Artificial Accommodation System Research Articles

Robust Design of an Optical Micromachine for an Ophthalmic Application.

This article describes an approach to the robust design of an optical micromachine consisting of a freeform optics, an amplification linkage, and an actuator. The robust design approach consists of monolithic integration principles to minimize assembly efforts and of an optimization of the functional components with respect to robustness against remaining assembly and manufacturing tolerances. The design approach presented involves the determination of the relevant tolerances arising from the domains manufacturing, assembly, and operation of the micromachine followed by a sensitivity analysis with the objective of identifying the worst offender. Subsequent to the above-described steps, an optimization of the functional design of the freeform optics with respect to a compensation of the effects of the tolerances is performed. The result leads to a robust design of the freeform optics and hence ensures a defined and optimal minimum performance of the micromachine in the presence of tolerances caused by the manufacturing processes and the operation of the micromachine. The micromachine under discussion is the tunable optics of an ophthalmic implant, an artificial accommodation system recently realized as a demonstration model at a scale of 2:1. The artificial accommodation system will be developed to replace the human crystalline lens in the case of a cataract.

Current progress of the artificial accommodation system

In case of presbyopia or cataract the "artificial accommodation system" represents one future possibility to durably restore the ability to accommodate. The work presented describes recent progress in the development of the artificial accommodation system. Major advances were achieved in the fields of the actuator system for the active optics, the pupil near reflex sensor, the communication system, the power supply system as well as in system integration. Beside the technical advances, first trials were performed to implant the artificial accommodation system into animals. These trials showed that the new lens shaped design and the C-shaped haptics are beneficial for implantation and secure fixation of the implant inside the capsular bag.

Mechatronic system to restore accommodation

AbstractThe Artificial Accommodation system is a mechatronic approach to restoring accommodation. It consists of an autonomous device that will be implanted into the capsular bag of the eye similar to implantation of intraocular lenses today. The device measures accommodation demand and accordingly adjusts its refractive power by means of an integrated active optical element. Realization of this far reaching vision requires development of the respective subsystems, their integration into a small hermetic and biocompatible housing and adapted surgical procedures. Development of subsystems is well under way and first integration steps are being taken starting from macro scale down to target size. In this talk, the concept of the overall system is described and the results obtained for the different subsystems are discussed.

The Pupil Can Control an Artificial Lens Intuitively

After cataract surgery, the ability to accommodate is lost. For this reason, a mechatronic IOL is being developed at the moment: The Artificial Accommodation System. This device requires an easily measureable indicator of the distance of the observed object to determine the demand of accommodation. As the pupil constricts with near vision, pupil size might be such an indicator. Our research focused on whether the pupil can control an artificial lens. A study with 14 healthy subjects aged between 24 and 64 years was conducted. An artificial lens with variable refractive power was mounted in front of one eye. In this eye, natural accommodation was greatly reduced or absent due to presbyopia, pseudophakia, or iatrogenic cycloplegia. The lens' refractive power was changed in a computer-controlled manner depending on changes in the pupil diameter of the second eye, which could not see the fixation stimulus. The subject's task was to get a clear focused image of the target in different distances. The lens can be controlled by the pupil intuitively (P < 1.8 × 10(-18)). Without prior knowledge, 11/14 subjects passed the first trial, and 31/41 trials were successful. Only one subject was not able to control the lens at all. Most subjects comprehended instantly how to use the unfamiliar lens control to bring a target into focus. This study emphasizes the plasticity of the visual control system. Positioning accuracy was acceptable, but the control must be optimized to facilitate maintaining a defined refractive power.

Enhanced power management unit for the Artificial Accommodation System

Article Enhanced power management unit for the Artificial Accommodation System was published on September 7, 2013 in the journal Biomedical Engineering / Biomedizinische Technik (volume 58, issue SI-1-Track-O).

RTS-MAC: A Relative Time Synchronization MAC Protocol for Low Duty Cycle Body Sensor Networks

Emerging applications in the medical field require body sensor networks to communicate in real-time in a very energy-efficient way. An example is the Artificial Accommodation System—a set of two small active medical implants aiming at restoring accommodation of the human eye—in which sensor data have to be exchanged continuously between both eyes. To achieve energy efficiency, it is essential to operate the radios with a very low duty cycle. Therefore, idle listening and general protocol overhead must be reduced as much as possible. In this paper, we present a relative time synchronization medium access control protocol (RTS-MAC), which keeps relative time synchronization between two or more sensor nodes in a very energy-efficient manner: RTS-MAC makes use of the periodic broadcast of regular data messages and exploits the inter-arrival times to predict future arrivals within tight boundaries. Thereby, no overhead is generated for synchronization purposes, and still, idle listening is reduced to a minimum, which solely depends on the short-term accuracy of the underlying clock systems. We implemented the proposed protocol using off-the-shelf components and employed the internal low-accuracy oscillators of the microcontrollers as clock sources. Thereby, we achieved very low duty cycles close to an ideal minimum. Further, our results indicate that through omitting external crystals in favor of a minimally larger battery, the battery life of a sensor node can be prolonged.

