Fiber-optic OCT sensor guided "SMART" micro-forceps for microsurgery

3D nanoprinted catadioptric fiber sensor for dual-axis distance measurement during vitrectomy

Retinal damage is a common intraoperative complication during vitrectomy, caused by a complex interplay between the suction of the vitrectome, the cut- and aspiration rate, and the distance of the instrument to the retina. To control this last factor, we developed two miniaturized fiber-optic distance sensors based on low-coherence interferometry for direct integration into the vitrectome. Both sensors have a diameter of 250 µm, which makes them compatible with a 25G vitrectome. The first sensor measures distance in the lateral direction. The second sensor is capable of simultaneously measuring distance in both the lateral and the axial direction. Axial and lateral directions correspond to the direction of the cutter port of the vitrectome and the direction along the vitrectome's shaft, respectively. In both sensors, a free-form mirror deflects and focuses the beam in the lateral direction. In the dual-axis distance sensor, an additional lens is integrated into the free-form mirror for distance measurement in the axial direction. The beam-shaping micro-optics at the tip of the sensor fibers were fabricated through two-photon polymerization and are selectively gold coated for increased reflectivity of the mirror. Distance measurements were successfully demonstrated in artificial samples and in ex vivo pig eyes with a back-end that uses a current-tuned VCSEL as a swept-source. We experimentally demonstrate that the complete sensor system can attain a S N R max of up to 80 dB. The small dimensions of the developed sensors make them a potential solution for various other medical applications.

Overcoming the impact of physiologic tremors in ophthalmology

PURPOSE

Ophthalmic surgery involves the manipulation of micron-level sized structures such as the internal limiting membrane where tactile sensation is practically absent. All humans have physiologic tremors that are of low amplitude and not discernible to the naked eye; they do not adversely affect the majority of the population's daily functioning. However, during microsurgery, such tremors can be problematic. In this review, we focus on the impact of physiological tremors on ophthalmic microsurgery and offer a comparative discussion on the impact of such tremors on other surgical specialties.

METHODS

A single investigator used the MEDLINE database (via PubMed) to search for and identify articles for inclusion in this systematic review. Ten key factors were identified as potentially having an impact on tremor amplitude: beta-blockers, muscle fatigue, robotic systems, handheld tools/micromanipulators, armrests/wrist supports, caffeine, diet, sleep deprivation, consuming alcohol, and workouts (exercise). These key terms were then searched using the advanced Boolean search tool and operators (i.e., AND, OR) available on PubMed: (*keyword*) AND (surgeon tremor OR microsurgery tremor OR hand steadiness OR simulator score).

RESULTS

Ten studies attempted to quantify the baseline severity of operator physiologic tremor. Approximately 89% of studies accessing the impact of tremors on performance in regards to surgical metrics reported an improvement in performance compared to 57% of studies concluding that tremor elimination was of benefit when considering procedural outcomes.

CONCLUSIONS

Robotic technology, new instruments, exoskeletons, technique modifications, and lifestyle factors have all demonstrated the potential to assist in overcoming tremors in ophthalmology.

Robotic Assistance for Intraocular Microsurgery: Challenges and Perspectives

Intraocular surgery, one of the most challenging discipline of microsurgery, requires sensory and motor skills at the limits of human physiological capabilities combined with tremendously difficult requirements for accuracy and steadiness. Nowadays, robotics combined with advanced imaging has opened conspicuous and significant directions in advancing the field of intraocular microsurgery. Having patient treatment with greater safety and efficiency as the final goal, similar to other medical applications, robotics has a real potential to fundamentally change microsurgery by combining human strengths with computer and sensor-based technology in an information-driven environment. Still in its early stages, robotic assistance for intraocular microsurgery has been accepted with precaution in the operating room and successfully tested in a limited number of clinical trials. However, owing to its demonstrated capabilities including hand tremor reduction, haptic feedback, steadiness, enhanced dexterity, micrometer-scale accuracy, and others, microsurgery robotics has evolved as a very promising trend in advancing retinal surgery. This paper will analyze the advances in retinal robotic microsurgery, its current drawbacks and limitations, as well as the possible new directions to expand retinal microsurgery to techniques currently beyond human boundaries or infeasible without robotics.

A Smart Vitrector Equipped by a Fiber-Based OCT Sensor Mitigates Intentional Attempts at Creating Iatrogenic Retinal Breaks During Vitrectomy in Pigs

Purpose

The occurrence of iatrogenic retinal breaks (RB) in pars plana vitrectomy (PPV) is a complication that compromises the overall efficacy of the surgery. A subset of iatrogenic RB occurs when the retina (rather than the vitreous gel) is cut accidentally by the vitrector. We developed a smart vitrector that can detect in real-time potential iatrogenic RB and activate promptly a PPV machine response to prevent them.

