Quantitative assessment of the effect of SARS-CoV-2 on the corneal sub-basal nerve plexus of post-COVID-19 patients using in vivo confocal microscopy

Abstract

Objectives: To investigate whether SARS-CoV-2 causes morphological changes in the corneal sub-basal nerve plexus (CSNP) of post-COVID-19 patients using in vivo confocal microscopy (IVCM). Methods: A total of 70 participants were included in the study and were divided into three groups. Post-COVID-19 patients with neurological manifestations were considered Group 1 (n = 24), and post-COVID-19 patients without neurological manifestations were considered Group 2 (n = 24). Healthy control participants were considered Group 3 (n = 22). The parameters of the CSNP, including nerve fibre density (NFD), nerve branch density (NBD), and nerve fibre length (NFL), were investigated in all participants using IVCM. Additionally, corneal sensitivity was tested by corneal esthesiometry. Results: The mean NFD, NBD, and NFL values of Group 1 (16.12 ± 4.84 fibre/mm2, 27.97 ± 9.62 branch/mm2, and 11.60 ± 2.89 mm/mm2) were significantly lower than those of Group 2 (19.55 ± 3.01 fibre/mm2, 40.44 ± 7.16 branch/mm2, and 15.92 ± 2.08 mm/mm2) and Group 3 (25.24 ± 3.75 fibre/mm2, 44.61 ± 11.80 branch/mm2, and 17.76 ± 3.32 mm/mm2) (p < 0.05 for all). Except the mean NFD value (p < 0.001), there were no significant differences in terms of the mean NBD and NFL values between Group 2 and Group 3 (p = 0.445, p = 0.085). The value of the mean corneal sensitivity was significantly higher in Group 3 (59.09 ± 1.97 mm) compared to Group 1 (55.21 ± 1.02 mm) and Group 2 (55.28 ± 1.18 mm) (p < 0.001, p < 0.001) but there was no significant difference between Group 1 and Group 2 (p = 1.000). Conclusion: In post-COVID-19 patients, the mean parameters of CSNP were lower than in the control group. These differences were more pronounced in patients who had neurological manifestations of COVID-19.