Foveal Avascular Zone Acircularity Research Articles

Optical coherence tomography angiography in intermediate uveitis-related cystoid macular edema.

Cystoid macular edema (CME) is the leading cause of permanent visual impairment in patients with uveitis, particularly in patients with intermediate uveitis (IU). This study was aimed at comparing the changes in the macular microvasculature in patients with IU with uveitic non-responsive CME and without macular edema. In this case-control study, 55 eyes of patients with IU were assessed for macular microvascular structures, including vascular density, foveal avascular zone (FAZ) measurement, and vascular morphological changes, using spectral-domain optical coherence tomography angiography (OCT-A) with the AngioVue OCT-A system. We divided patients into the following two groups: the case group, including 30 eyes with IU-related non-responsive CME, and the control group, including 25 eyes with IU without macular edema. Participants in the case and control groups had comparable age (P = 0.753) and sex (P = 0.124) distributions. Superficial capillary plexus vessel density in the case group was significantly decreased in the whole image (P = 0.027) and the parafoveal area (P = 0.001) compared to the control group. However, there were no statistically significant differences between the two groups in terms of foveal superficial vessel density, deep capillary plexus vessel density, FAZ area, FAZ perimeter, FAZ acircularity index, or foveal vessel density in a 300-µm-wide annulus around the FAZ (all P > 0.05). Vascular morphological changes, such as the capillary tuft, telangiectatic vessels, or micro-aneurism, were not different in the overview images of the OCT-A printout between the two groups. The mean superficial capillary plexus vessel density was lower in eyes with IU-related nonresponsive CME than in those without macular edema. We observed more cystoid spaces in SCP than in DCP. Microcystic changes in the inner retina and ischemia may be the underlying cause in eyes with nonresponsive CME. Future prospective longitudinal studies with healthy, matched controls are warranted to confirm our findings.

The Effect of Pathological Retinal Changes on Retinal Capillary Circulation in Myopic Patients.

Myopia is a common ocular disorder worldwide, leading to degenerative changes in the retina which is highly susceptible to vascular impairment. The aim of the study was to investigate the effects of pathological retinal changes on the retinal capillary structures using optical coherence tomography angiography (OCTA) in myopic patients. Thirty-two patients with high myopia (HM), 29 patients with pathological myopia (PM), and 38 healthy subjects with emmetropia (EM) were enrolled in this study. OCTA was performed to measure the following parameters: Foveal avascular zone (FAZ) area; FAZ perimeter; FAZ acircularity index (AI); and superficial, deep, and radial peripapillary capillary (RPC) vessel densities. Axial length (AL), spherical equivalent, and anterior chamber depth were evaluated. Significant differences in the mean AL values were observed between the EM group and the other groups (p<0.001 for all); however, no significant differences were observed between the HM and PM groups (p=0.135). Significant differences in FAZ parameters, except for AI, were found among the three groups (p<0.05 for all). In all regions, except for the fovea and inside disc, the capillary plexus vessel densities were significantly lower in the PM group than in the other groups and were lower in the HM group than in the EM group (p<0.05 for all). Significant differences identified in capillary densities between the HM and PM groups, both of which present similar AL measurements, suggest that pathological retinal findings have significant effects on retinal perfusion independent of the effect of AL.

Evaluation of flow of chorioretinal capillaries in healthy black and white subjects using optical coherence tomography angiography

This study compared macular capillary parameters between healthy black and white subjects using optical coherence tomography angiography (OCTA). We measured vessel density (VD) of superficial (SCP), intermediate (ICP), and deep (DCP) capillary plexuses and choriocapillaris blood flow area (BFA) of the fovea, parafovea and total 3 mm-diameter circular area centered on the fovea, as well as the foveal avascular zone (FAZ) parameters, controlling for axial length. Black subjects had lower foveal and parafoveal VD in the SCP (p = 0.043 and p = 0.014) and the ICP (p = 0.014 and p = 0.002). In the DCP, black subjects had a trend toward lower foveal and parafoveal VD. Black subjects had decreased choriocapillaris BFA in the total 3 mm area (p = 0.011) and the parafovea (p = 0.033), larger FAZ area (p = 0.006) and perimeter (p = 0.014), and a higher capillary density in a 300 μm wide region around the FAZ (FD-300) (p = 0.001). There was no significant difference in FAZ acircularity index. To our knowledge, this is the first report analyzing the three distinct retinal capillary plexuses and identifying differing baseline VD, choriocapillaris and FAZ parameters in healthy young black compared to white subjects. Larger studies are needed to validate these findings and better understand racial differences in vulnerability to ocular diseases.

