Optical Coherence Tomography Angiography Signal Research Articles

Validity of a novel optical coherence tomography angiography flow index in a cohort of primary open angle glaucoma

BackgroundVascular mechanisms are implicated in many ocular diseases. Therefore, different vascular imaging modalities are used in management of such conditions. Optical coherence tomography angiography (OCTA) has high spatial resolution and segmentable 3D volumetric sampling enabling isolation of retinal and peripapillary vascular beds. However, OCTA only indirectly derives quantitative flow data i.e. velocimetry through methods and algorithms liable to limitations like signal saturation. This study introduces and validates novel mathematical OCTA flow indices that may compensate for some OCTA velocimetric limitations.MethodsThirty-seven eyes of 23 POAG patients were included. Each underwent baseline and follow-up assessment one month thereafter. Assessment comprised full ophthalmological examination, intraocular pressure (IOP), systemic arterial blood pressure (SABP) and OCTA macula and ONH. Angiograms were processed using ImageJ to calculate OCTA intensity-based flow indices (FIOs), for superficial vascular plexus (SVP), deep vascular plexus (DVP) and optic nerve head vascular plexus (ONH-RPC), i.e. SFIO, DFIO and ONHFIO respectively. Mean ocular perfusion pressure (MOPP) was calculated using IOP and SABP. OCTA vascular densities (VD) and MOPP were used to calculate three respective mathematical flow indices (FIMs) for SVP, DVP and ONH-RPC, based on Hagen-Poiseuille law, i.e. SFIM, DFIM, ONHFIM respectively. Pearson test was used for correlation between the two sets of indices. Intraclass correlation coefficient (ICC) was tested for baseline and follow-up values for each index.ResultsThere was positive correlation between the three FIMs and their respective FIOs at baseline and follow-up ranging between high and moderate. Correlation coefficients (CCs) were 0.773 and 0.609 for SFIM and SFIO P-value < 0.001, 0.829 and 0.624 for DFIM and DFIO P-value < 0.001 and 0.516 and 0.737 for ONHFIM P-value = 0.001 for baseline and follow-up respectively. ICCs were 0.772 P-value < 0.001, 0.328 P-value = 0.022 and 0.888 P-value < 0.001 for SFIM, DFIM and ONHFIM respectively. For SFIO, DFIO and ONHFIO, ICCs were 0.420 P-value = 0.004, 0.079 P-value = 0.320 and 0.833 P-value < 0.001 respectively.ConclusionThe novel FIMs are reliable alternatives to FIOs and may compensate for OCTA signal saturation in extremes of MOPP. SFIM and ONHFIM showed high ICCs with excellent reliability. While DFIM demonstrated low ICC indicating poor reliability, it still performed better than its corresponding DFIO.

Correlation of the macular microvasculature to the axial length in pediatric patients with high axial refractive errors.

To compare the vascular density (VD) of the macular superficial capillary plexus (SCP), deep capillary plexus (DCP), and choriocapillaris (CC), and the foveal avascular zone (FAZ) among high hyperopic, high myopic, and emmetropic children using optical coherence tomography angiography (OCTA). This was a cross sectional comparative study of otherwise healthy children with different refractive errors. Patients were recruited from Cairo University Children's Hospital. OCTA imaging was performed using the RTVue XR Avanti device with AngioVue software. Both the 3 × 3 and 6 × 6 mm macular scans were utilized. Automated measurements were obtained from the built-in machine software. Axial length (AL) measurements were done using Lenstar LS 900 optical biometer. Ninety eyes from 51 healthy children were included. Among high myopes, there was significant thinning of the parafovea (p < 0.001). SCP-VD was also lower in high myopes in all areas except the fovea (all p < 0.001). The DCP-VD was significantly lower in high myopes in the parafovea and perifovea. High hyperopes had lower subfoveal CC-VD. Despite high myopes showing a significantly lower OCTA signal strength, linear regression analysis revealed that AL was an independent and significant predictor for the FAZ-area, as well as parafoveal and perifoveal SCP and DCP-VD. High myopia results in a reduction of VD in both the SCP and DCP, which can be non-invasively detected and monitored using OCTA. While lower VD may, in part, be attributed to lower OCTA image quality, our findings demonstrate that AL independently and significantly predicts macular vascular parameters on OCTA in children.

