Nikhil Prasad Fact checked by:Thailand Medical News Team Aug 19, 2026 1 hour, 19 minutes ago
Researchers have uncovered striking changes in the tiny blood vessels of people with post-COVID-19 syndrome, commonly called Long COVID, suggesting that vascular problems can persist long after the original infection. The abnormalities were particularly pronounced among patients who also met the criteria for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).
Long COVID patients showed measurable abnormalities in tiny retinal blood vessels, with the strongest changes occurring
in those meeting ME/CFS criteria
Researchers Looked into the Eyes
The study involved 300 participants: 102 people with post-COVID-19 syndrome, 102 who had recovered from SARS-CoV-2 infection without persistent symptoms, and 96 people who had never been infected. Among the Long COVID patients, 62 met ME/CFS criteria.
Researchers used retinal vessel analysis, a non-invasive technique that examines tiny blood vessels at the back of the eye. Because retinal vessels share important characteristics with small blood vessels supplying the brain and other tissues, their condition can provide clues about wider microvascular health.
The researchers came from the Technical University of Munich and TUM University Hospital; LMU University Hospital; Charité-Universitätsmedizin Berlin; Max Delbrück Center for Molecular Medicine; Einstein Center Digital Future Berlin; Niederrhein University of Applied Sciences; University Hospital Düsseldorf and Heinrich-Heine-University Düsseldorf in Germany; University of Basel in Switzerland; and the German Centre for Infection Research.
Blood Vessels Responded Differently After Long COVID
One important measurement examined how retinal veins widen when exposed to flickering light. Healthy vessels normally dilate as blood-flow requirements increase. Long COVID patients showed average venular dilation of 3.7 percent, compared with 4.8 percent among recovered participants.
Researchers also found structural changes. Retinal arterioles averaged 178.3 micrometers in Long COVID patients, compared with 186.1 micrometers among recovered participants and 184.4 micrometers among never-infected controls.
Another measurement, the arteriolar-to-venular ratio, or AVR, was 0.83 in Long COVID patients, versus 0.86 in recovered participants and 0.87 in never-infected individuals. Many of the major findings remained after researchers accounted for age, sex and cardiovascular risk factors.
ME/CFS Patients Showed Strongest Changes
Importantly, this Thailand
Medical News report highlights that the vascular abnormalities followed a severity pattern. Long COVID patients meeting ME/CFS criteria generally displayed the most pronounced retinal microvascular alterations.
Greater symptom burden was also associated with lower AVR, particularly among people reporting neurocognitive problems. This raises the possibility that persistent changes involving small blood vessels could be connected with symptoms such as impaired concentration and other cognitiv
e difficulties.
Blood testing added another layer to the findings. Long COVID patients had increased levels of ICAM-1 and VCAM-1, molecules associated with activation and dysfunction of the blood-vessel lining. IL-6, an inflammatory signaling molecule, was also elevated in initial comparisons. Lower AVR was associated with inflammatory and iron-related markers.
A combined model incorporating AVR with IL-6, ICAM-1, creatine kinase, transferrin and neutrophils distinguished ME/CFS patients from other previously infected participants with an area under the curve of 0.79, indicating good discriminatory performance.
Conclusions
The findings suggest that Long COVID can be accompanied by persistent functional and structural abnormalities in the body's smallest blood vessels, especially in patients with severe symptoms or ME/CFS. Retinal vessel testing could eventually provide doctors with a simple, non-invasive method for monitoring vascular health, although larger longitudinal studies are needed before it can become a diagnostic or risk-prediction tool.
The study findings were published in the peer reviewed journal: BMC Medicine.
https://link.springer.com/article/10.1186/s12916-026-05144-9
Read Also:
https://www.thailandmedical.news/articles/long-covid
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