Monocular-Vision-Based Retinal Membrane Peeling with a Handheld Robot

Retinal membrane peeling requires delicate manipulation. The presence of the surgeon's physiological tremor, the high variability and often low quality of the ophthalmic image, and excessive forces make the tasks more challenging. Preventing unintended movement caused by tremor and unintentional forces can reduce membrane injury. With the use of an actively stabilized handheld robot, we employ a monocular camera-based surface reconstruction method to estimate the retinal plane and we propose the use of a virtual fixture with application of hard and soft stops and motion scaling to improve control of the tool tip during delaminating in a laboratory simulation of retinal membrane peeling. A hard stop just below the membrane surface helps to limit downward force exerted on the surface. Motion scaling also improves the user's control of contact force when delaminating. We demonstrate a reduction of maximum force and maximum surface-penetration distance from the estimated retinal plane using the proposed technique.

A lubrication equation for a simplified model of shear-thinning fluid

A lubrication equation is obtained for a simplified shear-thinning fluid. The simplified rheology consists of a piecewise linear stress tensor, resulting in a two-viscosity model. This can be interpreted as a modified Bingham fluid, which can be recovered in a specific limit. The lubrication equation is obtained in two steps. First two scalings are performed on the incompressible Navier-Stokes equations, namely the long-wave scaling and the slow motion scaling. Second, the resulting equations are averaged along the vertical direction. Numerical illustrations are provided, bringing to light the different possible behaviours.

Usability of cooperative surgical telemanipulation for bone milling tasks

Purpose Cooperative surgical systems enable humans and machines to combine their individual strengths and collaborate to improve the surgical outcome. Cooperative telemanipulated systems offer the widest spectrum of cooperative functionalities, because motion scaling is possible. Haptic guidance can be used to assist surgeons and haptic feedback makes acting forces at the slave side transparent to the operator, however, overlapping and masking of forces needs to be avoided. This study evaluates the usability of a cooperative surgical telemanipulator in a laboratory setting. Methods Three experiments were designed and conducted for characteristic surgical task scenarios derived from field studies in orthopedics and neurosurgery to address bone tissue differentiation, guided milling and depth sensitive milling. Interaction modes were designed to ensure that no overlapping or masking of haptic guidance and haptic feedback occurs when allocating information to the haptic channel. Twenty participants were recruited to compare teleoperated modes, direct manual execution and an exemplary automated milling with respect to usability. Results Participants were able to differentiate compact and cancellous bone, both directly manually and teleoperatively. Both telemanipulated modes increased effectiveness measured by the mean absolute depth and contour error for guided and depth sensitive millings. Efficiency is decreased if solely a boundary constraint is used in hard material, while a trajectory guidance and manual milling perform similarly. With respect to subjective user satisfaction trajectory guidance is rated best for guided millings followed by boundary constraints and the direct manual interaction. Haptic feedback only improved subjective user satisfaction. Conclusion A cooperative surgical telemanipulator can improve effectiveness and efficiency close to an automated execution and enhance user satisfaction compared to direct manual interaction. At the same time, the surgeon remains part of the control loop and is able to adjust the surgical plan according to the intraoperative situation and his/her expertise at any time.