Quantification of Choriocapillaris with Optical Coherence Tomography Angiography: A Comparison Study

Calcified Drusen Prevent the Detection of Underlying Choriocapillaris Using Swept-Source Optical Coherence Tomography Angiography

Purpose

In age-related macular degeneration (AMD), choriocapillaris flow deficits (CCFDs) under soft drusen can be measured using established compensation strategies. This study investigated whether CCFDs can be quantified under calcified drusen (CaD).

Methods

CCFDs were measured in normal eyes (n = 30) and AMD eyes with soft drusen (n = 30) or CaD (n = 30). CCFD density masks were generated to highlight regions with higher CCFDs. Masks were also generated for soft drusen and CaD based on both structural en face OCT images and corresponding B-scans. Dice similarity coefficients were calculated between the CCFD density masks and both the soft drusen and CaD masks. A phantom experiment was conducted to simulate the impact of light scattering that arises from CaD.

Results

Area measurements of CCFDs were highly correlated with those of CaD but not soft drusen, suggesting an association between CaD and underlying CCFDs. However, unlike soft drusen, the detected optical coherence tomography (OCT) signals underlying CaD did not arise from the defined CC layer but were artifacts caused by the multiple scattering property of CaD. Phantom experiments showed that the presence of highly scattering material similar to the contents of CaD caused an artifactual scattering tail that falsely generated a signal in the CC structural layer but the underlying flow could not be detected. Similarly, CaD also caused an artifactual scattering tail and prevented the penetration of light into the choroid, resulting in en face hypotransmission defects and an inability to detect blood flow within the choriocapillaris. Upon resolution of the CaD, the CC perfusion became detectable.

Conclusions

The high scattering property of CaD leads to a scattering tail under these drusen that gives the illusion of a quantifiable optical coherence tomography angiography signal, but this signal does not contain the angiographic information required to assess CCFDs. For this reason, CCFDs cannot be reliably measured under CaD, and CaD must be identified and excluded from macular CCFD measurements.

Improved MRI methods to quantify retinal and choroidal blood flow applied to a model of glaucoma

Purpose

Blood flow (BF) of the retinal and choroidal vasculatures can be quantitatively imaged using MRI. This study sought to improve methods of data acquisition and analysis for MRI of layer-specific retinal and choroidal BF and then applied this approach to detect reduced ocular BF in a well-established mouse model of glaucoma from both eyes.

Methods

Quantitative BF magnetic resonance imaging (MRI) was performed on glaucomatous DBA/2J and normal C57BL/6J mice. Arterial spin labeling MRI was applied to image retinal and choroidal BF using custom-made dual eye coils that could image both eyes during the same scan. Statistics using data from a single eye or two eyes were compared. BF values were calculated using two approaches. The BF rate per quantity of tissue was calculated as commonly done, and the peak BF values of the retinal and choroidal vasculatures were taken. Additionally, the BF rate per retinal surface area was calculated using a new analysis approach to attempt to reduce partial volume and variability by integrating BF over the retinal and choroidal depths.

Results

Ocular BF of both eyes could be imaged using the dual coil setup without effecting scan time. Intraocular pressure was significantly elevated in DBA/2J mice compared to C57BL/6J mice (P<0.01). Both retinal and choroidal BF were significantly decreased in DBA/2J mice in comparison to the age-matched normal C57BL/6J mice across all measurements (P < 0.01). From simulations, the values from the integrated BF analysis method had less partial volume effect, and from in vivo scans, this analysis approach also improved power.

Conclusion

The dual eye coil setup allows bilateral eye data acquisition, increasing the amount of data acquired without increasing acquisition times in vivo. The reduced ocular BF found using the improved acquisition and analysis approaches replicated the results of previous studies on DBA/2J mice. The ocular hypertensive stress-induced BF reduction found within these mice may represent changes associated with glaucomatous progression.

Retinal Vessel Analysis and Microvascular Abnormalities in Patients with Philadelphia-Negative Chronic Myeloproliferative Neoplasms

Background: Philadelphia-negative chronic myeloproliferative neoplasms are a group of clonal hematopoietic disorders including polycythemia vera, essential thrombocythemia, and primary myelofi-brosis. These neoplasms are characterized by an increased risk of thrombotic complications. Several studies have highlighted that the study of vessels of the retina offers the opportunity to visualize, in vivo, the damage to microcirculation that is common in various systemic pathologies. Methods: in our study, forty patients underwent an ophthalmological examination, using non-invasive imaging tech-niques, for analyses of their retinal vascularization. The objective was to correlate the findings ob-tained from this study of the retina with different markers of thrombotic risk, to demonstrate the usefulness of studying retinal vessels as a possible new prognostic biomarker of thrombotic risk in patients affected by Philadelphia-negative chronic myeloproliferative neoplasms. Results: retinal imaging demonstrated changes in the microcirculation, with a reduced vascular density of the deep and superficial capillary plexuses with respect to a normal group, and a correlation between retinal changes and blood parameters. Conclusions: additional research will allow us to determine whether retinal changes in individuals with chronic myeloproliferative neoplasms could be predictive of the development of thrombotic events in these subjects.

Impact of slab selection on the relationship between choriocapillaris flow deficits and enlargement rate of geographic atrophy

OBJECTIVE

To evaluate the effect of changing slab position on the correlation between choriocapillaris (CC) flow deficits (FD) in eyes with geographic atrophy (GA) and yearly enlargement rate (yER) of GA.

METHODS

OCT and OCTA images obtained on Cirrus HD-OCT device were collected from patients with GA. Each patient underwent OCTA scan at baseline and two OCT scans, one at baseline and one after at least 12 months. GA was delineated on en-face fundus image to calculate yER. OCTA images were generated from three 10 µm thick slabs 11, 21 and 31 µm posterior to RPE-fit line. 100 µm-wide concentric rings were generated around GA to calculate FD% in each ring which was correlated with yER.

RESULTS

For the 11-21 µm slab, FD% was not significantly correlated with yER for any of the rings (p > 0.05). For the 21-31 and 31-41 µm slab, FD% of rings located in the 600 µm region around GA was significantly correlated with yER (p < 0.05). However, in all slab locations, there was no significant correlation between yER and CC FD% of rings located beyond the 600 µm region (p > 0.05).

CONCLUSIONS

Slab selection for quantification of CC FD% may have a significant impact on quantitative results in eyes with GA.

Flow Void Analysis Using Different Thresholding Methods on a Choriocapillaris Optical Coherence Tomography Angiography Image Complemented with a Structural En Face Image

PURPOSE

To investigate the flow characteristics using different thresholding methods on a choriocapillaris optical coherence tomography angiography (OCTA) image complemented with a structural En Face image.

METHODS

The 42 choriocapillaris OCTA images from healthy subjects were obtained with swept-source OCTA device and the 3 × 3-mm area OCTA images were processed with ImageJ. Using a raw choriocapillaris OCTA image and structural En Face image, we adjusted the different structural signal intensity. Then, the raw images and adjusted images were binarized with a global threshold and an auto local threshold using the Phansalkar method at 1- or 2-intercapillary distance. Then, the mean area, number, and size of the flow void, were compared among the images using different thresholding methods.

RESULTS

Mean flow void area, number, and size were different according to the different binarization method both in raw and adjusted images (all p < 0.001). The mean flow void area analyzed with global threshold method were well correlated with those with auto local threshold method both in raw and adjusted images (all intraclass correlations, >0.929).

CONCLUSIONS

Flow void features varied according to the different binarization methods but showed good correlation. The flow void characteristics according to the different binarization methods should be considered for the analysis of the choriocapillaris OCTA images complemented with a structural En Face image.

The Impact of Carotid Endarterectomy on Choriocapillaris Perfusion

Purpose

The impact of carotid endarterectomy (CEA) on choriocapillaris (CC) perfusion was investigated using swept-source optical coherence tomography angiography (SS-OCTA) imaging before and after surgery in patients with clinically significant carotid artery stenosis (CAS).

Methods

In this prospective observational study, patients with clinically significant CAS undergoing unilateral CEA had SS-OCTA imaging performed in both eyes before and within 1 week after surgery. The percent CC flow deficits (CC FD%) and CC thickness were assessed using previously validated algorithms. Multivariable regression analysis was conducted to evaluate the impact of variables on the change in CC measurements.

Results

A total of 112 eyes from 56 patients with an average age of 72.6 ± 6.9 years were enrolled. At baseline, significantly higher CC FD% and thinner CC thickness were observed on the surgical side (eyes ipsilateral to the side of CEA) versus the nonsurgical side (eyes contralateral to the side of CEA) (P = 0.001 and P = 0.03, respectively). Following CEA, a significant reduction in CC FD% and a significant increase in CC thickness were detected on the surgical as compared with the nonsurgical side (P = 0.008 and P = 0.01, respectively). Smoking status positively affected CC FD% change (coefficient of variation [CV] = 0.84, P = 0.01) on the surgical side and negatively affected CC thickness change on both the surgical side (CV = -0.382, P = 0.009) and the nonsurgical side (CV = -0.321, P = 0.04). The degree of stenosis demonstrated a positive influence on CC FD% change (CV = 0.040, P = 0.02) on the surgical side.

