Choroidal Blood Flow Changes in Central Serous Chorioretinopathy: Impact on Pigment Epithelial Detachment and Subretinal Fluid

doi:10.21203/rs.3.rs-4908110/v1

Purpose

Investigate how choroidal blood flow affacts pigment epithelial detachment (PED) and subretinal fluid (SRF) in central serous chorioretinopathy (CSC) .

Methods

We collected CSC patients, dividing into group with PED and without PED, as well as healthy individuals. Using SS-OCT to measure three-dimensional choroidal vascular index (CVI), choroidal vascular volume (CVV), SRF and PED area and volume, subfoveal choroidal thickness (SFCT), and the choroid thickness beneath the highest point of PED(PED-ct). Image-J was used to analyze and calculated flow void area (FVa) and flow void area percentage (FV%) of choriocapillary.

Results

The SFCT, three-dimensional CVI, CVV, FVa and FV% of CSC patients were higher than normal group, compared to CSC without PED, three-dimensional CVI in CSC with PED is higher, both difference was significant (P < 0.05). Among CSC patients, the FV% and SRF area, the CVV and SFCT all showed positive correlation. In CSC with PED, the CVV and PED-ct, the FVa, FV% and PED, SRF area were both positively correlated.

Conclusions

The occurrence of PED and SRF in CSC is not only related to the low blood flow of choriocapillary, but also related to the increase in the vascular density and the expansion of Sattler and Haller.

Health sciences/Diseases/Eye diseases/Retinal diseases

Health sciences/Diseases/Eye diseases/Uveal diseases

central serous chorioretinopathy

choroidal vascular index

pigment epithelial detachment

subretinal fluid

choriocapillary

The detachment of the retinal pigment epithelium and neural epithelium serves as the primary contributor to visual impairment and distortion in central serous chorioretinopathy (CSC)^1–3. As the disease continues to progress, patients may undergo photoreceptor degeneration, retinal pigment epithelium atrophy, choroidal neovascularization, and other tissue alterations^4–6. Extensive research has demonstrated that patients diagnosed with CSC exhibit various ocular manifestations, including choroidal thickening, vortical vein congestion, vascular dilation^7–9. In the diagnosis and assessment for CSC, choroidal thickness and serous detachment of the neuroepithelium are considered crucial follow-up indicators^10–12. Although the subfoveal choroidal thickness (SFCT) can reflect the changes of the choroidal in CSC patients to some extent, this index has limitations in evaluating the changes of choroidal vasculature, and is affected by circadian rhythm with high variability^13–16. In recent years, some scholars have proposed applying parameters such as the flow void area (FVa) and flow void area percentage (FV%) of choriocapillary layer^17–20, three-dimensional choroidal vascular index (CVI)⁷, choroidal vascular volume (CVV)⁷ to the evaluation of CSC disease, to more comprehensively reflect the changes of choriocapillary, sattler and haller layers. It is worth noting that previous studies mainly used two-dimensional CVI to evaluate the changes of choroidal vessels in unit area, but it could not accurately reflect the changes of the whole choroidal vascular system^21–23. Recently, some studies have used three-dimensional CVI to evaluate the changes of choroidal vessels in unit volume, which can provide more information than two-dimensional CVI⁷.

The pathogenesis of CSC is complex, and intricately linked to the malfunctioning of the choroidal vasculature and retinal pigment epithelium pump^9,24. During follow-up, whether it is acute or chronic CSC, PED phenomenon may occur^23,26. Even when the subretinal fluid (SRF) gradually diminishes and disappears, the pigment epithelial detachment (PED) perhaps persists fpr some patients²⁵. It was observed that certain cases of CSC accompanied by flat irregular PED gradually progressed to neovascular PED28, whereas a minority of finger-like PEDs underwent a transition into polypoidal choroidal vasculopathy^21,26–27. Nevertheless, the precise mechanisms underlying the emergence and progression of PED and SRF remain incompletely understood, there is no previous research on the correlation between the change of choroidal blood flow and the formation of PED and SRF. Consequently, the objective of this study is to assess parameters such as FVa, FV%, three-dimensional CVI, and CVV in CSC patients with or without PED, delve into the potential associations between these indicators and the formation of PED and SRF. Thereby providing scientific groundwork for further elucidating the pathogenesis of CSC.

