Quantifying Ocular Surface Changes with Contact Lens Wear

TL;DR

The paper introduces the first open-eye, emergent lens-eye coupling that treats the contact lens configuration, suction pressure, and ocular shape as outcomes of a nonlinear, axisymmetric framework. It combines a Maki–Ross thin-shell description of the lens with an isotropic linear-elastic eye model (homogeneous and heterogeneous) and couples them through the suction pressure under the lens applied to the ocular surface, solved iteratively via a finite-element approach. Key findings show micrometer-scale central and limbal deformations, with displacements and stresses increasing with lens stiffness and with heterogeneity in the eye; curvature mismatches between lens and eye shapes modulate center versus edge responses, and thickness profiles can mitigate central displacement. The work provides a physically grounded basis for predicting lens-fit effects, informing lens design and potentially improving comfort predictions before clinical testing, while outlining future enhancements such as tear-film dynamics and non-axisymmetric geometries.

Abstract

Over 140 million people worldwide and over 45 million people in the United States wear contact lenses; it is estimated that 12%-27.4% contact lens users stop wearing them due to discomfort. Contact lens mechanical interactions with the ocular surface have been found to affect the ocular surface itself. These mechanical interactions are difficult to measure and calculate in a clinical setting, and the research in this field is limited. This paper presents the first mathematical model that captures the interactions between the contact lens and the open eye, where the contact lens configuration, the contact lens suction pressure, and the deformed ocular shape are all emergent properties of the model. The non-linear coupling between the contact lens and the eye is achieved by assuming that the suction pressure under the lens is applied directly to the ocular surface through the post-lens tear film layer. The contact lens mechanics are modeled using a previous published model. We consider homogeneous and heterogeneous linear elastic eye models, different ocular shapes, different lens shapes and thickness profiles, and extract lens deformations, suction pressure profiles, and ocular deformations and stresses for all the considered scenarios. The model predicts higher ocular deformations and stresses at the center of the eye and in the limbal/scleral regions. Accounting for heterogeneous material eye parameters increases the magnitude of such deformations and stresses. The ocular displacements and stresses non-linearly increase as we increase the stiffness of the contact lens. Inserting a steeper contact lens on the eye results in a reduction of the ocular displacement at the center of the eye and a larger displacement at the edge of the contact lens. The model predictions are compared with experimental data and previously developed mathematical models.

Figures (15)

• Figure 1: A schematic of the reference frames of the eye and the contact lens models (left) and of the coupled deformed eye and contact lens (right). In blue, we highlight the deformation map for the end-point of the undeformed lens domain, located at radial coordinate $\mathfrak{R}_{lens}$, and the corresponding point on the undeformed ocular domain, located at radial coordinate $\chi\left(\mathfrak{R}_{lens}\right)$, to the deformed configuration located at radial coordinate $R_{eye}(\chi\left(\mathfrak{R}_{lens}\right),h(\chi\left(\mathfrak{R}_{lens}\right)))=R_{lens}(\mathfrak{R}_{lens})$.
• Figure 2: ( A) Different ocular surface profiles considered. ( B) Different contact lens profiles considered, placed on an average-shaped eye. All the lens profiles in ( B) and the ocular surfaces profiles in ( A), except the flat cornea, have been shifted vertically to facilitate illustrating the differences.
• Figure 3: Spatially-dependent Young's modulus values in the different ocular regions considered.
• Figure 4: (A) Results of the mesh convergence study performed. (B) Mesh of the reference ocular domain $\Omega$ with 2806 vertices, corresponding to the red diamond mesh reported in (A).
• Figure 5: Homogeneous average-shaped eye and average-shaped contact lens of constant thickness. ( A) Contact lens displacements. ( B) Contact lens suction pressure, see Eq (\ref{['eq:p']}). ( C) Ocular surface displacements. ( D) The radial eye displacements. ( E) The vertical eye displacements. ( F) Eye displacement in the outward normal direction to the ocular surface. The solid black lines in the contour plots D-- F are the zero level curves and the positive or negative signs indicate the sign of the displacement near the level curves.