Page 24 - Advances in Biomechanics and Tissue Regeneration

18 1. PERSONALIZED CORNEAL BIOMECHANICS

In this vein, the use of numerical tools such as artificial neural networks, response surfaces, or K-nn methods is
highly useful. The main caveat of these tools, however, is the need for a reliable and extensive dataset to train or
fit the models. Among these tools, K-nn showed a satisfactory trade-off between accuracy and prediction time, being
amenable for a real-time clinical application. It should be noted, though, that for using K-nn, the dataset must present a
fine grid size in which neighbors are not quite far from the patient under analysis or, otherwise, it could introduce
higher errors.
Only when both patient-specific geometry and materials are set should these models be encouraged for clinical use.
Currently, many surgical applications are under analysis, such as laser refractive surgeries, relaxing incisions, cataract
surgery, or other techniques such as the insertion of intracorneal segment rings for preventing the evolution of Ker-
atoconus. But, at this point, it is essential to remark that unless patient-specific optical validation is provided, it is
impossible to assess the predictive abilities of these models.
In this chapter, we showed two examples of how in silico models can be used for predicting clinical outcomes if
calibrated properly. The first example showed that given patient-specific geometry, material, and optics, we could
assess qualitatively and quantitatively the postsurgical visual acuity of the patient, being below the error of measure-
ment of commercial devices. In the second example, we explored the possibility of predicting the effective relaxation of
the corneal stroma affected by Keratoconus after the implantation of intracorneal ring segments. As Keratoconus has
been suggested to be promoted by tensile stresses on corneal stroma, this assessment is extremely important and can-
not be done by any commercial device. These two examples are just a peek into the vast world of possibilities that
in silico models could open in modern ophthalmology.
Still, the cornea presents a clear interplay between different features such as geometry (thickness), material stiffness,
and IOP. Corneal stability, which is ruled by corneal biomechanics, is the one leading the final visual acuity of the
patient. Hence, it is not possible to assess the final visual acuity of the patient without first thoroughly assessing
the patient’s corneal biomechanics. Devices such as noncontact tonometers are a great contribution to the ophthalmo-
logical field because, currently, there is no alternative to induce a mechanical deformation in vivo. However, the diag-
nosis should be handled with care as they are not measuring the physiological response of the cornea, nor the total
contribution of the fibers as the anterior stroma is compressed during bending. Still, the use of these commercial
devices in conjunction with in silico approaches is an appealing alternative to assessing corneal biomechanics and,
hopefully, to improving unexpected postsurgical outcomes.
Although further research must be done in this field such as exploring fluid-structure interaction simulations so as
to carry out more precise material optimizations or instructing models with microstructural features essential for some
specific surgeries, we are facing exciting days that will eventually end up with a full coupling between in silico models
and clinical practice.

Acknowledgments
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 group T24_17R). J. Flecha was supported by
the Spanish Ministry of Economy and Competitiveness (BES-2015-073630).

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I. BIOMECHANICS