Conclusions

Unilateral CEA on the side of clinically significant CAS increases carotid blood flow, which further results in improved CC perfusion.

Choriocapillaris flow deficit and the risk of referable diabetic retinopathy: a longitudinal SS-OCTA study

AIMS

To investigate the association between the choriocapillaris flow deficit percentage (CC FD%) and the 1-year incidence of referable diabetic retinopathy (RDR) in participants with type 2 diabetes mellitus (DM).

METHODS

This prospective cohort study included participants with type 2 DM. The DR status was graded based on the ETDRS-7 photography. The CC FD% in the central 1 mm area, inner circle (1.5 mm to 2.5 mm), outer circle (2.5 mm to 5.0 mm) and the entire area in the macular region were measured using swept-source optical coherence tomography angiography (SS-OCTA). Logistic regression analysis was used to examine the association between baseline CC FD% and 1-year incident RDR.

RESULTS

A total of 1222 patients (1222 eyes, mean age: 65.1±7.4 years) with complete baseline and 1-year follow-up data were included. Each 1% increase in baseline CC FD% was significantly associated with a 1.69 times (relative risk 2.69; 95% CI 1.53 to 4.71; p=0.001) higher odds for development of RDR after 1-year follow-up, after adjusting for other confounding factors.

CONCLUSIONS

A greater baseline CC FD% detected by SS-OCTA reliably predicted higher risks of RDR in participants with type 2 DM. Thus, CC FD% may act as a novel biomarker for predicting the onset and progression of DR.

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.

Decreased Central Macular Choriocapillaris Perfusion Correlates With Increased Low Luminance Visual Acuity Deficits

PURPOSE

Correlations between low luminance visual acuity deficits (LLVADs) and central choriocapillaris perfusion deficits were investigated to help explain how increases in LLVAD scores at baseline predict annual growth rates of geographic atrophy (GA).

DESIGN

Prospective cross-sectional study.

METHODS

Photopic luminance best-corrected visual acuity (PL-BCVA) and low luminance BCVA (LL-BCVA) were measured using the Early Treatment Diabetic Retinopathy Study chart. LL-BCVA was measured using a 2.0-log unit neutral density filter. LLVADs were calculated as the difference between PL-BCVA and LL-BCVA. Within a fovea-centered 1-mm circle, the percentage of choriocapillaris flow deficits (CC FD%), drusen volume, optical attenuation coefficient (OAC) elevation volume, and outer retinal layer (ORL) thickness were assessed.

RESULTS

In all 90 eyes (30 normal eyes; 31 drusen-only eyes; 29 non-foveal GA eyes), significant correlations were found between the central CC FD% and PL-BCVA (r = -0.393, P < .001), LL-BCVA (r = -0.534, P < .001), and the LLVAD (r = 0.439, P < .001). Central cube root (cubrt) drusen volume, cubrt OAC elevation volume, and ORL thickness were correlated with PL-BCVA, LL-BCVA, and LLVADs (all P < .05). Stepwise regression models showed that central cubrt OAC elevation volume and ORL thickness were associated with PL-BCVA (R2 = 0.24, P < .05); central CC FD%, cubrt OAC elevation volume, and ORL thickness were associated with LL-BCVA (R2 = 0.44, P < .01); and central CC FD% and ORL thickness were associated with LLVAD (R2 = 0.24, P < .01).

CONCLUSIONS

The significant correlations between central CC FD% and LLVAD support the hypothesis that the ability of LLVAD to predict the growth of GA is mediated through a decrease in macular choriocapillaris perfusion.

Quantitative assessment of choriocapillaris flow deficits and type 1 macular neovascularization growth in age-related macular degeneration

During the past 15 years, new treatment paradigms for neovascular age-related macular degeneration (nvAMD) have evolved due to the advent of intravitreal anti-vascular endothelial growth factor (VEGF) therapy and rapid advances in retinal imaging. Recent publications describe eyes with type 1 macular neovascularization (MNV) as showing more resistance to macular atrophy than eyes with other lesion types. We sought to explore whether the perfusion status of the native choriocapillaris (CC) surrounding type 1 MNV influences its pattern of growth. To evaluate this effect, we analyzed a case series of 22 eyes from 19 nvAMD patients with type 1 MNV exhibiting growth on swept-source optical coherence tomography angiography (SS-OCTA) over a minimum follow-up of 12 months. We observed an overall weak correlation between type 1 MNV growth and CC flow deficits (FDs) average size (τ = 0.17, 95% CI [- 0.20, 0.62]) and a moderate correlation with CC FD % (τ = 0.21, 95% CI [- 0.16, 0.68]). Type 1 MNV was located beneath the fovea in most of the eyes (86%) and median visual acuity was 20/35 Snellen equivalent. Our results support that type 1 MNV recapitulates areas of CC blood flow impairment while serving to preserve foveal function.

Decreased Macular Choriocapillaris Perfusion in Eyes With Macular Reticular Pseudodrusen Imaged With Swept-Source OCT Angiography

Purpose

To determine if macular reticular pseudodrusen (RPD) were associated with markers of impaired macular choroidal perfusion, we investigated measurements of macular choriocapillaris (CC) flow deficits (FDs), CC thickness, and mean choroidal thickness (MCT) in eyes with macular RPD compared with normal eyes and eyes with soft drusen.

Methods

Eyes with intermediate age-related macular degeneration (iAMD) and normal eyes underwent 6 × 6 mm swept-source optical coherence tomography angiography (SS-OCTA) imaging to diagnose macular RPD, occupying over 25% of the fovea-centered 5 mm diameter circle, and measure outer retinal layer (ORL) thickness, CC FDs, CC thickness, MCT, and choroidal vascularity index (CVI) using previously published strategies within the same fovea-centered 5 mm circle.

Results

Ninety eyes were included; 30 normal eyes, 30 eyes with soft drusen, and 30 eyes with macular RPD. The RPD eyes showed higher macular CC FDs than normal eyes (P < 0.001) and soft drusen eyes (P = 0.019). Macular CC thickness was decreased in RPD eyes compared with normal eyes (P < 0.001) and soft drusen eyes (P = 0.016). Macular MCT in RPD eyes was thinner than normal eyes (P = 0.005) and soft drusen eyes (P < 0.001). No statistically and clinically significant differences were found in the ORL thickness and CVI measurements between RPD eyes and the other two groups (all P > 0.05).

Conclusions

Eyes with macular RPD had decreased macular CC perfusion, decreased CC thickness, and decreased MCT measurements compared with normal and soft drusen eyes, suggesting that RPD may result from impaired choroidal perfusion.

Choriocapillaris Flow Signal Impairment in Patients With Pseudoxanthoma Elasticum

Purpose

To quantify choriocapillaris flow alterations in patients with pseudoxanthoma elasticum (PXE) in pre-atrophic stages and its association with structural changes of the choroid and outer retina.

Methods

Thirty-two eyes of 21 patients with PXE and 35 healthy eyes of 35 controls were included. The density of choriocapillaris flow signal deficits (FDs) was quantified on 6 × 6-mm optical coherence tomography angiography (OCTA) images. Spectral-domain optical coherence tomography (SD-OCT) images were analyzed for thicknesses of the choroid and outer retinal microstructure and correlated with choriocapillaris FDs in the respective Early Treatment Diabetic Retinopathy Study subfield.

Results

The multivariable mixed model analysis for choriocapillaris FDs revealed significantly higher FDs associated with the group (PXE patients vs. controls +13.6; 95% confidence interval [CI] 9.87-17.3; P < 0.001), with increasing age (+0.22% per year; 95% CI 0.12-0.33; P < 0.001), and with retinal location (significantly higher FDs in nasal compared to temporal subfields). Choroidal thickness (CT) did not differ significantly between both groups (P = 0.078). The CT and choriocapillaris FDs were inversely correlated (-1.92 µm per %FDs; interquartile range -2.81 to -1.03; P < 0.001). Larger values of the choriocapillaris FDs were associated with significant thinning of the overlying photoreceptor layers (outer segments: -0.21 µm per %FDs, P < 0.001; inner segments: -0.12 µm per %FDs, P = 0.001; outer nuclear layer: -0.72 µm per %FDs; P < 0.001).

Conclusions

Patients with PXE display significant alterations of the choriocapillaris on OCTA even in pre-atrophic stages and in the absence of significant choroidal thinning. The analysis favors choriocapillaris FDs over choroidal thickness as a potential early outcome measure for future interventional trials in PXE. Further, increased FDs in nasal compared to temporal locations mirror the centrifugal spread of Bruch's membrane calcification in PXE.

