Projection-resolved optical coherence tomography angiography exhibiting early flow prior to clinically observed retinal angiomatous proliferation

Associations between the retinal/choroidal microvasculature and carotid plaque in patients with CAD: An OCTA study

Background

To investigate the associations between retinal/choroidal microvasculature and carotid plaque in patients with CAD assessed by optical coherence tomography angiography (OCTA).

Methods

This study included 127 CAD patients with and 79 without carotid plaque. Each patient had both OCTA taken and digitized to determine retinal/choroidal thickness, vessel density and flow area and carotid ultrasound for carotid plaque size and stability measurement. The superficial capillary plexus (SCP), deep capillary plexus (DCP), out retina and choriocapillaris vessel density, out retina and choriocapillaris flow area, and full retina thickness were analyzed in the fovea centered 6 × 6 mm area. The association between OCTA measurements and carotid plaque characteristics in patients with CAD were evaluated.

Results

The duration of hypertension and diabetes mellitus (DM) was significantly longer in CAD patients with carotid plaque than that without (p < 0.001). The mean values for vessel density SCP and DCP (except fovea zone), and choriocapillaris nasal zone were significantly lower in plaque group (p < 0.05). Negative correlations between the carotid plaque width and vessel density SCP and DCP (except fovea zone) (p < 0.05) were also found in this study.

Conclusions

In patients with CAD, carotid plaque, a risk factor and marker of atherosclerosis and stenosis, is significantly and independently associated with retinal and choroidal microvascular changes by OCTA.

OCT angiography and its retinal biomarkers [Invited]

Optical coherence tomography angiography (OCTA) is a high-resolution, depth-resolved imaging modality with important applications in ophthalmic practice. An extension of structural OCT, OCTA enables non-invasive, high-contrast imaging of retinal and choroidal vasculature that are amenable to quantification. As such, OCTA offers the capability to identify and characterize biomarkers important for clinical practice and therapeutic research. Here, we review new methods for analyzing biomarkers and discuss new insights provided by OCTA.

Optical Coherence Tomography Angiography in Retinal Vascular Disorders

Traditionally, abnormalities of the retinal vasculature and perfusion in retinal vascular disorders, such as diabetic retinopathy and retinal vascular occlusions, have been visualized with dye-based fluorescein angiography (FA). Optical coherence tomography angiography (OCTA) is a newer, alternative modality for imaging the retinal vasculature, which has some advantages over FA, such as its dye-free, non-invasive nature, and depth resolution. The depth resolution of OCTA allows for characterization of the retinal microvasculature in distinct anatomic layers, and commercial OCTA platforms also provide automated quantitative vascular and perfusion metrics. Quantitative and qualitative OCTA analysis in various retinal vascular disorders has facilitated the detection of pre-clinical vascular changes, greater understanding of known clinical signs, and the development of imaging biomarkers to prognosticate and guide treatment. With further technological improvements, such as a greater field of view and better image quality processing algorithms, it is likely that OCTA will play an integral role in the study and management of retinal vascular disorders. Artificial intelligence methods-in particular, deep learning-show promise in refining the insights to be gained from the use of OCTA in retinal vascular disorders. This review aims to summarize the current literature on this imaging modality in relation to common retinal vascular disorders.

Artificial intelligence in OCT angiography

Optical coherence tomographic angiography (OCTA) is a non-invasive imaging modality that provides three-dimensional, information-rich vascular images. With numerous studies demonstrating unique capabilities in biomarker quantification, diagnosis, and monitoring, OCTA technology has seen rapid adoption in research and clinical settings. The value of OCTA imaging is significantly enhanced by image analysis tools that provide rapid and accurate quantification of vascular features and pathology. Today, the most powerful image analysis methods are based on artificial intelligence (AI). While AI encompasses a large variety of techniques, machine-learning-based, and especially deep-learning-based, image analysis provides accurate measurements in a variety of contexts, including different diseases and regions of the eye. Here, we discuss the principles of both OCTA and AI that make their combination capable of answering new questions. We also review contemporary applications of AI in OCTA, which include accurate detection of pathologies such as choroidal neovascularization, precise quantification of retinal perfusion, and reliable disease diagnosis.

Customized Slab-Segmentation Method for Projection-Artifact Elimination in Best Vitelliform Macular Dystrophy: A Swept-Source Optical Coherence Tomography Angiography Study

Purpose

To assess the efficacy of customized slab segmentation in eliminating projection artifacts in swept-source optical coherence tomography angiography (SS-OCTA) images of Best vitelliform macular dystrophy (BVMD).

