Features of the choriocapillaris on four different optical coherence tomography angiography devices

Spatial Distribution of Hyperreflective Choroidal Foci in the Macula of Normal Eyes

Purpose

To investigate variations in the spatial distribution of hyperreflective foci in the choroid of the macula in normal eyes.

Methods

We included eyes with a normal fundus from patients who had undergone optical coherence tomography angiography, covering a 6-mm × 6-mm area centered on the fovea. The macular area was divided into nine sectors according to the modified Early Treatment of Diabetic Retinopathy Study grid. Hyperreflective choroidal foci (HCF) distribution, choriocapillaris vascular density, and choroidal stromal density were determined on en face images of the choroid in each sector.

Results

We included 35 eyes from 35 participants, with a mean age of 52.7 ± 16.8 years. The mean number and area fraction of HCF at the 5-mm macular area were 35.6 ± 7.8 foci/mm2 and 3.0% ± 0.7%, respectively. The number of HCF in the central circle (50.7 ± 20.9 foci/mm2) was greater than that in the inner (35.1 ± 13.0 foci/mm2) or outer rings (35.6 ± 6.5 foci/mm2) (P < 0.001, P < 0.001, respectively). The area fraction of HCF in the central circle (4.84% ± 3.36%) was greater than that in the inner (2.62% ± 1.17%; P < 0.001) or outer rings (3.12% ± 0.67%; P = 0.004). The HCF distribution did not significantly correlate with the choriocapillaris vascular density or choroidal stromal density in each sector.

Conclusions

HCF were more densely distributed in the macular center than in the pericentral or peripheral macular areas.

Translational Relevance

HCF measurement and spatial distribution could provide additional information for evaluating choroidal stromal characteristics.

Comparison of retinal thickness measurements among four different optical coherence tomography devices

We sought to compare the retinal thickness measurements collected using different optical coherence tomography (OCT) devices. This prospective study included 21 healthy cases, and the retinal thickness was measured using the PLEX Elite (Carl Zeiss Meditec, Dublin, California, USA), DRI OCT-1 Atlantis (Topcon Corp, Tokyo, Japan), Cirrus 5000 HD-OCT (Carl Zeiss Meditec), and Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany), respectively. The mean central retinal thickness (CRT) and mean retinal thickness of the Early Treatment of Diabetic Retinopathy Study (ETDRS) area were compared. The CRT varied significantly among the different OCT devices (P < 0.001). Post-hoc analysis revealed that the CRT measured using PLEX Elite (278.95 ± 20.04 µm) and Spectralis (271.86 ± 17.92 µm) were similar, and both were greater than the CRT measurements of DRI OCT-1 (239.57 ± 21.06 µm) and Cirrus (256.76 ± 17.82 µm). Additionally, the mean retinal thickness in each ETDRS area showed significant differences among the four devices (all P < 0.001). The mean retinal thickness measured varied according to the device used, and this needs to be considered when comparing retinal thickness measurements taken with different devices.

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.

Repeatability of choriocapillaris flow voids by optical coherence tomography angiography in central serous chorioretinopathy

PURPOSE

To assess the repeatability of flow signal voids (FSV) measurements of the choriocapillaris (CC) and choroid (CH) in central serous chorioretinopathy (CSCR) by Swept-Source optical coherence tomography angiography (SS-OCTA).

METHODS

Cross-sectional study including 104 eyes of 52 patients with unilateral CSCR. Two consecutive macular 6x6 mm SS-OCTA scans (Plex Elite 9000; Zeiss, Dublin, CA) were obtained from the affected eyes with persistent subretinal fluid (SRF) (CSCR group) and the fellow unaffected eyes (control group). FSV area and the number of contours measurements were analyzed using three slabs: inner CC, outer CC and CH. The repeatability of the measurements was assessed with intraclass correlation coefficients (ICC) and coefficients of variation (CV).

