CORNEAL REINNERVATION AFTER PHOTOREFRACTIVE KERATECTOMY AND LASER IN-SITU KERATOMILEUSIS - AN IN-VIVO STUDY WITH A CONFOCAL VIDEOMICROSCOPE

The purpose of this study was to compare the regeneration of corneal n erves after photorefractive keratectomy (PRK) versus laser in situ ker atomileusis (LASIK) in vivo with a confocal videomicroscope. In all, 1 5 eyes that had undergone PRK and 15 eyes that had been subjected to L ASIK were compared with a confocal in vivo slit-scanning videomicrosco pe. The subepithelial nerves were observed preoperatively and at 3, 6, and 12 months postoperatively. In all eyes, good microscope images of the subepithelial nerve plexus could be obtained preoperatively. Beca use of postoperative light reflection and scattering in the treated ar ea, subepithelial nerve-fiber regeneration could be followed satisfact orily only in seven eyes after PRK and in five eyes following LASIK. I n the eyes treated with PRK, recovery of subepithelial reinnervation s tarted from the margin of the ablation zone, being directed toward the center of the cornea. At 8 weeks postoperatively, rarefied subepithel ial nerve fibers were visible at the edges, and after 3 months, single nonbranched nerve fibers could be visualized in the center of the abl ation zone. At 6-8 months following PRK, subepithelial nerve regenerat ion seemed to be completed: how ever, abnormal branching and accessory thin nerve fibers were present without exception. After LASIK, cornea l nerve-fiber regeneration followed the same course described for PRK except that regenerated subepithelial nerve fibers were barely visible in the center after 6 months. Further changes in nerve structure were visible for up to 12 months postoperatively. Recovery of corneal sens itivity in humans has been reported to start at 4-6 weeks after PRK an d is said to be completed within 6-12 months of surgery. Slit-scanning videomicroscope findings were in accordance with these observations.