State of corneal nerve fibers after laser-assisted in situ keratomileusis

Abstract

To assess the state of corneal nerve fibers (CNF) based on quantitative parameters after laser correction of myopia using LASIK. The study examined 141 eyes - 80 eyes with myopia and 61 emmetropic eyes. In 47 cases a microkeratome was used to form a corneal flap, and in 33 cases a femtosecond laser was used (LASIK and FemtoLASIK, respectively). Confocal microscopy was performed before, as well as 1, 3, and 6 months after correction. Objective analysis of CNF involved automatic calculation of the anisotropy (KΔL) and symmetry (Ksym) coefficients of CNF orientation in the Liner 1.2S software. Lower values of KΔL were revealed in myopia as compared to emmetropia. Regardless of the method of flap formation, no CNF could be detected in the central cornea 1 month after myopia correction. In all cases after FemtoLASIK and in 2 cases after LASIK, CNF in the central cornea were first visualized after 3 months, and after 6 months CNF could be detected in all cases. At a similar observation time, CNF were visualized both after LASIK and after FemtoLASIK in the superior and inferior peripheral portions of the cornea. Analysis of long-term postoperative changes in KΔL and Ksym revealed a decrease in the former and an increase in the latter. Evaluation of the state of CNF after corneal refractive correction should take into account the initial changes in CNF in myopia that are possibly associated with an increase in axial eye length. A more dynamic restoration of innervation was noted in cases where the flap was formed with the femtosecond laser, which may be explained by the fact that the mechanism of tissue separation when using this type of coherent radiation is gentler. Considering the changes in the quantitative indicators characterizing the state of CNF, the question of «completeness» of the restored CNF as a result of reinnervation remains open.