A medical apparatus can include an instrument comprising a shaft and a jaw assembly coupled to an end of the shaft; an image capture device; and a controller operably coupled to the image capture device to receive image data from the image capture device. The image data is from images of material gripped between jaw members of the jaw assembly and captured by the image capture device, with the controller programmed to process the received image data using at least one of optical flow and digital image correlation. A medical apparatus can include an instrument comprising a shaft, and a jaw assembly coupled to an end of the shaft, the jaw assembly comprising a pair of jaw members having opposing surfaces configured to grasp material between the opposing surfaces, wherein at least a portion of the opposing surface of a first jaw member of the pair of jaw members is transparent.