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D. Tilch, J.M. Selbach, T. Laube, C. Theiss, K.P. Steuhl, D. Meller; Corneal Substance-P-ergic Innervation after Laser Epithelial Keratomileusis (LASEK) in Comparison to Photorefractive Keratectomy (PRK) in Rabbits . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2682.
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Purpose: Previous studies have shown that stromal wound healing in PRK is delayed in comparison to LASEK. Corneal afferent nerve fibers deriving from the trigeminal ganglion and with substance P (SP) as neurotransmitter are believed to have trophic function. Therefore, we investigated corneal substance-P-ergic innervation after LASEK and conventional PRK in rabbits. Methods: LASEK and PRK were performed in rabbits and studied after 1, 3, 10 and 20 days (each group n=3-5). In all eyes, hemidesmosomes of corneal epithelium were weakened with 30% ethanol for 3.5 min. In the PRK group, the whole epithelium was removed, but in the LASEK group epithelial flap was repositioned and left to adhere to the underlying stromal bed. Excimer photoablation was performed unilaterally with a 6.0mm ablation zone and 80µ m depth equivalent to –6.0 dpt using the SUMMIT APEX PLUS laser with photorefractive keratectomy (PRK) mode. After enucleation and fixation, serial tangential cryosections were collected and labeled with a rat monoclonal antibody directed against SP. Sections were analyzed by means of scanning laser confocal microscopy. Results: One day after LASEK, eyes showed minor epithelial defects, whereas PRK treated eyes developed a distinct wound. After 10 days a smooth, stable and optically transparent cornea was documented in all eyes. Untreated control eyes showed a dense network of SP-IR nerve fibers especially in the outer part of the cornea spreading from the limbus to the central cornea. In both experimental groups a dramatic reduction of SP-immunoreactive (IR) nerve fibers was noted 1 day after surgery in the central part of the cornea. In general, recovery of SP-IR nerve fibers was delayed after PRK as compared to LASEK. Three and 10 days after surgery, LASEK treated eyes showed a significant higher amount of SP-IR nerve fibers in the central cornea than those treated with PRK. After 20 days, moderate increase of SP-IR nerve fibers was observed in the PRK group, but recovery of SP-IR nerve fibers remained less than in the LASEK group. Conclusions: In general, LASEK seems to promote wound healing in the acute phase after laser photoablation which is reflected by an accelerated recovery of SP-IR nerve fibers in the subepithelial layer and anterior corneal stroma. Further studies have to show whether the remaining epithelial flap acts passively as a protective shield or actively releases neurotrophic factors influencing nerve recovery after photorefractive surgery.
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