Intraocular Microsurgery Research Articles

A Novel Electromagnetic Driving System for 5-DOF Manipulation in Intraocular Microsurgery.

This work presents a novel electromagnetic driving system that consists of eight optimized electromagnets arranged in an optimal configuration and employs a control framework based on an active disturbance rejection controller (ADRC) and virtual boundary. The optimal system configuration enhances the system's compatibility with other ophthalmic surgical instruments, while also improving its capacity to generate magnetic force in the vertical direction. Besides, the optimal electromagnet parameters provide a superior comprehensive performance on magnetic field generation capacity and thermal power. Hence, the presented design achieves a stronger capacity for sustained work. Furthermore, the ADRC controller effectively monitors and further compensates the total disturbance as well as gravity to enhance the system's robustness. Meanwhile, the implementation of virtual boundaries substantially enhances interactive security via collision avoidance. The magnetic and thermal performance tests have been performed on the electromagnet to verify the design optimization. The proposed electromagnet can generate a superior magnetic field of 2.071 mT at a distance of 65 mm with an applied current of 1 A. Moreover, it demonstrates minimal temperature elevation from room temperature (25 °C) to 46 °C through natural heat dissipation in 3 h, thereby effectively supporting prolonged magnetic manipulation of intraocular microsurgery. Furthermore, trajectory tracking experiments with disturbances have been performed in a liquid environment similar to the practical ophthalmic surgery scenarios, to verify the robustness and security of the presented control framework. The maximum root mean square (RMS) error of performance tests in different operation modes remains 35.8 μm, providing stable support for intraocular microsurgery.

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.

Laser-induced deformation and fragmentation of droplets in an array

Droplet–droplet interactions is ubiquitous in various applications ranging from medical diagnostics to enhancing and optimizing liquid jet propulsion. We employ an experimental technique where the laser pulse interacts with a micron-sized droplet and causes optical breakdown. The interaction of a nanosecond laser pulse and an isolated spherical droplet is accurately controlled and manipulated to influence the deformation and fragmentation of an array of droplets. We elucidate how the fluid dynamic response (such as drop–drop and shock–drop interactions) of an arrangement of droplets can be regulated and optimally shaped by laser pulse energy and its interplay with the optical density of liquid target. A new butterfly type breakup is revealed, which is found to result in controlled and efficient fragmentation of the outer droplets in an array. The spatio-temporal characteristics of a laser-induced breakdown dictate how shock wave and central droplet fragments can influence outer droplets. The incident laser energy and pulse width employed in this work are representative of diverse industrial applications such as surface cleaning, nano-lithography, microelectronics, and medical procedures such as intraocular microsurgery.

EyeSAM: graph-based localization and mapping of retinal vasculature during intraocular microsurgery.

Robot-assisted intraocular microsurgery can improve performance by aiding the surgeon in operating on delicate micron-scale anatomical structures of the eye. In order to account for the eyeball motion that is typical in intraocular surgery, there is a need for fast and accurate algorithms that map the retinal vasculature and localize the retina with respect to the microscope. This work extends our previous work by a graph-based SLAM formulation using a sparse incremental smoothing and mapping (iSAM) algorithm. The resulting technique, "EyeSAM," performs SLAM for intraoperative vitreoretinal surgical use while avoiding spurious duplication of structures as with the previous simpler technique. The technique also yields reduction in average pixel error in the camera motion estimation. This work provides techniques to improve intraoperative tracking of retinal vasculature by handling loop closures and achieving increased robustness to quick shaky motions and drift due to uncertainties in the motion estimation.

EyeSLAM: Real-time simultaneous localization and mapping of retinal vessels during intraocular microsurgery.

Fast and accurate mapping and localization of the retinal vasculature is critical to increasing the effectiveness and clinical utility of robot-assisted intraocular microsurgery such as laser photocoagulation and retinal vessel cannulation. The proposed EyeSLAM algorithm delivers 30Hz real-time simultaneous localization and mapping of the human retina and vasculature during intraocular surgery, combining fast vessel detection with 2D scan-matching techniques to build and localize a probabilistic map of the vasculature. In the harsh imaging environment of retinal surgery with high magnification, quick shaky motions, textureless retina background, variable lighting and tool occlusion, EyeSLAM can map 75% of the vessels within two seconds of initialization and localize the retina in real time with a root mean squared (RMS) error of under 5.0 pixels (translation) and 1° (rotation). EyeSLAM robustly provides retinal maps and registration that enable intelligent surgical micromanipulators to aid surgeons in simulated retinal vessel tracing and photocoagulation tasks.

