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Comparative Study
. 2014 Jun;40(6):971-80.
doi: 10.1016/j.jcrs.2013.08.065.

Comparison of biomechanical effects of small-incision lenticule extraction and laser in situ keratomileusis: finite-element analysis

Abhijit Sinha Roy  1 , William J Dupps Jr  1 , Cynthia J Roberts  2
Affiliations
Comparative Study

Comparison of biomechanical effects of small-incision lenticule extraction and laser in situ keratomileusis: finite-element analysis

Abhijit Sinha Roy et al. J Cataract Refract Surg. 2014 Jun.

Abstract

Purpose: To theoretically compare the corneal stress distribution of laser in situ keratomileusis (LASIK) with the stress distribution of small-incision lenticule extraction.

Setting: Cleveland Clinic Cole Institute, Cleveland, and The Ohio State University, Columbus, Ohio, USA.

Design: Computational modeling study.

Methods: A finite-element anisotropic collagen fiber-dependent model of myopic surgery using patient-specific corneal geometry was constructed for LASIK, small-incision lenticule extraction, and a geometry analog model with unaltered material properties from preoperative but with postoperative geometry including thickness. Surgical parameters, magnitude of myopic correction, LASIK flap thickness, and lenticule depth in small-incision lenticule extraction were varied. Two sets of models, 1 with uniform and 1 with depth-dependent material properties, were constructed.

Results: Stress distribution between small-incision lenticule extraction simulations and the geometry analog model were similar. In contrast, LASIK consistently reduced stress in the flap and increased stress in the residual stromal bed (RSB) compared with the geometry analog model. An increase in flap thickness or lenticule depth resulted in a greater increase in RSB stress in the LASIK model than in the small-incision lenticule extraction model.

Conclusions: Small-incision lenticule extraction may present less biomechanical risk to the residual bed of susceptible corneas than comparable corrections involving LASIK flaps. Deeper corrections in the stroma may be possible in small-incision lenticule extraction without added risk for ectasia.

Financial disclosures: Proprietary or commercial disclosures are listed after the references.

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Figures

Figure 1.
Figure 1.
A: En face and cross-sectional view of the finite element mesh for LASIK and small-incision lenticule extraction models. B: Schematic representation of LASIK and small-incision lenticule extraction finite element models. The schematic shows the LASIK flap or small-incision lenticule extraction cap (brown), RSB (dark green), anterior stroma adjacent to flap/cap (light green), and the healed wound layer along the interface between the flap/cap and RSB (dark line). Section A and Section B represent the cross-section view of the cornea along the vertical meridian and horizontal meridian, respectively (LASIK = laser in situ keratomileusis).
Figure 2.
Figure 2.
Comparison of von-Mises stresses in the flap/cap region and the RSB of the cornea with a −9.0 D correction, 100 μm flap/cap, and nonuniform material properties through the depth for the geometric analog model, LASIK with material property changes, and small-incision lenticule extraction with material property changes. The units of stress are Pa (LASIK = laser in situ keratomileusis; RSB = residual stromal bed).
Figure 3.
Figure 3.
Comparison of von-Mises stresses in the flap/cap and the RSB with a −9.0 D correction, 300 μm flap/cap, and nonuniform material properties through the depth for the geometric analog model, LASIK with material property changes, and small-incision lenticule extraction with material property changes. The units of stress are Pa (LASIK = laser in situ keratomileusis; RSB = residual stromal bed).
Figure 4.
Figure 4.
Comparison of von-Mises stresses in the flap/cap region and the RSB with a −9.0 D correction, 100 μm flap/cap, and uniform material properties through the depth for the geometric analog model, LASIK with material property changes, and small-incision lenticule extraction with material property changes. The units of stress are Pa (LASIK = laser in situ keratomileusis; RSB = residual stromal bed).
Figure 5.
Figure 5.
Comparison of von-Mises stress in the flap/cap and the RSB with a −9.0 D correction, 300 μm flap/cap, and uniform material properties through the depth for the geometric analog model, LASIK with material property changes, and small-incision lenticule extraction with material property changes. The units of stress are Pa (LASIK = laser in situ keratomileusis; RSB = residual stromal bed).
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