Comparisons Between Histology and Optical Coherence Tomography Angiography of the Periarterial Capillary-Free Zone

Quadrant asymmetry alteration of deep retinal capillary plexus degeneration in pathological myopia

BACKGROUND

To measure quadrant asymmetry (QA) alterations of macular retinal microvascular density and determine their effect on pathological myopia.

METHODS

Optical coherence tomography angiography (OCTA) images of 20 control, 42 simple high myopia and 20 pathological myopia eyes were analyzed to quantify the density of the macular retinal microvascular network that included the superficial and deep retinal capillary plexuses (SRCP and DRCP). The definition of QA was calculated by subtracting the minimum value from the maximum value among the four macular respective subfields. The comparison of the QAs of SRCP and DRCP density among the three groups and the effect of QAs on the occurrence of pathological myopia were analyzed.

RESULTS

In pathological myopia, densities of the SRCP and DRCP were lower than in simple high myopia and control (P < 0.05). The higher QAs of SRCP and DRCP density occurred in pathological myopia than in simple high myopia and control (P < 0.05). In multivariate binary logistic regression, higher QA of DRCP density was associated significantly with the occurrence of pathological myopia (Odds Ratio = 2.000, P = 0.035) while the QA of SRCP density didn't (P = 0.065). Comparing the intra-quadrant effect on the occurrence of pathological myopia with the analysis of binary multivariate logistic regression, the decreased DRCP density in the macular inferior subfield showed a high risk (Odds Ratio = 0.435, P = 0.030).

CONCLUSIONS

The occurrence of pathological myopia affected the quadrant asymmetry alterations of macular retinal microvascular density, especially the increased QA of DRCP density with significantly decreased DRCP density in the macular inferior subfield.

Preferential Sites of Retinal Capillary Occlusion in Sickle Cell Disease

Purpose

To assess the preferential sites of retinal capillary occlusion at the parafovea in patients with sickle cell disease (SCD) using optical coherence tomography angiography (OCT-A).

Methods

OCT-A scans from 107 patients with SCD and 51 race-matched unaffected controls were obtained using a commercial spectral domain-OCT system. At least eight sequential 3 × 3 mm scans centered at the fovea were acquired and averaged for image analysis. In each participant, foveal avascular zone (FAZ) metrics, perivascular, and quadrant-based capillary densities were measured on the averaged full vascular retinal OCT-A slab. Intermittent capillary perfusion at the FAZ border was also identified using sequential registered OCT-A scans.

Results

Perivascular and quadrant-based capillary densities were significantly lower in SCD groups (Kruskal-Wallis tests; P < 0.001) with preferential sites of capillary nonperfusion occurring along periarteriolar aspect of the vascular bed and at the temporal aspect of the fovea. FAZ perimeter and acircularity index were significantly higher in SCD groups (Kruskal-Wallis tests; P ≤ 0.05). However, no significant differences in FAZ area between unaffected control and SCD groups were observed (Kruskal-Wallis test; P = 0.08). The number of capillary segments with intermittent perfusion was higher in the SCD groups.

Conclusions

Our findings suggest that the periarteriolar aspect of the vascular bed is the preferential site of retinal capillary occlusion in patients with SCD with more involvement of the temporal aspect of the parafovea.

Location and Extent of Paravascular Nerve Fiber Layer Clefts in Eyes with Epiretinal Membranes

Purpose: The clinical use of en face optical coherence tomography (OCT) has revealed nerve fiber layer clefts in the retinal nerve fibers in eyes with macula-centered epiretinal membranes (ERMs). The purpose of this study is to describe the location and the extent of retinal nerve fiber layer (RNFL) clefts in eyes with symptomatic ERMs. Methods: We conducted a retrospective review of 17 individual eyes in 17 patients with symptomatic ERMs and a control group of 10 healthy eyes from 10 subjects who had been examined for unrelated causes. The examinations performed included best-corrected visual acuity, rebound tonometry, fundus photography, structural OCT and angiographic OCT (OCTA) made in the form of 12 × 12 mm angiographic volume scans. Results: Hyporeflective RNFL clefts, seen in 14 out of 17 eyes with ERMs, were sharply demarcated in the en face presentation of slabs extending from the internal limiting membrane through the RNFL or including only the latter. The clefts were capillary-free on OCTA scans and formed depressions of the retinal surface. Most of the clefts were adjacent to and followed the course of the retinal trunk vessels, but clefts were also seen along smaller macular vessels and beyond the retinal vascular arcades. Conclusions: Paravascular RNFL clefts can be observed beyond the vascular arcades and adjacent to small vessels on OCTA block scan data. This suggests that the direction and magnitude of tractional displacement of the inner retina in eyes with epimacular membranes can extend beyond the vascular arcades and add to an improved analysis of abnormal fundus findings.

Perfusion Deficits in Diabetes Without Retinopathy Localize to the Perivenular Deep Capillaries Near the Fovea on OCT Angiography

Purpose

To localize early capillary perfusion deficits in patients with diabetes mellitus (DM) without clinical diabetic retinopathy (DR) using averaged OCT angiography (OCTA).

Design

Retrospective cross-sectional study.

Participants

Patients with DM without DR and healthy controls.

Methods

We measured perfusion deficits in the full retina, superficial capillary plexus (SCP), and deep capillary plexus (DCP) on averaged 3 × 3-mm OCTA images. Perfusion deficits were defined as the percentage of retinal tissue located >30 μm from blood vessels, excluding the foveal avascular zone (FAZ). One eye from each patient was selected based on image quality. We measured deficits in the parafoveal region, the 300 μm surrounding the FAZ, and 300 to 1000 μm surrounding the FAZ. If a capillary layer within one of these regions was significantly different in DM without DR compared with controls, we further characterized the location of perfusion deficit as periarteriolar, perivenular, or the capillaries between these 2 zones.

Main Outcome Measures

Location of increased perfusion deficits in patients with DM without DR compared with controls.

Results

Sixteen eyes from 16 healthy controls were compared with 16 eyes from 16 patients with DM without DR (age 45.1 ± 10.7 and 47.4 ± 15.2 years respectively, P = 0.64). Foveal avascular zone area and perfusion deficits in the entire parafovea and the 300 to 1000-μm ring around the FAZ were not significantly different between groups (P > 0.05 for all). Perfusion deficits in 300 μm around the FAZ were significantly increased in patients with DM without DR in full retinal thickness, SCP, and DCP (P < 0.05 for all). When analyzing the perivenular, periarteriolar, and capillary zones, only the perivenular DCP perfusion deficits were significantly increased (5.03 ± 2.92% in DM without DR and 2.73 ± 1.97% in controls, P = 0.014).

Conclusions

Macular perfusion deficits in patients with DM without DR were significantly increased in the region nearest the FAZ, mainly at the perivenular deep capillaries. Further research on these early changes may improve our understanding of the capillaries most susceptible to vascular injury and disruption during diabetes.

Financial Disclosures

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

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

A two-year longitudinal observational study of the peripapillary microvasculature in pediatric type 1 diabetes mellitus patients without visual impairment or diabetic retinopathy

•Neurodegeneration precede microcirculatory deterioration in DR. Early signs can be seen in DM patients without visible DR symptoms, such as glial cell apoptosis and thinner retinal nerve fiber layer.•Peripapillary microvascular abnormalities in the peripapillary region may affect the normal metabolism of neurons and eventually aggravate the process of DR.•Prompting ongoing research to monitor the peripapillary microcirculation and microvasculature among T1DM children for early detection and prevention.•In longitudinal observation, the vessel density of the peripapillary superficial capillary plexus were slightly affected, while vessel density, blood flow, vessel morphological abnormalities and flow impairment area were significantly deteriorated in the deep capillary plexus.•The peripapillary deep capillary plexus is more susceptible and vulnerable to DR progression and could be used as a target for DR screening.

Imaging Histology Correlations of Intraretinal Fluid in Neovascular Age-Related Macular Degeneration

Purpose

Fluid presence and dynamism is central to the diagnosis and management of neovascular age-related macular degeneration. On optical coherence tomography (OCT), some hyporeflective spaces arise through vascular permeability (exudation) and others arise through degeneration (transudation). Herein we determined whether the histological appearance of fluid manifested this heterogeneity.

Methods

Two eyes of a White woman in her 90s with anti-vascular endothelial growth factor treated bilateral type 3 neovascularization secondary to age-related macular degeneration were osmicated, prepared for submicrometer epoxy resin sections, and correlated to eye-tracked spectral domain OCT. Examples of intraretinal tissue fluid were sought among similarly prepared donor eyes with fibrovascular scars, in a web-based age-related macular degeneration histopathology resource. Fluid stain intensity was quantified in reference to Bruch's membrane and the empty glass slide.

Results

Exudative fluid by OCT was slightly reflective and dynamically responded to anti-vascular endothelial growth factor. On histology, this fluid stained moderately, possessed a smooth and homogenous texture, and contained blood cells and fibrin. Nonexudative fluid in degenerative cysts and in outer retinal tubulation was minimally reflective on OCT and did not respond to anti-vascular endothelial growth factor. By histology, this fluid stained lightly, possessed a finely granular texture, and contained mainly tissue debris. Quantification supported the qualitative impressions of fluid stain density. Cells containing retinal pigment epithelium organelles localized to both fluid types.

Conclusions

High-resolution histology of osmicated tissue can distinguish between exudative and nonexudative fluid, some of which is transudative.

Translational Relevance

OCT and histological features of different fluid types can inform clinical decision-making and assist in the interpretation of newly available automated fluid detection algorithms.

INFLAMMATORY CELL ACTIVITY IN TREATED NEOVASCULAR AGE-RELATED MACULAR DEGENERATION: A Histologic Case Study

BACKGROUND

Imaging indicators of macular neovascularization risk can help determine patient eligibility for new treatments for geographic atrophy secondary to age-related macular degeneration. Because type 1 macular neovascularization includes inflammation, we assessed by histology the distribution of cells with inflammatory potential in two fellow eyes with age-related macular degeneration.

