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 < 0.01) and age (ro: −0.5; p < 0.05). Moreover, microglia activation was correlated with blood oxygen levels (ro: −0.554; p < 0.05). Conclusions: Different stages of glial activation and neuronal alterations are present in COVID‐19 retinas and are significantly correlated with the duration of the disease, age and respiratory failure.

Purpose: Retinal neurodegeneration in diabetic patients appears to occur along with the vascular abnormalities. Some structural and functional changes have been described in the retina of these patients. The aim was to describe the morphological alterations present in the retinal cells and the vascular network in the macula of human donor with diabetes. Methods: Retinas of human donor with diabetes or diabetic retinopathy (n = 5) and control (n = 3) were processed in cross‐sections or flat mount retinas. The vascular network and the retinal cells were analysed in the macula through immunohistochemistry and confocal microscopy. Analysis of the vessel density was performed with the Angio‐tool software. Results: Diabetic and control group had a mean age of 60 ± 10 and 62 ± 2 years, respectively. Capillary bends, vascular loops, microaneurysms and an increase of the vascular density were the main findings in the intermediate and deep capillary plexuses of the diabetic group. Disruption of the basement membrane of the retinal vessels and tractions due to the epiretinal membrane were observed in the superficial vessels. Interpericyte tunnelling nanotubes appeared altered in the plexuses of the diabetic retinas. Endothelial cell marker was accumulated inside the microaneurysms, and microglial nodules were surrounding them. Disruption of the external limiting membrane and swelling of Müller cells were present. Disorganization or loss of the outer plexiform layer observed with bassoon, vesicular glutamate transporter and synaptophysin as well as sprouting of the horizontal cells existed in some diabetic retinas. Cone photoreceptors seem to extend their axons to maintain the synaptic connectivity in the intraretinal cysts. Synaptic terminals of the bipolar cells in the plexiform layers were altered. Conclusions: In addition to the specific vascular changes, alterations in the synaptic connectivity and the morphology of retinal cells are present in the fovea of diabetic patients.

Purpose: The omega‐3 fatty acid, DHA, is enriched in the outer disk and synapse membranes, and it exerts an anti‐inflammatory and anti‐apoptotic effect in the neuron cells. Animal models and patients with retinal dystrophies were reported to have reduced levels of DHA in the retina, so different nutraceuticals were designed for these patients. Nevertheless, it is still unknown how DHA is cached and distributed in the retina. MFSD2a was reported as the putative transporter of omega‐3, but its expression was only described in the endothelial cells. In this study, we assessed the expression of MFSD2a in the different cell populations of the neural retina. Methods: The expression of MFSD2a was studied by immunofluorescence in cryostat sections of the retina from healthy human donors. Double immunolabelling with different cell markers was used to study MFSD2a expression in the different retinal cell populations. Cone arrestin was used for the identification of cone photoreceptor cells. Parvalbumin is a cell marker for all horizontal cells. The transcription factors Chx10 and Pax6 were used for the identification of bipolar and amacrine cells, respectively. KDEL, an endoplasmic retention signal peptide, was used for the visualization of ganglion cells. Müller cells and RPE are positive for CRALBP. Results: We found that MFSD2a was expressed in the outer nuclear layer as well as in the inner segments of the photoreceptor cells. Outer segments showed weak or negative immunostaining. Immunoreactivity with anti‐MFSD2a was also detected in the inner nuclear layer. Double immunostaining with parvalbumin and the transcriptional factors Chx10 and Pax6 confirmed that all populations of horizontal, bipolar, and amacrine cells, respectively, expressed the omega‐3 transporter. Also, ganglion cells expressed MFSD2a. In the double immunolabelling with anti‐MFSD2a and anti‐CRALBP, Müller cells showed punctae of immunolabelling in the tips of the external limiting membrane. Although, RPE did not seem to express MFSD2a. Conclusions: MFSD2a is expressed by the neural cells of the retina. Photoreceptor cells, Müller cells, and all populations of bipolar, amacrine, horizontal, and ganglion cells expressed the transporter of the omega‐3 fatty acid, DHA.

PurposeRetinal degeneration compromises retinal metabolism and signaling, including lipid pathways. Fatty acids are highly enriched in the retina and they impact photoreceptor survival. In this study, we aimed to identify fatty acids that could be relevant in retinal degeneration. For this purpose, we analyzed the fatty acid profile of the retina of rd10 mice, model of retinitis pigmentosa.MethodsFatty acids of the retina of C57BL/6J and rd10 mice were extracted by the Folch method and analyzed by GC/MS. Morphological changes were studied by immunohistochemistry.ResultsIn the retina of rd10 mice, there was a drop of photoreceptor rows compared to healthy retinas. Rhodopsin, a protein expressed in outer segments, was delocalized into the cell bodies of photoreceptors in dystrophic retinas, and axons and outer segments of cones were shortened. In these animals, we found a decrease of specific saturated, monounsaturated and polyunsaturated fatty acids. Remarkably, docosahexaenoic acid (DHA) experienced a marked drop, leading to a heightening of the n‐3/n‐6 ratio, an indicator of inflammation. We found a positive correlation of cerotic acid, hypogeic acid, and DHA with photoreceptor rows.ConclusionsSpecific saturated and unsaturated fatty acids dropped in retinitis pigmentosa. Remarkably, diminished levels of the omega‐3 DHA could be contributing to the neurodegeneration process due to a shift to pro‐inflammatory pathways and a lack of neuroprotective signals, promoting photoreceptor death. Fatty acids could have decisive roles in the retinal degeneration outcome and should be considered to improve therapy.MICINN‐FEDER PID2019‐106230RB‐I00; RETICS‐FEDER RD16/0008/0016; ACIF/2020/203; IDIFEDER/2017/064; FPU16/04114; FPU18/02964.

PurposeCentral choroidal dystrophies are retinal diseases characterized by progressive choriocapillaris atrophy and retinal degeneration that are usually associated with a single mutation in the PRPH2 gene. Thus, the purpose of this work was to generate a mouse model with the same p.Arg195Leu mutation described in diagnosed human patients.MethodsPrph2KI/WT and Prph2KI/KI mice have been designed and generated using the CRISPR system to introduce the Arg195Leu mutation. The retinal function was analyzed by electroretinography (ERG) and optomotor test. The structural integrity of the retinas was evaluated using optical coherence tomography and immunohistochemistry.ResultsGenetic sequencing confirmed that both Prph2KI/WT and Prph2KI/KI mice presented the same codon mutation and degeneration pattern found in humans suffering from this dystrophy. A progressive loss of retinal function was found from 3 months of age, with significantly reduced mice visual acuity, measured by optomotor test. At 6 months of age, decreased a‐ and b‐wave amplitudes of the ERG responses were observed. Moreover, morphological analysis of the retinas correlated with functional findings, showing a decreased number of photoreceptor rows and retinal thickness, also presenting an increased inflammation with activation of microglia and Müller cellsConclusionsThe new Prph2KI/WT and Prph2KI/KI mouse models show a similar degeneration pattern to human disease and may facilitate the study of the pathophysiological process, also displaying their potential to be a model for evaluation of different therapeutic strategies.SupportMinisterio de Ciencia e Innovación (FEDER‐ PID2019‐106230RB‐I00). Ministerio de Universidades (FPU16/04114, FPU18/02964). Instituto Carlos III (RETICS‐FEDER RD16/0008/0016). Retina Asturias/Cantabria. FARPE‐FUNDALUCE. Generalitat Valenciana (IDIFEDER/2017/064, ACIF/2020/203). Es Retina Asturias (2019/00286/001).