Good News From Switzerland: A History of Retinal Reattachment Surgery Authors: Peter Leaver, Richard Keeler 2013 ISBN: 978-1-85315-993-0 RSM Press

The visionary title of the book “Good News from Switzerland”was obtained from an earlier statement by Frank Juler in his article in the British Journal of Ophthalmology; in1930, he realized the importance of Jules Gonin’s invention. Today, we agree that Gonin’s concept revolutionized retinal detachment from an untreatable disease to a standardized approach with a high success rate. The book presents an excellent historic review on treatment approaches for retinal detachment surgery, on 138 pages with numerous illustrations and personal portraits of their inventors and leaders of that particular period. The authors divide the historic development into three periods: The prehistoric era covers the time from the first ophthalmoscope and first surgical attempts to repair retinal detachments up to Gonin’s revolutionary invention. The middle age describes refinements in the surgical method with laser, plumage, cerclage and cryotherapy. Finally, the modern era highlights numerous diagnostic and additional surgical modifications to the closed intraocular microsurgery approach, where retinal detachment became a treatable condition and important area in vitreoretinal surgery. The strength of this book is the well-structured and systematic description. It provides privileged information on the stepwise progress of new technologies, modifications, breakthrough steps and their impact on the progression, but also on drawbacks in redetachment surgery. The progress had many layers: examination optics, surgical techniques, surgical instrumentations, liquids or gasses, equipment and illumination. Numerous and constant improvements over the past 80 years have led to an improvement of the advanced prognosis from barely 30 % to nearly 100 % as of today. The book also describes the considerable delay before the technique's effectiveness was widely acknowledged, by a period of 10 years, during which Gonin fought bravely to overcome disagreement and skepticism among colleagues. The enforcement of additional developments also required the reputation and recognition of each inventor, his or her character, as well as the constant exchange in journals and meetings with the community of experts. The experienced authors give great insight on the protagonists of each decade and their heritage from Europe, Asia or America. Many anecdotes nicely outline the course of events, and the characters of talented surgeons and inspiring inventors that led to important contributions towards the current approach. The book gives valuable information for beginners and experienced vitreoretinal surgeons. Today, many young surgeons grow up with the latest vitreoretinal technology; however, they are often no longer aware of previous treatment approaches. The well-respected experience of elderly physicians includes their knowledge of these simplified approaches, as they still may be required in certain conditions or when new, e.g., biomedical solutions, become available on the horizon. The view of the past is essential to understand our current approach, identify asof-yet unmet needs, and search for their future solutions. In summary, this is a wonderful book than belongs in the library of every retinal department.

Assessment of a Hexapod Surgical System for Robotic Micro-Macro Manipulations in Ocular Surgery

Purpose: Robotic intraocular microsurgery requires a remote center of motion (RCM) at the site of ocular penetration. We designed and tested the Hexapod Surgical System (HSS), a microrobot mounted on the da Vinci macrorobot for intraocular microsurgery. Material and Methods: Translations and rotations of the HSS were tested for range of motion and stability. Precision and dexterity were assessed by pointing and inserting a coupled probe into holes of various sizes. The stability of a nonmechanical RCM was quantified. HSS functionalities were observed on porcine eyes. Results: The HSS maximal translations were 10 (x and y axes) and 5 cm (z axis). The maximal rotations were 15 and 22° (x and y axes). The precision was within 0.5 mm away from targets in 26/30 tests and maximal in 16/30 tests. The mean translational and rotational stability at the tip of the probe were 1.2 (0.6–1.9) and 1 mm (0–2), respectively. The average dexterity times were 5.2 (4.4–6.5), 7.1 (5.6–10.8) and 12.3 s (7.8–21.7) for 5-, 2- and 1-mm holes, respectively. The RCM was stable (within 0.1 mm). A vitreous cutter coupled to the HSS moved into porcine eyes through a sclerotomy with a stable RCM. Conclusion: The HSS provides an RCM dedicated for intraocular robotic surgery with a high level of precision and dexterity. Although it can be further improved, the micro-macro robotic system is a feasible approach for ocular surgery.