METHODS

Two eyes of a White woman in her 90's with type 3 macular neovascularization treated with antivascular endothelial growth factor were prepared for high-resolution histology. Eye-tracked spectral domain optical coherence tomography applied to the preserved donor eyes linked in vivo imaging to histology. Cells were enumerated in the intraretinal, subretinal, and subretinal retinal pigment epithelium (RPE)-basal lamina compartments on 199 glass slides. Cells with numerous organelles were considered to RPE-derived; cells with sparse RPE organelles were considered non-RPE phagocytes.

RESULTS

Both eyes had soft drusen and abundant subretinal drusenoid deposit. In the retina and subretinal space, RPE-derived cells, including hyperreflective foci, were common (n = 125 and 73, respectively). Non-RPE phagocytes were infrequent (n = 5 in both). Over drusen, RPE morphology transitioned smoothly from the age-normal layer toward the top, suggesting transdifferentiation. The sub-RPE-basal lamina space had RPE-derived cells (n = 87) and non-RPE phagocytes (n = 49), including macrophages and giant cells.

CONCLUSION

Numerous sub-RPE-basal lamina cells of several types are consistent with the documented presence of proinflammatory lipids in drusen and aged Bruch's membrane. The relatively compartmentalized abundance of infiltrating cells suggests that drusen contents are more inflammatory than subretinal drusenoid deposit, perhaps reflecting their environments. Ectopic RPE occurs frequently. Some manifest as hyperreflective foci. More cells may be visible as optical coherence tomography technologies evolve.

Inference of Capillary Nonperfusion Progression on Widefield OCT Angiography in Diabetic Retinopathy

Purpose

The purpose of this study was to explore the spatial patterns of the nonperfusion areas (NPAs) on widefield optical coherence tomography angiography (OCTA) images in diabetic retinopathy (DR) and to investigate their associations with NPA progression and DR severity.

Methods

We prospectively enrolled 201 eyes from 158 patients with DR. Widefield images were obtained using a swept-source OCTA device (Xephilio OCT-S1), followed by the creation of 20-mm (1614 pixels) en face images. Nonperfusion squares (NPSs) were defined as 10 × 10-pixel squares without retinal vessels. Eyes with high-dimensional spatial data were mapped onto a two-dimensional space using the uniform manifold approximation and projection algorithm and divided by clustering. The patterns of NPA distribution were statistically compared between clusters.

Results

All eyes were mapped onto a two-dimensional space and divided into six clusters based on the similarity of NPA distribution. Eyes in clusters 1 and 2 had minimal and small NPAs, respectively. Eyes in clusters 3 and 4 exhibited NPAs in the temporal and inferotemporal regions, respectively. Eyes in cluster 5 displayed NPAs in both superonasal and inferonasal areas. The unique NPA distributions in each cluster encouraged us to propose eight possible pathways of NPA progression. DR severity was not equal between clusters (P < 0.001), for example, 8 (15.7%) of 51 eyes and 15 (65.2%) of 23 eyes had PDR in clusters 1 and 5, respectively.

Conclusions

Dimensionality reduction and subsequent clustering based on the NPA distribution on widefield OCTA enabled the inference of possible NPA progression in DR.

Macular Perfusion Deficits on OCT Angiography Correlate with Nonperfusion on Ultrawide-field Fluorescein Angiography in Diabetic Retinopathy

OBJECTIVE

To evaluate the correlation between nonperfusion parameters on OCT angiography (OCTA) and ultrawide-field fluorescein angiography (UWF-FA) in subjects with diabetes mellitus (DM).

DESIGN

Prospective, cross-sectional study.

SUBJECTS

Subjects with DM and a wide range of diabetic retinopathy (DR) severity seen at a tertiary referral center.

METHODS

We used averaged 3 × 3 mm OCTA scans to measure geometric perfusion deficit (GPD), vessel density, and vessel length density in the full retina, superficial capillary plexuses (SCPs), and deep capillary plexuses (DCPs). Nonperfusion was manually delineated on UWF-FA to quantify central, peripheral, and total retinal nonperfusion (mm2 and % area).

MAIN OUTCOME MEASURES

Correlation between OCTA parameters and UWF-FA nonperfusion, and accuracy of these OCTA and UWF-FA parameters in detecting clinically referable eyes, using receiver operating characteristic (ROC) curve analysis, sensitivity, specificity, and area under the ROC curve (AUC).

RESULTS

The study included 67 eyes (12 eyes with no signs of DR, 8 mild, 22 moderate, 14 severe nonproliferative DR, and 11 treatment-naive proliferative DR). There was a fair-to-moderate correlation between either central or total retinal nonperfusion on UWF-FA (mm2) and GPD in the SCP (r = 0.482 and r = 0.464, respectively) and DCP (r = 0.470 and r = 0.456, respectively). Receiver operating characteristic analysis showed the DCP GPD significantly superior to other OCTA parameters at the DCP with the largest overall AUC on OCTA for distinguishing referable DR (0.905). Furthermore, the GPD parameter had the largest AUC in each respective capillary layer compared with other parameters. Overall, the total UWF-FA nonperfusion area showed a comparable AUC (0.907) and performed significantly better than peripheral nonperfusion (P = 0.041). Comparing the AUC values between GPD and UWF-FA nonperfusion parameters showed no significant difference in discerning referable DR.

CONCLUSIONS

Nonperfusion as quantified on OCTA (3 × 3 mm) correlated with UWF-FA parameters and both were comparable in detecting referable DR. These macular OCTA metrics, particularly DCP GPD, have the potential for gauging the overall ischemic status of the retina, with an important clinical role in identifying eyes with clinically referable DR.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Retinal capillary and choriocapillaris assessment using a beam modifier optical coherence tomography angiography module to increase lateral optical resolution

PURPOSE

To assess a new optical coherence tomography angiography (OCTA) technology and its contribution to retinal vascularization and choriocapillaris (CC) exploration.

METHODS

A new module, named "Beam expander" (BE), which increases the lateral resolution of OCTA, was used in combination with a prototype software in the PLEX® Elite 9000 Swept-Source OCT instrument (ZEISS, Dublin, CA). This prospective study involved 22 healthy subjects imaged with and without BE. Qualitative analysis of superficial capillary plexus (SCP), deep capillary complex (DCC) retinal and CC angiograms were performed. Perfusion density (PD), vessel density (VD), and foveal avascular zone (FAZ) measurements were also compared.

RESULTS

Qualitative analysis of single SCP and DCC retinal angiograms acquired with BE showed significantly better vessel sharpness (respectively, p = 0.0002, and p<0.0001), and greater peripheral image quality (p = 0.028 and p = 0.007) compared to standard OCTA images. Mean VD of whole retina single scans was significantly higher for BE angiograms compared to classic angiograms (28.16 ±1.29 mm-1 and 23.36 ±0.92 mm-1, respectively, p<0.0001). Repeatability of VD, PD and FAZ raw size were found to be similar between the two methods (intraclass correlation coefficient: 0.671, 0.604 and 0.994 with BE versus 0.764, 0.638 and 0.990 without BE). CC image quality was found to be significantly superior with BE, and flow deficits were more visible in all BE scans compared to standard scans.

CONCLUSIONS

An increase in lateral resolution of the OCT beam resulted in higher quality of retinal and choriocapillaris OCTA images in healthy subjects. These results provide significant insights into the future OCTA imaging enhancements.

An assessment of microvascular hemodynamics in human macula

An adequate blood supply to meet the energy demands is essential for any tissue, particularly for high energy demand tissues such as the retina. A critical question is: How is the dynamic match between neuronal demands and blood supply achieved? We present a quantitative assessment of temporal and spatial variations in perfusion in the macular capillary network in 10 healthy human subjects using a non-invasive and label-free imaging technique. The assessment is based on the calculation of the coefficient of variation (CoV) of the perfusion signal from arterioles, venules and capillaries from a sequence of optical coherence tomography angiography images centred on the fovea. Significant heterogeneity of the spatial and temporal variation was found within arterioles, venules and capillary networks. The CoV values of the capillaries and smallest vessels were significantly higher than that in the larger vessels. Our results demonstrate the presence of significant heterogeneity of spatial and temporal variation within each element of the macular microvasculature, particularly in the capillaries and finer vessels. Our findings suggest that the dynamic match between neuronal demands and blood supply is achieved by frequent alteration of local blood flow evidenced by capillary perfusion variations both spatially and temporally in the macular region.

Optical Coherence Tomography Angiography of Volumetric Arteriovenous Relationships in the Healthy Macula and Their Derangement in Disease

Purpose

To characterize relative arteriovenous connectivity of the healthy macula imaged by optical coherence tomography angiography (OCTA) using a new volumetric tool.

Methods

OCTA volumes were obtained for 20 healthy controls (20 eyes). Two graders identified superficial arterioles and venules. We implemented a custom watershed algorithm to identify capillaries most closely connected to arterioles and venules by using the large vessels as seeds to flood the vascular network. We calculated ratios of arteriolar- to venular-connected capillaries (A/V ratios) and adjusted flow indices (AFIs) for superficial capillary plexuses (SCPs), middle capillary plexuses (MCPs), and deep capillary plexuses (DCPs). We also analyzed two eyes with proliferative diabetic retinopathy (PDR) and one eye with macular telangiectasia (MacTel) to evaluate the utility of this method in visualizing pathological vascular connectivity.

Results

In healthy eyes, the MCP showed a greater proportion of arteriolar-connected vessels than the SCP and DCP (all P < 0.001). In the SCP, the arteriolar-connected AFI exceeded the venular-connected AFI, but this pattern reversed in the MCP and DCP, with higher venular-connected AFI (all P < 0.001). In PDR eyes, preretinal neovascularization originated from venules, whereas intraretinal microvascular abnormalities were heterogeneous, with some originating from venules and others representing dilated MCP capillary loops. In MacTel, diving SCP venules formed the epicenter of the outer retinal anomalous vascular network.

