A clinical research team, based at the Federal University of São Paulo, Brazil, has reported that COVID-19 proteins have been identified within cells of the inner and the outer nuclear layers of the retina. Data in the report suggested that SARS-CoV-2 viral particles were identified by immunofluorescence and transmission electron microscopy images. Independent analyses highlighted that the study is an important finding, indicating that COVID-19 becomes “disseminated throughout the body in patients with severe infections”. The publication in JAMA Ophthalmology (doi:10.1001/ jamaophthalmol.2021.2795) concluded that, “the present observations show presumed SARS-CoV-2 viral particles in various layers of the human retina, suggesting that they may be involved in some of the infection’s ocular clinical manifestations”.
As well established, SARS-CoV-2 is an enveloped positive-sense RNA coronavirus belonging to the Coronaviridae family, now estimated to cause 200 million infections globally for COVID-19. As of today’s date, there are >197M cases for COVID-19, >4.2M deaths globally and >4.1BN vaccines have been administered (John Hopkins University). Entry depends mainly on the binding of S-protein to angiotensin-converting enzyme-2, a specific cellular receptor located at the surface of the host cells. RT-PCR and immunological methods have previously reported viral particles in the retina and other organs however, in the current study, researchers looked at fluorescence microscopy of tissues immune-stained for S1, and nucleocapsid proteins and transmission electron microscopy of thin tissue sections.
In the current study, three patients who died of COVID-19 (two patients were men and 1 was a woman) had a recorded age at death of being between 69 to 78 years. Immunofluorescence microscopy (directed against specific COVID-19 antigens) was observed by putative COVID19 proteins within endothelial cells of the inner and the outer nuclear layers of the retina. Transmission electron microscopy (TEM) images were seen in double-membrane vacuoles, shown at the perinuclear region of the endothelial cells, which the authors interpret to contain COVID-19 viral particles. These observations show presumed SARS-CoV-2 viral particles which may “reach the various layers of the human retina and also could be associated with this infection’s ocular clinical manifestations”. An independent invited commentary in the journal stated that, “this article demonstrates convincing evidence of SARSCo-V in multiple layers of the retina and the choroid using both immunofluorescent studies directed against specific COVID-19 antigens and transmission electron microscopy. This is an important finding that suggests that COVID-becomes disseminated throughout the body in patients with severe infections”.