Choroidal thickness, and area and volume of SRF

The SFCT In CSC with PED(496.593±69.409) and without PED(528.885±100.251) were significantly elevated compared to the normal group(381.556±87.928), and the difference was statistically significant (P<0.001). There was no significant difference in the SFCT between CSC without PED and those with PED (P=0.144). The measurement of SFCT is depicted in Fig.1A, indicated by the designated blue line area, it is observed that choroidal thickness exhibits a notable thickening in CSC. Within the CSC cohort featuring PED, no statistically significant variation was observed in terms of SFCT or choroidal thickness beneath the apical region of PED (488.593±83.875, t=0.704). As depicted in Fig.1B, the choroidal thickness beneath the highest point of PED is represented by the designated blue line area. As depicted in Fig.1D, the orange-colored region signifies the SRF area, and in CSC with PED exhibit a greater area and volume of SRF(9.685±6.636, 1.174±1.133) compared to those without PED(9.302±5.861, 1.076±1.110), however, it is not statistically significant (t=0.825, t=0.753).

Structural of choroidal vascular layer

As shown in Fig.1F, the macular foveal is divided into 1, 3, and 6mm circular regions using the ETDRS. Fig.1E illustrates the orange-colored region, depicting choroidal Sattler and Haller layer, and it is evident from the vessels are dilated. Fig.1C illustrates a notable enlargement of the vascular lumen within the choroidal region beneath the PED. Furthermore, Fig.1G highlights the PED area denoted by the red box, observed a locally elevated pixel density on the dilation choroidal vascular. In comparison to the normal group, tthree-dimensional CVI values observed in the 1, 3, and 6mm circular regions of CSC patients with PED exhibited a marked elevation, yielding a statistically significant difference (P<0.001). Conversely, in CSC patients without PED, the three-dimensional CVI was solely elevated in the 6mm circular region compared to the normal group, also reaching a statistically significant difference (P<0.05). Three-dimensional CVI in CSC with PED was higher within the circular regions of 1mm, 3mm, and 6mm circular regions in comparison to those without PED, with statistically significant differences (P<0.01). The CVV measurements within the circular regions of 1, 3, and 6mm diameters in CSC with and without PED were notably increased compared to the normal group, demonstrating statistically significant disparities (P<0.001) (table 1).

As shown in Fig.2, dark particles with low-pixel values regions represents the FVa. Evidently, the choriocapillary layer of CSC patients perform pixel inhomogeneity, with more dark particles with low-pixel values regions compared to the normal group, as well as the FVa and FV% of CSC without or with PED exhibited significant increases, as indicated by statistically significant differences (P<0.05). However, upon further analysis, it was observed that the FVa and FV% were no statistically significant differences between the groups of CSC with PED and those without PED (table 1).

Pearson correlation analysis

Regardless of the CSC with PED or not, there is a strong positive correlation between CVV and SFCT in the 1, 3, and 6mm regions. CVV at 1 and 3mm exhibits an extremely strong positive correlation with choroidal thickness beneath the highest point of PED in CSC with PED, while at 6mm demonstrates a strong positive correlation, CVV at 6mm area have a weak negative relationship with FV% in all CSC(r=0.424, P=0.028), these differences are statistically significant (table 2). Meanwhile, statistically significant positive correlation has been observed between the SRF area and FV% in CSC, there is no correlation with FVa. Analysis has revealed that in CSC with PED, there exists a statistically significant positive correlation between the area and volume of PED and both FVa and FV% (table 3).

