key: cord-0828696-fi8sedcj
authors: Turker, Ibrahim Cagri; Dogan, Ceylan Uslu; Dirim, Ayşe Burcu; Guven, Dilek; Kutucu, Oguz Kaan
title: Evaluation Of Early And Late Covid-19-Induced Vascular Changes With Optical Coherence Tomography Angiography
date: 2021-05-21
journal: Can J Ophthalmol
DOI: 10.1016/j.jcjo.2021.05.001
sha: 99564e82291eea6bb4ead633aa91bdfbd20fd3f7
doc_id: 828696
cord_uid: fi8sedcj

OBJECTIVE: To evaluate vascular changes in the early period after COVID-19 infection and at a 6-month follow-up. METHODS: This study included 50 eyes of 25 patients who had been hospitalized for PCR-positive COVID-19 infection and 50 eyes of 25 healthy individuals. All subjects underwent optical coherence tomography angiography (OCT-A) using a 6 × 6 macular protocol in the early period after hospital discharge and 6 months later. Foveal vessel density (VD) and parafoveal VD values were measured from 4 quadrants (superior, inferior, nasal, temporal) of the superficial capillary plexus (SCP) and the deep capillary plexus (DCP). Choriocapillaris (CC) flow area and foveal avascular zone (FAZ) area were also measured. The OCT-A measurements of the patient group were compared both between time points and with the control group at each time point. RESULTS: COVID-19 patients showed lower VD values than control subjects in all parafoveal quadrants of both the SCP (superior, p=0.01; inferior, p=0.048; nasal, p=0.003; temporal, p=0.048) and the DCP (superior, p=0.001; inferior, p=0.011; nasal, p=0.012; temporal, p=0.018) at the initial checkup and in all parafoveal quadrants of the SCP (superior, p=0.0001; inferior, p=0.007; nasal, p=0.001; temporal, p=0.017) and in 2 of the parafoveal quadrants of the DCP (superior, p=0.003; inferior, p=0.016) at the 6-month follow-up. CC flow area values were significantly lower at the 6-month follow-up compared with the initial examination (p=0.044). CONCLUSION: It is important to perform appropriate follow-up for COVID-19 patients as retinal vascular flow changes may persist in the long term.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID- 19) , was identified in January of 2020 following research conducted to investigate a group of patients with respiratory symptoms such as fever, cough, and shortness of breath in the Wuhan Province of China. COVID-19 shows a pathology ranging from minimal symptoms to acute respiratory distress syndrome and multiorgan damage. 1 Complement activation and the intense inflammatory response caused by SARS-CoV-2 can lead to microvascular damage and coagulopathy, which in turn can lead to multisystemic organ damage. 2 SARS-CoV-2 can directly impair endothelial cell function by binding to angiotensin converting enzyme 2 (ACE2). This virus can cause endothelial cell damage from the inflammatory response it triggers, leading to widespread vascular damage. 3 Because of its multisystemic nature, COVID-19 can also affect ocular tissues. The presence of the virus in conjunctival swabs on the ocular surface has been demonstrated by PCR. 4, 5 Due to its dense microvascular circulation, the retina can be affected by microvasculopathy caused by COVID-19. Abrishami et al. reported that COVID-19 can cause retinal ischemia. 6 Optical coherence tomography angiography (OCT-A) is a modern, noninvasive, repeatable technology that uses an algorithm to measure blood flow velocity using serial measurements of vascular flow taken at the same point. This study aimed to compare short-and long-term OCT-A changes in patients who were hospitalized with PCR-positive COVID-19 infection but who did not have a history of intubation or intensive care hospitalization with a healthy control group.

This study was carried out with the approval of the Şişli Hamidiye Etfal Training and Research Hospital Ethics Committee and in compliance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants.

This study included patients who were hospitalized between May and June 2020 due to PCRpositive COVID-19 infection, who had no history of intubation or intensive care hospitalization, and who had been discharged after showing PCR-negative. Thus, all patients were PCR-positive at admission and PCR-negative at discharge. OCT-A imaging was performed for each subject shortly after discharge and at a 6-month follow-up. A control group with similar age and gender demographics was selected from healthy subjects who presented at our ophthalmology clinic for routine ophthalmological examination.

The best corrected visual acuity of each subject was measured with a Snellen chart. Intraocular pressures and pachymetric values were also recorded. Slit-lamp anterior segment and fundus examinations were performed. Foveal vascular flow changes were evaluated using the OCT-A 6x6 macular protocol.

All patients volunteered to participate in this study. The majority of the study group consisted of hospital personnel. No patients showed a second COVID-19 infection or a new systemic disease after discharge. Two patients were lost to follow-up and were thus excluded from the study.