Corneal endothelial cytotoxicity of diluted povidone–iodine

Purpose To assess corneal endothelial toxicity of diluted povidone–iodine (PI) in vivo and in vitro. Setting Cell Biology Laboratory and the Laboratory for Intraocular Microsurgery and Implants, Goldschleger Eye Research Institute, Sackler School of Medicine, Tel-Aviv University, Chaim Sheba Medical Center, Tel-Hashomer, Israel. Methods In an in vitro study, cultured bovine corneal endothelial cells were exposed to diluted PI. The degree of cell damage was determined by staining with trypan blue and by comparing the results to those in a control group. In an in vivo study, a single dose of diluted PI was injected into the anterior chamber of rabbit eyes, completely replacing the aqueous humor. The eyes were evaluated by clinical examination, specular microscopy, pachymetry, pneumotonometry, and histopathology and compared to a control group injected with a balanced salt solution. Results In vitro, PI concentrations of 0.05% or less did not induce endothelial cell damage. Significant damage was observed with a PI concentration of 0.1%. Calf serum concentrations of 1% and higher in the culture media protected the endothelial cell monolayer from cytotoxic damage by PI. Aqueous humor did not have a similar effect. In vivo, PI concentrations of 0.1% or less did not induce changes in corneal endothelium morphology or function as assessed by specular microscopy and pachymetry. A PI concentration of 1% served as a positive control, causing corneal edema and endothelial cell loss as demonstrated by pachymetry, histopathology, and elevated intraocular pressure. Conclusions The concentrations of PI tolerated by animal endothelium in vitro and in vivo were higher than the reported bactericidal levels. These findings justify further investigation of the safety and efficacy of PI for intracameral prophylaxis during surgery.

Experimental studies of capsular equator rings of soft latex

Purpose To determine the efficacy of wide equatorial rings of various materials in reducing posterior capsule opacification (PCO) and maintaining the circular contour of the capsular equator in a rabbit model. Setting Laboratory for Intraocular Microsurgery and Implants, Goldschleger Eye Research Institute, Tel-Aviv University, Sheba Medical Center, Tel-Hashomer, Israel. Methods Closed rings made of poly(methyl methacrylate), Teflon®, polyurethane, and latex were introduced into the capsular bags of rabbit eyes after removal of the lens material. The soft latex rings were deemed the only practical rings for atraumatic implantation through a small incision. Latex rings of 2 dimensions with rectangular edges were implanted in 8 rabbits. One eye served as a control after lens removal and no ring implantation. The eyes were followed for up to 5 months and then evaluated by light microscopy. Results Posterior capsule opacification was minimal or absent in all animals implanted with the latex rings. Mild to moderate inflammatory reaction was noted in most eyes. It was caused by the ring material or secondary to long-standing pressure on the ciliary tissue. The rings also maintained well the circular contour of the capsular bags. Conclusions Equatorial rings of soft latex with sharp rectangular edges were effective in minimizing PCO and maintaining the shape of the capsule after lens removal in rabbits. Soft rings made of a biocompatible material may be effective in humans.

Hollow-glass waveguide delivery of an infrared free-electron laser for microsurgical applications

The purpose of this research is to deliver free-electron-laser (FEL) pulses for intraocular microsurgery. The FEL at Vanderbilt University is tunable from 1.8 to 10.8 microm. To deliver the FEL beam we used a metallic-coated hollow-glass waveguide of 530-mum inner diameter. A 20-gauge cannula with a miniature CaF2 window shielded the waveguide from water. Open-sky retinotomy was performed on cadaver eyes. The system delivered as much as 6 x 10(5) W of FEL peak power to the intraocular tissues without damage to the waveguide or to the surgical probe.

Influence of optical aberrations on laser-induced plasma formation in water and their consequences for intraocular photodisruption

The influence of spherical aberrations on laser-induced plasma formation in water by 6-ns Nd:YAG laser pulses was investigated for focusing angles that are used in intraocular microsurgery. Waveform distortions of 5.5lambda and 18.5lambda between the optical axis and the 1/e(2) irradiance values of the laser beam were introduced by replacement of laser achromats in the delivery system by planoconvex lenses. Aberrations of 18.5lambda increased the energy threshold for plasma formation by a factor of 8.5 compared with the optimized system. The actual irradiance threshold for optical breakdown was determined from the threshold energy in the optimized system and the spot size measured with a knife-edge technique. For aberrations of 18.5lambda the irradiance threshold was 48 times larger than the actual threshold when it was calculated by use of the diffraction-limited spot size but was 35 times smaller when it was calculated by use of the measured spot size. The latter discrepancy is probably due to hot spots in the focal region of the aberrated laser beam. Hence the determination of the optical-breakdown threshold in the presence of aberrations leads to highly erroneous results. In the presence of aberrations the plasmas are as much as 3 times longer and the transmitted energy is 17-20 times higher than without aberrations. Aberrations can thus strongly compromise the precision and the safety of intraocular microsurgery. They can further account for a major part of the differences in the breakdown-threshold and the plasma-transmission values reported in previous investigations.

