Evaluation of the Optic Nerve Head Using Optical Coherence Tomography Angiography in Systemic Sclerosis Patients

Introduction This study aims to quantify retinal microvascular vessel density using optical coherence tomography angiography (OCTA) in patients with systemic sclerosis (SS), whether there is a difference in values with the controls and to correlate it with the disease activity, damage risk and drug usage. Material- method SSc patients were enrolled, and age- and gender-matched controls underwent OCTA, after basic ophthalmological and rheumatological examinations in this cross-sectional, prospective study. Results 61 eyes of 61 consecutive SSc patients with a median age 52 years were investigeted. There was no statistically signicant difference between patients and control groups regarding RNFL and OCTA measurements. As the ANA titer increases (RNFLs (p=0.01, r=-0.327), RPCwhole (p= 0.029, r= 0.279), RPCperipapiller (p=0.037, r=-0.267), RPC superior (p= 0.003, r=-0.371), RPCinferior (p=0.02, r=0.297)); there was a statistically signicant decrease. RPC inside values were found to be lower in Anti Scl 70 positive patients compared to negative ones (p=0.021). RNFLn (p = 0.03), r =-0.278) value decreased as the years of disease increased. RPCinside value was found to be higher in patients using hydroxychloroquine and calcium channel blocker than those who did not use hydroxychloroquine respectively (p=0.021, p=0.027). RPC whole, RPC peripapillary, RPCnasal values were found to be statistically signicantly higher in corticosteroid users than those who did not, respectivly (p = 0.043; 0.030; 0.033) Conclusion safe, fast eye in single scan.


Introduction
Systemic sclerosis (SS) is a chronic multisystem disorder with vasculitis. Immune activation, vasculopathy, and excessive brosis are seen in the articulars and internal organs [1]. These vascular anomalies result in tissue hypoxia [2].
Endothelial cell dysfunction has been demonstrated, especially in the microvascular system [3].
Cutaneous manifestations, such as Raynaud's phenomenon, nail fold capillary changes, and digital ulcers, have been observed as a result of vascular damage. Moreover, ischemic damage is present in other target organs, such as the heart, lung, kidney, muscles, and gastrointestinal system [4].
Previous studies found that OCTA offers large repeatability at intra-and inter-visit [6]. OCTA has also been examined in connective tissue diseases, such as systemic lupus erythematosus and vasculitis, such as Bechet's disease [7,8].
The association of SS with glaucoma and changes in choroidal thickness has been discussed in previous studies using optical coherence tomography (OCT) [9,10]. To our knowledge, no attempt has been made to evaluate the peripapillary retinal vasculature using OCTA in SS patients.
This study quanti ed the retinal microvascular vessel density in SS patients using OCTA and identi ed whether there is a difference in values between SS patients and healthy individuals, correlating it with disease activity, damage risk, and drug usage.

Material-Method
This prospective, observational, comparative cross-sectional study was performed between July and OCT angiography was examined by the same person (FY) using the spectral domain OCT (RTVue-XR Avanti version 2018.0.0.14, Optovue, Fremont, CA, USA) in the morning (9:00-11:00am) to avoid possible diurnal variations. The volumetric scans were processed by the SSADA algorithm. One eye of each participant was examined and scanned during the same visit. The eye with higher image quality in OCTA measurement was included to the study.
All scans were made up of two 4.5 mm × 4.5 mm images of the optic disc area. RNFL thickness was averaged from a circular sampling pro le with a diameter of 3.4 mm centered on the disc.
The peripapillary retinal area was de ned as a 700-µm-wide elliptical annulus extending outward from the optic disc boundary (Fig. 1). The sectorial division of the peripapillary region was automatically performed by the OCTA device as superior and inferior hemi-radial peripapillary capillaries, and all quantitative results were recorded.
The peripapillary vessel density was de ned as the proportion of the total scanned area occupied by blood vessels. These vessels were de ned as pixels with decorrelation values over the threshold in the noise region, which were two standard deviations higher than the mean decorrelation value [11].
All measurements were performed using the manufacturer's tools and Analytical AngioVue software.

Statistical analysis
Data analyses were performed using SPSS software (SPSS for Windows, v. 20.0; SPSS, Inc., Chicago, IL, USA). Descriptive statistics included the mean and standard deviation for normally distributed variables and the median for non-normally distributed variables. A p value of ≤ 0.05 was considered statistically signi cant. The Kruskal-Wallis test was performed to compare the differences between the two groups. A chi-square test was used to analyze the frequency data on gender. Spearman correlation analysis was performed to determine the relationships between the peripapillary perfusion parameters and related factors. An independent t-test was used for comparing the normally distributed independent variables, and the Mann-Whitney U test was used for the analysis of the independent variables that did not conform to a normal distribution. Regression analysis was performed for values with signi cant correlations.

Results
A total of 61 eyes of 61 consecutive SS patients (59 women and 2 men), with a mean age 52 ± 12 (34-76) years, were investigated using OCTA imaging with SD-OCT. Table 1 shows the demographics and clinical characteristics of the study.    The negative correlation between nasal RNFL and time from disease diagnosis was shown in Fig. 2. No signi cant relationship was found between anti-Cenp positivity and the RPC and RNFL values (p > 0.005).
No correlation was found between the RNFL and RPC values, depending on whether the disease was diffuse or localized (p > 0.005).

