Clemens Wagner

Intraocular surgery on a virtual eye

The EyeSi surgical simulation immerses the surgeon in an environment of real surgical instruments, virtual tissue deformations, and interactive 3D graphics.

EyeSi - A Simulator for Intra-ocular Surgery

We present a computer-based medical workstation for the simulation of a vitrectomy that allows training and rehearsal of eye surgeons. The surgeon manipulates two original instruments inside a cardanically suspended mechanical model of the eye. The instrument positions are tracked by CCD cameras and monitored by a PC which then renders the scenery using a computer graphical model of the eye and the instruments. Stereoscopic images are presented to the user through two small LCD displays that are mounted to the system and emulate the stereo microscope used in real operations. The simulator offers the training of intra-ocular navigation as well as first approaches to interaction with pathological tissues using mass-spring and 3D-ChainMail models. All operations (tracking, rendering, collision detection, tissue manipulation) are computed in real-time on a PC.

Collision detection and tissue modeling in a VR-simulator for eye surgery

This paper gives a survey of techniques for tissue interaction and discusses their application in the context of the intra-ocular training system EyeSi. As key interaction techniques collision detection and soft tissue modeling are identified. For collision detection in EyeSi, an enhanced image-based approach for collisions between deformable surfaces and rigid objects is presented. By exploiting the computing power of graphics processing units, it achieves higher performance than existing geometry-based approaches. Deformation vectors are computed and used for the biomechanical model. A mass-spring approach is shown to be powerful enough to bridge the gap between low computational demands and a convincing tissue behavior.

Virtuelle Realitäten für die augenchirurgische Ausbildung

ZusammenfassungVorgestellt wird ein computergestützter, medizinischer Simulator, der die Durchführung virtueller Augenoperationen ermöglicht. Der Operateur arbeitet dabei mit Originalinstrumenten an einem mechanischen Auge. Neben dem Training der Navigation im Auge wird aufgrund enthaltener biomechanischer Modelle die Interaktion mit pathologischen Strukturen im Auge ermöglicht. Der Simulatoraufbau umfasst ein Modell des Operationstisches, ein mechanisches Auge, 3 CCD-Kameras zur Positionsbestimmung, das am Ort des Mikroskops fixierte Stereodisplay und einen Computer. Die Bewegung der Instrumente und des mechanischen Auges werden von Kameras erfasst und an den Computer übermittelt. Die Kombination von 2 Kamerabildern erlaubt über stereoskopische Rückprojektion die Berechnung der Positionen im Raum. Aus den Positionsdaten berechnet ein PC die Reaktion des Gewebes und ein computergrafisches Modell der Szenerie. Statt des Stereomikroskops verwendet der Simulator 2 kleine LCD-Monitore, die durch Okulare betrachtet werden und stereoskopische Bilder liefern. Die Simulation läuft mit einer Wiederholrate von mindestens 20 Hz.AbstractWe present a computer-based medical training workstation for the simulation of intraocular eye surgery. The surgeon manipulates two original instruments inside a mechanical model of the eye. The instrument positions are tracked by CCD cameras and monitored by a PC which renders the scenery using a computer-graphic model of the eye and the instruments. The simulator incorporates a model of the operation table, a mechanical eye, three CCD cameras for the position tracking, the stereo display, and a computer. The three cameras are mounted under the operation table from where they can observe the interior of the mechanical eye. Using small markers the cameras recognize the instruments and the eye. Their position and orientation in space is determined by stereoscopic back projection. The simulation runs with more than 20 frames per second and provides a realistic impression of the surgery. It includes the cold light source which can be moved inside the eye and the shadow of the instruments on the retina which is important for navigational purposes.

Clinical Efficacy of Simulated Vitreoretinal Surgery to Prepare Surgeons for the Upcoming Intervention in the Operating Room

Purpose To evaluate the efficacy of the virtual reality training simulator Eyesi to prepare surgeons for performing pars plana vitrectomies and its potential to predict the surgeons’ performance. Methods In a preparation phase, four participating vitreoretinal surgeons performed repeated simulator training with predefined tasks. If a surgeon was assigned to perform a vitrectomy for the management of complex retinal detachment after a surgical break of at least 60 hours it was randomly decided whether a warmup training on the simulator was required (n = 9) or not (n = 12). Performance at the simulator was measured using the built-in scoring metrics. The surgical performance was determined by two blinded observers who analyzed the video-recorded interventions. One of them repeated the analysis to check for intra-observer consistency. The surgical performance of the interventions with and without simulator training was compared. In addition, for the surgeries with simulator training, the simulator performance was compared to the performance in the operating room. Results Comparing each surgeon’s performance with and without warmup trainingshowed a significant effect of warmup training onto the final outcome in the operating room. For the surgeries that were preceeded by the warmup procedure, the performance at the simulator was compared with the operating room performance. We found that there is a significant relation. The governing factor of low scores in the simulator were iatrogenic retinal holes, bleedings and lens damage. Surgeons who caused minor damage in the simulation also performed well in the operating room. Conclusions Despite the large variation of conditions, the effect of a warmup training as well as a relation between the performance at the simulator and in the operating room was found with statistical significance. Simulator training is able to serve as a warmup to increase the average performance.

Simulation of the continuous curvilinear capsulorhexis procedure

The capsulorhexis procedure is a key part of cataract surgery. During capsulorhexis, a circular opening is torn into the lens capsule. For managing a circular tear, the medical literature details a set of instructions for the inexperienced surgeon. We have translated these instructions into a descriptive algorithm that simulates the behavior of the capsulorhexis tear. The lens capsule is modeled by a mass-spring mesh. To enable smooth tear propagation within the mesh, we adapted an algorithm originally developed for interactive cutting in triangulated surfaces that constantly re-triangulates around the tear end. The capsulorhexis procedure is implemented as a module for the ophthalmosurgical training simulator EYESI

Interactive Real-Time Simulation of the Internal Limiting Membrane

The paper describes three new tissue deformation algorithms. We present a Mass-spring simulation with a quasi-static modification of the Euler integration to increase the stability of the simulation. A directed length correction for springs and an algorithm called Dragnet are suggested to enhance propagation of large local displacements through the Mass-spring mesh. The new algorithms are compared with methods already in use. The combination of Dragnet and the quasi-static Mass-spring modification is used for the interactive real-time simulation of an ophthalmological procedure, the removal of the Internal Limiting Membrane (ILM).