Quantification of Choriocapillaris with Phansalkar Local Thresholding: Pitfalls to Avoid

Outer retina dysfunction and choriocapillaris impairment in type 1 diabetes

To study the outer retina morpho-functional characteristics and the choriocapillaris (CC) features in type 1 diabetic (T1D) patients, with and without signs of diabetic retinopathy (NPDR and NoDR). Twenty-five NPDR and 18 NoDR eyes were imaged by Optical Coherence Tomography Angiography. Ellipsoid zone (EZ) “normalized” reflectivity and CC perfusion density parameters, as flow deficits number (FDn), flow deficit average area (FDa) and flow deficit percentage (FD%), were analysed. Multifocal electroretinogram (mfERG) response amplitude densities (RADs) were measured. Mean EZ “normalized” reflectivity, CC FDn and FD% values, were similar (p > 0.05) in both groups, FDa was significant greater (p > 0.05) in NPDR compared with NoDR eyes. MfERG-RADs were similar in both groups. NPDR eyes showed a significant (p < 0.05) linear correlation between RADs and both, CC FDa and FD%. The EZ “normalized” reflectivity was negatively correlated with CC FD% in NoDR eyes. In NPDR T1D eyes a significant relationship between abnormal outer retina functional responses and CC impairment was observed, while in NoDR eyes the photoreceptor reflectivity was correlated to CC abnormalities. The outer retina dysfunction in NPDR correlated to CC drop-out let hypothesize that the outer retinal elements are functionally impaired in proportion to the CC vascular supply deficit.

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.

Imaging Biomarkers of 1-Year Activity in Type 1 Macular Neovascularization

Purpose

The purpose of this study was to evaluate the predictive value of optical coherence tomography (OCT) and OCT angiography (OCTA) parameters at baseline on lesion's activity at the 1-year follow-up in type 1 macular neovascularizations (MNVs) treated with 1-year fixed regimen of intravitreal aflibercept injections (q8 IAIs).

Methods

All patients were imaged by structural OCT to evaluate central macular thickness (CMT), subretinal fluid (SRF), subretinal hyper-reflective material (SHRM), intraretinal fluid (IRF) and intraretinal hyper-reflective dots (HRDs), and by Swept-Source OCTA to measure baseline MNV area, perfusion density (PD), vessel length density (VLD), and vessel diameter index. At the end of q8 IAI, patients were classified in two groups: active-MNV (A-MNV) and inactive-MNV (I-MNV), considering the OCT signs of activity. Three binary logistic regression models were developed: (1) OCT-based, (2) OCTA-based, and (3) OCT/OCTA-based model.

Results

Thirty-one treatment-naïve type 1 MNVs were enrolled (13 A-MNV and 18 I-MNV). No differences were observed in baseline OCT and OCTA characteristics between A-MNV and I-MNV. Among the models developed, model 3 that combined OCT/OCTA parameters showed a performance of 87.5% and excellent sensitivity for A-MNV lesions (100%). By analyzing the model, the A-MNV group appears more likely to show at baseline SRF, greater CMT, wider MNV area, and lower PD and VLD compared to I-MNV.

Conclusions

Our study demonstrated that the combination of baseline OCT and OCTA parameters allowed to achieve a good models’ performance in the prediction of MNV activity permitting to correctly classifying the active lesions at the end of follow-up period, with excellent sensitivity.

Translational Relevance

OCT/OCTA could integrate statistical models potentially useful for artificial intelligence.

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.

Correlation Between Choriocapillaris Density and Retinal Sensitivity in Age-Related Macular Degeneration

Purpose

The purpose of this study was to investigate the relationship between perfusion of the choriocapillaris (CC) and retinal sensitivity in eyes with intermediate age-related macular degeneration (iAMD).

Methods

This prospective study included patients with iAMD and healthy controls. All enrolled subjects underwent optical coherence tomography angiography (OCT-A) in order to compute the percent perfused choriocapillaris area (PPCA). In patients with iAMD, microperimetry (MP) testing was performed in order to quantify: mean retinal sensitivity (MRS), over an area of 10 degrees; mean macular sensitivity (MMS), over the macular area scanned with OCT-A; and retinal sensitivity (RS) in each macular point.

Results

Eighteen eyes of 13 patients were included in the analysis. In addition, 18 eyes of 12 healthy subjects were enrolled as controls. No statistically significant difference (P value > 0.2) was observed in age between patients (73.9 ± 2.0 years) and controls (70.1 ± 2.8 years). We observed significantly lower values of PPCA between patients with iAMD and healthy controls (42.0% ± 3.8% vs. 66.4% ± 3.0%; -β = 23.8%; P value < 0.001). Among iAMD eyes, higher values of PPCA were significantly associated with higher values of MRS (P value = 0.002) and MMS (P value = 0.013). Finally, higher values of RS in each macular point analyzed with MP were significantly (P value < 0.001) associated with higher values of PPCA computed in circular regions of interest (ROIs) centered in each analyzed MP point with radii of 0.5 degrees and 1.0 degree.

