One of the long-term effects of COVID-19 may be small fiber neuropathy in the ocular surface causing similar symptoms to dry eye disease and diabetic neuropathy, a recent study found.
Regardless of case severity, COVID-19 has a wide range of short- and long-term symptoms, including potential chronic issues with respiratory capacity, vasculopathy, or fatigue. A recent study published in Ocular Surface found associations between past COVID-19 infection and small fiber neuropathy in the ocular surface, with symptoms similar to dry eye disease (DED) and diabetic neuropathy.
The observational retrospective study included a cohort of 23 patients who overcame COVID-19 between March and December 2020 and 46 uninfected volunteers as a control group. Patients in the recovered COVID-19 cohort had not received prior ocular surface surgery procedures and had no history of ocular infectious disease or systemic disease that could indirectly cause corneal innervation.
All patients were assessed with in vivo confocal microscopy (IVCM) to obtain images of corneal subbasal nerve fibers to study the presence of neuroma-like structures, axonal beadings and dendritic cells. DED and ocular surface pathology were gauged with the Ocular Surface Disease Index (OSDI) questionnaire and Schirmer tear test.
Twenty-one of 23 patients (91.31%) in the cohort previously infected with COVID-19 showed corneal subbasal plexus and corneal tissue alterations typically present in small fiber neuropathy, while images from healthy individuals did not show significant nerve fiber or corneal tissue damage.
Of the previously infected patients, 8 reported increased feelings of ocular dryness and had DED indicators after COVID-19 infection. In 82.60% of cases, mainly individuals reporting ocular irritation, beaded axons—signs of small fiber neuropathy—were found. A total of 65.22% (15) patients previously infected with COVID-19 showed neuroma-like images, and 69.56% had dendritic cells (DC), which were more common in younger (under 35 years of age) asymptomatic (low OSDI scores) patients. DC play a role in corneal immunoregulation and inflammation.
Neuroma were more common in patients who reported severe DED symptoms (OSDI greater than 13 and Schirmer 3.00 ± 0.49 mm) and in those with low OSDI (less than 12) who had been diagnosed with COVID-19 less than 3 months prior to examination.
“DC were also observed also in patients that had overcome Sars-CoV-2 infection up to 10 months earlier, suggesting that the immunocompromised environment is persistent for long periods of time,” the authors wrote, “and supporting also the hypothesis of the generation of a chronic DED-like state on the ocular surface of post-COVID-19 patients.”
With IVCM already used in other contexts to assess corneal nerves, such as in diabetic neuropathy, other peripheral neuropathies, and DED, the study’s findings suggest it can be used to study COVID-19.
“Our results add new evidence for the use of IVCM technology in the diagnosis and follow up of post-COVID-19 syndromes or complications, as well as to the study of small fiber neuropathies,” study authors wrote.
Barros A, Queiruga-Piñeiro J, Lozano-Sanroma J, et al. Small fiber neuropathy in the cornea of Covid-19 patients associated with the generation of ocular surface disease. Ocul Surf. Published online November 12, 2021. doi:10.1016/j.jtos.2021.10.010