The synergy of synchrotron imaging and convolutional neural networks towards the detection of human micro-scale bone architecture and damage

The growing health and economic burden of bone fractures, their intricate multiscale features and the existing knowledge gaps in the comprehension of micro-scale bone damage occurrence make fracture diagnosis a challenging issue. In this scenario, deep-learning and artificial intelligence embody the new frontier of healthcare system, by overcoming the subjectivity of clinicians in the analysis of medical images. However, the preliminary attempts in exploiting the power of machine learning algorithms such as neural networks are still limited to bone macro-scale, while there is an evident lack in their application to smaller scales, where damage starts nucleating. Currently, speculations at the micro-scale are only feasible with the aid of high-resolution imaging techniques, that are particularly time consuming in terms of output images analysis. In this context, this works aims at combining the visualization of the micro-crack propagation mechanism with the promising application of convolutional neural networks. The implemented artificial intelligence tool is based for the first time on a large number of human synchrotron images coming from healthy and osteoporotic femoral heads tested under micro-compression. The designed convolutional neural networks are able to automatically detect lacunae and micro-cracks at different compression levels with high accuracy levels; indeed, with the baseline setup, networks achieve more than 0.99 level of accuracy for both cracks and lacunae, and more than 0.87 of the meanIoU adopted as validation metric. This approach is particularly encouraging for the development of powerful recognition system to comprehend bone micro-damage initiation and propagation, paving the way to the application of machine learning studies to bone micromechanics. This could be additionally crucial for future patient specific micro-scale observations to be related to the clinical practice.

Impact of Reticular Pseudodrusen on Choriocapillaris Flow Deficits and Choroidal Structure on Optical Coherence Tomography Angiography

PURPOSE

To examine the impact of reticular pseudodrusen (RPD) on choriocapillaris blood flow and choroidal structure in individuals with intermediate age-related macular degeneration (AMD).

METHODS

Individuals with bilateral large drusen underwent optical coherence tomography (OCT), color fundus photography, near-infrared reflectance, and fundus autofluorescence imaging to determine the presence of RPD. These participants also underwent swept-source OCT angiography (SS-OCTA) imaging to determine (1) choriocapillaris flow deficit (FD) parameters, including the percentage, mean size, and number of FDs present; and (2) choroidal structural parameters, including mean choroidal thickness and choroidal vascularity index. Differences in these parameters between eyes with and without coexistent RPD were examined with and without adjustment for potential key confounders such as drusen volume from the SS-OCTA scans and age.

RESULTS

This study included 102 eyes from 51 individuals with bilateral large drusen, and the analyses showed that there were no significant differences in the choriocapillaris FD parameters (P ≥ 0.062 for all) and choroidal structural parameters (P ≥ 0.059 for all), with or without adjustment for potential confounders in this cohort. However, the percentage of FDs and the mean FD size were both significantly greater with increasing drusen volume (P ≤ 0.038 for both).

CONCLUSIONS

The coexistence of RPD in eyes of individuals with intermediate AMD was not associated with significant impairments in choriocapillaris blood flow and choroidal vascular structural changes, with or without adjustment for key confounders. These findings suggest that macular changes in these vascular parameters may not be associated with the presence of RPD.

Analysis of Structured Data in Biomedicine Using Soft Computing Techniques and Computational Analysis

In the field of biomedicine, enormous data are generated in a structured and unstructured form every day. Soft computing techniques play a major role in the interpretation and classification of the data to make appropriate decisions for making policies. The field of medical science and biomedicine needs efficient soft computing-based methods which can process all kind of data such as structured data, categorical data, and unstructured data to generate meaningful outcome for decision-making. The soft-computing methods allow clustering of similar data, classification of data, predictions from big-data analysis, and decision-making on the basis of analysis of data. A novel method is proposed in the paper using soft-computing methods where clustering mechanisms and classification mechanisms are used to process the biomedicine data for productive outcomes. Fuzzy logic and C-means clustering are devised as a collaborative approach to analyze the biomedicine data by reducing the time and space complexity of the clustering solutions. This research work is considering categorical data, numeric data, and structured data for the interpretation of data to make further decisions. Timely decisions are very important especially in the field of biomedicine because human health and human lives are involved in this field and delays in decision-making may cause threats to human lives. The COVID-19 situation was a recent example where timely diagnosis and interpretations played significant roles in saving the lives of people. Therefore, this research work has attempted to use soft computing techniques for the successful clustering of similar medical data and for quicker interpretation of data to support the decision-making processes related to medical fields.

The Impact of Image Processing Algorithms on Optical Coherence Tomography Angiography Metrics and Study Conclusions in Diabetic Retinopathy

Purpose

The purpose of this study was to evaluate the impact of image processing on quantitative metrics in optical coherence tomography angiography (OCTA) images and study conclusions in patients with diabetes.

Methods

This was a single center, retrospective cross-sectional study. OCTA imaging with the Cirrus HD-OCT 5000 AngioPlex of patients with diabetes was performed. The 8 × 8 mm superficial slab images underwent 4 different preprocessing methods (none, background subtraction [BGS], foveal avascular zone brightness adjustment, and contrast limited adaptive histogram equalization [CLAHE]) followed by 4 different binarization algorithms (global Huang, global Otsu, local Niblack, and local Phansalkar) in ImageJ. Vessel density (VD), skeletonized VD (SVD), and fractal dimension (FD) were calculated. Mixed-effect multivariate linear regressions were performed.

Results

Two hundred eleven scans from 104 patients were included. Of these scans, 67 (31.8%) had no diabetic retinopathy (DR), 99 (46.9%) had nonproliferative DR (NPDR), and 45 (21.3%) had proliferative DR (PDR). Forty-eight of 211 (22.7%) scans had diabetic macular edema (DME). The image processing method used significantly impacted values of VD, SVD, and FD (all P -values < 0.001). On multivariate analysis, the image processing method changed the clinical variables significantly associated with VD, SVD, and FD. However, BGS and CLAHE yielded more consistent significant covariates across multiple binarization algorithms.

Conclusions

The image processing method can impact the conclusions of any given study analyzing quantitative OCTA metrics. Thus, caution is urged in the interpretation of such studies. Background subtraction or CLAHE may play a role in the standardization of image processing.

Translational Relevance

This work proposes strategies to achieve robust and consistent analysis of OCTA imaging, which is especially important for clinical trials.

Computerized Texture Analysis of Optical Coherence Tomography Angiography of Choriocapillaris in Normal Eyes of Young and Healthy Subjects

Computerized texture analysis uses higher-order mathematics to identify patterns beyond what the naked eye can recognize. We tested its feasibility in optical coherence tomography angiography imaging of choriocapillaris. Our objective was to determine sets of parameters that provide coherent and consistent output when applied to a homogeneous, healthy group of patients. This observational cross-sectional study involved 19 eyes of 10 young and healthy Caucasian subjects. En-face macular optical coherence tomography angiography of superficial choriocapillaris was obtained by the RTVue-XR Avanti system. Various algorithms were used to extract texture features. The mean and standard deviation were used to assess the distribution and dispersion of data points in each metric among eyes, which included: average gray level, gray level yielding 70% threshold and 30% threshold, balance, skewness, energy, entropy, contrast, edge mean gradient, root-mean-square variation, and first moment of power spectrum, which was compared between images, showing a highly concordant homology between all eyes of participants. We conclude that computerized texture analysis for en-face optical coherence tomography angiography images of choriocapillaris is feasible and provides values that are coherent and tightly distributed around the mean in a homogenous, healthy group of patients. Homology of blob size among subjects may represent a “repeat pattern” in signal density and thus a perfusion in the superficial choriocapillaris of healthy young individuals of the same ethnic background.

Quantitative Analysis of Choriocapillaris Using Swept-Source Optical Coherence Tomography Angiography in Eyes with Angioid Streaks

Purpose: to quantitatively analyze choriocapillaris perfusion using swept-source optical coherence tomography angiography (SS-OCTA) in eyes presenting with angioid streaks in comparison with control eyes. Methods: Macular 6 × 6 mm SS-OCTA scans were retrospectively analyzed in eyes with angioid streaks and in control eyes. En face choriocapillaris flow images were compensated with en face choriocapillaris structure images, followed by the Phansalkar local thresholding method (with a window radius of four and eight pixels). Quantitative analysis was performed in the four peripheral 1 × 1 mm corners of the 6 × 6 mm SS-OCTA image to include equidistant and comparable regions. The percentage of flow deficits (FD%), the number and size of the flow deficits (FDs) and the total area of FDs were then calculated. Results: 54 eyes of 31 patients were included in the study: 27 eyes diagnosed with angioid streaks and 27 controls. Analysis of the four 1 × 1 mm peripheral corners of the 6 × 6 mm SS-OCTA image showed that eyes with angioid streaks had a higher FD% compared to the control group (47.62 ± 8.06 versus 38.90 ± 6.38 using a radius of four pixels (p < 0.001); 48.37 ± 7.65 versus 39.66 ± 6.51 using a radius of eight pixels (p < 0.001). The average size of FDs as well as the total area size of the FDs were significantly higher in eyes with angioid streaks compared to control eyes (p < 0.001). Eyes with angioid streaks present reduced choriocapillaris flow compared to control eyes. Decreased choriocapillaris perfusion may contribute, among other factors, to the development of neovascularization and atrophy in patients with angioid streaks.

