Numerical and Experimental Study of Collagen Crosslinking
Treatment for Keratoconus – FEA Study
2010 RET Final Report
Prepared by
Matthew Ranft
Lyons Township High School, Lagrange IL
Laboratory for Product for Process Design
Director: Professor Andreas Linninger
_____________________________
Matthew Ranft
RET Fellow
___________________________
Dr. Craig Foster
RET Mentor
University of Illinois at Chicago, Chicago IL
Date: 08/06/2010
Image Reconstruction of Brain Structures
Matthew Ranft
Math & Science Teacher
Lyons Township High School
Advisors: Dr. Craig Foster
University of Illinois at Chicago
Director: Dr. Andreas Linninger
University of Illinois at Chicago
Abstract
The purpose of this project is to seek out various Finite Element Analysis (FEA) software
programs that are capable of performing specific functions to assist in the overall analysis
of the human cornea. Better understanding of the structure of the human cornea will
hopefully lead to better understanding and treatment of eye defects such as the
degenerative eye disease Keratoconus. The human cornea is complex both in geometry
and material [1]. The proper FEA software will allow for complex analysis of cornea to
be performed that otherwise would be impossible. Requirements for an acceptable FEA
software for this project is that it has to be able to export information in text or excel
formats, mesh triangles quadrilaterals, tetrahedral and hexahedral, produce a
3dimensional mesh, can post process, user friendly and low cost. Of the FEA software I
looked into I found ANSYS and ADINA best meet these criteria.
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Table of Contents
Abstract ............................................................................................................................... 2
Table of Contents ................................................................................................................ 3
Introduction ......................................................................................................................... 4
Material & Methods ............................................................................................................ 6
Results ................................................................................................................................. 7
Conclusion ........................................................................................................................ 10
Discussion and Future Results .......................................................................................... 12
Acknowledgements ........................................................................................................... 13
References ......................................................................................................................... 14
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Introduction
Keratoconus is a degenerative eye disease that effects one in two thousand people
primarily between the ages of 16 to 30. The disease causes the cornea to lose its
spherical shape and bulge out to form a shape more similar to a cone (hence the name
Keratoconus, derived from the Greek word for cornea (‘kerato’) and cone shaped
(‘conus’)[2]. Figure 1 shows a drawing on a normal cornea compared to one
that has been affected with Keratoconus.
These irregularities of the cornea severely distorts vision.
The exact cause of Keratoconus is not known;
however it is believed to have some genetic ties. Several
treatment options do exist for Keratoconus. Contact
lenses are effective in the early stages; however as the disease progresses surgery is
usually required. With surgery, such as corneal transplants, the cornea does not always
respond well to incisions and it fails to stop the progressive loss of stiffness and strength
of the cornea. An alternative treatment is Collagen Crosslinking. This non invasive
procedure is relatively inexpensive. A riboflavin solution (vitamin B-12) is applied to the
stroma layer of the cornea. Once the riboflavin has been applied for the required time the
eye is then exposed to UVA radiation. This procedure allows for the collagen fibrils to
crosslink (bond) which restores strength and stiffness to cornea. While this treatment
shows much promise the results are inconsistent in the amount of reversal experienced by
patients. It is not known how variations in riboflavin concentration and/or UVA
exposure affect the outcomes of treatment. Therefore further research of this treatment is
required.
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A tool that can be used to further evaluate this treatment is Finite Element Analysis
(FEA). By using FEA software a computer generated model of the cornea can be
created. Because the cornea is mechanically and geometrically complex, stress and
deformation analysis become extremely difficult and time consuming. FEA will allow
for an approximate analysis to be performed fairly easily. Additionally the graphics
capability of FEA software will allow for a clear visual depiction of the cornea as well in
both normal and Keratoconic states.
FEA allows analysis of objects to be performed that would otherwise be impossible.
While the analysis of the object is an approximate solution, the accuracy is kept to within
a given tolerance. Additionally, FEA software allows for a more detailed analysis of the
object. Instead of having to analyze a complex geometry and or material as a whole,
FEA allows for the object to be broken down into much smaller pieces called elements.
These elements come in the shapes of triangles, quadrilaterals, tetrahedral and hexahedral
(Figure 2). Additionally these elements are comprised of nodes which are specific points
located on the element. Analysis of the object is performed at these node locations within
the object. The connecting of all the nodes and elements within an object is called a
mesh (Figure 3).
Figure 2
Example of elements used
within FEA. The points
located on the elements are
called nodes.
Figure 3
Example of a mesh applied over a
simulated cornea shape using FEA
software.
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The goal of the research done during this study was to find an acceptable FEA software
to use for this project. The requirements for the software are that it must be able to:

