Improved method for optical coherence tomography angiography: from reconstruction to clinical indicator quantification

Objective: The foveal avascular zone (FAZ) is the round capillary-free zone within the macula and is supplied only by a single-layered parafoveal capillary arcade. This study aimed to evaluate the quantitative FAZ and retino-choroidal vessel density (VD) using optical coherence tomography angiography (OCTA) in a healthy Indian population.Methods: This was a cross-sectional observational study that was conducted for evaluating the quantitative FAZ and retino-choroidal VD of 200 eyes of 100 healthy Indian subjects, including 62 males and 38 females (age range 17-50 years) having the best-corrected visual acuity (BCVA) of logMAR 0 (20/20; 6/6) and spherical equivalent refractive error of not more than 1 D. The subjects were examined using OCTA automated software on spectral-domain OCT (SD-OCT; Nidek RS 3000 Advance 2; Nidek, Inc., Fremont, CA) on a 3 x 3 mm OCTA macular scan centred on the fovea. The FAZ size, perimeter and circularity index, VD in superficial, deep, and outer retina (OR), outer retinal chorio-capillaries (ORCC), chorio-capillaries (CC) and choroid (C) were analysed in the circular and quadrant-segmented zones. A correlation was found between the FAZ size, perimeter and circularity, and VD in retino-choroidal layers, and between BCVA, age, central foveal thickness (CFT) and sub-foveal choroidal thickness (SFCT), and OCTA parameters.Results: The FAZ and surrounding vascular arcades were intact in all eyes, showing either a vertical or horizontal oval-shaped symmetrical formation without gaps, holes or interruption of the capillary network. The mean value of CFT was 237.5±26.0 microns and SFCT was 269.6±53.0 microns. The mean FAZ area was 0.42±0.23 mm2, FAZ perimeter was 3.3±1.0 mm and FAZ circularity index was 0.46±0.1. The mean VD in superficial capillary plexus (SCP) was 23.87±10.66, in deep capillary plexus (DCP) was 16.03±9.90, in OR was 13.22± 12.27, in ORCC was 39.74±14.32, in CC was 37.02±16.43 and in choroid was 37.43±16.76. The increasing order of VD in different retino-choroidal layers was OR<DCP<SCP<CC<C<ORCC. The FAZ area and perimeter had a statistically significant (SS) negative correlation with the VD in SCP, DCP and OR, while the FAZ perimeter additionally had a SS negative correlation with the VD in the choroid. The FAZ circularity had a SS positive correlation with VD in SCP, DCP and OR. There was no SS correlation between the age of subjects and OCTA parameters. The BCVA had a SS correlation with only one parameter, i.e. ORCC foveal (r=-0.15; p=0.03). There was a SS negative correlation between CFT and FAZ area and perimeter, and a SS positive correlation between the CFT and VD in SCP, DCP and OR. There was a SS positive correlation between the SFCT and VD in different layers including SCP, DCP, ORCC, CC and choroid.Conclusions: VD is the highest in the ORCC and lowest in the OR segment. A better VD in SCP, DCP and OR is associated with a reduced FAZ area/FAZ perimeter and an increased FAZ circularity index. A lower VD in the ORCC is associated with worse BCVA. In a healthy subject, a relatively thicker foveal region is likely to have better vascularity of SCP, DCP and OR and a smaller FAZ area/FAZ perimeter. In the absence of diseases, relatively thicker sub-foveal choroid is expected to have better vascularity of SCP, DCP, ORCC, CC and choroid.

