DETECTION OF CLINICALLY UNSUSPECTED RETINAL NEOVASCULARIZATION WITH WIDE-FIELD OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY

Optical coherence tomography angiography in diabetic retinopathy: A major review

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

Peripheral retinal lesions in diabetic retinopathy on ultra-widefield imaging

Peripheral retinal imaging plays a crucial role in the diagnosis, management, and prognosis of diabetic retinopathy (DR). Traditional fundus imaging techniques have limited coverage of the retina, resulting in missed peripheral lesions. The advent of ultra-widefield (UWF) imaging has revolutionized the assessment of the peripheral retina. UWF imaging modalities provide comprehensive visualization of the retina, enabling the detection of peripheral lesions without the need for mydriasis. Integration of UWF imaging with other modalities, including fluorescein angiography (FA), indocyanine green angiography, pseudocolor imaging, and fundus autofluorescence, further enhances our understanding of peripheral retinal lesions. UWF imaging has demonstrated improved detection of DR lesions and presumably more accurate management of DR compared to traditional fundus photography and dilated fundus examination. UWF-FA and UWF-optical coherence tomography angiography have emerged as valuable tools for assessing retinal and choroidal vascular abnormalities, nonperfusion areas, neovascularization, and microvascular abnormalities. The presence and increasing extent of predominantly peripheral lesions detected using UWF FA are associated with a higher risk of DR progression and proliferative DR. UWF imaging provides a comprehensive evaluation of DR severity, aiding in more accurate risk stratification and treatment decision-making. Overall, UWF imaging modalities have significantly advanced our understanding of peripheral retinal lesions in DR, facilitating early detection and targeted management for better visual outcomes.

Visualizing features with wide-field volumetric OCT angiography

Optical coherence tomography (OCT) and its extension OCT angiography (OCTA) have become essential clinical imaging modalities due to their ability to provide depth-resolved angiographic and tissue structural information non-invasively and at high resolution. Within a field of view, the anatomic detail available is sufficient to identify several structural and vascular pathologies that are clinically relevant for multiple prevalent blinding diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and vein occlusions. The main limitation in contemporary OCT devices is that this field of view is limited due to a fundamental trade-off between system resolution/sensitivity, sampling density, and imaging window dimensions. Here, we describe a swept-source OCT device that can capture up to a 12 × 23-mm field of view in a single shot and show that it can identify conventional pathologic features such as non-perfusion areas outside of conventional fields of view. We also show that our approach maintains sensitivity sufficient to visualize novel features, including choriocapillaris morphology beneath the macula and macrophage-like cells at the inner limiting membrane, both of which may have implications for disease.

Detection of diabetic neovascularisation using single-capture 65°-widefield optical coherence tomography angiography

AIM

To assess the detection rate of retinal neovascularisation (NV) in eyes with proliferative diabetic retinopathy (PDR) using widefield optical coherence tomography angiography (WF-OCTA) in comparison to ultrawidefield fluorescein angiography (UWF-FA).

METHODS

Single-capture 65°-WF-OCTA-imaging was performed in patients with NV at the disc or elsewhere (NVE) detected on UWF-FA using a modified PlexElite system and B-scans were examined for blood flow signals breaching the internal limiting membrane. Sensitivity of WF-OCTA and UWF colour fundus (UWF-CF) photography for correct diagnosis of PDR was determined and interdevice agreement (Fleiss' κ) between WF-OCTA and UWF-FA for detection of NV in the total gradable area and each retinal quadrant was evaluated.

RESULTS

Fifty-nine eyes of 41 patients with PDR detected on UWF-FA were included. Sensitivity of detecting PDR on WF-OCTA scans was 0.95 in contrast to 0.78 on UWF-CF images. Agreement in detecting NVE between WF-OCTA and UWF-FA was high in the superotemporal (κ=0.98) and inferotemporal (κ=0.94) and weak in the superonasal (κ=0.24) and inferonasal quadrants (κ=0.42). On UWF-FA, 63% of NVEs (n=153) were located in the temporal quadrants with 93% (n=142) of them being detected on WF-OCTA scans.

CONCLUSION

The high reliability of non-invasive WF-OCTA imaging in detecting PDR can improve clinical examination with the potential to replace FA as a single diagnostic tool.

Association of Diabetic Lesions and Retinal Nonperfusion Using Widefield Multimodal Imaging

PURPOSE

To evaluate the association of microvascular lesions on ultrawidefield (UWF) color fundus (CF) images with retinal nonperfusion (RNP) up to the midperiphery on single-capture widefield (WF) OCT angiography (OCTA) in patients with diabetic retinopathy (DR).

DESIGN

Cross-sectional study.

SUBJECTS

Seventy-five eyes of 50 patients with mild to severe nonproliferative DR (NPDR) and proliferative DR (PDR) were included in this analysis.

METHODS

ETDRS level and presence of predominantly peripheral lesions (PPLs) were assessed on UWF-CF images acquired with a Zeiss Clarus 700. Single-capture 65°-WF-OCTA was performed using a PlexElite prototype (Carl Zeiss Meditec, Inc.). A custom grid consisting of a central ETDRS grid extended by 2 rings reaching up to the midperiphery was overlaid to subdivide retinal areas visible on WF-OCTA en face images. Retinal nonperfusion was measured in each area and in total. Nonperfusion index (NPI) was calculated from total RNP. On UWF-CF images, the number of microaneurysms, hemorrhages, neovascularizations, and areas with intraretinal microvascular abnormalities (IRMAs) were evaluated using the same grid.

MAIN OUTCOME MEASURES

Association of diabetic lesions with RNP was calculated using Spearman correlations (rs).

RESULTS

Median RNP on WF-OCTA was 0 mm2 (0-0.9), 4.9 mm2 (1.9-5.4), 23.4 mm2 (17.8-37), and 68.4 mm2 (40.8-91.7) in mild, moderate, and severe NPDR and PDR, respectively. We found a statistically significant correlation (P < 0.01) of overall RNP (rs = 0.96,) and NPI (rs = 0.97) on WF-OCTA with ETDRS level. Number of grid-fields affected by IRMAs on CF images was highly associated with NPI (rs = 0.86, P < 0.01). Intraretinal microvascular abnormalities and RNPs had similar topographic distributions with high correlations in affected areas. Eyes with PPLs (n = 43 eyes, 57%) on CF images had a significantly higher NPI (P = 0.014) than eyes without PPLs.

