Nerve fibre loss and rise in key immune cells on eye surface
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Nerve fibre loss and an increase in key immune (dendritic) cells on the surface of the eye (cornea) may be an identifying feature of 'long COVID', suggests 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, the findings show.

The researchers used a real time, non-invasive, high-resolution imaging laser technique called corneal confocal microscopy, or CCM for short, to pick up nerve damage in the cornea. CCM has been used to identify nerve damage and inflammatory changes attributable to diabetic neuropathy, multiple sclerosis, and fibromyalgia.

Forty people who had recovered from confirmed COVID-19 infection between 1 and 6 months earlier completed a National Institute of Health and Clinical Excellence (NICE) questionnaire to find out if they had long COVID. This questionnaire consists of 28 items in nine domains including generalised, respiratory, cardiovascular, neurological, musculoskeletal, psychological/psychiatric, gastrointestinal, dermatological, and ear, nose and throat symptoms, with a total score ranging from 0 to 28.

Neurological symptoms were present at 4 and 12 weeks in 22 out of 40 (55%) and 13 out of 29 (45%) patients, respectively. Participants' corneas were then scanned using CCM to look for small nerve fibre damage and the density of dendritic cells. These cells have a key role in the primary immune system response by capturing and presenting antigens from invading organisms.

The corneal scans were compared with those of 30 healthy people who hadn't had COVID-19 infection. Twenty two (55%) of the 40 COVID patients had no clinical signs of pneumonia; 11 (28%) had clinical signs of pneumonia not requiring oxygen therapy; four (10%) had been admitted to hospital with pneumonia and received oxygen therapy; and three (8%) with pneumonia had been admitted to the intensive care.

The corneal scans revealed that patients with neurological symptoms 4 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. The questionnaire responses indicative of long COVID symptoms correlated strongly with corneal nerve fibre loss.

Source:
https://bjo.bmj.com/content/early/2021/07/08/bjophthalmol-2021-319450
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