Purpose:To evaluate the effects of scanning tilt on the macular vessel density (VD) measurements in healthy subjects using optical coherence tomography angiography (OCTA).Methods:OCTA imaging was performed on healthy subjects to acquire nasal and temporal oblique scans. Quantitative analyses included as follows: (1) VD in whole-image, annular, and quadrant regions of the superficial capillary plexus (SCP), deep capillary plexus (DCP), and choriocapillaris (CC) layer; (2) Foveal avascular zone (FAZ) parameters (area, perimeter, circularity index) in the SCP.Results:Twenty-eight eyes of 28 healthy participants were included. Nasal inclination significantly affected VD measurement in the SCP temporal quadrant, DCP nasal/temporal/inferior quadrants, and all CC regions (all P < 0.05). Temporal tilt influenced VD measurements in all regions except the SCP superior and temporal quadrants (all P < 0.05). While FAZ area and perimeter remained unaffected by tilt, temporal tilt significantly reduced FAZ circularity (P = 0.022).Conclusion:The tilt of the OCTA scan has different effects on the VD measurements of the whole, annular, and quadrant regions of macular layers and the FAZ circularity index.

PURPOSE To evaluate a fully automated local fractal dimension method to quantify vessel density and foveal avascular zone (FAZ) area in optical coherence tomography angiography (OCTA) images. METHODS Fifty-two healthy Asian Indian eyes underwent imaging prospectively with OCTA system. Superficial and deep retinal vascular plexus was imaged. Local fractal analysis was applied to the OCTA images. A scan area of 3 × 3 mm was selected in the superficial and deep retinal layers. Foveal avascular zone area and vessel density were quantified in circular and sectoral zones around the fovea. A unique contour map of vessel density and dropout zones was developed to perform regional comparisons. RESULTS Foveal avascular zone of superficial (0.35 ± 0.013 mm2) and deep (0.49 ± 0.012 mm2) retinal vascular plexus was segmented. The agreement between the manually segmented and local fractal dimension segmented FAZ area was 0.97 (95% confidence interval [CI]: 0.94-0.98) and did not change significantly with age (P = 0.94 and 0.21, respectively). The vessel density was greater in the deep than the superficial retinal vascular plexus (P < 0.0001). When the image was subdivided into sectors around the FAZ, inferior sector had greater vessel density than the others (temporal, superior, and nasal) in both superficial and deep retinal vascular plexus (P < 0.05). These observations were similar to recent studies on animal retinal vasculature map. CONCLUSIONS A novel implementation of local fractal dimension to calculate vessel density and FAZ area was demonstrated. Age did not impact vessel density but sectoral analyses showed greater vessel density in the inferior zone.

To evaluate a fully automated local fractal dimension method to quantify vessel density and foveal avascular zone (FAZ) area in optical coherence tomography angiography (OCTA) images. Fifty-two healthy Asian Indian eyes underwent imaging prospectively with OCTA system. Superficial and deep retinal vascular plexus was imaged. Local fractal analysis was applied to the OCTA images. A scan area of 3 × 3 mm was selected in the superficial and deep retinal layers. Foveal avascular zone area and vessel density were quantified in circular and sectoral zones around the fovea. A unique contour map of vessel density and dropout zones was developed to perform regional comparisons. Foveal avascular zone of superficial (0.35 ± 0.013 mm2) and deep (0.49 ± 0.012 mm2) retinal vascular plexus was segmented. The agreement between the manually segmented and local fractal dimension segmented FAZ area was 0.97 (95% confidence interval [CI]: 0.94-0.98) and did not change significantly with age (P = 0.94 and 0.21, respectively). The vessel density was greater in the deep than the superficial retinal vascular plexus (P < 0.0001). When the image was subdivided into sectors around the FAZ, inferior sector had greater vessel density than the others (temporal, superior, and nasal) in both superficial and deep retinal vascular plexus (P < 0.05). These observations were similar to recent studies on animal retinal vasculature map. A novel implementation of local fractal dimension to calculate vessel density and FAZ area was demonstrated. Age did not impact vessel density but sectoral analyses showed greater vessel density in the inferior zone.

