Changes in retinal vascular density measured by optical coherence tomography angiography in patients with carotid artery stenosis after carotid artery stenting and angioplasty

Purpose The aim of this study was to compare the effect of carotid artery stenting and angioplasty (CASA) on retinal vascular density (VD) in patients with severe carotid stenosis with a healthy control group and to evaluate using optical coherence tomography angiography (OCTA). Methods For this prospective study, eyes on the operated side constituted the ipsilateral eye group, and the other eye constituted the contralateral eye group. 40 eyes of 40 patients with ipsilateral eye of carotid artery stenosis (CAS), 34 eyes on contralateral side, and 30 healthy eyes (control group) were included in this study. We performed quantitative OCTA analyses of retinal VD changes, before and after CASA. The main outcome measures were the quantitative changes of VD of super�cial capillary plexus (SCP) and deep capillary plexus (DCP). Results We evaluated the VD of ipsilateral eyes and contralateral eyes separately before and after the procedure. All patients did not have visual symptoms. There was no signi�cant difference in the VD of SCP in all groups before the procedure. No signi�cant change was observed in all groups when the VD of the SCP was compared before and after the procedure. The VD of the DCP in the ipsilateral and contralateral group improved signi�cantly after CASA. Conclusion OCTA could noninvasively detect retinal VD improvements after CASA in CAS patients. Quantitative changes in VD evaluated using OCTA are thought to be early indicators in the diagnosis of CAS and in the follow-up of treatment success.


Introduction
Carotid artery stenosis (CAS) is one of the major causes of transient ischemic attacks, vascular dementia, and ischemic stroke [1].Reduction of vascular risk factors, anticoagulant therapy, and various invasive surgical procedures (carotid angioplasty and stenting, carotid endarterectomy) are the treatment methods used in the management of CAS.The clinical manifestations of CAS re ect a lack of perfusion of the ipsilateral hemisphere or ocular tissue, including acute neurological de cit and ocular ischemic syndrome [2].Various imaging tests have been used in recent years to evaluate CAS, including doppler ultrasonography, magnetic resonance angiography, and computer tomography angiography [3,4].
Ophthalmic manifestations are common in CAS, as the ophthalmic artery is the rst branch of the internal carotid artery (ICA).An eye examination is usually performed when clinical ocular symptoms, such as sudden or progressive vision loss, occur in patients with internal CAS [5].The retina, one of the most energy-consuming tissues in the body, is particularly susceptible to ischemia [6].Due to the intense metabolism of the photoreceptor layer in the retina, it needs a signi cantly greater ow provided by retinal vascular plexuses.Direct visualization of the retinal vasculature with various imaging modalities provides us with an important opportunity to determine vascular and circulatory function.Abnormal retinal microvascular structure is considered as a new biomarker, indicating that it may be associated with many systemic diseases, especially those underlying cardiovascular and neurodegenerative diseases [7][8][9].The ICA provides most of the blood supply to the retina.We hypothesized that retinal vascular density (VD) changes after carotid artery stenting may have therapeutic effects, as ICA provides most of the ow to the retina.
Optical coherence tomography angiography (OCTA) is a new technology that creates high-resolution images of retinal vascularity [10].OCTA also provides a quantitative assessment of retinal ow [11].Until recently, retinal assessment in patients with CAS was mainly limited to classical angiography, which is invasive and has potential side effects.In contrast, OCTA is a convenient and non-invasive method for detecting and quantitatively measuring retinal perfusion changes.
However, there is limited data in the literature regarding the use of OCTA in the clinical setting of CAS.The aim of this study was to use quantitative OCTA to analyze changes in retinal vascular plexuses before and after carotid artery stenting and angioplasty (CASA) in patients affected by CAS.

Materials and Methods
This prospective study adhered to the principles of the Declaration of Helsinki and was approved by the local ethics committee.Aproval was granted by the Ethics Committee of Basaksehir Cam and Sakura City Hospital (2022.12.405).
Informed consent was obtained from all individual participants included in the study.The participants in the study included patients who underwent CASA the interventional radiology department of our hospital between January 2020 and July 2022 and healthy volunteers.The patients with ipsilateral carotid stenosis formed the ipsilateral eye group, and the other eyes formed the fellow eye group.The exclusion criteria were as follows: patients with refractive error > ± 3D, media opacities, age-related macular degeneration, retinal vascular diseases, retinal dystrophies, ocular surgery in the last six months, uncontrollable systemic vascular disease, and ocular ischemic syndrome, as well as patients with signi cant stenosis of the other ICA, treated or untreated.Patients with these conditions were also excluded from the control group.

