Eyes may signal 'long Covid': Study

Nerve fibre loss and an increase in key immune (dendritic) cells on the surface of the eye -- cornea -- may help identify patients with 'long Covid', according to a small study.

These changes were particularly evident among those with neurological symptoms, such as loss of taste and smell, headache, dizziness, numbness, and neuropathic pain, following Covid-19 infection, said researchers from the Necmettin Erbakan University Meram Medical Faculty Hospital in Konya, Turkey.

The cornea is the transparent part of the eye that covers the pupil, iris, and the fluid-filled interior. Its main function is to focus most of the light entering the eye.

Around one in 10 of all those infected with Covid-19 infection will develop long Covid.

The findings, published in the British Journal of Ophthalmology, suggested corneal confocal microscopy (CCM) -- a real time, non-invasive, high-resolution imaging laser technique -- to identify long Covid symptoms correlated strongly with corneal nerve fibre loss.

CCM has been used to identify nerve damage and inflammatory changes attributable to diabetic neuropathy, multiple sclerosis, and fibromyalgia (all over body pain).

"We show that patients with long Covid have evidence of small nerve fibre damage which relates to the severity of long Covid and neuropathic as well as musculoskeletal symptoms," said Gulfidan Bitirgen, from the Hospital's Department of Ophthalmology.

The team scanned corneas of 40 people who had recovered from confirmed Covid-19 infection between one and six months using CCM.

The corneal scans were compared with those of 30 healthy people who hadn't had Covid-19 infection.

The corneal scans revealed that patients with neurological symptoms four weeks after they had recovered from acute Covid-19 had greater corneal nerve fibre damage and loss, with higher numbers of dendritic cells, than those who hadn't had Covid-19 infection.

Those without neurological symptoms had comparable numbers of corneal nerve fibres as those who hadn't been infected with Covid-19, but higher numbers of dendritic cells.

However, this is an observational study, and as such, can't establish cause, the researchers said.

"Corneal confocal microscopy may have clinical utility as a rapid objective ophthalmic test to evaluate patients with long Covid," Bitirgen said.