Tear Neuromediator and Corneal Denervation following SMILE

Abstract

PURPOSE: To investigate the changes in tear neuromediators and corneal subbasal nerve plexus following small incision lenticule extraction (SMILE) and to study its association with different refractive power of corrections. METHODS: Thirty patients were included for tear neurome diator analysis (40 eyes) and corneal nerve analysis using in vivo confocal microscopy scans (20 eyes). Tear samples were collected preoperatively and 1 week and 1, 3, 6, and 12 months postoperatively and analyzed for the substance P, cal citonin gene-related peptide (CGRP), and nerve growth factor (NGF) concentrations using the enzyme-linked immunosor bent assay (ELISA). RESULTS: Corneal nerve fiber density (CNFD), corneal nerve fiber length (CNFL), and corneal nerve branch density (CNBD) decreased significantly postoperatively, then gradu ally increased from 3 months onward, but did not recover to the baseline levels at 12 months. Tear substance P and CGRP levels remained stable over 12 months. Tear NGF levels dem onstrated a small peak at 1 week before decreasing signifi cantly compared to preoperative levels at 6 months (P = .03) and 12 months (P = .007). The 1-month reduction in CNFL, tear substance P, and CGRP concentrations were significantly correlated with the corrected spherical equivalent (SE) (r = 0.71 for CNFL; r = -0.33 to -0.52 at different time points for substance P and CGRP, respectively, all P < .05). Compared to the low to moderate myopia group, the high myopia group (corrected SE greater than -6.00 diopters) had a significantly greater decrease in CNFD, significantly higher tear substance P concentrations at 1 week, 1 month, and 6 months, and sig nificantly higher tear CGRP concentrations at 1 and 6 months. CONCLUSIONS: These results provide new insight into the neurobiological responses and their potential implications in corneal nerve damage and recovery after SMILE. High myopia treatment was associated with greater corneal denervation and neuroinflammation.