Characterisation of corneal fibrotic wound repair at the LASIK flap margin

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Abstract
Aim: To characterise temporal changes in corneal wound repair at the LASIK flap margin. Methods: 18 rabbits received monocular LASIK and were evaluated during 6 months using slit lamp and in vivo confocal microscopy. In three corneas, the exposed stroma was stained with DTAF. At various time points, corneas were processed for histology and stained for nuclei, f-actin, ED-A fibronectin, α-smooth muscle actin, TGF-β1, TGF-β2, TGF-β receptor II, and CTGF. Results: At day 1, leucocytes migrated from the conjunctival vessels into the cornea. Near the limbus, the leucocytes were organised in long chains stretching towards the flap edge. From day 4, elongated fibroblasts migrated from the periphery to align in a circumferential band (approximately 250 μm wide) next to the flap edge. The lateral extension of this stromal band was delimited by the incisional gap in the epithelial basement membrane. TGF-β1, TGF-β2, TGF-β receptor II, and CTGF were expressed in the band from day 2. Myofibroblasts were identified at week 3 and over time a 50 μm thick layer of fibrotic matrix was deposited. Concurrently, the peripheral circumferential band became narrower (width decreasing to 33% (SD 7%) at 4 months; n = 5) and showed an increased organisation with a gradual decline in reflectivity. At all time points, keratocytes within and below the flap remained quiescent and only minimal fibrosis developed at the interface. Conclusions: Fibrotic wound repair following LASIK is restricted to a narrow band peripheral to the corneal flap edge. The lateral extension of the fibrosis is sharply delimited by the incisional gap in the epithelial basement membrane. The fibrotic wound healing at the LASIK flap margin is associated with myofibroblast transformation and wound contraction and involves a TGF-β signalling pathway.