Fluid structure interaction of the non-contact tonometry test

Miguel Ángel Ariza-Gracia,José Félix Rodriguez Matas,Begoña Calvo,Wei Wu,Mauro Malve

doi:10.35119/maio.v2i2.76

Abstract

The study of corneal biomechanics has gained interest due to its applications on predicting refractive surgery outcomes and the study of a number of pathologies affecting the cornea. In this regard, non-contact tonometry (NCT) has become a popular diagnostic tool in ophthalmology and as an alternative method to characterize corneal biomechanics. Since identification of material parameters using NCT tests rely on the inverse finite element method, accurate and reliable simulations are required. In this work, we present a full fluid structure simulation of a NCT test accounting for the eff ect of the presence of the humors. The results indicate that when inertial effects are considered, not including humors may lead to overestimating corneal displacement, and therefore, to an overestimation of the actual corneal stiffness when using the inverse finite element method.

Highlights

In a non-contact tonometry (NCT) test, a high-velocity air jet is applied to the cornea for a very short time (< 30 ms), causing the cornea to deform, while corneal motion is recorded by a high-speed camera
Most approaches model the NCT test as a quasi-static problem, considering only the cornea subjected to a constant intraocular pressure (IOP), and neglecting the inner structures of the eye, i.e., the lens, ciliary muscles, and most importantly, the aqueous and vitreous humors
The air jet caused a deflection in the cornea that reached its maximum value of 0.41 mm in correspondence with the peak velocity of the air jet (Fig. 2), as observed in actual application with the CorVis ST (OCULUS Optikgeräte GmbH Wetzlar, Germany) NCT.[4]

Summary

Introduction

A number of biomarkers associated with corneal motion, i.e., maximum corneal displacement and time between first and second applanation, among others, have been proposed to characterize pre- and postoperative biomechanical changes.[1,2,3,4] Identification of the material parameters associated with corneal mechanical behavior by means of a NCT test is usually performed using the inverse finite element method.[5,6] an accurate simulation of the NCT test is required In this regard, most approaches model the NCT test as a quasi-static problem, considering only the cornea subjected to a constant intraocular pressure (IOP), and neglecting the inner structures of the eye, i.e., the lens, ciliary muscles, and most importantly, the aqueous and vitreous humors. Results indicate that when inertial effects are accounted for in the simulations, neglecting the humors in the model will lead to non-physiological results

Methods

Results

Conclusion