Export information in text or excel. The desired information is nodal coordinates,
elements connectivity, element connectivity arrays, node sets, sides sets.

Can pre-process by producing duce a mesh using triangles, quadrilaterals,
tetrahedral, hexahedral.

Can post process – analyze data

User friendly

Low cost
Material & Methods
Analyzing FEA software essentially consisted of using a ClientPro 385 PC with
Windows XP operating system. Using this PC I was able to visit various FEA software
sites and request free software trials. Additionally a website
(http://www.andrew.cmu.edu/user/sowen/softsurv.html) created by Steve Owen PhD was
used. This website was a survey of approximately 80 different FEA software programs
available. While the survey is not a complete list, it did serve as a useful tool to focus
and narrow the search of FEA software on the market today. Finally, some other
popular FEA software programs were looked at as well because of their use at UIC
campus or known popularity in the market today
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Results
The following FEA software programs were evaluated using free trial versions of the
software as supplied by developer, ADINA, ABAQUS, Cubit and GID. Additionally,
ANSYS 11.0 was also evaluated as it is widely available in the UIC Engineering
Department. The following is a summary of the findings for each of the above listed
Software
.
ANSYS 11.0
Cost – Free. ANSYS 11.0 is made widely available within the UIC Engineering
Department.
Exportability – The Desired output data is easily available. Through the list
option on the top utility menu node connectivity and sets are available and
exportable to a txt file (lists -> nodes select coordinates only then select OK. This
will create a data table in a .lis format which needs to be converted .txt. In the
data file choose file -> saveas -> choose name. Then go to the newly saved file
right click -> rename -> choose name with .txt at the end of it) Additionally,
element connectivity is available through the same means (lists -> elements ->
nodes + attributes then covert to .txt as mentioned above). Additionally, a “pick”
options exists under the list option that allows using the mouse to click on the
geometry and select attributes to be displayed in tabular exportable form.
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Meshing – ANSYS has the ability to mesh various different elements such as
triangles, quadrilaterals, tetrahedral, and hexahedral (type solid186)
Post Processing – is easily performed in ANSYS although only simple
mathematical models were used. More complex or project specific codes was not
tested.
User Friendly – This is the area of ANSYS that was found to be of the lowest
quality. When compared with other FEA software the interface of actually
learning to draw three dimensional geometries was cumbersome and time
consuming. Creating a new model was not as intuitive and required much help
from the tutorial. Additionally, the controls to create and manipulate computer
generated models required a great deal of effort to learn and become familiar
with. Finally, ANSYS was found to “freeze” quite often and required the saving
of data to be performed regularly to avoid losing work.
Note: There is a new version ANSYS 12.0 available. This version was not evaluated
although it does appear to be more user friendly.
ADINA
Cost - $1200.00
Exportability - Nodal coordinates and element connectivity are easily available
through Adina. Under the meshing option of the top utility menu tabular data is
easily generated and put into and exportable to a .txt file. Additionally nodes sets
and surface sets can be generated using the meshing option however this can only
be performed on surfaces that were created during the preprocessing phase.
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Meshing - ADINA has the ability to mesh various different elements such as
triangles, quadrilaterals, tetrahedral, and hexahedral.
Post Processing - is easily performed in ADINA although only simple
mathematical models were used. More complex or project specific codes were
not tested.
User Friendly – ADINA was found to be user friendly. Majority of operations
were windows based and creating/manipulating the actual geometry was simple.
Points within the geometry were defined, then using the line function to connect
points to create a surface and then rotating the surface about a desired axis to
CUBIT
