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      Optical coherence tomography-based assessment of macular vessel density, retinal layer metrics and sub-foveal choroidal thickness in COVID-19 recovered patients

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          Abstract

          Purpose:

          The primary objective of the study was to assess the macular retinal vessel density, subfoveal choroidal thickness, and retinal layer metrics by optical coherence tomography angiography (OCTA), enhanced-depth imaging optical coherence tomography (EDI-OCT), and spectral domain optical coherence tomography (SD-OCT), respectively, in recovered COVID-19 patients and its comparison with the same in control subjects. The secondary objective was to evaluate differences in OCTA parameters in relation with the severity of COVID-19 disease and administration of corticosteroids.

          Methods:

          A case–control study was performed that included patients who had recovered from COVID-19 and age-matched healthy controls. Complete ocular examination including OCTA, SD-OCT, and EDI-OCT were performed three months following the diagnosis.

          Results:

          Three hundred sixty eyes of 180 subjects were enrolled between the two groups. A decreased mean foveal avascular zone area in both superficial capillary plexuses ( P = 0.03) and deep capillary plexuses ( P < 0.01), reduced average ganglion cell layer-inner plexiform layer thickness ( P = 0.04), and increased subfoveal choroidal thickness ( P < 0.001) were observed among cases in comparison to the control group. A significant correlation was found between sectoral macular vessel density in relation to disease severity and a decrease in vessel density with greater severity of the disease.

          Conclusion:

          OCTA detected retinal microvascular alterations following SARS-CoV-2 infection in subjects with the absence of any clinical ocular manifestation or systemic thrombotic events. These parameters could be used to help identify patients with a higher incidence of systemic thromboembolism on longer follow-ups and identify the impact of corticosteroids on retinal architecture.

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          Most cited references26

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          Endothelial cell infection and endotheliitis in COVID-19

