A new study from Germany looked at the eyes of people who recovered from COVID-19, even months later.
Using a non-invasive retinal imaging tool (OCTA), they found signs of microvascular injury - even in people who had only mild illness.
And it links to long COVID fatigue🧵
Using a non-invasive retinal imaging tool (OCTA), they found signs of microvascular injury - even in people who had only mild illness.
And it links to long COVID fatigue🧵
COVID-19 leaves microvascular damage, even after mild infection
People who had COVID-19 showed a larger foveal avascular zone (FAZ) - basically a patch in the retina where tiny capillaries are missing.
This was most pronounced in patients who were not hospitalized.
People who had COVID-19 showed a larger foveal avascular zone (FAZ) - basically a patch in the retina where tiny capillaries are missing.
This was most pronounced in patients who were not hospitalized.
This is similar to patterns seen in diseases like diabetes and glaucoma, where it predicts future vision problems.
Fatigue is tied to microvascular dysfunction in neural tissue.
Patients with long COVID fatigue had a larger FAZ than those without fatigue and healthy controls.
Patients with long COVID fatigue had a larger FAZ than those without fatigue and healthy controls.
This fits with the idea that long COVID involves - ongoing endothelial injury, microthrombosis, impaired oxygen delivery, neural energy failure.
Severe fatigue showed a different, surprising pattern. People with extreme fatigue had higher vessel density than other groups.
This might be a statistical quirk (small sample), but it could also be compensation - new vessel growth, dilation, or congestion in response to chronic ischemia.
In other diseases, this shows up when systems are struggling, not recovering.
This might be a statistical quirk (small sample), but it could also be compensation - new vessel growth, dilation, or congestion in response to chronic ischemia.
In other diseases, this shows up when systems are struggling, not recovering.
Vision is currently normal - but future risk exists. Participants didn’t report vision problems, and visual acuity was fine.
But in other diseases, an enlarged FAZ often precedes - vision loss, disease progression
Think diabetes - years of silent changes - sudden decline.
Early microvascular damage is meaningful even without symptoms.
But in other diseases, an enlarged FAZ often precedes - vision loss, disease progression
Think diabetes - years of silent changes - sudden decline.
Early microvascular damage is meaningful even without symptoms.
The retina reflects what’s happening in the brain.
The retina is part of the central nervous system and shares the same type of microvasculature.
In COVID-19, neuropathology has shown ischemic lesions, perivascular inflammation, neuronal injury
Clinically - brain fog, slowed thinking, fatigue, mood changes.
The retina gives us a window into brain microcirculation without an MRI.
The retina is part of the central nervous system and shares the same type of microvasculature.
In COVID-19, neuropathology has shown ischemic lesions, perivascular inflammation, neuronal injury
Clinically - brain fog, slowed thinking, fatigue, mood changes.
The retina gives us a window into brain microcirculation without an MRI.
FAZ could serve as a practical biomarker for long COVID. It’s not perfect (AUC ~0.68), but it’s quantitative, cheap, fast, widely available.
It could help with , risk stratification, monitoring progression, response to treatments
A much needed objective measurement in a condition full of subjective symptoms.
It could help with , risk stratification, monitoring progression, response to treatments
A much needed objective measurement in a condition full of subjective symptoms.
This supports a model of long COVID as microvascular disease of the nervous system.
Chronic processes like endothelial dysfunction, thrombo-inflammation, impaired microcirculation, metabolic stress on neurons.
Chronic processes like endothelial dysfunction, thrombo-inflammation, impaired microcirculation, metabolic stress on neurons.
In patients with mild disease (non-ICU), FAZ enlargement was detected at the group level - that is, as a statistically significantly higher mean value compared to controls. However, the study does not report the proportion of individual patients with this change, only the group-level effect.
It is plausible that a majority of patients with mild COVID exhibited some level of FAZ enlargement, but we cannot provide a specific proportion (eg 60% or 80%) since this was not assessed in the study.
Sum:
COVID-19 leaves measurable microvascular damage in neural tissue, most clearly in people with long COVID fatigue.
The retina may give us a simple, non-invasive biomarker to identify and monitor it.
A small study, but an important direction.
COVID-19 leaves measurable microvascular damage in neural tissue, most clearly in people with long COVID fatigue.
The retina may give us a simple, non-invasive biomarker to identify and monitor it.
A small study, but an important direction.
Spielmann et al., Association of foveal avascular zone enlargement with SARS-CoV-2 infection and long COVID-19. BMC Ophthalmology 2025. link.springer.com/article/10.118…
Long COVID looks less like a post-infectious syndrome
and more like a metabolic, microvascular, neurodegenerative disease triggered by an acute viral insult.
and more like a metabolic, microvascular, neurodegenerative disease triggered by an acute viral insult.
What makes this new study important
is that it doesn’t focus on symptoms, but on tissue-level changes.
And it finds them exactly where we’d expect them biologically-
in the microcirculation of neural tissue.
is that it doesn’t focus on symptoms, but on tissue-level changes.
And it finds them exactly where we’d expect them biologically-
in the microcirculation of neural tissue.
The enlarged FAZ and other post-COVID retinal findings are not random.
They match a micro ischemic pattern that ophthalmology already recognizes as high-risk, progressive, and potentially damaging.
They match a micro ischemic pattern that ophthalmology already recognizes as high-risk, progressive, and potentially damaging.
Ophthalmology has shown us for decades that structural microvascular changes appear years before vision declines.
Just like in diabetes, hypertension, or glaucoma,
what we’re seeing now may be the beginning of a process - not the end of it. @szupraha @ZdravkoOnline @adamvojtech86
Just like in diabetes, hypertension, or glaucoma,
what we’re seeing now may be the beginning of a process - not the end of it. @szupraha @ZdravkoOnline @adamvojtech86
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