Discussion
Vasculopathy in SS affects small arteries and capillaries. It reduces capillary density [12]. Sahin Atik et al. found that there was a predisposition to optic nerve head damage and glaucoma as a result of generalized vasospasm [13]. There are other studies on non-glaucomatous optic neuropathy [14]. The frequency of glaucoma in autoimmune diseases has also been linked to vascular dysregulation and has been considered to be related to endothelin-1 [15].
Allanore et al. found that the incidence of glaucomatous optic neuropathy was higher than ocular hypertension (HT), although IOP was normal in a prospective cohort study [9]. Sahin Atik et al. extended Allanore's study by examining the retinal nerve ber and optic disc morphology using OCT in scleroderma patients who were not diagnosed with glaucoma and found that only those with a c/d ratio > 0.5 showed a statistically signi cant thinning in the inf RNFL quadrant [13]. Coskun et al. found a statistically signi cant difference in choroidal thickness in scleroderma patients, and they attributed this to the choroidal hypoperfusion shown in the fundus oresein angiography (FFA) [16].
Serup et al. showed some changes, especially in pigment epitheliopathy and retinal arterioles, which are considered to be associated with it, and persistent hyper uorescence in the temporal venules in the FFA [17]. Farkes et al. found some choroidal changes with endothelial damage. These changes were considered to be similar alterations to skin and renal affection and could be related to the ow in the optic nerve [18]. Although the exact cause of RPE atrophy in primary SS could not be determined, it was considered to be associated with choroidal ow and choroidal disorder secondary to hypertensive retinopathy. Usiyama et al. found that retinopathy ndings were higher in normotensive SS than in the control group [19]. Grennan et al. found choroidal hypoperfusion areas in the FFA except for one patient, no HT was found [20].
Only the super cial optic nerve head vessel can be seen with the optic disc circulation in the FFA. Deep vessels cannot be seen [21]. Capillary ow in the small retina area can be measured with a laser Doppler owmeter, but its results have been found to be variable [22]. OCTA is a reproducible technique that enables the understanding of the vascular structure of the optic disc and macula in a non-invasive manner based on ow [23]. OCTA visualizes the microvasculature by detecting motion contrast from owing blood without dye injection [24]. OCTA has been found to be more precise in scanning macular capillaries and the RPC than FFA [25]. Many studies have been conducted using FFA, some with the Heidelberg retina owmeter and the confocal scanning technique, to evaluate ocular blood ow. However, as some techniques are invasive, they cannot measure quantitatively and have some limitations because they cannot show the microvascular bed well [26]. The AngioVue automatically analyzes vessel density in different layers, which is its major advantage over conventional angiography.
It is known that RNFL thickness and RPC density decreases with age [27]. We selected age-matched controls to prevent them from affecting our measurements.
The quantitative data from these retinal vessels is likely be useful in analyzing metabolic activity from the retina [28]. In the current study, the decrease between the values of RNFL and RPC OCTA values and the disease duration suggests that these parameters are affected as the years of disease increase.
Although ANA is not used in SS activity, studies have pointed out ANA subsets to be useful in anticipating long-term outcomes [29]. In the current study, the increase in the ANA titer and the decrease in RNFL superior, RPC whole, peripapillary, inferior, and temporal values suggest that vascular values are affected. The decrease in the RPCinside value in anti-Scl 70-positive patients also supports this nding.
Many reasons can be attributed to the perfusion of the optic disc. The main cause is vasculopathy and immune activation, resulting in excessive brosis [30]. Ischemia occurs as a result of intimal broblastic proliferation and vasospastic episodes in SS [31]. Endothelin-1 and angiotensin 2, which are potential vasoconstrictors, are known to increase in SS patients and play a role in the vasospastic process. 32 These structural changes and prolonged vasospasm are considered to be due to decreased blood ow [33].
Calcium channel blockers are widely used agents for reducing the frequency and severity of ischemic attacks in Reynaud's phenomenon [34]. Esen et al. found no difference in choroid thickness and central macular thickness in terms of calcium channel blocker users [10]. In the present study, the RPC inside value was found to be higher in patients using calcium channel blockers. In addition, the higher RPC values in those who use hydroxychloroquine, immunosuppressive drugs, and corticosteroids suggest that these drugs are effective against vascular density and in amation in SS disease. Therefore, there is a need for a randomized controlled study on this subject.
To the best of our knowledge, there has been no research on OCTA that searches the optic disc RPC parameters. Only one study has investigated the RPC values in the macular region. Hekimsoy et al. conducted OCTA measurements in the macular region in patients with SS. Accordingly, the super cial capillary plexus vessel density and the deep capillary plexus vessel density of the fovea were signi cantly lower than those in the healthy control subjects [35].
This study is limited by the small sample size, the cross-sectional design, and the inclusion of SS patients with a relatively short follow-up period, such as a median of six years. We recommend conducting further longitudinal studies with a larger sample size and including patients diagnosed with SS for over 10 years to establish the correlation between disease activity and damage scores.
In conclusion, SS is an uncommon multisystem disorder that is related to immune activation and vasculopathy-associated complications. It results in the overproduction and accumulation of collagen and other extracellular matrix proteins. OCTA is a safe, fast, and non-invasive examination and can be used to investigate subclinical eye involvement in rheumatologic diseases using a single scan.

Declarations
Con icts of interest: The rst draft of the manuscript was written by Sibel Zirtiloglu and all authors commented on previous versions of the manuscript. All authors read and approved the nal manuscript.