Previous studies have found that choroidal thickening of CSC may be related to the expansion of the outer blood vessels in the choroid, which is similar to our research results^7,29. Our study reveal that CSC patients exhibit a notable thickening of SFCT in comparison to healthy individuals. In CSC eye, there is a significant upward trend in both three-dimensional CVI and CVV within the ETDRS rings of 1, 3, and 6mm in the macular area. This indicates that the increase in the density of Sattler and Haller vessels, and expansion of the lumen perform, these pathological changes will promote the increase of vascular high permeability and the exudation of fluid in the tube³⁰. It is particularly noteworthy that in CSC patients presenting with PED, the elevationchoroidal vascular density (1, 3, 6 mm area) was particularly prominent. It can be seen that the increase of three-dimensional CVI may damage the function of RPE layer and participate in the formation of PED. There is a robust positive relationship between the SFCT, the choroidal thickness under the highest point of PED with CVV(1, 3, 6 mm) in CSC with PED. It can be seen that the choroidal vascular expansion may be one of the factors that affect the thickening of the choroid. We also observed that PED is mainly located in the expanded Sattler and Haller choroidal vascular area. Previous studies have found that PED is mainly located in the fluorescein leakage points of choroidal blood vessels and areas of high vascular permeability^7,9, which is consistent with the phenomenon we observed. Therefore, we speculate that the significantly expanded areas of choroidal blood vessels may be high-risk areas for PED.

CSC disease also involves changes in the choriocapillary³¹. In our study, both FVa and FV% of the choriocapillary layer showed a pronounced increasing trend in CSC patients, these observations suggest that the choriocapillary layer may be experiencing ischemia and hypoxia. Given that the choriocapillary layer primarily facilitates the delivery of nutrients and metabolic processes to the outer retinal tissues, any decrement in blood flow within this layer would maybe result in dysfunctional and morphological alterations in RPE cells. Additionally, an elevation in FV% within the choriocapillary layer also perhaps affects the size of the SRF area in CSC patients, with a positive correlation existing between the two, particularly evident in CSC with PED, which triggers the migration of fluid in choroidal vessel penetrate the RPE layer, towards the subretinal neural epithelium layer, leading to fluid accumulation²⁴. Prolonged accumulation of SRF may promote degenerative alterations in photoreceptors, as well as retard RPE cell metabolism, thereby promoting the buildup of photoreceptor outer segments. In CSC patients with PED, there exists a positive correlation between the FV% and FVa of the choriocapillary layer with the area and volume of PED. Consequently, as FV% and FVa of the choriocapillary layer increase, enhancing the likelihood of fluid in choroidal vessel infiltrating into the RPE-Bruch membrane region and accumulating, thereby facilitating the formation of PED. It is inferred that the increase of FVa and FV% in the choriocapillary layer also may participate in fluid in choroidal vessel into the RPE-Bruch membrane area and accumulating, which is closely related to the formation of PED. In addition, we observed a weakened blood flow signal in the choriocapillary layer beneath PED, as well as a significant vascular dilation of Sattler and Haller layer, show a weak negative relationship between CVV at 6mm area with FV%. Some scholars have proposed that the vascular dilation of Sattler and Haller in CSC may affect the blood flow changes in choriocapillary layer^24,29, which is consistent with the phenomenon we observed.

There are some deficiencies in our research. Due to the insufficient sample size, we did not accurately stage the CSC. Increasing the sample size of CSC patients may help the study of related parameters of the choroidal vascular layer and reduce the impact of age on the choroidal blood vessels. This study did not follow up on outcomes in PED and SRF, so it was unable to observe the changes in related parameters of the choroidal blood vessels after the improvement or deterioration of CSC eyes, as well as their effects on subretinal fluid. These shortcomings will be improved in subsequent experiments.