Factors affecting optical coherence tomography angiography signal strength index in patients receiving intravitreal injection treatment.

To investigate the clinical factors affecting optical coherence tomography angiography (OCTA) signal strength index (SSI) and its change after intravitreal injection treatment in patients with retinal disorders. OCTA data from 186 eyes of 166 patients with various retinal disorders including age-related macular degeneration, diabetic macular edema (DME), and retinal vein occlusions who received intravitreal injections were analyzed. The associations between SSI and clinical factors, including age, best-corrected visual acuity (BCVA), media opacity severity, and central macular thickness (CMT), were evaluated both before and after injection. After injection, BCVA improved and CMT decreased significantly, and SSI increased significantly (p = 0.030). BCVA showed a significant positive correlation with media opacity severity before and after injection and with CMT only before injection. In the multivariate analysis, age, presence of DME, BCVA, and media opacity severity were negatively associated with SSI both before and after injection, while CMT was negatively associated with SSI only before injection. After injection, a negative correlation was found between SSI change and both BCVA and CMT change. Our findings suggest that OCTA SSI is influenced by various clinical factors, including age, visual acuity, media opacity severity, and macular thickening, especially in cases of DME. The results also indicate that SSI may decrease in patients with macular disorders due to the presence of macular edema and the associated decrease in visual acuity. Therefore, it is crucial to consider these factors when interpreting OCTA data and ensure an adequate level of SSI.

Gradient mapping of multi-timescale optical coherence tomography angiography signals for enhancing signal-to-noise ratio of flow detection

Optical coherence tomography (OCT) is a three-dimensional imaging technique based on low coherence interferometry of near-infrared broadband light and has been applied to medical diagnoses, such as structural diagnosis of the retina in ophthalmology. For several decades, functional variations of OCT have been also developed. OCT angiography (OCTA) is one of the functional variations of OCT and can visualize blood flows (microvasculature) in biological tissues by analyzing the time-series of OCT signals. Recently, several studies suggested the possibility that OCTA can not only visualize blood flows but also detect the blood flow velocity quantitatively, where the blood flow velocity is estimated by analyzing OCTA signals computed with multiple time separations from the time-series of OCT signals measured at a short time interval. OCTA signals computed with short time separations, however, reduce its contrast between dynamic tissues (blood flows) and other static tissues, resulting in the decrease of signal-to-noise (SN) ratio of the flow detection. This study proposed a novel method to enhance the SN ratio of the flow detection from such OCTA signals computed with short time separations, by means of mapping the gradient of OCTA signals against the time separations. In the experiments, a flow phantom and human skins were employed to compare SN ratios among OCTA with a long time separation (standard OCTA), OCTA with a short time separation, and the proposed method. The results showed that the proposed methods can detect flow signals with a high SN ratio equivalent to that of the standard OCTA and, therefore, suggested that quantitative detection of the flow velocity with OCTA will be possible with a high SN ratio of flow detection.

An Enhanced Image Segmentation From 3D to 2D by Using Modified Neural Network

Abstract: Optical coherence tomography angiography (OCTA) is an imaging which can applied in ophthalmology to provide detailed visualization of the perfusion of vascular networks in the eye. compared to previous state of the art dye-based imaging, such as fluorescein angiography. OCTA is non-invasive, time efficient, and it allows for the examination of retinal vascular in 3D. These advantage of the technique combined with the good usability in commercial devices led to a quick adoption of the new modality in the clinical routine. However, the interpretation of OCTA data is not without problems commonly observed image artifacts and the quite involved algorithmic details of OCTA signal construction can make the clinical assessment of OCTA exams challenging. In this paper we describe the technical background of OCTA and discuss the data acquisition process, common image visualization techniques, as well as 3D to 2D projection using high pass filtering, relu function and convolution neural network (CNN) for more accuracy and segmentation results.

