Abstract:
A virtual environment for eye surgery simulation has been developed to form part of a teleoρerated ophthalmic microsurgical robotic system. The virtual environment is unique in that it incorporates a detailed continuum model of the mechanics of eye tissue which is coupled with anatomically detailed computer graphics. Li addition to providing a realistic visual display of the eye being operated on, the virtual environment is designed to simulate tissue properties during manipulation and cutting. Tissue deformation, stress distribution and the forces involved are calculated from a large deformation non-linear finite element model of the tissue. The use of the surgical virtual to simulate a comeal incision during radial keratotomy is illustrated. To generalize the creation of virtual anatomy a method has been developed for the addition of graphical realism to biomechanical models. The method is based on constructing volume representations of tissue in 3D finite elements and has.applications in surgical simulation and bioengineering visualization. Virtual tissue is modelled as volumes so that internal features may also be defined. The volumes are graphically represented using isosurface methods. To facilitate the modelling of these forms, the established computer graphics techniques of implicit surface modelling, volume sculpting, solid texturing and free form deformation have been integrated with nonlinear finite element modelling techniques. Volumes are modelled in finite element material coordinates, so that they deform with the biomechanically based finite element tissue models. This also means that attributes such as textures are linked with material points and deform correctly with the volumes. The modelling system has a Boolean operation / CSG facility, which operates directly on the isosurfaces rather than the volumetric definitions to avoid unwanted smoothing and to construct sharp boundaries. A new approach is taken by performing the Boolean operations on a cell by cell basis during isosurface generation. This offers improved performance over the previously employed approach of operating on the surfaces post generation. The modeller creates multiple level of detail models to meet the constraints of virtual environments. Anatomical detail produced by the anatomical modelling system is applied to a finite element biomechanical model of ventricular anatomy to produce a realistic, beating virtual heart and a visualization of the stress field at the level of the tissue microstructure. The modeller is used to construct external features of a virtual human body containing the eye and heart models together with coupled finite element / boundary element models of the skull and torso.