Purpose:To compare foveal avascular zone (FAZ) area and circularity, ganglion cell layer (GCL) thickness, retinal perfusion density (PD), and vessel density (VD) in eyes with branch retinal vein occlusion (BRVO) after resolution of cystoid macular edema (CME) to fellow control eyes and to correlate these parameters with visual acuity (VA).Methods:SD-OCTA scans (Zeiss Angioplex; Carl Zeiss Meditec Version 10) obtained on 32 eyes with BRVO after resolution of the CME with their fellow eyes used as controls were retrospectively evaluated. Parameters analyzed were FAZ size and circularity, PD, and VD in the superficial capillary plexus measured in the Early Treatment Diabetic Retinopathy Study (ETDRS) grid pattern using the automated algorithm. GCL thickness was generated from the Macular Cube 512 × 218 protocol. VA measured on the same day as OCTA examination was recorded.Results:The mean FAZ area was greater (P = 0.01) in BRVO eyes (0.239 ± 0.108 mm2) when compared with fellow eyes (0.290 ± 0.127 mm2). The FAZ was more irregular in BRVO eyes compared with fellow eyes (circularity index = 64.6 ± 12.8% vs 71.1 ± 10.8%, respectively, P = 0.03). GCL thickness was lower in BRVO eyes compared with control eyes (67.19 ± 27.71 vs 77.79 ± 6.41 respectively, P = 0.006). The mean VD and PD were significantly lower in the ETDRS outer ring in BRVO eyes (P = 0.04 and 0.038, respectively). On comparison of the affected quadrant with the unaffected quadrant in BRVO eyes, the affected quadrant had a lower outer PD (P = 0.04), outer VD (P = 0.04), and GCL thickness (P = 0.02). There was no significant correlation of VA with FAZ, VD, or GCL thickness (P >0.05).Conclusion:FAZ is more irregular and enlarged, and GCL is thinner, in eyes with BRVO after resolution of CME especially in the affected quadrant suggesting neuronal degeneration as a sequela of BRVO. Both perfusion and VD are reduced in the quadrant affected by the BRVO demonstrating regional quantitative differences in the retinal microvasculature. These parameters may prove useful in monitoring the disease progression and treatment response.

To assess the relationship between the size of the foveal avascular zone (FAZ; area and perimeter) and vessel density (VD) at various retinal regions using optical coherence tomography angiography (OCTA) in patients with open-angle glaucoma (OAG). In this retrospective cross-sectional study, OAG eyes were grouped according to the presence/absence of central visual field (CVF) defects. A control group of normal eyes was also included. OCTA images were obtained from the optic nerve (4.5 × 4.5 mm2) and macular (3 × 3 mm2) area, in which VDs were measured in the circumpapilla, parafovea, and fovea regions. Partial correlation analyses between FAZ parameters representing size and VDs at different retinal regions were performed. The correlation between FAZ parameters and macular ganglion cell-inner plexiform layer thickness (mGCIPLT) and CVF mean sensitivity (MS) was also assessed. For spatial correspondence, correlations between FAZ parameters and corresponding VD, mGCIPLT, and CVF-MS measurements were assessed at each hemiretina. A total of 126 OAG eyes and 40 controls were reviewed. Overall, FAZ parameters showed statistically significant correlations with VDs measured at the fovea, parafovea, and circumpapilla (FAZ area: r = -0.603, -0.385, -0.256; P < 0.001, < 0.001, and 0.003, respectively). These correlations were observed regardless of the presence of CVF defects (all P < 0.05). FAZ size showed significant spatial correlations with VD, mGCIPLT, and CVF-MS measurements at each hemiretina. OCTA-derived FAZ area and perimeter showed statistically significant correlations with VDs measured at various retinal locations with spatial correspondence in OAG.