Conclusions

Using OCT-A, we demonstrated a significant association between CC impairment and macular dysfunction, quantified by MP, in iAMD eyes.

Translational Relevance

OCT-A could be a useful tool for detecting CC alterations and to monitor disease progression.

Topography of choriocapillaris flow deficit predicts development of neovascularization or atrophy in age-related macular degeneration

PURPOSE

To evaluate the relationship between choriocapillaris (CC), flow deficits (FD), and structural optical coherence tomography (OCT) biomarkers, and the progression of intermediate age-related macular degeneration (iAMD) to complete retinal pigment epithelial and outer retinal atrophy (cRORA) or macular neovascularization (MNV).

METHODS

Consecutive patients with iAMD were sequentially reviewed to define three equal sized groups: progressed to MNV, progressed to cRORA, or remained stable over 12 months of follow-up. Odds ratios for progression to cRORA and MNV were estimated by logistic regression for intraretinal hyperreflective foci (IHRF), hyporeflective drusen cores (hDC), subretinal drusenoid deposits (SDDs), high central drusen volume, fellow eye with late AMD, and peripheral and central CC FD.

RESULTS

Thirty iAMD eyes from 30 patients were enrolled into each group. The CC FD was greater in the peripheral sectors of the macula of eyes which progressed to cRORA compared to the other two groups (P < 0.0001). The central CC FD was also significantly impaired in eyes that progressed to cRORA or MNV compared to eyes that did not progress (P = 0.001 and P = 0.02, respectively). CC FD in the peripheral macula was significantly and independently associated with the development of cRORA, while CC FD in the center was significantly and independently associated with the development of MNV.

CONCLUSIONS

While the CC is diffusely impaired throughout the macula in iAMD eyes that progress to cRORA, it is relatively spared in the more peripheral macula among eyes which progress to MNV. These differential findings may have implications for the pathophysiology of the different late-stage manifestations of AMD.

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.

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.

Differential effects of high-intensity interval training (HIIT) on choriocapillaris perfusion in healthy adults and patients with type 1 diabetes mellitus (T1DM)

PURPOSE

To investigate the effects of a four-week high-intensity interval training (HIIT) on choriocapillaris (CC) perfusion in young healthy adults and type 1 diabetes mellitus (T1DM) patients.

METHODS

Data of two HIIT studies with baseline to follow-up comparison were retrospectively analysed. Twenty healthy participants and twenty T1DM patients without clinical signs of diabetic retinopathy were included. All participants had performed a four-week all-out HIIT protocol with a total of 8 training sessions. Changes in physical fitness were assessed using power output at the individual aerobic lactate threshold (IANT). Optical coherence tomography angiography (OCTA) imaging was performed at baseline and follow-up. CC images were analysed for number, size and total area of flow deficits (FD), mean signal intensity, signal intensity standard deviation and kurtosis of signal intensity distribution.

RESULTS

At baseline, CC OCTA revealed a lower and more heterogeneous intensity signal in T1DM eyes (mean intensity signal and standard deviation of signal intensity, p < 0.001). Percent of CC FD area was greater in T1DM eyes (p < 0.001). While T1DM patients showed greater improvement of exercise capacity at IANT than healthy controls (group×time p = 0.0403), CC FD area and standard deviation of intensity increased in healthy controls but not in T1DM patients (group×time p ≤ 0.029). Moreover, linear regression slopes of FD region distribution differed significantly at baseline and follow-up (p = 0.0002) in healthy individuals but not in T1DM patients.

CONCLUSIONS

Effects of regular physical exercise performed as HIIT on CC perfusion were only seen in healthy participants, not in T1DM patients suggesting impaired CC adaptation in T1DM.

[Evaluation of choriocapillaris with high-speed spectral-domain optical coherence tomography angiography and image averaging]

PURPOSE

To study the capabilities of high-speed spectral-domain optical coherence tomography angiography (SD-OCTA) with image averaging in the evaluation of choriocapillaries in healthy individuals and patients with central serous chorioretinopathy (CSC).

MATERIAL AND METHODS

All participants underwent OCTA examination on the SOLIX tomograph (Optovue, USA) using quadruplicate 3×3 mm scan with image averaging. Image analysis was performed in 9-µm custom slab with Phansalkar auto local threshold algorithm and calculation of flow voids larger than 5000 µm² and 10 000 µm². The optimal slab depth was determined in healthy eyes by consecutive analysis of the slabs with a 3-µm shift from zero position to 33 µm below Bruch's membrane.

