Numerical simulation of mechanical properties of epiretinal membrane peeling.

An epiretinal membrane (ERM) is a fibrocellular proliferation on the inner surface of the retina causing blurred and distorted central vision. Surgery is the only effective method for ERM removal. This paper investigated the mechanical properties of ERM peeling using the finite element (FE) method. A FE model of ERM formation on the retina surface was constructed. The failure criterion was applied to the attachment pegs to represent the adhesive force between the ERM and retina. The simulation results were consistent with the experimental data in published research. The maximum peeling force was 4.1 mN at a peeling velocity of 2 mm/s and an angle of 30°. The peeling force was minimum at the peeling angle of 45° and increased with the increase in peeling velocity and Young's modulus of the membrane. The outcome of this paper can improve the safety and efficiency of ERM removal.

Evaluation of the Hand Motion and Peeling Force in Inner Limiting Membrane Peeling.

Purpose: Robot assistance in membrane peeling may improve precision and dexterity or prevent complications by task automation. To design robotic devices, surgical instruments' velocity, acceptable position/pose error, and load ability need to be precisely quantified. Methods: A fiber Bragg grating and inertial sensors are attached to forceps. Data collected from forceps and microscope images are used to quantify a surgeon's hand motion (tremor, velocity, posture perturbation) and operation force (voluntary and involuntary) in inner limiting membrane peeling. All peeling attempts are performed on rabbit eyes in vivo by expert surgeons. Results: The root mean square (RMS) of the tremor amplitude is 20.14 µm (transverse, X), 23.99 µm (transverse, Y), and 11.68 µm (axial, Z). The RMS posture perturbation is 0.43° (around X), 0.74° (around Y), and 0.46° (around Z). The RMS angular velocities are 1.74°/s (around X), 1.66°/s (around Y), and 1.46°/s (around Z), whereas the RMS velocities are 1.05 mm/s (transverse) and 1.44 mm/s (axial). The RMS force is 7.39 mN (voluntary force), 7.41 mN (operation force), and 0.5 mN (involuntary force). Conclusions: Hand motion and operation force are measured in membrane peeling. These parameters provide a potential baseline for determining a surgical robot's accuracy, velocity, and load capacity. Translational Relevance: Baseline data are obtained that can be used to guide ophthalmic robot design/evaluation.

Operation behaviours of surgical forceps in continuous curvilinear capsulorhexis.

BACKGROUND: Continuous curvilinear capsulorhexis (CCC) is a delicate ophthalmic procedure which may benefit from robot technology. Measuring the behaviours (physiological tremor, operation force) of surgeons provides baseline data to develop assistive CCC robot. METHODS: A forceps with fibre bragg grating and inertial sensors is used to measure the surgeons' behaviours while experts/novices perform CCC on ex-vivo pig eyes, in-vivo rabbit eyes and ex-vivo human lens. RESULTS: In pig/rabbit tests, the root-mean-square (RMS) tremor amplitude is 35.26/59.04 µm (expert/novice, transverse), 13.3/20.55 µm (axial). The RMS voluntary force (VF) and involuntary force (IF) are 8.97/17.16 mN, and 0.66/1.90 mN, respectively. In human lens test, the RMS tremor amplitude is 24.0 µm (transverse, expert only), 9.88 µm (axial). The RMS VF and RMS IF are 9.04 mN (expert only) and 0.17 mN, respectively. CONCLUSIONS: The expert surgeons have better precision and less operation force.

A study for lens capsule tearing during capsulotomy by finite element simulation.