Conclusions

Healthy eyes showed a higher MCP A/V ratio but relatively slower arteriolar vs. venular flow velocity in the MCP and DCP, which may explain deep retinal vulnerability to ischemia. In eyes with complex vascular pathology, our connectivity findings were consistent with histopathologic studies.

Signal attenuation-compensated projection-resolved OCT angiography

Projection artifacts are a significant limitation of optical coherence tomographic angiography (OCTA). Existing techniques to suppress these artifacts are sensitive to image quality, becoming less reliable on low-quality images. In this study, we propose a novel signal attenuation-compensated projection-resolved OCTA (sacPR-OCTA) algorithm. In addition to removing projection artifacts, our method compensates for shadows beneath large vessels. The proposed sacPR-OCTA algorithm improves vascular continuity, reduces the similarity of vascular patterns in different plexuses, and removes more residual artifacts compared to existing methods. In addition, the sacPR-OCTA algorithm better preserves flow signal in choroidal neovascular lesions and shadow-affected areas. Because sacPR-OCTA processes the data along normalized A-lines, it provides a general solution for removing projection artifacts agnostic to the platform.

AV-casNet: Fully Automatic Arteriole-Venule Segmentation and Differentiation in OCT Angiography

Automatic segmentation and differentiation of retinal arteriole and venule (AV), defined as small blood vessels directly before and after the capillary plexus, are of great importance for the diagnosis of various eye diseases and systemic diseases, such as diabetic retinopathy, hypertension, and cardiovascular diseases. Optical coherence tomography angiography (OCTA) is a recent imaging modality that provides capillary-level blood flow information. However, OCTA does not have the colorimetric and geometric differences between AV as the fundus photography does. Various methods have been proposed to differentiate AV in OCTA, which typically needs the guidance of other imaging modalities. In this study, we propose a cascaded neural network to automatically segment and differentiate AV solely based on OCTA. A convolutional neural network (CNN) module is first applied to generate an initial segmentation, followed by a graph neural network (GNN) to improve the connectivity of the initial segmentation. Various CNN and GNN architectures are employed and compared. The proposed method is evaluated on multi-center clinical datasets, including 3 ×3 mm2 and 6 ×6 mm2 OCTA. The proposed method holds the potential to enrich OCTA image information for the diagnosis of various diseases.

Histology of type 3 macular neovascularization and microvascular anomalies in treated age-related macular degeneration: a case study

Purpose

To investigate intraretinal neovascularization and microvascular anomalies by correlating in vivo multimodal imaging with corresponding ex vivo histology in a single patient.

Design

A case study comprising clinical imaging from a community-based practice, and histologic analysis at a university-based research laboratory (clinicopathologic correlation).

Participants

A White woman in her 90s treated with numerous intravitreal anti-VEGF injections for bilateral type 3 macular neovascularization (MNV) secondary to age-related macular degeneration (AMD).

Methods

Clinical imaging comprised serial infrared reflectance, eye-tracked spectral-domain OCT, OCT angiography, and fluorescein angiography. Eye tracking, applied to the 2 preserved donor eyes, enabled the correlation of clinical imaging signatures with high-resolution histology and transmission electron microscopy.

Main Outcome Measures

Histologic/ultrastructural descriptions and diameters of vessels seen in clinical imaging.

Results

Six vascular lesions were histologically confirmed (type 3 MNV, n = 3; deep retinal age-related microvascular anomalies [DRAMAs], n = 3). Pyramidal (n = 2) or tangled (n = 1) morphologies of type 3 MNV originated at the deep capillary plexus (DCP) and extended posteriorly to approach without penetrating persistent basal laminar deposit. They did not enter the subretinal pigment epithelium (RPE)-basal laminar space or cross the Bruch membrane. Choroidal contributions were not found. The neovascular complexes included pericytes and nonfenestrated endothelial cells, within a collagenous sheath covered by dysmorphic RPE cells. Deep retinal age-related microvascular anomaly lesions extended posteriorly from the DCP into the Henle fiber and the outer nuclear layers without evidence of atrophy, exudation, or anti-VEGF responsiveness. Two DRAMAs lacked collagenous sheaths. External and internal diameters of type 3 MNV and DRAMA vessels were larger than comparison vessels in the index eyes and in aged normal and intermediate AMD eyes.

Conclusions

Type 3 MNV vessels reflect specializations of source capillaries and persist during anti-VEGF therapy. The collagenous sheath of type 3 MNV lesions may provide structural stabilization. If so, vascular characteristics may be useful in disease monitoring in addition to fluid and flow signal detection. Further investigation with longitudinal imaging before exudation onset will help determine if DRAMAs are part of the type 3 MNV progression sequence.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Deep Capillary Geometric Perfusion Deficits on OCT Angiography Detect Clinically Referable Eyes with Diabetic Retinopathy

PURPOSE

To evaluate the sensitivity (SN) and specificity (SP) of OCT angiography (OCTA) parameters for detecting clinically referable eyes with diabetic retinopathy (DR) in a cohort of patients with diabetes mellitus (DM).

DESIGN

Retrospective, cross-sectional study.

SUBJECTS

Patients with DM with various levels of DR.

METHODS

We measured vessel density, vessel length density (VLD), and geometric perfusion deficits (GPDs) in the full retina, superficial capillary plexus (SCP), and deep capillary plexus (DCP) on 3 × 3-mm OCTA images. Geometric perfusion deficit was recently described as retinal tissue located further than 30 μm from blood vessels, excluding the foveal avascular zone (FAZ). We modified the GPD metric by including the FAZ as an additional variable. Clinically referable eyes were defined as moderate nonproliferative DR (NPDR) or worse retinopathy, or diabetic macular edema (DME). One eye from each patient was selected for the analysis based on image quality. We used a binary logistic regression model to adjust for covariates.

MAIN OUTCOME MEASURES

Sensitivity, SP, and area under the curve (AUC).

RESULTS

Seventy-one of 150 included eyes from 150 patients (52 with DM without DR, 27 with mild NPDR, 16 with moderate NPDR, 10 with severe NPDR, 30 with proliferative DR, and 15 with DME) had clinically referable DR. Geometric perfusion deficit metric that included the FAZ performed better than GPD in detecting referable DR in the SCP (P = 0.025) but not the DCP or full retina (P > 0.05 for both). Deep capillary plexus GPD had the largest AUC for detecting clinically referable eyes (AUC = 0.965, SN = 97.2%, SP = 84.8%), which was significantly larger than the AUC for vessel density of any layer (P < 0.05 for all) but not DCP VLD (P = 0.166). The cutoff value of 2.5% for DCP GPD resulted in a highly sensitive test for detecting clinically referable eyes without adjusting for covariates (AUC = 0.955, SN = 97.2%, SP = 79.7%).

CONCLUSIONS

Vascular parameters in OCTA, especially in the DCP, have the potential to identify eyes that warrant further evaluation. Geometric perfusion deficits may better distinguish these clinically referable eyes with DR than standard vessel density parameters.

Clinically Significant Nonperfusion Areas on Widefield OCT Angiography in Diabetic Retinopathy

Purpose

To investigate the distribution of clinically significant nonperfusion areas (NPAs) on widefield OCT angiography (OCTA) images in patients with diabetes.

Design

Prospective, cross-sectional, observational study.

Participants

One hundred and forty-four eyes of 114 patients with diabetes.

Methods

Nominal 20 × 23 mm OCTA images were obtained using a swept-source OCTA device (Xephilio OCT-S1), followed by the creation of en face images 20-mm (1614 pixels) in diameter centering on the fovea. The nonperfusion squares (NPSs) were defined as the 10 × 10 pixel squares without retinal vessels, and the ratio of eyes with the NPSs to all eyes in each square was referred to as the NPS ratio. The areas with probabilistic differences (APD) for proliferative diabetic retinopathy (PDR) and nonproliferative diabetic retinopathy (NPDR) (APD[PDR] and APD[NPDR]) were defined as sets of squares with higher NPS ratios in eyes with PDR and NPDR, respectively. The P ratio (NPSs within APD[PDR] but not APD[NPDR]/all NPSs) was also calculated.

Main Outcome Measures

The probabilistic distribution of the NPSs and the association with diabetic retinopathy (DR) severity.

Results

The NPSs developed randomly in eyes with mild and moderate NPDR and were more prevalent in the extramacular areas and the temporal quadrant in eyes with severe NPDR and PDR. The APD(PDR) was distributed mainly in the extramacular areas, sparing the areas around the vascular arcades and radially peripapillary capillaries. The APD(PDR) contained retinal neovascularization more frequently than the non-APD(PDR) (P = 0.023). The P ratio was higher in eyes with PDR than in those with NPDR (P < 0.001). The multivariate analysis designated the P ratio (odds ratio, 8.293 × 10⁷; 95% confidence interval, 6.529 × 10²-1.053 × 10¹³; P = 0.002) and the total NPSs (odds ratio, 1.002; 95% confidence interval, 1.001-1.003; P < 0.001) as independent risk factors of PDR. Most eyes with NPDR and 4-2-1 rule findings of DR severity had higher P ratios but not necessarily greater NPS numbers.