RESULTS

The study included 18 eyes of 18 healthy volunteers (40.4±6.0 years old) and 18 fellow eyes of 18 unilateral CSC patients (37.4±10.7 years old). The slab 12 µm below the Bruch's membrane showed the minimal number of flow voids (23.1±7.0 of >5000 µm² voids per scan) and was chosen for further analysis. The number of flow voids of >5000 µm² in healthy paired eyes of CSC patients was statistically significantly higher than in the eyes of healthy individuals (32.7±10.7 and 25.3±8.1 voids/scan, respectively; p=0.022). The number of flow voids of >10000 µm² was also statistically significantly higher in CSC eyes compared to healthy eyes (5.6±3.3 and 3.5±1.9 voids/scan, respectively; p=0.045). There was no statistically significant difference in total area of the voids between the eyes of healthy individuals and CSC patients (96406.1±3924.5 µm² and 95395.7 ± 3615.1 µm², respectively; p=0.42).

CONCLUSION

The optimal settings for choriocapillaris imaging on the SOLIX tomograph include 9-µm slab 9 to 18 µm below the Bruch's membrane. Using a 9-µm slab 12 µm below the Bruch's membrane, a substantial difference was found in choriocapillaris perfusion between eyes of healthy individuals and CSC patients.

Effect of vessel enhancement filters on the repeatability of measurements obtained from widefield swept-source optical coherence tomography angiography

We assessed the inter-visit repeatability of 15 × 9-mm² swept-source OCTA (SS-OCTA; PLEX Elite 9000, Carl Zeiss Meditec) metrics in 14 healthy participants. We analysed the perfusion density (PD) of large vessels, superficial capillary plexus (SCP), and deep capillary plexus (DCP) as well as choriocapillaris flow voids in 2 different regions: the macular region and peripheral region. Also, retinal plexus metrics were processed further using different filters (Hessian, Gabor and Bayesian) while choriocapillaris flow voids were calculated with 1 and 1.25 standard deviation (SD) thresholding algorithms. We found excellent repeatability in the perfusion densities of large vessels (ICC > 0.96). Perfusion densities varied with different filters in the macular region (SCP: 24.12–38.57% and DCP: 25.16–38.50%) and peripheral (SCP: 30.52–39.84% and DCP: 34.19–41.60%) regions. The ICCs were lower in the macular region compared to the peripheral region and lower for DCP than for SCP. For choriocapillaris flow voids, the 1.25 SD threshold resulted in fewer flow voids, while a good ICC (ICC > 0.81) was achieved using either threshold settings for flow void features in both regions. Our results suggest good repeatability of widefield SS-OCTA for the measurements of retinal perfusion density and choriocapillaris flow voids, but measurements from different filters should not be interchanged.

Correlation between the Angiographic Choriocapillaris and the Structural Inner Choroid

Purpose: To assess the correlation between the choriocapillaris (CC) on optical coherence tomography (OCT) angiography and the inner choroid (IC) on structural OCT.Methods: In this prospective, cross-sectional, observational, pilot study, consecutive healthy subjects were imaged with a 6x6mm macular scan using OCTA PlexElite. Angiographic images of the CC were isolated using 10 μm-thick slab starting 21 μm posterior to the automatically segmented retinal pigment epithelium (RPE) band centerline. The structural en face OCT images of the IC were isolated using five 10 μm-thick slabs starting 11 to 51 μm posterior to the automatically segmented RPE band centerline. Retinal vessels masking was obtained by two methods: automated OCTA superficial vessel slab and automated structural OCT outer retina to CC (ORCC) slab. The en face OCT images were binarized for computation of the stromal index (SI). The flow deficits (FD) of the angiographic CC were correlated with the SI of the structural en face OCTs of the IC.Results: Twenty eyes of 20 subjects were enrolled. The strongest correlation was observed between the CC FD and the inner choroid SI of the 31-41 slab (IC SI_31-41) using the ORCC mask (R = 0.603, p = .005). Similar results were observed when the analysis was repeated when using IC SI_31-41 values obtained with the superficial vessels mask (R = 0.561, p = .01).Conclusions: The angiographic CC FD was significantly correlated with the structural inner choroidal stromal index. These findings suggest that there may be an opportunity to use structural OCT data to analyze the CC, which may allow longitudinal assessment from historical structural OCT datasets.

