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Customized Finite Element Modelling of the Human Cornea.

Simonini I, Pandolfi A - PLoS ONE (2015)

Bottom Line: Corneal elevation maps of five human eyes were taken with a rotating Scheimpflug camera combined with a Placido disk before and after refractive surgery.Patient-specific solid models were created and discretized in finite elements to estimate the corneal strain and stress fields in preoperative and postoperative configurations and derive the refractive parameters of the cornea.Patient-specific models can be used as indicators of feasibility before performing the surgery.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Matematica, Politecnico di Milano, Milano, Italy.

ABSTRACT

Aim: To construct patient-specific solid models of human cornea from ocular topographer data, to increase the accuracy of the biomechanical and optical estimate of the changes in refractive power and stress caused by photorefractive keratectomy (PRK).

Method: Corneal elevation maps of five human eyes were taken with a rotating Scheimpflug camera combined with a Placido disk before and after refractive surgery. Patient-specific solid models were created and discretized in finite elements to estimate the corneal strain and stress fields in preoperative and postoperative configurations and derive the refractive parameters of the cornea.

Results: Patient-specific geometrical models of the cornea allow for the creation of personalized refractive maps at different levels of IOP. Thinned postoperative corneas show a higher stress gradient across the thickness and higher sensitivity of all geometrical and refractive parameters to the fluctuation of the IOP.

Conclusion: Patient-specific numerical models of the cornea can provide accurate quantitative information on the refractive properties of the cornea under different levels of IOP and describe the change of the stress state of the cornea due to refractive surgery (PRK). Patient-specific models can be used as indicators of feasibility before performing the surgery.

No MeSH data available.


Related in: MedlinePlus

Example of extra circumferences added to reach the horizontal visible iris diameter (HVID).
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pone.0130426.g003: Example of extra circumferences added to reach the horizontal visible iris diameter (HVID).

Mentions: The software associated to the Sirius corneal topographer provides the Cartesian coordinates of points belonging to the anterior surface of the cornea, located on concentric circumferences and meridians of the cornea. Data are exportable in different formats, and in general readable by standard commercial software. In general, a topographer’s performance in acquiring data is strongly dependent on some patient’s characteristics and external factors might affect the measurement process [7]. In particular, the presence of eyelashes or involuntary ocular movements may interfere with the data acquisition; the thickness and the stability of the tear film may also alter the image. Thus in some cases the sequence of data is characterized by gaps located in the periphery of the cornea, close to the limbus (Fig 1). When gaps are present, the cloud of points has to be completed by means of interpolation between existing values. To obtain a smooth filling of the gaps, the best choice is to adopt a linear interpolation between points belonging to the same circumference and a quadratic interpolation between points belonging to adjacent circumferences (Fig 2). In some cases, whole circles of points are missing and circumferences need to be added in order to fully cover the horizontal visible iris diameter (HVID), also called white to white distance (WTW). The additional circumferences are added by using quadratic interpolation of existing data (Fig 3).


Customized Finite Element Modelling of the Human Cornea.

Simonini I, Pandolfi A - PLoS ONE (2015)

Example of extra circumferences added to reach the horizontal visible iris diameter (HVID).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4476710&req=5

pone.0130426.g003: Example of extra circumferences added to reach the horizontal visible iris diameter (HVID).
Mentions: The software associated to the Sirius corneal topographer provides the Cartesian coordinates of points belonging to the anterior surface of the cornea, located on concentric circumferences and meridians of the cornea. Data are exportable in different formats, and in general readable by standard commercial software. In general, a topographer’s performance in acquiring data is strongly dependent on some patient’s characteristics and external factors might affect the measurement process [7]. In particular, the presence of eyelashes or involuntary ocular movements may interfere with the data acquisition; the thickness and the stability of the tear film may also alter the image. Thus in some cases the sequence of data is characterized by gaps located in the periphery of the cornea, close to the limbus (Fig 1). When gaps are present, the cloud of points has to be completed by means of interpolation between existing values. To obtain a smooth filling of the gaps, the best choice is to adopt a linear interpolation between points belonging to the same circumference and a quadratic interpolation between points belonging to adjacent circumferences (Fig 2). In some cases, whole circles of points are missing and circumferences need to be added in order to fully cover the horizontal visible iris diameter (HVID), also called white to white distance (WTW). The additional circumferences are added by using quadratic interpolation of existing data (Fig 3).

Bottom Line: Corneal elevation maps of five human eyes were taken with a rotating Scheimpflug camera combined with a Placido disk before and after refractive surgery.Patient-specific solid models were created and discretized in finite elements to estimate the corneal strain and stress fields in preoperative and postoperative configurations and derive the refractive parameters of the cornea.Patient-specific models can be used as indicators of feasibility before performing the surgery.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Matematica, Politecnico di Milano, Milano, Italy.

ABSTRACT

Aim: To construct patient-specific solid models of human cornea from ocular topographer data, to increase the accuracy of the biomechanical and optical estimate of the changes in refractive power and stress caused by photorefractive keratectomy (PRK).

Method: Corneal elevation maps of five human eyes were taken with a rotating Scheimpflug camera combined with a Placido disk before and after refractive surgery. Patient-specific solid models were created and discretized in finite elements to estimate the corneal strain and stress fields in preoperative and postoperative configurations and derive the refractive parameters of the cornea.

Results: Patient-specific geometrical models of the cornea allow for the creation of personalized refractive maps at different levels of IOP. Thinned postoperative corneas show a higher stress gradient across the thickness and higher sensitivity of all geometrical and refractive parameters to the fluctuation of the IOP.

Conclusion: Patient-specific numerical models of the cornea can provide accurate quantitative information on the refractive properties of the cornea under different levels of IOP and describe the change of the stress state of the cornea due to refractive surgery (PRK). Patient-specific models can be used as indicators of feasibility before performing the surgery.

No MeSH data available.


Related in: MedlinePlus