AimTo 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).MethodCorneal 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.ResultsPatient-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.ConclusionPatient-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 abstract

Ocular analyzers are used in the current clinical practice to estimate, by means of a rapid air jet, the intraocular pressure and other eye's parameters. In this study, we model the biomechanical response of the human cornea to the dynamic test with two approaches. In the first approach, the corneal system undergoing the air puff test is regarded as a harmonic oscillator. In the second approach, we use patient-specific geometries and the finite element method to simulate the dynamic test on surgically treated corneas. In spite of the different levels of approximation, the qualitative response of the two models is very similar, and the most meaningful results of both models are not significantly affected by the inclusion of viscosity of the corneal material in the dynamic analysis. Finite element calculations reproduce the observed snap-through of the corneal shell, including two applanate configurations, and compare well with in vivo images provided by ocular analyzers, suggesting that the mechanical response of the cornea to the air puff test is actually driven only by the elasticity of the stromal tissue. These observations agree with the dynamic characteristics of the test, since the frequency of the air puff impulse is several orders of magnitude larger than the reciprocal of any reasonable relaxation time for the material, downplaying the role of viscosity during the fast snap-through phase

No abstract