Methods

We fabricated the smart vitrectors by attaching a miniaturized fiber-based OCT sensor on commercial vitrectors (25G). The system's response time to an iatrogenic RB onset was measured and compared to the literature reported physiologically limited response time of the average surgeon. Two surgeons validated its ability to prevent simulated iatrogenic RB by performing PPV in pigs. Note that the system is meant to control the PPV machine and requires no visual or audio signal interpretation by the surgeons.

Results

We found that the response time of the system (28.9 ± 6.5 ms) is 11 times shorter compared to the literature reported physiologically limited reaction time of the average surgeon (P < 0.0001). Ex vivo validation (porcine eyes) showed that the system prevents 78.95% (15/19) (95% confidence interval [CI] 54.43–93.95) of intentional attempts at creating RB, whereas in vivo validation showed that the system, prevents 55.68% (30/54) (95% CI 41.40–69.08), and prevents or mitigates 70.37% (38/54) (95% CI 56.39–82.02) of such attempts. A subset of failures was classified as “early stop” (i.e., false positive), having a prevalence of 5.26% (1/19) in ex vivo tests and 24.07% (13/54) in in vivo tests.

Conclusions

Our results indicate the smart vitrector can prevent iatrogenic RB by providing seamless intraoperative feedback to the PPV machine. Importantly, the use of the smart vitrector requires no modifications of the established PPV procedure. It can mitigate a significant proportion of iatrogenic RB and thus improve the overall efficacy of the surgery.

Translational Relevance

Potential clinical adoption of the smart vitrector can reduce the incidence of iatrogenic RB in PPV and thus increase the therapeutic outcome of the surgery.

Investigation of Micro-motion Kinematics of Continuum Robots for Volumetric OCT and OCT-guided Visual Servoing

Continuum robots (CR) have been recently shown capable of micron-scale motion resolutions. Such motions are achieved through equilibrium modulation using indirect actuation for altering either internal preload forces or changing the cross-sectional stiffness along the length of a continuum robot. Previously reported, but unexplained, turning point behavior is modeled using two approaches. An energy minimization approach is first used to explain the source of this behavior. Subsequently, a kinematic model using internal constraints in multi-backbone CRs is used to replicate this turning point behavior. An approach for modeling the micro-motion differential kinematics is presented using experimental data based on the solution of a system of linear matrix equations. This approach provides a closed-form approximation of the empirical micro-motion kinematics and could be easily used for real-time control. A motivating application of image-based biopsy using 3D optical coherence tomography (OCT) is envisioned and demonstrated in this paper. A system integration for generating OCT volumes by sweeping a custom B-mode OCT probe is presented. Results showing high accuracy in obtaining 3D OCT measurements are shown using a commercial OCT probe. Qualitative results using a miniature probe integrated within the robot are also shown. Finally, closed-loop visual servoing using OCT data is demonstrated for guiding a needle into an agar channel. Results of this paper present what we believe is the first embodiment of a continuum robot capable of micro and macro motion control for 3D OCT imaging. This approach can support the development of new technologies for CRs capable of surgical intervention and micro-motion for ultra-precision tasks.

Spotlight-based 3D Instrument Guidance for Autonomous Task in Robot-assisted Retinal Surgery

Retinal surgery is known to be a complicated and challenging task for an ophthalmologist even for retina specialists. Image guided robot-assisted intervention is among the novel and promising solutions that may enhance human capabilities during microsurgery. In this paper, a novel method is proposed for 3D navigation of a microsurgical instrument based on the projection of a spotlight during robot-assisted retinal surgery. To test the feasibility and effectiveness of the proposed method, a vessel tracking task in a phantom with a Remote Center of Motion (RCM) constraint is performed by the Steady-Hand Eye Robot (SHER). The results are compared to manual tracking, cooperative control tracking with the SHER and spotlight-based automatic tracking with SHER. The reported results are that the spotlight-based automatic tracking with SHER can reach an average tracking error of 0.013 mm and keeping distance error of 0.1 mm from the desired range demonstrating a significant improvement compared to manual or cooperative control methods alone.

CNN-based CP-OCT sensor integrated with a subretinal injector for retinal boundary tracking and injection guidance

SIGNIFICANCE

Subretinal injection is an effective way of delivering transplant genes and cells to treat many degenerative retinal diseases. However, the technique requires high-dexterity and microscale precision of experienced surgeons, who have to overcome the physiological hand tremor and limited visualization of the subretinal space.

