- Original Article
- Open Access
Research and Realization of a Master-Slave Robotic System for Retinal Vascular Bypass Surgery
© The Author(s) 2018
- Received: 6 June 2017
- Accepted: 16 August 2018
- Published: 28 August 2018
Retinal surgery continues to be one of the most technical demanding surgeries for its high manipulation accuracy requirement, small and constrained workspace, and delicate retinal tissue. Robotic systems have the potential to enhance and expand the capabilities of surgeons during retinal surgery. Thus, focusing on retinal vessel bypass surgery, a master-slave robot system is developed in this paper. This robotic system is designed based on characteristics of retinal vascular bypass surgery and analysis of the surgical workspace in eyeball. A novel end-effector of two degrees of freedom is designed and a novel remote center of motion mechanism is adopted in the robot structure. The kinematics and the mapping relationship are then established, the gravity compensation control strategy and the hand tremor elimination algorithm are applied to achieve the high motion accuracy. The experiments on an artificial eyeball and an in vitro porcine eye are conducted, verifying the feasibility of this system.
- Retinal robotic system
- Mechanism design
- Gravity compensation
Retinal vein occlusion (RVO), as the main cause of blindness in retinal vascular disease after diabetic retinopathy , has affected estimated 16.4 million adults worldwide . It is caused by the formation of a clot blocking the circulation of blood in retinal veins. With blockage, pressure increases in capillaries, causing blood leak, macula obscurity and other various retinopathies, and ultimately loss of sight. So far, the most effective way to treat this disease is to apply intraocular surgery, such as retinal vascular bypass surgery (RVBS). RVBS is a new and promising treatment. However, manual RVBS is difficult and risky because of two problems: the limited workspace and the rigorous requirements of manipulating accuracy. First, the target retinal tissue is as thin as 25 μm and the retinal vessel diameter is as tiny as 80 μm, while surgeon physiological hand tremor’s amplitude is 182 μm . Thus, eye tissue will suffer serious injuries from any surgoen’s unintended movement. Secondly, surgeon has to manipulate the instruments in a confined space under microscope, all the surgical operations need to be conducted through a trocar mounted on one side of sclera (the white part of eyeball). Therefore, the surgery result is subjected to the surgeon’s limited dexterity.
To overcome the two difficulties mentioned above, scholars have resorted to the microsurgical robot systems with high motion accuracy and stability. A fair number of research has been carried out unremittingly to pursue the technical breakthroughs in this field . One of the first ocular robotic systems is the stereotaxical micro- manipulator (SMOS) developed by Guerrouad and Vidal in 1989. SMOS can achieve six degrees of freedom (DoF) motion using a spherical micromanipulator . A similar robotic system was introduced by Yu et al.  for intravascular drug delivery with a spherical manipulator. Charles et al.  described a master-slave robotic system called RAMS for eye surgery consisting of a six DoF cable-driven manipulator with 10-micron precision in 1997. Wei et al.  developed a novel hybrid two-armed microsurgical robot, and each arm consists of a two DoF intraocular dexterity manipulator and a six DoF parallel stage. Ueta et al.  at Tokyo University proposed a spherical manipulator to assist vitreoretinal surgery in 2009. Taylor’s group in John Hopkins University (JHU)  has researched on steady hand eye robot (SHER) for years. SHER is a co-operative surgical device, which allows surgeon directly hold the robot end-effector and manipulate the instrument. Rahimy et al.  developed IRISS eye robot to perform cataract surgery, IRISS has two circle sliders to construct manipulators.
Recently, Nasseri et al.  introduced a very compact robotic system for ophthalmic surgery as small as the average adult hand in 2013. Pooerten’s group in Katholieke Universiteit Leuven  developed a co-manipulation and tele-manipulation robotic system for retinal surgery composed of a salve manipulator and a cable-driven master controller. Researchers from TU Eindhoven  conducted the similar research with Pooerten’s and proposed the PRESEYES micromanipulator. PRESEYES consists of a motion controller and a table mounted manipulator. Yang et al. in Beihang University have researched on the robotic system for eye surgery for years, proposed corneal hyper-viscoelastic model , investigated needle insertion force in robot assisted corneal suturing [16, 17], and developed a robot assistance for retinal surgery . Researchers also investigated the application of da Vinci surgical system in eye surgery , however, due to its cumbersome end-effector, da Vinci system is not suitable to conduct eye surgery. Besides the robotic manipulators, other types of robotic devices have been developed, including handheld devices [20, 21], flexible micromanipulators [22, 23], untethered micro robots , force-sensing micro-instruments [25, 26]. Recently, two robot assisted retinal surgeries have been performed successfully on human patients [27, 28], demonstrating the clinical feasibility of the robotic technology for retinal microsurgery.
