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A numerical study comparing the biomechanical effects of LASIK flap and ReLEx SMILE cap incisions

Session Details

Session Title: Corneal biomechanics

Session Date/Time: Tuesday 08/10/2013 | 08:00-10:30

Paper Time: 09:26

Venue: Elicium 1 (First Floor)

First Author: : H.Studer SWITZERLAND

Co Author(s): :    C. Roberts               Delcourt

Abstract Details


A parametric numerical study was performed to analyze and compare the anterior corneal changes induced by LASIK flap and ReLEx smile cap cuts.


Integrated Scientific Services AG, Port, Switzerland and The Ohio State University, Columbus, OH, USA.


A biomechanical model of the human cornea was used to simulate the flap and cap incisions of the LASIK and smile refractive surgical procedures, respectively. For both procedures three diameters (7, 8, and 9 millimeters), and three flap/cap depths (90, 120, and 180 microns) were simulated. In addition, two flap hinge sizes (3 millimeters vs 90°), and two cap incision widths (3 millimeters vs 90°) were compared.


LASIK flap simulations induce central flattening (-1.07D to -0.13D), which is consistent with reported clinical results. The smile cap is more neutral (-0.34D to +0.19D). Yet, the surgically induced astigmatism (SIA) was greater in cap (min: 0.09D, max: 0.74D), than for flap (min: 0.03D, max: 0.14D). Analyzing stress distributions revealed that the smile procedure maintains stresses mostly unchanged in the anterior cornea and in the stromal bed below the cap (pre-op: 0.0126MPa±0.0038MPa; post-op cap: 0.0133MPa±0.0041MPa), while the flap does not carry any load immediately after cut and the stromal bed shows higher stresses than preoperatively (post-op flap: 0.0162MPa±0.0044MPa). With diameter (7, 8, and 9 millimeters), the bed under the flap delta stress increase is 0.0033, 0.0038, and 0.0044MPa, respectively, while delta increase for the bed under the cap only is 0.0007, 0.0007, and 0.0008MPa, respectively. With depth (90, 120, and 180 microns), the bed under the flap delta stress increase is 0.0026, 0.0033, and 0.0051MPa, respectively, and the delta increase for the bed under the cap only is 0.0006, 0.0007, and 0.0010MPa, respectively. Finally, the delta stress increase is almost independent of hinge/incision size (3 millimeters, 90°) for the bed under the flap (0.0038, 0.0035MPa) and the cap (0.0004, 0.0010MPa).


Our results suggest that even though the smile cap incision induces some astigmatism, it is generally less invasive for the cornea, and induces less biomechanical change than a LASIK flap. Further, the almost unchanged stress distribution in the postoperative smile cornea indicates the potential for safe treatments at greater depths.

Financial Interest:

... research is funded, fully or partially, by a company producing, developing or supplying the product or procedure presented

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