Background and Objectives: Open-angle glaucoma subtypes share a structural phenotype but differ in pathophysiology: pseudoexfoliative glaucoma (PXG) involves vascular endothelial dysfunction associated with deposition of exfoliative material, whereas normal-tension glaucoma (NTG) reflects primary vascular dysregulation in the absence of elevated intraocular pressure. We characterized subtype-specific OCT angiography (OCTA) profiles obtained from a 3 × 3 mm macular scan and evaluated their discriminatory power for pairwise subtype classification. Materials and Methods: This was a single-center, cross-sectional study of 304 eyes: 198 glaucomatous eyes—primary open-angle glaucoma (POAG, glaucoma simplex in our clinical nomenclature), n = 102; PXG (glaucoma capsulare), n = 68; NTG (glaucoma sine tensio), n = 28—and 106 healthy controls. The Cirrus HD-OCT 5000 AngioPlex 3 × 3 mm OCTA protocol was used to assess vessel density (VD), perfusion density, foveal avascular zone (FAZ) morphology, ganglion cell complex (GCC), and retinal nerve fiber layer (RNFL) thickness. Analyses included Kruskal–Wallis tests with Bonferroni post hoc correction, ROC analysis with DeLong comparison of combined versus structural-only models, multivariate regression, and an exploratory XGBoost classifier with SHAP-based interpretation. Results: VD Inner and Perfusion Inner were lower in PXG (16.37 ± 3.33%; 0.31 ± 0.05) than in POAG (18.73 ± 3.41%; 0.34 ± 0.05; both p < 0.001); Perfusion Inner was also lower than in NTG (p < 0.05). FAZ Area was largest in NTG (0.27 ± 0.11 mm2) and greater than in PXG (0.19 ± 0.08; p < 0.01); FAZ Circularity differed across subtypes (p < 0.001). Combined OCTA–structural models outperformed structural-only models for POAG vs. PXG (DeLong p = 0.002) and for PXG vs. NTG (AUC = 0.770; p = 0.010). Sector-resolved Spearman analysis revealed subtype-specific coupling: in NTG, VD Inner and Perfusion Inner correlated with the inferior RNFL (r = 0.53 and r = 0.52; both p < 0.01); in PXG, coupling shifted nasally (r = 0.41 and r = 0.46; both p < 0.001). The exploratory XGBoost classifier separated glaucoma from controls with an internal cross-validated AUC of 0.975 ± 0.008 (5-fold CV; not externally validated); FAZ Circularity (mean |SHAP| = 0.418) and FAZ Area (0.411) were the top inter-subtype features, supported by case-level SHAP. RNFL avg and average GCC independently predicted MD across subtypes; in PXG, Perfusion Inner also predicted MD (β = −32.78; p = 0.032). Conclusions: In this single-center, cross-sectional cohort, OCTA revealed subtype-associated macular microvascular profiles that are complementary to structural OCT. Reduced vessel and perfusion density characterized PXG, whereas FAZ enlargement and reduced circularity distinguished NTG and PXG. Vascular–structural coupling was nasal-predominant in PXG and inferior-predominant in NTG. Combined multimodal models outperformed structural-only approaches. Macular perfusion additionally predicted MD in PXG. The XGBoost/SHAP analysis is exploratory; prospective and externally validated studies are required before clinical deployment.

PurposeTo analyze the repeatability of vessel density (VD) measurements and manual foveal avascular zone (FAZ) measurements using optical coherence tomography angiography (OCTA) in patients with retinal vein occlusion (RVO) without macular edema.MethodsThe study population consisted of patients with RVO and central macular thickness <300 μm. For each subject, measurements were performed twice with a 5-minute interval. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated to analyze the repeatability of results obtained with the OCTA device. To identify factors related to repeatability, we performed Pearson correlation analyses based on the CV of potential factors.ResultsA total of 48 eyes were included in the study. The ICCs of the VDs in superficial capillary plexus (SCP) and the deep capillary plexus (DCP) were 0.748 and 0.665, respectively, and the CVs of the VDs in SCP and DCP were 9.1% and 12.6%, respectively. The ICCs associated with the FAZ of the superficial layer (SFAZ) and that of the deep layer (DFAZ) were 0.965 and 0.956, respectively, and the CV of the SFAZ and DFAZ were 8.8% and 9.7%, respectively. From Pearson correlation analyses, OCTA quality was significantly correlated with the CV of the VDs of SCP and DCP. However, there were no variables that were significantly correlated with the CV of SFAZ and DFAZ, including OCTA quality.ConclusionsVD measurements in the SCP layer using OCTA exhibited good repeatability, and VD measurements in the DCP layer exhibited relatively low repeatability compared to that of SCP layer measurements in patients with RVO without macular edema after treatment with bevacizumab. Manual measurement of the FAZ area in both SCP and DCP layers resulted in good repeatability. In addition, the repeatability of VD measurements in SCP and DCP layers was correlated with OCTA image quality.

