Effect of myopic LASIK on corneal sensitivity and morphology of subbasal nerves

Purpose. To investigate whether the morphology of the subbasal nerves corresponds to corneal sensitivity after laser in situ keratomileusis (LASIK). Methods. In a case series study, 59 patients were examined at 2 to 4 hours, 3 days, 1 to 2 weeks, 1 to 2 months, 3 months, or 6 or more months after undergoing LASIK for myopia, by using a Cochet-Bonnet esthesiometer and an in vivo confocal microscope, and were compared with control subjects. Corneal sensitivity and confocal images of subbasal nerves were obtained centrally and 2 mm nasally and temporally. Subbasal nerve fiber bundles (NFBs) were grouped as follows: corneas with no nerve images; corneas with short (<200 μm), unconnected NFBs; corneas with long (>200 μm) NFBs without interconnections; and corneas with long NFBs with interconnections. Results. Corneal sensitivity was at its lowest at 1 to 2 weeks after LASIK. Sensitivity of the hinge area was higher than temporal or central areas at every time point. At 6 or more months the sensitivity values were comparable with the values observed in control subjects. The central area showed mainly short, unconnected subbasal NFBs, even at 6 months. In general, the temporal area presented with long NFBs from 3 months onward, whereas the nasal area showed long NFBs at every time point. Conclusions. The results suggest that the corneal areas with no nerve images or short, unconnected NFBs are associated with lower sensitivities than corneal areas with long NFBs with or without interconnections. In vivo confocal microscopy reveals LASIK-induced alterations of subbasal nerve morphology and thus enables a direct comparison of corneal sensory innervation and sensitivity.