RESULTS

In the CSCR group, ICCs for the FSV area in the three slabs were all ≥0.859, observing higher values for the outer CC and the CH (0.959 and 0.964) than for the inner CC (0.859). Similar ICC values were obtained for the FSV area in control eyes, observing the highest values for the outer CC (0.949), followed by the CH (0.932) and inner CC (0.844). Regarding the FSV number of contours measurements, ICCs were higher for the outer CC and CH (0.949 and 0.932) than for inner CC (0.844). CV for the FSV area was 4.7%, 3.8% and 8.6% in the CSCR eyes and 4.8%, 3.9% and 9.3% in the control group for the inner CC, outer CC and CH respectively.

CONCLUSION

SS-OCTA offers good repeatability to quantify macular FSV in CSCR eyes and fellow eyes.

Comparison of choroidal hyperreflective spots on optical coherence tomography images between both eyes of normal subjects

Background

Advancement of optical coherence tomography (OCT) technology allows for better in vivo visualization of the choroidal architecture, which comprises vessels and stroma. However, most OCT studies using image binarization methods have focused only on choroidal vessels represented by dark pixels. This study aimed to compare the distribution of choroidal hyperreflective spots on swept-source OCT (SS-OCT) images between both eyes of normal subjects.

Methods

In this observational comparative study, we included SS-OCT images of healthy subjects, which were prospectively obtained to compare images among the devices. SS-OCT images acquired using PLEX Elite 9000 and DRI-OCT Triton were analyzed. En-face OCT images were obtained at five different depth positions of the inner choroid at the macula. The mean reflectivity of the choroidal slabs, the number, total area, and circularity of hyperreflective spots were quantitatively compared between the devices and between both eyes of the same subjects.

Results

In 30 eyes of 15 healthy subjects, the mean reflectivity of the choroidal slabs varied with the scan depth on both devices (P<0.001 and P<0.001). Hyperreflective spots were similarly distributed in the images from both devices, but at different depths. The number and area of hyperreflective spots in the second and third layers of the DRI-OCT Triton were positively correlated with those in the fourth and fifth layers of the PLEX Elite 9000, respectively (all P<0.05). The intraclass correlation coefficients (ICC) for the area of hyperreflective spots were excellent for the third slab of the DRI-OCT and the fifth slab of the PLEX Elite (ICC =0.798; 95% CI, -0.576-0.904). The number and area of hyperreflective spots were correlated between both eyes in the third, fourth and fifth layers on DRI-OCT Triton (all P<0.05) and in the first, second, and fifth layers on PLEX Elite 9000 (all P<0.05).

Conclusions

Hyperreflective spots in en-face images from two different SS-OCT devices were similarly observed between both eyes of the same person. The distributions of spots between the two eyes of the same person were correlated. These findings suggest that the distribution of hyperreflective spots on the choroid reflects the choroidal characteristics of the subject.

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.

Hyperreflective foci in the choroid of normal eyes

PURPOSE

To investigate hyperreflective choroidal foci (HCF) using en face swept-source optical coherence tomography (SS-OCT) and determine the factors that contribute to the distribution of HCF in normal eyes.

METHODS

In this retrospective study, we included healthy eyes with a normal fundus. HCF were defined as hyperreflective spots on en face SS-OCT images. The number, mean area, total area, and circularity of the HCF were compared with various choroid measurements obtained using SS-OCT, SS-OCT angiography, and fundus photography.

RESULTS

We investigated 51 eyes from 51 patients. The mean patient age was 56.0 ± 14.7 years, and 32 (62.7%) were female. The number and total area of HCF did not differ between the female and male patients and the right and left eyes. The number of HCF was correlated with the stromal area of the choroid (r = 0.291, P = 0.040) and subfoveal choroidal vascularity index (r =  - 0.364, P = 0.009). The total area of HCF was correlated with the stromal area of the choroid (r = 0.283, P = 0.045). However, the number and total area of HCF were not correlated with age, degree of macular tessellation, subfoveal choroidal thickness, and choriocapillaris vascular density and flow void area.