CONCLUSION

The combination of UWF-CF imaging and single-capture WF-OCTA allows precise and noninvasive analysis of the retinal vasculature up to the midperiphery in patients with DR. The presence and extent of IRMAs on CF images may serve as an indicator for underlying RNP, which is more pronounced in eyes with PPLs.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Optical coherence tomography angiography in diabetic retinopathy

There remain many unanswered questions on how to assess and treat the pathology and complications that arise from diabetic retinopathy (DR). Optical coherence tomography angiography (OCTA) is a novel and non-invasive three-dimensional imaging method that can visualize capillaries in all retinal layers. Numerous studies have confirmed that OCTA can identify early evidence of microvascular changes and provide quantitative assessment of the extent of diseases such as DR and its complications. A number of informative OCTA metrics could be used to assess DR in clinical trials, including measurements of the foveal avascular zone (FAZ; area, acircularity, 3D para-FAZ vessel density), vessel density, extrafoveal avascular zones, and neovascularization. Assessing patients with DR using a full-retinal slab OCTA image can limit segmentation errors and confounding factors such as those related to center-involved diabetic macular edema. Given emerging data suggesting the importance of the peripheral retinal vasculature in assessing and predicting DR progression, wide-field OCTA imaging should also be used. Finally, the use of automated methods and algorithms for OCTA image analysis, such as those that can distinguish between areas of true and false signals, reconstruct images, and produce quantitative metrics, such as FAZ area, will greatly improve the efficiency and standardization of results between studies. Most importantly, clinical trial protocols should account for the relatively high frequency of poor-quality data related to sub-optimal imaging conditions in DR and should incorporate time for assessing OCTA image quality and re-imaging patients where necessary.

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.

Utility of En Face OCT for the Detection of Clinically Unsuspected Retinal Neovascularization in Patients with Diabetic Retinopathy

PURPOSE

To assess the value of en face OCT for detecting clinically unsuspected retinal neovascularization (RNV) in patients with nonproliferative diabetic retinopathy (NPDR).

DESIGN

A retrospective, cross-sectional study.

PARTICIPANTS

Treatment-naïve patients clinically graded as NPDR in an ongoing prospective observational OCT angiography (OCTA) study at a tertiary care center.

METHODS

Each patient underwent imaging of 1 eye with a spectral-domain OCTA, generating a 17 × 17-mm widefield image by montaging four 9 × 9-mm scans. Two independent graders examined a combination of en face OCT, en face OCTA with a custom vitreoretinal interface slab, and cross-sectional OCTA to determine the presence of RNV. We measured the area of RNV flow within RNV lesions on en face OCTA.

MAIN OUTCOME MEASURES

Detection rate of clinically occult RNV with OCT and OCTA.

RESULTS

Of 63 enrolled eyes, 27 (43%) were clinically graded as severe NPDR, 16 (25%) as moderate NPDR, and 20 (32%) as mild NPDR. Using the combination of en face OCT, en face OCTA, and cross-sectional OCTA, the graders detected 42 RNV lesions in 12 (19%) eyes, of which 8 (67%) were graded as severe NPDR, 2 (17%) as moderate NPDR, and 2 (17%) as mild NPDR. The sensitivity of en face OCT alone for detecting eyes with RNV was similar to that of en face OCTA alone (100% vs. 92%; P = 0.32), whereas the specificity of en face OCT alone was significantly lower than that of en face OCTA alone (32% vs. 73%; P < 0.001). For detecting individual RNV lesions, the en face OCT was 100% sensitive, compared with 67% sensitivity for the en face OCTA (P < 0.001). The area of RNV lesions that manual grading with en face OCTA alone missed was significantly smaller than that of manually detectable RNV (Mean [standard deviation] RNV flow area, 0.015 [0.020] mm2 vs. 0.16 [0.36] mm2; P < 0.001).

CONCLUSION

The combination of en face OCT and OCTA can detect clinically occult RNV with high sensitivity. For screening these small lesions, en face OCT may be a useful imaging modality.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Automated Macular Fluid Volume As a Treatment Indicator for Diabetic Macular Edema

Introduction: To assess the diagnostic accuracy of automatically quantified macular fluid volume (MFV) for treatment-required diabetic macular edema (DME). Methods: This retrospective cross-sectional study included eyes with DME. The commercial software on optical coherence tomography (OCT) produced the central subfield thickness (CST), and a custom deep-learning algorithm automatically segmented the fluid cysts and quantified the MFV from the volumetric scans of an OCT angiography system. Retina specialists treated patients per standard of care based on clinical and OCT findings without access to the MFV. The main outcome measures were the area under the receiver operating characteristic curve (AUROC), sensitivity, and specificity of the CST, MFV, and visual acuity (VA) for treatment indication. Results: Of 139 eyes, 39 (28%) were treated for DME during the study period and 101 (72%) were previously treated. The algorithm detected fluid in all eyes; however, only 54 eyes (39%) met the DRCR.net criteria for center-involved ME. The AUROC of MFV predicting a treatment decision of 0.81 was greater than that of CST (0.67) (P = .0048). Untreated eyes that met the optimal threshold for treatment-required DME based on MFV (>0.031 mm3) had better VA than treated eyes (P = .0053). A multivariate logistic regression model showed that MFV (P = .0008) and VA (P = .0061) were significantly associated with a treatment decision, but CST was not. Conclusions: MFV had a higher correlation with the need for treatment for DME than CST and may be especially useful for ongoing management of DME.

Imaging-based Assessment of Choriocapillaris: A Comprehensive Review

PURPOSE

Over the past two decades, advancements in imaging modalities have significantly evolved the diagnosis and management of retinal diseases. Through these novel platforms, we have developed a deeper understanding of the anatomy of the choroidal vasculature and the choriocapillaris. The recently developed tools such as optical coherence tomography (OCT) and OCT angiography (OCTA) have helped elucidate the pathological mechanisms of several posterior segment diseases. In this review, we have explained the anatomy of the choriocapillaris and its close relationship to the outer retina and retinal pigment epithelium.

METHODS

A comprehensive search of medical literature was performed through the Medline/PubMed database using search terms: choriocapillaris, choroid, quantification, biomarkers, diabetic retinopathy, age-related macular degeneration, choroidal blood flow, mean blur rate, flow deficit, optical coherence tomography, optical coherence tomography angiography, fluorescein angiography, indocyanine green angiography, OCTA, Doppler imaging, uveitis, choroiditis, white dot syndrome, tubercular serpiginous-like choroiditis, choroidal granuloma, pachychoroid, toxoplasmosis, central serous chorioretinopathy, multifocal choroiditis, choroidal neovascularization, choroidal thickness, choroidal vascularity index, choroidal vascular density, and choroidal blood supply. The search terms were used either independently or combined with choriocapillaris/choroid.

RESULTS

The imaging techniques which are used to qualitatively and quantitatively analyze choriocapillaris are described. The pathological alterations in the choriocapillaris in an array of conditions such as diabetes mellitus, age-related macular degeneration, pachychoroid spectrum of diseases, and inflammatory disorders have been comprehensively reviewed. The future directions in the study of choriocapillaris have also been discussed.

CONCLUSION

The development of imaging tools such as OCT and OCTA has dramatically improved the assessment of choriocapillaris in health and disease. The choriocapillaris can be delineated from the stromal choroid using the OCT and quantified by manual or automated methods. However, these techniques have inherent limitations due to the lack of an anatomical distinction between the choriocapillaris and the stromal choroid, which can be overcome with the use of predefined segmentation slabs on OCT and OCTA. These segmentation slabs help in standardizing the choriocapillaris imaging and obtain repeatable measurements in various conditions such as diabetic retinopathy, age-related macular degeneration, pachychoroid spectrum, and ocular inflammations. Additionally, Doppler imaging has also been effectively used to evaluate the choroidal blood flow and quantifying the choriocapillaris and establishing its role in the pathogenesis of various retinochoroidal diseases. As tremendous technological advancements such as wide-field and ultra-wide field imaging take place, there will be a significant improvement in the ease and accuracy of quantifying the choriocapillaris.