          Cardiovascular complications are rapidly emerging as a key threat in coronavirus disease 2019 (COVID-19) in addition to respiratory disease. The mechanisms underlying the disproportionate effect of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on patients with cardiovascular comorbidities, however, remain incompletely understood.1, 2 SARS-CoV-2 infects the host using the angiotensin converting enzyme 2 (ACE2) receptor, which is expressed in several organs, including the lung, heart, kidney, and intestine. ACE2 receptors are also expressed by endothelial cells. 3 Whether vascular derangements in COVID-19 are due to endothelial cell involvement by the virus is currently unknown. Intriguingly, SARS-CoV-2 can directly infect engineered human blood vessel organoids in vitro. 4 Here we demonstrate endothelial cell involvement across vascular beds of different organs in a series of patients with COVID-19 (further case details are provided in the appendix). Patient 1 was a male renal transplant recipient, aged 71 years, with coronary artery disease and arterial hypertension. The patient's condition deteriorated following COVID-19 diagnosis, and he required mechanical ventilation. Multisystem organ failure occurred, and the patient died on day 8. Post-mortem analysis of the transplanted kidney by electron microscopy revealed viral inclusion structures in endothelial cells (figure A, B ). In histological analyses, we found an accumulation of inflammatory cells associated with endothelium, as well as apoptotic bodies, in the heart, the small bowel (figure C) and lung (figure D). An accumulation of mononuclear cells was found in the lung, and most small lung vessels appeared congested. Figure Pathology of endothelial cell dysfunction in COVID-19 (A, B) Electron microscopy of kidney tissue shows viral inclusion bodies in a peritubular space and viral particles in endothelial cells of the glomerular capillary loops. Aggregates of viral particles (arrow) appear with dense circular surface and lucid centre. The asterisk in panel B marks peritubular space consistent with capillary containing viral particles. The inset in panel B shows the glomerular basement membrane with endothelial cell and a viral particle (arrow; about 150 nm in diameter). (C) Small bowel resection specimen of patient 3, stained with haematoxylin and eosin. Arrows point to dominant mononuclear cell infiltrates within the intima along the lumen of many vessels. The inset of panel C shows an immunohistochemical staining of caspase 3 in small bowel specimens from serial section of tissue described in panel D. Staining patterns were consistent with apoptosis of endothelial cells and mononuclear cells observed in the haematoxylin-eosin-stained sections, indicating that apoptosis is induced in a substantial proportion of these cells. (D) Post-mortem lung specimen stained with haematoxylin and eosin showed thickened lung septa, including a large arterial vessel with mononuclear and neutrophilic infiltration (arrow in upper inset). The lower inset shows an immunohistochemical staining of caspase 3 on the same lung specimen; these staining patterns were consistent with apoptosis of endothelial cells and mononuclear cells observed in the haematoxylin-eosin-stained sections. COVID-19=coronavirus disease 2019. Patient 2 was a woman, aged 58 years, with diabetes, arterial hypertension, and obesity. She developed progressive respiratory failure due to COVID-19 and subsequently developed multi-organ failure and needed renal replacement therapy. On day 16, mesenteric ischaemia prompted removal of necrotic small intestine. Circulatory failure occurred in the setting of right heart failure consequent to an ST-segment elevation myocardial infarction, and cardiac arrest resulted in death. Post-mortem histology revealed lymphocytic endotheliitis in lung, heart, kidney, and liver as well as liver cell necrosis. We found histological evidence of myocardial infarction but no sign of lymphocytic myocarditis. Histology of the small intestine showed endotheliitis (endothelialitis) of the submucosal vessels. Patient 3 was a man, aged 69 years, with hypertension who developed respiratory failure as a result of COVID-19 and required mechanical ventilation. Echocardiography showed reduced left ventricular ejection fraction. Circulatory collapse ensued with mesenteric ischaemia, and small intestine resection was performed, but the patient survived. Histology of the small intestine resection revealed prominent endotheliitis of the submucosal vessels and apoptotic bodies (figure C). We found evidence of direct viral infection of the endothelial cell and diffuse endothelial inflammation. Although the virus uses ACE2 receptor expressed by pneumocytes in the epithelial alveolar lining to infect the host, thereby causing lung injury, the ACE2 receptor is also widely expressed on endothelial cells, which traverse multiple organs. 3 Recruitment of immune cells, either by direct viral infection of the endothelium or immune-mediated, can result in widespread endothelial dysfunction associated with apoptosis (figure D). The vascular endothelium is an active paracrine, endocrine, and autocrine organ that is indispensable for the regulation of vascular tone and the maintenance of vascular homoeostasis. 5 Endothelial dysfunction is a principal determinant of microvascular dysfunction by shifting the vascular equilibrium towards more vasoconstriction with subsequent organ ischaemia, inflammation with associated tissue oedema, and a pro-coagulant state. 6 Our findings show the presence of viral elements within endothelial cells and an accumulation of inflammatory cells, with evidence of endothelial and inflammatory cell death. These findings suggest that SARS-CoV-2 infection facilitates the induction of endotheliitis in several organs as a direct consequence of viral involvement (as noted with presence of viral bodies) and of the host inflammatory response. In addition, induction of apoptosis and pyroptosis might have an important role in endothelial cell injury in patients with COVID-19. COVID-19-endotheliitis could explain the systemic impaired microcirculatory function in different vascular beds and their clinical sequelae in patients with COVID-19. This hypothesis provides a rationale for therapies to stabilise the endothelium while tackling viral replication, particularly with anti-inflammatory anti-cytokine drugs, ACE inhibitors, and statins.7, 8, 9, 10, 11 This strategy could be particularly relevant for vulnerable patients with pre-existing endothelial dysfunction, which is associated with male sex, smoking, hypertension, diabetes, obesity, and established cardiovascular disease, all of which are associated with adverse outcomes in COVID-19.
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            WHO Declares COVID-19 a Pandemic

