Features of testing and selection of implant-valves to reduce intraocular pressure
Keywords:glaucoma, glaucoma drainage devices, Ahmed glaucoma valve, IOP, intraocular fluid, pressure
Introduction. The progress of microelectronic technology and its associated element base stimulates its widespread introduction into various spheres of human activity. By using micro miniaturization, we get new devices and systems with increased reliability and extended functional and operational capabilities and improved metrological parameters. This fully applies to the field of medical instrumentation and bioengineering, especially in the field of ophthalmology new devices and sys, is characterized by the wide use of implants ranging from lens replacement to radiated (at 914 MHz) microchip (size 1.2x2.4 mm) to measure and regulate eye pressure, only goes through laboratory testing. One of the most severe diseases in ophthalmology is glaucoma of the eye, which leads to an increase in intraocular pressure, most of which leads to a loss of human vision and is the second most frequently occurring. The most effective method of treatment is eye surgery, which is the patient's last chance to keep his eyesight, an implant (valve) to regulate the pressure within 9-21 mm Hg. The obligatory preoperative procedure should be the control of the operation parameter and determination of parameters, the opening pressure, closing pressure, and reproducibility of the characteristic at reactivation, which will contribute to the efficiency of performed operations.
Analysis of known research results. There are known several methods of implants testing for workability, which can divide into two directions: methods with the use of earth gravity by lifting the tank with saline solution to the graduated height with using of measuring bar or analog or digital manometer and method of hardware creation of excess pressure. The disadvantages of the considered methods and devices for their realization are the considerable inaccuracy and insufficient sensitivity, as well as the difficulty of recording the moment of valve actuation, which depends on the operator's professionalism and, correspondingly, some subjectivity in determining the implants' parameters, which reduces the effectiveness of determining their suitability for use.
Purpose of work description of an automated system. Taking into account the revealed disadvantages the authors set a task to develop a simplified measurement scheme with increasing sensitivity, accuracy and objectivity of implant parameters determination and their effectiveness by determining their suitability for use in medical-surgical practice. For the realization of the target, the authors developed a structural scheme of the automated system for measuring and controlling the parameters of the intraocular pressure regulation implants on the basis of the microsystem technology elements. The system contains a computer, a microcontroller, with a control impulse generator, a unit of discrete (step-by-step) pressure increase with 0.025 ml/step, a microelectromechanical pressure sensor, resistive liquid sensor, analog-to-digital converter, and two feedback lines to the microcontroller, with a microelectromechanical pressure sensor and liquid detector. The algorithm of the system operation is developed, which implies checking the system in the "zero adjustment mode" and the mode of measuring and controlling the implant parameters "testing mode". It is showed that the error of determining the system pressure parameters does not exceed 0,5%.
Experimental verification of system operation. There are three possible cases in which the implant is opened earlier and there is a risk of hypotension to the patient's eye, and later there is a risk of hypertension and works in the normal pressure zone. The authors give graphs of such measurements, as well as a graph of the reproducibility of the characteristics of the non-defective implant.
Conclusions. Thus, the proposed system provides: -- simplification of the circuit with the simultaneous possibility to automate the process of preoperative verification of different implant types; -- allows increasing of sensitivity, accuracy of measurement and objectivity of implant parameters determination; -- determining their suitability for use in medical surgery by fluid output parameters, opening pressure, closing pressure, and reactivation characteristics that will improve the efficiency of the operation; -- reduction of implant testing time, which is limited to 2-3 minutes, and the ability to store parameter information in both electronic (computer) and paper form.
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