The document presents a finite element analysis of corneal wrinkling due to external forces from a patient interface during eye surgery. The objectives were to model corneal wrinkling using accurate biological material properties. Various material property models (isotropic, hyperelastic, orthotropic) were tested in simulation software. The orthotropic model best maintained tissue integrity and allowed simulation of wrinkling up to 80% displacement, while other models had limitations. Future work could improve the orthotropic and hyperelastic models to simulate 100% displacement.

1. Finite Element Modeling of
Corneal Wrinkling Due to a
Patient Interface
Vanessa Corrales
Sukhmani Dhaliwal
Cassandra Lo
Mathew Najera
Marko Tomov
Michele Van

2. Background/Introduction
Macroscopic Deformation from Patient Interface

3. Objectives
 To perform Finite Element Analysis
(FEA) on corneal wrinkling as it
would occur from the patient
interface during Lasik cataract eye
surgery, and compute it as
accurately as possible to its
biological material properties.

4. Methods
 Solid Works
 Comsol
 Matlab

5. Material Properties
Isotropic Hyperelastic Orthotropic
Definition Constant
properties
in every direction
Material properties
are direction
dependent
Material properties
are different along
the direction of each
axis
Usage: Non-biological
materials
Ideal elastic material Polymers with
fibrils
Plane of
symmetery
Infinite number of
symmetry planes
No planes of
symmetry
(anisotropic)
At least 2 plane of
symmetry where
mechanical
properties are
different along the
directions of each of
the axes

6. Boundaries
Our Models are:
1. Independent of Dimension
a. The cornea is a semicircle with arbitrary dimensions
2. Dependent on Material Properties
A. Isotropic and Anisotropic
3. Two Forces are applied:
A. Intraocular Pressure (IOP) – Internal [15mmHg]
B. Patient Interface – External [1N]
Internal
(IOP)
External (Patient Interface)

7. Results
A Comsol Simulated Model of Corneal Wrinkling Using
Isotropic Material Properties
Displacement of the cornea with
Isotropic material properties. Red regions
have a higher displacement than the blue
regions.
A boundary image of corneal
displacement. Red regions have a higher
displacement than the blue regions.

8. Results (cont’)
A Comsol Simulated Model of Corneal Wrinkling
Using Hyperelastic Material Properties
Simulation of corneal wrinkling up to 60% in Comsol. Left image is x-y
view and right image is bottom view

9. Results (cont’)
Displacement of the cornea
simulated up to 80% in Comsol.
Red regions have a higher displacement
than the blue regions.
A Comsol Simulated Model of Corneal Wrinkling
Using Orthotropic Material Properties
A boundary image of corneal
displacement simulated up to 80% in
Comsol. Red regions have a higher
Displacement than the blue regions.

10. Goals reached
 No corneal wrinkling presented in
the Isotropic Model
 Modeled one-layer Hyperelastic
Model but achieved 60% simulation.
 Achieved corneal wrinkling in a
two-layered Orthotropic Model

11. Conclusion
 Currently, orthotropic modeling is the most
feasible for FEA in Comsol. It is also superior
at maintaining material integrity.
Isotropic Hyperelastic Orthotropic
- Too linear to
accurately model
biological tissues
- Too nonlinear for
FEA in Comsol only
simulated up to 60%
- Deformation is too
large to calculate in Comsol
- Material is unstable
- Not too linear or
nonlinear for Comsol.
- Simulated up to 80%

12. Future
 Simulate Anisotropic corneal
models to 100%
 Orthotropic 80%  100%
 Hyperelastic 60%  100%