Maximum a posteriori signal recovery for optical coherence tomography angiography image generation and denoising

Optical coherence tomography angiography (OCTA) is a novel and clinically promising imaging modality to image retinal and sub-retinal vasculature. Based on repeated optical coherence tomography (OCT) scans, intensity changes are observed over time and used to compute OCTA image data. OCTA data are prone to noise and artifacts caused by variations in flow speed and patient movement. We propose a novel iterative maximum a posteriori signal recovery algorithm in order to generate OCTA volumes with reduced noise and increased image quality. This algorithm is based on previous work on probabilistic OCTA signal models and maximum likelihood estimates. Reconstruction results using total variation minimization and wavelet shrinkage for regularization were compared against an OCTA ground truth volume, merged from six co-registered single OCTA volumes. The results show a significant improvement in peak signal-to-noise ratio and structural similarity. The presented algorithm brings together OCTA image generation and Bayesian statistics and can be developed into new OCTA image generation and denoising algorithms.

Polarization sensitive optical coherence tomography for imaging microvascular information within living tissue without polarization-induced artifacts.

When imaging birefringent samples using optical coherence tomography angiography (OCTA), the phase retardation may appear opposite to the phase change due to the blood flow in the orthogonal signals, for which a cancellation effect can occur when deriving OCTA signals. This effect can diminish the ability of OCTA to detect vascular information, leading to an erroneous interpretation of the final OCTA images. To mitigate this issue, we demonstrate polarization-sensitive optical coherence tomography (PS-OCT) to image microvascular information within a living sample without polarization induced artifacts. The system is furnished with a swept source OCT (SS-OCT) that incorporates two imaging modes: OCTA imaging and polarization-sensitive imaging. PS-OCT is used to provide birefringent contrast where the color-encoded Stokes parameters are used to obtain high contrast polarization-state images. OCTA is used to acquire high-resolution images of functional microvascular networks permeating the scanned tissue volume. Taking the advantages of the dual-channel PS-OCT configuration, the polarization induced artifacts are eliminated from OCTA vascular imaging. The proposed PS-OCTA system is employed to visualize the birefringent components and the vascular networks of the human skin in vivo. It is expected that the proposed system setup would have useful and practical applications in the investigations of the vasculature in the birefringent tissue samples both pre-clinically and clinically.

Visibility of microvessels in Optical Coherence Tomography angiography depends on angular orientation.

Optical Coherence Tomography angiography (OCTA) is a widespread tool for depth-resolved imaging of chorioretinal vasculature with single microvessel resolution. To improve the clinical interpretation of OCTA, the conditions affecting visualization of microvessels must be defined. Here we inject a scattering plasma tracer (Intralipid) during OCTA imaging of the anesthetized rat eye. In the retina, we find that interlaminar (vertical) vessels that connect laminae have one-fourth to one-third the OCTA red blood cell to tracer (RBC-to-tracer) signal ratio of intralaminar (horizontal) vessels. This finding suggests that the OCTA signal from microvessels depends on angular orientation, making vertically-oriented vessels more difficult to visualize using intrinsic contrast alone. Clinicians should be aware of this potential artifact when interpreting OCTA.

Peripapillary vessel parameters and mean ocular perfusion pressure in young healthy eyes: OCT angiography study

BackgroundTo investigate the relationship between estimated mean ocular perfusion pressure (MOPP) and peripapillary perfusion density (PD) or vessel density (VD) as measured by spectral-domain optical coherence tomography angiography (OCTA) in...

Optical coherence tomography angiography measures blood pulsatile waveforms at variable tissue depths.

Photoplethysmography (PPG) is routinely used to detect the blood pulse signal from skin tissue beds in clinics. However, the origin of the PPG signal remains controversial. The purpose of this study is to explore optical coherence tomography angiography (OCTA) to indicate pulsatile waveforms in the papillary plexus and dermal plexus separately under different hand elevations. Optical microangiography (OMAG) algorithm was used to obtain a 3D OCTA signals, from which the depth-resolved pulsatile blood flow signals were extracted from different skin vascular plexus. The systolic amplitude, crest time, and delta T were measured from the OCTA pulsatile signals when the hand was placed at the positions of 50 cm below, 0 cm, and 50 cm above the heart level. The pulse signal integrated from all the depths has a similar waveform to that of the PPG and showed the same morphological change at different hand elevations. The pulsatile patterns from the papillary plexus and dermal plexus showed distinct morphological changes at different local blood pressure. Less amplitude difference was found from papillary plexus comparing to that of the dermal plexus. Crest time was found in an increasing trend in the OCTA pulsatile waveform from both plexuses when the arm was raised from the position below to above the heart level. In contrast, a decreasing trend of Delta T was detected in the dermal pulsatile but was not observed from that of the papillary plexus, indicating that vascular resistance associated with the arm elevations does not necessarily have the same effect on the two plexuses. OCTA can provide depth-resolved pulsatile waveforms within different microvascular plexus within tissue skin beds. This technique could open doors to understanding the mechanisms of how blood flow changes at different skin circulatory plexus.

