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Blinking Orbital Prosthesis
Andrew Bremer, Padraic Casserly, Rebecca Clayman, Katie Pollock
Department of Biomedical Engineering
Client: Greg Gion, Medical Art Prosthetics, LLC Advisor: Mitch Tyler
BACKGROUND
FINAL DESIGN
Motivation
Every year 11,000 people in the United
States have an orbital exenteration – a
complete removal of an eye and the
surrounding tissues. This can occur due to
an injury or disease, such as squamous or
sebaceous cell carcinoma. While sight in
that eye is permanently lost, it is possible
to replace the eye with a realistic
prosthesis to give the user their original
appearance.
Problem Statement
When a patient has an orbital exenteration the large cavity is
restored with an acrylic eye surrounded by a detailed but static
silicone rubber restoration of the soft tissues (lids, etc). It is
retained with adhesive, osseointegrated percutaneous fixtures or
by gentle anatomical fit. The patient may insert or remove the
structure as necessary. There seems to be adequate volume in a
well lined cavity to house the needed mechanism for animation.
The goal is to fabricate a patient simulator model with prosthesis
that blinks, and a mechanism developed that would synchronize
blinking with the working eye.
Client Requirements
•Actuating mechanism is
self–contained
•Contained sagittally between
the lacrimal and the zygomatic
bone and transversely between
the maxilla and frontal bone
•Mimics a typical spontaneous
blink (110 mm/s)
•Not noticeably audible (less than 15 dB)
•Safe for use within orbital cavity
ABSTRACT
Current orbital prostheses mimic the visual appearance of a normal
eye, but are static and not animated. This makes a prosthesis quite
noticeable, especially when a person blinks their normal eye –
giving the appearance of constant winking. This project aims to
create a blinking orbital prosthesis that will mimic the blink of a
normal eye.
An orbital prosthesis is made using an
acrylic eye. The hard tissue surrounding
the eye is made of poly-methylmethacrylate (PMMA). The acrylic eye is
set in a static silicone restoration of the
soft tissues. These soft tissues include the
eyelid and all of the skin surrounding the
orbital cavity lost during the exenteration.
This unit can then be inserted and
removed on a day-by-day basis.
FUTURE WORK
•Testing to actuate accurate angular
velocity
•Synchronization with working eye using
infrared sensors.
•Miniaturize entire mechanism
Our final design consists of an
electromagnet that attracts a neodymium
magnet enclosed within a slotted, nonmetallic tube. When a magnetic field is
induced by the electromagnet via an electric
current, the neodymium magnet actuates
towards the electromagnet. Upon attraction,
the neodymium magnet pulls two rods which
connect to the eyelid and rotate about the
sagital axis of the eye. This causes the
eyelid to close. When the current is
removed (and the magnetic field ceases), a
spring within the slotted, non-metallic tube
pushes the neodymium magnet and
reverses the actuation as described above;
the eyelid then opens.
COST ANALYSIS
Four feet of Wire: $0.96
Screw: $0.09
Hole Pokers: $2.49
Misc. Tools/Parts: $4.79
Snap-off Knife: $1.69
Sandpaper: $3.99
Storage Box: $4.29
Fimo Soft Clay: $1.76
AA Battery: $0.25
Electronic Switch: $5.59
Poly-methyl-methacrylate: $2.99
2 6mm Neodymium magnets: $0.68
To determine the ideal force, F, created by
the electromagnet, Ampere’s Law is first
used to determine the strength of the
magnetic field:
Grand Total: $29.57
Where the magnetic constant is μo of 4π x
the relative
permeability is 5000, the number of loops N is 55, the
current I is 0.01 A, and the length of the rod L is 0.0325 m.
10-7,
Thus, β = 0.1063 Tesla
REFERENCES
Similarly, the force F created by the
electromagnet is determined by the
equation:
Where the magnetic field β is 0.1063 T, the cross-sectional area
A is 1.59*10-5m², and the magnetic constant is μo of 4π x
10-7.
Thus, F = 0.0715 Newtons
Design Advantages:
•Mechanism almost completely
contained within the orbital cavity
•No energy usage during resting
state (i.e. when the eye is open)
•Cost Effective
•Safe
•Mimics a single spontaneous blink
•Not noticeably audible
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<http://www.lessemf.com/emf-news.html>.
The Cranium: A General Overview. 1 May 1999. California State University, Chico. 11
Oct
2008. <http://www.csuchico.edu/anth/Module/skull.html>.
“Electromagnets.” Hyperphysics. 2005. Department of Physics and Astronomy, Georgia State
University. 10 Oct 2008. <http://hyperphysics.phy-astr.gsu.edu/hbase/
hframe.html>.
Guitton, Daniel, Raymod SImard and François Codère. “Upper Eyelid Movements
Measured with a Search Coil during Blinks and Vertical Saccades.” Investigative
Opthalmology &Visual Science. Vol. 32, No. 13, December 1991.
Kimmel, Ryan, Alison Mcarton, Joel Gaston, Hallie Kreitlow. “Blinking Orbital
Prosthesis.”
Final Report. BME 201. Department of Biomedical Engineering.
University of
Wisconsin- Madison. 12 May 2008.
Lee, P., C.C. Wang, A.P. Adamis. “Ocular Neovascularization: An Epidemiologic Review.” Survey
of Ophthalmology (1998). Vol. 43, No. 3, 245-269
ACKNOWLEDGMENTS
We would like to give a big thanks to our client Greg Gion and our
advisor Mitch Tyler for helping us through the entire design process. We
would also like to thank the Biomedical Engineering program and the
University of Wisconsin Madison for providing us with the opportunity to
work on this project.