Interest of Widefield-Optical Coherence Tomography Angiography for Diagnosis and Follow-Up of Retinal Neovascularisation in Proliferative Diabetic Retinopathy

Aim

The primary aim was to evaluate the use of optical coherence tomography angiography (OCTA) versus fluorescein angiography (FA) for detecting and monitoring retinal neovascularization (NV) in patients with proliferative diabetic retinopathy (PDR) receiving treatment with anti-vascular endothelial growth factor (anti-VEGF).

Methods

Treatment-naïve patients with PDR, willing to begin anti-VEGF treatment without laser from 9/2018–2/2020 were included. FA and OCTA scans were obtained at baseline, and a second OCTA scan was performed after 6 months of anti-VEGF therapy. We calculated sensitivity and specificity for two masked graders with respect to identifying NV on OCTA versus FA. Using ImageJ software, we also measured the change in NV size, at baseline and 6-month follow-up.

Results

Ten eyes in eight patients were included, of which three eyes in three patients received a 6-month follow-up examination. Mean age was 51.7 ± 11.2 years, and 75% of patients were male. Overall, 21 NV sites in the 10 eyes were identified both clinically and on FA. Using OCTA scans, the sensitivity and specificity for both graders were extremely high, ranging from 95.2% to 100%. At 6-month follow-up, NV size decreased by 69.8%.

Conclusion

These results suggest that OCTA may provide a suitable alternative to FA for visualizing, measuring, and monitoring changes in retinal NV in patients with PDR who receive anti-VEGF therapy.

Sparse-based Domain Adaptation Network for OCTA Image Super-Resolution Reconstruction

Retinal Optical Coherence Tomography Angiography (OCTA) with high-resolution is important for the quantification and analysis of retinal vasculature. However, the resolution of OCTA images is inversely proportional to the field of view at the same sampling frequency, which is not conducive to clinicians for analyzing larger vascular areas. In this paper, we propose a novel Sparse-based domain Adaptation Super-Resolution network (SASR) for the reconstruction of realistic [Formula: see text]/low-resolution (LR) OCTA images to high-resolution (HR) representations. To be more specific, we first perform a simple degradation of the [Formula: see text]/high-resolution (HR) image to obtain the synthetic LR image. An efficient registration method is then employed to register the synthetic LR with its corresponding [Formula: see text] image region within the [Formula: see text] image to obtain the cropped realistic LR image. We then propose a multi-level super-resolution model for the fully-supervised reconstruction of the synthetic data, guiding the reconstruction of the realistic LR images through a generative-adversarial strategy that allows the synthetic and realistic LR images to be unified in the feature domain. Finally, a novel sparse edge-aware loss is designed to dynamically optimize the vessel edge structure. Extensive experiments on two OCTA sets have shown that our method performs better than state-of-the-art super-resolution reconstruction methods. In addition, we have investigated the performance of the reconstruction results on retina structure segmentations, which further validate the effectiveness of our approach.

Association Between Fluid Volume in Inner Nuclear Layer and Visual Acuity in Diabetic Macular Edema

PURPOSE

In diabetic macular edema (DME), the correlation between visual acuity (VA) and central subfield thickness (CST) is weak. We hypothesize that fluid volume (FV) in the inner nuclear layer (INL) may correlate more strongly with VA.

DESIGN

Retrospective, cross-sectional study.

METHODS

One eye each of diabetic patients with DME was included. We measured intraretinal fluid volume that was detected by automated fluid detection algorithm on 3- × 3-mm optical coherence tomography angiogram volume scans. The detected fluid was subdivided into inner FV, bounded by the INL, and outer FV, the fluid between the outer border of INL to the ellipsoid zone.

RESULTS

We enrolled 125 patients with DME (60 women; mean age, 61 years). The mean detected inner FV was 0.013 mm3 in 109 eyes (87%). The mean detected outer FV was 0.042 mm3 in 124 eyes (99%). Univariate analysis demonstrated that the VA significantly correlated with the inner FV (P < .0001), whole macular FV (P = .010), and CST (P = .036). Multivariate analysis demonstrated that the inner FV was the only significant factor (β = -0.41, P = .004). These correlations were consistent when the treatment-naïve group (n = 33) and the eyes without previous laser treatments (n = 93) were analyzed separately. The area under the receiver operating characteristic curve of inner FV for VA of 20/32 or worse was significantly higher than that for CST (0.66 vs 0.54, P = .018).

CONCLUSIONS

The inner FV has a stronger association with VA than other OCT biomarkers in DME and may be more clinically useful.

Optical coherence tomography angiography for the detection and evaluation of ptic disc neovascularization: a retrospective, observational study

Background

To assess and characterize neovascularization of the optic disc (NVD) using optical coherence tomography angiography (OCTA) and different OCTA-based methods.

Methods

This retrospective, observational study included patients who were suspected of having early PDR with no presence of clinically apparent neovascularization (NV) bur were clinically diagnosed with proliferative diabetic retinopathy (PDR), or severe NPDR. Patients underwent standard clinical examinations and OCTA imaging using a 6 × 6 montage scan. Two trained graders identified NVD using different imaging systems (ultra-widefield-colour fundus photography (UWF-CFP), OCT, OCTA and fluorescein angiography (FA)). Moreover, morphological classification of NVD was performed. The detection and morphological classification of NVD by different OCTA-based methods (B-scan OCTA, En-face OCTA, VRI Angio and VRI Structure) were compared.

Results

A total of 169 eyes (126 eyes with PDR and 43 eyes with severe NPDR) of 123 participants were included in this study. The detection rate of NVD was 34.91% by UWF-CFP compared with 59.76% by OCT, 59.76% by OCTA, and 62.72% by FA. After excluding 2 cases with epiretinal membranes, the NVD diagnosis detected by OCT was used as the standard. Among 99 eyes diagnosed with NVD by OCT, B-scan OCTA detected NVD with a sensitivity of 97.98%, which was higher than that by en face OCTA (80.81%), VRI Angio (65.66%), and VRI Structure (61.62%) (all P < 0.05). According to its characteristics on OCTA, NVD was divided into four types (12 cases of type I, 6 cases of type II, 39 cases of type III, and 42 cases of type IV). For type I, B-scan OCTA exhibited a higher diagnostic sensitivity than other methods (P < 0.05). For types II and IV, there were no statistically significant differences in the sensitivity of various methods between the two groups (P > 0.05).

Conclusion

OCTA and different OCTA-based methods are significant to the diagnosis of NVD, and the diagnostic accuracy of different detection methods may be related to different types of NVD.

