Mild coronavirus infections can cause severe and long-term eye problems, according to research from Linköping University in Sweden. The study also explains why patients have difficulty getting help. This is because abnormal eye movements cannot be detected using standard methods. Researchers have developed a diagnostic model to detect eye problems associated with the new coronavirus.
“I think it’s very important that this problem is recognized and that we can show that it can be measured by objective tests, which are not available to patients today. We studied people in Sweden, but we believe that many people around the world experience these problems,” says Neil Lagari, professor of experimental ophthalmology at Linköping University, who led the study. nature communications.
The study began with people seeking treatment for eye problems following a mild coronavirus infection. They were experiencing a lot of discomfort, sensitivity to light, and often severe eye pain, difficulty reading and focusing their gaze.
After testing the affected people, the research team found that the problem was significant, not only in terms of prevalence but also in terms of impact on quality of life. Those affected included those who would like to continue studying or working but are unable to do so because they are unable to read or suffer from pain or extreme eye strain. Medical professionals couldn’t see anything wrong with their eyes, couldn’t diagnose them, let alone explain their symptoms.
In the new study, researchers tested 100 people who had eye problems after contracting the coronavirus and were not hospitalized. They suffered from eye conditions for anywhere from three months to up to three years, and one in three took full-time or part-time sick leave. Researchers compared the affected group to a control group of 32 people who also had a mild case of COVID-19 but had no eye problems.
It turns out that the problems experienced by those affected cannot be detected by standard tests. Professional inspections had to be carried out to detect deviations. Then the pieces of the puzzle fell into place and an explanation for the symptoms was found. ”
Neil Ragali, Professor of Experimental Ophthalmology, Linköping University
In their study, researchers found long-term inflammation and deterioration of several eye functions controlled by nerves in the brain.
One of the more advanced tests involves proteomics, where different proteins in tear fluid are analyzed. Researchers have discovered abnormal patterns in proteins that regulate nerve and immune cells, so-called T cells, in people with eye problems. This finding was consistent with advanced ophthalmic microscopy techniques they used to measure T cells and nerves in the eye. Remarkably, other studies have found the same protein pattern in blood and tissue from severe and deadly coronavirus infections.
“Our findings suggest that these people suffer from a severe ocular response to COVID-19 infection, with long-term inflammation and effects on the nerves that control multiple eye functions,” said Petros Moustadas, a senior researcher at Linköping University who conducted the proteomic analysis and lead author of the study.
Many affected people become extremely sensitive to light. Researchers can now offer an explanation: the pupil lets a lot of light into the eye. Additionally, impaired pupillary function was associated with headaches, difficulty reading, and difficulty focusing the eyes.
Another discovery was that the eyes were unable to work together properly. Known as strabismus or cross-eyed, this occurs almost exclusively in young children. This type of adult-onset strabismus is rare. According to Neil Ragali, this can be explained by the fact that the nerves that control the eye muscles are affected.
The various abnormalities the researchers found are indicative of eye syndromes that occur after COVID-19 infection. To develop diagnostic criteria that currently do not exist, researchers devised two diagnostic models. One model uses only measurements from equipment typically used in the eye clinic of a large academic hospital. The second model adds some tear protein values and is more accurate.
“These people are really struggling in their daily lives. Now we know what’s wrong with their eyes and have some clues as to how COVID-19 may have caused these problems. We hope that this discovery will lead to effective treatment and alleviate their problems in the long run, but unfortunately we don’t know yet,” says Neil Laghari.
The study was carried out in collaboration with Helen Seterud and Björn Johansson from the Eye Clinic of Linköping University Hospital and partners from Linnaeus University in Kalmar. This study was funded by the Swedish Research Council.
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References:
Moustadas, P. Others. (2026). Long-term ocular symptoms after COVID-19 infection are associated with immune dysregulation, autonomic dysfunction, and peripheral neuropathy. nature communications. DOI: 10.1038/s41467-026-74858-4. https://www.nature.com/articles/s41467-026-74858-4
