Article
Biomechanical differences between FLEx and SmILE refractive procedures tested by 2D-extensiometry in ex-vivo porcine eyes
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Published: | February 15, 2017 |
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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.