Optical coherence tomography

Optical coherence tomography (OCT) is a non-contact method for imaging the topological and internal microstructure of samples in three dimensions. OCT can be configured as a conventional microscope, as an ophthalmic scanner, or using endoscopes and small diameter catheters for accessing internal biological organs. In this Primer, we describe the principles underpinning the different instrument configurations that are tailored to distinct imaging applications and explain the origin of signal, based on light scattering and propagation. Although OCT has been used for imaging inanimate objects, we focus our discussion on biological and medical imaging. We examine the signal processing methods and algorithms that make OCT exquisitely sensitive to reflections as weak as just a few photons and that reveal functional information in addition to structure. Image processing, display and interpretation, which are all critical for effective biomedical imaging, are discussed in the context of specific applications. Finally, we consider image artifacts and limitations that commonly arise and reflect on future advances and opportunities.

Optical Coherence Tomography Angiography in Diabetic Patients: A Systematic Review

Background: Diabetic retinopathy (DR) is the leading cause of legal blindness in the working population in developed countries. Optical coherence tomography (OCT) angiography (OCTA) has risen as an essential tool in the diagnosis and control of diabetic patients, with and without DR, allowing visualisation of the retinal and choroidal microvasculature, their qualitative and quantitative changes, the progression of vascular disease, quantification of ischaemic areas, and the detection of preclinical changes. The aim of this article is to analyse the current applications of OCTA and provide an updated overview of them in the evaluation of DR. Methods: A systematic literature search was performed in PubMed and Embase, including the keywords “OCTA” OR “OCT angiography” OR “optical coherence tomography angiography” AND “diabetes” OR “diabetes mellitus” OR “diabetic retinopathy” OR “diabetic maculopathy” OR “diabetic macular oedema” OR “diabetic macular ischaemia”. Of the 1456 studies initially identified, 107 studies were screened after duplication, and those articles that did not meet the selection criteria were removed. Finally, after looking for missing data, we included 135 studies in this review. Results: We present the common and distinctive findings in the analysed papers after the literature search including the diagnostic use of OCTA in diabetes mellitus (DM) patients. We describe previous findings in retinal vascularization, including microaneurysms, foveal avascular zone (FAZ) changes in both size and morphology, changes in vascular perfusion, the appearance of retinal microvascular abnormalities or new vessels, and diabetic macular oedema (DME) and the use of deep learning technology applied to this disease. Conclusion: OCTA findings enable the diagnosis and follow-up of DM patients, including those with no detectable lesions with other devices. The evaluation of retinal and choroidal plexuses using OCTA is a fundamental tool for the diagnosis and prognosis of DR.

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

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

An Open-Source Deep Learning Network for Reconstruction of High-Resolution OCT Angiograms of Retinal Intermediate and Deep Capillary Plexuses

Purpose

We propose a deep learning-based image reconstruction algorithm to produce high-resolution optical coherence tomographic angiograms (OCTA) of the intermediate capillary plexus (ICP) and deep capillary plexus (DCP).

Methods

In this study, 6-mm × 6-mm macular scans with a 400 × 400 A-line sampling density and 3-mm × 3-mm scans with a 304 × 304 A-line sampling density were acquired on one or both eyes of 180 participants (including 230 eyes with diabetic retinopathy and 44 healthy controls) using a 70-kHz commercial OCT system (RTVue-XR; Optovue, Inc., Fremont, California, USA). Projection-resolved OCTA algorithm removed projection artifacts in voxel. ICP and DCP angiograms were generated by maximum projection of the OCTA signal within the respective plexus. We proposed a deep learning-based method, which receives inputs from registered 3-mm × 3-mm ICP and DCP angiograms with proper sampling density as the ground truth reference to reconstruct 6-mm × 6-mm high-resolution ICP and DCP en face OCTA. We applied the same network on 3-mm × 3-mm angiograms to enhance these images further. We evaluated the reconstructed 3-mm × 3-mm and 6-mm × 6-mm angiograms based on vascular connectivity, Weber contrast, false flow signal (flow signal erroneously generated from background), and the noise intensity in the foveal avascular zone.

Results

Compared to the originals, the Deep Capillary Angiogram Reconstruction Network (DCARnet)-enhanced 6-mm × 6-mm angiograms had significantly reduced noise intensity (ICP, 7.38 ± 25.22, P < 0.001; DCP, 11.20 ± 22.52, P < 0.001), improved vascular connectivity (ICP, 0.95 ± 0.01, P < 0.001; DCP, 0.96 ± 0.01, P < 0.001), and enhanced Weber contrast (ICP, 4.25 ± 0.10, P < 0.001; DCP, 3.84 ± 0.84, P < 0.001), without generating false flow signal when noise intensity lower than 650. The DCARnet-enhanced 3-mm × 3-mm angiograms also reduced noise, improved connectivity, and enhanced Weber contrast in 3-mm × 3-mm ICP and DCP angiograms from 101 eyes. In addition, DCARnet preserved the appearance of the dilated vessels in the reconstructed angiograms in diabetic eyes.

Conclusions

DCARnet can enhance 3-mm × 3-mm and 6-mm × 6-mm ICP and DCP angiogram image quality without introducing artifacts.

Translational Relevance

The enhanced 6-mm × 6-mm angiograms may be easier for clinicians to interpret qualitatively.

Optical coherence tomography angiography in the management of diabetic retinopathy

The introduction of optical coherence tomography angiography (OCTA) has granted a significant improvement in the assessment of patients with diabetes. In this review, we will provide a description of the prominent OCTA findings in diabetes. In detail, this imaging technology proved that both the retinal and choroidal circulation is affected in diabetic subjects. The recent employment of widefield technology and a three-dimensional (3D) visualization in OCTA imaging are also discussed.

[Diabetic retinopathy]

Diabetic retinopathy (DR) is a vision-threatening microvascular complication of diabetes and the leading cause of blindness in working-age people. At the beginning of the metabolic disorder and in early stages of DR the patient's eyesight is often not affected. Depending on the duration of diabetes and in more advanced stages of DR the vision is compromised through the presence of diabetic macular edema (DME) and/or proliferative retinal complications. The management of DR comprises regular ophthalmic examinations according to clinical guidelines, the targeted application of multimodal imaging, and the specific treatment of DME and proliferative DR including secondary disorders such as neovascular glaucoma or persistent vitreous haemorrhage. Innovative ocular imaging techniques like optical coherence tomography (OCT), OCT angiography (OCT-A) and ultrawide field imaging play an important role in the assessment of diabetic patients. Various non-invasive imaging modalities have become part of the routine clinical work-up and help to identify new biomarkers for early diagnosis and long-term prognosis. In early stages of DR, the multifactorial intervention including glucose level and blood pressure control as well as optimizing the patient's cardiovascular risk profile is essential. A specific ophthalmic therapy is available for DME and proliferative DR (PDR). In patients with PDR the treatment regime includes panretinal laser photocoagulation or alternatively intravitreal anti-VEGF (vascular endothelial growth factor)-injections accompanied by close-meshed clinical monitoring. In patients with both, DME and PDR, it is suggested to start with Anti-VEGF drugs. In severe PDR with persistent vitreous haemorrhage, tractional maculopathy or tractional retinal detachment vitreoretinal surgery is recommended.