AIM

To automatically guide the axial motion of microsurgical tools (i.e., a subretinal injector) with microscale precision in real time using a fiber-optic common-path swept-source optical coherence tomography distal sensor.

APPROACH

We propose, implement, and study real-time retinal boundary tracking of A-scan optical coherence tomography (OCT) images using a convolutional neural network (CNN) for automatic depth targeting of a selected retinal boundary for accurate subretinal injection guidance. A simplified 1D U-net is used for the retinal layer segmentation on A-scan OCT images. A Kalman filter, combining retinal boundary position measurement by CNN and velocity measurement by cross correlation between consecutive A-scan images, is applied to optimally estimate the retinal boundary position. Unwanted axial motions of the surgical tools are compensated by a piezoelectric linear motor based on the retinal boundary tracking.

RESULTS

CNN-based segmentation on A-scan OCT images achieves the mean unsigned error (MUE) of ∼3  pixels (8.1  μm) using an ex vivo bovine retina model. GPU parallel computing allows real-time inference (∼2  ms) and thus real-time retinal boundary tracking. Involuntary tremors, which include low-frequency draft in hundreds of micrometers and physiological tremors in tens of micrometers, are compensated effectively. The standard deviations of photoreceptor (PR) and choroid (CH) boundary positions get as low as 10.8  μm when the depth targeting is activated.

CONCLUSIONS

A CNN-based common-path OCT distal sensor successfully tracks retinal boundaries, especially the PR/CH boundary for subretinal injection, and automatically guides the tooltip's axial position in real time. The microscale depth targeting accuracy of our system shows its promising possibility for clinical application.

Oblique injection depth correction by a two parallel OCT sensor guided handheld SMART injector

We present a SMART injector with two parallel common-path optical coherence tomography fibers to enable angle measurements and injection depth corrections for oblique subretinal injection. The two optical fibers are attached to opposite sides of a 33 G needle with known offsets and designed to pass through a 23 G trocar that has an inner diameter of 0.65 mm. By attaching a SMART system to a rotational stage, the measured angles are calibrated for minimal error from reference angles. A commercial eye model was used to evaluate the control performance, and injection experiments were performed on a phantom made of agarose gel and a porcine eye.

Automatic Light Pipe Actuating System for Bimanual Robot-Assisted Retinal Surgery

Retinal surgery is a bimanual operation in which surgeons operate with an instrument in their dominant hand (more capable hand) and simultaneously hold a light pipe (illuminating pipe) with their non-dominant hand (less capable hand) to provide illumination inside the eye. Manually holding and adjusting the light pipe places an additional burden on the surgeon and increases the overall complexity of the procedure. To overcome these challenges, a robot-assisted automatic light pipe actuating system is proposed. A customized light pipe with force-sensing capability is mounted at the end effector of a follower robot and is actuated through a hybrid force-velocity controller to automatically illuminate the target area on the retinal surface by pivoting about the scleral port (incision on the sclera). Static following-accuracy evaluation and dynamic light tracking experiments are carried out. The results show that the proposed system can successfully illuminate the desired area with negligible offset (the average offset is 2.45 mm with standard deviation of 1.33 mm). The average scleral forces are also below a specified threshold (50 mN). The proposed system not only can allow for increased focus on dominant hand instrument control, but also could be extended to three-arm procedures (two surgical instruments held by surgeon plus a robot-holding light pipe) in retinal surgery, potentially improving surgical efficiency and outcome.

A Cooperative Human-Robot Interface for Constrained Manipulation in Robot-Assisted Endonasal Surgery

Endoscopic endonasal surgery (EES) is a minimally invasive technique for removal of pituitary adenomas or cysts at the skull base. This approach can reduce the invasiveness and recovery time compared to traditional open surgery techniques. However, it represents challenges to surgeons because of the constrained workspace imposed by the nasal cavity and the lack of dexterity with conventional surgical instruments. While robotic surgical systems have been previously proposed for EES, issues concerned with proper interface design still remain. In this paper, we present a cooperative, compact, and versatile bimanual human-robot interface aimed to provide intuitive and safe operation in robot-assisted EES. The proposed interface is attached to a robot arm and holds a multi-degree-of-freedom (DOF) articulated forceps. In order to design the required functionalities in EES, we consider a simplified surgical task scenario, with four basic instrument operations such as positioning, insertion, manipulation, and extraction. The proposed cooperative strategy is based on the combination of force based robot control for tool positioning, a virtual remote-center-of-motion (VRCM) during insertion/extraction tasks, and the use of a serial-link interface for precise and simultaneous control of the position and the orientation of the forceps tip. Virtual workspace constraints and motion scaling are added to provide safe and smooth control of our robotic surgical system. We evaluate the performance and usability of our system considering reachability, object manipulability, and surgical dexterity in an anatomically realistic human head phantom compared to the use of conventional surgical instruments. The results demonstrate that the proposed system can improve the precision, smoothness and safety of the forceps operation during an EES.

