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 tool-to-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.
Insights
This study developed a novel sensorized tool for retinal vein cannulation, improving safety by precisely measuring delicate forces during the procedure. The tool accurately detects forces at the vein and sclera, preventing eye injury during treatment for retinal vein occlusion.
Area of Science:
- Ophthalmology
- Biomedical Engineering
- Surgical Instrumentation
Background:
- Retinal vein occlusion (RVO) is a leading cause of vision loss.
- Retinal vein cannulation offers a promising treatment for RVO by delivering anticoagulants directly to the occluded vein.
- Current cannulation techniques lack precise force feedback, risking ocular injury due to the significant difference in forces required for vein puncture versus scleral contact.
Purpose of the Study:
- To develop and validate a sensorized cannulation tool for precise force detection during retinal vein cannulation.
- To address the challenge of managing tool-to-tissue forces at vastly different scales (mN for veins, 100 mN for sclera).
- To enhance the safety and efficacy of retinal vein cannulation procedures.
Main Methods:
- Development of a dual-stiffness cannulation tool combining a flexible nitinol tip with a stiffer stainless steel shaft.
- Integration of three fiber Bragg grating (FBG) sensors to measure transverse forces at the tip and sclerotomy, and to determine tool insertion depth.
- Calibration and validation of the sensorized tool using experimental measurements.
Main Results:
- The sensorized tool accurately detected tool-tip forces (RMS error: 0.70 mN) and sclerotomy forces (RMS error: 1.59 mN).
- Tool insertion depth was measured with high accuracy (RMS error: 0.69 mm).
- The dual-stiffness design enabled sensitive detection of small vein puncture forces while maintaining tool integrity.
Conclusions:
- The developed sensorized cannulation tool effectively measures critical forces during retinal vein cannulation.
- This technology has the potential to significantly reduce the risk of ocular injury associated with the procedure.
- Precise force monitoring represents a crucial advancement for the safety and success of retinal vein cannulation treatments.