Evaluation of the choroidal features in pachychoroid spectrum diseases by optical coherence tomography and optical coherence tomography angiography.

To evaluate choroidal area, stroma/lumen ratio, choriocapillaris vessel density, and choriocapillaris flow area in eyes with central serous chorioretinopathy, uncomplicated pachychoroid, and pachychoroid pigment epitheliopathy using enhanced depth imaging-optical coherence tomography and optical coherence tomography angiography. This retrospective study analyzed enhanced depth imaging-optical coherence tomography and optical coherence tomography angiography scans of 142 eyes of 92 patients with central serous chorioretinopathy, uncomplicated pachychoroid, and pachychoroid pigment epitheliopathy. The choroidal area and stroma/lumen ratio were measured by binarization of enhanced depth imaging-optical coherence tomography images. Choriocapillaris vessel density and choriocapillaris flow area were measured at the choriocapillaris level by manual segmentation of optical coherence tomography angiography scans. The mean stroma/lumen ratio results were 0.361, 0.345, and 0.354 in central serous chorioretinopathy, uncomplicated pachychoroid, and pachychoroid pigment epitheliopathy groups, respectively (p > 0.05). The mean whole image choriocapillaris vessel density in uncomplicated pachychoroid group was higher compared with central serous chorioretinopathy and pachychoroid pigment epitheliopathy groups (p < 0.0001). The mean foveal, parafoveal, and perifoveal choriocapillaris vessel densities were lower in central serous chorioretinopathy group than in uncomplicated pachychoroid group (p < 0.0001). The mean choriocapillaris flow area was lower in central serous chorioretinopathy group than in uncomplicated pachychoroid and pachychoroid pigment epitheliopathy groups (p < 0.0001 and p = 0.01, respectively). Our findings suggest that both choroidal vessels and stroma are equally involved in central serous chorioretinopathy, uncomplicated pachychoroid, and pachychoroid pigment epitheliopathy. The choriocapillaris segment seems to be more affected in central serous chorioretinopathy compared to uncomplicated pachychoroid and pachychoroid pigment epitheliopathy. However, the reduced optical coherence tomography angiography signal in central serous chorioretinopathy group could be due to shadowing artifact or choriocapillaris hypoperfusion and further studies with higher quality imaging tools are needed.

Assessment of Exudative Activity of Choroidal Neovascularization in Age-Related Macular Degeneration by OCT Angiography

Purpose: Based on exudative activity, choroidal neovascularization (CNV) in age-related macular degeneration (AMD) can be classified as “active” aCNV, pretherapied “silent” sCNV (i.e., a treatment-free interval >12 weeks), or treatment-naïve “quiescent” qCNV. We evaluated the qualitative and quantitative optical coherence tomography angiography (OCTA) features of these CNV subgroups. Methods: The presence of small-caliber vessels, peripheral arcades, and a ­perilesional OCTA signal attenuation as well as values for vessel length, density, and branching index were evaluated for each CNV network in a 6 × 6 mm OCTA scan pattern. Results: Fifty-one eyes of 51 patients with AMD (age 75.9 ± 7.5 years; 20 males [39.2%]) were included. The qCNV subgroup (n = 8) showed the highest prevalence of qualitative and quantitative values for OCTA activity criteria, reaching significance with regard to small-caliber vessels (p = 0.003), peripheral arcades (p = 0.039), vessel length (p = 0.020), and branching index (p < 0.001) when compared to the aCNV (n = 32) and sCNV (n = 11) subgroups. Qualitative criteria were inversely associated with the number of previous anti-VEGF injections (each p < 0.03), while quantitative metrics also suggested lower values. Conclusions: These findings suggest that OCTA may be supportive in the phenotypical differentiation of CNV lesions secondary to AMD, while the assessed structural changes appeared to be more indicative of previously administered anti-VEGF therapy than current exudative activity.