            The World Health Organization (WHO) on March 11, 2020, has declared the novel coronavirus (COVID-19) outbreak a global pandemic (1). At a news briefing, WHO Director-General, Dr. Tedros Adhanom Ghebreyesus, noted that over the past 2 weeks, the number of cases outside China increased 13-fold and the number of countries with cases increased threefold. Further increases are expected. He said that the WHO is “deeply concerned both by the alarming levels of spread and severity and by the alarming levels of inaction,” and he called on countries to take action now to contain the virus. “We should double down,” he said. “We should be more aggressive.” Among the WHO’s current recommendations, people with mild respiratory symptoms should be encouraged to isolate themselves, and social distancing is emphasized and these recommendations apply even to countries with no reported cases (2). Separately, in JAMA, researchers report that SARS-CoV-2, the virus that causes COVID-19, was most often detected in respiratory samples from patients in China. However, live virus was also found in feces. They conclude: “Transmission of the virus by respiratory and extrarespiratory routes may help explain the rapid spread of disease.”(3). COVID-19 is a novel disease with an incompletely described clinical course, especially for children. In a recente report W. Liu et al described that the virus causing Covid-19 was detected early in the epidemic in 6 (1.6%) out of 366 children (≤16 years of age) hospitalized because of respiratory infections at Tongji Hospital, around Wuhan. All these six children had previously been completely healthy and their clinical characteristics at admission included high fever (>39°C) cough and vomiting (only in four). Four of the six patients had pneumonia, and only one required intensive care. All patients were treated with antiviral agents, antibiotic agents, and supportive therapies, and recovered after a median 7.5 days of hospitalization. (4). Risk factors for severe illness remain uncertain (although older age and comorbidity have emerged as likely important factors), the safety of supportive care strategies such as oxygen by high-flow nasal cannula and noninvasive ventilation are unclear, and the risk of mortality, even among critically ill patients, is uncertain. There are no proven effective specific treatment strategies, and the risk-benefit ratio for commonly used treatments such as corticosteroids is unclear (3,5). Septic shock and specific organ dysfunction such as acute kidney injury appear to occur in a significant proportion of patients with COVID-19–related critical illness and are associated with increasing mortality, with management recommendations following available evidence-based guidelines (3). Novel COVID-19 “can often present as a common cold-like illness,” wrote Roman Wöelfel et al. (6). They report data from a study concerning nine young- to middle-aged adults in Germany who developed COVID-19 after close contact with a known case. All had generally mild clinical courses; seven had upper respiratory tract disease, and two had limited involvement of the lower respiratory tract. Pharyngeal virus shedding was high during the first week of symptoms, peaking on day 4. Additionally, sputum viral shedding persisted after symptom resolution. The German researchers say the current case definition for COVID-19, which emphasizes lower respiratory tract disease, may need to be adjusted(6). But they considered only young and “normal” subjecta whereas the story is different in frail comorbid older patients, in whom COVID 19 may precipitate an insterstitial pneumonia, with severe respiratory failure and death (3). High level of attention should be paid to comorbidities in the treatment of COVID-19. In the literature, COVID-19 is characterised by the symptoms of viral pneumonia such as fever, fatigue, dry cough, and lymphopenia. Many of the older patients who become severely ill have evidence of underlying illness such as cardiovascular disease, liver disease, kidney disease, or malignant tumours. These patients often die of their original comorbidities. They die “with COVID”, but were extremely frail and we therefore need to accurately evaluate all original comorbidities. In addition to the risk of group transmission of an infectious disease, we should pay full attention to the treatment of the original comorbidities of the individual while treating pneumonia, especially in older patients with serious comorbid conditions and polipharmacy. Not only capable of causing pneumonia, COVID-19 may also cause damage to other organs such as the heart, the liver, and the kidneys, as well as to organ systems such as the blood and the immune system. Patients die of multiple organ failure, shock, acute respiratory distress syndrome, heart failure, arrhythmias, and renal failure (5,6). What we know about COVID 19? In December 2019, a cluster of severe pneumonia cases of unknown cause was reported in Wuhan, Hubei province, China. The initial cluster was epidemiologically linked to a seafood