Cost - $300.00. Free 30 day trial version was used for this analysis.
Exportability – Not able to fully evaluate this aspect. While it does appear that
node connectivity and element and sides sets can be produced, I was not able to
figure out how to get this data into an exportable format.
Meshing – CUBIT has the ability to mesh various different elements such as
triangles, quadrilaterals, tetrahedral, and hexahedral
Post Processing - is easily performed in CUBIT although only simple
mathematical models were used. More complex or project specific codes were
not tested.
User Friendly – Aside from the exportability issue CUBIT was found to be
extremely user friendly. Creating the geometry was easy. This only required
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making a simple sketch, putting the correct dimension on the sketch and the
software created an accurate shape. Additionally, in the tutorial, actual video are
supplied that show step by step how to pre and post process.
ABAQUS
Cost - $1000.00
Exportability – Nodal connectivity as well as elements sets are available through
the query option. However I was not able to determine how to export this data
during the duration of this project.
Meshing – ABAQUS has the ability to mesh various different elements such as
triangles, quadrilaterals, tetrahedral, and hexahedral
Post Processing - is easily performed in ABAQUS although only simple
mathematical models were used. More complex or project specific codes was not
tested.
User Friendly – Through the use of the tutorial ABAQUS was found to be user
friendly. Creating a geometry was found to be fairly simple as well as creating
and analyzing a mesh. However the ease or capability of exporting data remains
unknown at this time.
GID
Although this software is windows based it was found to be the most difficult to
use software. The time required to learn to use this software was high and
frustration level of following tutorial made creating a quality working geometry
impractical
Conclusion
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The use of FEA software to analyze the human cornea for this project is crucial. Based on
the analysis of various different FEA software, it appears that ANSYS and ADINA would
best serve this project. ANSYS is capable to perform all of the required parameters.
Although the user may have to spend time necessary to become more familiar with the
aspects of operating ANSYS once this time is invested ANSYS it appears to be very
capable. While ADINA does appear to be more user friendly and should require less time to
create and analyze models, the cost of $1200.00 needs to be considered.
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Discussion and Future Results
The overall objective of this project is to use available tools to gain a better
understanding of the complicated human cornea. Hopefully by gaining this better
understanding improved treatments for disorders such as Keratoconus will result. Once
an acceptable FEA software is chosen for this project the next step will be to develop and
incorporate FEA software a complex mathematical equation that models the cornea’s
behavior in both the normal and Keratoconic states. Eventually the developed model will
need to be compared to actual human corneas obtained from the Illinois Eye Bank.
Variations in Collagen Crosslinking procedure will be performed on the human corneas
and results will be compared to the mathematical/FEA model.
Ideally what may be developed is an eye model that is patient specific. A patient specific
model may prove to be useful in developing individualized treatment of patients on a case
by case basis.
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Acknowledgements

Financial support by NSF RET Grant – EEC 0743068 (Andreas Linninger, PI) is
gratefully acknowledged

Andreas Linninger

Dr. Craig Foster

Dipika Gongal

Brain J. Sweetman

Sukhraaj S. Basati
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References
1. Dr. Craig Foster, Numerical and Experimental Study of Collagen Treatment for
Keratoconus – Research Proposal, 2010
2. Yaron S. Rabinowitz,M.D., http://keratoconus.com/Keratocus.com, accessed
August 5, 2010
3. http://en.wikipedia.org/wiki/Keratoconus, accessed August 5 2010.
4. Owen, Steven J., "A Survey of Unstructured Mesh Generation Technology",
Proceedings 7th International Meshing Roundtable, Dearborn, MI, October 1998
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