Methods

Prospective case series including different stages of BVMD. We analyzed SS-OCTA images for flow signals in the outer retina and coregistered B-scan images for distortion of the segmentation slabs defining the outer retina. We applied a customized method for slab realignment whenever BVMD lesions produced distortion of the slabs. Afterward, we checked the images to determine whether the previously noted flow signal had persisted or disappeared, described as “true flow” or “pseudoflow”, respectively. Categorical variables were analyzed with X² or Fisher’s exact tests, while quantitative variables were analyzed with independent t-test at p<0.05.

Results

The study included 39 eyes of 22 patients. We detected BVMD patterns I (dome-shaped hyperreflective lesion without neurosensory retinal detachment), II (knob-like hyperreflective lesion with localized neurosensory retinal detachment), and III (heterogeneous scattered hyperreflective material) in 49%, 23%, and 28% of eyes, respectively. Pseudoflow was evident mostly in eyes with pattern II lesions, presence of flow signal within BVMD lesions, and lesions whose height represented >80% of the retinal thickness (p<0.001).

Conclusion

Customized slab segmentation is effective in eliminating projection artifact in SS-OCTA images of BVMD.

Summary

Projection artifact is a significant confounding factor in emerging SS-OCTA technology through production of pseudoflow signals that can lead to misinterpretation of images of BVMD lesions. The present study proposes a customized method for correction of segmentation errors to eliminate projection artifacts in SS-OCTA images of BVMD patients.

Artifacts and artifact removal in optical coherence tomographic angiography

Optical coherence tomographic angiography (OCTA) enables rapid imaging of retinal vasculature in three dimensions. While the technique has provided quantification of healthy vessels as well as pathology in several diseases, it is not unusual for OCTA data to contain artifacts that may influence measurement outcomes or defy image interpretation. In this review, we discuss the sources of several OCTA artifacts-including projection, motion, and signal reduction-as well as strategies for their removal. Artifact compensation can improve the accuracy of OCTA measurements, and the most effective use of the technology will incorporate hardware and software that can perform such correction.

Standardization of OCT Angiography Nomenclature in Retinal Vascular Diseases: First Survey Results

PURPOSE

To develop a consensus nomenclature for OCT angiography (OCTA) findings in retinal vascular diseases.

DESIGN

Online survey using the Delphi Method.

PARTICIPANTS

Members of The Retina Society, the European Society of Retina Specialists, and the Japanese Retina and Vitreous Society.

METHODS

An online questionnaire on OCTA terminology in retinal vascular diseases was sent to members of The Retina Society, the European Society of Retina Specialists, and the Japanese Retina and Vitreous Society. The respondents were divided into 2 groups ("experts" vs. "users") according to the number of their publications in this field. The respondents who had more than 5 publications in the field of OCTA and retinal vascular diseases were considered the OCTA "experts" group.

MAIN OUTCOME MEASURES

Consensus and near consensus on OCTA nomenclature.

RESULTS

The complete responses of 85 retina specialists were included in the analysis. Thirty-one were categorized as "experts." There was a consensus in both groups that OCTA parameters such as foveal avascular zone (FAZ) parameters, areas of nonperfusion, and presence of neovascularization (NV) should be implemented in the identification and staging of diabetic retinopathy (DR) and that OCTA can be applied to differentiate between ischemic and nonischemic retinal vein occlusion (RVO). Diabetic macular ischemia (DMI) also can be assessed via OCTA. Further, there was consensus that the terminology should differ on the basis of the underlying causes of decreased vascular flow signal. There was disagreement in other areas, such as which terms should be applied to describe decreased OCTA signal from different causes, the definition of wide-field OCTA, and how to quantify DMI and area of decreased flow signal. These discrepancies form the basis for the upcoming expert Delphi rounds that aim to develop a standardized OCTA nomenclature.

CONCLUSIONS

Although there was agreement in some areas, significant differences were found in many areas of OCTA terminology among all respondents, but also between the expert and user groups. This indicates the need for standardization of the nomenclature among all specialists in the field of retinal vascular diseases.