Diabetische Retinopathie

Die diabetische Retinopathie (DR) ist die häufigste Ursache für schwere Sehbehinderung und Erblindung im erwerbstätigen Alter. Eine subjektive Beeinträchtigung des Sehvermögens tritt häufig erst in fortgeschrittenen Stadien der DR ein. Daher sind Screening-Maßnahmen asymptomatischer Patienten und eine stadiengerechte Behandlung essenziell. Dieser Beitrag gibt einen praxisbezogenen Überblick über diagnostische und therapeutische Prinzipien der nicht-proliferativen und proliferativen Form.

Characterizing Flow and Structure of Diabetic Retinal Neovascularization after Intravitreal Anti-VEGF Using Optical Coherence Tomography Angiography: A Pilot Study

Background/Aims. This study evaluates changes of flow and structure of diabetic retinal neovascularization (NV) treated with intravitreal antivascular endothelial growth factor (VEGF) agents using optical coherence tomography angiography (OCTA). With OCTA, retinal blood vessels are visualized at high resolution to separately look at flow and structure information without the need for dye injection. We introduce a new measurement method including and combining information of flow and structure. Methods. Retrospective observational case series. Patients with proliferative diabetic retinopathy (PDR) were treated with intravitreal antiVEGF injections. Retinal NV were repeatedly imaged using swept-source OCTA (Zeiss PlexElite 9000) at baseline, after initial treatment block with 3-4 monthly injections, and during a follow-up period of up to 51 weeks. Change of size and flow density of the structural and angio area of NV was assessed. Results. Nine NV in eight eyes of five patients were analyzed with a median follow-up time of 45 weeks. After the initial treatment block, en face structural area regressed, 18.7% ± 39.0% (95% CI 44.2–6.8%, p=0.26), and en face angio area regressed, 51.9% ± 29.5% (95% CI 32.6 to 71.2%, p=0.007). Flow density within the en face structural area decreased by 33% ± 19.2% (95% CI 20.5–45.5%, p=0.0077). Flow density within the en face angio area decreased by mean 17.9% ± 25.2% (95% CI 1.4–34.4%, p=0.066). In two fellow eyes, NV recurrence could be observed before the onset of vitreous bleeding in one. Conclusion. Our study introduces a new quantitative measurement for NV in PDR, combining structure and flow measurement. The structure area remained after treatment, while its flow density and angio area regressed. We propose this measurement method as a more physiological and possibly more comparable metrics.

Study on the Optic Nerve Fiber Layer Thickness and Changes in Blood Flow in Myopic Children

Objective

The present study aims to observe the optic nerve fiber layer thickness and blood flow density in the papillary area and investigate the effects of axial length (AL) and the refractive state of the optic papilla blood flow density in children with different refractive conditions.

Methods

The present study was a clinical control study. The right eyes of 204 minors aged 6-17 years were studied. The eyes were divided into four groups according to myopic refractive states. OCTA analyzed the data to compare the radial peripapillary capillary (RPC) density and the difference in the retinal nerve fiber layer (RNFL) thickness adjacent to the optic papilla between the four refraction groups.

Results

The intra-optic disc blood flow density was significantly and negatively correlated with the AL and was negatively correlated with the AL in the inferior temporal quadrants. The RNFL in the superior, nasal, and inferior quadrants was negatively correlated with the AL. The RNFL in the temporal quadrant was positively correlated with the AL.

Conclusion

Our present study revealed that aAs myopia increased and the AL grew in children, the blood density of the entire image of the optic papilla, in the optic disc, and the retinal capillaries in the inferior parapapillary and temporal quadrant would change significantly. With increasing AL, a significant decrease in the intra-disc and para-disc RNFL was observed in the superior, nasal, and inferior quadrants, while a substantial increase in RNFL was observed in the temporal quadrant.

Comparison of Central Macular Fluid Volume With Central Subfield Thickness in Patients With Diabetic Macular Edema Using Optical Coherence Tomography Angiography

IMPORTANCE

Diabetic macular edema (DME) is the predominant cause of visual impairment in patients with type 1 or 2 diabetes. Automated fluid volume measurements using optical coherence tomography (OCT) may improve the diagnostic accuracy of DME screening.

OBJECTIVE

To assess the diagnostic accuracy of an automated central macular fluid volume (CMFV) quantification using OCT for DME.

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional observational study was conducted at a tertiary academic center among 215 patients with diabetes (1 eye each) enrolled from January 26, 2015, to December 23, 2019. All participants underwent comprehensive examinations, 6 × 6-mm macular structural OCT horizontal raster scans, and 6 × 6-mm macular OCT angiography volumetric scans. From January 1 to March 30, 2020, 2 retinal specialists reviewed the structural OCT scans independently and diagnosed DME if intraretinal or subretinal fluid was present. Diabetic macular edema was considered center involved if fluid was present within the central fovea (central 1-mm circle). A third retinal specialist arbitrated any discrepancy. The mean central subfield thickness (CST) within the central fovea was measured on structural OCT horizontal raster scans. A deep learning algorithm automatically quantified fluid volumes on 6 × 6-mm OCT angiography volumetric scans and within the central foveas (CMFV).

MAIN OUTCOMES AND MEASURES

The area under the receiver operating characteristic curve (AUROC) and the sensitivity and specificity of CST and CMFV for DME diagnosis.

RESULTS

We enrolled 1 eye each of 215 patients with diabetes (117 women [54.4%]; mean [SD] age, 59.6 [12.4] years). Diabetic macular edema was present in 136 eyes; 93 cases of DME were center involved. The AUROC of CMFV for diagnosis of center-involved DME (0.907 [95% CI, 0.861-0.954]) was greater than the AUROC of CST (0.832 [95% CI, 0.775-0.889]; P = .02). With the specificity set at 95%, the sensitivity of CMFV for detection of center-involved DME (78.5% [95% CI, 68.8%-86.3%]) was higher than that of CST (53.8% [95% CI, 43.1%-64.2%]; P = .002). Center-involved DME cases not detected by CST but detected by CMFV were associated with a thinner CST (290.8 μm [95% CI, 282.3-299.3 μm] vs 369.4 μm [95% CI, 347.1-391.7 μm]; P < .001), higher proportion of previous macular laser treatment (11 of 28 [39.3%; 95% CI, 21.5%-59.4%] vs 12 of 65 [18.5%; 95% CI, 9.9%-30.0%]; P = .03), and female sex (20 of 28 [71.4%; 95% CI, 51.3%-86.8%] vs 31 of 65 [47.7%; 95% CI, 35.1%-60.5%]; P = .04).

CONCLUSIONS AND RELEVANCE

These findings suggest that an automated CMFV is a more accurate diagnostic biomarker than CST for DME and may improve screening for DME.