Longitudinal Analysis of the Choriocapillaris Using Optical Coherence Tomography Angiography Reveals Subretinal Fluid as a Substantial Confounder in Patients with Acute Central Serous Chorioretinopathy.

IntroductionTo describe the influence of subretinal fluid (SRF) in analysis of the flow signal from the choriocapillaris (CC) via optical coherence tomography angiography (OCTA) in patients with acute central serous chorioretinopathy (CSC).MethodsObservational, longitudinal, cross-sectional case–control study. Twenty-three eyes of 22 patients with acute CSC were compared with 20 eyes of 20 healthy controls. OCTA images (AngioPlex®, Zeiss) were recorded at baseline and follow-up examination and automatically quantified using an image-processing algorithm. Abnormal CC decorrelation signals (increased and decreased flow, IF and DF) were quantified using a custom image-processing algorithm. To analyze the spatial correlation between SRF and OCTA, CC signal heat-map images containing macular thickness information were used.ResultsChoriocapillaris flow alterations were significantly more pronounced at baseline than at follow-up examination in patients with acute CSC and resolving SRF (IF: p < 0.002; DF: p < 0.003). The extent of SRF correlated significantly with the abnormal CC decorrelation signals when comparing baseline with follow-up examinations (IF: rho = 0.56, p < 0.005; DF: rho = 0.64, p < 0.001). In particular, the reduced OCTA flow signal in the area occupied by SRF at baseline disappeared at follow-up examination (p < 0.02). In comparison with controls, CSC patients with complete resorption of SRF continued to show a reduced OCTA flow signal in the CC (p < 0.008).ConclusionsThe temporospatial association between SRF and reduced OCTA signal from the CC demonstrates that fluid might be a significant confounder for OCTA analysis in patients with CSC. CSC patients with complete absorption of the SRF at follow-up, however, show persistently reduced CC flow signals.

Optical Coherence Tomography Angiography in Mice: Quantitative Analysis After Experimental Models of Retinal Damage.

We implemented optical coherence tomography angiography (OCT-A) in mice to: (1) develop quantitative parameters from OCT-A images, (2) measure the reproducibility of the parameters, and (3) determine the impact of experimental models of inner and outer retinal damage on OCT-A findings. OCT-A images were acquired with a customized system (Spectralis Multiline OCT2). To assess reproducibility, imaging was performed five times over 1 month. Inner retinal damage was induced with optic nerve transection, crush, or intravitreal N-methyl-d-aspartic acid injection in transgenic mice with fluorescently labeled retinal ganglion cells (RGCs). Light-induced retinal damage was induced in albino mice. Mice were imaged at baseline and serially post injury. Perfusion density, vessel length, and branch points were computed from OCT-A images of the superficial, intermediate, and deep vascular plexuses. The range of relative differences measured between sessions across the vascular plexuses were: perfusion density (2.8%-7.0%), vessel length (1.9%-4.1%), and branch points (1.9%-5.0%). In mice with progressive RGC loss, imaged serially and culminating in around 70% loss in the fluorescence signal and 18% loss in inner retinal thickness, there were no measurable changes in any OCT-A parameter up to 4 months post injury that exceeded measurement variability. However, light-induced retinal damage elicited a progressive loss of the deep vascular plexus signal, starting as early as 3 days post injury. Vessel length and branch points were generally the most reproducible among the parameters. Injury causing RGC loss in mice did not elicit an early change in the OCT-A signal.

Real-time cross-sectional and en face OCT angiography guiding high-quality scan acquisition.

Defocusing, vignetting, and bulk motion degrade the image quality of optical coherence tomography angiography (OCTA) more significantly than structural OCT. The assessment of focus, alignment conditions, and stability of imaging subjects in commercially available OCTA systems are currently based on OCT signal quality alone, without knowledge of OCTA signal quality. This results in low yield rates for further quantification. In this Letter, we developed a novel OCTA platform based on a graphics processing unit (GPU) for a real-time, high refresh rate, B-san-by-B-scan split-spectrum amplitude-decorrelation angiography. The GPU provides a real-time display of both cross-sectional and en face images to assist operators during scan acquisition and ensure OCTA scan quality.

