Treatment tactics and outcomes of complications of intrastromal MyoRing implantation and corneal crosslinking in keratoconus

Purpose. To analyze the nature and frequency of intra - and postoperative complications during MyoRing implantation and corneal crosslinking in patients with keratoconus and to develop methods for their treatment and prevention. Material and methods. We conducted a study of the results of MyoRing implantation in 131 patients (147 eyes) with keratoconus II-III. Corneal rings with a diameter of 5-6 mm and a thickness of 280-320 µm were implanted. PocketMaker microkeratome (Dioptex GmbH, Austria) was used to create a stromal pocket during the implantation of the ICR. The patients were divided into the control group (32 patients, 34 eyes) – using the standard ICR implantation technology and the main group (38 patients, 42 eyes) – ICR implantation using the developed tools. Results. Among the complications, intraoperatively, the eruption of the stromal pocket was noted due to the loss of vacuum during the application of the applicator in 4 cases. In the long term, after 10 and 12 months, patients underwent ICR reimplantation with a positive result. In 2 cases, the surface location of the implant led to ring extrusion, which may have been due to the thinning of the surface layers, and subsequently keratoplasty was performed on the patients. In 1 case, the patient's pronounced deposition of lamellar deposits caused dissatisfaction of a cosmetic nature. At the request of the patients, the rings were removed, and in the following terms, the patient made up for the visual defect by wearing hard contact lenses. Conclusion. A moderate number of complications indicates the relative safety of the method of intrastromal keratoplasty. The use of the proposed instruments during the operation provides a significant reduction in the frequency of complications compared to the results with the standard technique of forming a corneal tunnel. Thus, it was found that the optimized method of implantation of MyoRing intrastromal rings reduces corneal trauma, simplifies the manipulation of the ring and reduces the total operation time by 1.4 times. Key words: keratoconus, intrastromal corneal rings, MyoRing, corneal crosslinking, complications.

Metamorphosis of Contact Lenses

In 1971, soft contact lenses were a striking addition to the ophthalmic field that related functionally to the existing hard contact lenses by correctingrefractive error, but their properties and description were different so as to confound ophthalmic professionals in their introduction. Their inventor Otto Wichterle, a Czechoslovakian chemist and anticommunist dissident, developed the soft lens in the 1950-60s with little knowledge of the hard lens, but its potential was broad enough to break through the communist barriers and to spark international consumer interest and development.Challenges in manufacturing and developing soft contact lenses created a complex discipline around the cornea and lid physiology, and optics. This expanded greatly the scientific knowledge of the eye and adnexa to allow a soft, hydrophilic lens to remain symbiotic with the eye. Challenges were met over the past 50 years with a change in nomenclature and in automated manufacturing closer to hard lenses, optical advancements, new materials and surface treatments, and lens disinfection methods. The science developing from the diminutive soft lens led to the incorporation of related biomedical and polymer science within the broader ophthalmic field that inordinately influenced optical advancements, instrumentation,and ocular pathology.

Prediction of Best Corrected Visual Acuity with Hard Contact Lenses for Keratoconus Patients

Background: To develop a prediction formula for best corrected visual acuity with hard contact lenses (HCL-BCVA) and to identify clinical factors linearly related to HCL-BCVA in keratoconus patients. Methods: This retrospective study examined clinical data derived from 198 eyes of 131 keratoconus patients. The subjects were divided into a development group (102 eyes of 68 subjects) and a validation group (96 eyes of 63 subjects) on the basis of the date of their examination. HCL-BCVA measurement and anterior segment–optical coherence tomography (AS-OCT) were performed. A prediction formula for HCL-BCVA based on AS-OCT measurements was then developed. Single regression analysis was performed to identify clinical factors linearly related to HCL-BCVA. Results: Stepwise multiple regression analysis yielded a prediction formula for HCL-BCVA in keratoconus patients, with the correlation coefficient of the multiple regression equation being 0.728 (R2 = 0.530) for the development group. Application of the prediction formula to the validation group yielded a correlation coefficient for the multiple regression equation of 0.641 (R2 = 0.411). Single regression analysis identified anterior corneal refractive power, posterior corneal refractive power, and high-order aberrations as factors that are linearly correlated with HCL-BCVA, with R values of 0.606, -0.617, and 0.506, respectively. Conclusion: HCL-BCVA in keratoconus patients was predictable on the basis of AS-OCT measurements. Cutoff values for clinical factors found to correlate with HCL-BCVA may prove informative with regard to treatment options to maintain a favorable visual acuity in keratoconus patients.

Normal contact performance of mortise and tenon joint: theoretical analysis and numerical simulation

This article aims to investigate the contact characteristics of mortise and tenon (M&T) joints in the traditional timber structures. In particular, the normal embedded compressive contact between contact surfaces of M&T joint was investigated. Based on basic contact theory and contact characteristics between mortise and tenon, a normal elasto-plastic contact model, which can reflect the real normal contact behavior of M&T joints in traditional wooden structures, was proposed. Coulomb friction contact was utilized to describe the tangential slipping characteristics of the contact surfaces. Micro-morphology scanning tests of wood samples with different roughness were carried out to determine the parameters involved in the normal contact model. The normal contact model subroutine of M&T joint was compiled by FORTRAN language, implemented into ABAQUS through user-defined interface (UINTER). Then the proposed model was verified by shear tests of wood contact surfaces considering different normal pressures. Finally, a finite element model (FEM) of straight tenon joint subjected to cyclic reversed loading, based on the proposed normal elasto-plastic contact model, was developed, and a FEM considering normal “hard contact” between the contact surfaces, was also performed. The simulation results were validated by the experimental results. Results showed that the user-defined normal elasto-plastic contact FEM was more in line with the actual force state and mechanical behavior of M&T joints, which can more accurately predict the failure modes and simulate the hysteretic behavior of M&T joints, compared to the FEM considering normal “hard contact” of the contact surfaces.

