Immunohistological Evaluation of the Healing Response at the Flap Interface in Patients With LASIK Ectasia Requiring Penetrating Keratoplasty

Abstract

PURPOSE-To evaluate the healing response at the flap interface in corneas with LASIK ectasia that required penetrating keratoplasty (PK). METHODS-Corneasof five patients who developed corneal ectasia after LASIK (range: 2.5 to 5 years postoperative) were collected after corneal transplant surgery. The corneas were bisected and processed for conventional histologic analysis and immunofluorescence.RESULTS-Light microscopy showed a hypocellular fibrotic scar at the wound margin compared with the adjacent corneal stroma in all eyes. All corneas had positive staining for alpha-smooth muscle actin (SMA), a myofibroblast marker. In one eye, alpha-SMA cells were located in the fibrotic scar region in the area of the semicircular ring of haze along the margin of the LASIK flap corresponding to an area of epithelial ingrowth. In all other eyes, alpha-SMA positive cells were fewer and mainly located in the superficial stroma under the epithelial wound margin surface. Type III collagen was minimal or absent in the central zone and wound margin of all corneas except for the cornea with epithelial ingrowth present in the hypercellular fibrotic scar region. Chondroitin sulfate was stronger in the periphery of the flap wound coinciding with a higher presence of alpha-SMA-positive cells in that region. Positive staining for matrix metalloproteinase 9 (MMP-9) in the paracentral wound margin scar was seen.CONCLUSIONS-A wound-healing process characterized by absence of significant fibrosis and myofibroblasts at the wound edge in the flap interface was noted in all keratectatic eyes. However, changes in the composition of collagen and the presence of MMP-9 at the wound edge several years after LASIK indicates active wound remodeling that may explain the ongoing loss of tissue and tendency of the cornea to bulge.Ectasia after LASIK is a devastating complication of lamellar corneal surgery that results in a progressive deformation and thinning of the cornea associated with severe visual impairment. 1 Multiple risk factors have been implicated in the development of corneal ectasia. 2 Among them are abnormal or suspicious topography suggestive of pre-existing forme fruste keratoconus and an excessive resection of corneal tissue that makes the cornea mechanically unstable. However, in some cases none of these risk factors are identified. Additionally, this complication is seldom seen in deep lamellar keratoplasty. In such cases, the residual stromal bed thickness is usually no more than 10% to 20% of the corneal thickness (50 to 100 μm).We recently suggested that an increase in the amount of myofibroblasts induced by sutures at the edge of the flap in rabbit eyes may reduce the amount of steepening when intraocular pressure (IOP) is artificially increased up to 25 mmHg. 3 We postulated that corneal ectasia may be related to the clinically observed lack of corneal wound-healing response at the edge of the flap, which allows the cornea to bulge.Evaluations of the results and complications of LASIK surgery focus mainly on clinical o...

Progress in corneal wound healing

“…Myofibroblasts also appear transiently mainly at the flap margin, where hypercellularity and epithelial ingrowth are usually noted even in uneventful cases (Ivarsen et al, 2003; Fournié et al, 2010). The flap margin also displays increased MMP production and long-term accumulation of fibrotic ECM consisting of several collagens, various basement membrane components and tenascin-C, apparently reinforcing flap adhesion (Azar et al, 1998; Pérez-Santonja et al, 1998; Wachtlin et al, 1999; Maguen et al, 2007; 2008; Esquenazi et al, 2009). Contrary to the flap margin with clearly fibrotic changes that persist in humans for years (Maguen et al, 2007), the flap interface presents a hypocellular scar with little deposition of fibrotic ECM (Wachtlin et al, 1999; Schmack et al, 2005; Priglinger et al, 2006; Maguen et al, 2007).…”

Correlation between the matrix metalloproteinase-9 activity and chondroitin sulfate concentrations in tear fluid after laser in situ keratomileusis

“…CS increased MMPs activity in corneal explant cultures 11. MMP-9 and CS deeply participate in corneal ectasia which occurred several years after LASIK 12. Based on the findings of these previous reports, we therefore consider the relationship between MMP-9 and CS to be very important in corneal wound healing.…”

“…From these findings, it is likely that the corneal wound healing lasts for a long period following LASIK, implying that the insufficient attachment between the corneal flap and the corneal bed lasts for a prolonged period. There were a few subjects in which the dislocation of corneal flaps,15,16 or ectasia which consisted of a progressive deformation and thining of the cornea12 after LASIK, and these cases appear to be related to corneal wound healing. Although no case of either a dislocation of corneal flaps or ectasia has occurred so far, there is a possibility for such an occurrence.…”

Comparison of self-reported quality of vision outcomes after myopic LASIK with two femtosecond lasers: a prospective, eye-to-eye study

“…A smoother interface is another potential explanation, with the caveat that perhaps a “rougher” stromal interface rendered by the slower FS 60 kHz system smoothens over time due to remodeling 16. Were this true, it might explain the trend toward equivalence of UDVA between the FS 60 kHz and iFS 150 kHz systems 1 year after an initial advantage in the latter group.…”