Toward Safe Retinal Microsurgery: Development and Evaluation of an RNN-Based Active Interventional Control Framework

OBJECTIVE

Robotics-assisted retinal microsurgery provides several benefits including improvement of manipulation precision. The assistance provided to the surgeons by current robotic frameworks is, however, a "passive" support, e.g., by damping hand tremor. Intelligent assistance and active guidance are, however, lacking in the existing robotic frameworks. In this paper, an active interventional control framework (AICF) has been presented to increase operation safety by actively intervening the operation to avoid exertion of excessive forces to the sclera.

METHODS

AICF consists of the following four components: first, the steady-hand eye robot as the robotic module; second, a sensorized tool to measure tool-to-sclera forces; third, a recurrent neural network to predict occurrence of undesired events based on a short history of time series of sensor measurements; and finally, a variable admittance controller to command the robot away from the undesired instances.

RESULTS

A set of user studies were conducted involving 14 participants (with four surgeons). The users were asked to perform a vessel-following task on an eyeball phantom with the assistance of AICF as well as other two benchmark approaches, i.e., auditory feedback (AF) and real-time force feedback (RF). Statistical analysis shows that AICF results in a significant reduction of proportion of undesired instances to about 2.5%, compared with 38.4% and 26.2% using AF and RF, respectively.

CONCLUSION

AICF can effectively predict excessive-force instances and augment performance of the user to avoid undesired events during robot-assisted microsurgical tasks.

SIGNIFICANCE

The proposed system may be extended to other fields of microsurgery and may potentially reduce tissue injury.

Robot-assisted tremor control for performance enhancement of retinal microsurgeons

Pars plana vitrectomy is a challenging, minimally invasive microsurgical procedure due to its intrinsic manoeuvres and physiological limits that constrain human capability. An important human limitation is physiological hand tremor, which can significantly increase the risk of iatrogenic retinal damage resulting from unintentional manoeuvres that affect anatomical and functional surgical outcomes. The limitations imposed by normal physiological tremor are more evident and challenging during ‘micron-scale’ manoeuvres such as epiretinal membrane and internal limiting membrane peeling, and delicate procedures requiring coordinated bimanual surgery such as tractional retinal detachment repair. Therefore, over the previous three decades, attention has turned to robot-assisted surgical devices to overcome these challenges. Several systems have been developed to improve microsurgical accuracy by cancelling hand tremor and facilitating faster, safer and more effective microsurgeries. By markedly reducing tremor, microsurgical precision is improved to a level beyond present human capabilities. In conclusion, robotics offers potential advantages over free-hand microsurgery as it is currently performed during ophthalmic surgery and opens the door to a new class of revolutionary microsurgical modalities. The skills transfer that is beyond human capabilities to robotic technology is a logical next step in microsurgical evolution.

70 μm diameter optical probe for common-path optical coherence tomography in air and liquids

We investigate and validate a novel method to fabricate ultrathin optical probes for common-path optical coherence tomography (CP-OCT). The probes are obtained using a 65 μm barium titanate microsphere inserted into an inward concave cone chemically etched at the end of a single-mode fiber. We demonstrate that the high refractive index (n=1.95) of the barium titanate microspheres allows one to maintain high sensitivity even while imaging in liquids, reaching a sensitivity of 83 dB. Due to its low cost, flexibility, and ease of use, the probe holds promise for the development of a new generation of ultrathin needle-based OCT systems.

Demonstration of Subretinal Injection Using Common-Path Swept Source OCT Guided Microinjector

In this paper, we present the development of a handheld common-path swept source optical coherence tomography (CP-SSOCT) guided microinjector system and demonstrated its utility by precisely injecting fluorescein dye in the subretinal layer of ex vivo bovine eyes. The system enables precise subretinal injection with micron-level injection depth control. This was achieved by using a high-resolution CP-SSOCT distal sensor and signal processing using a graphics-processing unit (GPU), which made a real-time smart motion control algorithm possible. The microinjector performance was first evaluated using a gelatin phantom in terms of its ability for dynamic depth targeting and injection depth. This is followed by using an ex vivo bovine eye model to perform multiple consecutive subretinal injections of fluorescein dye. The results validated the OCT guided injector’s ability to precisely guide and lock in the needle tip to the target depth during injection. The ex vivo evaluation tests demonstrate that an OCT-guided injector can consistently guide the injecting needle to the desired depth and is able to maintain the position with 9.38 μm average root mean square error during the injections.

