Characterisation of corneal fibrotic wound repair at the LASIK flap margin

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, a-smooth muscle actin, TGF-b1, TGF-b2, TGF-b 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 mm 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-b1, TGF-b2, TGF-b receptor II, and CTGF were expressed in the band from day 2. Myofibroblasts were identified at week 3 and over time a 50 mm 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-b signalling pathway. L aser in situ keratomileusis (LASIK) is a modern refractive surgical procedure that involves temporary displacement of a hinged corneal tissue flap during laser treatment of the underlying stromal bed. LASIK is associated with a high risk of complications related to the corneal flap including epithelial ingrowth, flap melting, and traumatic flap dislocation.1-4 These complications may be related to the clinically observed lack of corneal wound healing that allows the corneal flap to be separated from its stromal bed for an indeterminate time after surgery. Thus, the LASIK interface is readily accessible for re-treatment more than 1 year after the initial procedure, 5 and corneal flap dehiscence has been observed several years after uneventful surgery. 4 Using slit lamp biomicroscopy, a white reflecting band is typically observed in the corneal flap periphery after LASIK (Fig 1). 2 6 Over time, this circumferential band undergoes characteristic changes in width, texture, and reflectivity. The band is generally believed to represent corneal wound healing 2 7-10 ; however, its exact nature, localisation, and significance have not been thoroughly investigated. Using a rabbit eye model, the present study characterises temporal ch...

Corneal Densitometry as a Tool to Measure Epithelial Ingrowth After Laser In Situ Keratomileusis

“…For those exceptions, the flap edge was usually green, most likely having higher densitometry values due to minor fibrotic repair that occurs at the flap edge after primary treatment (Ivarsen et al, 2003). A study by Ori et al found that healthy corneas have a maximum densitometry value of 19 ± 4.4, which fell close to our pre-operative values that ranged from 21.8-27.2 (Ori et al, 2012).…”

Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome

“…To our knowledge, the only studies to evaluate microkeratome-created flap edges have been performed in animals. 11,13,14 The present study compared the morphology of corneal flaps created using 1 of 3 femtosecond lasers or a microkeratome. We examined flap thickness and side-cut angle using Fourier-domain optical coherence tomography (OCT) analysis.…”

All-Femtosecond Laser Keratorefractive Surgery

“…In accordance, a recent study in rabbits has demonstrated ReLEx flex to induce less wound healing and inflammation than FS-LASIK, particularly after high myopic corrections [49]. Whether this observation has any clinical consequence remains to be determined; however, wound repair after LASIK and, in particular, PRK has been extensively investigated and is known to influence the postoperative outcome [48,50,51].…”