Biomedical Interactive Technology Center
Eye Surgery Simulation
The Georgia Institute of Technology and the Medical College of Georgia have developed a proof-of-concept eye surgery simulation that provides both visual and tactile feedback while a surgeon operates on a computer model of the eye in a virtual environment. In practice, ophthalmic surgeons operate on an eye by looking through a stereo microscope while steadying their hands (holding the surgical instruments) on a wrist rest that surrounds the patient's head. The simulator also includes a stereo operating scope and a wrist rest, but instead of looking directly at a real eye, the surgeon interacts with a virtual eye using a virtual surgical instrument controlled by a hand held 3D position tracking stylus that continuously reports position and orientation to the computer. The tip of the stylus is connected to three motors that generate component force feedback in response to the tool-tissue interaction. The simulation includes options to change instruments, record and playback training sessions, reset the models, and peel away outer layers of the eye to reveal interior anatomical components. Dials allow the surgeon to rotate the model, change transparency, zoom, and adjust stereo viewing parameters. An instrument activation switch on the stylus controls actions such as opening and closing forceps and scissors.
In the virtual environment, the eye and the surgical instruments exist only as computer models. The eye is represented by a collection of deformable three-dimensional models. The models of the sclera, iris, zonules, and retina are texture mapped with photographic images of these components. The lens and cornea are modeled as semi-transparent objects. An overhead light source included in the simulation produces specular highlights on the ocular components. Interaction between the instruments and the eye is dependent upon the currently selected tool, the location of the instrument in the anatomy, and the kind of action requested by the surgeon. For example, as the knife makes contact, the sclera slightly deforms until the blade penetrates and starts to cut. The tactile feedback system produces a compliant resistance as the sclera deforms and then allows the blade to slice through the sclera with a small viscous resistance in the cutting direction after penetration. As the blade is cutting, a strong compliant resistance is generated at the stylus tip in the direction orthogonal to the cutting direction to produce the same type of resistance that would be experienced if the surgeon tried to lift the incision with the flat portion of the blade. Forceps can be used to grasp and stretch the sclera while opening the wound. Both visual and tactile feedback are provided to the user: if the forceps are opened during the grasp and pull action, the sclera reverts to its original shape, and the tactile resistance is removed.