Robot-assisted vitreoretinal surgery: current perspectives

Vitreoretinal microsurgery is among the most technically challenging of the minimally invasive surgical techniques. Exceptional precision is required to operate on micron scale targets presented by the retina while also maneuvering in a tightly constrained and fragile workspace. These challenges are compounded by inherent limitations of the unassisted human hand with regard to dexterity, tremor and precision in positioning instruments. The limited human ability to visually resolve targets on the single-digit micron scale is a further limitation. The inherent attributes of robotic approaches therefore, provide logical, strategic and promising solutions to the numerous challenges associated with retinal microsurgery. Robotic retinal surgery is a rapidly emerging technology that has witnessed an exponential growth in capabilities and applications over the last decade. There is now a worldwide movement toward evaluating robotic systems in an expanding number of clinical applications. Coincident with this expanding application is growth in the number of laboratories committed to "robotic medicine". Recent technological advances in conventional retina surgery have also led to tremendous progress in the surgeon's capabilities, enhanced outcomes, a reduction of patient discomfort, limited hospitalization and improved safety. The emergence of robotic technology into this rapidly advancing domain is expected to further enhance important aspects of the retinal surgery experience for the patients, surgeons and society.

Motorized Micro-Forceps with Active Motion Guidance based on Common-Path SSOCT for Epiretinal Membranectomy

In this study, we built and tested a handheld motion-guided micro-forceps system using common-path swept source optical coherence tomography (CP-SSOCT) for highly accurate depth controlled epiretinal membranectomy. A touch sensor and two motors were used in the forceps design to minimize the inherent motion artifact while squeezing the tool handle to actuate the tool and grasp, and to independently control the depth of the tool-tip. A smart motion monitoring and a guiding algorithm were devised to provide precise and intuitive freehand control. We compared the involuntary tool-tip motion occurring while grasping with a standard manual micro-forceps and our touch sensor activated micro-forceps. The results showed that our touch-sensor-based and motor-actuated tool can significantly attenuate the motion artifact during grasping (119.81 μm with our device versus 330.73 μm with the standard micro-forceps). By activating the CP-SSOCT based depth locking feature, the erroneous tool-tip motion can be further reduced down to 5.11μm. We evaluated the performance of our device in comparison to the standard instrument in terms of the elapsed time, the number of grasping attempts, and the maximum depth of damage created on the substrate surface while trying to pick up small pieces of fibers (Ø 125 μm) from a soft polymer surface. The results indicate that all metrics were significantly improved when using our device; of note, the average elapsed time, the number of grasping attempts, and the maximum depth of damage were reduced by 25%, 31%, and 75%, respectively.

Review of intraoperative optical coherence tomography: technology and applications [Invited]

During microsurgery, en face imaging of the surgical field through the operating microscope limits the surgeon's depth perception and visualization of instruments and sub-surface anatomy. Surgical procedures outside microsurgery, such as breast tumor resections, may also benefit from visualization of the sub-surface tissue structures. The widespread clinical adoption of optical coherence tomography (OCT) in ophthalmology and its growing prominence in other fields, such as cancer imaging, has motivated the development of intraoperative OCT for real-time tomographic visualization of surgical interventions. This article reviews key technological developments in intraoperative OCT and their applications in human surgery. We focus on handheld OCT probes, microscope-integrated OCT systems, and OCT-guided laser treatment platforms designed for intraoperative use. Moreover, we discuss intraoperative OCT adjuncts and processing techniques currently under development to optimize the surgical feedback derivable from OCT data. Lastly, we survey salient clinical studies of intraoperative OCT for human surgery.

Development and preliminary results of bimanual smart micro-surgical system using a ball-lens coupled OCT distance sensor

Bimanual surgery enhances surgical effectiveness and is required to successfully accomplish complex microsurgical tasks. The essential advantage is the ability to simultaneously grasp tissue with one hand to provide counter traction or exposure, while dissecting with the other. Towards enhancing the precision and safety of bimanual microsurgery we present a bimanual SMART micro-surgical system for a preliminary ex-vivo study. To the best of our knowledge, this is the first demonstration of a handheld bimanual microsurgical system. The essential components include a ball-lens coupled common-path swept source optical coherence tomography sensor. This system effectively suppresses asynchronous hand tremor using two PZT motors in feedback control loop and efficiently assists ambidextrous tasks. It allows precise bimanual dissection of biological tissues with a reduction in operating time as compared to the same tasks performed with conventional one-handed approaches.

