Even a mild case of COVID-19 can result in persistent vision problems, according to a new study from Linköping University in Sweden. Researchers found that the respiratory virus can affect eyesight for months or even years after infection, impacting daily life for those affected.
The study examined 100 individuals who had experienced eye problems following a COVID-19 infection but had not been hospitalized. These participants reported vision issues lasting from three months to three years. A significant portion, one-third, were on full or part-time sick leave due to their symptoms, which included discomfort, severe eye pain, difficulty focusing, and an inability to read text.
A key challenge for those affected was that standard eye examinations did not reveal any abnormalities, making diagnosis difficult for healthcare professionals. The research team compared this group to a control group of 32 individuals who had mild COVID-19 without subsequent eye problems.
Using specialized diagnostic tests, the scientists identified chronic inflammation and deterioration in eye functions controlled by the brain's nerves. One advanced method involved proteomics, analyzing proteins in tear fluid, which revealed an abnormal protein pattern associated with nerve and immune cell regulation, similar to patterns seen in severe COVID-19 cases.
Another test utilized instruments typically found in larger hospital eye clinics. The findings, published in the journal Nature Communications, indicated that nerve damage could explain symptoms such as increased sensitivity to light, as damaged nerves may cause pupils to allow too much light in. This impaired pupil function can lead to headaches and difficulties with reading and focusing.
Lead author Neil Lagali, professor of experimental ophthalmology at Linköping University, stated that the eye problems were not detectable with standard tests and required specialized examinations to identify deviations. "The puzzle pieces then fell into place, and we found explanations for the symptoms," he said.
The study concluded that some individuals experience a severe reaction to COVID-19 that manifests in the eyes, causing long-term inflammation and nerve damage that affects multiple eye functions. Nerve damage was also identified as a potential cause for strabismus, a condition where the eyes do not work in unison.
Researchers hope their findings will lead to wider recognition of these vision problems and the development of effective treatments. They noted that while the study focused on a small sample of Swedish patients, similar issues are likely occurring globally. "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," Lagali added.
Long COVID is estimated to affect around 2 million people in the UK, according to 2024 figures from the Office for National Statistics. Studies have shown that long COVID can cause changes in the gut, heart, and brain, and research has linked it to cognitive impairment.