1. 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. BACKGROUND 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 FINAL DESIGN Andrew Bremer, Padraic Casserly, Rebecca Clayman, Katie Pollock Department of Biomedical Engineering Client: Greg Gion, Medical Art Prosthetics, LLC Advisor: Mitch Tyler An orbital prosthesis is made using an acrylic eye. The hard tissue surrounding the eye is made of poly-methyl- methacrylate (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. REFERENCES “Are There any Standards for EMF Exposure?” Lessemf.com. 2008. 11 Oct 2008.. The Cranium: A General Overview. 1 May 1999. California State University, Chico. 11 Oct 2008.. “Electromagnets.” Hyperphysics. 2005. Department of Physics and Astronomy, Georgia State University. 10 Oct 2008.. 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 Blinking Orbital Prosthesis 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. Our final design consists of an electromagnet that attracts a neodymium magnet enclosed within a slotted, non- metallic 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. To determine the ideal force, F, created by the electromagnet, Ampere’s Law is first used to determine the strength of the magnetic field: Where the magnetic constant is μ o of 4π x 10 -7, 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. Thus, β = 0.1063 Tesla 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*1 0 -5 m², and the magnetic constant is μ o 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 FUTURE WORK Testing to actuate accurate angular velocity Synchronization with working eye using infrared sensors. Miniaturize entire mechanism 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 Grand Total: $29.57