Photoreceptor alteration in intermediate age-related macular degeneration

The aim of this study was to analyze photoreceptor alterations occurring in eyes with intermediate age-related macular degeneration (AMD) and to investigate their associations with choriocapillaris (CC) flow. In this retrospective case-control study, we collected data from 35 eyes with intermediate AMD from 35 patients who had swept source optical coherence tomography structural and angiography imaging obtained. A control group of 35 eyes from 35 healthy subjects was included for comparison. Our main outcome measure for comparison between groups was the normalized reflectivity of en face image segmented at the ellipsoid zone (EZ) level, which was calculated to quantify the photoreceptor damage. OCTA metrics to quantify CC flow signal were also computed. These metrics were measured in a circle centered on the fovea and with a diameter of 5 mm. In intermediate AMD eyes, the macular area occupied by drusen was identified. Therefore, the EZ reflectivity and CC flow signal were separately measured in regions without drusen ("drusen-free" region). Measurements were generated using previously published algorithms. Mean ± SD age was 74.1 ± 6.8 years in the intermediate AMD group and 72.1 ± 6.0 years in the control group (p = 0.206). The normalized EZ reflectivity was 0.76 ± 0.10 in the intermediate AMD group and 0.85 ± 0.08 in the control group (p < .0001). In the "drusen-free" region, the normalized EZ reflectivity was 0.77 ± 0.10 (p < .0001  vs. healthy controls) and was positively correlated with the CC flow signal density (ρ = - 0.340 and p = 0.020). In conclusion, eyes with intermediate AMD exhibit a diffuse reduced EZ normalized reflectivity, and this reduction is correlated with CC flow signal in the regions without drusen. This study supports the concept of the damage of the unit comprised of photoreceptor, CC, and intervening tissues as an early event in AMD.

Guidelines on Optical Coherence Tomography Angiography Imaging: 2020 Focused Update

Optical coherence tomography angiography (OCTA) has significantly expanded our knowledge of the ocular vasculature. In this review, we provide a discussion of the fundamental principles of OCTA and the application of this imaging modality to study the retinal and choroidal vessels. These guidelines are focused on 2020, and include updates since the 2019 publication. Importantly, we will comment on recent findings on OCTA technology with a special focus on the three-dimensional (3D) OCTA visualization.

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.

Using the Pathophysiology of Dry AMD to Guide Binarization of the Choriocapillaris on OCTA: A Model

Especially since the incorporation of swept laser sources, optical coherence tomography angiography (OCTA) has enabled quantification of choriocapillaris perfusion. A critical step in this process is binarization, which makes angiographic images quantifiable in terms of perfusion metrics. It remains challenging to have confidence that choriocapillaris perfusion metrics reflect the reality of pathophysiologic flow, largely because choice of binarization method can result in significantly different perfusion metric outcomes. This commentary discusses a proof-of-concept case involving comparative assessment of binarization methods for a set of dry age-related macular degeneration OCTA data. One of these methods was deemed preferable based on superior agreement with suspected physiologic and pathophysiologic characteristics, thus demonstrating the principle that, in the absence of gold standards for measurement of choriocapillaris perfusion, the best available approximations of pathophysiology may be used to guide choice of binarization method.

Choroidal luminal and stromal areas and choriocapillaris perfusion are characterised by a non-linear quadratic relation in healthy eyes

PURPOSE

To assess the associations among different optical coherence tomography (OCT) structural and angiography quantitative metrics used to characterise the choroid in healthy subjects.

METHODS

In this cross-sectional study, macular structural OCT and OCT angiography (OCTA) images were acquired from healthy subjects. The main outcome measures were: (i) choriocapillaris (CC) flow deficits percentage (FD%), (ii) choroidal luminal (LA) and stromal (SA) areas and (iii) choroidal vascularity index (CVI), which was calculated as the LA divided by the total choroidal area. These measurements were generated using previously published algorithms and were separately computed in the foveal and extrafoveal regions.

RESULTS

Eighty-five eyes from 85 subjects (44 males, 41 females) were included in the analysis. Mean±SD age was 47.9±22.4 years (range: 19.0 to 85.0 years). Linear regression analysis displayed no significant associations between CC FD% and other parameters (LA, SA and CVI). Importantly, non-linear regression analysis showed that the relations of LA and SA to CC FD% were all best fitted by a quadratic function. Compared with the linear models, the use of the quadratic function allowed a relative increase in the R² coefficients. No significant non-linear associations were found between CC FD% and CVI.

CONCLUSION

Based on our models, changes in the luminal and stromal areas in the choroid lead to an initial increase in CC perfusion. Subsequently, further increases in LA and SA amounts are accompanied by a progressive increment in CC FD%.

New Frontiers in Retina: highlights of the 2020 angiogenesis, exudation and degeneration symposium

We summarize the most important findings presented at the 2020 angiogenesis, exudation and degeneration symposium in five topic areas: (1) epidemiology of retinal vascular disease and macular degeneration; (2) dry AMD and geographic atrophy; (3) neovascular age-related macular degeneration; (4) drug delivery and devices and (5) diabetic retinopathy.