wholesale market in Wuhan, although many of the initial 41 cases were later reported to have no known exposure to the market (7). A novel strain of coronavirus belonging to the same family of viruses that cause severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), as well as the 4 human coronaviruses associated with the common cold, was subsequently isolated from lower respiratory tract samples of 4 cases on 7 January 2020. On 30 January 2020, the WHO declared that the SARS-CoV-2 outbreak constituted a Public Health Emergency of International Concern, and more than 80, 000 confirmed cases had been reported worldwide as of 28 February 2020 (8). On 31 January 2020, the U.S. Centers for Disease Control and Prevention announced that all citizens returning from Hubei province, China, would be subject to mandatory quarantine for up to 14 days. But from China COVID 19 arrived to many other countries. Rothe C et al reported a case of a 33-year-old otherwise healthy German businessman :she became ill with a sore throat, chills, and myalgias on January 24, 2020 (9). The following day, a fever of 39.1°C developed, along with a productive cough. By the evening of the next day, he started feeling better and went back to work on January 27. Before the onset of symptoms, he had attended meetings with a Chinese business partner at his company near Munich on January 20 and 21. The business partner, a Shanghai resident, had visited Germany between January 19 and 22. During her stay, she had been well with no signs or symptoms of infection but had become ill on her flight back to China, where she tested positive for 2019-nCoV on January 26. This case of 2019-nCoV infection was diagnosed in Germany and transmitted outside Asia. However, it is notable that the infection appears to have been transmitted during the incubation period of the index patient, in whom the illness was brief and nonspecific. The fact that asymptomatic persons are potential sources of 2019-nCoV infection may warrant a reassessment of transmission dynamics of the current outbreak (9). Our current understanding of the incubation period for COVID-19 is limited. An early analysis based on 88 confirmed cases in Chinese provinces outside Wuhan, using data on known travel to and from Wuhan to estimate the exposure interval, indicated a mean incubation period of 6.4 days (95% CI, 5.6 to 7.7 days), with a range of 2.1 to 11.1 days. Another analysis based on 158 confirmed cases outside Wuhan estimated a median incubation period of 5.0 days (CI, 4.4 to 5.6 days), with a range of 2 to 14 days. These estimates are generally consistent with estimates from 10 confirmed cases in China (mean incubation period, 5.2 days [CI, 4.1 to 7.0 days] and from clinical reports of a familial cluster of COVID-19 in which symptom onset occurred 3 to 6 days after assumed exposure in Wuhan (10-12). The incubation period can inform several important public health activities for infectious diseases, including active monitoring, surveillance, control, and modeling. Active monitoring requires potentially exposed persons to contact local health authorities to report their health status every day. Understanding the length of active monitoring needed to limit the risk for missing infections is necessary for health departments to effectively use resources. A recent paper provides additional evidence for a median incubation period for COVID-19 of approximately 5 days (13). Lauer et al suggest that 101 out of every 10 000 cases will develop symptoms after 14 days of active monitoring or quarantinen (13). Whether this rate is acceptable depends on the expected risk for infection in the population being monitored and considered judgment about the cost of missing cases. Combining these judgments with the estimates presented here can help public health officials to set rational and evidence-based COVID-19 control policies. Note that the proportion of mild cases detected has increased as surveillance and monitoring systems have been strengthened. The incubation period for these severe cases may differ from that of less severe or subclinical infections and is not typically an applicable measure for those with asymptomatic infections In conclusion, in a very short period health care systems and society have been severely challenged by yet another emerging virus. Preventing transmission and slowing the rate of new infections are the primary goals; however, the concern of COVID-19 causing critical illness and death is at the core of public anxiety. The critical care community has enormous experience in treating severe acute respiratory infections every year, often from uncertain causes. The care of severely ill patients, in particular older persons with COVID-19 must be grounded in this evidence base and, in parallel, ensure that learning from each patient could be of great importance to care all population,
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              Angiotensin-converting enzyme 2 (ACE2) as a SARS-CoV-2 receptor: molecular mechanisms and potential therapeutic target