Optical coherence tomography angiography quantification of choriocapillaris blood-flow after half-fluence photodynamic therapy for chronic central serous chorioretinopathy

PURPOSE

To quantitatively analyze characteristics of choriocapillaris flow using spectral domain optical coherence tomography angiography (SD-OCTA) in eyes with chronic central serous chorioretinopathy (CSC) before and after treatment by photodynamic therapy (PDT).

METHODS

Retrospective interventional study. Macular 3X3 SD-OCT scans were analyzed in eyes diagnosed with chronic CSC before and after treatment with half-fluence PDT. The choriocapillaris en face slabs were extracted from the SD-OCTA device after manual segmentation. En face choriocapillaris flow images were compensated with en face choriocapillaris structure images. Phansalkar local thresholding method was then used with a radius of 4 and 8 pixels. Percentage of flow deficits (FD%), number, size, and total area of FDs were computed for comparison, before and after treatment by half-fluence PDT.

RESULTS

Mean choriocapillaris FD% before PDT was of 58.36 + / - 11.88 and of 60.82 + / - 11.08 after PDT using radius 4 pixels with no significant difference (p = 0.140). Mean choriocapillaris FD% was of 58.63 + / - 11.08 before PDT and of 60.87 + / - 10.36 after PDT using radius 8 pixels with no significant difference (p = 0.200). Similarly, no significative difference was found in number, size, and total area of FDs, before and after half-fluence PDT, using radius 4 and 8 pixels in patients with chronic CSC.

CONCLUSION

Using Phansalkar local thresholding method, quantitative analysis of choriocapillaris with SD-OCTA found no significant change in choriocapillaris flow deficits before and after successful half-fluence PDT in patients with chronic CSC. Therefore, it seems that half-fluence PDT may not alter choriocapillaris perfusion, at least on a relative short-term basis.

Choriocapillaris Flow Deficits in Normal Chinese Imaged by Swept-Source Optical Coherence Tomographic Angiography

PURPOSE

To evaluate the ocular and systemic determinants of the choriocapillaris flow deficits percentage (CC FD%) in normal eyes.

DESIGN

Observational cross-sectional study.

METHODS

Healthy Chinese participants without ocular or systemic diseases underwent detailed ophthalmic evaluations, including swept-source optical coherence tomography angiography (SS-OCTA) with 6- × 6-mm macular choriocapillaris images. The CC FD% was assessed in circular regions with diameters of 1.0 and 5.0 mm, rings with 1.0- to 2.5-mm diameters, and rings with 2.5- to 5.0-mm diameters.

RESULTS

The study included 830 individuals (mean ± SD age 58.66 ± 8.75 years). CC FD% (mean ± SD 22.05% ± 1.13%) was the lowest in the 2.5- to 5.0-mm ring, followed by the 1.0- to 2.5-mm ring, and highest in the 1.0-mm circle. In multivariable analysis, a higher CC FD% was associated with older age (β = 0.16 [95% confidence interval {CI}] 0.08-0.24, P < .001), higher intraocular pressure (β = 0.34 [95% CI 0.25-0.42], P < .001), higher serum concentrations of high-density lipoprotein cholesterol (β = 0.24 [95% CI 0.17-0.32], P < .001), and lower image quality score (β = -0.22 [95% CI -0.30 to -0.14], P < .001). CC FD% was also independent of axial length.

CONCLUSIONS

In healthy adult Chinese individuals, a higher CC FD% was associated with older age, higher intraocular pressure, and higher high-density lipoprotein cholesterol serum concentration. These factors may influence clinical assessments of the choriocapillaris. The lack of an association between CC FD% and axial length is consistent with similar findings for Bruch membrane thickness, macular retinal thickness, and macular retinal pigment epithelium cell density.

Combining retinal and choroidal microvascular metrics improves discriminative power for diabetic retinopathy

PURPOSE

To use optical coherence tomography angiography (OCTA) parameters from both the retinal and choroidal microvasculature to detect the presence and severity of diabetic retinopathy (DR).

METHOD

This is a cross-sectional case-control study. OCTA parameters from retinal vasculature, fovea avascular zone (FAZ) and choriocapillaris were evaluated from 3×3 mm² fovea-centred scans. Areas under the receiver operating characteristic (ROC) curve were used to compare the discriminative power on the presence of diabetes mellitus (DM), the presence of DR and need for referral: group 1 (no DM vs DM no DR), group 2 (no DR vs any DR) and group 3 (non-proliferative DR (NPDR) vs proliferative DR (PDR)).

RESULTS

35 eyes from 27 participants with no DM and 132 eyes from 75 with DM were included. DR severity was classified into three groups: no DR group (62 eyes), NPDR (51 eyes), PDR (19 eyes). All retinal vascular parameters, FAZ parameters and choriocapillaris parameters were strongly altered with DR stages (p<0.01), except for the deep plexus FAZ area (p=0.619). Choriocapillaris parameters allowed to better discriminate between no DM versus DM no DR group compared with retinal parameters (areas under the ROC curve=0.954 vs 0.821, p=0.006). A classification model including retinal and choroidal microvasculature significantly improved the discrimination between DR and no DR compared with each parameter separately (p=0.029).

CONCLUSIONS

Evaluating OCTA parameters from both the retinal and choroidal microvasculature in 3×3 mm scans improves the discrimination of DM and early DR.

OCTAVA: An open-source toolbox for quantitative analysis of optical coherence tomography angiography images

Optical coherence tomography angiography (OCTA) performs non-invasive visualization and characterization of microvasculature in research and clinical applications mainly in ophthalmology and dermatology. A wide variety of instruments, imaging protocols, processing methods and metrics have been used to describe the microvasculature, such that comparing different study outcomes is currently not feasible. With the goal of contributing to standardization of OCTA data analysis, we report a user-friendly, open-source toolbox, OCTAVA (OCTA Vascular Analyzer), to automate the pre-processing, segmentation, and quantitative analysis of en face OCTA maximum intensity projection images in a standardized workflow. We present each analysis step, including optimization of filtering and choice of segmentation algorithm, and definition of metrics. We perform quantitative analysis of OCTA images from different commercial and non-commercial instruments and samples and show OCTAVA can accurately and reproducibly determine metrics for characterization of microvasculature. Wide adoption could enable studies and aggregation of data on a scale sufficient to develop reliable microvascular biomarkers for early detection, and to guide treatment, of microvascular disease.

Mapping of choriocapillaris vascular density in young and aged healthy subjects

PURPOSE

To compare macular vascular density (VD) of the choriocapillaris (CC) between young and aged healthy individuals.

METHODS

A cross-sectional study was performed enrolling young and senior healthy individuals of Caucasian race and an axial length (AL) lower than 26 mm, and without systemic or ophthalmological diseases. CC VD was imaged with DRI Triton OCTA using a 6 × 6 mm macular analysis. Internal software delimited CC boundaries and gave colour pictures, which were analysed and codified into numbers, and a grid of 30 × 30 VD values was obtained. Two-dimension (2D) and three-dimension (3D) representations were created.

RESULTS

53 eyes of 53 young healthy individuals and 30 eyes of 30 senior healthy individuals were enrolled. Mean age was 27.17 ± 3.90 years, and 67.00 ± 7.41 years, respectively (p < 0.001). There were no differences in intraocular pressure (IOP) or AL (23.73 ± 0.79 mm, 23.18 ± 0.80 mm, respectively, p = 0.24). There were differences in foveal VD and in temporal perifoveal macula, but not in nasal perifoveal macula. Foveal VD was the highest in both groups.

CONCLUSIONS

Foveal CC VD has been found to be considerably high with this method, and it is the area which most decreases with age. Nasal perifoveal VD is not reduced in older individuals. These outcomes are opposite to other studies using different methods but they are in line with previous histological findings.

The characteristics of choriocapillaris flow void in the unilateral polypoidal choroidal vasculopathy fellow eyes

To evaluate the morphological characteristics of flow void (FV) in the fellow eyes of the unilateral polypoidal choroidal vasculopathy (PCV). Fifty PCV fellow eyes (PCVF) and 31 age-matched normal ocular circulation controls were recruited in this retrospective study. The number of FV was analyzed according to the size in a centered 5 × 5 mm swept source optical coherence tomography angiography scans. We used indocyanine green angiography images to determine whether choroidal vascular hyperpermeability (CVH) has occurred. For the PCVF, the prevalence rate of CVH was 70% (35 of 50) The number of FVs was significantly lower in 400-25,000 μm2 (P = 0.005), 400-500 μm2 (P = 0.001), 525-625 μm2 (P = 0.001) and 650-750 μm2 (P = 0.018). compared to the controls. And showed no difference in size from 775 to 1125 μm2 between the two groups. The area under the receiver operating characteristic curve of PCVF with CVH and controls was 0.94 (95% CI 0.88-1.00) (P < 0.001). We found that the number of small FVs was significantly lower in the PCV fellow eyes than that in the eyes with control group.

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 .

Progression of choriocapillaris flow deficits in clinically stable intermediate age-related macular degeneration

PURPOSE

To evaluate the choriocapillaris (CC) flow deficit (FD) in eyes with stable intermediate age-related macular degeneration (AMD) eyes over 12 months of follow-up.

