Toward robotically assisted membrane peeling with 3-DOF distal force sensing in retinal microsurgery

Abstract

Retinal microsurgery requires steady and precise manipulation of delicate eye tissues in a very small space. Physiological hand tremor and lack of force sensing are among the main technical challenges, limiting surgical performance. We present a system that consists of the cooperatively controlled Steady-Hand Eye Robot and a miniaturized 3-DOF force sensing instrument to address these limitations. While the robot can effectively suppress hand tremor, enable steady and precise tissue manipulation, the force sensing instrument can provide three dimensional force measurements at the tool tip with submillinewton resolution. Auditory sensory substitution is used to give the user real time force information. Evaluation experiments are conducted using artificial and biological membrane peeling phantoms. Experimental results show that the robotic assistance and force-to-audio sensory substitution can effectively control the magnitude of the tool-to-tissue force. The direction profiles of the membrane peeling forces reflect the different delaminating strategies for different membrane phantoms.

Fig. 1

The Steady-Hand Eye Robot with the 3-DOF force sensing pick instrument firmly attached in the tool holder. The tool coordinate axes are aligned with the robot when the robot is at the home position. The 3D force vector is described using azimuth (α) and elevation (β) angles in the tool coordinate frame, as shown in the close-up view of the tool tip. The micro-pick is pointing toward the positive X-direction.

Fig. 2

Experimental setup: membrane peeling with robotic assistance using bandage strip phantom (a), free hand membrane peeling using bandage strip phantom (b), membrane peeling with robotic assistance using ISM phantom (c), close-up view of the 3-DOF force sensing micro-pick delaminating the bandage strip phantom (d), and close-up view of the micro-pick peeling off the ISM (e). Blue arrows show the direction of the peeling motion.

Fig. 3

Force plots of example experimental trials with bandage strip (a) and ISM (b) phantoms. Experimental condition is robot-assisted with audio feedback (RA). Red curve shows the force magnitude, while green, brown, and blue curves are the force components along X-, Y-, and Z-axes in the tool coordinate frame, respectively. The transverse force measurements, F_x and F_y, exhibit lower noise than the axial force measurement, F_z, because the force sensing tool has better force resolution and accuracy in the transverse directions than those in the axial direction.

Fig. 4

The normalized force direction histograms are plotted on the α-β angle grid with forces recorded in the bandage strip (a) and ISM (c) peeling. Vertical axis shows the normalized frequency of the corresponding force direction. Heat maps on a unit sphere show the normalized force direction frequency of the forces recorded in the bandage strip (b) and ISM (d) peeling. While delaminating bandage strip phantom concentrates force in one direction consistently, the ISM peeling exerts more distributed forces due to the circular movement. Both are robotically assisted with audio feedback (RA).

Fig. 5

Tool tip trajectory (black curves) with overlay of 3D force vectors (red arrows) shown in two examples of bandage strip membrane peeling (a) and ISM peeling (b). Both are robotically assisted with audio feedback (RA).