Plexus-specific retinal vascular anatomy and pathologies as seen by projection-resolved optical coherence tomographic angiography

Optical coherence tomographic angiography (OCTA) is a novel technology capable of imaging retinal vasculature three-dimensionally at capillary scale without the need to inject any extrinsic dye contrast. However, projection artifacts cause superficial retinal vascular patterns to be duplicated in deeper layers, thus interfering with the clean visualization of some retinal plexuses and vascular pathologies. Projection-resolved OCTA (PR-OCTA) uses post-processing algorithms to reduce projection artifacts. With PR-OCTA, it is now possible to resolve up to 4 distinct retinal vascular plexuses in the living human eye. The technology also allows us to detect and distinguish between various retinal and optic nerve diseases. For example, optic nerve diseases such as glaucoma primarily reduces the capillary density in the superficial vascular complex, which comprises the nerve fiber layer plexus and the ganglion cell layer plexus. Outer retinal diseases such as retinitis pigmentosa primarily reduce the capillary density in the deep vascular complex, which comprises the intermediate capillary plexus and the deep capillary plexus. Retinal vascular diseases such as diabetic retinopathy and vein occlusion affect all plexuses, but with different patterns of capillary loss and vascular malformations. PR-OCTA is also useful in distinguishing various types of choroidal neovascularization and monitoring their response to anti-angiogenic medications. In retinal angiomatous proliferation and macular telangiectasia type 2, PR-OCTA can trace the pathologic vascular extension into deeper layers as the disease progress through stages. Plexus-specific visualization and measurement of retinal vascular changes are improving our ability to diagnose, stage, monitor, and assess treatment response in a wide variety of optic nerve and retinal diseases. These applications will be further enhanced with the continuing improvement of the speed and resolution of the OCT platforms, as well as the development of software algorithms to reduce artifacts, improve image quality, and make quantitative measurements.

Optical Coherence Tomography Angiography in Intermediate and Late Age-Related Macular Degeneration: Review of Current Technical Aspects and Applications

Optical coherence tomography angiography (OCTA) is a non-invasive diagnostic instrument that has become indispensable for the management of age-related macular degeneration (AMD). OCTA allows quickly visualizing retinal and choroidal microvasculature, and in the last years, its use has increased in clinical practice as well as for research into the pathophysiology of AMD. This review provides a discussion of new technology and application of OCTA in intermediate and late AMD.

OCT-A characterisation of recurrent type 3 macular neovascularisation

Purpose

To investigate optical coherence tomography angiography (OCT-A) findings in recurrent type 3 macular neovascularisation (MNV).

Methods

In this retrospective cohort study, consecutive patients with type 3 MNV secondary to age-related macular degeneration underwent OCT-A at three different time points: baseline, after anti-vascular endothelial growth factor treatment with complete resolution of the exudative signs (ie, non-exudative stage) and at the recurrence of exudation (ie, recurrence stage). Demographics and clinical findings were analysed, including OCT-A features of type 3 MNV recurrence.

Results

Twelve eyes (12 patients, mean age 78±7 years) were included. Using OCT-A, at baseline all type 3 MNVs showed the presence of detectable flow downgrowing from the deep vascular complex (DVC) to the retinal pigment epithelium (RPE)/sub-RPE space. 6/12 eyes (50%) showed anomalous flow under the RPE, while the other 6 eyes showed flow reaching the RPE without anomalous flow in the sub-RPE space. At the non-exudative stage (after treatment), BCVA and CMT significantly improved (p=0.004 and p=0.036), and flow inside the retinal lesions reduced; interestingly the connection to the RPE/sub-RPE space regressed. At the time of recurrence, all type 3 MNVs showed the presence of intra/sub-retinal exudation with restoration of the flow deepening from the DVC to the RPE/sub-RPE space.

Conclusions

Detectable flow deepening from the DVC to the RPE/sub-RPE space using OCT-A is mandatory to have a new exudation secondary to recurrent type 3 MNV. Early detection of type 3 MNV recurrence by OCT-A characterisation may prompt retreatment and potentially prevent progression to late stages of the disease.