METHODS

Thirty four patients with intermediate AMD were prospectively enrolled and evaluated by swept-source optical coherence tomography (SS-OCT) and OCT-angiography (OCTA) using the PLEX-Elite 9000. A 6 × 6 mm foveal-centered scan was used for both modalities and the study eyes were scanned twice to allow subsequent averaging. En face OCTA CC slabs (31-41 µm below the RPE-band) were exported and compensated for signal attenuation. Two compensated CC en-face images were registered and averaged prior to binarization and CC FD computation. The CC FD of the entire 6 × 6 macular region was quantified at baseline and at 12-months. The presence of high-risk features, namely intraretinal hyper-reflective foci (HRF), subretinal drusenoid deposits (SDD), and hyporeflective-core-drusen, were evaluated using SS-OCT volume scans.

RESULTS

Among the 34 eyes, 25 eyes from 25 patients were noted on exam and OCT to remain stable as intermediate AMD at 12-months without the development of late AMD. Eleven eyes had high-risk features at baseline compared to 14 eyes at the end of the follow-up (p = 0.094). The mean ± SD FD% across the whole 6 × 6 macular region at baseline was 19.32 ± 4.64% and significantly increased to 28.62 ± 4.71% at the end of the study (p = 0.001). The CC FD progressed significantly both in non-HR and HR-eyes.

CONCLUSIONS

Choriocapillaris flow impairment significantly deteriorated over one year in relatively stable intermediate AMD. This might suggest that underlying progression of CC dysfunction occurs before structural changes appears on OCT and lead to the progression to late-stage AMD.

Choroidal Blood Flow After Intravitreal Ranibizumab in Vitrectomized and Non-Vitrectomized Eyes with Diabetic Macular Edema

Aim

Diabetic retinopathy staging system and progression predictors are soon to be considered insufficient for ophthalmologic practice. Given the growing evidence of the role of choroidal dysfunction, our purpose was to assess choroidal vascular changes with intravitreal ranibizumab (RBZ) treatment in diabetic macular edema (DME).

Methods

This was a prospective longitudinal cohort study. The study included DME eyes, grouped in vitrectomized (group 1) and non-vitrectomized (group 2) eyes, submitted to RBZ in a pro re nata regimen, with 24 weeks of follow-up. Main outcome measures such as central subfield foveal thickness (CFT), choroidal thickness (CT), and choroidal vascular index (CVI) were obtained from structural OCT, and choriocapillaris flow density (CCD) was obtained from OCT angiography and analyzed before and after treatment.

Results

Thirty-one patients were included, 10 eyes in group 1 and 24 eyes in group 2. The mean number of injections was 5.18 (range 2–6). Globally, there was an improvement in BCVA (+4.3 ETDRS letters, p=0.004) and CFT (−84.6 µm, p<0.001) with no changes in CT, CVI, or CCD (p>0.05). When considering only group 2, there was a significant decrease in CT (p=0.033) and a significant increase in CCD (p=0.010) 6 months after treatment, with no differences in CVI (p=0.111). Baseline CVI was correlated with visual acuity at week 24 both globally (r=0.406, p=0.029) and in group 2 (r=0.604, p=0.004).

Conclusion

In non-vitrectomized eyes, choriocapillaris blood flow improves with RBZ. Baseline CVI may correlate with visual function after RBZ. ClinicalTrials.gov NCT04387604.

CHORIOCAPILLARIS FLOW IMPAIRMENT IN TYPE 3 MACULAR NEOVASCULARIZATION: A Quantitative Analysis Using Swept-Source Optical Coherence Tomography Angiography

PURPOSE

To quantitatively analyze choriocapillaris alterations using swept-source optical coherence tomography angiography in eyes presenting with Type 3 macular neovascularization (MNV) and to compare these alterations with eyes presenting with intermediate AMD (iAMD).

METHODS

Macular 3 × 3-mm swept-source optical coherence tomography angiography scans were retrospectively analyzed in eyes with Type 3 MNV and in eyes with iAMD. The choriocapillaris en face slabs were extracted from the swept-source optical coherence tomography angiography device after manual segmentation. En face choriocapillaris flow images were compensated with en face choriocapillaris structure images, followed by the Phansalkar local thresholding method using a window radius of 4 and 8 pixels. The percentage of flow deficits (FD%), the number, size, and total area of FDs were computed for comparison. A secondary analysis was performed in the four corners of the image to include equidistant regions in all eyes.

RESULTS

Twenty-six Type 3 MNV eyes of 21 patients and 26 iAMD eyes of 17 patients were included. Compared with iAMD eyes, eyes with Type 3 MNV displayed a higher FD% (41.37% ± 14.74 vs. 19.80% ± 9.63 using radius 4 pixels [P < 0.001]; 45.24% ± 11.9 vs. 26.63% ± 8.96 using radius 8 pixels [P < 0.001]). The average size of FDs was significantly larger in Type 3 MNV eyes compared with iAMD eyes (P < 0.001), whereas the number of FDs was significantly lower in Type 3 MNV compared with iAMD eyes (P < 0.001).

CONCLUSION

Type 3 MNV eyes present with increased choriocapillaris flow impairment compared with iAMD eyes. Reduced choriocapillaris perfusion may contribute to Type 3 MNV development and pathogenesis.

Visualising the choriocapillaris: Histology, imaging modalities and clinical research - A review

The choriocapillaris plays a considerable role in the normal physiology of the eye as well as in various diseases. Assessing the changes in the choriocapillaris can therefore provide important information about normal ageing and pathogenesis of visual impairment, and even some systemic diseases. In vivo imaging of the choriocapillaris has evolved from non-depth resolved, dye-based angiography to advanced, high-resolution optical coherence tomography angiography (OCTA). However, the intricate microvascular networks within the choriocapillaris are still beyond the resolving limits of most OCTA instruments. Knowledge of histology, meticulous image acquisition methods, recognition of artefact and post-acquisition processing techniques are necessary for optimising OCTA choriocapillaris images. Qualitative and quantitative analyses of the choriocapillaris provide clinical information in age-related macular degeneration (AMD), diabetic retinopathy (DR), pathologic myopia and central serous chorioretinopathy (CSC). Furthermore, studies have revealed choriocapillaris changes in posterior uveitis that are correlated with treatment outcome and have important prognostic significance. In addition to retinal diseases, choriocapillaris changes have been observed in systemic vascular diseases and complications associated with pregnancy.

Impact of large choroidal vessels on choriocapillaris flow deficit analyses in optical coherence tomography angiography

PURPOSE

To investigate the impact of large choroidal vessels (LCV) on Choriocapillaris (CC) flow deficit (FD) analyses with swept-source optical coherence tomography angiography (SS-OCTA).

DESIGN

Prospective, cross-sectional study.

METHODS

Macular 6x6mm SS-OCTA scans were obtained from intermediate age-related macular degeneration (iAMD) and healthy eyes. Images were captured and processed according to most common standards and analyzed for percentage of flow-deficits (FD%) within four 1x1mm squares at the corners of each image. Choroidal thickness (CT), iris color and refraction error were considered as potential influential factors for LCV visibility. A linear mixed model and logistic regression models were calculated for statistical evaluation.

RESULTS

Sixty-nine iAMD and 49 age-matched healthy eyes were enrolled. LCV were visible in at least one sector in 52% of iAMD and 47% of healthy eyes. Within the iAMD group FD% were significantly lower in areas containing LCV (p = 0.0029). Increasing CT resulted in an odds ratio decrease of LCV (OR: 0.94, p<0.0001). Below a CT value of ≤118μm LCV could be expected with a sensitivity of 86% and a specificity of 85%.

CONCLUSIONS

LCV can significantly affect CC FD analyses of SS-OCTA images. Their visibility is negatively associated with CT. The impact of LCV should be taken into account when performing CC FD assessments, especially in patients where reduced CT is to be expected and inclusion of affected areas should be considered carefully.

Investigation of the Peripapillary Choriocapillaris in Normal Tension Glaucoma, Primary Open-angle Glaucoma, and Control Eyes

PRECIS

The peripapillary choriocapillaris (CC) was observed to be significantly impaired in normal tension glaucoma (NTG) subjects compared with normal controls using optical coherence tomography angiography (OCTA).

PURPOSE

The aim was to quantitatively evaluate the peripapillary CC in NTG, primary open-angle glaucoma (POAG), and control eyes using OCTA.

MATERIALS AND METHODS

Ninety eyes (30 controls, 30 NTG, and 30 POAG) from 73 patients were imaged using the Zeiss Plex Elite 9000. Five repeat 3×3 mm OCTA scans were acquired both nasally and temporally to the optic disc and subsequently averaged. Four CC flow deficit (FD) measures were calculated using the fuzzy C-means approach: FD density (FDD), mean FD size (MFDS), FD number (FDN), and FD area (FDA).