Surgical Procedure
The CASA procedure was performed by a single experienced interventional neuroradiologist.Patients received daily dual antiplatelet therapy consisting of acetylsalicylic acid (100 mg) and clopidogrel (75 mg) administered orally seven days before the carotid stenting procedure.A clopidogrel resistance test was given to all patients.A transfemoral arterial approach was used to obtain a complete neuroangiogram of the supra-aortic arteries and their branches, including the bilateral carotid, bilateral vertebral, and bilateral subclavian arteries.The degree of stenosis was calculated according to the calculation de ned in NASCET [12].After intravenous injection of heparin 5,000 IU, a guide sheath was placed in the common carotid artery on the side to be stented.Prior to stenting, the distal lter of the cerebral protection device was passed through the stenotic lesions and opened in a straight segment of the ICA.Afterwards, predilatation was achieved with a balloon when deemed necessary, and an self-expandable stent was placed.Post-dilatation is usually required after stent placement.The operation is terminated with the collection of the lter.In the post-operative period, patients were given three months of dual antiplatelet therapy (75 mg clopidogrel and 100 mg acetylsalicylic acid daily) followed by routine treatment of 100 mg acetylsalicylic acid daily.

Examination
Snellen best-corrected visual acuity, slit lamp biomicroscopy, color fundus photography, and OCTA images were evaluated in the detailed ophthalmological examinations of all patients one or two days before and one month after stenting and angioplasty.For the control group, OCTA imaging was performed twice with an interval of one month, the rst OCTA images were called pre-procedure and the second OCTA images were called post-procedure.OCTA imaging was performed using Topcon DRI OCT Triton Swept Source-OCTA (Topcon Corporation, Tokyo, Japan).The OCTA has a scanning speed of 100,000 A-scans/s; a central wavelength of 1050 nm; full width at half-maximum of 100 nm, allowing 2 µm axial resolution in tissue; and lateral resolution on the retinal surface of 15 µm.The OCTA scans the macular area centered on the fovea and measures an area of 3 × 3 mm 2 scanning cubes with each cube consisting of 320 clusters of B-scans.Each B-scan is repeated four times for 3 × 3 images during the acquisition.The super cial capillary plexus (SCP) and deep capillary plexus (DCP) was analyzed using commercial default automatic segmentation boundaries.

Statistical Methods
Statistics on continuous variables are reported as mean ± standard deviation/median (minimum-maximum) values, and descriptive statistics on categorical variables are reported as numbers and percentages.The conformity of continuous variables to normal distribution was evaluated with the Shapiro-Wilk test.Comparisons between groups were examined with the t-test or the Mann-Whitney U test in independent groups, depending on the distribution structure.Pre-and postprocedure comparisons were also examined with the paired-sample test or the Wilcoxon test, depending on the distribution structure.Relationships between categorical variables were examined with the chi-square test.IBM SPSS Statistics version 28 was used for statistical analysis.The level of signi cance was considered as 95%, and the results were interpreted as statistically signi cant when the p value was ≤ 0.05.

Results
Forty eyes with CASA on the ipsilateral side, 34 eyes on the contralateral side without stenting and angioplasty, and 30 healthy eyes were included in the study.The mean age of the ipsilateral group (75.0%male) was 63.4 ± 9.1 years, that of the contralateral group (70.6% male) was 62.4 ± 12.2, and that of the control group (86.7% male) was 66.7 ± 10.2.The groups were all similar in age and gender (p > 0.05).Descriptive information about the groups is given in Table 1.  2 lists the averages of the whole image, superior, temporal, inferior, and nasal VD of the SCP.In the preoperative and postoperative evaluations, no signi cant difference in VD of the SCP was observed between groups.In the preoperative evaluation, when the groups were compared in pairs, only the ipsilateral group's average nasal VD was signi cantly lower than the control group's.Likewise, no signi cant increase was observed in the whole image, superior, temporal, inferior, or nasal VD of the SCP after the procedure in the ipsilateral and contralateral groups compared to before the procedure (p < 0.05).after the procedure between and within each group.Upon evaluating the preoperative DCP's whole image, superior, temporal, and nasal VD, the control group emerged as signi cantly higher, though no difference was observed in the inferior quadrant.In the postoperative evaluation, only the VD of the DCP in the temporal quadrant of the ipsilateral group was lower than the control group.A signi cant increase was observed in the superior, temporal, inferior, and nasal VD averages of the DCP after the procedure in both the ipsilateral and contralateral groups compared to before the procedure (p < 0.05).
In the control group, VD of DCP was signi cantly higher in all quadrants before the procedure than in the other groups, but no signi cant difference arose for the SCP.There was also no signi cant difference between the pre-and post-procedure variables in the control group (p > 0.05).