Silicon linkage with novel compliant mechanism for piezoelectric actuation of an intraocular implant

An implantable mechatronic microsystem is a new approach to restore the accommodation ability of the human eye. For change of refractive power a lens shift is performed by an actuator. This paper reports on the first actuator solution for such an implant. It is based on a piezoelectric bender the displacement of which has to be amplified in a very limited design space to sufficiently drive the optics of an Artificial Accommodation System. This challenge is solved by a novel compliant mechanism realized in single-crystal silicon that additionally ensures the tilt-free translational displacement of the lens required for optical imaging quality. The design is free of any surface-friction to achieve high durability. Finite element analysis is conducted to calculate and optimize the performance of three linkage design variants. They were fabricated on a scale of 1.5:1 using deep reactive ion etching. Measurements were carried out to characterize the geometry, elastic behavior, and kinematic performance of the linkage samples. The results are in very good agreement with the calculations and indicate sufficient amplification of the piezoelectric bender's displacement by the linkage to generate the required lens shift.

Comparison of different power supply topologies to improve power efficiency of the Artificial Accommodation System

Comparison of different power supply topologies to improve power efficiency of the Artificial Accommodation System

Energie- und speichereffiziente Berechnung des Akkommodationsbedarfs im Künstlichen Akkommodationssystem

Presbyopia and cataract are gaining more and more importance in the ageing society. Both age-related complaints are accompanied with a loss of the eye's ability to accommodate. A new approach to restore accommodation is the Artificial Accommodation System, an autonomous micro system, which will be implanted into the capsular bag instead of a rigid intraocular lens. The Artificial Accommodation System will, depending on the actual demand for accommodation, autonomously adapt the refractive power of its integrated optical element. One possibility to measure the demand for accommodation non-intrusively is to analyse eye movements. We present an efficient algorithm, based on the CORDIC technique, to calculate the demand for accommodation from magnetic field sensor data. It can be shown that specialised algorithms significantly shorten calculation time without violating precision requirements. Additionally, a communication strategy for the wireless exchange of sensor data between the implants of the left and right eye is introduced. The strategy allows for a one-sided calculation of the demand for accommodation, resulting in an overall reduction of calculation time by 50 %. The presented methods enable autonomous microsystems, such as the Artificial Accommodation System, to save significant amounts of energy, leading to extended autonomous run-times.

Ein neues mechatronisches System zur Wiederherstellung der Akkommodationsfähigkeit des menschlichen Auges

In this paper a new approach for restoring human accommodation is presented. It is an artificial accommodation system based on the latest results of microtechnology, electronics and automatic control. The concept of the overall system is described and the results obtained for the different subsystems are discussed.

Kapselung eines mechatronischen Systems zur Wiederherstellung der Akkommodationsfähigkeit

In order to restore the ability of accommodation of the human eye, a lens implant manufactured by micro system technology can be used. This highly integrated Artificial Accommodation System contains sensitive electronics as well as moving components in order to adapt its refractive power. One challenge of the production of this system is the encapsulation. It has to be a biocompatible and long-term reliable package. In this paper the advantages of a hermetic glass package over other approaches of encapsulation are introduced. Concepts of production for a glass package are presented. The package is thereby optimised to be placed in the optical path of the eye, but it can also be used for the encapsulation of other implants.

Triple-Optic-Ansatz für das Künstliche Akkommodationssystem

Use of an implantable mechatronic microsystem (artificial accommodation system) is a novel approach to restoration of the accommodative capacity of the human eye. One such system, based on the triple-optic approach, has been selected for investigation of its suitability. Optical modelling of the dioptric apparatus is carried out by means of an optical simulation tool. Postoperative refractive compensation plus at least 3 dpt of accommodation are required. An axial shift of 300 microm or less is achieved for the entire range of biometric data ascertained before surgery. In addition, the defined requirements made of optical imaging quality are met. The triple-optic approach is basically suitable for application in the restoration of accommodative capacity. It seems that flexure hinges could be used in association with conducting polymers as actuator material. One question that is still open concerns the deformability of such implants as this relates to minimally invasive corneal incisions.