RESULTS

Temporal NTG CC parameters were associated with visual field index and mean deviation (P<0.05). The control group showed a significantly lower nasal FDD (nasal: 3.79±1.26%, temporal: 4.48±1.73%, P=0.03), FDN (nasal: 156.43±38.44, temporal: 178.40±45.68, P=0.02), and FDA (nasal: 0.22±0.08, temporal: 0.26±0.10, P=0.03) when compared with temporal optic disc. The NTG group showed a significantly higher FDD (NTG: 5.04±2.38%, control: 3.79±1.26%, P=0.03), FDN (NTG: 185.90±56.66, control: 156.43±38.44, P=0.04), and FDA (NTG: 0.30±0.14 mm2, control: 0.22±0.08 mm2, P=0.03) nasal to the optic disc compared with controls.

CONCLUSIONS

Association between CC parameters and glaucoma severity in NTG, but not POAG subjects, suggests vascular abnormalities may be a potential factor in the multifactorial process of glaucoma damage in NTG patients.

Choriocapillaris: Fundamentals and advancements

The choriocapillaris is the innermost structure of the choroid that directly nourishes the retinal pigment epithelium and photoreceptors. This article provides an overview of its hemovasculogenesis development to achieve its final architecture as a lobular vasculature, and also summarizes the current histological and molecular knowledge about choriocapillaris and its dysfunction. After describing the existing state-of-the-art tools to image the choriocapillaris, we report the findings in the choriocapillaris encountered in the most frequent retinochoroidal diseases including vascular diseases, inflammatory diseases, myopia, pachychoroid disease spectrum disorders, and glaucoma. The final section focuses on the development of imaging technology to optimize visualization of the choriocapillaris as well as current treatments of retinochoroidal disorders that specifically target the choriocapillaris. We conclude the article with pertinent unanswered questions and future directions in research for the choriocapillaris.

Analysis of correlations between local geographic atrophy growth rates and local OCT angiography-measured choriocapillaris flow deficits

The purpose of this study is to quantitatively assess correlations between local geographic atrophy (GA) growth rates and local optical coherence tomography angiography (OCTA)-measured choriocapillaris (CC) flow deficits. Thirty-eight eyes from 27 patients with GA secondary to age-related macular degeneration (AMD) were imaged with a commercial 1050 nm swept-source OCTA instrument at 3 visits, each separated by ∼6 months. Pearson correlations were computed between local GA growth rates, estimated using a biophysical GA growth model, and local OCTA CC flow deficit percentages measured along the GA margins of the baseline visits. The p-values associated with the null hypothesis of no Pearson correlation were estimated using a Monte Carlo permutation scheme that incorporates the effects of spatial autocorrelation. The null hypothesis (Pearson's ρ = 0) was rejected at a Benjamini-Hochberg false discovery rate of 0.2 in 15 of the 114 visit pairs, 11 of which exhibited positive correlations; even amongst these 11 visit pairs, correlations were modest (r in [0.30, 0.53]). The presented framework appears well suited to evaluating other potential imaging biomarkers of local GA growth rates.

The Spectrum of Central Choriocapillaris Abnormalities on Swept-Source Optical Coherence Tomography Angiography in the Fellow Eye of Unilateral Exudative Age-Related Macular Degeneration Patients: From Flow Deficits to Subclinical Non-Exudative Neovascularization

We evaluated the spectrum of choriocapillaris (CC) abnormalities in the fellow eyes of unilateral exudative age-related macular degeneration (AMD) patients using swept-source optical coherence tomography angiography (SS-OCTA). Fellow eyes of unilateral exudative AMD patients were prospectively included between May 2018 and October 2018. Patients underwent a multimodal imaging including a SS-OCTA. Demographics and clinical findings were analyzed. The estimated prevalence of macular neovascularization (MNV) was computed. Number and size of flow deficits (FDs) and percentage of flow deficits (FD%) were computed on the compensated CC flow images with the Fiji software. We included 97 eyes of 97 patients (mean age was 80 ± 7.66 years, 39 males, 58 females). The prevalence of MNV in the studied eyes was 8.25% (8/97 eyes). In the 89 non-neovascular eyes, FD% averaged 45.84% ± 11.63%, with a corresponding total area of FDs of 4.19 ± 1.12 mm². There was a higher prevalence of drusenoid pigment epithelial detachment in eyes with subclinical neovascularization (p = 0.021). Fellow eyes with unilateral exudative AMD encompassed a series of CC abnormalities, from FDs of the aging CC to subclinical non-exudative MNV.

CHORIOCAPILLARIS FLOW DEFICITS AS A RISK FACTOR FOR PROGRESSION OF AGE-RELATED MACULAR DEGENERATION

PURPOSE

To evaluate the association between choriocapillaris (CC) flow deficits and structural optical coherence tomography biomarkers and the progression of intermediate age-related macular degeneration (iAMD) to complete retinal pigment epithelial and outer retinal atrophy.

METHODS

Retrospective analysis of consecutive patients with iAMD with a minimum follow-up of 12 months. Odds ratios of intraretinal hyperreflective foci, hyporeflective drusen cores, subretinal drusenoid deposits, the presence of drusen volume ≥0.03 mm3 within a central 3-mm circle, fellow eye with late stage of AMD, and CC flow deficits at baseline and months of follow-up were estimated from logistic regression.

RESULTS

A total of 112 eyes with iAMD were included. Eyes that progressed were significantly more likely to show intraretinal hyperreflective foci, hyporeflective drusen cores, and drusen volume ≥0.03 mm3. The CC flow deficit was also significantly greater in eyes that developed complete retinal pigment epithelial and outer retinal atrophy. Intraretinal hyperreflective foci, hyporeflective drusen cores, drusen volume ≥0.03 mm3, and higher CC flow deficits were significantly and independently associated with the development of complete retinal pigment epithelial and outer retinal atrophy.

CONCLUSION

The CC flow deficit was significantly greater in iAMD eyes that progressed to complete retinal pigment epithelial and outer retinal atrophy and remained an independent risk factor when structural optical coherence tomography biomarkers were considered. CC flow deficits may be useful for enhancing risk stratification and prognostication of patients with iAMD.

Correlations Between Choriocapillaris and Choroidal Measurements and the Growth of Geographic Atrophy Using Swept Source OCT Imaging

PURPOSE

Correlations among enlargement rates (ERs) of geographic atrophy (GA) and choriocapillaris (CC) flow deficits (FDs), mean choroidal thickness (MCT), and choroidal vascularity index (CVI) were investigated using swept source-optical coherence tomography (SS-OCT) in age-related macular degeneration (AMD).

DESIGN

A retrospective review of prospective, observational case series.

METHODS

Eyes with GA from AMD were imaged with SS-OCT using 6 × 6-mm scan pattern. GA lesions were identified and measured using customized en face structural images, and annual square root ERs of GA were calculated. At baseline, choriocapillaris FDs from different regions outside the GA were measured, and MCT and CVI from the entire scan area were measured. All measurements were performed using previously published and validated algorithms.

RESULTS

A total of 38 eyes from 27 patients were included. The CC FDs within each region around GA lesions were highly correlated with ERs of GA (all P < .005). CVI inside the GA region was correlated with the ERs (P = .03), whereas other choroidal measurements had no significant correlation with the ERs of GA (P > .06).

CONCLUSIONS

Statistically significant correlations were found between the ERs of GA and CC percentage of FD (FD%) from the entire scan region outside the GA and not just the region immediately adjacent to the GA. These results suggest that abnormal CC perfusion throughout the macula contributes to disease progression in eyes with GA. CVI inside the GA region could also be a potential indicator for the growth of GA.

Exploring the Relationship Between Multilayered Choroidal Neovascularization and Choriocapillaris Flow Deficits in AMD

Purpose

We used optical coherence tomography angiography to test the hypothesis that more complex, multilayered choroidal neovascular (CNV) membranes in AMD are associated with worse flow deficits (FD) in the choriocapillaris.

Methods

Retrospective, cross-sectional study including 29 eyes of 29 subjects with neovascular AMD. En face choriocapillaris images were compensated for signal attenuation using the structural OCT slab and signal normalization based on a cohort of healthy subjects. We binarized the choriocapillaris using both local Phansalkar and global MinError(I) methods and quantified FD count, FD density, and mean FD size in the entire area outside the CNV, in the 200-µm annulus surrounding the CNV, and in the area outside the annulus. We used projection-resolved optical coherence tomography angiography to quantify CNV complexity, including highest CNV flow height, number of flow layers, and flow layer thickness. We explored the relationship between CNV complexity and choriocapillaris FD using Spearman correlations.

Results

The highest CNV flow signal significantly correlated with lower FD count (P < 0.01), higher FD density (P < 0.05), and higher mean FD size (P < 0.05) in the area outside the annulus and the entire area outside the CNV using both Phansalkar and MinError(I). Within the annulus, CNV complexity was not consistently correlated with choriocapillaris defects.

Conclusions

CNV vascular complexity is correlated with choriocapillaris FD outside the CNV area, providing evidence for the importance of choriocapillaris dysfunction in neovascular AMD, as well as the potential role of choroidal ischemia in the pathogenesis of complex CNV membranes.