ObjectiveThe study aimed to evaluate the quantitative characteristics of the macular vessel density (VD) and foveal avascular zone (FAZ) in glaucoma using optical coherence tomography angiography (OCT-A).DesignCross-sectional, age- and sex-matched case–control study.MethodsFifty-two eyes of 52 patients with primary open angle glaucoma and 52 eyes from 52 healthy participants were recruited retrospectively. OCT-A was performed on a 3 x 3-mm macular region centered on the fovea. OCT-A scans were manually graded to define the FAZ. Parafoveal VD in superficial and deep retina were analyzed in the circular- and quadrant-segmented zone. The FAZ parameters included size, perimeter, and circularity index. The regression analysis among VD and FAZ-related parameters and ocular parameters was performed, and the diagnostic ability was calculated with refractive error adjusted.ResultsFor both groups, the mean age and the sex ratio was not different between groups. With refractive error adjusted, the average macular VD was lower in glaucoma than in the control group for superficial (P = 0.013), deep (P<0.001), and the whole retina (P = 0.002). There were increased FAZ perimeter and decreased FAZ circularity index in glaucoma when compared with controls (P<0.001). In the multivariate regression models, FAZ circularity index were significantly associated with decreased peripapillary RNFL thickness (P = 0.007) and macular GCIPL thickness (P = 0.009) measured by OCT. The refractive-error adjusted area under receiver operating characteristics was highest for FAZ circularity index (0.905; 95% CI, 0.844–0.966), followed by temporal deep retinal VD (0.870; 95% CI, 0.803–0.937) and FAZ perimeter (0.858; 95% CI, 0.784–0.932).ConclusionsDecreased macular VD, increased FAZ perimeter, and decreased FAZ circularity index were observed in eyes with glaucoma using OCT-A. With refractive error adjusted, these parameters showed considerable diagnostic value for glaucoma. FAZ circularity index may be a novel biomarker representing disruption of the parafoveal capillary network in glaucoma, as supported by its association with structural parameters.

To assess the macular capillary networks and foveal avascular zone (FAZ) with swept-source optical coherence tomography angiography in healthy eyes. This cross-sectional, prospective, observational study enrolled 222 eyes of 116 healthy participants with no ocular or systemic disease. SS-OCTA images were captured using the PLEX Elite 9000 (Carl Zeiss Meditec Inc., Dublin, CA, USA) with a 6 × 6 mm pattern centered on the foveal center. Vessel length density (VLD), perfusion density (PD), and FAZ parameters were analyzed using the manufacturer's automated software. A significant negative correlation was observed between age and average VLD in the superficial plexus, and average PD in both the superficial plexus and the whole retina. A significant positive correlation between age and foveal avascular zone perimeter and area was also noted. Age-wise comparisons showed a trend for an increase in VLD and PD until 40 years of age, with a subsequent decrease in the older age in the macular region. The central subfield showed a decrease in the vessel density measurements in the 21-40 age group. FAZ area and perimeter were the mirror inverse of the central subfield vessel density measurements with a numerically greater area and perimeter in the 21-40 age group compared to the 0-20 and 41-60 age groups. FAZ circularity was significantly reduced after 40 years of age. Age-related changes in the vessel density and FAZ parameters in the healthy macula are complex and vary with the macular location. These results carry significance when interpreting the data from diseased eyes.

