• Researchers looked at the cornea of people recovering from COVID-19
  • Nerve damage and immune cell build-up in the cornea could signify long COVID
  • The method can be used to identify long COVID patients

Researchers may have found another sign of what's known as "long COVID," and it's not as noticeable as the other symptoms. This time, they found it in patients' eyes.

Many people get better from a COVID-19 infection within weeks, but there are some who experience "returning or ongoing" post-COVID symptoms that last four or more weeks after being infected. Called long COVID, people who experience it may report symptoms such as shortness of breath, fatigue, heart palpitations, brain fog and sleeping problems even months after first being infected.

According to the researchers of a new study, published in the British Journal of Ophthalmology, some 10% of patients who recovered from acute COVID-19 experience long COVID.

The researchers looked at 40 patients within one to six months of COVID-19 and 30 healthy control subjects for their study. The patients also answered a questionnaire to identify if they had persisting symptoms four and 12 weeks after being diagnosed with COVID-19 and another about neuropathic pain.

Among the 40 COVID-19 participants, 22 had lingering neurological symptoms four weeks after recovering from the initial illness.

The researchers used corneal confocal microscopy (CCM), which is a non-invasive, high-resolution imaging method that can quantify corneal sub-basal nerve fibers and dendritic cells (DC) or the cells responsible for initiating an adaptive immune response. Previous work with other conditions had suggested that damage in the small-fiber nerves of the cornea could indicate similar damage somewhere else in the body, according to Live Science.

"This is like a very good barometer, almost, of nerve damage elsewhere," study senior author, Dr. Rayaz Malik of Weill Cornell Medicine-Qatar in Doha, said as per the outlet.

They found that those who had neurological symptoms after being diagnosed with COVID-19 had "significant" fiber nerve loss in the cornea compared to COVID-19 patients who did not have lingering neurological symptoms. When compared to the participants with no history of COVID-19, those who had the disease also had larger amounts of dendritic cells on the corneas, with those who displayed lingering symptoms having a "fivefold" increase in dendritic cells compared to the healthy controls.

"To the best of our knowledge, this is the first study reporting corneal nerve loss and an increase in DC density in patients who have recovered from COVID-19, especially in subjects with persisting symptoms consistent with long COVID," the researchers wrote.

The researchers noted that the study is quite small and cannot confirm if it was COVID-19 that caused the abnormalities in the patients' corneas. However, the study contributes to the body of evidence suggesting that the neurological damage from COVID-19 is not caused by the virus directly infecting the nerve cells, but from inflammation.

"Infection revs up your immune cells to start firing, to fight the enemy, and there's going to be collateral damage," Dr. Anne Louise Oaklander of Harvard Medical School and Massachusetts General Hospital, who was not involved in the study, explained as per Live Science.

"Further studies of larger cohorts of patients using additional measures of neuropathy and CCM are required," the researchers wrote. "Corneal confocal microscopy may have clinical utility as a rapid objective ophthalmic test to evaluate patients with long COVID."

Woman's Eyes
Woman's eyes. Pixabay