STRESS ANALYSIS FOR SCLERAL BUCKLING OF THE EYE by Raed Aldhafeeri B. S. in Mechanical Engineering King Fahd University of Petroleum and Minerals, 2009 Submitted to the Graduate Faculty of Swanson School of Engineering in partial fulfillment of the requirements for the degree of M. S. in Mechanical Engineering University of Pittsburgh 2015
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STRESS ANALYSIS FOR SCLERAL BUCKLING OF THE
EYE
by
Raed Aldhafeeri
B. S. in Mechanical Engineering
King Fahd University of Petroleum and Minerals, 2009
Submitted to the Graduate Faculty of
Swanson School of Engineering in partial fulfillment
of the requirements for the degree of
M. S. in Mechanical Engineering
University of Pittsburgh
2015
UNIVERSITY OF PITTSBURGH
SWANSON SCHOOL OF ENGINEERING
This thesis was presented
by
Raed Aldhafeeri
It was defended on
July 15, 2015
and approved by
Patrick Smolinski, PhD, Associate Professor
Mark C Miller, PhD, Associate Professor
Qing-Ming Wang PhD, Professor
Thesis Advisor: Patrick Smolinski, PhD, Associate Professor
To assess the effect of mesh refinement on the results, the number of elements in the
sclera, which is the main structural tissue of the eye, was varied. This was done for the case of a
5 mm buckle width with a 1.5 mm constriction and for the cornea with a 25% reduction in
thickness. For this the number of elements across its thickness was increased from 8 to 12
0
0.2
0.4
0.6
0.8
1
3 5 7
Max
. von
Mis
ses s
tress
(M
Pa)
Buckle Width (mm)(a)
0
0.2
0.4
0.6
0.8
1
3 5 7Max
. von
Mis
ses s
tress
(M
Pa)
Buckle Width (mm)(b)
0
0.2
0.4
0.6
0.8
1
3 5 7Max
. von
Mis
ses s
tress
(M
Pa)
Buckle Width (mm)(c)
24
elements. Comparison of the results showed that the axial length change varied from 2.62 to 2.58
mm (1.65%) and the maximum von Mises stress increased from 721 to 750 kPa (4%). Based on
this result, the model with 8 elements across the thickness of the sclera was deemed sufficient for
the study.
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6.0 CONCLUSIONS
The stress analysis for the scleral buckling of the eye was explored using finite element analysis
and the effect of the scleral buckling selection and corneal thinning on the axial length of the eye
was evaluated.
An axisymmetric finite element model of the human eye was constructed in terms of the
known geometries and material properties. The eye structures included the sclera, cornea and
lens.. The properties of the tissue were chosen to be linear elastic based on properties available in
the literature and the humors were considered incompressible fluids. The scleral band was
modeled as rigid. The effect of different band widths and constrictions and different corneal
thickness on the axial length of the eye were evaluated.
Based on this model, the results showed that the axial length of the eye increases as the
width of the buckle and the amount of the tightness increase and a thinner buckle with greater
constriction will produce higher the maximum stress concentration at the edges than wider
buckle. Cornea thinning shows less effect on the axial length and the maximum stress.
Because of the lack of the materials constants, one limitation of the model is the linear
elastic properties used for the tissue. Experimental characterizations of the hyperelastic constants
for the eye tissue especially for the sclera and cornea would be very advantageous in modeling
the eye using finite element analysis.
26
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