Automated diagnosis and segmentation of choroidal neovascularization in OCT angiography using deep learning

Accurate identification and segmentation of choroidal neovascularization (CNV) is essential for the diagnosis and management of exudative age-related macular degeneration (AMD). Projection-resolved optical coherence tomographic angiography (PR-OCTA) enables both cross-sectional and en face visualization of CNV. However, CNV identification and segmentation remains difficult even with PR-OCTA due to the presence of residual artifacts. In this paper, a fully automated CNV diagnosis and segmentation algorithm using convolutional neural networks (CNNs) is described. This study used a clinical dataset, including both scans with and without CNV, and scans of eyes with different pathologies. Furthermore, no scans were excluded due to image quality. In testing, all CNV cases were diagnosed from non-CNV controls with 100% sensitivity and 95% specificity. The mean intersection over union of CNV membrane segmentation was as high as 0.88. By enabling fully automated categorization and segmentation, the proposed algorithm should offer benefits for CNV diagnosis, visualization monitoring.

Analysis of Parafoveal Microvascular Abnormalities in Behcet's Uveitis Using Projection-Resolved Optical Coherence Tomographic Angiography

Purpose: To assess the characteristics of parafoveal microvascular abnormalities in Behcet's uveitis (BDU) using projection-resolved optical coherence tomographic angiography (PR-OCTA).Methods: A retrospective study of BDU patients who underwent PR-OCTA examination between April 1, 2017 and October 31, 2018.Results: Sixty consecutive BDU patients (102 eyes) were included. Sixty-two (124 eyes) healthy subjects served as normal controls (NCs). As compared with NCs, the vessel densities (VDs) of superficial and deep retinal capillary plexuses were decreased, and the fovea avascular zone area, perimeter and acircularity index were increased in BDU eyes (all p < .001). Macular edema (p < .001) and long uveitis course (p = .033) were identified as risk factors for capillary disruptions. Consistent VD reductions were observed in the quiescent fellow eyes of BDU patients during unilateral uveitis relapse.Conclusions: BDU patients had significant OCTA changes. Macular circulatory disturbances may exist in the quiescent fellow eyes during unilateral BDU attack.

Pseudoflow with OCT Angiography in Eyes with Hard Exudates and Macular Drusen

PURPOSE

To analyze "pseudoflow," a false positive flow-artifact observed with optical coherence tomography angiography (OCTA) of stationary hyperreflective structures corresponding to hard exudates and macular drusen.

METHODS

Retrospective case series of patients with hard exudates (due to diabetic macular edema [DME] or retinal vein occlusion [RVO]) or macular drusen (due to nonneovascular, or dry, age-related macular degeneration [AMD]) studied with OCTA by using volume-based projection artifact removal (3D PAR).

RESULTS

OCTA of 20 eyes (10 DME/10 RVO) with hard exudates were analyzed. All eyes exhibited pseudoflow corresponding to hard exudates. Seven eyes concurrently demonstrated hard exudates without pseudoflow that were noted in areas lacking vascular flow in the overlying retina. Eight eyes exhibited suspended scattering particles in motion. In 26 of 30 eyes with nonneovascular AMD, pseudoflow associated with macular drusen of any type was noted. Two of 11 eyes with small drusen, 16 of 17 eyes with medium or large drusen, 5 of 5 eyes with drusenoid pigment epithelial detachment, 12 of 16 eyes with ribbon-like subretinal drusenoid deposits, and 13 of 17 eyes with dot-like SDD exhibited pseudoflow.

CONCLUSIONS

Pseudoflow due to projection artifact is common in eyes with hard exudates or macular drusen. 3D PAR reduces but does not eliminate pseudoflow, and pseudoflow may be detected within the foveal avascular zone, indicating that other factors, such as Z-axis micromotion, may also contribute to pseudoflow.

TRANSLATIONAL RELEVANCE

This study provides insight into the etiology of pseudoflow noted on OCTA and will guide more accurate clinical interpretation and investigation of OCTA images.

Projection resolved optical coherence tomography angiography to distinguish flow signal in retinal angiomatous proliferation from flow artifact

PURPOSE

To investigate whether hyperreflective foci (HRF) exhibit flow projection artifact on OCTA, and study the efficacy of commercial projection artifact removal software (PAR-OCTA, Optovue, Inc), and a custom projection resolved OCTA (PR-OCTA) in distinguishing artifacts from true flow in retinal angiomatous proliferation (RAP).

METHODS

The study included five eyes with HRF representing pigment migration in dry age-related macular degeneration (AMD), five eyes with leaking treatment-naïve RAP, and ten eyes with diabetic hard exudates. We examined flow signal on OCTA cross-sections using PAR, and performed PR-OCTA to study the effect of increasingly stringent projection removal thresholds. Flow signal intensity was analyzed and quantified using imageJ (NIH, Bethesda, MD, USA), by calculating the percentage of red pixels (R) representing flow, compared to green (G) and blue (B) pixels.

