Haptic feedback with active contstraints in MIS

Retinal Vein Occlusion is an eye condition which affects an estimated 16,4 million people worldwide. The disease occurs when clots are formed inside retinal veins and disturb the oxygen delivery throughout the retina. This causes partial or even complete blindness in the affected eye. Current treatment methods can only slow down vision loss by tempering the side effects. A promising curative treatment method is retinal vein cannulation. In such procedure, the surgeon would insert a needle via a small incision in the eye into the affected veins and subsequently inject an adequate dose of a clot-dissolving drug. A surgical microscope, placed above the patient's eye lens, is used to visualize the instrument while it is being manoeuvred inside the eye. Despite promising pre-clinical studies, high complication rates keep surgeons from practising this treatment. The targeted vessels have a thickness ranging from 30 µm tot 400 µm and are extremely fragile. Unintended motions, such as the surgeon’s hand tremor and rotations of the patient’s eye due to instrument manipulation, make it extremely difficult to precisely insert the needle into the occluded vessel. Further, the surgeon can hardly detect whether the vessel is correctly punctured as puncture forces are mostly below the perceptible level and also visual information is not conclusive. Lastly, even if correctly inserted, the surgeon still needs to keep the needle steady throughout the injection phase which can be as long as 45 minutes. In short, the risk of damaging the vessel or the retina is extremely high. Because of these reasons, retinal vein cannulation remains a controversial therapy and is not performed in clinical practice today.

This work reports on the development and evaluation of dedicated robotic technology to enable surgeons to perform retinal vein cannulation in a safe and successful manner. A prototype of a robotic system developed prior to this research is taken as a starting point. The robot offers a solution to immobilize the eye throughout the intervention and is designed to position a needle with µm-level precision. In this work, the system is further developed. An additional robotic platform enables the surgeon to pre-operatively position the system with respect to the patient in a timely and precise manner. Further, both a comanipulation and a telemanipulation strategy are proposed to control the system. In the case of comanipulation, the surgeon and the robot simultaneously hold the instrument. The surgeon retains full control over the instrument motion. Viscous forces generated by the robot minimize the surgeon's hand tremor such that the needle can be precisely inserted into the targeted vessel. In fact, the surgeon acquires a superhuman positioning precision. In the case of telemanipulation, the surgeon controls the tool indirectly via a joystick. To this end, a novel joystick based on an innovative mechanism is developed. Motion scaling between the joystick and the robot is used to minimize the effect of the surgeon's hand tremor. Another challenge exists in the development of an injection needle which is sufficiently slender to cannulate a wide range of vessels. In this research, the world's thinnest stainless steel injection needle is developed, having a tip diameter of only 80 µm. Additionally, the needle is equipped with an optic force sensor which is shown to be capable of automatically detecting 98% of all puncture events. Auditory feedback is used to inform the surgeon on such event. Finally, the robot can lock the needle into position once inserted into the vessel. This enables a prolonged hands-free injection of the drug.

The different functionalities of the developed technology are thoroughly validated with the aid of a number of dedicated test setups that were developed in the course of this research. Further, a junior retinal surgeon was invited to perform retinal vein cannulation on retinal vessels of ennucleated porcine eyes with the aid of the developed technology. The best results were obtained under assistance of the comanipulation system while receiving auditory feedback on the puncture events. The results are extremely encouraging as the technology enabled the surgeon to perform twenty successful cannulations and injections out of twenty attempts. When asked which operation mode he preferred, i.e. comanipulation or telemanipulation, the surgeon indicated to favour the comanipulation system as it closely mimics conventional retinal surgery. He indicated that he found it very intuitive to use and that the system delivers adequate levels of precision to reliably cannulate retinal vessels.

Based on the promising research results and the accompanying scientific dissemination, a major step was made in the technology transfer of the presented developments. An IOF leverage project aimed at valorizing the technology was granted and a bilateral project in collaboration with a leading pharmaceutical company was established with the ultimate goal to clinically enable robot-assisted retinal vein cannulation. Further, the current robot design together with promising alternative robot embodiments presented in this PhD are covered in a patent application. Finally, EurEyeCase, a H2020 European project coordinated by KULeuven, was granted. The project broadens the application of the robotic system to other challenging retinal procedures. The final goal of the project is to conduct a number of human trials with the aid of the developed technology.