In summary, in CSC, the expansion of the lumen in Sattler and Haller vascular may be one of the influencing factors in raising SFCT and choroidal thickness under the highest point of PED, its district may be a high-risk area of PED. In addition, the increase in expansion a.nd congestion of the in Sattler and Haller, and the decrease in blood flow of choriocapillary may jointly lead to SRF, lumen expansion of Sattler and Haller also maybe lead to decrease in blood flow of choriocapillary. It is noteworthy that the density of Sattler and Haller vascular increased more significantly, as well as FVa and FV% of choriocapillary increased in CSC patients with PED, which may aggravate the occurrence and development of PED. Certainly, three-dimensional CVI, CVV, and the FVa and FV% of choriocapillary layer maybe helpful for evaluating the progression of PED and SRF in CSC. These indicators potential contribution for understand the pathogenesis of CSC and are expected to be tracking indicators for disease outcomes.

General Information

This study was conducted in accordance with tenets of the Declaration of Helsinki and was approved by the Ethical Review Committee of Renmin Hospital of Wuhan University (WDRY2021-k162). The study employed a cross-sectional design to incorporate 53 patients with CSC who were admitted to the ophthalmology department of the Eastern Renmin Hospital of Wuhan University, spanning from March 2020 to June 2024. The CSC cohort was categorized into two distinct subgroups: a PED-associated subgroup encompassing 27 individuals, comprising 25 males and 2 females, with an age range from 31 to 59 years (mean age: 43.26 ± 7.88 years), and a non-PED subgroup, consisting of 26 cases, including 21 males and 5 females, with an age span ranging from 29 to 69 years (mean age: 45.85 ± 10.52 years). Patients with CSC who present with only SRF are categorized into a group without PED, while manifesting both SRF and PED with double-walled appearance are classified into a group with PED. Patients with CSC were diagnosed based on multi-mode imaging, including Swept-source Optical Coherence Tomography Angiography (SS-OCTA) showed serous detachment of the retinal nerve epithelial layer involving the macular, RPE layer exhibited a wavy appearance or accompanied by finger-like serous detachments, and liquid dark areas between RPE and bruch membrane, with image signal intensity exceeding a threshold value of 8. Fluorescein fundus angiography revealed active leakage and visible pigment epithelial window defects, additionally, Indocyanine green angiography demonstrated typical hyperfluorescent characteristics of the choroid. the course of disease was < 6 months, and the first onset. Exclusion criteria encompassed: patients who had undergone photodynamic therapy or laser photocoagulation, with choroidal neovascularization, ametropia with a spherical equivalent ranging from − 3D to 1D, with poor image quality due to media opacity or insufficient cooperation, with other explaining subretinal fluid or systemic glucocorticoid treatment history, senile macular degeneration, polypoidal choroidal vasculopathy, and other retinal vascular diseases. A total of 27 healthy normal eyes, comprising 22 males and 5 females, were selected for inclusion in the study. These eyes were carefully matched with the patients in terms of gender and age, with the age ranging from 30 to 59 years old (mean age: 44.41 ± 11.53 years old). The inclusion criteria for the healthy control group are as follows: possession of clear optical media, absence of any systemic diseases, absence of any other ocular pathologies, and ametropia with a spherical equivalent ranging from − 3D to 1D. Notably, no statistically significant differences were observed in terms of gender and age between the healthy control group and either the PED-associated or non-PED groups (χ²=1.848, P = 0.397; P > 0.05).

Routine Examination

All subjects underwent basic eye examinations including visual acuity, optometry, and intraocular pressure. The anterior segment of both eyes of the subjects was conducted using a slit lamp microscope. Furthermore, scanning laser ophthalmoscopy was employed to thoroughly assess the retinal status of both eyes, with detailed medical history records made.

