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.

Keywords:

• keratorefractive surgery
• ectasia
• ultra-high speed Scheimpflug camera
• Corvis
• tomography
• corneal biomechanics

Acknowledgments

We want to express our gratitude to those who made this work possible and are not referred as co-authors, mainly the other residents and the technicians who performed the exams and, above all, to the chief of the Ophthalmology Department from the Centro Hospitalar e Universitário do Porto, Prof. Dr Pedro Menéres, for his vision and enthusiasm with new technologies and resources to improve the ophthalmic care of the population.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This study received no funding. There is no financial, activity relationships or affiliations disclosures regarding any of the authors. The authors do not have any proprietary interest.