Acircularity and circularity indexes of the foveal avascular zone in high myopia

This study explored the association between foveal avascular zone (FAZ) parameters and high myopia using optical coherence tomography angiography. We divided 106 eyes of 106 patients into quartiles based on the axial length. The upper quartile was then defined as the high myopia group (n = 27), while the lower quartile was the non-high myopia group (n = 26). The areas and minor axis lengths of superficial and deep FAZ, the perimeters and major axis lengths of deep FAZ were significantly larger in eyes with high myopia than in eyes with non-high myopia (P < 0.05). Inversely, the subfoveal choroidal thickness was significantly thinner in eyes with high myopia than in those with non-high myopia. Linear regression analyses showed that no significant correlation was observed between FAZ areas and acircularity and circularity indexes of FAZ in non-high myopia group. Conversely, FAZ areas strongly correlated with acircularity and circularity indexes of FAZ in high myopia group. We found that an increase in the FAZ area in highly myopic eyes was accompanied by a significant variation in FAZ acircularity and circularity indexes. Further research should address whether these findings are associated with future disease development in highly myopic eyes.

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

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

OCT Angiography Assessment of Retinal Microvascular Changes in Diabetic Eyes in an Urban Safety-Net Hospital

To determine whether quantitative OCT angiography (OCTA) parameters can be used to distinguish among eyes at various stages of diabetic retinopathy (DR) in an urban safety-net hospital population. Prospective cross-sectional study. Three hundred twenty-nine eyes from 329 patients were included in this study: 90 nondiabetic patients, 170 diabetic patients without DR, 57 diabetic patients with mild to moderate nonproliferative DR (NPDR), and 12 diabetic patients with severe NPDR to proliferative DR. Patients underwent OCTA imaging and ultra-widefield fundus photography at Zuckerberg San Francisco General Hospital and Trauma Center between April and October 2018. For participants with diabetes, imaging was classified according to DR severity by a telemedicine reading center. Eight OCTA parameters were analyzed. Perfusion density and vessel length density (VD) were examined from both the superficial capillary plexus (SCP) and deep capillary plexus. The other 4 parameters were examined only from the SCP. Total extrafoveal avascular area (tEAA) was based on the area of absent capillary vessels. Foveal avascular zone (FAZ)-related metrics consisted of FAZ area, FAZ circularity index, and FAZ acircularity index. Area under the receiver operating characteristic curve (AUC) for OCTA parameters to distinguish among groups according to DR severity. All OCTA parameters demonstrated a significant relationship with DR severity (P < 0.05). No significant difference was found when comparing nondiabetic participants versus diabetic participants without retinopathy. The FAZ area was the only metric that demonstrated a significant difference between genders: mean of 0.29±0.12 mm2 in men and 0.34±0.13 mm2 in women (P < 0.001). Receiver operating characteristic curve analyses showed that tEAA had the highest AUC when comparing various stages of the disease. In this urban, public hospital population, quantification of retinal vascular findings with OCTA imaging was a useful means of distinguishing patients according to DR severity. Because these results were similar to those of other tertiary referral centers, it would be reasonable to perform further DR-related OCTA studies in this population and expect generalizable results.

The use of optical coherence tomography angiography and optical coherence tomography to predict visual acuity in diabetic retinopathy.

Diabetic macular ischaemia (DMI) is associated with reduced visual acuity. Limitations exist in assessing the ischaemic component of diabetic retinopathy. Optical coherence tomography angiography (OCTA) is a non-invasive imaging technique to distinguish retinal capillary layers and allow microvascular assessment. Evaluation of DMI is of prognostic significance when planning treatment regimens for diabetic maculopathy. The aims of this study were to evaluate OCTA to assess DMI and correlate findings with structural optical coherence tomography (OCT) features to predict visual acuity. Cross sectional study of fifty-seven eyes (n = 57) of thirty-seven subjects with diabetic retinopathy. 26/57 (46%) eyes had diabetic macular cysts. OCT and OCTA data from a single visit were analysed. Central retinal thickness, the presence of intraretinal cysts, ellipsoid zone (EZ) disruption, disorganisation of the retinal inner layers (DRIL), foveal avascular zone (FAZ) area, FAZ acircularity, and level of DMI in the superficial capillary plexus were graded according to ETDRS protocols. The deep vascular plexus was also graded for ischaemia. Correlations between measures and visual acuity were explored using regression models. Median age was 55 years. Multiple regression analysis showed EZ disruption (p < 0.05), horizontal DRIL length (p < 0.01), DMI grade, and FAZ area (p < 0.1) correlated with visual acuity. Central retinal thickness and the presence of intraretinal cysts did not predict visual acuity in this study. FAZ area, DMI grade, EZ disruption, and DRIL length correlate with visual acuity and could be incorporated into longitudinal clinical assessment of individual patients with diabetic retinopathy.

