Recovery of corneal nerve morphology following laser in situ keratomileusis

Morphological changes in the corneal nerves after laser in situ keratomileusis (LASIK) were investigated and the changes were compared with those observed after creation of the keratectomy flap without subsequent photoablation. After creating the hinged flap, a multizone excimer laser photoablation (myopic correction from 6.00 to 6.66 D; diameter 6 mm) was performed on 27 rabbit corneas. Seven of these 27 rabbits received an automated keratectomy without laser photoablation on the fellow eye. A histochemical acetylcholinesterase reaction was used to demonstrate the changes in the morphology of the corneal nerves 3 days, 2.5 and 5 months after the operations. In all specimens the deepest stromal nerve bundles showed normal morphology. Cut nerve trunks were found at the wound margins and at the level of the flap interphase in the stromal bed. At 3 days, both epithelial and basal epithelial/subepithelial nerves were found at the hinge of the flap but the rest of the flap showed a major loss of epithelial, basal epithelial/subepithelial and superficial stromal nerves. A few new regenerating thin nerve fibers were found to emerge from the cut stromal nerve trunks. They appeared to pass the wound margin into the flap area below the epithelium. At 2.5 and 5 months an increasing number of regenerating nerve leashes were observed to emerge from the cut stromal nerve trunks. They appeared to send anastomosing fibers among the neighboring stromal nerves. By this time the epithelial, basal epithelial/subepithelial and anterior stromal innervation had gained an almost normal nerve density and architecture. In the corneas with the flap only, the epithelial innervation was slightly better spared in the center of the flap, and the stromal changes were somewhat less prominent compared with the LASIK corneas.