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31. Kongress der Deutschsprachigen Gesellschaft für Intraokularlinsen-Implantation, Interventionelle und Refraktive Chirurgie (DGII)

Deutschsprachige Gesellschaft für Intraokularlinsen-Implantation, Interventionelle und Refraktive Chirurgie (DGII) (DGII)

16.02. - 18.02.2017, Dortmund

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Biomechanical differences between FLEx and SmILE refractive procedures tested by 2D-extensiometry in ex-vivo porcine eyes

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  • Bogdan Spiru - Marburg
  • S. Kling - Laboratory of Ocular Cell Biology, Center for Applied Biotechnology and Molecular Medicine, Universität Zürich, Switzerland
  • F. Hafezi - Laboratory of Ocular Cell Biology, Center for Applied Biotechnology and Molecular Medicine, Universität Zürich, Switzerland; Dietikon-Zurich, Switzerland; University of Southern California, Los Angeles, USA
  • W. Sekundo - Marburg

Deutschsprachige Gesellschaft für Intraokularlinsen-Implantation, Interventionelle und Refraktive Chirurgie. 31. Kongress der Deutschsprachigen Gesellschaft für Intraokularlinsen-Implantation, Interventionelle und Refraktive Chirurgie (DGII). Dortmund, 16.-18.02.2017. Düsseldorf: German Medical Science GMS Publishing House; 2017. Doc17dgii051

doi: 10.3205/17dgii051, urn:nbn:de:0183-17dgii0519

Published: February 15, 2017

© 2017 Spiru et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.

Outline

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Purpose: To evaluate the biomechanical stability of ex vivo porcine corneas after FLEx and SmILE refractive surgeries. Design: experimental study.

Methods: 45 porcine eyes were equally divided into 3 groups: Corneas from group 1 and 2 were treated with the FLEx and SmILE procedure, respectively. Corneas from group 3 remained untreated and served as controls. Porcine corneas are considerably thicker than human corneas, thus groups 1 and 2 were subjected to a refractive correction of -14D with a 7mm zone using either a 160µm flap (FLEx) or 160µm cap (SmILE). For 2D-biomechanical measurements, corneo-scleral buttons were excised. Two testing cycles (pre-conditioning stress-strain curve from 1.27 to 12.5N, stress-relaxation at 12.5N during 120s) were performed in order to analyze the elastic and viscoelastic material properties. The Young’s modulus and Prony constants were calculated.

Results: At 0.8% of strain, FLEx (370±36 kPa) could resist a significantly lower stress than SmILE (392±19 kPa, P=0.046) and the control group (402±30 kPa, P=0.013). Also, FLEx (46.1±4.5 Mpa) had a significantly lower Young’s modulus than the control group (50.2±3.4 Mpa, P=0.008). The Young’s modulus of SmILE (48.6±2.5 Mpa) had values situated between untreated corneas and FLEx treated corneas, but the difference did not reach the level of statistical significance in comparison to FLEx (P=0.065) or controls (P=0.159). When compared to untreated controls, the stress resistance decreased by 8.0% with FLEx and 2.5% with SmILE; Young’s modulus decreased by 5.1% with FLEx and 1.04% with SmILE.

Conclusions: Compared to flap-based procedures like FLEx, the SmILE technique can be considered superior in terms of biomechanical stability, when measured experimentally in porcine corneas.