QUANTIFICATION OF RETINAL VESSEL TORTUOSITY IN DIABETIC RETINOPATHY USING OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY.

To investigate the association of vessel tortuosity with severity of diabetic retinopathy (DR) using optical coherence tomography angiography. We retrospectively analyzed 30 healthy eyes and 121 eyes of diabetic subjects with no DR, mild nonproliferative DR (NPDR), moderate to severe NPDR and proliferative DR (PDR). Binarized images were used to quantify the vessel tortuosity, vessel density, foveal avascular zone (FAZ) area, and FAZ acircularity. The vessels were divided vertically as superficial retinal layer and deep retinal layer, and horizontally as circular areas with 3 mm and 1.5 mm diameters. Analysis of variance was performed for multiple comparisons. Correlation analysis evaluated the association between the quantified parameters. Compared with healthy eyes, vessel tortuosity increased as DR severity was more in NPDR, but decreased in PDR (P = 0.033). The decrease in vessel density and the increase in both FAZ area and FAZ acircularity were consistent, while DR approached PDR. Among all parameters, statistically significant difference between no DR and mild NPDR was observed only in vessel tortuosity, especially within the 1.5 mm area of superficial retinal layer (P = 0.011). Correlations of vessel tortuosity with FAZ area and acircularity were confined to the 3 mm and 1.5 mm areas of superficial retinal layer (r = -0.185, P = 0.023 for FAZ area; r = 0.268, P = 0.001 for FAZ acircularity), while vessel density strongly correlated with FAZ parameters in the superficial retinal layer and deep retinal layer. Vessel tortuosity increased as the stage of NPDR was more severe, but decreased in PDR. The vessel tortuosity determined using optical coherence tomography angiography might be a useful parameter indicating the progression to PDR, circumventing the risk from invasive conventional angiography.

Assessing the Accuracy of Foveal Avascular Zone Measurements Using Optical Coherence Tomography Angiography: Segmentation and Scaling.

PurposeThe foveal avascular zone (FAZ) is altered in numerous diseases. We assessed factors (axial length, segmentation method, age, sex) impacting FAZ measurements from optical coherence tomography (OCT) angiography images.MethodsWe recruited 116 Caucasian subjects without ocular disease, and acquired two 3 × 3 mm AngioVue scans per each right eye (232 total scans). In images of the superficial plexus, the FAZ was segmented using the AngioVue semiautomatic nonflow measurement tool and ImageJ manual segmentation. In images from the full retinal thickness, the FAZ was segmented using the AngioAnalytics automatic FAZ tool. Repeatability, reliability, and reproducibility were calculated for FAZ measurements (acircularity, area).ResultsFAZ area (mean ± SD) for manual segmentation was 0.257 ± 0.104 mm2, greater than both semiautomatic (0.231 ± 0.0939 mm2) and automatic (0.234 ± 0.0933 mm2) segmentation (P < 0.05). Not correcting for axial length introduced errors up to 31% in FAZ area. Manual area segmentation had better repeatability (0.022 mm2) than semiautomatic (0.046 mm2) or automatic (0.060 mm2). FAZ acircularity had better repeatability with automatic than manual segmentation (0.086 vs. 0.114). Reliability of all area measurements was excellent (intraclass correlation coefficient [ICC] = 0.994 manual, 0.969 semiautomatic, 0.948 automatic). Reliability of acircularity measurements was 0.879 for manual and 0.606 for automatic.ConclusionWe identified numerous factors affecting FAZ measurements. These errors confound comparisons across studies and studies examining factors that may correlate with FAZ measures.Translational RelevanceUsing FAZ measurements as biomarkers for disease progression requires assessing and controlling for different sources of error. Not correcting for ocular magnification can result in significant inaccuracy in FAZ measurements, while choice of segmentation method affects both repeatability and accuracy.