Development of the dual SMART micro-surgical system using common-path swept source optical coherence tomography

Manual micro-surgical tasks are fundamentally divided into grasping, cutting and injecting maneuvers performed on biological tissues. Efficient dissection of fibrous tissue from the surface of the retina often requires grasping and cutting maneuvers carried out simultaneously. True bimanual surgery requires that the surgeon contend with the innate hand tremor of two hands at once as well as unpredicted patient's movement. In this study, we develop and test a dual SMART micro-surgical system to suppress bimanual hand tremor during micro-surgical dissection.

FBG-based sensorized light pipe for robotic intraocular illumination facilitates bimanual retinal microsurgery

In retinal surgery, microsurgical instruments such as micro forceps, scissors and picks are inserted through the eye wall via sclerotomies. A handheld intraocular light source is typically used to visualize the tools during the procedure. Retinal surgery requires precise and stable tool maneuvers as the surgical targets are micro scale, fragile and critical to function. Retinal surgeons typically control an active surgical tool with one hand and an illumination source with the other. In this paper, we present a "smart" light pipe that enables true bimanual surgery via utilization of an active, robot-assisted source of targeted illumination. The novel sensorized smart light pipe measures the contact force between the sclerotomy and its own shaft, thereby accommodating the motion of the patient's eye. Forces at the point of contact with the sclera are detected by fiber Bragg grating (FBG) sensors on the light pipe. Our calibration and validation results demonstrate reliable measurement of the contact force as well as location of the sclerotomy. Preliminary experiments have been conducted to functionally evaluate robotic intraocular illumination.

Dual optical coherence tomography sensor guided, two-motor, horizontal SMART micro-scissors

In microsurgery, the physiological hand tremor of the surgeon remains an important factor affecting procedure efficiency, risk of complications, and ultimately, the efficacy of treatment. The micro-scissors are routinely employed to perform precise sharp dissection of delicate tissues. Here, we present a dual optical coherence tomography (OCT) distance sensor guided, two-motor, horizontal smart micromanipulation aided robotic-surgery tool (SMART) micro-scissors. It is intended to improve surgeon performance by retaining all of the attributes of the horizontal scissors while implementing proof-of-concept use of two functional motors to provide tremor cancellation.

Use of a new intra-ocular spectral domain optical coherence tomography in vitreoretinal surgery

PURPOSE

To describe the use of a novel intra-ocular side-scanning probe enabling the acquisition of spectral-domain optical coherence tomography (SD-OCT) images during surgery in a series of patients with complex forms of retinal detachment.

METHODS

A 23-gauge, side-scanning SD-OCT probe (C7 System; LightLab Imaging, Inc/St Jude Medical, St. Paul, MN, USA) in a 20-gauge catheter, was used to acquire the intra-operative OCT images in seven patients with vitreoretinal diseases. Twenty-five gauge pars plana vitrectomy (PPV) was performed in every patient in a standard fashion. After enlarging the temporal sclerotomy to a 20-gauge port, all the patients were scanned with intra-ocular side-scanning SD-OCT, during different steps of the surgery based on surgeon needs. Scans were recorded real time and directly evaluated on a screen during surgery. Optical coherence tomography (OCT) scans were judged beneficial when they would recognize structures otherwise not seen on biomicroscopy.

RESULTS

The intra-ocular SD-OCT has been helpful in acquiring extra information during vitreoretinal surgery such as the detection of the presence of otherwise invisible membranes (epiretinal membrane, subretinal membrane), the location of small tears and the identification of the retinal plane under suboptimal conditions for visualization.

CONCLUSION

The use of an intra-ocular SD-OCT can expand upon visual cues during surgery, helping in the decision-making process and allowing additional deliberate surgical manoeuvres aimed at improving surgical outcomes.