Discussion
CAS causes decreased ophthalmic arterial ow, which can lead to ocular complications [2].While this ocular involvement is rare because of the multiple anastomoses in the ophthalmic artery, identifying patients at risk of this side effect is crucial, as retinal damage can lead to irreversible consequences [2].In our study, we investigated short-term retinal changes in the microvascular area after CASA in patients who developed severe CAS.The included patients did not exhibit signs of ocular ischemic syndrome; therefore, as is the case with ocular complications, we considered vascular anastomoses to be present.
In this study, we quantitatively evaluated retinal microvascular parameters using OCTA, a high-resolution retinal imaging device.OCTA is a quick, easy, and non-invasive procedure that shows the VD value of the retina without injecting dye into the vein.This technology has received great attention in clinical research in recent years, with its clinical use becoming increasingly more common.The reproducibility of quantitative VD analysis is an active realm of study in healthy subjects and patients with multiple retinal diseases.With this study, we showed that the OCTA device can also be used for the evaluation and follow-up of successful CASA procedures.
Stenosis of the carotid artery leads to reduced ocular blood ow [5,13,14].In our study, patients with CAS showed decreased VD of DCP values when compared to healthy controls.The importance of the gender difference in retinal microvascular perfusion changes due to CAS has been noted in previous studies on coronary and cerebral microvascular diseases [15,16].Gender-speci c differences in cardiovascular disease have been hypothesized to be related to other gender-based differences in microvascular structure and metabolic reaction [17].In our study, we thus determined the study groups by considering the gender differences in the regulation of tissue blood perfusion via microcirculation modulation.
The VD of the SCP of all groups did not differ signi cantly in all quadrants.VD of the DCP showed a signi cant difference between the ipsilateral and contralateral groups However, this analysis should be interpreted with caution because the VD of the DCP is di cult to measure and affected by projection artifacts, and reproducibility is poor.As patients with unilateral CAS were included in our study, we expected a signi cant difference between VD of the SCP and DCP of the ipsilateral group and the basal VD of the contralateral group, but this was not the case.This result may be related to collateral development.Further, after carotid stenting, VD in the ipsilateral and contralateral groups did not change in the super cial layer, but increased signi cantly in the deep layer.The DCP is a vascularized low-pressure network from branches of the central retinal artery.Therefore, decreased perfusion pressure is expected to primarily affect the DCP [18,19].In our study, the signi cant increase in DCP after CASA was in parallel with extant research.
Carotid stenting surgery improves cerebral perfusion and has a positive effect on contralateral cerebral blood ow through collateral circulation [20,21].In our study, we also found a positive effect on retinal VD in the contralateral group.This effect may be secondary to CASA's positive effect on cerebral blood ow or the result of a general improvement in blood circulation secondary to anticoagulant and antiaggregant treatments administered before and after the procedure.The positive effect of carotid stenting on ipsilateral retinal blood ow has been previously reported [22].The same researcher also demonstrated bilateral increased choroidal thickness using Enhanced depth imaging optical coherence tomography in patients with CAS after carotid stenting, further hypothesizing that this may have potential as an adjunct to the examination of ocular perfusion after carotid endarterectomy [22].Although OCTA is highly rapid, non-invasive, and reproducible, an important limitation of this device is that it does not indicate the direction of vascular ow, only VD.
In comparing our ndings to the literature, there is consensus regarding the increase in VD associated with CAS in asymptomatic eyes [23].However, con icting data from different studies may be related to the limited number of patients included in such studies and the variability of concomitant ocular or systemic diseases.Therefore, comprehensive multicenter prospective studies are needed to reach more accurate results.
Additionally, the number of patients in our study was higher than those presented in the literature, and we focused only on VD assessment with the OCTA device.Therefore, we believe that our research can provide useful information about the role of quantitative OCTA in detecting early retinal vascular changes by examining changes in retinal VDs during and after CASA.In this way, we can better evaluate the treatment strategies and success of the surgical procedure.Because OCTA examination is quick and noninvasive, the OCTA device stands out as an important aid in classifying the risk of complications in CAS patients.
This study is limited by the small number of included patients and volunteers, as well as the short follow-up period.We also did not record information about high-risk plaque characteristics such as plaque hypo-/hyperechoicity, plaque length, and plaque surface area.Because the presence of these high-risk plaques may affect retinal microvascular circulation, it should be evaluated in future studies.Further studies with larger numbers of patients and longer follow-up periods are also necessary to evaluate whether OCTA can be used as an important marker in the diagnosis of CAS and evaluating treatment success.
In conclusion, patients with CAS showed a signi cant reduction in VD of the SCP and DCP compared to healthy controls.While there was no signi cant change in VD of the SCP after surgery, a signi cant change was observed VD of the DCP.
OCTA measurement and quantitative VD analyses may thus represent a useful, rapid, non-invasive, and objective approach to diagnose CAS and evaluate treatment success. Declarations

Table 1
Continuous variables are presented as the mean ± standard deviation or median (min-max).Categorical variables are presented as number (%) a Independent-samples t test, b Chi Square test, c Mann Whitney U Table