Edge strength of core drilled and waterjet cut holes in architectural glass

In structural glass design, an often-applied connection is a bolted connection subjected to in-plane tensile loads. Traditionally, the hole in the glass pane is manufactured by core drilling and conical edge finishing. An alternative method is by waterjet cutting the holes, resulting in cylindrically shaped holes. This research compares the edge strength of core drilled and waterjet cut holes. It focuses on in-plane tensile tests and consists of an experimental part in combination with a numerical part. In the in-plane tensile tests, peak stresses occur perpendicular to the load direction. These stresses are found to be higher for waterjet cut holes (+ 13%) compared to core drilled holes. As a result, the characteristic ultimate load is lower for waterjet cut holes (− 16%). Furthermore, the influence of thermally toughening the glass is found to be more favourable for the characteristic ultimate load of specimens containing core drilled holes than it is for waterjet cut holes. Next to that, it was found that the ultimate load linearly increases with the panel thickness. Eccentric loading, caused by insufficient bushing material or rotation of the bolt, only slightly decreases the ultimate load, provided that no hard contact between bolt and glass occurs. In addition, coaxial double ring tests were performed in the hole area, showing that waterjet cut holes result in larger stresses near the hole edge than core drilled holes. Furthermore, waterjet cut holes are found not to be perfectly round, while drilled holes are. This un-roundness negatively influences the ultimate load and the stresses in the glass; the larger the extent of un-roundness, the higher the stresses and the lower the ultimate load. Also, the orientation of the un-round hole is of influence on the stresses and ultimate load for the tensile test. It is concluded that waterjet cut holes result in lower characteristic ultimate loads and higher stresses. Due to the different edge finishing, the ultimate load still is lower compared to core drilled holes, even if the waterjet cut holes are perfectly round.

Mechanical behavior of thin-walled steel under hard contact with rigid seabed rock: Theoretical contact approach and nonlinear FE calculation

This work aims to investigate the mechanical behavior of steel-plated structures under a raking incident and to quantify the effect of the mesh size in nonlinear finite element (NLFE) analysis. To conveniently comprehend nonlinear phenomena, i.e., the grounding which takes place in this work, a series of theoretical contact formulations was defined. In the main analysis, raking, which is a part of the grounding scenario, was strictly assumed as contact between a tanker, which was assumed to have thin-walled steel, and a seabed rock in the form of a solid obstruction. Designed raking scenarios were calculated using the FE method by using the nonlinear phenomena of the material behavior in the calculation. The findings of this work indicated that the possibility of expanding the recommended mesh size in FE simulation should be evaluated by quantifying the behavior of structural responses, such as energy, the force damage pattern, and acceleration, subjected to a variety of applied meshing techniques. The results concluded that a notable difference occurred when the mesh size was more than 132 mm (ratio 11 based on the plate dimension in this work), and this size is strictly recommended to be used for calculation of the element length-to-thickness (ELT) ratio. Assessment in time simulation showed that applying larger mesh sizes will reduce the simulation time but increase the maximum values of the crashworthiness parameters, i.e., energy, force, acceleration, and displacement.

Compliance Control of Slave Manipulator Using EMG Signal for Telemanipulation

Telemanipulation systems have been widely utilized in industrial, surgical, educational, and even military fields. One of the important issues is that when a robot interacts with environment or objects, it can damage the robot itself or the objects due to hard contact. To address this problem, we propose a novel compliance control of a slave robot using the electromyography (EMG) signal, which is measured by the sensors attached onto the master operator’s arm. The EMG signal is used since it is easy to process and it provides humans with an intuitive capability to perform the operational work. Furthermore, it has been proved that the EMG signal is useful in the control of the stiffness of the slave robot. This research identifies the muscle that is the best suitable to a precision-grip operation, and a series of experiments were performed. A compliance control algorithm with a variable stiffness of a slave robot is proposed, where the stiffness is changed based on the EMG signal, and it is confirmed by a series of experiments using a two-channel force/position teleoperation architecture.

Penetrating Keratoplasty for Keratoconus in Vietnamese Patients

BACKGROUND: Keratoconus is an ectatic corneal disorder that can impair the visual acuity. Up to now, penetrating keratoplasty (PK) remains the most common surgical procedure to treat severe keratoconus. In Vietnam, most keratoconus patients come to visit doctor at severe stage and were treated by PK, so we conduct this study. AIM: To evaluate the results of PK for keratoconus in Vietnamese patients. METHODS: This was a retrospective study of 31 eyes with keratoconus who underwent PK in VNIO from January 2005 to December 2014. RESULTS: The average visual acuity was 0.86 ± 0.37 logMAR (20/145). In the group of patients without amblyopia, best spectacle-corrected visual acuity of 20/60 or better was recorded in 75.9% of eyes and 93.1% of eyes achieved a best corrected visual acuity with hard contact lenses of 20/40 or better. Mean postoperative corneal power was 43.8 ± 4.5D. Mean corneal astigmatism was 5.9 ± 2.7D. 94.6% of grafts remained clear. Posterior subcapsular cataract developed in 22.6% of eyes. Graft rejection was recognized in 12.9% of eyes. CONCLUSION: PK is an effective procedure with high rate of graft survival for keratoconus patients. However, patients should be aware of the necessary of optical correction to gain the best VA after surgery.