Biomechanics and Modeling in Mechanobiology

, Volume 17, Issue 4, pp 923–938 | Cite as

Template-based methodology for the simulation of intracorneal segment ring implantation in human corneas

  • Julio Flecha-LescúnEmail author
  • Begoña Calvo
  • Jesús Zurita
  • Miguel Ángel Ariza-Gracia
Review Paper


Keratoconus is an idiopathic, non-inflammatory and degenerative corneal disease characterised by a loss of the organisation in the corneal collagen fibrils. As a result, keratoconic corneas present a localised thinning and conical protrusion with irregular astigmatism and high myopia that worsen visual acuity. Intracorneal ring segments (ICRSs) are used in clinic to regularise the corneal surface and to prevent the disease from progressing. Unfortunately, the post-surgical effect of the ICRS is not explicitly accounted beforehand. Traditional treatments rely on population-based nomograms and the experience of the surgeon. In this vein, in silico models could be a clinical aid tool for clinicians to plan the intervention, or to test the post-surgical impact of different clinical scenarios. A semi-automatic computational methodology is presented in order to simulate the ICRS surgical operation and to predict the post-surgical optical outcomes. For the sake of simplicity, circular cross section rings, average corneas and an isotropic hyperelastic material are used. To determine whether the model behaves physiologically and to carry out a sensitivity analysis, a \(3^k\) full-factorial analysis is carried out. In particular, how the stromal depth insertion, horizontal distance of ring insertion (hDRI) and diameter of the ring’s cross section (\(\phi _\mathrm{ICRS}\)) are impacting in the spherical and cylindrical power of the cornea is analysed. Afterwards, the kinematics, mechanics and optics of keratoconic corneas after the ICRS insertion are analysed. Based on the parametric study, we can conclude that our model follows clinical trends previously reported. In particular and although there is an improvement in defocus, all corneas presented a change in their optical aberrations. The stromal depth insertion is the parameter that affects the corneal optics the most, whereas hDRI and \(\phi _\mathrm{ICRS}\) are less important. Not only that, but it is almost impossible to achieve an optimal trade-off between spherical and cylindrical correction. Regarding the mechanical behaviour, inserting the rings at 65% depth or above will cause the cornea to slightly bend. This abnormal stress distribution greatly distorts the corneal optics and, more importantly, could be the cause of clinical problems such as corneal extrusion. Not only that, but our model also supports that rings are acting as restraint elements which relax the stresses of the corneal stroma in the cone of the disease. However, depending on the exact spatial location of the keratoconus, the insertion of rings could promote its evolution instead of preventing it. ICRS inserted deeper will prevent keratoconus in the posterior stroma from growing (relaxation of posterior surface), but will promote its growing if they are located in the anterior surface (increment of stress). In conclusion, the methodology proposed is suitable for simulating long-term mechanical and optical effects of ICRS insertion.


Corneal biomechanics Template-based automatisation Keratoconus Intracorneal segment ring Corneal ectasia Finite element methodology 



This work was supported by the Spanish Ministry of Economy and Competitiveness (Projects DPI2014-54981-R and DPI2017-84047-R), Department of Industry and Innovation (Government of Aragón) and European Social Fund 2014-2020 (FSE-DGA T88). J. Flecha was supported by the Spanish Ministry of Economy and Competitiveness (BES-2015-073630). M.Á. Ariza-Gracia was supported by the Swiss Government through the ESKAS program (ESKAS-No: 2016.0194. Federal Commission for Scholarships for Foreign Students FCS, Switzerland).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

Supplementary material 1 (mp4 14963 KB)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Julio Flecha-Lescún
    • 1
    Email author
  • Begoña Calvo
    • 1
    • 2
  • Jesús Zurita
    • 3
  • Miguel Ángel Ariza-Gracia
    • 1
    • 4
  1. 1.Applied Mechanics and Bioengineering (AMB); Aragón Institute for Engineering Research(i3A)University of ZaragozaZaragozaSpain
  2. 2.Bioengineering, Biomaterials and Nanomedicine OnlineBiomedical Research Center (CIBBER-BBN)MadridSpain
  3. 3.Department of Mechanical EngineeringPublic University of NavarraPamplonaSpain
  4. 4.Computational Biomechanics (CB), Institute for Surgical Technology and Biomechanics(ISTB)University of BernBernSwitzerland

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