              A novel infectious disease, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was detected in Wuhan, China, in December 2019. The disease (COVID-19) spread rapidly, reaching epidemic proportions in China, and has been found in 27 other countries. As of February 27, 2020, over 82,000 cases of COVID-19 were reported, with > 2800 deaths. No specific therapeutics are available, and current management includes travel restrictions, patient isolation, and supportive medical care. There are a number of pharmaceuticals already being tested [1, 2], but a better understanding of the underlying pathobiology is required. In this context, this article will briefly review the rationale for angiotensin-converting enzyme 2 (ACE2) receptor as a specific target. SARS-CoV-2 and severe acute respiratory syndrome coronavirus (SARS-CoV) use ACE2 receptor to facilitate viral entry into target cells SARS-CoV-2 has been sequenced [3]. A phylogenetic analysis [3, 4] found a bat origin for the SARS-CoV-2. There is a diversity of possible intermediate hosts for SARS-CoV-2, including pangolins, but not mice and rats [5]. There are many similarities of SARS-CoV-2 with the original SARS-CoV. Using computer modeling, Xu et al. [6] found that the spike proteins of SARS-CoV-2 and SARS-CoV have almost identical 3-D structures in the receptor-binding domain that maintains van der Waals forces. SARS-CoV spike protein has a strong binding affinity to human ACE2, based on biochemical interaction studies and crystal structure analysis [7]. SARS-CoV-2 and SARS-CoV spike proteins share 76.5% identity in amino acid sequences [6] and, importantly, the SARS-CoV-2 and SARS-CoV spike proteins have a high degree of homology [6, 7]. Wan et al. [4] reported that residue 394 (glutamine) in the SARS-CoV-2 receptor-binding domain (RBD), corresponding to residue 479 in SARS-CoV, can be recognized by the critical lysine 31 on the human ACE2 receptor [8]. Further analysis even suggested that SARS-CoV-2 recognizes human ACE2 more efficiently than SARS-CoV increasing the ability of SARS-CoV-2 to transmit from person to person [4]. Thus, the SARS-CoV-2 spike protein was predicted to also have a strong binding affinity to human ACE2. This similarity with SARS-CoV is critical because ACE2 is a functional SARS-CoV receptor in vitro [9] and in vivo [10]. It is required for host cell entry and subsequent viral replication. Overexpression of human ACE2 enhanced disease severity in a mouse model of SARS-CoV infection, demonstrating that viral entry into cells is a critical step [11]; injecting SARS-CoV spike into mice worsened lung injury. Critically, this injury was attenuated by blocking the renin-angiotensin pathway and depended on ACE2 expression [12]. Thus, for SARS-CoV pathogenesis, ACE2 is not only the entry receptor of the virus but also protects from lung injury. We therefore previously suggested that in contrast to most other coronaviruses, SARS-CoV became highly lethal because the virus deregulates a lung protective pathway [10, 12]. Zhou et al. [13] demonstrated that overexpressing ACE2 from different species in HeLa cells with human ACE2, pig ACE2, civet ACE2 (but not mouse ACE2) allowed SARS-CoV-2 infection and replication, thereby directly showing that SARS-CoV-2 uses ACE2 as a cellular entry receptor. They further demonstrated that SARS-CoV-2 does not use other coronavirus receptors such as aminopeptidase N and dipeptidyl peptidase 4 [13]. In summary, the SARS-CoV-2 spike protein directly binds with the host cell surface ACE2 receptor facilitating virus entry and replication. Enrichment distribution of ACE2 receptor in human alveolar epithelial cells (AEC) A key question is why the lung appears to be the most vulnerable target organ. One reason is that the vast surface area of the lung makes the lung highly susceptible to inhaled viruses, but there is also a biological factor. Using normal lung tissue from eight adult donors, Zhao et al. [14] demonstrated that 83% of ACE2-expressing cells were alveolar epithelial type II cells (AECII), suggesting that these cells can serve as a reservoir for viral invasion. In addition, gene ontology enrichment analysis showed that the ACE2-expressing AECII have high levels of multiple viral process-related genes, including regulatory genes for viral processes, viral life cycle, viral assembly, and viral genome replication [14], suggesting that the ACE2-expressing AECII facilitate coronaviral replication in the lung. Expression of the ACE2 receptor is also found in many extrapulmonary tissues including heart, kidney, endothelium, and intestine [15–19]. Importantly, ACE2 is highly expressed on the luminal surface of intestinal epithelial cells, functioning as a co-receptor for nutrient uptake, in particular for amino acid resorption from food [20]. We therefore predict that the intestine might also be a major entry site for SARS-CoV-2 and that the infection might have been initiated by eating food from the Wuhan market, the putative site of the outbreak. Whether SARS-CoV-2 can indeed infect the human gut epithelium has important implications for fecal–oral transmission and containment of viral spread. ACE2 tissue distribution in other organs could explain the multi-organ dysfunction observed in patients [21–23]. Of note, however, according to the Centers for Disease Control and Prevention [24], whether a person can get COVID-19 by touching surfaces or objects that have virus on them