Berit Byström“I think it’s very important that the problem is recognised and that we show that it can be measured by objective testing. Patients don’t have access to that today. We’ve studied people in Sweden, but believe that many people around the world are experiencing these problems,” says Neil Lagali, professor of experimental ophthalmology at Linköping University, who led the study published in Nature Communications.
The study originated with people seeking care for eye problems following a mild COVID-19 infection. They were experiencing a lot of discomfort, sensitivity to light and in many cases severe eye pain, difficulty reading and focusing their gaze.
Big impact on quality of life
Following examination of those affected, the research team realised that the problem was substantial, not only in terms of prevalence but also in impact on quality of life. Among those affected were people who wanted to continue their studies or work but were unable to do so, as they could no longer read text and were suffering from pain and extreme eye fatigue. Healthcare professionals could not find anything wrong with their eyes, nor provide any explanation for their symptoms, let alone a diagnosis.
Theresa LagaliIn the current study, the researchers examined 100 people with eye problems following COVID-19 who had not been hospitalised. They had suffered from eye problems for 3 months up to 3 years, and one in three were on full or part-time sick leave. The researchers compared the affected group with a control group of 32 people, who had also had mild COVID-19 but without eye problems.
“We found that the problems experienced by those affected were not detectable by standard tests. We had to perform specialised examinations to detect deviations. The puzzle pieces then fell into place, and we found explanations for the symptoms,” says Neil Lagali.
Inflammation and impact on nerves
In their study, the researchers found long-term inflammation and deterioration of several eye functions controlled by the nerves in the brain.
One of the advanced tests involved proteomics, where a variety of proteins in the tear fluid are analysed. In those with eye problems, the researchers found an abnormal pattern of proteins regulating nerves and immune cells, so-called T cells. The findings were consistent with advanced eye microscopy that they used to measure the T cells and nerves in the eye. Strikingly, the same protein pattern has been found in blood and tissue in cases of severe and fatal COVID in other studies.
“Our findings suggest that these people have suffered a severe reaction to COVID-19 manifested in the eyes, with long-term inflammation and an impact on the nerves that control multiple eye functions,” says Petros Moustardas, senior research associate at Linköping University and lead author of the study, who performed the proteomics analyses.
Unusual symptoms explained
Many of those affected became highly sensitive to light. The researchers can now provide an explanation: their pupils let too much light into the eye. The impaired pupil function was furthermore linked to headaches, difficulty reading text and in focusing the eyes.
Another finding was that both eyes could not cooperatively function in a normal way. Known as strabismus, or crossed-eyes, this occurs almost exclusively in young children. This type of adult-onset strabismus is unusual. According to Neil Lagali, it can be explained by the fact that the nerves that control the eye muscles have been affected.
A step towards diagnosis
The various abnormalities discovered by the researchers point to an eye syndrome that occurs following COVID-19. To develop diagnostic criteria, which do not exist today, the researchers came up with two diagnostic models. One model uses only measurements from instruments usually found in eye clinics in larger academic hospitals. In the second model, a few tear fluid protein values are added, making it even more accurate.
“These people are really struggling in their daily lives. Now we know what’s wrong with their eyes, and have several clues as to how COVID-19 may have caused these problems. We hope that the findings can lead to effective treatment and that in the long run their problems will ease, but unfortunately we don’t know yet,” says Neil Lagali.
The study was conducted in collaboration with Helen Setterud and Björn Johansson at the Linköping University Hospital Eye Clinic, and partners at Linnaeus University in Kalmar. The study was financed by the Swedish Research Council.
Article: Long-term ocular symptoms following COVID-19 linked to immune dysregulation, dysautonomia and peripheral neuropathy. Petros Moustardas, Helen Setterud, Helena Meijer, Gunnel Andersson, Jenny Roth, Ava Dashti, Björn Johansson, António Felipe Macedo and Neil Lagali, (2026), Nature Communications, published 8 July 2026, doi: 10.1038/s41467-026-74858-4
