September 2016
Volume 57, Issue 12
Open Access
ARVO Annual Meeting Abstract  |   September 2016
Depth-dependent extrafibrillar matrix stiffness of the human cornea predicts spherical aberration induced by laser refractive surgery
Author Affiliations & Notes
  • Mengchen Xu
    Mechanical Engineering, University of Rochester, Rochester, New York, United States
    Flaum Eye Institute, University of Rochester, Rochester, New York, United States
  • Mark Buckley
    Biomedical Engineering, University of Rochester, Rochester, New York, United States
  • Amy L. Lerner
    Mechanical Engineering, University of Rochester, Rochester, New York, United States
    Biomedical Engineering, University of Rochester, Rochester, New York, United States
  • Geunyoung Yoon
    Flaum Eye Institute, University of Rochester, Rochester, New York, United States
    Biomedical Engineering, University of Rochester, Rochester, New York, United States
  • Footnotes
    Commercial Relationships   Mengchen Xu, None; Mark Buckley, None; Amy Lerner, None; Geunyoung Yoon, None
  • Footnotes
    Support  NIH EY014999
Investigative Ophthalmology & Visual Science September 2016, Vol.57, 2371. doi:
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    • Get Citation

      Mengchen Xu, Mark Buckley, Amy L. Lerner, Geunyoung Yoon; Depth-dependent extrafibrillar matrix stiffness of the human cornea predicts spherical aberration induced by laser refractive surgery. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2371.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : To investigate the influence of depth-dependent corneal extrafibrillar matrix stiffness on wavefront aberrations induced by laser refractive surgery.

Methods : Three-dimensional anisotropic hyperelastic corneal models with a regional fibril distribution (Pandolfi, 2008) were implemented in finite element software (ABAQUS 6.14). Two material cases were compared: (1) averaged uniform extrafibrillar matrix stiffness along depth, (2) five material layers with depth-dependent extrafibrillar matrix stiffness based on previous experimental data (Sloan, 2014). Three preoperative (preOP) model eyes with different axial lengths to induce 5, 7 and 9 diopters (D) myopic refractive error were generated for each material case. An iterative algorithm was used to identify the stress-free configurations of preOP eyes. Myopic corrections were simulated by removing tissue with ablation thickness calculated by the Munnerlyn equation for a 6 mm optical zone. Anterior and posterior corneal surface profiles were exported from each preOP and postoperative (postOP) model eye and used to calculate wavefront aberrations for a 6 mm pupil using a custom-developed surface fitting and ray-tracing program.

Results : For the uniform matrix stiffness model, the trend observed for induced spherical aberration (SA) was opposite to the clinical observation. In contrast, the depth-dependent extrafibrillar matrix stiffness model showed a significant positive linear correlation between the induced positive SA and the amount of attempted diopter correction, in accordance with clinical data. Induced SA predicted after 5, 7 and 9D correction was 0.35, 0.48 and 0.63μm, respectively. PostOP refractive power results predicted that the biomechanical response to the tissue ablation would cause an under-correction in myopia of 15 – 20%. An increasing trend was also found for other aberrations such as astigmatism and quadrafoil with increasing amount of myopic correction.

Conclusions : The uniform and depth-dependent extrafibrillar matrix stiffness of the human cornea lead to different trends of wavefront aberrations induced by laser refractive surgery when fibril distribution remains unchanged. Characterization of the depth-dependent matrix stiffness improves reliability in predicting clinical trends and may be key to understanding the role of biomechanics in optical outcomes after laser refractive surgery.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

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