Optical Coherence Tomography Angiography of the Choriocapillaris in Age-Related Macular Degeneration

The advent of optical coherence tomography angiography (OCTA) has allowed for remarkable advancements in our understanding of the role of the choriocapillaris in age-related macular degeneration (AMD). As a relatively new imaging modality, techniques to analyze and quantify choriocapillaris images are still evolving. Quantification of the choriocapillaris requires careful consideration of many factors, including the type of OCTA device, segmentation of the choriocapillaris slab, image processing techniques, and thresholding method. OCTA imaging shows that the choriocapillaris is impaired in intermediate non-neovascular AMD, and the severity of impairment may predict the advancement of disease. In advanced atrophic AMD, the choriocapillaris is severely impaired underneath the area of geographic atrophy, and the level of impairment surrounding the lesion predicts the rate of atrophy enlargement. Macular neovascularization can be readily identified and classified using OCTA, but it is still unclear if neovascularization features with OCTA can predict the lesion’s level of activity. The choriocapillaris surrounding macular neovascularization is impaired while the more peripheral choriocapillaris is spared, implying that choriocapillaris disruption may drive neovascularization growth. With continued innovation in OCTA image acquisition and analysis methods, advancement in clinical applications and pathophysiologic discoveries in AMD are set to follow.

Guidelines for Imaging the Choriocapillaris Using OCT Angiography

PURPOSE

To provide guidance on how to appropriately quantitate various choriocapillaris (CC) parameters with optical coherence tomography angiography (OCTA).

DESIGN

Evidence-based perspective.

METHODS

Review of literature and experience of authors.

RESULTS

Accurate and reliable quantification of CC using OCTA requires that CC can be visualized and that the measurements of various CC parameters are validated. For accurate visualization, the selected CC slab must be physiologically sound, must produce images consistent with histology, and must yield qualitatively similar images when viewing repeats of the same scan or scans of different sizes. For accurate quantification, the measured intercapillary distances (ICDs) should be consistent with known measurements using histology and adaptive optics and/or OCTA, the selected CC parameters must be physiologically and physically meaningful based on the resolution of the instrument and the density of the scans, the selected algorithm for CC binarization must be appropriate and generate meaningful results, and the CC measurements calculated from multiple scans of the same and different sizes should be quantitatively similar. If the Phansalkar local thresholding method is used, then its parameters must be optimized for CC based on the OCTA instrument and scan patterns used. It is recommended that the window radius used in the Phansalkar method should be related to the expected average ICD in normal eyes.

CONCLUSIONS

Quantitative analysis of CC using commercially available OCTA instruments is complicated, and researchers need to tailor their strategies based on the instrument, scan patterns, anatomy, and thresholding strategies to achieve accurate and reliable measurements.

Optimizing 3D retinal vasculature imaging in diabetic retinopathy using registration and averaging of OCT-A

High resolution visualization of optical coherence tomography (OCT) and OCT angiography (OCT-A) data is required to fully take advantage of the imaging modality's three-dimensional nature. However, artifacts induced by patient motion often degrade OCT-A data quality. This is especially true for patients with deteriorated focal vision, such as those with diabetic retinopathy (DR). We propose a novel methodology for software-based OCT-A motion correction achieved through serial acquisition, volumetric registration, and averaging. Motion artifacts are removed via a multi-step 3D registration process, and visibility is significantly enhanced through volumetric averaging. We demonstrate that this method permits clear 3D visualization of retinal pathologies and their surrounding features, 3D visualization of inner retinal capillary connections, as well as reliable visualization of the choriocapillaris layer.

Validation of a Compensation Strategy Used to Detect Choriocapillaris Flow Deficits Under Drusen With Swept Source OCT Angiography

PURPOSE

A compensation strategy that was developed to measure the choriocapillaris (CC) flow deficits (FDs) under drusen was tested in eyes with large drusen from age-related macular degeneration (AMD) before and after the drusen spontaneously resolved without evidence of disease progression.

DESIGN

Prospective, observational consecutive case series.

METHODS

Patients with AMD were enrolled in a prospective swept-source optical coherence tomography (SS-OCT) imaging study. Consecutive eyes with large drusen were followed, and eyes that underwent spontaneous collapse of drusen without evidence of disease progression were identified retrospectively. The drusen-resolved regions were manually outlined. CC FDs were measured using a previously published compensation strategy that adjusted for the decreased signal intensity underlying drusen. Both the percentage of FDs (FD%) and the mean FD sizes (MFDSs) were measured before and after drusen resolution.

RESULTS

Resolution of drusen was identified in 8 eyes from 8 patients. The average interval between the 2 visits was 7.8 months. The average drusen volumes measured between visits were 0.23 and 0.04 mm³, respectively. After the drusen resolved, the average follow-up time without evidence of disease progression was 10.1 months. When the 2 visits were compared, there were no statistically significant differences in any of the CC parameters within the drusen resolved regions once the compensation strategy was applied (all P values >.22).

CONCLUSIONS

In this naturally occurring experiment in which drusen collapsed without evidence of disease progression, the CC parameters were similar once our compensation strategy was applied both before and after the drusen resolved.

Can the Onset of Neovascular Age-Related Macular Degeneration Be an Acceptable Endpoint for Prophylactic Clinical Trials?

Many studies over the past 20 years have pursued the goal of preventing or deferring progression from early and intermediate age-related macular degeneration (AMD) to advanced AMD. The onset of neovascular AMD has been used as a primary endpoint in some prophylactic clinical trials because it is easy to assess and relatively well-defined. Nevertheless, the use of this endpoint for assessing progression of AMD lacks validation. The aims of this paper are to review the current practice of clinical trials investigating the prevention of progression of early or intermediate AMD to neovascular AMD, so-called prophylactic trials, as well as identify ongoing efforts to standardize endpoints and select the ideal population for such studies.

Scotopic microperimetric sensitivity and inner choroid flow deficits as predictors of progression to nascent geographic atrophy

BACKGROUND/AIMS

To assess the role of microperimetric retinal sensitivity (MPRS) and inner choroid flow deficits (IC FD) in predicting the development of incomplete retinal pigment epithelial and outer retinal atrophy (iRORA) in intermediate AMD (i-AMD).

METHODS

Thirty eyes with i-AMD evaluated at the Doheny-UCLA Eye Centres were enrolled in this prospective IRB-approved study. Subjects underwent several diagnostic tests: (a) 6×6 mm swept-source optical coherence tomography angiography (SS-OCTA) with the IC slab used to quantify the FDs, (b) 20°×20° spectral-domain optical coherence tomography (SD-OCT) to monitor progression to iRORA and (c) scotopic MPRS within an area of 18° centred on the fovea. All subjects were followed-up for 24 months. The baseline IC FD and MPRS were correlated with the development of iRORA. At 24-month follow-up, the stage of AMD was re-assessed and the eyes were divided into two sub-groups based on the development of iRORA.

RESULTS

Twenty-eight eyes completed the 2-year follow-up. At baseline, the mean MPRS was 13.40±4.66 dB and the mean IC FD was 27.55±8.67%. The morpho-functional regression showed a significant correlation between baseline MPRS and IC FD and the development of iRORA within 24 months (R²=0.744, p<0.05). A Kaplan-Meier survival curve was fit to determine the cumulative incidence of iRORA over the 24 months.

CONCLUSIONS

A lower MPRS and greater IC FD at baseline were predictors of progression to iRORA in eyes with i-AMD. These parameters may be useful biomarkers for risk stratification and prognostication.

Optimizing the Repeatability of Choriocapillaris Flow Deficit Measurement From Optical Coherence Tomography Angiography

PURPOSE

To evaluate the impact of processing technique and slab selection on the repeatability of choriocapillaris (CC) flow deficit (FD) measurements as assessed using optical coherence tomography angiography (OCTA) DESIGN: Prospective, cross-sectional study.

METHODS

Healthy subjects were imaged with 4 consecutive 3 × 3-mm OCTA using a swept-source OCT (PLEX elite 9000; Carl Zeiss Meditec). OCTA images were generated using the Max projection, and three 10-μm-thick slabs starting 11, 21, and 31 μm posterior to the automatically segmented retinal pigment epithelial band. The resultant images were binarized using the Phansalkar method with a 43.94-μm radius and then the CCFD% was computed. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were computed for the 4 acquisitions to assess the repeatability of the CCFD%. This entire analysis was repeated after separately modulating several parameters: (1) Sum instead of the Max projection, (2) retinal pigment epithelial fit instead of the retinal pigment epithelial band as the offset reference, (3) 14.65 and 87.88 μm radius values instead of 43.94 μm.

RESULTS

Twenty-four healthy eyes (mean age; 36.4 years) were enrolled. The CCFD% in the 11-21-, 21-31-, and 31-41-μm slabs generated by the Max algorithm and the retinal pigment epithelial band showed high repeatability values (ICCs = 0.963, 0.975, and 911; CVs = 0.05, 0.05, and 0.05, respectively). As most of the cases were confounded with the hypointense region when the 11-21-μm slab was used, however, this slab could not be included in the subsequent analyses. Those values in the 21-31- and 31-41-μm slabs were higher than those of the corresponding slabs by the Sum algorithm (ICC = 0.916 and 0.776; CV = 0.15 and 0.19, respectively) or by the retinal pigment epithelial fit (ICC = 0.907 and 0.802; CV = 0.06 and 0.06, respectively). The Phansalkar radius of 43.94 μm had the highest ICC numerically, but this was not statistically significantly greater than for a radius of 14.65 μm (ICC = 0.960 and 0.911, respectively) or a radius of 87.88 μm (ICC = 0.958 and 0.897, respectively). Regardless of which parameter was modulated, the 21-31-μm slab was the most repeatable.

