Retinal tissue and microvasculature loss in COVID-19 infection, 2023, Kalaw et al

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RedFox

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Retinal tissue and microvasculature loss in COVID-19 infection

By Fritz Gerald P. Kalaw, Alexandra Warter, Melina Cavichini, Darren Knight, Alexandria Li, Daniel Deussen, Carlo Galang, Anna Heinke, Veronica Mendoza, Shyamanga Borooah, Sally L. Baxter, Dirk-Uwe Bartsch, Lingyun Cheng & William R. Freeman

https://www.nature.com/articles/s41598-023-31835-x

Abstract
This cross-sectional study aimed to investigate the hypothesis that permanent capillary damage may underlie the long-term COVID-19 sequela by quantifying the retinal vessel integrity. Participants were divided into three subgroups; Normal controls who had not been affected by COVID-19, mild COVID-19 cases who received out-patient care, and severe COVID-19 cases requiring intensive care unit (ICU) admission and respiratory support. Patients with systemic conditions that may affect the retinal vasculature before the diagnosis of COVID-19 infection were excluded. Participants underwent comprehensive ophthalmologic examination and retinal imaging obtained from Spectral-Domain Optical Coherence Tomography (SD-OCT), and vessel density using OCT Angiography. Sixty-one eyes from 31 individuals were studied. Retinal volume was significantly decreased in the outer 3 mm of the macula in the severe COVID-19 group (p = 0.02). Total retinal vessel density was significantly lower in the severe COVID-19 group compared to the normal and mild COVID-19 groups (p = 0.004 and 0.0057, respectively). The intermediate and deep capillary plexuses in the severe COVID-19 group were significantly lower compared to other groups (p < 0.05). Retinal tissue and microvascular loss may be a biomarker of COVID-19 severity. Further monitoring of the retina in COVID-19-recovered patients may help further understand the COVID-19 sequela.
 
From a quick skim of the paper:

They had a control group that hadn't had Covid-19, and they had groups who had mild and severe Covid-19. The participants were carefully selected to not have other diseases that might confound the results. But, given that the abstract talks about a hypothesis about long-term Covid-19 sequelae, it's odd that they didn't have a group who had had mild Covid-19 but reported persistent symptoms, ideally meeting ME/CFS criteria.

It's a small study - only 11 controls, 13 mild patients and 7 severe patients.

They found that retinal density was lower in the severe group (people who had been admitted to the ICU and had had respiratory support), as compared to people who had not had Covid or just had a mild Covid infection. The authors suggested that the changes in the severe group 'may not cause significant visual symptoms'.

I didn't understand the charts, although didn't bother trying to work out what was going on. It's worth noting that the variation between the mean vessel density in the mild group was 27.0, controls 25.8, severe 24.1. So, mean vessel density was actually higher in the mild group than in the controls, although the two groups were not statistically different. The fairly large difference in means between the controls and mild group is almost certainly due to sampling noise - worth noting for any study of Long Covid patients (i.e. sample size needs to be substantially larger).

This group seems to have all the equipment for doing this type of study. It would be great if they did another study on people with persistent symptoms after Covid-19 infection.
 
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