Conclusions

The APD(PDR) is uniquely distributed on widefield OCTA images, and the NPA location patterns are associated with DR severity, independent of the entire area of NPAs.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Studies of the retinal microcirculation using human donor eyes and high-resolution clinical imaging: Insights gained to guide future research in diabetic retinopathy

The microcirculation plays a key role in delivering oxygen to and removing metabolic wastes from energy-intensive retinal neurons. Microvascular changes are a hallmark feature of diabetic retinopathy (DR), a major cause of irreversible vision loss globally. Early investigators have performed landmark studies characterising the pathologic manifestations of DR. Previous works have collectively informed us of the clinical stages of DR and the retinal manifestations associated with devastating vision loss. Since these reports, major advancements in histologic techniques coupled with three-dimensional image processing has facilitated a deeper understanding of the structural characteristics in the healthy and diseased retinal circulation. Furthermore, breakthroughs in high-resolution retinal imaging have facilitated clinical translation of histologic knowledge to detect and monitor progression of microcirculatory disturbances with greater precision. Isolated perfusion techniques have been applied to human donor eyes to further our understanding of the cytoarchitectural characteristics of the normal human retinal circulation as well as provide novel insights into the pathophysiology of DR. Histology has been used to validate emerging in vivo retinal imaging techniques such as optical coherence tomography angiography. This report provides an overview of our research on the human retinal microcirculation in the context of the current ophthalmic literature. We commence by proposing a standardised histologic lexicon for characterising the human retinal microcirculation and subsequently discuss the pathophysiologic mechanisms underlying key manifestations of DR, with a focus on microaneurysms and retinal ischaemia. The advantages and limitations of current retinal imaging modalities as determined using histologic validation are also presented. We conclude with an overview of the implications of our research and provide a perspective on future directions in DR research.

MF-AV-Net: an open-source deep learning network with multimodal fusion options for artery-vein segmentation in OCT angiography

This study is to demonstrate the effect of multimodal fusion on the performance of deep learning artery-vein (AV) segmentation in optical coherence tomography (OCT) and OCT angiography (OCTA); and to explore OCT/OCTA characteristics used in the deep learning AV segmentation. We quantitatively evaluated multimodal architectures with early and late OCT-OCTA fusions, compared to the unimodal architectures with OCT-only and OCTA-only inputs. The OCTA-only architecture, early OCT-OCTA fusion architecture, and late OCT-OCTA fusion architecture yielded competitive performances. For the 6 mm×6 mm and 3 mm×3 mm datasets, the late fusion architecture achieved an overall accuracy of 96.02% and 94.00%, slightly better than the OCTA-only architecture which achieved an overall accuracy of 95.76% and 93.79%. 6 mm×6 mm OCTA images show AV information at pre-capillary level structure, while 3 mm×3 mm OCTA images reveal AV information at capillary level detail. In order to interpret the deep learning performance, saliency maps were produced to identify OCT/OCTA image characteristics for AV segmentation. Comparative OCT and OCTA saliency maps support the capillary-free zone as one of the possible features for AV segmentation in OCTA. The deep learning network MF-AV-Net used in this study is available on GitHub for open access.

A Deep Learning Network for Classifying Arteries and Veins in Montaged Widefield OCT Angiograms

Purpose

To propose a deep-learning-based method to differentiate arteries from veins in montaged widefield OCT angiography (OCTA).

Design

Cross-sectional study.

Participants

A total of 232 participants, including 109 participants with diabetic retinopathy (DR), 64 participants with branch retinal vein occlusion (BRVO), 27 participants with diabetes but without DR, and 32 healthy participants.

Methods

We propose a convolutional neural network (CAVnet) to classify retinal blood vessels on montaged widefield OCTA en face images as arteries and veins. A total of 240 retinal angiograms from 88 eyes were used to train CAVnet, and 302 retinal angiograms from 144 eyes were used for testing. This method takes the OCTA images as input and outputs the segmentation results with arteries and veins down to the level of precapillary arterioles and postcapillary venules. The network also identifies their intersections. We evaluated the agreement (in pixels) between segmentation results and the manually graded ground truth using sensitivity, specificity, F1-score, and Intersection over Union (IoU). Measurements of arterial and venous caliber or tortuosity are made on our algorithm's output of healthy and diseased eyes.

Main Outcome Measures

Classification of arteries and veins, arterial and venous caliber, and arterial and venous tortuosity.

Results

For classification and identification of arteries, the algorithm achieved average sensitivity of 95.3%, specificity of 99.6%, F1 score of 94.2%, and IoU of 89.3%. For veins, the algorithm achieved average sensitivity of 94.4%, specificity of 99.7%, F1 score of 94.1%, and IoU of 89.2%. We also achieved an average sensitivity of 76.3% in identifying intersection points. The results show CAVnet has high accuracy on differentiating arteries and veins in DR and BRVO cases. These classification results are robust across 2 instruments and multiple scan volume sizes. Outputs of CAVnet were used to measure arterial and venous caliber or tortuosity, and pixel-wise caliber and tortuosity maps were generated. Differences between healthy and diseased eyes were demonstrated, indicating potential clinical utility.

Conclusions

The CAVnet can classify arteries and veins and their branches with high accuracy and is potentially useful in the analysis of vessel type-specific features on diseases such as branch retinal artery occlusion and BRVO.

Correlation of Optical Coherence Tomography Angiography of Type 3 Macular Neovascularization With Corresponding Histology

Importance

By validating optical coherence tomography angiography (OCTA) in the analysis of type 3 macular neovascularization secondary to age-related macular degeneration, the overall value of clinical OCTA for disease observation, diagnosis, and staging is increased.

Objective

To assess the association of in vivo OCTA of type 3 macular neovascularization secondary to age-related macular degeneration with corresponding ex vivo histology.

Design, Setting, and Participants

This study included clinical imaging, laboratory microscopy, and eye-tracked clinicopathologic correlation of a single case from a community-based practice evaluated at a university-based research laboratory from 2014 to 2019.

Exposures

Infrared reflectance and eye-tracked spectral-domain OCTA clinical imaging was correlated with ex vivo high-resolution histologic images of the preserved donor eye. Eye tracking, applied to the donor eye, enabled identification of histologic features corresponding with clinical OCTA signatures. Projection artifact removal based on 2-dimensional vessel-shape estimation and a Gaussian blur filter demonstrated a robust preservation of neovascular flow signal.

Main Outcomes and Measures

Histology findings associated with clinical OCTA signatures. Three-dimensional view of neovascularization via video.

Results

A White woman in her 90s with type 3 neovascularization secondary to age-related macular degeneration was treated with 37 intravitreal injections of ranibizumab and aflibercept in the right eye. The index lesion displayed a drusenoid pigment epithelium detachment, characteristic of type 3 neovascularization. OCTA decorrelation signal in the index lesion corresponded in histology to a collagen-ensheathed vascular complex contacting basal laminar deposit that outlasted the retinal pigment epithelium. The subretinal pigment epithelium-basal laminar space contained calcified material and glial processes. No connection between the choriocapillaris and this space was observed. Video showed a columnar tangle of flow signal in the outer nuclear layer, with inflow and outflow vessels connecting to the superficial artery and vein.

Conclusions and Relevance

While this study presents only 1 case in which a vascular connection between subretinal pigment epithelium-basal laminar space and choriocapillaris was undetected, these results support the potential value of OCTA for diagnosis. OCTA decorrelation signal of type 3 neovascularization corresponded with intraretinal neovessels on histology. Projection artifact removal based on 2-dimensional vessel-shape estimation and Gaussian blur filter demonstrated their potential value for further use in OCTA decorrelation signal processing.

Variability in Retinal Neuron Populations and Associated Variations in Mass Transport Systems of the Retina in Health and Aging

Aging is associated with a broad range of visual impairments that can have dramatic consequences on the quality of life of those impacted. These changes are driven by a complex series of alterations affecting interactions between multiple cellular and extracellular elements. The resilience of many of these interactions may be key to minimal loss of visual function in aging; yet many of them remain poorly understood. In this review, we focus on the relation between retinal neurons and their respective mass transport systems. These metabolite delivery systems include the retinal vasculature, which lies within the inner portion of the retina, and the choroidal vasculature located externally to the retinal tissue. A framework for investigation is proposed and applied to identify the structures and processes determining retinal mass transport at the cellular and tissue levels. Spatial variability in the structure of the retina and changes observed in aging are then harnessed to explore the relation between variations in neuron populations and those seen among retinal metabolite delivery systems. Existing data demonstrate that the relation between inner retinal neurons and their mass transport systems is different in nature from that observed between the outer retina and choroid. The most prominent structural changes observed across the eye and in aging are seen in Bruch's membrane, which forms a selective barrier to mass transfers at the interface between the choroidal vasculature and the outer retina.

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.

Peripheral Chorioretinal Imaging Through a Front Prism on Optical Coherence Tomography Angiography

Purpose

To evaluate the clinical feasibility of peripheral chorioretinal imaging through a front prism on swept-source optical coherence tomography angiography (SS-OCTA).

Methods

We prospectively obtained en face OCTA images using SS-OCTA in 10 eyes of 10 healthy volunteers. For the peripheral chorioretinal imaging, the scanning laser passed and refracted through a 45°-90°-45° right-angle prism. We evaluated the qualitative and quantitative characteristics of chorioretinal vessels in the periphery.

Results

Using peripheral chorioretinal imaging through a prism, the retinal vasculature was delineated to the equator on the OCTA images, and varices of the vortex vein ampullae were observed on choroidal OCT images. The 3 × 3-mm images revealed three-dimensional morphologies unique to the peripheral vasculature, such as the gap between retinal arterioles and venules in the superficial capillary plexus (SCP) and elliptical and greater lobules in the choriocapillaris layer. Compared with OCTA images obtained without the prism, those obtained through the prism demonstrated an approximately 1.24-fold increase in the lengths in the base apex direction, whereas the lengths in the perpendicular direction showed concordance. The peripheral vessel density (VD) in the inferior quadrant was lower than those in the other quadrants on the SCP and deep capillary plexus, whereas on the SCP images of the macula the lowest VD was observed in the temporal subfield.

Conclusions

Peripheral chorioretinal imaging allowed us to generate ultra-widefield panoramic OCTA images and demonstrated morphologic characteristics unique to peripheral chorioretinal vessels.

Translational Relevance

OCTA imaging through a front prism can be a technique for acquiring chorioretinal vasculature images in the periphery.