CONCLUSIONS

In normal eyes, en face CC OCTA images generated using the Max projection and a 10-μm-thick slab offset of 21 μm below the instrument-generated retinal pigment epithelial band yielded the most repeatable CCFD%. These findings have implications for the design of standardized processing algorithms for quantitative CC assessment.

Choroidal and retinal structural, cellular and vascular changes in a rat model of Type 2 diabetes

Increasing evidence points to inflammation as a key factor in the pathogenesis of diabetic retinopathy (DR). Choroidal changes in diabetes have been reported and several attempts were made to validate in vivo choroidal thickness (CT) as a marker of retinopathy. We aimed to study choroidal and retinal changes associated with retinopathy in an animal model of spontaneous Type 2 diabetes, Goto-Kakizaki (GK) rats. Sclerochoroidal whole mounts and cryosections were prepared from 52-week-old GK and age-matched control Wistar Han rats. CT was measured by optical coherence tomography. Microglia reactivity, pericyte and endothelial cells distribution, and immunoreactivity of vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2) were evaluated by immunofluorescence. Choroidal vessels were visualized by direct perfusion with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). Choroidal vascular density was evaluated by fluorescence microscopy. GK rats had increased CT (58.40 ± 1.15 μm versus 50.90 ± 1.58 μm, p < 0.001), reduced vascular density of the choriocapillaris (CC) (p = 0.045), increased Iba1⁺ cells density in the outer retina (p = 0.003) and increased VEGFR2 immunoreactivity in most retinal layers (p = 0.021 to 0.037). Choroidal microglial cells and pericytes showed polarity in their distribution, sparing the innermost choroid. This cell-free gap in the inner choroid was more pronounced in GK rats. In summary, GK rats have increased CT with decreased vascular density in the innermost choroid, increased VEGFR2 immunoreactivity in the retina and increased Iba1⁺ cells density in the outer retina.

Evaluation of the inner choroid using OCT angiography

The advent of optical coherence tomography angiography (OCTA) has allowed a qualitative and quantitative analysis of the retinal vasculature and the choriocapillaris. With the use of OCTA, several studies evaluated the changes in the choriocapillaris showing how this vascular structure plays a significant role in the pathogenesis of different conditions. This article reviews the current methods of analysis of the choriocapillaris and the relevant findings in different chorioretinal diseases.

Evaluation of the different thresholding strategies for quantifying choriocapillaris using optical coherence tomography angiography

BACKGROUND

In this paper, we evaluate the different thresholding strategies that have been used for the quantification of the choriocapillaris (CC) and explore their repeatability and the interchangeability of the measurements resulting from its application.

METHODS

Observational study. Eighteen eyes from nine healthy volunteers aged >18 years were imaged four consecutive times with a SD-OCTA system (Heidelberg Engineering, Germany) using a 10°×10° high-resolution protocol centered on the fovea. Projection artifacts were removed, and the CC was bracketed between 10 and 30 µm below Bruch's membrane. For the quantification of CC, we used four flow deficits (FD) parameters: FD number, mean FD size, total FD area and FD density. We performed a systematic review of literature to collect the thresholding methods that have been used for the quantification of CC. The CC quantification parameters were then evaluated after applying each of the thresholding strategies. Intraclass correlation coefficient (ICC) and Pearson's correlation analysis were used to compare the repeatability and interchangeability among the different thresholding strategies for quantifying the CC.

RESULTS

A total of 72 optical coherence tomography angiography (OCTA) examinations were considered. The systematic review allowed us to conclude that three local thresholding strategies (Phansalkar, mean and Niblack) and three global thresholding strategies (mean, default, Otsu) have been used for CC quantification. These strategies were evaluated in our observational study. We found a high agreement within the same method in the quantification of FD number, mean FD size, total FD area and FD density but a poor agreement with different strategies. Local strategies achieved a significantly superior ICC than global ones in CC quantification.

CONCLUSIONS

In conclusion, the interchangeability of the CC quantification using different thresholding strategies is low, and direct comparisons should not be performed. Local thresholding strategies are significantly superior to global ones for quantifying CC and should be preferred. There is an unmet need for a uniform strategy to quantify CC in future studies.

Assessing the Influence of OCT-A Device and Scan Size on Retinal Vascular Metrics

Purpose

The purpose of this study was to investigate the effect of device and scan size on quantitative optical coherence tomography angiography (OCT-A) metrics.

Methods

The 3 × 3 mm scans from Optovue AngioVue and Zeiss AngioPlex systems were included for 18 eyes of 18 subjects without ocular pathology. The foveal avascular zone (FAZ) was segmented manually by two observers, from which estimates of FAZ area (using both the nominal image scale and the axial length corrected image scale) and acircularity were derived. Three scan sizes (3 mm, 6 mm HD, and 8 mm) from the AngioVue system were included for 15 eyes of 15 subjects without ocular pathology. For each subject, larger image sizes were resized to the same resolution as 3 × 3 mm scans, aligned, then cropped to a common area. FAZ area, FAZ acircularity, average and total parafoveal intercapillary area, vessel density, and vessel end points were computed.

Results

Between the devices used here, there were no significant differences in FAZ acircularity (P = 0.88) or FAZ area using scaled (P = 0.11) or unscaled images (P = 0.069). Although there was no significant difference in FAZ area across scan sizes (P = 0.30), vessel morphometry metrics were all significantly influenced by scan size.

Conclusions

The scan devices and sizes used here do not affect FAZ area measures derived from manual segmentations. In contrast, vessel morphometry metrics are affected by scan size. As individual differences in axial length induce differences in absolute scan size, extreme care should be taken when interpreting metrics of vessel morphometry, both between and within OCT-A devices.

Translational Relevance

A better characterization of the confounds surrounding OCT-A retinal vasculature metrics can lead to improved application of these metrics as biomarkers for retinal and systemic diseases.

Repeatability of binarization thresholding methods for optical coherence tomography angiography image quantification

Binarization is a critical step in analysis of retinal optical coherence tomography angiography (OCTA) images, but the repeatability of metrics produced from various binarization methods has not been fully assessed. This study set out to examine the repeatability of OCTA quantification metrics produced using different binarization thresholding methods, all of which have been applied in previous studies, across multiple devices and plexuses. Successive 3 × 3 mm foveal OCTA images of 13 healthy eyes were obtained on three different devices. For each image, contrast adjustments, 3 image processing techniques (linear registration, histogram normalization, and contrast-limited adaptive histogram equalization), and 11 binarization thresholding methods were independently applied. Vessel area density (VAD) and vessel length were calculated for retinal vascular images. Choriocapillaris (CC) images were quantified for VAD and flow deficit metrics. Repeatability, measured using the intra-class correlation coefficient, was inconsistent and generally not high (ICC < 0.8) across binarization thresholds, devices, and plexuses. In retinal vascular images, local thresholds tended to incorrectly binarize the foveal avascular zone as white (i.e., wrongly indicating flow). No image processing technique analyzed consistently resulted in highly repeatable metrics. Across contrast changes, retinal vascular images showed the lowest repeatability and CC images showed the highest.

Choriocapillaris Flow Deficits and Treatment-Naïve Macular Neovascularization Secondary to Age-Related Macular Degeneration

Purpose

To evaluate choriocapillaris (CC) flow deficits (FD) in eyes with treatment-naïve macular neovascularization (MNV) and to compare CC FD around exudative versus nonexudative MNV.

Methods

Treatment-naïve eyes with a diagnosis of either exudative or nonexudative AMD and type 1 MNV were included. Normal control eyes were age-matched to each AMD eye one to one. En face optical coherence tomography angiograms were analyzed for percentage of CC FD (FD%) in two concentric 500 µm rings, ring 1 and ring 2, surrounding the dark halo around MNV. The mean CC FD% in ring 1 and ring 2 was evaluated for each eye. A secondary analysis was similarly carried out to investigate the differences in CC FD% in exudative versus nonexudative treatment-naïve MNV.

Results

Twenty-three eyes with treatment-naïve MNV were age matched with 23 normal controls. The mean CC FD% was significantly greater in both rings in the MNV versus the normal control group (P < 0.05) and was significantly greater in the inner ring, closer to the lesion, than the outer ring. The mean FD% was also greater in both rings in the exudative versus the nonexudative MNV group, but this difference did not reach statistical significance.

Conclusions

The CC FD% was greater in the area surrounding MNV versus age-matched normal controls and in the ring closer to the MNV lesion. Further, CC FD was greater in eyes with exudative versus nonexudative MNV in both rings surrounding the associated dark halo, although this difference was not statistically significant.