CONCLUSION

HCF were observed in normal eyes, and their distribution was associated with the underlying stromal component of the choroid. The results of this study can be used as a reference for determining abnormal hyperreflective foci in the choroid of the eyes with various diseases.

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.

Quantitative Comparison of the Vascular Structure of Macular Neovascularizations Between Swept-Source and Spectral-Domain Optical Coherence Tomography Angiography

Purpose

The aim of this study was to ascertain and quantify the differences between swept-source (SS) and spectral-domain (SD) optical coherence tomography angiography (OCTA) imaging of macular neovascularizations (MNV) in neovascular age-related macular degeneration (nAMD).

Patients and Methods

SD-OCTA (RTVue Avanti) and SS-OCTA (PLEX^® Elite 9000) were performed in 37 patients with MNV in nAMD. The MNV was delineated and the data were processed via ImageJ. The parameters MNV area, nodes per area, fractal dimension (FD), and flow density were analyzed using MatLab.

Results

There was close agreement between the two devices regarding MNV area (ICCc 0.977, ICCa 0.977, R² 0.977), but only slight agreement regarding nodes per area (ICCa 0.008, ICCc 0.548, R² 0.51), FD (ICCa 0.425, ICCc 0.846, R² 0.96), and flow density (ICCa 0.451, ICCc 0.656, R² 0.65). The difference between the two devices was insignificant for MNV area (type 1: p=0.328; type 2: p=0.426; type 3: p=0.615), but significant for nodes per area (type 1: p=0.002; type 2: p=0.00001; type 3: p=0.003), FD (type 1: p<0.00001; type 2: p<0.00001; type 3: p=0.015) and flow density (type 1: p=0.0004; type 2: p=0.004; type 3: p=0.052).

Conclusion

MNV area is closely comparable between devices using SS-OCTA and SD-OCTA imaging. However, the two methods differ significantly in their precise assessment of the vascular morphology (FD, flow density, nodes per area). Therefore, results obtained using different devices are not comparable and should not be amalgamated in clinical trials.

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.

Swept-source optical coherence tomography angiography alleviates shadowing artifacts caused by subretinal fluid

Purpose

To characterize the choriocapillaris (CC) structure in relation to subretinal fluid (SRF) as a possible systematic error source using spectral domain (SD-OCTA) compared to swept-source optical coherence tomography angiography (SS-OCTA).

Methods

This is a prospective case-control study of 23 eyes. Ten patients with acute central serous chorioretinopathy (CSC), three patients with partial macular-off retinal detachment (RD) and ten healthy, age-matched controls were included. Abnormal CC decorrelation signals were quantitatively compared in CSC and controls by means of custom image processing. To investigate the influence of SRF on CC OCTA signal, the extent of SRF was quantified with a macular heatmap and compared with the corresponding OCTA signal of the CC.

Results

SS-OCTA yielded a more homogeneous OCTA signal from the CC than SD-OCTA, offering less signal dispersion and variability in healthy and diseased eyes. Both devices demonstrated CC signal voids in CSC and RD, respectively. In CCS, the voids were predominantly located in the area with SRF. Compared to SD-OCTA, SS-OCTA delivered a more homogenous OCTA signal and reduced signal voids in the CC underneath SRF in both RD and CSC (CSC, 7.6% ± 6.3% vs, 19.7% ± 9.6%, p < 0.01). Despite this significant attenuation of signal voids, SS-OCTA continued to reveal signal voids below SRF and more pixels with reduced OCTA signals in CSC patients compared to controls (7.6% ± 6.3%, 0.1% ± 0.1%, p < 0.0001).

Conclusion

Understanding OCTA artifacts is critical to ensure accurate clinical evaluations. In this study, we describe the presence of SRF as an important shadow-causing artifact source for CC OCTA analysis which can be mitigated but not completely eliminated by employing SS-OCTA.