Automated stereo vision instrument tracking for intraoperative OCT guided anterior segment ophthalmic surgical maneuvers

Microscope-integrated intraoperative OCT (iOCT) enables imaging of tissue cross-sections concurrent with ophthalmic surgical maneuvers. However, limited acquisition rates and complex three-dimensional visualization methods preclude real-time surgical guidance using iOCT. We present an automated stereo vision surgical instrument tracking system integrated with a prototype iOCT system. We demonstrate, for the first time, automatically tracked video-rate cross-sectional iOCT imaging of instrument-tissue interactions during ophthalmic surgical maneuvers. The iOCT scan-field is automatically centered on the surgical instrument tip, ensuring continuous visualization of instrument positions relative to the underlying tissue over a 2500 mm(2) field with sub-millimeter positional resolution and <1° angular resolution. Automated instrument tracking has the added advantage of providing feedback on surgical dynamics during precision tissue manipulations because it makes it possible to use only two cross-sectional iOCT images, aligned parallel and perpendicular to the surgical instrument, which also reduces both system complexity and data throughput requirements. Our current implementation is suitable for anterior segment surgery. Further system modifications are proposed for applications in posterior segment surgery. Finally, the instrument tracking system described is modular and system agnostic, making it compatible with different commercial and research OCT and surgical microscopy systems and surgical instrumentations. These advances address critical barriers to the development of iOCT-guided surgical maneuvers and may also be translatable to applications in microsurgery outside of ophthalmology.

IRIS: Integrated Robotic Intraocular Snake

Retinal surgery is one of the most technically challenging surgical disciplines. Many robotic systems have been developed to enhance the surgical capabilities. However, very few of them provide the surgeon the dexterity within the patient's eye to enable more flexible, more advanced surgical procedures. This paper presents a sub-millimeter intraocular dexterous robot, the Integrated Robotic Intraocular Snake (IRIS). The variable neutral-line mechanism is used to provide very high dexterity with a very small form factor. The IRIS distal dexterous unit is 0.9 mm in diameter and about 3 mm in length. It enables two rotational degrees of freedom at the distal end of the ophthalmic instruments. The analysis on contact mechanics provides a reference for the adjustment of the wire pretension. Redundant actuation is implemented by using one motor for each wire. A motion scaling transmission is developed to overcome the suboptimal resolution of the motors. A scale-up model of the IRIS is built for initial experimental evaluation. Preliminary results show that the scale-up IRIS can provide large range of motion. For given bending angle, the kinematic model can estimate the desired wire translation when the friction is not significant. The first prototype of the actual-scale IRIS is assembled and tested.

Accurate real-time depth control for CP-SSOCT distal sensor based handheld microsurgery tools

This paper presents a novel intuitive targeting and tracking scheme that utilizes a common-path swept source optical coherence tomography (CP-SSOCT) distal sensor integrated handheld microsurgical tool. To achieve micron-order precision control, a reliable and accurate OCT distal sensing method is required; simultaneously, a prediction algorithm is necessary to compensate for the system delay associated with the computational, mechanical and electronic latencies. Due to the multi-layered structure of retina, it is necessary to develop effective surface detection methods rather than simple peak detection. To achieve this, a shifted cross-correlation method is applied for surface detection in order to increase robustness and accuracy in distal sensing. A predictor based on Kalman filter was implemented for more precise motion compensation. The performance was first evaluated using an established dry phantom consisting of stacked cellophane tape. This was followed by evaluation in an ex-vivo bovine retina model to assess system accuracy and precision. The results demonstrate highly accurate depth targeting with less than 5 μm RMSE depth locking.

Evaluation of microsurgical tasks with OCT-guided and/or robot-assisted ophthalmic forceps

Real-time intraocular optical coherence tomography (OCT) visualization of tissues with surgical feedback can enhance retinal surgery. An intraocular 23-gauge B-mode forward-imaging co-planar OCT-forceps, coupling connectors and algorithms were developed to form a unique ophthalmic surgical robotic system. Approach to the surface of a phantom or goat retina by a manual or robotic-controlled forceps, with and without real-time OCT guidance, was performed. Efficiency of lifting phantom membranes was examined. Placing the co-planar OCT imaging probe internal to the surgical tool reduced instrument shadowing and permitted constant tracking. Robotic assistance together with real-time OCT feedback improved depth perception accuracy. The first-generation integrated OCT-forceps was capable of peeling membrane phantoms despite smooth tips.

Injection-depth-locking axial motion guided handheld micro-injector using CP-SSOCT

This paper presents a handheld micro-injector system using common-path swept source optical coherence tomography (CP-SSOCT) as a distal sensor with highly accurate injection-depth-locking. To achieve real-time, highly precise, and intuitive freehand control, the system used graphics processing unit (GPU) to process the oversampled OCT signal with high throughput and a smart customized motion monitoring control algorithm. A performance evaluation was conducted with 60-insertions and fluorescein dye injection tests to show how accurately the system can guide the needle and lock to the target depth. The evaluation tests show our system can guide the injection needle into the desired depth with 4.12 um average deviation error while injecting 50 nl of fluorescein dye.

