Clinical parameters related to the glial activation and neuronal alterations present in the retinas of COVID‐19 patients

Purpose: Ocular and eye fundus alterations have been described in COVID‐19 patients. In this study, the aim was to establish several stages of response to damage in the retinal cells from human donors with COVID‐19 and analyse their relationship with clinical parameters. Methods: Retinal sections and flat‐mount retinas from human donors with COVID‐19 (n = 16) and control (n = 12) were analysed with immunohistochemistry. The location of angiotensin‐converting enzyme 2 (ACE2) and the morphology of microglial cells, Müller cells, astrocytes, and photoreceptors were evaluated by confocal microscopy. Microglial analysis and cell death were measured. Clinical data were correlated with different retinal parameters. Results: Müller cells, outer segment of cones and retinal pigment epithelium presented the ACE2 protein. Larger staining of ACE2 and cellular retinaldehyde–binding protein (CRALBP) was found in the cell bodies of Müller cells in COVID‐19 group. Disorganization of honeycomb‐like pattern formed by Müller cells and disruption of external limiting membrane were observed in the 81.3% of COVID‐19 patients. The 53.3% of COVID‐19 patients showed reactive gliosis as well as astrocytes protruding and epiretinal membranes. Cone degeneration was aggravated in the COVID‐19 group. Activated or ameboid‐shape microglia was found in the 93.8% of COVID‐19 patients. Most retinas showed a reduction of the area occupied by microglia and presented microglial nodules around vessels. Retinal degeneration in COVID‐19 group correlated with the duration of the disease (ro: 0.655; p