Recent advances in wide field and ultrawide field optical coherence tomography angiography in retinochoroidal pathologies

Introduction: With the advent of wide field (WF) and ultra-wide field (UWF) imaging in color fundus photography and fluorescein angiography (FA), the importance of an expanded field-of-view (FOV) has been illustrated for early detection of several chorioretinal disorders. The need to bring similar utility to optical coherence tomography angiography (OCTA) is imperative.Areas covered: For this review, we explored all research items with WF or UWF on Pubmed Central and Google Scholar. Software-based methods included algorithms for motion correction, artifact reduction, image pre-processing, post-processing and montage protocols while hardware methods included swept-source OCTA, faster scanning sources, hardware-based motion tracking and image registration, scanning sources with faster speeds and lower resolution. For various disorders such as diabetic retinopathy, uveitis, vascular disorders, among others, the increased FOV showed demonstrably increased detection rates and diagnostic yield.Expert opinion: Increased FOV in OCTA imaging is a meaningful and impactful step in ophthalmic imaging. Overcoming the hardware-based limitations can potentially yield higher FOV without loss of important details. In addition to improvements in the hardware and available equipment, better software tools and image processing algorithms may greatly enhance the utility of UWF OCTA in care of patients with various retinochoroidal diseases.

Wide Field Swept Source Optical Coherence Tomography Angiography for the Evaluation of Proliferative Diabetic Retinopathy and Associated Lesions: A Review

Retinal imaging remains the mainstay for monitoring and grading diabetic retinopathy. The gold standard for detecting proliferative diabetic retinopathy (PDR) requiring treatment has long been the seven-field stereoscopic fundus photography and fluorescein angiography. In the past decade, ultra-wide field fluorescein angiography (UWF-FA) has become more commonly used in clinical practice for the evaluation of more advanced diabetic retinopathy. Since its invention, optical coherence tomography (OCT) has been an important tool for the assessment of diabetic macular edema; however, OCT offered little in the assessment of neovascular changes associated with PDR until OCT-A became available. More recently, swept source OCT allowed larger field of view scans to assess a variety of DR lesions with wide field swept source optical coherence tomography (WF-SS-OCTA). This paper reviews the role of WF-SS-OCTA in detecting neovascularization of the disc (NVD), and elsewhere (NVE), microaneurysms, changes of the foveal avascular zone (FAZ), intraretinal microvascular abnormalities (IRMA), and capillary non-perfusion, as well as limitations of this evolving technology.

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.

Optical Coherence Tomography Angiography in Diabetes

ABSTRACT

The introduction of optical coherence tomography angiography (OCTA) has significantly improved our knowledge on the ocular vascular alterations occurring in diabetes. In this article, we will provide a review of the prominent OCTA findings in diabetes. In details, OCTA demonstrated that both the retinal vessels and the choriocapillaris are affected in diabetic subjects. The recent employment of widefield technology and a 3-dimensional (3D) visualization in OCTA imaging are also discussed.

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 diabetes: focus on microaneurysms

The introduction of optical coherence tomography angiography (OCTA) has remarkably expanded our knowledge of the ocular vascular alterations occurring in diabetes. In this article, a review of the prominent OCTA findings in diabetes is followed by a description of salient histological and anatomical features of microaneurysms, essential for the proper interpretation of in vivo imaging of these retinal vascular abnormalities. The recent employment of a three-dimensional (3D) visualization in OCTA imaging is also discussed. The latter imaging technique has granted a detailed characterization of microaneurysms in vivo.

Standardisation of optical coherence tomography angiography nomenclature in uveitis: first survey results

Aim

To standardise the nomenclature for reporting optical coherence angiography (OCT-A) findings in the field of uveitis.

Methods

Members of the International Uveitis Study Group, of the American Uveitis Society and of the Sociedad Panamericana de Infermedades Oculares that choose to participate responded to an online questionnaire about their preferred terminology when reporting on OCT-A findings in uveitis. The response of individuals with several publications on OCT-A (experts) was compared with uveitis specialists (users) who have less than five publications on the field of uveitis and OCT-A.

Results

A total of 108 uveitis specialists who participated in the survey were included in the analysis. Of those, 23 were considered OCT-A ‘experts’. There was an agreement in both groups for the definition of wide-field (WF)-OCT-A, and definition of neovascularisation in uveitis. Moreover, there was a difference in the responses in other areas, such as quantification of ischaemia, definition of ‘large’ areas of ischaemia or terms to describe decreased OCT-A signal from different causes. There was an unanimous need of ‘users’ and ‘experts’ to distinguish size of decreased OCT-A signal in uveitis, to implement a quantitative measurement of decreased flow specifically for WF-OCT-A and to use different terms for different causes of decreased OCT-A signal.

Conclusions

While there was considerable agreement in the terminology used by all uveitis experts, significant differences in terminology were noted between ‘users’ and ‘experts’. These differences indicate the need for standardisation of nomenclature among all uveitis specialists both for the purpose of reporting and in clinical use.

Diabetes Update 2020: das Wichtigste für die ärztliche Praxis

Bei der virtuellen Veranstaltung Diabetes Update 2020 wurden zahlreiche neue Erkenntnisse und Empfehlungen zu Diagnostik, Therapie und Management des Diabetes und benachbarter Themen vorgestellt, von denen die Bereiche Typ-2-Diabetes, Diabetes und Herz, Diabetes und Schwangerschaft sowie Impfungen im aktuellen Heft von Der Diabetologe in separaten Beiträgen ausführlich beschrieben werden. Im Folgenden sollen die aus Sicht des Autors wichtigsten und für die Praxis relevantesten Neuigkeiten aus den anderen referierten diabetesbezogenen Themengebieten in aller Kürze wiedergegeben werden.

Real-time retinal layer segmentation of OCT volumes with GPU accelerated inferencing using a compressed, low-latency neural network

Segmentation of retinal layers in optical coherence tomography (OCT) is an essential step in OCT image analysis for screening, diagnosis, and assessment of retinal disease progression. Real-time segmentation together with high-speed OCT volume acquisition allows rendering of en face OCT of arbitrary retinal layers, which can be used to increase the yield rate of high-quality scans, provide real-time feedback during image-guided surgeries, and compensate aberrations in adaptive optics (AO) OCT without using wavefront sensors. We demonstrate here unprecedented real-time OCT segmentation of eight retinal layer boundaries achieved by 3 levels of optimization: 1) a modified, low complexity, neural network structure, 2) an innovative scheme of neural network compression with TensorRT, and 3) specialized GPU hardware to accelerate computation. Inferencing with the compressed network U-NetRT took 3.5 ms, improving by 21 times the speed of conventional U-Net inference without reducing the accuracy. The latency of the entire pipeline from data acquisition to inferencing was only 41 ms, enabled by parallelized batch processing. The system and method allow real-time updating of en face OCT and OCTA visualizations of arbitrary retinal layers and plexuses in continuous mode scanning. To the best our knowledge, our work is the first demonstration of an ophthalmic imager with embedded artificial intelligence (AI) providing real-time feedback.

Different Scan Protocols Affect the Detection Rates of Diabetic Retinopathy Lesions by Wide-Field Swept-Source Optical Coherence Tomography Angiography

PURPOSE

To compare different scan protocols of wide-field swept-source optical coherence tomography angiography (SS-OCTA) for the detection of diabetic retinopathy (DR) lesions.

DESIGN

Comparison of diagnostic approaches.

