Decoding Long COVID: Insights into the Condition through Eye Blood Vessels

In the course of an ocular examination, the measurement of the diameter of minuscule blood vessels (depicted on the left) and the response of vessels to light pulses (depicted on the right) can be undertaken. Such parameters exhibit alterations in individuals grappling with long Covid. Credit: Department of Nephrology / TUM

In the near future, a standardized eye examination may hold the key to identifying individuals enduring the aftermath of COVID-19, commonly referred to as long Covid or post-Covid. A group of scientists has successfully established a direct link between this condition and specific modifications in the blood vessels within the eye.

Long after initial COVID-19 infection, a noteworthy portion—ranging from 10 to 35 percent—of afflicted individuals continue to grapple with persisting symptoms, such as respiratory issues and chronic fatigue. Regrettably, hitherto, no concrete physical indicators or biomarkers have surfaced that could serve as a dependable diagnostic tool for identifying long Covid.

One hallmark of COVID-19 lies in its impact on blood vessels, particularly on the endothelium—the inner lining of blood vessels. These alterations result in an inadequate supply of blood to various organs within the body.

Directing Attention to Smaller Blood Vessels

Historically, the focus of blood vessel research has predominantly centered on larger vessels. Nevertheless, a staggering 90 percent of endothelial cells reside within the body’s smaller and more delicate vessels. The effects of long Covid on these smaller blood vessels remain relatively uncharted territory, as asserted by Professor Christoph Schmaderer, the lead investigator of the study and Managing Senior Physician in the Department of Nephrology at Klinikum rechts der Isar, TUM’s university hospital.

According to Schmaderer, “The blood vessels within the eye could potentially offer vital insights into the condition of small blood vessels throughout the entire body.” These vessels are readily accessible for examination, and the requisite methods and instruments have been rigorously tested, eliminating the need for invasive procedures.

Constriction and Reduced Dilation in Vessels

Schmaderer, along with co-lead researcher Dr. Timon Kuchler and their research team, has documented their findings in the scientific journal “Angiogenesis.” Two specific parameters exhibited a robust correlation with long Covid cases. Firstly, the arterioles, which are the smallest arteries, displayed significant constriction when compared to a healthy control group. Secondly, the venules—although not the arterioles—manifested an altered response when exposed to flickering light stimulation. In healthy individuals, such stimulation leads to dilation of blood vessels, yet in long Covid patients, this response was markedly diminished.

Furthermore, the study revealed that the extent of alterations corresponded with the levels of inflammatory markers detected in the participants’ blood. This aligns with previous research suggesting that persistent inflammatory responses may constitute a pivotal element in long Covid.

Continued Research Imperative

Given that the study comprised a relatively modest cohort of 41 afflicted participants and was conducted solely within a single medical institution, it remains premature to devise a definitive long Covid diagnostic test based on these results. The researchers emphasize the necessity for further investigations to corroborate their findings. Professor Christoph Schmaderer expresses his confidence that their results could serve as the foundation for the development of a robust diagnostic tool for long Covid. Additionally, it is posited that microcirculatory impairment may extend beyond the eye and could make this method particularly suited for evaluating the efficacy of forthcoming therapies targeting long Covid.

Reference: “Persistent endothelial dysfunction in post-COVID-19 syndrome and its associations with symptom severity and chronic inflammation” by Timon Kuchler, Roman Günthner, Andrea Ribeiro, Renate Hausinger, Lukas Streese, Anna Wöhnl, Veronika Kesseler, Johanna Negele, Tarek Assali, Javier Carbajo-Lozoya, Maciej Lech, Heike Schneider, Kristina Adorjan, Hans Christian Stubbe, Henner Hanssen, Konstantin Kotilar, Bernhard Haller, Uwe Heemann and Christoph Schmaderer, 28 July 2023, Angiogenesis.
DOI: 10.1007/s10456-023-09885-6

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• Angiogenesis Journal Article