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.

Many algorithms exist for the topographic/tomographic detection of corneas at risk for post-refractive surgery ectasia. It is proposed that the reason for the difficulty to find a universal screening tool based on corneal morphologic features is that curvature, elevation, and pachymetric changes are all secondary signs of keratoconus and post-refractive surgery ectasia and that the primary abnormality is in the biomechanical properties. It is further proposed that the biomechanical modification is focal in nature, rather than a uniform generalized weakening, and that the focal reduction in elastic modulus precipitates a cycle of biomechanical decompensation that is driven by asymmetry in the biomechanical properties. This initiates a repeating cycle of increased strain, stress redistribution, and subsequent focal steepening and thinning. Various interventions are described in terms of how this cycle of biomechanical decompensation is interrupted, such as intrastromal corneal ring segments, which redistribute the corneal stress, and collagen crosslinking, which modifies the basic structural properties.

Purpose To evaluate the feasibility, safety, and utility of intraoperative optical coherence tomography (OCT) for use during ophthalmic surgery. Design Prospective, consecutive, case series Methods A prospective, single-center, consecutive, case series was initiated to assess intraoperative OCT in ophthalmic surgery. Intraoperative scanning was performed with a microscope mounted spectral domain OCT system. Disease specific or procedure-specific imaging protocols (e.g., scan type, pattern, size, orientation, density) were utilized for anterior and posterior segment applications. A surgeon feedback form was recorded as part of the study protocol to answer specific questions regarding intraoperative OCT utility immediately after the surgical procedure was completed. Results During the first 24 months of the PIONEER study, 531 eyes were enrolled (275 anterior segment cases and 256 posterior segment surgical cases). Intraoperative OCT imaging was obtained in 518 of 531 eyes (98%). Surgeon feedback indicated that intraoperative OCT informed surgical decision-making and altered surgeon understanding of underlying tissue configurations in 69/144 (48%) lamellar keratoplasty cases and 63/146 (43%) membrane peeling procedures. The most common anterior segment surgical procedure was descemet stripping automated endothelial keratoplasty (DSAEK, n = 135). Vitrectomy with membrane peeling was the most common procedure for posterior segment surgery (n = 154). The median time that surgery was paused to perform intraoperative OCT was 4.9 minutes per scan session. No adverse events were specifically attributed to intraoperative OCT scanning during the procedure. Conclusions Intraoperative OCT is feasible for numerous anterior and posterior segment ophthalmic surgical procedures. A microscope mounted intraoperative OCT system provided efficient imaging during operative procedures. The information gained from intraoperative OCT may impact surgical decision-making in a high frequency of both anterior and posterior segment cases.