Vascular Microanatomy of Small Resolved Paracentral Acute Middle Maculopathy Lesions

PURPOSE

To study microvascular characteristics of small resolved paracentral acute middle maculopathy (PAMM) lesions in fellow eyes of patients with unilateral retinal vein occlusion (RVO).

DESIGN

Prospective cross-sectional study.

PARTICIPANTS

Patients with prior unilateral branch or central RVO and OCT evidence of resolved PAMM in the fellow, otherwise normal, eye were recruited prospectively and imaged with OCT angiography (OCTA).

METHODS

The resolved PAMM lesions were identified as focal areas of inner nuclear layer thinning over an anteriorly displaced outer plexiform layer (OPL). En face OCTA projections showing the location and size of the resolved PAMM lesions were created using 2 OPL segmentation lines with -9-μm and 0-μm offsets, and the cumulative distribution was evaluated. Anterior to the resolved PAMM lesions, vessels in the superficial vascular plexus were traced to identify small arterioles supplying the affected areas.

MAIN OUTCOME MEASURES

Cumulative spatial distribution on small resolved PAMM lesions.

RESULTS

From 24 fellow eyes of 24 patients with unilateral RVO (15 men and 9 women; mean age, 62.1 ± 13.6 years), 152 resolved PAMM lesions were identified. Of these lesions, 130 (85.5%) were found within the perifoveal region, and only 12 (7.9%) were found within the temporal quadrant. Of 28 lesions analyzed, the arteriole supplying the affected area was a single side branch of a larger vessel, with only 3 supplied by a terminal branch.

CONCLUSIONS

Small resolved PAMM lesions in fellow eyes of patients with unilateral RVO are most prevalent in perifoveal regions supplied by side branches of low-order retinal arteries.

OCTA reveals remodeling of the peripheral capillary free zones in normal aging

The retinal neurovascular unit consists of blood vessel endothelial cells, pericytes, neurons, astrocytes, and Müller cells that form the inner retinal blood barrier. A peripheral capillary free zone (pCFZ) represents the distance that oxygen and nutrients must diffuse to reach the neural retina, and serves as a metric of retinal tissue oxygenation. The pCFZs are formed based on oxygen saturation in the retinal arterioles and venules. Because retinal arterioles contain a larger concentration of oxygenated blood than venules, there is a reduced need for capillaries to exist closely to arterioles compared to venules. Therefore, in a healthy individual, larger periarteriole CFZs are expected compared to perivenule CFZs. With normal aging, there is atrophy of the inner retinal neurons, and consequently reduced extraction of oxygen and nutrients from the retinal vessels (i.e., increased oxygen saturation). Therefore, we hypothesized that the peripheral CFZ will remodel with normal aging. Using Optical Coherence Tomography Angiography, we showed that the pCFZs do remodel in normal aging with large (perivenule: η²_p = 0.56) and moderate (periarteriole: η²_p = 0.12) effect sizes, opening the possibility that such changes may be further increased by neurodegenerative diseases that adversely impact the health of the retinal neural cell layers.

Volume Rendering of Angiographic Optical Coherence Tomography Angiography in Fovea Plana and Normal Foveal Pit

This paper aims to study adaptative vascular arrangements in idiopathic fovea plana with volume-rendered optical coherence tomography angiography (OCTA). A retrospective review of two cases of idiopathic fovea plana (mean age: 26.5 years) and two age-matched controls imaged with OCTA was conducted using spectral-domain OCTA (RTVue XR Avanti, Optovue, Inc., Fremont, CA) equipped with the AngioVue software. Both en face OCTA slabs and OCTA b scans were processed through Fiji software (http://fiji.sc; software version 2.0.0-rc-68/1.52e), and then extracted as image sequences for volume rendering reconstructions using the ImageVis3D volume rendering system (3.1.0 release). Eyes with idiopathic fovea plana demonstrated a regular superficial vascular plexus connecting to a single vascular monolayer representing the deeper vascular plexuses. At this location, several vertical short path connections were demonstrated, in contraposition with normal eyes where short path connections were infrequently observed. Advances in three-dimensional OCTA reconstruction increase the understanding of vascular connections and arrangement in retinal plexuses and possible anatomical variations that cannot be detected with conventional two-dimensional b scans.

FOVEAL AVASCULAR ZONE VOLUME: A New Index Based on Optical Coherence Tomography Angiography Images

PURPOSE

To propose a new clinical evaluation index, foveal avascular zone (FAZ) volume, and analyze its statistical significance.

METHODS

A semiautomatic method is proposed to measure the FAZ volume in optical coherence tomography angiography images as follows: The region of interest was flattened and annotated axially. The labeled pixels in the restored region of interest were counted as the FAZ volume. Linear regression and the independent samples t-test were performed for the statistical analysis.

RESULTS

Sixty-one normal, 64 high myopia, and 42 diabetic retinopathy eyes were imaged using optical coherence tomography angiography. For normal eyes, the FAZ volume correlates inversely with central macular thickness (superficial: P = 0.004; deep: P < 0.001) and positively with area (P < 0.001). For high myopia eyes, the deep plexus FAZ (P = 0.34) and total FAZ (P = 0.38) volumes show no significant difference, whereas the superficial plexus FAZ volume is significantly larger than control (P < 0.001). For diabetic retinopathy eyes, the superficial plexus FAZ (P = 0.001), deep plexus FAZ (P = 0.014), and total volumes (P = 0.002) are significantly larger than control.

CONCLUSION

The FAZ volume is proposed for depicting the 3D structure of the FAZ. It shows greater sensitivity for vascular alteration that makes it meaningful for clinical analysis.

Wide-Field Swept-Source Optical Coherence Tomography Angiography Analysis of the Periarterial Capillary-Free Zone in Branch Retinal Vein Occlusion

Purpose

To investigate the characteristics of the retinal periarterial capillary-free zone (paCFZ) with wide-field swept-source optical coherence tomography angiography (SS-OCTA) in eyes with branch retinal vein occlusion (BRVO).

Methods

Seventy treatment-naïve eyes with BRVO and 35 healthy eyes were included. The paCFZ areas, artery calibers, and areas of the major arteries in the unaffected quadrants of BRVO eyes were measured in 12 × 12-mm SS-OCTA images and compared with those of the contralateral eyes and healthy eyes. Other multimodal imaging data were collected.

Results

There were no significant differences in the unaffected artery caliber or area among the three groups (all P > 0.05). The unaffected paCFZ areas and the ratios of the unaffected paCFZ area to the counterpart artery area (paCFZ/artery area) of the major arteries were significantly larger than those in the contralateral or healthy eyes (all P < 0.05). Subgroup analysis revealed that the paCFZ/artery area value differed significantly between ischemic and nonischemic BRVO eyes (P < 0.01). The paCFZ/artery area value was positively correlated with logMAR best-corrected visual acuity, symptom duration, central macular thickness, and retinal nonperfusion area in BRVO.

Conclusions

Quantitative SS-OCTA measurements confirmed enlarged paCFZs along the unaffected major retinal arteries in BRVO eyes. The paCFZ parameters were correlated with symptom duration, retinal ischemia, and visual function.

Translational Relevance

Retinal periarterial capillary-free zones in BRVO can be non-invasively measured by SS-OCTA, assisting in clinically identifying retinal ischemia and evaluating visual function.

Associations Between Capillary Diameter, Capillary Density, and Microaneurysms in Diabetic Retinopathy: A High-Resolution Confocal Microscopy Study

Purpose

To use high-resolution histology to define the associations between microaneurysms, capillary diameter and capillary density alterations in diabetic retinopathy (DR).

Methods

Quantitative comparisons of microaneurysm number, capillary density and capillary diameter were performed between eight human donor eyes with nonproliferative DR and six age- and eccentricity-matched normal donor eyes after retinal vascular perfusion labelling. The parafovea, 3-mm, 6-mm, and 9-mm retinal eccentricities were analyzed and associations between microvascular alterations defined.

Results

Mean capillary density was reduced in all retina regions in the DR group (P = 0.013). Microaneurysms occurred in all retina regions in the DR group, but the association between decreased capillary density and microaneurysm number was only significant in the 3-mm (P = 0.040) and 6-mm (P = 0.007) eccentricities. The mean capillary diameter of the DR group (8.9 ± 0.53 µm) was greater than the control group (7.60 ± 0.40 µm; P = 0.033). There was no association between capillary diameter increase and capillary density decrease (P = 0.257) and capillary diameter increase and microaneurysm number (P = 0.147) in the DR group. Within the parafovea of the DR group, capillary density was significantly reduced, and capillary diameter was significantly increased in the deep capillary plexus compared with the superficial and intermediate plexuses (all P < 0.05).

Conclusions

In DR, capillary density reduction occurs across multiple retina eccentricities with a predilection for the deep capillary plexus. The association between microaneurysm number and capillary density is specific to retina eccentricity. Capillary diameter increase may be an early biomarker of DR. These findings may refine the application of optical coherence tomography angiography techniques for the management of DR.

Use of the Retinal Vascular Histology to Validate an Optical Coherence Tomography Angiography Technique

Purpose

To determine the fidelity of optical coherence tomography angiography (OCTA) techniques by direct comparison of the retinal capillary network images obtained from the same region as imaged by OCTA and high-resolution confocal microscope.

Method

Ten porcine eyes were perfused with red blood cells for OCTA image acquisition from the area centralis and then perfusion-fixed, and the vessels were labeled for confocal imaging. Two approaches involving post-processing of two-dimensional projection images and vessel tracking on three dimensional image stacks were used to obtain quantitative measurements. Data collected include vessel density, length of visible vessel track, count of visible branch points, vessel track depth, vessel diameter, angle of vessel descent, and angle of dive for comparison and analysis.