METHODS

A prospective, observational study was conducted at Massachusetts Eye and Ear from December 2018 to July 2019. Proliferative diabetic retinopathy (PDR), nonproliferative diabetic retinopathy (NPDR), and diabetic patients without DR were included. All patients were imaged using SS-OCTA using the following scan protocol: 3- × 3-mm Angio centered on the fovea; 6- × 6-mm Angio centered on the fovea and the optic disc; 15- × 9-mm Montage; and 12- × 12-mm Angio centered on the fovea and the optic disc. Images were independently evaluated by 2 graders for the presence or absence of DR lesions including microaneurysms, intraretinal microvascular abnormalities, neovascularization, nonperfusion areas, venous looping, and hard exudates. All statistical analyses were performed using commercial software.

RESULTS

A total of 176 eyes in 119 participants were included in the study. The detection rate of neovascularization on 6- × 6-mm Angio centered on the fovea was approximately one-half that on 15- × 9-mm Montage (P < .05) imaging. Combining 6- × 6-mm Angio imaging centered on the fovea and the optic disc could increase the rate to approximately two-thirds (P < .05). The 12- × 12-mm Angio imaging centered on the combination of fovea and optic disc had detection rates comparable to those of 15- × 9-mm Montage imaging for all DR lesions (P > .05). For microaneurysms, 6- × 6-mm Angio had better performance than 15- × 9-mm Montage (P < .05).

CONCLUSIONS

Wide-field SS-OCTA images were useful in detecting DR lesions. The 12- × 12-mm Angio imaging centered on the fovea and on the optic disc may be an optimal balance between speed and efficacy for evaluation of DR in clinical practice.

Reconstruction of high-resolution 6×6-mm OCT angiograms using deep learning

Typical optical coherence tomographic angiography (OCTA) acquisition areas on commercial devices are 3×3- or 6×6-mm. Compared to 3×3-mm angiograms with proper sampling density, 6×6-mm angiograms have significantly lower scan quality, with reduced signal-to-noise ratio and worse shadow artifacts due to undersampling. Here, we propose a deep-learning-based high-resolution angiogram reconstruction network (HARNet) to generate enhanced 6×6-mm superficial vascular complex (SVC) angiograms. The network was trained on data from 3×3-mm and 6×6-mm angiograms from the same eyes. The reconstructed 6×6-mm angiograms have significantly lower noise intensity, stronger contrast and better vascular connectivity than the original images. The algorithm did not generate false flow signal at the noise level presented by the original angiograms. The image enhancement produced by our algorithm may improve biomarker measurements and qualitative clinical assessment of 6×6-mm OCTA.

Sensorless adaptive-optics optical coherence tomographic angiography

Optical coherence tomographic angiography (OCTA) can image the retinal blood flow but visualization of the capillary caliber is limited by the low lateral resolution. Adaptive optics (AO) can be used to compensate ocular aberrations when using high numerical aperture (NA), and thus improve image resolution. However, previously reported AO-OCTA instruments were large and complex, and have a small sub-millimeter field of view (FOV) that hinders the extraction of biomarkers with clinical relevance. In this manuscript, we developed a sensorless AO-OCTA prototype with an intermediate numerical aperture to produce depth-resolved angiograms with high resolution and signal-to-noise ratio over a 2 × 2 mm FOV, with a focal spot diameter of 6 µm, which is about 3 times finer than typical commercial OCT systems. We believe these parameters may represent a better tradeoff between resolution and FOV compared to large-NA AO systems, since the spot size matches better that of capillaries. The prototype corrects defocus, astigmatism, and coma using a figure of merit based on the mean reflectance projection of a slab defined with real-time segmentation of retinal layers. AO correction with the ability to optimize focusing in arbitrary retinal depths - particularly the plexuses in the inner retina - could be achieved in 1.35 seconds. The AO-OCTA images showed greater flow signal, signal-to-noise ratio, and finer capillary caliber compared to commercial OCTA. Projection artifacts were also reduced in the intermediate and deep capillary plexuses. The instrument reported here improves OCTA image quality without excessive sacrifice in FOV and device complexity, and thus may have potential for clinical translation.

Optical coherence tomography features of neovascularization in proliferative diabetic retinopathy: a systematic review

Background

Diabetic retinopathy (DR) is a leading cause of blindness due to diabetic macular edema (DME) or complications of proliferative diabetic retinopathy (PDR). Optical coherence tomography (OCT) is a noninvasive imaging technique well established for DME but less used to assess neovascularization in PDR. Developments in OCT imaging and the introduction of OCT angiography (OCTA) have shown significant potential in PDR.

Objectives

To describe the tomographic features of PDR, namely of neovascularization, both of the optic disc (NVD) and elsewhere (NVE), intraretinal microvascular abnormalities (IRMA), retinal nonperfusion areas (NPA), status of the posterior vitreous, vitreoschisis and vitreous and subhyaloid/sub-ILM hemorrhages.

Data sources

Electronic database search on PubMed and EMBASE, last run on December 19th 2019.

Study eligibility criteria, participants and interventions

Publications assessing OCT and/or OCTA findings in PDR patients. All study designs were allowed except for case-reports, conference proceedings and letters.

Study appraisal

Newcastle–Ottawa Scale for observational studies was used for purposes of risk of bias assessment.

Results

From the 1300 studies identified, 283 proceeded to full-text assessment and 60 were included in this comprehensive review. OCT was useful in detecting NVD and NVE, such as in characterizing disease activity and response to laser and/or anti-VEGF therapies. The absence of posterior vitreous detachment seemed determinant for neovascular growth, with the posterior hyaloid acting as a scaffold. OCTA allowed a more detailed characterization of the neovascular complexes, associated NPA and disease activity, allowing the quantification of neovessel area and flow index. However, changes in OCTA blood flow signal following local therapies did not necessarily correlate with structural regression. Widefield and ultra-widefield OCTA were highly sensitive in the detection of PDR, adding value to disease staging and monitoring. Compared to fluorescein angiography, OCTA was more sensitive in detecting microvascular changes indicating disease progression.

Limitations

Publication languages were restricted. Most included studies were observational and non-comparative. Risk of bias regarding case representativeness.

Conclusions

OCT-based retinal imaging technologies are advancing rapidly and the trend is to be noninvasive and wide-field. OCT has proven invaluable in diagnosing, staging and management of proliferative diabetic disease with daily application in clinical and surgical practices.

Comparison of widefield swept-source optical coherence tomography angiography with ultra-widefield colour fundus photography and fluorescein angiography for detection of lesions in diabetic retinopathy

AIMS

To compare widefield swept-source optical coherence tomography angiography (WF SS-OCTA) with ultra-widefield colour fundus photography (UWF CFP) and fluorescein angiography (UWF FA) for detecting diabetic retinopathy (DR) lesions.

METHODS

This prospective, observational study was conducted at Massachusetts Eye and Ear from December 2018 to October 2019. Proliferative DR, non-proliferative DR and diabetic patients with no DR were included. All patients were imaged with a WF SS-OCTA using a Montage 15×15 mm scan. UWF CFP and UWF FA were taken by a 200°, single capture retinal imaging system. Images were independently evaluated for the presence or absence of DR lesions including microaneurysms (MAs), intraretinal microvascular abnormalities (IRMAs), neovascularisation elsewhere (NVE), neovascularisation of the optic disc (NVD) and non-perfusion areas (NPAs). All statistical analyses were performed using SPSS V.25.0.