Energy balance of optical breakdown in water at nanosecond to femtosecond time scales

During optical breakdown, the energy delivered to the sample is either transmitted, reflected, scattered, or ab- sorbed. Pathways for the division of the absorbed energy are the evaporation of the focal volume, the plasma radiation, and the mechanical effects such as shock wave emission and cav- itation. The partition of laser energy between these channels during breakdown in water was investigated for four selected laser parameters typical for intraocular microsurgery ( 6-ns pulses of 1 and 10 mJ focused at an angle of 22 ,a nd30-ps pulses of 50 mJ and 1m Jfocused at 14 ,a ll at1064 nm). Scattering and reflection were found to be small compared to transmission and absorption during optical breakdown. The ratio of the shock wave energy and cavitation bubble energy was approximately constant (between 1.5:1 and 2:1). These results allowed us to perform a more comprehensive study of the influence of pulse duration ( 100 fs- 76 ns )a nd focus- ing angle (4- 32) on the energy partition by measuring only the plasma transmission and the cavitation bubble energy. The bubble energy was used as an indicator for the total amount of mechanical energy. We found that the absorption at the breakdown site first decreases strongly with decreasing pulse duration, but increases again for < 3p s. The conversion of the absorbed energy into mechanical energy is 90% with ns pulses at large focusing angles. It decreases both with de- creasing focusing angle and pulse duration (to < 15 %f or fs pulses). The disruptive character of plasma-mediated laser effects is therefore strongly reduced when ultrashort laser pulses are used.

Experimental studies on viscofluids for intraocular surgery

Purpose: To investigate the feasibility and efficacy of using diluted viscofluids during intraocular surgery.Setting: Laboratory for Intraocular Microsurgery and Implants, Goldschleger -Eye Research Institute, and the Sackler School of Medicine, Tel-Hashomer, Israel.Methods: Diluted hyaluronic acid (0.06 to 0.12%) in balanced salt solutions were irrigated through the phacoemulsification machine or a separate irrigation line (i.e., anterior chamber maintainer). Irrigation was facilitated by increasing the atmospheric pressure in the bottle using compressed air. Experimental surgery was done in rabbit eyes.Results: A viscous fluid could be irrigated at any practical rate by increasing the height of the bottle, increasing the atmospheric pressure within the bottle, or both. Experimental surgeries showed that viscofluids maintained intraocular pressure and anterior chamber volume, allowed safe intraocular manipulations, reduced turbulence in the anterior chamber, and probably provided tissue protection.Conclusion: Viscofluids irrigated using a high-pressure system combined the advantages of continuous irrigation of fluids and the protective qualities of viscoelastics in this rabbit eye study.

Nonlinear absorption: intraocular microsurgery and laser lithotripsy

The paper reviews the principles of nonlinear absorption with reference to the present major clinical applications of plasma-mediated effects: intraocular microsurgery and laser lithotripsy. Emphasis is laid on the analysis of the working mechanisms, sources of collateral damage, and on strategies for both the optimization of efficacy and the minimization of side effects.

Plasma formation in water by picosecond and nanosecond Nd:YAG laser pulses. II. Transmission, scattering, and reflection

For pt.I see ibid., vol.2, no.4, p.847-60 (1996) We investigated the transmission, scattering, and reflection of plasmas produced in water by Nd:YAG laser pulses of 6-ns and 30-ps duration. The transmission measurements comprise a large energy range at wavelengths of 1064 and 532 nm and various focusing angles between 1.7/spl deg/ and 22/spl deg/. This parameter range covers the parameters used for intraocular microsurgery, but also allows one to assess the influence of self-focusing on plasma shielding, which is only relevant at small focusing angles. We found that most of the laser light is either absorbed or transmitted; scattering and reflection amount to only a few percent of the incident laser energy. The transmission is considerably higher for picosecond pulses than for nanosecond pulses, regardless of the focusing angle. The plasma transmission increases with decreasing focusing angle. Self-focusing, which occurs at focusing angles below 2/spl deg/, leads to a further increase of transmission. The experimental results were compared with the predictions of the moving breakdown distributed shielding model. Only partial agreement could be achieved, because the model assumes a spatially and temporally constant absorption coefficient within the plasma which is not realistic. The model can, however, be used to determine the average absorption coefficient. Fits of calculated transmission curves to the experimental data at /spl theta/=22/spl deg/ yielded 900 cm/sup -1//spl les//spl alpha//spl les/1800 cm/sup -1/ nanosecond plasmas and 360 cm/sup -1//spl les//spl alpha//spl les/570 cm/sup -1/ picosecond plasmas. The efficacy of plasma-mediated intraocular laser surgery is higher with 6-ns pulses than with 30-ps pulses, because with the nanosecond pulses nearly 50% of the laser pulse energy is absorbed already at threshold, whereas it is only 8% with the picosecond pulses.