Results

Comparing vascular images acquired from OCTA and confocal microscopy, we found (1) a good representation of the larger caliber retinal vessels, (2) an underrepresentation of retinal microvessels smaller than 10 µm and branch points in all four retinal vascular plexuses, particularly the intermediate capillary plexus, (3) reduced visibility associated with an increase in the angle of descent, (4) a tendency to loss visibility of vessel track at a branch point or during a sharp dive, and (5) a reduction in visibility with increase in retinal depth on OCTA images.

Conclusions

Current OCTA techniques can visualize the retinal capillary network, but some types of capillaries cannot be detected by OCTA, particularly in the middle to deeper layers.

Translational Relevance

The information indicates the limitation in clinical use and scopes for improvement in the current OCTA technologies.

Relationship Between Choriocapillaris Flow and Scotopic Microperimetry in Early and Intermediate Age-related Macular Degeneration

PURPOSE

To evaluate the correlation between choriocapillaris (CC) flow alterations and scotopic macular sensitivity (sMS) in patients with early and intermediate age-related macular degeneration (AMD).

DESIGN

Prospective cross-sectional study.

METHODS

We acquired 2 3 × 3 mm and 2 6 × 6 mm swept-source optical coherence tomography angiography (OCTA) images of 1 eye of consecutive early or intermediate AMD patients at the Doheny UCLA Eye Centers. After 30 minutes of dark adaptation, the same eye underwent scotopic microperimetry with an 18-degree-wide grid (52 stimuli) centered on the fovea. The 2 en face CC angiograms obtained from each scan pattern were compensated for signal loss and averaged. The main outcome measures were correlation between percentages of flow deficits (FD_3mm and FD_6mm) and sMS in the central 10° (MS₁₀) and the overall pattern (MS₁₈).

RESULTS

Thirty eyes of 30 patients were enrolled, with 14 (46.7%) having subretinal drusenoid deposits (SDD). In the averaged OCTA scans, the FD_3mm was 12.56% ± 2.41% while the FD_6mm was 9.33% ± 1.84%. The mean MS₁₀ and MS₁₈ were 13.84 ± 5.89 dB and 14.64 ± 5.21 dB, respectively. For the MS_10, the multivariate regression analysis showed a significant association only with FD_3mm (β: -0.628, P < .001) while the MS₁₈ was significantly correlated with both SDD (β: -0.32, P = .047) and FD_6mm (β: -0.473, P = .005).

CONCLUSIONS

Our study reports a significant correlation between the CC flow impairment and the sMS in eyes with early or intermediate AMD. If replicated in future longitudinal studies, the choriocapillaris FD may prove to be a useful parameter for evaluating the functional status and prognosis of these eyes.

Three-Dimensional Characterization of the Normal Human Parafoveal Microvasculature Using Structural Criteria and High-Resolution Confocal Microscopy

Purpose

To use structural criteria to reconcile the three-dimensional organization and connectivity of the parafoveal microvasculature.

Methods

The parafoveal microvasculature was perfused and labeled in 16 normal human donor eyes for lectin, alpha smooth muscle actin, and filamentous actin. Established structural criteria gathered using confocal microscopy, including vessel diameter, endothelial cell morphology, and presence/density of smooth muscle cells, were used to differentiate arteries, arterioles, capillaries, venules, and veins. Three-dimensional visualization strategies were used to define the connections between retinal arteries and veins within the superficial vascular plexus (SVP), intermediate capillary plexus (ICP), and deep capillary plexus (DCP).

Results

The parafoveal microvasculature has two different inflow patterns and seven different outflow patterns. The SVP and ICP were connected to retinal arteries by arterioles. Inflow into the DCP occurred only via small arterioles (a1; mean diameter, 8.3 µm) that originated from the ICP. Direct connections between the DCP and retinal arteries were not identified. Each capillary plexus formed its own venule that drained independently or in conjunction with venules from other plexuses into a retinal vein at the level of the ganglion cell layer. For the DCP, a1 was significantly smaller than its draining venule (mean diameter, 18.8 µm; P < 0.001).

Conclusions

The SVP and ICP of the parafoveal microvasculature have both in series and in parallel arterial and venous connections. Arterial supply to the DCP originates from the ICP, but with direct drainage to the retinal vein. These findings may help to develop an understanding of the pattern of retinal lesions characterizing a myriad of retinal vascular diseases.

In vivo retinal imaging in translational regenerative research

Regenerative translational studies must include a longitudinal assessment of the changes in retinal structure and function that occur as part of the natural history of the disease and those that result from the studied intervention. Traditionally, retinal structural changes have been evaluated by histological analysis which necessitates sacrificing the animals. In this review, we describe key imaging approaches such as fundus imaging, optical coherence tomography (OCT), OCT-angiography, adaptive optics (AO), and confocal scanning laser ophthalmoscopy (cSLO) that enable noninvasive, non-contact, and fast in vivo imaging of the posterior segment. These imaging technologies substantially reduce the number of animals needed and enable progression analysis and longitudinal follow-up in individual animals for accurate assessment of disease natural history, effects of interventions and acute changes. We also describe the benefits and limitations of each technology, as well as outline possible future directions that can be taken in translational retinal imaging studies.

Non-Proliferative Diabetic Retinopathy Is Characterized by Nonuniform Alterations of Peripapillary Capillary Networks

Purpose

The purpose of this study was to use three-dimensional confocal microscopy to quantify the spatial patterns of capillary network alterations in nonproliferative diabetic retinopathy (NPDR).

Methods

The retinal microvasculature was perfusion-labelled in seven normal human donor eyes and six age-matched donor eyes with NPDR. The peripapillary microcirculation was studied using confocal scanning laser microscopy. Capillary density and diameters of the radial peripapillary capillary plexus (RPCP), superficial capillary plexus (SCP), intermediate capillary plexus (ICP), and deep capillary plexus (DCP) were quantified and compared. Three-dimensional visualization strategies were also used to compare the communications between capillary beds and precapillary arterioles and postcapillary venules.

Results

Mean capillary diameter was significantly increased in the NPDR group (P < 0.001). Intercapillary distance was significantly increased in the DCP (P = 0.004) and RPCP (P = 0.022) of the NPDR group (P = 0.010) but not the SCP (P = 0.155) or ICP (P = 0.103). The NPDR group was associated with an increased frequency of inflow communication between the SCP and ICP/DCP and a decreased frequency of communication between the SCP and RPCP (P = 0.023). There was no difference in the patterns of outflow communications between the two groups (P = 0.771).

Conclusions

This study demonstrates that capillary plexuses are nonuniformly perturbed in NPDR. These structural changes may be indicative of perturbations to blood flow patterns between different retinal layers. Our findings may aid the interpretation of previous clinical observations made using optical coherence tomography angiography as well as improve our understanding of the pathogenesis of NPDR.

Deep Retinal Capillary Plexus Decreasing Correlated With the Outer Retinal Layer Alteration and Visual Acuity Impairment in Pathological Myopia

Purpose

The purpose of this study was to measure alterations of inner retinal microvascular density and outer retinal sublayer thicknesses in pathological myopia, and to correlate the measured parameters with best corrected visual acuity (BCVA).

Methods

Optical coherence tomography (OCT) and OCT angiography (OCTA) images of 21 control, 48 simple high myopia, and 22 pathological myopia eyes were analyzed to quantify the thicknesses of the outer retinal sublayers and the density of the inner retinal microvascular network that includes the superficial retinal capillary plexus (SRCP) and deep retinal capillary plexus (DRCP). Retinal sublayer thicknesses and microvascular densities were compared among the three groups, and correlations of sublayer thicknesses and microvascular densities with BCVA were determined.

Results

In pathological myopia, density of the DRCP, thicknesses of myoid and ellipsoid zone (MEZ), interdigitation zone and retinal pigment epithelium/Bruch complex (IZ + RPE), and choroid were lower than in simple high myopia (P < 0.05). The decreased DRCP density was correlated with thinner MEZ and IZ+RPE in pathological myopia (P < 0.05), but not in simple high myopia (P > 0.05). Simple linear regression showed that axial length, female, thicknesses of outer plexiform layer (OPL), MEZ, IZ + RPE, choroid, and density of the SRCP and DRCP were correlated with BCVA. In multiple regression analysis, worse BCVA was associated only with thinner MEZ, thinner choroid, and decreased DRCP (P < 0.05).

Conclusions

Alteration of inner retinal microvascular density and outer retinal sublayer thicknesses occurred in pathological myopia, especially decreased DRCP and thinner MEZ, which were significantly associated with worse BCVA.

Colocalization of optical coherence tomography angiography with histology in the mouse retina

Optical coherence tomography angiography (OCT-A) allows in vivo, non-invasive, functional imaging of retinal perfusion. The purpose of this study was to determine the reliability of OCT-A in visualizing the complete retinal vasculature by comparing in vivo OCT-A images to matched ex vivo retinal tissue in mice. Adult female C57BL/6 mice were imaged to obtain OCT-A images of the superficial vascular complex, intermediate capillary plexus and deep capillary plexus. Z-stack fluorescence images of whole-mounted retinas, labeled for vascular endothelial cells by anti-isolectin immunohistochemistry and FITC-dextran perfusion, were generated. The OCT-A and fluorescence images were manually colocalized and vessel length measured for each of the techniques. Mean vessel length among all plexuses showed less than 13% difference between OCT-A and lectin immunohistochemistry and less than 4% difference between OCT-A and FITC-dextran perfusion. The strength of the correlation between OCT-A and lectin immunohistochemistry ranged from 0.46-0.95, while that between OCT-A and FITC-perfusion ranged from 0.67-0.88. OCT-A visualized retinal vasculature in vivo to a similar extent in matched ex vivo histology images. Our results show that OCT-A is a reliable method for acquiring in vivo images of retinal perfusion in mice, with the ability to differentiate each vascular plexus.

