Relationship of the main indicators of systemic COVID-associated endotheliopathy with the morphofunctional state and hemodynamics of the retina and chorioid in the acute period of the disease

BACKGROUND: Nonspecific angio- and retinopathy is one of the clinical manifestations of a new coronavirus infection. The frequency of occurrence of these changes in people with severe COVID-19 does not exceed 55%. The causes, course and consequences of these microcirculatory disorders of the retina are currently not well understood. 
AIM: To study and compare of retinal morphometric parameters and systemic endothelial dysfunction markers, as well as the main clinical and laboratory parameters in patients with moderate and severe coronavirus infection during convalescence. 
MATERIALS AND METHODS: The study involved 44 patients (86 eyes) who had COVID-19 during the previous 3 months, who were divided into 2 groups: with moderate and severe disease. The control group consisted of 18 healthy volunteers (36 eyes). All patients underwent a standard ophthalmological examination and optical coherence tomography, which included an assessment of the choroidal thickness (CT) and measurement of the mean diameter of the peripapillary arteries (MAD) and veins (MVD). During hospitalization, all patients underwent a laboratory study of venous blood parameters, as well as an assessment of the microcirculation of the sublingual plexus by examining the density of the endothelial glycocalyx (PBR) using the GlycoCheck. 
RESULTS: In patients who underwent COVID-19, there was a significant increase in CT relative to the control group, amounting to 308, 344 and 392 m, respectively. The most pronounced difference was observed between MVD in patients with severe infection and the control group (119.1 m vs. 99.2 m). In patients with moderate and severe COVID-19, MAD and MVD were positively correlated with TC, with r = 0.389 and r = 0.584, respectively. MVD also correlated with the level of leukocytes (r = 0.504), the ESR value (r = 0.656). Correlations between MVD and data characterizing the state of the glycocalyx in the sublingual vascular plexus were revealed: the filling of small capillaries with erythrocytes (r = 0.587), as well as the marginal perfusion value in large capillaries 2025 m (r = 0.479) and PBR (r = 0.479). Only significant differences and correlations are shown (p 0.005). 
CONCLUSIONS: In patients who underwent moderate and severe COVID-19 during the convalescence period (up to 30 days), an increase in the diameter of peripapillary vessels and TC is observed, proportional to the severity of COVID-19, laboratory markers of systemic inflammation and hypercoagulation (the number of leukocytes, the ESR value, D-dimer and prothrombin), which indicates the inflammatory nature of the changes. The severity of postcovid retinal microangiopathy correlates with indicators detecting a decreasing of the endothelial glycocalyx thickness in the sublingual capillary plexus, which indirectly indicates a connection with systemic endotheliopathy.