RESULTS

One hundred and fifty-two eyes of 101 participants were included in the study. When compared with UWF CFP, WF SS-OCTA was found to be superior in detecting IRMAs (p<0.001) and NVE/NVD (p=0.007). The detection rates of MAs, IRMAs, NVE/NVD and NPAs in WF SS-OCTA were comparable with UWF FA images (p>0.05). Furthermore, when we compared WF SS-OCTA plus UWF CFP with UWF FA, the detection rates of MAs, IRMAs, NVE/NVD and NPAs were identical (p>0.005). Agreement (κ=0.916) between OCTA and FA in classifying DR was excellent.

CONCLUSION

WF SS-OCTA is useful for identification of DR lesions. WF SS-OCTA plus UWF CFP may offer a less invasive alternative to FA for DR diagnosis.

Optical Coherence Tomography Angiography in Diabetes and Diabetic Retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes mellitus that disrupts the retinal microvasculature and is a leading cause of vision loss globally. Recently, optical coherence tomography angiography (OCTA) has been developed to image the retinal microvasculature, by generating 3-dimensional images based on the motion contrast of circulating blood cells. OCTA offers numerous benefits over traditional fluorescein angiography in visualizing the retinal vasculature in that it is non-invasive and safer; while its depth-resolved ability makes it possible to visualize the finer capillaries of the retinal capillary plexuses and choriocapillaris. High-quality OCTA images have also enabled the visualization of features associated with DR, including microaneurysms and neovascularization and the quantification of alterations in retinal capillary and choriocapillaris, thereby suggesting a promising role for OCTA as an objective technology for accurate DR classification. Of interest is the potential of OCTA to examine the effect of DR on individual retinal layers, and to detect DR even before it is clinically detectable on fundus examination. We will focus the review on the clinical applicability of OCTA derived quantitative metrics that appear to be clinically relevant to the diagnosis, classification, and management of patients with diabetes or DR. Future studies with longitudinal design of multiethnic multicenter populations, as well as the inclusion of pertinent systemic information that may affect vascular changes, will improve our understanding on the benefit of OCTA biomarkers in the detection and progression of DR.

High-resolution wide-field OCT angiography with a self-navigation method to correct microsaccades and blinks

In this study, we demonstrate a novel self-navigated motion correction method that suppresses eye motion and blinking artifacts on wide-field optical coherence tomographic angiography (OCTA) without requiring any hardware modification. Highly efficient GPU-based, real-time OCTA image acquisition and processing software was developed to detect eye motion artifacts. The algorithm includes an instantaneous motion index that evaluates the strength of motion artifact on en face OCTA images. Areas with suprathreshold motion and eye blinking artifacts are automatically rescanned in real-time. Both healthy eyes and eyes with diabetic retinopathy were imaged, and the self-navigated motion correction performance was demonstrated.

[Biomarkers of diabetic retinopathy on optical coherence tomography angiography]

Pathogenesis of diabetic retinopathy (DR) is complex and multifactorial, giving rise to a wide range of potential biomarkers - quantitatively and objectively measurable indicators of the biological, pathological processes or pharmacological response to therapy. This non-systemic review is devoted to a vital problem - possibility of using biomarkers acquired with optical coherence tomography angiography (OCTA-biomarkers) in DR. The review examines the qualitative and quantitative indicators obtained using OCTA as potential biomarkers of DR. Of greatest interest is the assessment of diabetic microvascular abnormalities such as microaneurysms, intraretinal microvascular abnormalities, neovascularization and non-perfusion (ischemia) zones. A separate section is devoted to currently well-studied indices reflecting the area and regularity of the foveolar avascular zone, and microcirculation indices such as capillary perfusion density, blood flow indices, fractal dimension of retinal microcirculation vessels, etc. The relationship of OCTA-biomarkers and diabetic macular edema is also discussed. Biomarkers obtained with wide-field OCTA, such as indices quantitatively reflecting ischemia and neovascularization are paid special attention in the review. The problems and solutions associated with the use of OCTA-biomarkers in DR are also considered. In general OCTA-biomarkers in DR are becoming an important tool for screening, diagnosis, monitoring of DR, and for predicting and preventing patients' clinical response to treatment.

Widefield Optical Coherence Tomography Angiography in Diabetic Retinopathy

PURPOSE

To summarize the role of widefield optical coherence tomography angiography (WF-OCTA) in diabetic retinopathy (DR), extending from the acquisition strategies to the main clinical findings.

METHODS

A PubMed-based search was carried out using the terms "Diabetic retinopathy", "optical coherence tomography angiography", "widefield imaging", and "ultra-widefield imaging". All studies published in English up to August 2020 were reviewed.

RESULTS

WF-OCTA can be obtained with different approaches, offering advantages over traditional imaging in the study of nonperfusion areas (NPAs) and neovascularization (NV). Quantitative estimates and topographic distribution of NPA and NV are useful for treatment monitoring and artificial intelligence-based approaches. Curvature, segmentation, and motion artifacts should be assessed when using WF-OCTA.

CONCLUSIONS

WF-OCTA harbors interesting potential in DR because of its noninvasiveness and capability of objective metrics of retinal vasculature. Further studies will facilitate the migration from traditional imaging to WF-OCTA in both the research and clinical practice fields.

Imaging Artifacts and Segmentation Errors With Wide-Field Swept-Source Optical Coherence Tomography Angiography in Diabetic Retinopathy

Purpose

To analyze imaging artifacts and segmentation errors with wide-field swept-source optical coherence tomography angiography (SS-OCTA) in diabetic retinopathy (DR).

Methods

We conducted a prospective, observational study at Massachusetts Eye and Ear from December 2018 to March 2019. Proliferative diabetic retinopathy (PDR), nonproliferative diabetic retinopathy (NPDR), diabetic patients with no diabetic retinopathy (DR), and healthy control eyes were included. All patients were imaged with a SS-OCTA and the Montage Angio (15 × 9 mm) was used for analysis. Images were independently evaluated by two graders using the motion artifact score (MAS). All statistical analyses were performed using SPSS 25.0 and R software.

Results

One hundred thirty-six eyes in 98 participants with the montage image were included in the study. Patients with more severe stages of DR had higher MAS by trend test analysis (P < 0.05). The occurrence of segmentation error was 0% in the healthy group, 10.53% in the no DR group, 10.00% in the NPDR group, and 50% in the PDR group. Multivariate regression analysis showed that the severity of DR and dry eye were the major factors affecting MAS (P < 0.05). There were some modifiable artifacts that could be corrected to improve image quality.

Conclusions

Wide field SS-OCTA assesses retinal microvascular changes by noninvasive techniques, yet distinguishing real alterations from artifacts is paramount to accurate interpretations. DR severity and dry eye correlated with MAS.

Translational Relevance

Understanding contributing factors and methods to reduce artifacts is critical to routine use and clinical trial with wide-field SS-OCTA.