A series of problems about robot assisted retinal surgery have been solved in the past years. However, little research has investigated robotic assisted RVBS in the previous works, and further studies are needed to address the motion error compensation and the tremor canceling in the microsurgical robotic systems. Therefore, this work proposed a master-slave robotic system aimed to enhance the robot motion accuracy and reduce the requirements of surgeon’s operation skills in RVBS. In the rest of this paper, the surgical workspace in the eyeball was first analyzed on the basis of the procedures of RVBS. Secondly, the robotic system design and the structure of a novel end-effector was presented. Then, the kinematics and the coordinates mapping relationship of the robotic system were established, and the gravity compensation control strategy was applied to achieve high robotic system motion accuracy. Next, the recursive least square algorithm was adopted to eliminate the hand tremors from the master manipulators. Finally, the experiments conducted an artificial eyeball model and a porcine eyeball demonstrated the feasibility of the robotic system.
Today, no treatment has been proven effective for RVO , the current solutions including pharmaceutical method (e.g. retinal vein cannulation) and laser surgery cannot permanently solve the retinal ischemia. However, RVBS has been widely recognized as a promising treatment for vascular occlusion due to its excellent treatment effect in recent years. The Eye Hospital of Wenzhou Medical College has accomplished the first RVBS on a vivo porcine model in 2009, successfully cured the RVO preset manually in the porcine eyeball .
extract the crystalline lens and drill two or three operative incisions on sclera to fix trocars as the access to insert the surgical instruments;
import the tiny vascular prosthesis use a hollow needle through the trocar into eyeball, and then clamping the vascular prosthesis by an intraocular microforceps inserted through another trocar;
operate bypass for the blocked blood vessel by inserting two ends of the vascular prosthesis into two sides of blockage;
operate the end-diathermy.
3.1 Instruments Workspace
3.2 Remote Center of Motion (RCM) Manipulator Design
3.3 End-effector Design
Two slave manipulators have different end-effectors to conduct different surgery tasks. The left manipulator is equipped with a hollow needle or an intraocular cautery or a vitreous cutter in different steps, and the right manipulator is equipped with the intraocular microforceps. Unlike the instruments of the left end-effector, the intraocular microforceps needs to rotate around its own axis, and its jaw needs to be opened and closed to perform surgical tasks. Thus two DoF (rotational DoF and forceps open/close DoF) are required in right end-effector.
3.4 Robotic System Implementation
two PHANTOM Omnis with six DoF (SensAble Technologies Inc.) served as the master controllers;
two identical slave manipulators made up of the SCARA stages of three DoF (Yamaha Motor Co.) and the novel RCM mechanisms;
a novel end-effector of two DoF;
a PC host computer and a custom robot control cabinet consisting of a Programmable Multi-Axis Controller (PMAC) (Googol Technology (HK) Ltd.).
The SCARA stage is used to adjust the endpoint position of the slave manipulator at the beginning of the surgery, and the RCM mechanism is responsible for the intraocular operations.
4.1 Controller Implementation
Firstly, the HMI has a higher priority than the master controller, and the instructions from the latter can be blocked by the commands from former in any time to avoid the manipulation errors from the main surgeon, such as accidental hand movements.
Secondly, motor commands from the HMI are valid during whole surgical process, while the main surgeon control mode is active only during the intraocular operation procedure.
4.2 Kinematics Analysis
4.3 Gravity Compensation
Because the RCM mechanism comprises of multiple links, the gravity of these components will apply extra force for the joints and affect the location accuracy of instrument. To achieve fine control of the RCM mechanism, the gravity compensation for actuator control is solved via dynamic analysis and the computed torque method .