and then touching mucus membranes is yet to be confirmed. Potential approaches to address ACE2-mediated COVID-19 There are several potential therapeutic approaches (Fig. 1). Spike protein-based vaccine. Development of a spike1 subunit protein-based vaccine may rely on the fact that ACE2 is the SARS-CoV-2 receptor. Cell lines that facilitate viral replication in the presence of ACE2 may be most efficient in large-scale vaccine production. Inhibition of transmembrane protease serine 2 (TMPRSS2) activity. Hoffman et al. [25] recently demonstrated that initial spike protein priming by transmembrane protease serine 2 (TMPRSS2) is essential for entry and viral spread of SARS-CoV-2 through interaction with the ACE2 receptor [26, 27]. The serine protease inhibitor camostat mesylate, approved in Japan to treat unrelated diseases, has been shown to block TMPRSS2 activity [28, 29] and is thus an interesting candidate. Blocking ACE2 receptor. The interaction sites between ACE2 and SARS-CoV have been identified at the atomic level and from studies to date should also hold true for interactions between ACE2 and SARS-CoV-2. Thus, one could target this interaction site with antibodies or small molecules. Delivering excessive soluble form of ACE2. Kuba et al. [10] demonstrated in mice that SARS-CoV downregulates ACE2 protein (but not ACE) by binding its spike protein, contributing to severe lung injury. This suggests that excessive ACE2 may competitively bind with SARS-CoV-2 not only to neutralize the virus but also rescue cellular ACE2 activity which negatively regulates the renin-angiotensin system (RAS) to protect the lung from injury [12, 30]. Indeed, enhanced ACE activity and decreased ACE2 availability contribute to lung injury during acid- and ventilator-induced lung injury [12, 31, 32]. Thus, treatment with a soluble form of ACE2 itself may exert dual functions: (1) slow viral entry into cells and hence viral spread [7, 9] and (2) protect the lung from injury [10, 12, 31, 32]. Notably, a recombinant human ACE2 (rhACE2; APN01, GSK2586881) has been found to be safe, with no negative hemodynamic effects in healthy volunteers and in a small cohort of patients with ARDS [33–35]. The administration of APN01 rapidly decreased levels of its proteolytic target peptide angiotensin II, with a trend to lower plasma IL-6 concentrations. Our previous work on SARS-CoV pathogenesis makes ACE2 a rational and scientifically validated therapeutic target for the current COVID-19 pandemic. The availability of recombinant ACE2 was the impetus to assemble a multinational team of intensivists, scientists, and biotech to rapidly initiate a pilot trial of rhACE2 in patients with severe COVID-19 (Clinicaltrials.gov #NCT04287686). Fig. 1 Potential approaches to address ACE2-mediated COVID-19 following SARS-CoV-2 infection. The finding that SARS-CoV-2 and SARS-CoV use the ACE2 receptor for cell entry has important implications for understanding SARS-CoV-2 transmissibility and pathogenesis. SARS-CoV and likely SARS-CoV-2 lead to downregulation of the ACE2 receptor, but not ACE, through binding of the spike protein with ACE2. This leads to viral entry and replication, as well as severe lung injury. Potential therapeutic approaches include a SARS-CoV-2 spike protein-based vaccine; a transmembrane protease serine 2 (TMPRSS2) inhibitor to block the priming of the spike protein; blocking the surface ACE2 receptor by using anti-ACE2 antibody or peptides; and a soluble form of ACE2 which should slow viral entry into cells through competitively binding with SARS-CoV-2 and hence decrease viral spread as well as protecting the lung from injury through its unique enzymatic function. MasR—mitochondrial assembly receptor, AT1R—Ang II type 1 receptor
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                Author and article information

                Journal
                Indian J Ophthalmol
                Indian J Ophthalmol
                IJO
                Indian J Ophthalmol
                Indian Journal of Ophthalmology
                Wolters Kluwer - Medknow (India )
                0301-4738
                1998-3689
                February 2023
                02 February 2023
                : 71
                : 2
                : 385-395
                Affiliations
                [1]Department of Ophthalmology, All India Institute of Medical Sciences Bhopal, Saket Nagar, Bhopal, Madhya Pradesh, India
                Author notes
                Correspondence to: Dr. Samendra Karkhur, Retina, Uveitis & ROP Services, Department of Ophthalmology, All India Institute of Medical Sciences, Bhopal – 462 020, Madhya Pradesh, India. E-mail: karkhurs@ 123456gmail.com
                Article
                IJO-71-385
                10.4103/ijo.IJO_1236_22
                10228904
                36727324
                20175c41-ffe0-4550-ace8-d95dfae2ada4
                Copyright: © 2023 Indian Journal of Ophthalmology

                This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.

                History
                : 23 May 2022
                : 22 September 2022
                : 17 November 2022
                Categories
                Original Article

                Ophthalmology & Optometry
                covid-19,foveal avascular zone,macular vessel density,optical coherence tomography angiography,retinal layer metrics

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