Simulation of the biomechanical effects induced by laser in situ keratomileusis (LASIK) for different levels of ablation in normal corneas.

To employ a finite element (FE) stress model to simulate laser in situ keratomileusis (LASIK) surgery and its biomechanical consequences. The basic geometrical model we used for the cornea was patient-specific on which we manually incorporated seven simulations: three simulations evaluating the effect of a 120, 140 and 180 μm flap (without ablation); three simulations evaluating ablation depths of 40, 80 and 120 μm (with a 120 μm flap); and one control model, without any simulated surgical intervention. In all simulations, stress values were greatest in the centre of the cornea. Furthermore, when comparing the different treatments, stress values were highest in the cornea with the deepest ablation, and were lowest in the non-treated cornea. Specifically, peak effective stresses were 0.031, 0.028 and 0.025 MPa in 120, 80 and 40 µm ablation depths, respectively. In our model, the depth of tissue penetration using ablation or flap creation was correlated with tissue loads-the thinner the residual stromal bed is, the greater are the stresses occurring as a result of the same IOP. We based our model geometry on patient specific scans, allowing for customisation of the treatment to the patient's corneal structure.