmetry between fellow eyes (P < 0.05). Neither repeated images from the same eye nor repeated segmentation on the same image were significant sources of variance.

Conclusions

Metrics of FAZ morphology show excellent repeatability and reliability. Excluding FAZ area, there was a high amount of variance attributed to interocular differences for the other FAZ metrics; therefore, the fellow eye should not be considered a control for FAZ studies when using these metrics.

Translational Relevance

Vision scientists must be prudent when choosing FAZ metrics, as they display varying degrees of within-subject differences relative to between-subject differences. It seems likely that different metrics will be best suited for different tasks, such as monitoring small changes over time within a single subject or assessing whether a given FAZ is abnormal.