Structural and functional changes in corneal innervation after laser in situ keratomilesis and their relationship with dry eye signs and symptoms

Abstract

Laser in situ keratomileusis (LASIK) causes damage to the corneal sub-basal nerve plexus which may lead to dry eye symptoms, however, the direct relationship has not been reported. Also, the mechanisms which may be involved in nerve regeneration after LASIK has not yet studied. Tear neuropeptides are relevant to the health of corneal nerves and reinnervation, although their role in LASIK is unclear. Therefore this thesis evaluates the changes in dry eye, nerve morphology and tear neuropeptide concentrations and the relationship between the tested variables over time within 6 months after LASIK and in a long-term (12-16 months) post-LASIK group.

The primary outcomes are symptoms measured using Ocular comfort Index in Chinese, tear function and ocular surface integrity (volume, stability and osmolarity, ocular surface staining, goblet cells and function), corneal and conjunctival sensitivity measured using the Cochet-Bonnet aesthesiometer, corneal nerve morphology (nerve fibre density, width, number of interconnections and tortuosity) using in vivo confocal microscopy and tear neuropeptide concentration (substance P and calcitonin gene-related peptide) measured in basal tears using ELISA.

No changes in tear volume, tear film stability or symptoms were evident within 6 months post-LASIK. However, symptoms but not signs in the long-term group, were significantly higher than in the pre-LASIK group. NFD recovery occurred more rapidly at the mid-peripheral cornea than centrally and there were also differences in rate of recovery between nerve morphology variables. Our results confirm previous findings showing no association between recovery of corneal sensitivity and nerve fibre parameters. Associations between tear neuropeptides and NFD were found in both non-operated and post-LASIK participants, but the relationship was reversed. This suggests that tear neuropeptides maintain corneal nerve health in normal eyes and also facilitate reinnvervation immediately after LASIK.