Patients were excluded if they presented with a history of any ocular or systemic disease that could affect retinal circulation (such as diabetes, hypertension, or rheumatic diseases) or if they had an intraocular pressure above 21 mmHg, an axial length less than 20 mm or more than 24 mm, or a substantial refractive error (spherical above +3 diopters or -3 diopters; astigmatism above 1.5 diopters that may affect the OCT-A results). In addition, patients who were receiving systemic treatment with agents such as hydroxychloroquine or steroids that might have ocular effects were excluded.

OCT-A was used to measure deep capillary plexus (DCP) and superficial capillary plexus (SCP) vessel density (VD) in the foveal area as well as DCP and SCP VD within 4 quadrants (superior, inferior, nasal, temporal) of the parafoveal area. OCT-A was also used to evaluate choriocapillaris (CC) flow area and foveal avascular zone (FAZ) area. Data were compared both between the initial measurements and the 6-month follow-up and between the patient group and the control group.

A single technician performed all scans using the same device at the same time of day (between 10 a.m. and 2 p.m.) following pupil dilation with tropicamide. For infection control purposes, assessments of normal subjects were performed after all COVID-19 patients had completed their participation in the study. OCT-A images were obtained using the AngioVue Imaging System version 2017.1 (Optovue, Inc., Fremont, CA, USA). A previously described algorithm was used for OCT-A, which included obtaining OCT 3D macular images and activating the eye-tracking system. The device used in this study had two scanning area options (6x6 mm and 3x3 mm). Since we believe that 6x6 mm scans might be better than 3x3 mm scans in the evaluation of vascular changes and considering that a wider field of view would increase the sensitivity of additional areas of capillary non-perfusion, we used 6x6 mm scans in our study.

Automated quality index (scored between 0 to 10) provided by the AngioVue Imaging System was used to assess the quality of the scans, and the scans with a quality index of equal to or greater than 7 were included. Low-quality scans (signal strength index<7/10) were excluded, and patients were re-imaged until satisfactory image quality (≥7/10) was obtained.

For both SCP and DCP, VD values were calculated for the four quadrants of the parafoveal zone (nasal, temporal, superior, inferior) and for the foveal zone. In addition, CC flow area and FAZ area were calculated.

Previously defined retinal and choroidal layers automatically identified by the software algorithm were used. 7 The upper and lower boundaries of the SCP were 3 micrometers (µm) below the internal limiting membrane and 15 µm below the inner plexiform layer, respectively. The DCP was defined as the region between 15 and 70 µm below the inner plexiform layer. The upper and lower boundaries of the CC layer were considered to be 30 and 60 micrometers below the retinal pigment epithelium, respectively.

Foveal zone VD was defined as the percent density of vessels in a 1-mm diameter circle. The parafoveal zone VD was defined as the percent density of vessels in the area within a 3-mm diameter circle excluding the foveal zone. To calculate VD, a binary image of the blood vessels was extracted from the greyscale OCT-A image using AngioVue Analytics software (Optovue, Inc). Next, the percentage of pixels with a flow signal greater than a specific threshold was calculated for the relevant region and layer. Parafoveal zones were automatically divided into quadrants (temporal, nasal, inferior, and superior). In addition to calculating descriptive statistical methods (mean and standard deviation), Shapiro-Wilk normality tests were used to examine the distribution of variables; independent t-tests were used to compare normally distributed variables in binary groups, paired t-tests were used to compare the first examination with the 6-month follow-up; and chi-square tests were used to compare qualitative data. Results were considered significant at a threshold of p<0.05.

This study included 50 eyes of 25 patients hospitalized and discharged due to PCR-positive COVID-19 infection and 50 eyes of 25 healthy subjects as a control group. There were no statistically significant differences in either the mean age or the gender distributions between the patient group and the control group. The demographic data of the study participants are shown in Table 1 .

As detailed in the methods section, all scans were obtained with a signal strength index of 7 or higher. There were no statistically significant differences in the signal strength index values between the two groups. (Table 2) At the first examination, the OCT-A data of the COVID-19 group showed lower VD values than those of the control group in all 4 parafoveal quadrants of the SCP (superior, p=0.01;

inferior, p=0.048; nasal, p=0.003; temporal, p=0.048) and in all 4 parafoveal quadrants of the DCP (superior, p=0.001; inferior, p=0.011; nasal, p=0.012; temporal, p=0.018). At the 6-month follow-up appointment, VD values were found to be lower in the patient group compared to the control group in all 4 parafoveal quadrants of the SCP (superior, p=0.0001; inferior, p=0.007; nasal, p=0.001; temporal, p=0.017) and in 2 of the parafoveal quadrants of the DCP (superior, p=0.003; inferior, p=0.016). No significant differences were found between the patient group and the control group in terms of foveal SCP VD values, foveal DCP VD values, CC flow area, or FAZ area at either the initial check-up or the 6-month follow-up. (Table 3) The initial examination OCT-A data and the 6-month follow-up data were also compared within the study group. It was found that the 6-month follow-up CC flow area values were significantly lower than the initial examination CC flow area values (p=0.044). No other significant differences were observed.