Lipid Emulsion-Based OCT Angiography for Ex Vivo Imaging of the Aqueous Outflow Tract.

Contrast agents applicable for optical coherence tomography (OCT) imaging are rare. The intrascleral aqueous drainage system would be a potential application for a contrast agent, because the aqueous veins are of small diameter and located deep inside the highly scattering sclera. We tested lipid emulsions (LEs) as candidate OCT contrast agents in vitro and ex vivo, including milk and the anesthetic substance Propofol. Commercial OCT and OCT angiography (OCTA) devices were used. Maximum reflectivity and signal transmission of LE were determined in tube phantoms. Absorption spectra and light scattering was analyzed. The anterior chamber of enucleated porcine eyes was perfused with LEs, and OCTA imaging of the LEs drained via the aqueous outflow tract was performed. All LEs showed a significantly higher reflectivity than water (P < 0.001). Higher milk lipid content was positively correlated with maximum reflectivity and negatively with signal transmission. Propofol exhibited the best overall performance. Due to a high degree of signal fluctuation, OCTA could be applied for detection of LE. Compared with blood, the OCTA signal of Propofol was significantly stronger (P = 0.001). As a proof of concept, time-resolved aqueous angiography of porcine eyes was performed. The three-dimensional (3D) structure and dynamics of the aqueous outflow were significantly different from humans. LEs induced a strong signal in OCT and OCTA. LE-based OCTA allowed the ability to obtain time-resolved 3D datasets of aqueous outflow. Possible interactions of LE with inner eye's structures need to be further investigated before in vivo application.

OCT Angiography of the Choriocapillaris in Central Serous Chorioretinopathy: A Quantitative Subgroup Analysis.

IntroductionTo quantify optical coherence tomography angiography (OCTA) signal changes at the level of the choriocapillaris (CC) in patients with different stages of central serous chorioretinopathy (CSC) and to explore any correlation between subretinal fluid (SRF) and retinal pigment epithelium (RPE) alterations and the OCTA CC signal.MethodsOne hundred one CSC eyes and 42 healthy control eyes were included in this retrospective study. CSC patients were allocated into four groups: acute, non-resolving, chronic atrophic and inactive CSC. CC OCTA images (AngioPlex®, Zeiss) were automatically quantified using an image-processing algorithm. Spatial correlation analysis of OCTA signals was performed by overlapping macular edema heatmaps and fundus autofluorescence images with corresponding OCTA images.ResultsActive CSC subgroups demonstrated significantly more increased and decreased flow pixels in the CC compared with controls (p < 0.0001). No significant OCTA changes were seen within the active CSC groups or between the inactive and healthy subgroup. Spatial correlation analysis revealed a decreased OCTA signal in the SRF area and an increased signal outside the SRF area in acute CSC. Areas of RPE atrophy co-localized with areas of increased choriocapillaris OCTA signal, while areas with RPE alterations exhibited a normal signal compared with unaffected RPE.ConclusionThe decreased OCTA signal in the area of SRF in acute CSC could be evidence of localized CC hypoperfusion or due to shadowing artifacts. The missing CC OCTA changes in altered RPE adjacent to atrophy argues against CC injury. Studies with higher resolution and optimized image acquisition are warranted to further validate our findings.Electronic supplementary materialThe online version of this article (10.1007/s40123-018-0159-1) contains supplementary material, which is available to authorized users.

Gold Nanoprisms as Optical Coherence Tomography Contrast Agents in the Second Near-Infrared Window for Enhanced Angiography in Live Animals.