RESULTS

PAR-OCTA cross sections revealed persistent flow signal in all HRF, including RAP, hard exudates and pigment migration. In RAP, PR-OCTA detected intransigent flow, irrespective of the flow removal threshold. Mean R in the five RAP lesions remained higher than mean G and B at the most stringent PR-OCTA threshold (40.96% vs 29.52 and 29.52%, respectively), denoting persistence of flow. In contrast, increasing the PR-OCTA threshold in pigment migration and hard exudates removed the flow signal, with a statistically significant decrease in mean R with increasing threshold. (p = 0.017 and 0.0029, respectively).

CONCLUSION

Commercial PAR-OCTA is not completely effective at removing artifactual flow in hard exudates and HRF related to pigment migration. Custom built PR-OCTA, using a sliding scale of threshold, allowed us to distinguish true flow in RAP from artifactual flow in avascular HRF. Further studies are needed to validate the optimum threshold for projection artifact removal, which would preserve true flow in RAP and the small intraretinal capillaries.

An overview of optical coherence tomography angiography and the posterior pole

Optical coherence tomography angiography is a relatively new, noninvasive technology that has revolutionized imaging of the retinal and choroidal microvasculature. This technology is based on the detection of movement or changes that represent moving red cells in sequential optical coherence tomography scans. As with other established imaging technologies, it has unique benefits as well as certain disadvantages, which include a limited field of view and vulnerability to imaging artifacts. However, software and hardware improvements are continually evolving to mitigate these limitations. Optical coherence tomography angiography has been used to gain a better understanding of microvascular changes across a spectrum of ocular diseases including diabetic retinopathy, age-related macular degeneration, glaucoma, and retinal vein occlusions. In this article, we review algorithms and techniques commonly utilized in optical coherence tomography angiography systems and compare optical coherence tomography angiography to fluorescein angiography, the current gold standard for imaging the retinal vasculature. In addition, we provide an overview of important optical coherence tomography angiography findings in a variety of ocular diseases. Although the clinical role of this technology is still poorly defined, optical coherence tomography angiography has the potential to become an invaluable tool in the diagnosis and monitoring of vascular pathologies.

Retinal and choroidal vascular changes in coronary heart disease: an optical coherence tomography angiography study

To reveal the association between retinal microvasculature changes and coronary heart disease (CHD), we assessed the full retinal thicknesses of eight areas, the vessel density of four layers (consisting of nine areas) and the flow area in two layers with optical coherence tomography angiography (OCTA) in CHD patients and healthy controls. The mean vessel density of several layers was significantly lower in patients. The difference in choroid capillary flow (negative correlation) between the two groups was significant. Decreased vessel density and blood flow were associated with coronary artery and branch stenosis. The decreases in retinal vessel density, choroidal vessel density, and blood flow area are closely related to coronary artery and branch stenosis.

Treatment Effects in Retinal Angiomatous Proliferation Imaged with OCT Angiography

PURPOSE

This prospective case series is aimed at exploring optical coherence tomographic angiography (OCT-A) as a treatment monitoring tool in patients treated for retinal angiomatous proliferation (RAP).

METHODS

Twelve treatment-naïve RAP patients were included, with a median age of 79 years (range 65-90). Patients were imaged with an experimental 1,040-nm swept-source phase-resolved OCT-A instrument before and after treatment. Treatment consisted of either intravitreal bevacizumab or triamcinolone injections with or without photodynamic therapy (PDT). Abnormal blood flow after treatment was graded as increased, unchanged, decreased, or resolved.

RESULTS

OCT-A images before and after treatment could be obtained in 9 patients. The median follow-up period was 10 weeks (range 5-19). After various treatments, the RAP lesion resolved in 7 patients, in 1 patient the OCT-A depicted decreased flow in the lesion, and 1 patient showed unchanged abnormal blood flow. Monotherapy with intravitreal bevacizumab injections resolved RAP in 1 out of 2 patients. Combined therapy of bevacizumab with PDT resolved RAP in 6 out of 7 patients.

CONCLUSIONS

OCT-A visualized resolution of abnormal blood flow in 7 out of 9 RAP patients after various short-term treatment sequences. OCT-A may become an important noninvasive monitoring tool for optimizing treatment strategies in RAP patients.