Fluid-Structure Interaction Based Algorithms for IOP and Corneal Material Behavior

Abstract

Purpose: This paper presents and clinically validates two algorithms for estimating intraocular pressure (IOP) and corneal material behavior using numerical models that consider the fluid-structure interaction between the cornea and the air-puff used in non-contact tonometry. Methods: A novel multi-physics fluid-structure interaction model of the air-puff test was employed in a parametric numerical study simulating human eyes under air-puff pressure with a wide range of central corneal thickness (CCT = 445-645 µm), curvature (R = 7.4-8.4 mm), material stiffness and IOP (10-25 mmHg). Models were internally loaded with IOP using a fluid cavity, then externally with air-puff loading simulated using a turbulent computational fluid dynamics model. Corneal dynamic response parameters were extracted and used in development of two algorithms for IOP and corneal material behavior; fIOP and fSSI, respectively. The two algorithms were validated against clinical corneal dynamic response parameters for 476 healthy participants. The predictions of IOP and corneal material behavior were tested on how they varied with CCT, R, and age. Results: The present study produced a biomechanically corrected estimation of intraocular pressure (fIOP) and a corneal material stiffness parameter or Stress-Strain Index (fSSI), both of which showed no significant correlation with R (p > 0.05) and CCT (p > 0.05). Further, fIOP had no significant correlation with age (p > 0.05), while fSSI was significantly correlated with age (p = 0.001), which was found earlier to be strongly correlated with material stiffness. Conclusion: The present study introduced two novel algorithms for estimating IOP and biomechanical material behavior of healthy corneas in-vivo. Consideration of the fluid structure interaction between the cornea and the air puff of non-contact tonometry in developing these algorithms led to improvements in performance compared with bIOP and SSI.

Current Advances in Keratoconus Imaging

“…More recently, an improved version of the SSI, fSSI, was developed. The new algorithm takes into consideration the fluid-structure interaction of the Corvis air-puff with the cornea, and the results have also been validated clinically [62].…”

Correlation between corneal dynamic responses and keratoconus topographic parameters

“…2 However, this method relies on the subjective analysis of topographic maps, which makes detecting early-stage keratoconus, or keratoconus without obvious symptoms, clinically difficult and different observers may introduce bias into the diagnoses. [2][3][4][5][6] Detecting biomechanical instability, which is an early indicator of the disease, is also problematic. 7 In the early stages of keratoconus, subtle changes in the corneal microscopic structure may already be evident, resulting in abnormal mechanical stability that may occur even before notable changes in corneal morphology are detected.…”

“…Two indices have been proposed for this purpose: the Corvis Biomechanical Index (CBI) 12 and the Tomographic Biomechanical Index (TBI). 4 The CBI is based on a logistic regression analysis that uses Corvis ST response parameters to distinguish keratoconic from normal eyes. The TBI combines corneal tomography (using a Pentacam system) and biomechanical parameters from the Corvis ST device to assist in keratoconus detection.…”

Effects of intracorneal ring segments on the biomechanical response of the ectatic cornea to air-puff: A patient-specific numerical analysis

“…In recent years, the non-contact tonometry test (NCT) has become a popular diagnostic tool in ophthalmology which is employed for evaluation of the corneal biomechanics and IOP [9,10]. Corvis-ST (CorVis ST; Oculus Optikgerate GmbH, Wetzlar, Germany) is one of the most popular NCTs, providing various deformation parameters and a specific method to characterize the dynamic behavior of the cornea [11,12]. In particular, it can be integrated with tomographic analysis to study the biomechanical changes of keratoconus considering corneal shape structure and keratometry results.…”

“…In a recent ICRS study, Gracia et al [22] reported that intracorneal implant modifies corneal kinematics and regulates corneal shape, depending on the volume and position of the implant rather than induces a corneal strengthening. Statistical analyses [23][24][25] as well as numerical studies [10,26] attempted to understand the relationship between corneal geometric features and biomechanics by examining corneal dynamic behavior using the air-puff test or driving a biomechanical index to distinguish between healthy and ectatic corneas [27,28].…”