The current study compared OCT-A data between healthy controls and patients who had been hospitalized with PCR-positive COVID-19 infection and who did not have a history of intubation or hospitalization in intensive care. We report that, compared to the control group, the patient group showed significantly lower VD values in all parafoveal quadrants of both the SCP and the DCP in the early period as well as in all parafoveal quadrants of the SCP and 2 (superior, inferior) of the parafoveal quadrants of the DCP at a 6-month follow-up. When the early period and the 6-month follow-up OCT-A data were compared within the patient group, we found that the CC flow area measurements had significantly decreased at the 6month follow-up.

Coronaviruses consist of four structural proteins: spike (S) protein, membrane (M) protein, envelope (E) protein, and nucleocapsid (N) protein. Previous studies have reported that the S protein of SARS-CoV-2 is the functional receptor for ACE2. 8 Although ACE2 is known to be expressed at high rates in lung, heart, ileum, kidney, and bladder epithelial cells, this receptor is expressed at various levels in almost every organ in the body .9,10 In addition, ACE-2 receptors are present in all endothelial cells, especially in the heart, lungs, kidneys, and gastrointestinal system. 11 SARS-CoV-2 infection of endothelial cells can lead to many tissue changes, including ischemia, edema, and hypercoagulability. In addition, immune mediators such as TNF-alpha, IL-1, and IL-6 can greatly increase due to the intense inflammatory response caused by COVID-19, which may lead to coagulopathy or thrombosis due to an increase in leukocyte adhesion to endothelial cells. This increase in inflammatory mediators can lead to ARDS, disseminated intravascular coagulation (DIC), or hypercoagulation. 12 The retina has a dense vascular structure, and therefore is vulnerable to changes from COVID-19 due to the diffuse microangiopathy caused by this disease. Abrishami et al.

conducted an OCT-A study in patients with recent COVID-19 infection and reported that patient parafoveal VD values were decreased in the DCP and the SCP. 6 In that Abrishami study, 3x3 mm scans were used. In contrast, larger area scans (6x6 mm) were used in the present study and parallel findings were obtained. Another study reported that perfusion density was low in the radial peripapillary capillary plexus following COVID-19 infection. 13 Further, retinal hemorrhages, cotton wool spots, dilated veins, and increased venous tortuosity have each been detected by fundus examination of individuals infected with COVID-19; and patients were reported to show increased diameters of both arteries and veins compared to a control group. 14 Acute macular neuroretinopathy and paracentral acute middle maculopathy inducing sudden vision loss, negative scotomas, and dyschromatopsia are among the complications of COVID-19 infection reported in the literature. 15 In agreement with previous studies, the current study reports a decrease in VD values measured with OCT-A in all parafoveal quadrants of the SCP and DCP in the early period after COVID-19 infection.

While trying to elucidate the pathogenesis of inflammation and ischemia-based microvascular changes caused by COVID-19, a new phrase called "long COVID" has recently come into use to refer to the symptoms of COVID-19 that are prolonged for longer than expected. For example, 87% of people hospitalized for COVID-19 in Italy who were evaluated an average of 60 days after discharge still continued to experience COVID-19 symptoms. 16 Additionally, in a study of 384 patients who were followed-up for an average of 54 days after acute COVID-19 infection, continuous shortness of breath was reported in 53% of patients, cough in 34%, fatigue in 69%, and depression in 14.6%. In the same study, high D-dimer and C reactive protein (CRP) values were found at follow-up, especially in those who were discharged with high D-dimer and CRP values. 17 Puntmann et al. reported ongoing myocardial inflammation on cardiac magnetic resonance imaging after SARS-Cov-2 infection, emphasizing the necessity of late follow-up. 18 In agreement with these previous studies, the current study reports decreased VD values for all parafoveal quadrants of the SCP and for 2 parafoveal quadrants (superior, inferior) of the DCP at a 6-month follow-up in a patient group compared to a group of healthy controls. When patient data from the early period after infection and the 6-month follow-up were compared, a decrease in CC flow area values was found. infection.

In conclusion, this study performed OCT-A examinations in the early period after COVID-19 hospitalization and 6 months later and investigated changes in these results over time as well as differences between patient results and those of healthy controls. We detected a decrease in VD in all parafoveal quadrants of the SCP and the DCP in the early period as well as in the parafoveal region of the superficial capillary plexus for all quadrants and the deep capillary plexus for the superior and inferior quadrants at the 6-month follow-up. In addition, when comparing changes over time between the early period and the 6-month follow-up, we found a decrease in CC flow area values. Multi-centered, long-term studies with large numbers of cases are needed to clarify the early and long-term retinal and choroidal vascular changes caused by COVID-19.

Footnotes And Disclosure: The authors have no proprietary or commercial interest in any materials discussed in this article.

Meeting presentation: The study was not presented at a meeting.

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. SSI: strength signal index. Bolded p-values below 0.05 were considered statistically significant. 

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