Integrative advances for OCT-guided ophthalmic surgery and intraoperative OCT: microscope integration, surgical instrumentation, and heads-up display surgeon feedback

Purpose

To demonstrate key integrative advances in microscope-integrated intraoperative optical coherence tomography (iOCT) technology that will facilitate adoption and utilization during ophthalmic surgery.

Methods

We developed a second-generation prototype microscope-integrated iOCT system that interfaces directly with a standard ophthalmic surgical microscope. Novel features for improved design and functionality included improved profile and ergonomics, as well as a tunable lens system for optimized image quality and heads-up display (HUD) system for surgeon feedback. Novel material testing was performed for potential suitability for OCT-compatible instrumentation based on light scattering and transmission characteristics. Prototype surgical instruments were developed based on material testing and tested using the microscope-integrated iOCT system. Several surgical maneuvers were performed and imaged, and surgical motion visualization was evaluated with a unique scanning and image processing protocol.

Results

High-resolution images were successfully obtained with the microscope-integrated iOCT system with HUD feedback. Six semi-transparent materials were characterized to determine their attenuation coefficients and scatter density with an 830 nm OCT light source. Based on these optical properties, polycarbonate was selected as a material substrate for prototype instrument construction. A surgical pick, retinal forceps, and corneal needle were constructed with semi-transparent materials. Excellent visualization of both the underlying tissues and surgical instrument were achieved on OCT cross-section. Using model eyes, various surgical maneuvers were visualized, including membrane peeling, vessel manipulation, cannulation of the subretinal space, subretinal intraocular foreign body removal, and corneal penetration.

Conclusions

Significant iterative improvements in integrative technology related to iOCT and ophthalmic surgery are demonstrated.

Microscope-integrated intraoperative OCT with electrically tunable focus and heads-up display for imaging of ophthalmic surgical maneuvers

We present novel optical and mechanical designs for a microscope-integrated intraoperative optical coherence tomography (iOCT) system with enhanced function and ergonomics for visualization of ophthalmic surgical maneuvers. Integration of an electrically tunable lens allows rapid focal plane adjustment and iOCT imaging of both anterior and posterior segment tissue microstructures while maintaining parfocality with the ophthalmic surgical microscope. We demonstrate novel visualization of instrument positions relative to tissue layers of interest as colormap overlays onto en face OCT data, which may provide integrative display of volumetric information during surgical maneuvers. Finally, we implement a heads-up display system to provide real-time feedback as proof-of-principle for iOCT-guided ophthalmic surgery.

A Multi-Function Force Sensing Instrument for Variable Admittance Robot Control in Retinal Microsurgery

Robotic systems have the potential to assist vitreoretinal surgeons in extremely difficult surgical tasks inside the human eye. In addition to reducing hand tremor and improving tool positioning, a robotic assistant can provide assistive motion guidance using virtual fixtures, and incorporate real-time feedback from intraocular force sensing ophthalmic instruments to present tissue manipulation forces, that are otherwise physically imperceptible to the surgeon. This paper presents the design of an FBG-based, multi-function instrument that is capable of measuring mN-level forces at the instrument tip located inside the eye, and also the sclera contact location on the instrument shaft and the corresponding contact force. The given information is used to augment cooperatively controlled robot behavior with variable admittance control. This effectively creates an adaptive remote center-of-motion (RCM) constraint to minimize eye motion, but also allows the translation of the RCM location if the instrument is not near the retina. In addition, it provides force scaling for sclera force feedback. The calibration and validation of the multi-function force sensing instrument are presented, along with demonstration and performance assessment of the variable admittance robot control on an eye phantom.

Clinical applications of optical coherence tomography in urology

Since optical coherence tomography (OCT) was first demonstrated in 1991, it has advanced significantly in technical aspects such as imaging speed and resolution, and has been clinically demonstrated in a diverse set of medical and surgical applications, including ophthalmology, cardiology, gastroenterology, dermatology, oncology, among others. This work reviews current clinical applications in urology, particularly in bladder, urether, and kidney. Clinical applications in bladder and urether mainly focus on cancer detection and staging based on tissue morphology, image contrast, and OCT backscattering. The application in kidney includes kidney cancer detection based on OCT backscattering attenuation and non-destructive evaluation of transplant kidney viability or acute tubular necrosis based on both tissue morphology from OCT images and function from Doppler OCT (DOCT) images. OCT holds the promise to positively impact the future clinical practices in urology.