Corneal Damage Help Confirm Long COVID in People

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Researchers state that corneal nerve damage and the presence of increased dendritic cells in the cornea can point to long COVID in people.

Long COVID is defined as the persistence of symptoms despite recovering from an acute phase of COVID-19. It typically lasts for more than 4 weeks. Approximately 1 in 10 people who contract the disease, go on to develop long COVID. Common signs and symptoms include fatigue, brain fog, muscle pain, numbness, and palpitations. In one particular case, a 29-year-old musician developed such crippling fatigue that he was unable to play his guitar for more than 20 minutes at a time. It is unclear as to what causes the condition to occur. However, researchers believe that the presence of neurological symptoms points to nerve fibre damage in long COVID patients. Moreover, preliminary results from previous studies have also found evidence of small nerve fibre damage in long COVID patients.

While working with diabetics and people with multiple sclerosis, Dr. Rayaz Malik noticed similar symptoms in the patients as those with long COVID. At the time, his team was analyzing corneal damage in these patients using a non-invasive laser technique called corneal confocal microscopy (CCM). Corneal confocal microscopy not only detects nerve fibre damage but also assesses the level of dendritic cells in the cornea. Dendritic cells are a type of immune cell and are often increased in autoimmune disorders and diseases such as multiple sclerosis.

Thus, the team of researchers hypothesized that nerve damage in the eye can serve as a potential link to long COVID.

The fact that physicians will be able to objectively identify patients with Long COVID will enable us to identify those with a definite problem and also paves the way towards assessing the effect of therapies which may help nerve repair.

Dr. Rayaz A. Malik, senior author

Evidence of Nerve Fiber Damage

To test their hypothesis, the team recruited 40 patients who had had COVID-19 in the past 1 to 6 months. Additionally, they also included a group of 30 healthy adults to serve as control participants. The study participants underwent corneal scans to look for nerve damage. Results of the study are available in the British Journal of Ophthalmology.

The 40 patients had to complete questionnaires regarding any persisting symptoms, at 4 and 12 weeks after their infection. The questionnaire assessed for long COVID symptoms, neuropathic pain, and severity of muscle pain. All patients, along with the control group, then underwent corneal scans using CCM.

22 out of the 40 participants had neurological symptoms at 4 weeks after COVID-19 infections. Whereas 45% of patients had neurological symptoms at 12 weeks post-COVID. According to the results, those with neurological symptoms at 4 weeks, had greater corneal nerve fibre damage than the control group. They also had a higher number of dendritic cells.

Although all COVID-19 survivors had a greater number of dendritic cells than the control group, those without any neurological symptoms had similar nerve fibres as the control group.

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.

study authors

According to Dr. Malik, further research is required to confirm the study’s findings.


Bitirgen G, Korkmaz C, Zamani A, et al. Corneal confocal microscopy identifies corneal nerve fibre loss and increased dendritic cells in patients with long COVID. British Journal of Ophthalmology Published Online First: 26 July 2021. doi: 10.1136/bjophthalmol-2021-319450


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