The Role of Corneal Biomechanics in the Assessment of Ectasia Susceptibility Before Laser Vision Correction

Abstract

Purpose To describe the tomographic and corneal biomechanical status of a sample of eyes excluded from LVC and to present the differences in biomechanical behavior in relation to cutoffs of clinical- and tomography-based screening methods used in clinical practice. Patients and Methods Observational cross-sectional study including 61 eyes from 32 consecutive patients who were excluded from LVC in our department. Clinical and demographic data were collected from the patients’ clinical records. Tomographic data was assessed with a Scheimpflug camera (Pentacam, OCULUS ® ). Ablation depth (µm) and residual stromal bed (µm) were calculated by the WaveLight ® EX500 laser system software (Alcon, EUA). The corneal biomechanical assessment was made through ultra-high speed Scheimpflug imaging during noncontact tonometry (Corvis ST, OCULUS ® ). Several ectasia risk scores were analyzed. Results Mean age was 31.0±6 years old and mean manifest spherical equivalent was −2.01 ± 2.3D. Belin–Ambrósio deviation index was the tomographic parameter with higher proportion of eyes within the ectasia high risk interval. In the biomechanical assessment, more than 95% of eyes met the criteria for ectasia susceptibility in four of the first generation and in two of the second generation parameters. In a cutoff based comparative analysis, eyes with Kmax ≥45.5 D, eyes with VCOMA <0 and eyes with ARTmax ≤350 presented significantly softer corneal biomechanical behavior. Conclusion The majority of eyes excluded from LVC in the present study met the criteria for ectasia susceptibility in several biomechanical parameters, validating the clinical and tomographic based screening prior to LVC in our center. Differences found in the biomechanical assessment regarding cutoffs used in clinical practice highlight its differential role in characterizing risk profile of these patients. Tomography should not be overlooked and the integration of all data, including treatment-related parameters, can be the future of risk ectasia screening prior LVC.

Repeatability of Corneal Deformation Response Parameters by Dynamic Ultra High-speed Scheimpflug Imaging in Normal and Keratoconus Eyes

“…The analysis of corneal biomechanics has assumed great importance in recent years, for several reasons; among them are it value in the diagnosis of KC and its milder forms, 1,2 as a tool predicting post-LASIK ectasia risk 3,12 and in the evaluation of corneal biomechanics after CXL. [13][14][15] The Corvis ST has been shown to have high repeatability in normal eyes [4][5][6][7] ; however, limited information exists regarding repeatability in eyes with KC including the new indices CBI [6][7][8][9] that reflects the corneal biomechanics through a complex index that included CRP and pachymetric data and TBI 9 that measures corneal biomechanics and tomographic information from Scheimpflug analysis.…”