BACKGROUND AND OBJECTIVE: During capsulotomy, the force applied to the anterior capsule is a crucial parameter controlling capsule tears, that affects the clinical performance. This study aims to investigate the tear force in capsulotomy and analyze the effects of different tearing conditions on the tear force. METHODS: A three-dimensional model of the human lens was constructed based on published clinical data using the finite element (FE) method. The lens model consisted of four layers: the anterior and posterior lens capsule, the cortex, and the nucleus. Distortion energy failure criterion combined with the bilinear interface law was used to express the crack propagation process at the edge of the anterior lens capsule. At the clamping position, a local coordinate system was established to parameterize the capsule tearing. The simulation results were then validated by conducting a capsulorhexis experiment using isolated porcine eyes with force-sensing forceps. RESULTS: The simulation results showed a good agreement with the experimental data of two porcine specimens (No. 6 and 9) during a stable tearing process (p-values = 0.76 and 0.10). The mean force differences between the experimental data and the simulation were 3.10 ± 2.24 mN and 2.14 ± 1.73 mN, respectively. The tear direction with a minimum mean tear force was at θ1 = 0° and θ2 = 30°. The tear velocity was not significantly different to the variation in the tear force. However, an appropriate capsulorhexis diameter was found to contribute to the reduction of tear force. CONCLUSIONS: The outcome of this paper demonstrates that our FE model could be used in modeling lens capsule tearing and the theoretical study of tear mechanism.

[Design and Implementation of User-oriented Auxiliary Treatment Instrument for Meibomian Gland Dysfunction].

Dry eye is a common ophthalmic disease caused by eye maladjustment due to meibomian gland dysfunction (MGD), which is often accompanied by symptoms such as increased tear film osmotic pressure and ocular surface inflammation. In the treatment of dry eye patients, dredging gland obstruction caused by meibomian gland secretion is an effective treatment method. Based on electrothermal effect and hyperelasticity of the silicone, an auxiliary treatment instrument for MGD is designed, which can improve the blood circulation of the glands through heat compress and massage to achieve the purpose of dredging the meibomian glands. The therapy device can display the temperature and pressure during the treatment in real time, so that the surgeon can grasp the progress of the treatment in real time. The therapy device constructs a user-oriented interactive interface based on parametric modeling method, which can be customized by 3D printing according to the user's eyeball geometric parameters. The designed therapeutic device was finally tested on New Zealand white rabbits. The experimental results show that the therapeutic device has significant effectiveness and safety, as well as clinical application prospects.

[Three-dimensional Reconstruction of Retinal Vessels Based on Binocular Vision].

In robot-assisted eye surgery, such as retinal vascular bypass surgery, precise positioning of operating points is required. In this study, a binocular vision-based 3D reconstruction method is proposed to locate the incision points on retinal vessels. Vessels in the image were extracted by CLAHE algorithm to remove the influence of background, then stereo matching was performed. Finally, the retinal vessel image was reconstructed by using the principle of parallax in binocular vision. Experimental results show that this method can accurately locate the incision points on retinal vessels and meet the requirements of ophthalmic surgery.

Enhanced solar absorption and visible-light photocatalytic and photoelectrochemical properties of aluminium-reduced BaTiO3 nanoparticles.

Enhanced solar light absorption and photocatalytic and photoelectrochemical properties have been achieved in black BaTiO3 with a unique core/shell structure (crystalline BaTiO3@amorphous BaTiO3-x) using an Al-reduction method. This finding may open a new avenue to tune the inert ferroelectric materials toward excellent photocatalysts for advanced applications.

[An Emerging Simulation Method Used in System Simulation of Flow Chamber of Hematology Analyzer].

In fluid flow field analysis, the common simulation method is 1-D simulation or 3-D simulation, In order to analyze blood fluid system more quickly and accurately and choose the appropriate sample tube at the beginning of design for the system, this paper adopts a recently emerging 1D-3D simulation method to make simulations of flow chamber subsystem. Respectively using Flow master and ANSYS system modeling, use MpCCI connects the two parameter coupling, realize the sheath fluid velocity of research. The software can meet the needs of design and analysis of the Hematology Analyzer fluid system. In this paper, the method of co-simulation for medical apparatus and instruments of Hematology Analyzer fluid system development provides a new method, has important significance on the subsequent simulation.