Microvasculature Segmentation and Intercapillary Area Quantification of the Deep Vascular Complex Using Transfer Learning

Purpose

Optical coherence tomography angiography (OCT-A) permits visualization of the changes to the retinal circulation due to diabetic retinopathy (DR), a microvascular complication of diabetes. We demonstrate accurate segmentation of the vascular morphology for the superficial capillary plexus (SCP) and deep vascular complex (DVC) using a convolutional neural network (CNN) for quantitative analysis.

Methods

The main CNN training dataset consisted of retinal OCT-A with a 6 × 6-mm field of view (FOV), acquired using a Zeiss PlexElite. Multiple-volume acquisition and averaging enhanced the vasculature contrast used for constructing the ground truth for neural network training. We used transfer learning from a CNN trained on smaller FOVs of the SCP acquired using different OCT instruments. Quantitative analysis of perfusion was performed on the resulting automated vasculature segmentations in representative patients with DR.

Results

The automated segmentations of the OCT-A images maintained the distinct morphologies of the SCP and DVC. The network segmented the SCP with an accuracy and Dice index of 0.8599 and 0.8618, respectively, and 0.7986 and 0.8139, respectively, for the DVC. The inter-rater comparisons for the SCP had an accuracy and Dice index of 0.8300 and 0.6700, respectively, and 0.6874 and 0.7416, respectively, for the DVC.

Conclusions

Transfer learning reduces the amount of manually annotated images required while producing high-quality automatic segmentations of the SCP and DVC that exceed inter-rater comparisons. The resulting intercapillary area quantification provides a tool for in-depth clinical analysis of retinal perfusion.

Translational Relevance

Accurate retinal microvasculature segmentation with the CNN results in improved perfusion analysis in diabetic retinopathy.

Enhanced Visualization of Retinal Microvasculature in Optical Coherence Tomography Angiography Imaging via Deep Learning

Background: To investigate the effects of deep learning denoising on quantitative vascular measurements and the quality of optical coherence tomography angiography (OCTA) images. Methods: U-Net-based deep learning denoising with an averaged OCTA data set as teacher data was used in this study. One hundred and thirteen patients with various retinal diseases were examined. An OCT HS-100 (Canon inc., Tokyo, Japan) performed a 3 × 3 mm² superficial capillary plexus layer slab scan centered on the fovea 10 times. A single-shot image was defined as the original image and the 10-frame averaged image and denoised image generated from the original image using deep learning denoising for the analyses were obtained. The main parameters measured were the OCTA image acquisition time, contrast-to-noise ratio (CNR), peak signal-to-noise ratio (PSNR), vessel density (VD), vessel length density (VLD), vessel diameter index (VDI), and fractal dimension (FD) of the original, averaged, and denoised images. Results: One hundred and twelve eyes of 108 patients were studied. Deep learning denoising removed the background noise and smoothed the rough vessel surface. The image acquisition times for the original, averaged, and denoised images were 16.6 ± 2.4, 285 ± 38, and 22.1 ± 2.4 s, respectively (P < 0.0001). The CNR and PSNR of the denoised image were significantly higher than those of the original image (P < 0.0001). There were significant differences in the VLD, VDI, and FD (P < 0.0001) after deep learning denoising. Conclusions: The deep learning denoising method achieved high speed and high quality OCTA imaging. This method may be a viable alternative to the multiple image averaging technique.

Human Amniotic Membrane Plug to Restore Age-Related Macular Degeneration Photoreceptor Damage

PURPOSE

Age-related macular degeneration (AMD) is the leading cause of legal blindness in adults 65 years of age and older. Choroidal neovascularization (CNV) can complicate AMD and lead to severe visual acuity reduction. Despite the several treatments available, if the retinal pigment epithelium is damaged, we have to cope with the impossibility of restoring acceptable visual acuity using only medical treatments.

DESIGN

Prospective, consecutive, interventional study.

PARTICIPANTS

Eleven patients affected by AMD, 6 patients affected by CNV, and 5 patients affected by geographic atrophy.

METHODS

All patients underwent a pars plana vitrectomy with subretinal implantation of human amniotic membrane (hAM) to induce photoreceptor regeneration and partial visual acuity restoration.

MAIN OUTCOME MEASURES

Primary study outcome was visual acuity improvement. Secondary outcomes were multimodal imaging results.

RESULTS

Mean preoperative best-corrected visual acuity (BCVA) was 20/2000 (2 logarithm of the minimum angle of resolution [logMAR]), and all the patients showed a BCVA of counting fingers or less. Mean final BCVA was 20/400 (1.31 logMAR), ranging from 20/2000 to 20/100 (2-0.7 logMAR). OCT angiography was used to measure retinal vascularization in the treated eye compared with the fellow eye. A high correlation between BCVA and deep vascular density was evidenced. Adaptive optics findings, obtained over the retinal area where the highest functionality was observed, were evaluated using microperimetry. The images showed possible photoreceptor presence over the hAM membrane.

CONCLUSIONS

This work supports the feasibility and safety of the hAM to promote partial retinal function restoration 6 months after surgery with visual acuity improvement. The advanced diagnostics help to understand the interaction between the hAM and photoreceptors and suggest that photoreceptor regeneration may occur.

Clinically relevant factors associated with quantitative optical coherence tomography angiography metrics in deep capillary plexus in patients with diabetes

Background

To test clinically relevant factors associated with quantitative artifact-free deep capillary plexus (DCP) metrics in patients with diabetes mellitus (DM).

Methods

563 eligible eyes (221 with no diabetic retinopathy [DR], 135 with mild DR, 130 with moderate DR, and 77 with severe DR) from 334 subjects underwent optical coherence tomography-angiography (OCT-A) with a swept-source OCT (Triton DRI-OCT, Topcon, Inc., Tokyo, Japan). Strict criteria were applied to exclude from analysis those DCP images with artifacts and of poor quality, including projection artifacts, motion artifacts, blurriness, signal loss, B-scan segmentation error, or low-quality score. A customized MATLAB program was then used to quantify DCP morphology from the artifact-free DCP images by calculating three metrics: foveal avascular zone (FAZ), vessel density (VD), and fractal dimension (FD).

Results

166 (29.5%) eyes were excluded after quality control, leaving in the analysis 397 eyes (170 with no DR, 101 with mild DR, 90 with moderate DR, 36 with severe DR) from 250 subjects. In the multiple regression models, larger FAZ area was associated with more severe DR (β = 0.687; p = 0.037), shorter axial length (AL) (β = − 0.171; p = 0.003), thinner subfoveal choroid thickness (β = − 0.122; p = 0.031), and lower body mass index (BMI) (β = − 0.090; p = 0.047). Lower VD was associated with more severe DR (β = − 0.842; p = 0.001), shorter AL (β = 0.107; p = 0.039), and poorer visual acuity (VA) (β = − 0.133; p = 0.021). Lower FD was associated with more severe DR (β = − 0.891; p < 0.001) and with older age (β = − 0.142; p = 0.004).

Conclusions

Quantitative artifact-free DCP metrics are associated with VA, DR severity, AL, subfoveal choroidal thickness, age, and BMI in diabetic patients. The effects of ocular and systemic factors should be considered for meaningful interpretations of DCP changes in DM patients.

Retinal Nonperfusion Relationship to Arteries or Veins Observed on Widefield Optical Coherence Tomography Angiography in Diabetic Retinopathy

Purpose

To evaluate whether retinal capillary nonperfusion is found predominantly adjacent to arteries or veins in eyes with diabetic retinopathy (DR).

Methods

Sixty-three eyes from 44 patients with proliferative DR (PDR) or non-PDR (NPDR) were included. Images (12 × 12-mm) foveal-centered optical coherence tomography (OCT) angiography (OCTA) images were taken using the Zeiss Plex Elite 9000. In 37 eyes, widefield montages with five fixation points were also obtained. A semiautomatic algorithm that detects nonperfusion in full-retina OCT slabs was developed, and the percentages of capillary nonperfusion within the total image area were calculated. Retinal arteries and veins were manually traced. Based on the shortest distance, nonperfusion pixels were labeled as either arterial-side or venous-side. Arterial-adjacent and venous-adjacent nonperfusion and the A/V ratio (arterial-adjacent nonperfusion divided by venous-adjacent nonperfusion) were quantified.

Results

Twenty-two eyes with moderate NPDR, 16 eyes with severe NPDR, and 25 eyes with PDR were scanned. Total nonperfusion area in PDR (median: 8.93%) was greater than in moderate NPDR (3.49%, P < 0.01). Arterial-adjacent nonperfusion was greater than venous-adjacent nonperfusion for all stages of DR (P < 0.001). The median A/V ratios were 1.93 in moderate NPDR, 1.84 in severe NPDR, and 1.78 in PDR. The A/V ratio was negatively correlated with the total nonperfusion area (r = −0.600, P < 0.0001). The results from the widefield montages showed similar patterns.

Conclusions

OCTA images with arteries and veins traced allowed us to estimate the nonperfusion distribution. In DR, smaller nonperfusion tends to be arterial-adjacent, while larger nonperfusion tends toward veins.

Association of Retinal Inner Layer Disorganization With Ultra-Widefield Fluorescein Angiographic Features and Visual Acuity in Branch Retinal Vein Occlusion

BACKGROUND AND OBJECTIVE

To assess the impact of the disorganization of retinal inner layers (DRIL) on visual acuity (VA) and its correlation with ischemic index (IsI) on ultra-widefield fluorescein angiography (UWFFA) in eyes with acute, treatment-naïve branch retinal vein occlusion (BRVO).

PATIENTS AND METHODS

Retrospective, longitudinal study of BRVO eyes with 1 year of follow-up or more. Area of intraretinal cysts, DRIL length, extent of disruption of external limiting membrane (ELM), and ellipsoid zone (EZ) were graded on the central 1,000 μm of foveal optical coherence tomography (OCT) scan. Baseline IsI was calculated on UWFFA.

