Biomechanics and wound healing in the cornea

Abstract

The biomechanical and wound healing properties of the cornea undermine the predictability and stability of refractive surgery and contribute to discrepancies between attempted and achieved visual outcomes after LASIK, surface ablation and other keratorefractive procedures. Furthermore, patients predisposed to biomechanical failure or abnormal wound healing can experience serious complications such as keratectasia or clinically significant corneal haze, and more effective means for the identification of such patients prior to surgery are needed. In this review, we describe the cornea as a complex structural composite material with pronounced anisotropy and heterogeneity, summarize current understanding of major biomechanical and reparative pathways that contribute to the corneal response to laser vision correction, and review the role of these processes in ectasia, intraocular pressure measurement artifact, diffuse lamellar keratitis (DLK) and corneal haze. The current understanding of differences in the corneal response after photorefractive keratectomy (PRK), LASIK and femtosecond-assisted LASIK are reviewed. Surgical and disease models that integrate corneal geometric data, substructural anatomy, elastic and viscoelastic material properties and wound healing behavior have the potential to improve clinical outcomes and minimize complications but depend on the identification of preoperative predictors of biomechanical and wound healing responses in individual patients.

Influences on Enhancement Rates in Laser Vision Correction

“…However, this makes sense as patients who are more challenging to operate on require more time with the flap retracted and influences of dehydration of the stromal treated surface come in to play. 7 We also observed that neovascularization could mean that part of the treatment was blocked from the bleeding despite clearing the area as was typically of the surgeon's technique. In addition, we observed that rizatriptan, which appeared in 3.40% of the cases, was another association although we have no real evidence to support a reason behind it.…”

Enhanced Screening for Ectasia Risk prior to Laser Vision Correction

“…8,9 The excimer ablation itself has a biomechanical impact on the cornea, however, the LASIK flap has a more pronounced effect. 10 Interestingly, there are reported cases of unilateral keratectasia after LASIK, whereas the fellow eye remained stable after photorefractive keratectomy (PRK). 42 The relative contributions on corneal biomechanical properties of the lamellar delamination and side cuts at different depths were studied in vitro in organcultured human corneas using radial shearing speckle pattern interferometry.…”

“…9 This occurs due to the inability of the corneal tissue to support the unremitting stresses caused by intraocular pressure, extraocular muscles actions, eyelid blinking, and other forces, such as eye rubbing. 10,11 Since the first report, 1 the hypothesis that post-LASIK ectasia occurred due to the structural impact from the procedure on a cornea with altered biomechanical properties was considered. for ectasia may be related to three factors (Table 1):…”

“…35 The ocular response analyzer (ORA; Reichert, Buffalo, NY; Fig. 4), 10,22,28 the Corvis ST Interestingly, the CBI (corneal biomechanical index) is a novel biomechanical index that was developed by Vinciguerra et al to integrate corneal deformation response metrics from the Corvis ST, having high accuracy to detect clinical ectasia. 37 Ultimately, the integration of biomechanical data and corneal shape data has been proposed for further improving accuracy to detect mild ectasia or even its susceptibility.…”

Impact of chamber pressure and material properties on the deformation response of corneal models measured by dynamic ultra-high-speed Scheimpflug imaging

“…Enhanced refractive surgery screening goes beyond corneal tomography and should include corneal biomechanics assessment. The main objective is to identify refractive candidates with an increased biomechanical susceptibility to post-LASIK ectasia (1,10,11) . Refractive surgery results are also influenced by the biomechanical response in changing the corneal shape (12,13) .…”