OCTA Examination

All subjects underwent SS-OCTA examination (VG100, Henan, China: MicroVision Gmbh) by two highly experienced doctors, using mode Angio 6mmx6mm 512x512 R4 scanning the macular foveal, the wavelength was 1050nm, with a scanning speed of 200000A/s, 56°wide-angle scans, a scanning line length of 16mm, a tissue scanning depth of 2.7mm, an image signal intensity was maintained at a level greater than 8. The best-defined images were selected for analysis using the built-in software of the MicroVision system for calculating structural layers and regions, and manual verification was performed. The measurement of SFCT refers to the distance extending from the Bruch membrane to the scleral junction of the choroid at subfoveal; the measurement of choroidal thickness beneath the highest point of PED signifies the distance between the Bruch membrane to the scleral junction of the choroid; the measurement of PED liquid dark area involves quantifying the area and volume between the elevated RPE layer to Bruch membrane; the measurement of SRF entails determining the area and volume occupied by the space the retinal nerve epithelial layer to REP layer; three-dimensional CVI is defined as the ratio of the volume occupied by Sattler and Haller vascular volume within the total choroidal volume, mainly reflecting the vessel density of choroidal Sattler and Haller layer; CVV is defined as the Sattler and Haller vascular distribution volume of choroid; choriocapillary layer measurement was 25µm below Bruch membrane. Quantification of SFCT, choroidal thickness beneath the highest point of PED, PED, as well as SRF areas and volumes, three-dimensional CVI and CVV were automatically measured and calculated by MicroVision OCT system. The partitioning of the CVI and CVV was conducted by utilizing the circular regions of Early Treatment Diabetic Retinopathy Study (ETDRS), that is a diameter of 1mm, 3mm, and 6mm centered on the macular foveal.

Choriocapillary layer image processing

The choriocapillary layer image was scanned and exported utilizing the software SS-OCTA. Within this image, the presence of bright particles exhibiting a high pixel density serves as an indication of blood flow signals. Conversely, dark particles occupying low-pixel areas represent vascular FVa. The proportion of these dark particles with low-pixel areas, relative to the overall image area, is designated as FV%. To analyze and process the dark regions of the image, as well as calculate FVa and FV%, the ImageJ software is employed. The specific steps²⁸ involved are outlined as follows: 1. The initial 6*6mm image is converted to an 8-bit format. Subsequently, automatic local thresholding is applied to eliminate minor variations in image brightness. 2. The Phansalkar method is then utilized to mark the low-pixel dark areas within the image. 3. The Analyze Particles function is subsequently utilized to conduct a comprehensive analysis and measurement of the image. Within this analysis, FVa is defined as the cumulative area occupied by the dark particles with low-pixel values. Conversely, FV% represents the ratio of the total area occupied by these dark particles with low-pixel values, relative to the entire image area.

Statistical Aanlysis

SPSS 27.0 software was used for statistical analysis. The distribution of variables was rigorous tested by P-P plot, and data with normal distribution were expressed as mean ± SD. In the case of comparing three or more groups, a one-way ANOVA was conducted. Additionally, Levene's test was employed to assess the homogeneity of variance. If the variance was deemed homogeneous, LSD was chosen as the appropriate post hoc analysis method. Conversely, in the absence of homogeneity of variance, Dunnett's T3 test was utilized for post hoc analysis. For comparisons involving two groups, independent sample t-tests were appropriately applied. Furthermore. Furthermore, Pearson correlation analysis was performed to investigate the correlation between variables, provided that the distribution of the statistical variables adhered to normal distribution (statistical significance was determined at P < 0.05).

Informed Consent Statement

Informed consent was obtained form all subjects involved in the study.

commercial relationships disclosures

Amin Xu, None; Qiaoling Lai, None; Changzheng Chen, None; Zhen Chen, None.

funding information:

None

Author Contribution

Conceptualization, A.M.X. and Q.L.L.; methodology, A.M.X. and G.P.S.; software, Q.L.L. and G.P.S.; validation, A.M.X. and Q.L.L.; formal analysis, A.M.X. and Q.L.L.; investigation, A.M.X., Q.L.L.and C.Z.C.; resources, Z.C.; data curation, A.M.X. and Q.L.L.; writing—original draft preparation, A.M.X. and Q.L.L.; writing—review and editing, Z.C. and C.Z.C.; visualization, Q.L.L.; supervision, C.Z.C.; project administration, Z.C.; funding acquisition, Z.C. All authors have read and agreed to the published version of the manuscript.