RESULTS

Thirty eyes of 30 patients with a mean follow-up of 25.4 months ± 11.0 months were evaluated. At baseline, 50% had DRIL (mean 443.1 μm ± 460.4 μm). DRIL length at baseline was predictive of worse VA at 12 months (P = .029), and DRIL length at 12 months was predictive of worse final VA(P = .011). In multivariate analyses, DRIL length was associated with final VA (P = .008) after controlling for other OCT parameters. There was no association between baseline IsI on UWFFA and DRIL.

CONCLUSIONS

DRIL served as an independent OCT biomarker predictive of worse VA during a period of 2 years in acute, treatment-naïve BRVO. Development of DRIL was influenced by presence of CME, intraretinal cyst area, and extent of ELM and EZ disruption, but not by severity of baseline IsI. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:354-364.].

Interpretation of OCT and OCTA images from a histological approach: Clinical and experimental implications

Optical coherence tomography (OCT) and OCT angiography (OCTA) have been a technological breakthrough in the diagnosis, treatment, and follow-up of many retinal diseases, thanks to its resolution and its ability to inform of the retinal state in seconds, which gives relevant information about retinal degeneration. In this review, we present an immunohistochemical description of the human and mice retina and we correlate it with the OCT bands in health and pathological conditions. Here, we propose an interpretation of the four outer hyperreflective OCT bands with a correspondence to retinal histology: the first and innermost band as the external limiting membrane (ELM), the second band as the cone ellipsoid zone (EZ), the third band as the outer segment tips phagocytosed by the pigment epithelium (PhaZ), and the fourth band as the mitochondria in the basal portion of the RPE (RPEmitZ). The integrity of these bands would reflect the health of photoreceptors and retinal pigment epithelium. Moreover, we describe how the vascular plexuses vary in different regions of the healthy human and mice retina, using OCTA and immunohistochemistry. In humans, four, three, two or one plexuses can be observed depending on the distance from the fovea. Also, specific structures such as vascular loops in the intermediate capillary plexus, or spider-like structures of interconnected capillaries in the deep capillary plexus are found. In mice, three vascular plexuses occupy the whole retina, except in the most peripheral retina where only two plexuses are found. These morphological issues should be considered when assessing a pathology, as some retinal diseases are associated with structural changes in blood vessels. Therefore, the analysis of OCT bands and OCTA vascular plexuses may be complementary for the diagnosis and prognosis of retinal degenerative processes, useful to assess therapeutic approaches, and it is usually correlated to visual acuity.

Relationship of Geographic Altitude with Foveal Avascular Zone Metrics and Vascular Density Values Assessed by OCT Angiography

PURPOSE

To evaluate variations in vascular density (VD) and foveal avascular zone (FAZ) metrics in relation to geographic altitude in healthy subjects from 6 Latin American cities.

DESIGN

Cross-sectional study.

PARTICIPANTS

Healthy volunteers from 6 Latin American cities.

METHODS

One hundred eighty-five volunteers were recruited over a 3-month period. The RTVue-XR Avanti system (Optovue, Inc, Fremont, CA) was used along with split-spectrum amplitude-decorrelation angiography (SSADA) software 7.1 to obtain OCT angiography (OCTA) images from fovea-centered 3 × 3-mm² and 6 × 6-mm² angioscans for both the superficial and deep capillary plexuses (SCP and DCP, respectively). FAZ measurements were performed in a full retina slab based on the full retina vasculature using OCT angiograms. Analyses of variance were performed for all variables, and P < 0.05 indicated statistical significance.

MAIN OUTCOME MEASURES

Retinal SCP and DCP VD; FAZ area, perimeter, and parafoveal density at 300 μm (FD-300).

RESULTS

Three hundred seventy eyes of 185 participants (71 males and 114 females; mean age, 39.09±15.06 years; age range, 20-80 years) were assessed. The mean VD in the SCP and DCP was 46.94% (±3.11%) and 52.48% (±3.14%), respectively, with 3 × 3-mm² scans and 50.62% (±3.13%) and 52.87% (±5.5%), respectively, with 6 × 6-mm² scans. Mean FAZ area, perimeter, and FD-300 were 0.31 (± 0.11 mm²), 2.18 (± 0.43 mm), and 51.44 (± 3.64%), respectively. Mean SCP VD values in 3 × 3-mm² scans were significantly higher and lower in La Paz and Lima, respectively, compared to those in the other cities (P = 0.001). VD in the 6 × 6 mm² SCP scans, the DCP (all scans), and FAZ metrics showed no significant differences.

CONCLUSIONS

VD showed a direct relationship with geographic altitude in SCP 3 × 3-mm² scans in this group of healthy Hispanic volunteers. These findings indicate that geographic altitude should be accounted for when performing retinal OCTA evaluation of VD values.

Differentiating Veins From Arteries on Optical Coherence Tomography Angiography by Identifying Deep Capillary Plexus Vortices

PURPOSE

To introduce a simple method for differentiating retinal veins from arteries on optical coherence tomography angiography (OCTA).

DESIGN

Cross-sectional pilot study.

METHODS

Four default en face slabs including color depth encoded, grayscale full-thickness retina, superficial plexus, and deep capillary plexus (DCP) from nine 3×3-mm and nine 6×6-mm OCTA scans were exported and aligned. Nine ophthalmologists with minimum OCTA experience from 2 eye institutions were instructed to classify labeled vessels as arteries or veins in 3 stages. Classification was performed based on graders' own assessment at stage 1. Graders were taught that a capillary-free zone was an anatomic feature of arteries at stage 2 and were trained to identify veins originating from vortices within the DCP at stage 3. Grading accuracy was analyzed and correlated with grading time and graders' years in practice.

RESULTS

Overall grading accuracy in stages 1, 2, and 3 was (50.4% ± 17.0%), (75.4% ± 6.0%), and (94.7% ± 2.6%), respectively. Grading accuracy for 3×3-mm scans in stages 1, 2, and 3 was (49.9% ± 16.3%), (79.2% ± 9.6%), and (96.9% ± 3.1%), respectively. Accuracy for 6×6-mm scans in stages 1, 2, and 3 was (51.4% ± 20.8%), (72.3% ± 7.9%), and (93.2% ± 3.3%), respectively. Grading performance improved significantly at each stage (all P < .001). No significant correlation was found between accuracy and time spent grading or between accuracy and years in practice (r = -0.164 to 0.617, all P ≥ .077).

CONCLUSIONS

We describe a simple method for accurately distinguishing retinal arteries from veins on OCTA, which incorporates the use of vortices in the DCP to identify venous origin.

Normative database and determinants of macular vessel density measured by optical coherence tomography angiography

IMPORTANCE

To provide a normative vessel density (VD) database for the macula through swept-source optical coherence tomography angiography (OCTA) and to assess the main determinants of this measurement.

BACKGROUND

In contrast with dye angiography, the recently introduced OCTA technique allows for the non-invasive measurement of retinal and choroidal VD metrics.

DESIGN

Cross-sectional study.

PARTICIPANTS

The right eyes of 346 healthy subjects were studied. In 105 subjects both eyes were imaged.

METHODS

Foveal and parafoveal macular VD measurements were obtained in the retinal superficial capillary plexus (SCP), deep capillary plexus (DCP), and in the choriocapillaris (CC) layer. Also recorded were age, sex, axial length (AL), foveal and choroidal thickness (CT).

MAIN OUTCOME MEASURES

Normative database and determinants of macular VD measured by OCTA.

RESULTS

Mean participant age was 38.3 ± 20.1 years (mean ± SD) (range 5-83). Foveal VDs in the different plexuses were: SCP 22.1% ± 5.0% (7.3-35.1), DCP 19.9% ± 6.3% (6.9-51.2) and CC: 52.8% ± 4.3% (40.2-62.1). Parafoveal VDs ranged from 45.4% ± 3.7% to 51.8% ± 4.6%. Positive correlation was observed between foveal VD and foveal thickness (R = .327), as well as between parafoveal DCP VD and CT (R = .250;P ≤ .006), while correlation with age was negative in the SCP and CC (R = -.283;P < .001). No associations were detected between macular VD and sex or AL (P ≥ .05).

CONCLUSION AND RELEVANCE

Macular VD showed wide individual variation, was positively correlated with foveal thickness and with CT, negatively correlated with age, and showed no correlation with AL or sex.

Distances From Capillaries to Arterioles or Venules Measured Using OCTA and AOSLO

Purpose

To investigate distances from retinal capillaries to arterioles or venules noninvasively.

Methods

An adaptive optics scanning laser ophthalmoscope (AOSLO) and optical coherence tomography angiography (OCTA) imager acquired detailed maps of retinal vasculature. Using OCTA, we quantified the distance from the edge of an arteriole or venule to the middle of the nearest capillaries (periarteriole or perivenule capillary-free zones, respectively) within the superficial vascular plexus of 20 young healthy subjects with normal axial lengths. These distances were compared to AOSLO images for three subjects. We tested the relation between the peripheral capillary-free zones and FAZ horizontal, vertical, effective diameters, and asymmetry indices in the deep vascular plexus. We examined enlargement with OCTA of capillary-free zones in a type 2 diabetic patient.

Results

The periarteriole capillary-free zone (67.2 ± 25.3 μm) was readily visible and larger than the perivenule capillary-free zone (42.7 ± 14.4 μm), F_{(1, 998)} = 771, P < 0.0001. The distance from foveal center (P = 0.003) and diameter (P = 0.048) were predictive of perivenule capillary-free zone values. OCTA and AOSLO corresponded for arterioles. FAZ effective diameter was positively associated with asymmetry indices, r = 0.49, P = 0.028, but not peripheral capillary-free zones, although focal enlargements were found in a diabetic patient.

Conclusions

For normal retinas, periarteriole and perivenule capillary-free zones are readily visible with OCTA and AOSLO. Periarteriole capillary-free zones were larger, consistent with arterioles carrying oxygen rich blood that diffuses to support the retina.