Dual-Stiffness Force-Sensing Cannulation Tool for Retinal Microsurgery

Abstract

Retinal vein cannulation is a promising treatment for retinal vein occlusion that involves the injection of an anticoagulant directly into the occluded vein to dissolve the blockage. However, excessive forces applied by the injection tool during the procedure, at either the scleral incision or injection site, can result in injury to the eye. Furthermore, the force required to puncture retinal veins (around 10 mN) is well below human sensing ability and an order of magnitude smaller than those that can be safely applied at the sclera (around 100 mN). Detection and management of toolto-tissue forces on these different scales are some of the most challenging aspects of the cannulation procedure. This work describes the development of a sensorized cannulation tool capable of detecting both tool-to-vein puncture forces and tool-to-sclera contact forces. By combining two materials, nitinol alloy for the tool tip and stainless steel for the tool shaft, to achieve dual stiffness, the tool possesses a flexible tip to capture small vein puncture forces and a stiffer shaft to maintain straightness during use. Three segments of fiber Bragg grating sensors are calibrated to measure the transverse forces at both the tool tip and sclerotomy, as well as to determine the tool insertion depth within the eye. The results of the validation experiments show that the root mean square error of the measurements for the force at the tip, the force at the sclerotomy, and the tool position are 0.70 mN, 1.59 mN, and 0.69 mm, respectively.

An automatic drug injection device with spatial micro-force perception guided by an microscopic image for robot-assisted ophthalmic surgery

“…Because the deformation caused by force in the Z direction is very small, it is difficult to detect the real-time deformation in the Z direction through the FBG sensor. The literature ( Gonenc and Iordachita, 2016 ; Gonenc et al, 2018 ; Patel et al, 2020 ; He C. et al, 2019 ; Vander Poorten et al, 2020 ; He et al, 2020a , b ) mainly regarded the combined force of the needle tube in the X and Y directions as the puncture force. He X. et al (2019 ) created a curved section to reduce the stiffness of the distal part of the instrument shaft to increase the deformation in the Z direction and placed the FBG sensor in the center of the needle tube to directly measure the force in the Z direction.…”

“…During the operation, surgeons can observe the OCT image in front of the forceps in real time, thereby judging the distance of the forceps end relative to the tissue ( Yu et al, 2015 ). Researchers at Johns Hopkins University deployed fiber Bragg grating (FBG) sensors in the surgical instrument shaft and developed, for example, surgical forceps, surgical hooks, and injection needles, which could sense the lateral force of 2-DOF ( Gonenc and Iordachita, 2016 ; Gonenc et al, 2018 ; Patel et al, 2020 ; He C. et al, 2019 ; Vander Poorten et al, 2020 ; He et al, 2020a , b , He X. et al, 2019 ). Experiments were performed on self-made eyeball simulations.…”