Acknowledgments

Supported by Eye Center, Renmin hospital of Wuhan University.

Data Availability

Data is provided within the manuscript

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Table 1

Blood vessel indicators of each group

	normal (N=27)	without PED (N=26)	with PED (N=27)
FVa(pixel)	2.235±0.331	2.597±0.565^**	2.658±0.576^**
FV%	0.729±0.402	1.183±0.865^*	1.161±0.790^*
CVI(0-1mm)	0.478±0.0363	0.494±0.054_##	0.540±0.063^***
CVI(0-3mm)	0.485±0.031	0.494±0.038_##	0.522±0.027^***
CVI(0-6mm)	0.458±0.024	0.474±0.033^*_##	0.499±0.030^***
CVV(0-1mm)	0.124±0.033	0.184±0.037^***	0.190±0.043^***
CVV(0-3mm)	1.107±0.279	1.667±0.359^***	1.638±0.247^***
CVV(0-6mm)	3.836±0.968	6.036±1.518^***	6.014±1.102^***

Blood vessel indicators of each group. Normal group VS CSC with or without PED group: *P<0.05, **P<0.01, ***P<0.001; CSC with PED group VS CSC without PED group: ##P<0.01. Data are presented as the mean±SD. PED: retinal pigment epithelial detachment; FVa: choriocapillary flow void area; FV%: choriocapillary flow void area percentage; CVI: choroidal vascular index; CVV: choroidal vascular volume; CSC: central serous chorioretinopathy.

Table 2

Pearson correlation analysis of CVV and choroidal thickness

CVV(0-1mm)

CVV(0-3mm)

CVV(0-6mm)

with PED

(N=27)

SFCT

r

P

0.671

<0.001

0.781

<0.001

0.647

<0.001

PED-CT

r

P

0.835

<0.001

0.900

<0.001

0.797

<0.001

without PED

(N=26)

SFCT

r

P

0.798

<0.001

0.852

<0.001

0.741

<0.001

The pearson correlation analysis of Choroidal vascular volume and choroidal thickness in CSC. P<0.05 is statistically significant. PED-CT: the choroidal thickness below the highest point of retinal pigment epithelial detachment; CVV: choroidal vascular volume; SFCT: subfoveal choroidal thickness; CSC: central serous chorioretinopathy; r: Pearson correlation coefficient.

Table 3

Pearson correlation analysis of FVa, FV% and PED, SRF

with PED

（N=27）

CSC

（N=53）

PED area

PED volume

SRF area

FVa

r

P

0.424

0.028

0.485

0.010

0.297

0.132

0.263

0.057

FV%

r

P

0.493

0.009

0.625

P<0.001

0.404

0.036

0.350

0.01

Pearson correlation analysis of the area, volume of PED and SRF with CSC-related parameters including FVa, FV%. Data are presented as the mean±SD, P<0.05 is statistically significant. PED: retinal pigment epithelial detachment; CSC: central serous chorioretinopathy; FVa: choriocapillary flow void area; FV%: choriocapillary flow void area percentage; r: Pearson correlation coefficient.

No competing interests reported.

Choroidal Blood Flow Changes in Central Serous Chorioretinopathy: Impact on Pigment Epithelial Detachment and Subretinal Fluid

Status:

Version 1

Abstract

Purpose

Methods

Results

Conclusions

Figures

Introduction

Results

Discussion

Materials and Methods

General Information

Routine Examination

OCTA Examination

Choriocapillary layer image processing

Statistical Aanlysis

Declarations

Informed Consent Statement

commercial relationships disclosures

funding information:

Author Contribution

Acknowledgments

Data Availability

References

Tables

Additional Declarations

Status:

Version 1