Optical coherence tomography angiography (OCTA) is an important tool for investigating vascular networks and microcirculation in living tissue. Traditional OCTA detects blood vessels via intravascular dynamic scattering signals derived from the movements of red blood cells (RBCs). However, the low hematocrit and long latency between RBCs in capillaries make these OCTA signals discontinuous, leading to incomplete mapping of the vascular networks. OCTA imaging of microvascular circulation is particularly challenging in tumors due to the abnormally slow blood flow in angiogenic tumor vessels and strong attenuation of light by tumor tissue. Here, we demonstrate in vivo that gold nanoprisms (GNPRs) can be used as OCT contrast agents working in the second near-infrared window, significantly enhancing the dynamic scattering signals in microvessels and improving the sensitivity of OCTA in skin tissue and melanoma tumors in live mice. With GNPRs as contrast agents, the postinjection OCT angiograms showed 41 and 59% more microvasculature than preinjection angiograms in healthy mouse skin and melanoma tumors, respectively. By enabling better characterization of microvascular circulation in vivo, GNPR-enhanced OCTA could lead to better understanding of vascular functions during pathological conditions, more accurate measurements of therapeutic response, and improved patient prognoses.

Optic disc microvasculature dropout in primary open-angle glaucoma measured with optical coherence tomography angiography.

PurposeTo evaluate microvasculature dropout in the optic disc (Mvd-D) using optical coherence tomography angiography (OCTA) and investigate factors associated with Mvd-D in primary open-angle glaucoma (POAG) eyes.MethodsOne hundred twenty-three eyes of 123 POAG patients were included from the Diagnostic Innovations in Glaucoma Study. The 3.0×3.0-mm optic nerve head OCTA scans were acquired using a spectral-domain OCT instrument. Images with whole-signal-mode were evaluated. Eyes were classified into 3 categories (Mvd-D, pseudo-Mvd-D, and no Mvd-D). Mvd-D and pseudo-Mvd-D had complete loss of OCTA signals on the temporal side of the optic disc on the en face projection image. They were distinguished base on the visualization of the anterior lamina cribrosa in the horizontal B-scans of that area. No Mvd-D was defined when no complete signal loss of OCTA signals was observed. Covariates including focal lamina cribrosa defects assessed by swept-source OCT and microvasculature dropout in the parapapillary region (Mvd-P) were analyzed.ResultsForty-two, 37, and 44 eyes were identified as having Mvd-D, pseudo-Mvd-D, and no Mvd-D, respectively. The eyes with Mvd-D showed significantly lower intraocular pressure, worse visual field mean deviation, larger cup-to-disc ratio, thinner circumpapillary retinal nerve fiber layer (cpRNFL), and lower circumpapillary vessel density within the RNFL than the eyes with pseudo-Mvd-D or the eyes without Mvd-D. Multivariable logistic regression analysis showed significant associations of Mvd-D with larger cup-to-disc ratio (OR, 1.08; P = 0.001), worse visual field mean deviation (OR, 1.09; P = 0.048), higher prevalence of focal lamina cribrosa defect (OR, 9.05; P = 0.002), and higher prevalence of Mvd-P (OR, 10.33; P <0.001).ConclusionsOCTA-derived Mvd-D was strongly associated with the presences of Mvd-P and focal lamina cribrosa defects, and these 3 findings were topographically associated with each other.

Distinct Retinal Capillary Plexuses in Normal Eyes as Observed in Optical Coherence Tomography Angiography Axial Profile Analysis

Optical coherence tomography angiography (OCTA) allows the retinal microvasculature to be visualized at various retinal depths. Previous studies introduced OCTA axial profile analysis and showed regional variations in the number and location of axially distinct vascular retinal plexuses. OCTA acquisition and processing approaches, however, vary in terms of their resulting transverse and axial resolutions, and especially the latter could potentially influence the profile analysis results. Our study imaged normal eyes using the Spectralis OCT2 with a full-spectrum, probabilistic OCTA algorithm, that, in marked contrast to split-spectrum approaches, preserves the original high OCT axial resolution also within the resulting OCTA signal. En face OCTA images are generally created by averaging flow signals over a finite axial depth window. However, we assessed regional OCTA signal profiles at each depth position at full axial resolution. All regions had two sharp vessel density peaks near the inner and outer boundaries of the inner nuclear layer, indicating separate intermediate and deep capillary plexuses. The superficial vascular plexus (SVP) separated into two distinct peaks within the ganglion cell layer in the parafoveal zone. The nasal, superior, and inferior perifovea had a deeper SVP peak that was shifted anteriorly compared to the parafoveal zone. Axial vascular density analysis with high-resolution, full spectrum OCTA thus allows healthy retinal vasculature to be precisely reconstructed and may be useful for clinically assessing retinal pathology.