The purpose of this study is to identify and quantify preclinical changes with the help of optical coherence tomography angiography (OCTA) within the retinal microcirculation of young type 1 diabetes (T1D) patients without clinical signs of diabetic retinopathy (DR) and to compare these results with those obtained from healthy age-matched subjects. OCTA is currently used for monitoring diabetic retinopathy; however, there is no current consensus on which OCTA parameter alterations predict the first clinical signs of diabetic retinopathy. The main challenge that young patients with T1D face during the course of the disease is that they can rapidly progress to the development of DR, especially during adolescence. Moreover, they also present an increased risk of rapid progression toward advanced stages of DR and vision loss compared to type 2 diabetes patients, indicating the importance of early diagnosis and intervention. The limitations of the currently used screening procedures that led to the conceptualization of our study are the difficulties in performing fluorescein angiography tests for diagnosing the clinical signs of DR on young patients, namely the invasive procedure of dye injection, the risk of allergic reactions and the long duration of the examination. Moreover, given the long life expectancy of young T1D patients, it is essential to identify the preclinical changes in retinal microvasculature before reaching the first clinical signs quantifiable by FFA. The clinical study enrolled 119 subjects aged between 4 and 30 years old with a mean age of 13 years old, comprising 61 T1D patients with a mean duration of the disease of 4 years and 8 months and 58 healthy age-matched subjects for the control group. OCTA scans were performed using the RevoNX 130 OCTA device (Optopol) to evaluate the following retinal parameters: foveal avascular zone (FAZ) area, perimeter and circularity, overall foveal thickness, and superficial and deep vessel densities. Statistically significant differences between the two groups were identified for the following parameters: the FAZ area in the T1D group (0.42 ± 0.17) was larger than the control group (0.26 ± 0.080), the FAZ circularity (0.41 ± 0.11) was decreased compared to the control group (0.61 ± 0.08) and the FAZ perimeter was larger (3.63 ± 0.97) compared to the control group (2.30 ± 0.50). The overall foveal thickness was decreased in the T1D group (222.98 ± 17.33) compared to the control group (230.64 ± 20.82). The total vessel density of the superficial capillary plexus (SCP) on an investigated area of 6 X 6 mm centered around the fovea was decreased in the T1D group (37.4164 ± 2.14) compared to the control group (38.0241 ± 2.44). Our data suggest that specific imaging biomarkers such as FAZ perimeter, area and circularity, decreased overall foveal thickness and decreased vessel density in the SCP precede the clinical diagnosis of DR in young T1D patients and represent useful parameters in quantifying capillary nonperfusion in T1D patients without clinical signs of DR.

This study analyzed the optical coherence tomography angiography (OCTA) macular parameters in primary angle-closure glaucoma (PACG) patients after acute primary angle closure (APAC) episodes. Thirty-three patients with 33 APAC eyes and 33 primary angle closure suspect (PACS) eyes and 33 age-matched normal subjects (controls) were enrolled. Macular vessel density (VD) in central, inner, outer and full regions and foveal avascular zone (FAZ) parameters (area, perimeter and circularity index) were compared between APAC, PACS, and control eyes. For resolved APAC eyes, the VD in each macular region was significantly lower than that in control eyes, with less central and inner macular VD than PACS eyes. The central macular VD was significantly lower in PACS eyes than in controls. There was no difference in FAZ area and perimeter between APAC, PACS, and control eyes. FAZ circularity was highest in control eyes, followed by PACS eyes, and lowest in APAC eyes. The AUC, sensitivity and specificity of FAZ circularity were 0.944, 93.9% and 84.8%, respectively, in APAC eyes and 0.881, 84.8% and 81.8%, respectively, in PACS eyes. Therefore, FAZ circularity had the best discrimination capability for detecting both APAC and PACS eyes. Macular assessment with OCTA could provide an accurate early-stage diagnostic tool for PACG.

AimTo examine the correlation of best-corrected visual acuity (BCVA) with intercapillary area (ICA) measured from optical coherence tomography angiography (OCT-A) in patients with diabetes, and to compare the strength of...

AimTo evaluate the correlation between inner retinal layer thinning and the foveal microvasculature in type 2 diabetes using optical coherence tomography angiography (OCTA).MethodsA cross-sectional study involved 155 diabetic eyes. All...

OCT Angiography Metrics Predict Progression of Diabetic Retinopathy and Development of Diabetic Macular Edema: A Prospective Study