4.4 Map Relationship between the Master and the Slave
4.5 Tremor Cancelling
The experiment on the porcine eyeball is conducted in several steps. The first step “translation” is implemented to locate the sclerotomy site and align the instrument tip point with the sclerotomy site. In this mode, only the PC host computer is active to control the robot, and only the SCARA stages are actuated during this mode. The next step “pose adjustment’’ is applied to obtain a suitable pose of the instrument for further passing through the trocar, the robot is still controlled only by the PC host computer in this step, and the movements of the RCM mechanisms contribute to the tilt and roll pose adjustment of the end-effector. Then, the robotic system in the following steps is manipulated by the main surgeon with the master controller. Firstly, the step “insertion” is conducted to insert the instrument into the eye model, the instrument is moved into the eye model along its axial direction consecutively or intermittently without damage to the scleral insertion point. Then, the instrument tip is moved to a desired location and touches the target point on the retina to accomplish particular tasks such as stenting or endodiathermy. When the surgical operation is completed, the “retreat” mode is activated to remove the instrument from the eyeball by pressing the exit button on the master controller. Finally, the robot joints return to the initial site in “return-to-zero” mode controlled by the PC host computer. The experiments have demonstrated the possibility of the clinical use of the robot assisted RVBS in the future.
This paper focuses on the research and the realization of a robotic system assisted for RVBS, and this is also the early development of the ophthalmic robotic system in China.
The system consists of two salve manipulators and two master controllers. The slave manipulator is made up of a novel RCM mechanism (three DoF), a SCARA stage (three DoF), a novel end-effector (two DoF), and PHANTOM Omni as the master controller.
Control strategies, including motion scaling, gravity compensation and tremor canceling, are applied in the robotic system to achieve the precise control.
In the preliminary experiments, feasibility of the system is validated. The whole surgery operation procedures are conducted assisted by the robotic system and the system shows a good performance.
The novelty of this work includes: (a) a novel RCM mechanism is applied as the slave manipulator in the robot, this RCM mechanism enables robot to spatially rotate the instrument around a virtual fixed point as well as insert or retract the tool, (b) a novel end-effector is designed and enables robot to open or close the microforceps jaw, and rotate the microforceps around its axis, (c) the gravity compensation result and hand tremor filter provides steady motion of the robot, improves the manipulation safety.
In future, the force sensor will be integrated in surgical tool and the vision-based localization for end-effector will be implemented. In addition, more experiments will be carried out to quantify the differences between manual and robot-assisted procedures in RVBS.
C-YH was in charge of the whole trial, design and implemented the control systems, end-effector, kinematic analysis, and wrote the manuscript; LH designed RCM mechanism; YY provides workflow of the paper and experiment; Q-FL assisted to conduct the experiments; Y-KL assisted to analyze the dynamic systems. All authors read and approved the final manuscript.
Chang-Yan He, born in 1993, is currently a PhD candidate at School of Mechanical Engineering and Automation, Beihang University, China. He received his bachelor degree from Beijing Jiaotong University, China, in 2015. His research focuses on medical robotics.
Long Huang, born in 1988, is currently a PhD candidate at School of Mechanical Engineering and Automation, Beihang University, China. He received his master degree from School of Mechanical Engineering and Automation, Beihang University, China. His research interests include mechanism and robotics.
Yang Yang, born in 1962, is currently a professor and a PhD candidate supervisor at School of Mechanical Engineering and Automation, Beihang University, China. His main research interests include mechachonics engineering, robotics, and multi-fingered dexterous hand.
Qing-Feng Liang, born in 1971, is currently an associate chief physician and a professor at Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Key Laboratory of Ophthalmology and Visual Sciences, Beijing.
Yong-Kang Li, born in 1985, is currently a PhD candidate at School of Mechanical Engineering and Automation, Beihang University, China. His research interests include mechanism and robotics.
The authors declare that they have no competing interests.
Supported by National Natural Science Foundation of China (Grant Nos. 50675008, 51175013), National Hi-tech Research and Development Program of China (863 Program, Grant No. 2017YFB1302702).
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