The treatment of vitreoretinal scar tissue.

Methods of treating vitreoretinal scarring have been transformed by the introduction and development of closed intraocular microsurgery. Controlled access to the posterior segment of the eye, under excellent conditions for intraoperative viewing, have increased our understanding of the pathophysiology of epiretinal membranes. The ready ability to harvest tissue specimens for histopathological and immunochemical study, enabled by this type of surgery, has provided the stimulus for much basic research into the nature of fibrocellular (and fibrovascular) proliferative disease. Treatment of retinal conditions characterised by the proliferation of fibrocellular membranes has been improved, but the most important future advances are likely to be made in the fields of molecular biology and pharmacology.

Intraocular microsurgery with a picosecond Nd:YAG laser.

We investigated the use of picosecond Nd:YAG laser pulses for intraocular microsurgery. With a pulse duration of 100 picoseconds, only 70 microJ of pulse energy is required to consistently produce optical breakdown in the deep vitreous. This pulse energy is nearly two orders of magnitude less than the typical pulse energies used in conventional (nanosecond) photodisruptors. The reduced pulse energy results in a smaller zone of tissue damage, an important consideration when operating close to the retina or other sensitive ocular structures. Efficient cutting action is achieved by applying multiple pulses at a moderately high repetition rate of 50-200 Hz. An in vitro model was developed to assess axial confinement of picosecond photodisruption. In vivo vitreous membrane surgery was performed in experimental rabbit eyes to demonstrate a potential clinical application of picosecond laser-induced optical breakdown.

Mechanisms of intraocular photodisruption with picosecond and nanosecond laser pulses.

Nd:YAG laser photodisruption with nanosecond (ns) pulses is an established method for intraocular surgery. In order to assess whether an increased precision can be achieved by the use of picosecond (ps) pulses, the plasma size, the shock wave characteristics, and the cavitation bubble expansion after optical breakdown with ps- and ns-laser pulses were investigated by time-resolved photography and acoustic measurements. Nd:YAG laser pulses with a duration of 30 ps and 6 ns, respectively, were focused into a water-filled glass cuvette. Frequency doubled light from the same laser pulses was optically delayed between 2 ns and 136 ns and used as illumination light source for photography. Since the individual events were well reproducible, the shock wave and bubble wall position could be determined as a function of time. From the slope of these r(t) curves, the shock wave and bubble wall velocities were determined, and the shock wave pressure was calculated from the shock velocity. The plasma size at various laser pulse energies was measured from photographs of the plasma radiation. The breakdown thresholds at 30 ps and 6 ns pulse duration were found to be 15 microJ and 200 microJ, respectively. At threshold, ps-plasmas are shorter than ns-plasmas, but at the same pulse energy they are always approximately 2.5 times longer. The initial shock pressures were 17 kbar after ps-pulses with an energy of 50 microJ, and 21 kbar after 1 mJ ns-pulses. The pressure amplitude decayed much faster after the ps-pulses. The maximum expansion velocity of the cavitation bubble was 350 m/s after a 50 microJ ps-pulse, but 1,600 m/s after a 1 mJ ns-pulse. The side effects of intraocular microsurgery associated with shock wave emission and cavitation bubble expansion can be considerably reduced by the use of ps-pulses, and new applications of photodisruption may become possible.

Combined Vitrectomy, Intraocular Microsurgery and Liquid Silicone in the Treatment of Proliferative Vitreoretinopathy

Combined Vitrectomy, Intraocular Microsurgery and Liquid Silicone in the Treatment of Proliferative Vitreoretinopathy

COMBINED VITRECTOMY, INTRAOCULAR MICROSURGERY AND LIQUID SILICONE IN THE TREATMENT OF PROLIFERATIVE VITREORETINOPATHY

This study investigates the effectiveness of combining vitrectomy, scleral buckling, intraocular microsurgery and liquid silicone injection for the treatment of retinal detachment complicated by proliferative vitreoretinopathy: 48 eyes were treated using these techniques combined. Complete attachment was achieved in 16 eyes (33%), partial attachment in 20 eyes (42%), and 12 eyes (25%) remained detached. Vision was improved in 17 eyes (35%), unchanged in 17 eyes (35%), and worse in 14 eyes (30%). Complications included emulsification of the silicone, glaucoma, cataract, band degeneration of the cornea, reproliferation of membranes and passage of silicone into the subretinal space. Significant preservation of mobility vision was achieved. A larger series of patients with longer follow-up will ultimately determine the place of this technique in the management of this complicated problem.