The coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is affecting almost all countries in the world and because of its worldwide spread has been declared as pandemic in March 2020. While respiratory symptoms are the main manifestation of acute infection, there is also increasing evidence that neurological and vascular symptoms occur, and it is unknown whether residuals remain after patients have recovered. A recent report shows that changes in the human retina are even present one month after onset of symptoms. The eye, as an extension of the brain, offers the advantage that blood vessels as well as neural tissue can be visualized non-invasively in-vivo. Neurovascular coupling is the ability of neural tissue to adapt its blood flow to its metabolic demands, a phenomenon that does not only occur in the brain, but also in the retina. In the retina, neurovascular coupling can be studied by stimulating the retina with flicker light and measuring the response of the vessels. Retinal neurovascular coupling has been found to be impaired in diseases of the central nervous system (CNS) as well as in diseases associated with endothelial dysfunction. Since COVID-19 comes with CNS manifestations as well as endothelial dysfunction, we speculate that retinal neurovascular coupling might be impaired in patients even after they have recovered from COVID-19 infection. In the current study, retinal neurovascular coupling will be measured in patients who have recovered from COVID-19 infection with and without long COVID-19 and in healthy age- and sex-matched controls with no history of COVID-19 infection. In addition, retinal oxygen saturation, vessel diameters, vessel density as well as retinal and optic nerve head blood flow will be measured. To assess structural changes, measurement of central retinal thickness as well as retinal nerve fiber layer thickness will be performed.
The Study objective is to measure retinal neurovascular coupling and blood flow parameters in patients previously infected with COVID-19, long COVID-19 and healthy age- and sex- matched control subjects